Film-Tech Forum ARCHIVE: Do high-frequency speakers deteriorate over time? Or is it just my ears?

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Posted by Mike Blakesley (Member # 26) on 03-21-2012, 08:50 PM:

This is a sound question, but we have digital equipment so I guess it should go in this forum. (Maybe we need a sound forum?)

Anyway. Lately I have noticed that our sound seems to be kind of muddy, and the sibilant sounds aren't as strong as I think they should be sometimes. I notice this especially in action scenes. It makes the dialogue harder to understand. I also notice it in music segments...there doesn't seem to be enough treble.

When we've played movies with lots of British accented actors (Harry Potter, for example) I've had a couple of comments from people saying they had a hard time understanding the dialogue. I attributed it to the accents or maybe a lousy sound mix, but...now I'm not so sure.

We have Peavey 2-way speakers for our main stage speakers -- they each have two, 15" woofers and a horn mid/tweeter. We have two Peavey 18" subs. We do not have a baffle wall yet (although it's on my to-do list).

For amps, we have (4) QSC DCA1622s, and one QSC DCA3422. The 3422 runs the subs.

Our surround speakers aren't really the issue here of course, but just in the interest of completeness we have (10) EV 2-way speakers, don't know the model number but they have an 8" woofer and a 2" dome tweeter. In the balcony we have (2) JBL speakers which are slightly smaller (6" woofer).

Our processor is a Dolby CP650. And, our sound gets EQd every 6 months or so, so I don't think it's an alignment issue but maybe that's it too.

Last year we had a nice visit with the QSC guy at CinemaCon and almost went to 3-ways right then, but then I remembered I don't like to "impulse buy." So here we are. Any ideas, thoughts or suggestions (if we need to upgrade something) would be appreciated.

Posted by Tony Bandiera Jr (Member # 2365) on 03-21-2012, 09:19 PM:

Mike:

It is possible for HF drivers to deteriorate over time...usually by the metal diaphragm shattering or flaking apart.

The Peavey stage speakers suck in general...if you go to QSC's with the proper crossovers (or use a DCM monitor) you and your customers will be amazed at the difference in the sound quality. Getting the QSC's would be a very wise expenditure. If your budget won't let you replace the surrounds, leave them alone for now. The Peavey subs are ok, but again if you can, replace them with QSC.

Keep us posted on this.. [Smile]

Posted by Sam D. Chavez (Member # 1841) on 03-22-2012, 01:05 AM:

Even used JBL 4675 or similar are much better choices that Peavey for this application. I would bi-amp for sure.

Posted by Monte L Fullmer (Member # 2797) on 03-22-2012, 02:27 AM:

I've replaced quite a few HF diaphrams-hair line cracks at the edge of the fold can easily develop.

HF diaphrams have the thickness of very thin alum foil where all the flexing they have to go through, they can split and go raspy.

Posted by Louis Bornwasser (Member # 3063) on 03-22-2012, 06:45 AM:

I would leave the surrounds and subs alone; they are OK enough and you won't hear much change.

That said, I agree with Sam that good used JBLs (or new QSCs) are what the doctor ordered. Only the 3 stage speakers. Louis

Posted by David Buckley (Member # 2600) on 03-22-2012, 07:43 PM:

Horns tend to fail much more than they degrade, and when they do degrade, they generally do so making the sound not quieter but just uglier.

A Peavey 2x15 plus little horn isn't really the right tool for this sort of job. Fifteens aren't real good with voice ever, but for many purposes are an tolerable compromise. These are bar band territory.

So you either need to spring for "genuine" cinema speakers, or much higher quality sound reinforcement speakers.

Cinema main speakers are only able to get away with fifteen inch drivers because of the qualities of the cinema horn, which is a very different animal to a bar band speaker horn.

Posted by Mike Blakesley (Member # 26) on 03-23-2012, 11:00 AM:

quote:
So you either need to spring for "genuine" cinema speakers,

Well, these are "genuine" cinema speakers, or at least they were purported to be when we bought them in the late '80s. The horns aren't "little," they are almost as wide as the main cabinets (they sit on top of them).

At the time, we had 3 choices of systems and opted to go with the middle one due to the cost. The top system had JBL speakers if I remember correctly. The middle system had the same electronics, but substituted the Peavey speakers. The lowest priced system was only a center-surround setup. Glad I was smart enough not to go that route at least.

Posted by Sam D. Chavez (Member # 1841) on 03-23-2012, 12:05 PM:

I'm assuming you have the dual woofer boxes. If so, you could maybe save the bass cabinets and speakers and go with JBL or EV drivers and horns, either long or short as space behind the screen permits.

You could then Bi-amp if it's not already done. Sound will get much better.

Posted by David Buckley (Member # 2600) on 03-23-2012, 02:37 PM:

quote: Mike Blakesley
Well, these are "genuine" cinema speakers, or at least they were purported to be when we bought them in the late '80s. The horns aren't "little," they are almost as wide as the main cabinets (they sit on top of them).

Time for me to eat some humble pie; that description does indeed sound a long way from bar band boxes. I wasn't even aware that Peavey Archetectural did cinema stuff, but yes, they did, and still do, and some of it has the THX stamp of approval.

But having said that, even their current THX approved horn only goes down to 400Hz which (in my opinion) isn't low enough by most of an octave. They also have a 16 inch wide horn that would certainly look the part, but it only goes to 800Hz, nearly two octaves short, and that is almost in bar band territory. That horn is not THX approved!

Although Peavey is a brand that has always concentrated on value, their kit always worked and did what it said on the can.

Thus I have no idea why your intelligability has gone. But rather than guess, one could measure.

The best diagnostic tool I know of for dicovering sound problems is Smaart and its transfer function analysis. If you have or can acquire a reasonable mic and and a USB mic preamp then you can download it on a 30 day trial, and have a play, but it may be quicker, cheaper, easier and get a better result to find someone who has the tools and has done the training (Smaart is a dumb tool; it is the operator that makes sense of it) and have them come and evaluate the system. If you get stuck in cinema world try your local sound providers, anyone with a decent size ad in the yellow pages probably has Smaart.

Biamping as noted can make a difference, simply because an electronic crossiver is much easier to adjust than the passive thing in the back of a speaker box, enabling a much better mact of signal to the driver elements, and also modern DSP based corssovers allow time alighnment. But... if the system used to sound acceptable, then it shouldn't need biamping ito restore it to where it was.

Posted by Mike Blakesley (Member # 26) on 03-23-2012, 03:43 PM:

quote: David Buckley
Thus I have no idea why your intelligability has gone.

It's not exactly GONE, it's just less than I feel like it should be. We watched "The Lorax" last night and had no problems hearing everything. But, even so the sound just didn't sound as "crisp" as it should, to me at least.

We are already bi-amped.

Posted by David Buckley (Member # 2600) on 03-23-2012, 05:05 PM:

quote: Mike Blakesley
We are already bi-amped

That changes things quite a bit; there are a lot more elements in the path, and thge chances of it being a horn problem are diminishing.

Posted by Victor Liorentas (Member # 5272) on 03-23-2012, 06:49 PM:

Mike,I would try ordering a new tweeter diaphragm.I bet it will get you back to that like new crispness and at least it rules that out.
I have used some of the more expensive sound re-enforcement speakers from Peavey and they may not be the best but not crap either.

Posted by Darryl Spicer (Member # 711) on 03-24-2012, 03:33 PM:

Have your tech come in and check your B chain. High frequency problems will show up if there are problems with the horns. The EQ may be off a bit or something changed about it. I would do this before investing money into new equipment or replacing parts.

Posted by Dominic Espinosa (Member # 2122) on 03-24-2012, 04:28 PM:

Depending on the degree of degredation it could even been dust plugging up the holes in your screen or clogging the end of the driver assy.
Agree with Daryl on checking your B-Chain. If it is a natural decline due to environmental issues he may be able to eq it out.

Posted by Sam D. Chavez (Member # 1841) on 03-24-2012, 05:49 PM:

I would substitute the hf driver from the left or right channel to the center channels as this is where most of the dialog comes from and our ears are most sensitive to distortion from human voices.

See if that does the trick. If not, change the amp from the left or right and then the crossover if all three are the same type.

If you do get a tech out, have them use an audio sweep generator to check for crackling, rattling, etc.

FWIW, all the eq. and pink noise in the world will never find a distortion source, it has to be done with audio tones.

Posted by Marco Giustini (Member # 4544) on 03-24-2012, 06:33 PM:

Why do you have your EQ re-done every six months? Properly tune a sound system requires a lot of time, and several subjective tests to obtain a good result. Unless this is done every six months, I would not recommend to bother a properly eq'd sound system every 6 months. Unless the same long procedure is done by - possibly - the same person.

Now, don't get me wrong, I'm not saying not to touch your sound systems for years. What I want to say is that I've seen too many people around checking a system in half a hour, placing ONE microphone 2/3 away from the screen, dialing the perfect X-curve and winding up the cables without testing the result.
That is not checking/equalising. That is asking for random results depending on the microphone position and auditorium acoustic.

What I'd do, is to have the auditorium properly eq'd, then maintain it every year: you check the levels (with the microphone in the same position!), and channels. If no major disruptions, happy days.

Posted by Mike Blakesley (Member # 26) on 03-24-2012, 08:51 PM:

Lots of good ideas here. I'll start working on some of them and report back when I get any info.

We don't have a full EQ every six months. Just a basic check during the maintenance visit by our tech, and an EQ if needed. But, we had a full EQ last summer.

I have been lusting after 3-way QSC speakers ever since we talked to their rep at CinemaCon last year, but after reading some of the posts here, I'm still wondering if this problem isn't caused by my aging ears and not our aging speakers.

Posted by Monte L Fullmer (Member # 2797) on 03-24-2012, 09:03 PM:

quote: Mike Blakesley
I'm still wondering if this problem isn't caused by my aging ears and not our aging speakers.

This is when you need a second opinion from another person and ask them how the movie sounds - clear, or muddy.

For you know your tech would have brought this up on his prior visit if he gave you the full tune and checkup.

True, when we age, our ability to hear high freqs, unfortunately, do diminish slowly. But wait until you pick up some rinitis, then that is when you definitely need that second opinion.

Posted by Manny Knowles (Member # 1171) on 03-24-2012, 10:53 PM:

Hearing does tend to deteriorate over time -- usually starting with the highs. We did some informal testing in the Norris theatre at USC and most of the adults couldn't hear anything above 16kHz, whereas a few of of the younger "kids" could hear 17kHz.

Even so, your dialog should "suddenly" sound funky, unless you recently experienced some kind of trauma that could explain why your dialog suddenly sounds lousy.

There's an old saying that goes "if three people tell you you're drunk, lie down!" If you and several of your patrons are hearing this (all of a sudden) then there's a good chance that "it's not just you."

As Sam pointed out, don't rely on pink noise and your RTA -- it is possible to "tune" a busted speaker to the X-Curve. Amazing, but true.

This is where a test reel is worth its weight in gold. It should be a test reel containing dialogue (male and female) that you have heard before and you know what it ought to sound like when the system is functioning properly.

Dialog is important because we are very good at detecting poor reproduction of human speech. We don't *really* know what that dinosaur is supposed to sound like.

Even if you don't have DTS, I'd still recommend the DTS "Buzz and Bill Show" reel because it has dialog, it has a very quiet scene (from "Far and Away") and a very loud scene (from "Backdraft").

The Dolby "Jiffy" reel has sweep tones, but it suffers because the male voice (Ioan Allen) only appears at the very top of the reel (he reads the slate). And the woman's voice is a little too "smoky" for me. Distortion and hiss can easily hide in a voice like that. I've grown to really LOVE that goofy (Wendy Carlos) music that closes the reel.

Posted by Brad Miller (Member # 2) on 03-24-2012, 11:14 PM:

Mike, get the QSCs and a baffle wall and make sure the sound system is tuned properly with a D2. (Not all techs actually do this, they just "dial up the X curve" and walk out saying it sounds phenomenal.)

You won't believe the difference. Think going from 35mm to digital, but moreso. Peavey vs. QSC? That's going from arguably the worst to the best.

Posted by Dominic Espinosa (Member # 2122) on 03-24-2012, 11:49 PM:

Pardon me, but what exactly is the benefit of a baffle wall?
I've only ever seen one theater like this (and it was an incredibly old one at that with the original, rotted out 'voice of the theater' still in it).
New equipment was in use at the time.
So I couldn't listen to a difference.

I've never seen a baffle wall in any of the theaters I've worked in.

Is it's sole intent to eliminate audio reflections behind the screen?

Posted by Brad Miller (Member # 2) on 03-25-2012, 02:03 AM:

Come visit and I'll show you.

Posted by Cameron Glendinning (Member # 3516) on 03-25-2012, 03:25 AM:

Posted by Cameron Glendinning (Member # 3516) on 03-25-2012, 03:42 AM:

A baffle wall or even just some very solid wings added to the side of a speaker box can make a huge difference to the sound. The basic idea is pretty simple, the speaker is a pistion and the wall controls the air so that the formation of the soundwave is far more accurite and realistic than when the wave is distorted as it wrapes around the box and then into the backstage areas. This makes sense when you realise how big some sound waves are 100 hz is over 11 feet, 32hz is over 35ft. The use of fiberglass on the baffle wall also helps with seperation between channels.
As Brad emplies its the results which are well worth listening to not the logic behind it.

Posted by Dominic Espinosa (Member # 2122) on 03-25-2012, 10:18 AM:

Hmm...guess i might have to fly to texas this year. Darn [Wink]

Posted by Chuck McGregor (Member # 6826) on 03-25-2012, 02:11 PM:

Greetings,

This is my first post having just joined Film-Tech after reading the Forums for the better part of a year. I am ever-so grateful for the all the knowledge I've thus far gained from the members and this site.

quote:
Cameron wrote:
A baffle wall or even just some very solid wings added to the side of a speaker box can make a huge difference to the sound.

Huge is a relative term, however it will make differences. The question is what ARE the differences?

quote: Cameron Glendinning
The wall controls the air so that the formation of the soundwave is far more accurite and realistic than when the wave is distorted as it wrapes around the box and then into the backstage areas.

I would say instead that the dimensions of the radiating device determine its power response. The power response determines how the sound from a loudspeaker (or any source) couples to a room. If the power response varies with frequency then, among other things, the direct-to reverbrant ratio will vary with frequency. With loudspeakers this invariably means it decreases with frequency.

A baffle wall or wings increases the directivity with decreasing frequency from the frequency where the normal beamwidth starts to exceed 180 degrees. The maximum increase is where the frequencies of the "unaided" beamwidth would normally be 360 degrees. This means the loudspeaker's axial output also increases with decreasing frequency from 0 dB to 6 dB.

This is ONLY true if the width of the wings plus enclosure is at least 1/2 the wavelength of interest to be effective. There is a sharp discontinuity below this frequency transistioning rapidly from 2 pi to 4 pi radiation. Above this point the frequency response of the system will change with increasing frequency until the natural beamwidth of the system is reaches 2 pi radiation. Above that the baffle will have essentially no effect on directivity. So to be effective to say 50 Hz the baffle/enclosure width must be about 10 feet centered around the loudspeaker.

However this is not all a baffle can do. As Cameron noted, a baffle helps keep sound from the loudspeakers from reaching areas behind the screen. Any of this energy that is reflect back into the audience, whether discrete or diffuse, can cause all kinds of unwanted audio anomolies. I've got such problems in the theater I work with.

Another thing baffles can do is improve the performance of horns. When a wavefront leaves the mouth of a horn, the change from the horn wall to the "open air" creates a discontinuity in the wavefront. This diconinutity causes some of the energy to be reflected back into the horn. Then this reflection also gets reflected back out the horn, obviously later in time. Some of this reflected energy is also reflected back into the horn and so on. The frequencies most affected are related to the length of the horn. This casues a buildup of energy over time creating a sonic effect commonly referred to as horn honk. Obviously if a horn is used only above those frequencies this is not an issue but this is rarely true.

A baffle wall or wings can mitigate horn honk IF, repeating IF..., there is a relatively smooth transition from the plane of the horn walls at the horn mouth to the baffle surface. The smoother the better. If there is a angle between the horn mouth (excluding any mounting flange) and baffle surface this benefit will be reduced or relatively non-existent.

quote: Cameron Glendinning
The use of fiberglass on the baffle wall also helps with seperation between channels.

This will also have a frequency selective effect on the linearity of the loudspeaker's power response and thus frequency response This will depend on the above effects and the material's absorption characteristics. At frequencies above where the normal beamwith of the the loudspeaker goes below 180 degrees, the absorption will have little effect. At frequencies below it will have an effect but it will increase then decrease with frequency. This is not something I would do without modeling its effects (and they can be modeled) in combination with the wall or wing effects on the particular loudspeaker.

Overall baffle walls or wings can be good things. A wall is most effective while wings can introduce more frequency selective effects and these effects must be considered. Some of the benefits will depend on loudspeaker design, others not so much.

I just happen to be in the process of determining the effects of adding wings to the loudspeakers in the theater I work with. One fly in the ointment in figuring this out is that the modeling must take into account a rather arcane "soffit mounting" effect as the wings will only be as tall as the loudspeakers. Just another parameter to take into account.

While the results may be well worth it, achieving optimum results, especially with just wings is not just a matter of installing wings and calling it a day. The "logic" behind it does matter in understanding the impact on the sound projection and therefore what to expect.

The best measurement system in the world (I use Smaart and a proprietary loudspeaker measurement and modeling program called Rayleigh) is only as good as the analysis of the data collected. One really should know what to expect by adding wings or a baffle wall in order to properly interpret the measured results and make the proper corrections for the expected differences. This is especially true if the results are spatially variable.

How to predict, measure, and properly correct for any of these effects is whole other story... [Smile]

Posted by Monte L Fullmer (Member # 2797) on 03-25-2012, 02:34 PM:

A baffle wall is like a car's rear speakers with the speakers mounted in the rear deck - isolating the sound from the rear of the speaker from "rolling around" to the front. You wonder, when those early car stereos had such horrible sound with those surface mount speakers - sound was "rolling" around everywhere and couldn't project the sound where it needed to go.

Mount those speakers in that rear deck shelf and you have great sound since the sound is definitely projected upwards and reflecting from the rear glass. Also, the trunk space acts like a passive woofer to capture all of the LF's reflecting off of the rear of the cones.

Sound, even though with a speaker flush against the screen, still will reflect back behind the screen, esp if the back wall of the auditorium isn't covered with a sound insulating material, then return back through the screen holes...and you still have that "rolling around" syndrome of the sound. Put up a baffle wall and no reflection will occur and sound will definitely be projected forward.

Makes tonnage of difference when using a baffle wall.

Posted by Sam D. Chavez (Member # 1841) on 03-25-2012, 03:33 PM:

The main reason THX used the fiberglass was to absorb hf reflections coming off the back of the screen as all the sound coming out of the horn does not get through the screen.

The baffle wall serves all sorts of purposes as has been described, but mostly IMHO, serve to sharpen the imaging of each speaker. All those stray sounds that don't get through the screen, bounce off the back of it and then hit the back wall and bounce around and eventually get through the screen somewhere in between the speakers. This blurs the intended image as it were.

Posted by Dominic Espinosa (Member # 2122) on 03-25-2012, 05:16 PM:

Sam et al: Is this why the screening room at Dolby in SF sounds the way it does?
If I had to describe it I'd say the screen channels in particular sound "tighter" than your average auditorium. There's an implicit control and the channel separation is more noticeable.
IMHO of course.

Posted by Chuck McGregor (Member # 6826) on 03-25-2012, 05:18 PM:

quote: Monte L Fullmer
A baffle wall is like a car's rear speakers with the speakers mounted in the rear deck - isolating the sound from the rear of the speaker from "rolling around" to the front.

Not the same function. Loudspeakers in box already are bafffle as you describe. The THX wall, wings and similar have to do with the changing the radiation of a sound source into to a 2 Pi space, a 4 Pi space being omindirectional which is what LF drivers in boxes are at lower frequencies.

Absorbing reflections bouncing around between the screen and wall is an interesting point. The closer the loudspeaker/baffle is to the screen, the higher the frequency of the problem, essentially comb filtering that "smears" the transients. However, the less the absorptive material thickness can fit in between and the less the effectiveness. Just another problem to solve if one wants to get the acoustics "right." Otherwise it may or may not work well.

Posted by Sam D. Chavez (Member # 1841) on 03-25-2012, 06:11 PM:

The Dolby screening room was very well done, but there were no tricks of any kind. Store bought CD horns, HF drivers, bass bins etc. The idea was to show what could be done with off the shelf audio components.

The wall was built with no extra holes so even the old style Tru-Roll masking and curtain motors operate silently.

There is a matter of superb and somewhat adjustable reverb via bats in the wall spaces. More live for some apps, less so for film.

Yes, the wall does allow you to hear the precise imaging of each speaker as I mentioned previously.

The wall does work. It was not even a new idea to THX, Western Electric did a version of it many years ago. The fiberglass padding just makes it a little better.

Posted by Manny Knowles (Member # 1171) on 03-25-2012, 06:37 PM:

I'm sure that Tom (Holman) could list many benefits of the THX baffle wall, but the two that I always recall him mentioning first were the two reasons Sam cited -- mitigation of behind-the-screen reflections and improved stereo imaging.

I recall Dolby produced a publication called "Guideline for Dolby Stereo Theatres" or something like that. They recommended draping the screen loudspeakers in heavy fabric and ensuring that the fabric created a kind of "seal" between each speaker and the screen.

Posted by Trevor Anderson (Member # 2620) on 03-25-2012, 06:47 PM:

Hi folks

Yes it is sadly true that our hearing degrades over time. But a sudden decrease in performance from your sound system sounds more like an environmental issue.

Does the return air from your HVAC system suck through the screen, or generally pull air towards the screen end? If so this will lead to a more rapid build up of dust in screen perforations. Likewise your masking may be the issue. If it is getting clogged up with dust it will affect your 1.85 screenings (assuming your masking covers the L&R speakers at 1.85).
At an extreme, I had a call from a complex once that their sound was very tinny in one cinema. Went in to check and someone had stolen all the LF speakers out of the boxes.....tinny sound indeed!
Have you recently changed your screen?
Different screens have different performance characteristics for sound. So you it is recommended to do a new B chain when replacing the screen. (All those silver screens going in everywhere!!!)

Posted by Manny Knowles (Member # 1171) on 03-25-2012, 06:58 PM:

OK -- I just checked that "Dolby Theatre" publication -- Sections 2.2.3 talks about baffle walls and 4.1.5 offers suggestions in the absence of a baffle wall -- that's the section where the heavy draping fabric is mentioned.

The Dolby publication can be found here in the F-T warehouse -- which is awesome, since I lost my hard copy years ago.

quote: Trevor Anderson
Does the return air from your HVAC system suck through the screen, or generally pull air towards the screen end? If so this will lead to a more rapid build up of dust in screen perforations.

There's a wonderful story about this very thing happening at the Chinese theatre in Hollywood. The screen perf's had gotten clogged with popcorn grease and to compensate, over time, the HF was gradually cranked to the point where the HF drivers were destroyed. As the story goes, this was discovered after somebody "phoned THX" when "Godfather III" was being shown there.

Posted by Chuck McGregor (Member # 6826) on 03-25-2012, 07:19 PM:

Humidity is somewhere between about 5% and 40% can cause a loss of "crispiness." If it has it, failed humidity control in an HVAC system could cause this. The larger the theater, meaning longer "sound lines," the greater the potential problem.

Posted by Louis Bornwasser (Member # 3063) on 03-25-2012, 09:11 PM:

According to JBL, ALL SPEAKERS require the baffle wall to make spec. This is not limited to Cinema; all speakers. From the smallest to the largest are tested on an elevator at JBL that uses the roof of the building as a sound wall.

"Bookshelf speakers" require the books to make spec. I once installed a cinema system in a theatre where the owner had "every classical LP ever made." They were stored numerically behind the cinema screen. We used the mass of the record albums as a sound wall.

btw: Thx promoted a sound wall; too bad it was only just a copy of the old Western Electric sound wall of the 1930s. Louis

Posted by Mike Blakesley (Member # 26) on 03-25-2012, 09:12 PM:

Baffle wall questions.

How tall does it need to be above the speakers? All the way to the ceiling?

And:

quote: Chuck McGregor
So to be effective to say 50 Hz the baffle/enclosure width must be about 10 feet centered around the loudspeaker.

Our screen is wall to wall...how does that effect a baffle design?

Currently we have this "blanket" made out of 1/2" insulating material hanging behind the screen and surrounding each of the speakers. When the insulation showed up it was white in color, so we painted it black to minimize reflections. (I don't know if that was necessary or not.) Then later, somebody told me that the paint probably negated any advantage of the blanket. I don't know if that's true or not and I don't know if the blanket does any good or not. I will say that I don't remember noticing a huge difference in the way things sounded after we put the blanket in (sometime in the late 80s, I think it was).

I would like to get rid of the blanket and put in a proper baffle, for sure.

TO answer the HVAC question, the returns are above the screen. The outlets are all in the ceiling and no air is sucked thru the screen. Our heat is hot-water so we don't use the A/C fans except in hot weather.

Posted by Chuck McGregor (Member # 6826) on 03-25-2012, 10:56 PM:

A wall-to-wall baffle is ideal. The theater I work with is multi-purpose with stage productions so a wall-to-wall is not an option, needing a clear proscenium opening.

I would agree that painting probably did the absorptive properties of that white material no good at all.

Regarding JBL loudspeakers, it depends which specification one is referring to. They test and specify sensitivities and frequency responses for both half and whole space, depending on the loudspeaker. To my knowledge they always state which. However, they specify beamwidth/directivity and impedance from whole space data. Professional loudspeakers are normally specified in whole space (mostly) but sometimes both and this includes professional bookshelf size (they don't need the books to meet spec). Cinema and ceiling loudspeakers are exceptions. I have no idea how consumer loudspeakers are specified, bookshelf or otherwise...and probably don't want to know! [evil]

quote: Mike Blakesley
I don't remember noticing a huge difference in the way things sounded after we put the blanket in

This would not surprise me, even if it were today. One of the things about loudspeaker systems that is a relatively unknown characteristic and certainly not specified is their resolution. Even some otherwise very good sounding loudspeaker systems can be fairly low resolution and that can mask subtler improvements that might be more readily apparent with a high resolution system.

Posted by Christos Mitsakis (Member # 143) on 03-26-2012, 10:51 AM:

This is something of interest:

the THX patent

For the drawings see the accompanying pdf file

Posted by Chuck McGregor (Member # 6826) on 03-26-2012, 12:13 PM:

From the patent:

quote:
The sound absorptive means is frequency dependent and has a high frequency absorption characteristic complementary to the high frequency reflection characteristic of the screen, whereby the absorption increase as the reflection increases with frequency.

As I mentioned, you can't just apply some absorption if you want to do it correctly. The frequency dependent behavior of what you're doing is what you have to figure out to avoid unintended consequences. This is not a trivial task and the patent, of course, doesn't say how.

Some of the crossover stuff in the patent is often repeated today in various ways and still makes no sense.

Posted by Sam D. Chavez (Member # 1841) on 03-26-2012, 01:10 PM:

I think too fine a point is being placed on how much absorbtion is needed on a screen wall.

It's only used to mop up HF reflections off the back of the screen. In a perfect world all the audio would get through and there would be nothing to absorb. Also, each brand and type of screen is slightly different as to thickness, hole size...

An inch or two of black furnace duct has been standard practice for many years now.

Posted by Dave Macaulay (Member # 813) on 03-26-2012, 01:48 PM:

Exactly. The quoted paragraph says just about nothing. Any acoustic treatment will be frequency dependent, LF absorption is much more difficult than HF absorption. The localization improvement comes from reducing the reflected HF from the screen back, the reflected sound has both source point and time delay variations compared to the direct sound from the horn. With some duct liner on the baffle wall, this reduction is accomplished: complete eradication is not required - psychacoustic perception just requires a much lower level than direct sound. The localization difference is very noticeable between a typical installation with no baffle wall and a THX system.
The wall also produces much cleaner LF reproduction. This isn't a localization problem, just having the LF radiators in half space improves their response and efficiency.

Posted by Marco Giustini (Member # 4544) on 03-26-2012, 03:44 PM:

Chuck,

Thanks for your post, very interesting indeed.
It would be nice to learn a bit more about sound analisys. RTA analisys is somehow a non comprehensive way to do it, since it does not keep into account the time variable.

Posted by Chuck McGregor (Member # 6826) on 03-26-2012, 06:38 PM:

To give some insight into some of that analysis, here's one of the tools I use. (The author was my boss for 7 years.) This would be an ideal tool for analyzing the effects of absorption on resolution. I used this to optimize the DSP for my screen loudspeakers.

Transient Analysis

The other half of the pie is measurements. Here's a paper I co-wrote (blush) on one aspect of that subject:

Directional Response Measurements (pdf)

Posted by Robert Throop (Member # 61) on 03-26-2012, 10:46 PM:

I used to run a theatre that had been converted from a grange hall.The screen was about 1 ft. from the wall. The mono speaker (an Altec A5) was in a doghouse so there was a very effective baffle wall. The wall behind the screen was covered with fiberglass insulation. I had one customer who insisted there was a subwoofer.

Posted by Monte L Fullmer (Member # 2797) on 03-27-2012, 02:30 PM:

There's a theatre in Heber City, Utah where a fellow that lived in that town went totally crazy with sound in this theatre moons ago:

He was the originator of Rockford Fosgate.

Had all sorts of amps and E.Q. systems, but his speaker array behind the screen was where the results of all of this ended:

Interestingly enough, there was no baffle wall behind the screen, used VOTT A-7's for the stage speakers, surrounds were JBL units (didn't know the model) but he did make an interesting method for the sub channels:

he mad very large speaker bins made from poured concrete attached to the foundation of the building to mount 4, 18inch subs and had two TUBE amplifiers behind the screen to drive those four subs.

Needless to say, for just Dolby "A" optical sound from a Century R3 soundhead (with exciter lamp) with a Brenkhert Model 80 dbl shutter projector mounted on top and a crapola Christie CH-20 console for the light, presentations in that theatre were outstanding.

Posted by Louis Bornwasser (Member # 3063) on 03-27-2012, 04:10 PM:

Concrete subs: how very "old school." Louis

Posted by Fred Georges (Member # 505) on 03-27-2012, 06:35 PM:

"He was the originator of Rockford Fosgate."

That would be Jim Fosgate..An audio Madman to be sure! [beer]

Posted by Steven J Hart (Member # 2340) on 03-27-2012, 07:27 PM:

Wow, Tube amps on a sub...... A match made in heaven [Roll Eyes]

The concrete enclosure is an awfully cool idea though. I wonder if the front baffle where the drivers are mounted is concrete?

Posted by Chuck McGregor (Member # 6826) on 03-27-2012, 10:19 PM:

A subwoofer created by an old audio pioneer, Rudy Bozak, back in the early 50s had a baffle of two sandwiched 3/4 in plywood sheets. On the back were 2 x 4s (real 2 in x 4 in back then) fastened to the baffle with the 2-inch side in a diagonal checkerboard pattern. In each "square" thus formed was a 12-in woofer, eight in total. That was one solid baffle. The whole enclosure was on wheels. That was a real beast back then, especially with a -3 dB point of under 30 Hz.

Posted by Cameron Glendinning (Member # 3516) on 03-28-2012, 01:38 AM:

quote: Chuck McGregor
While the results may be well worth it, achieving optimum results, especially with just wings is not just a matter of installing wings and calling it a day. The "logic" behind it does matter in understanding the impact on the sound projection and therefore what to expect.

I disagree, my real world experience says otherwise. In the early 90's having actually hired a large warehouse and experimented with a variety of different wings on the typical set of JBL twin 15" cinema speakers, all I can say is they make a dramatic improvement to the sound when added. The science is very easy to understand and pretty much any width did make a difference, bigger however were better! The only important point that has to be emphisied is that structual strength of the wings or the baffle wall must be extreme, think concrete or more simply put... would you jump up and down on this thing?

Another issue is that a speaker will sound better when its not placed in the dead centre of a baffle (that includes speaker boxes).

Yes the sub bass is dramatically boosted when you add wings but after it is cinema eqed the additional boost disappears and the quality improvement and lower frequency response is all that is left.

On my next generation of cinema loudspeakers I dropped the bass refex port and its inherant distortion in favour of very large infinite baffle boxes with matching wings. The sound was even more realistic and honest, especially noticable in side by side tests with the reproduction of instuments such as the double bass.

Years ago Altecs had a THX aproved cinema speakers that were large sealed boxes, its a shame that the other manufactures did not take note...

quote: Mike Blakesley
How tall does it need to be above the speakers? All the way to the ceiling

The typical THX wall does go foor to ceiling, tripple layered gyprock on a strong steel frame in the cinema.

Does it need to go this high? technically its the width not the hight that is more important, though with the wings that I use to build I would extend them up next to the horn with the black tissue faced fiberglass on the front to remove the early reflections that bounce off the screen. In reality the full wall is the ideal but only if its built solid!

So to be effective to say 50 Hz the baffle/enclosure width must be about 10 feet centered around the loudspeaker.

You have never built a set off wings? firstly the speaker should not ideally be centred, secondly a usable response closer to 30hz in the real world, ( even though the JBL speaker box tested was tuned to 40hz....)

The other practical experiments with cinema audio I did was with trying to contain sound leaking between auditoriums. I got great results with using less reactive (ie smaller magnet and voice coil) 15" and 18" woofers than the typical cinema models.

Posted by Monte L Fullmer (Member # 2797) on 03-28-2012, 03:09 AM:

quote: Steven J Hart
I wonder if the front baffle where the drivers are mounted is concrete?

There was a wooden round frame to hang the 18's in that was embedded in the concrete.

(Sorry - wrong sound head. Not an R3 but a Motiograph Mirrorphonic - the side mounted motor got me thinking of the R3-it's been over 20yrs since I saw this setup)

Posted by Robert Throop (Member # 61) on 03-28-2012, 09:52 AM:

In the early seventies the New York Experience opened in NYC. This was a multi media tourist attraction with many slide projectors and 2 or 3 16mm film projectors IIRC. Audio was multi channel from 1/2 in. tape.
When it first opened it had a straight horn for a subwoofer. This beast was 26 feet long and 11 feet square at the mouth. Apparently they kept blowing drivers and by the time I saw it in 1977 they were using Sensurround subs. The projectionist did show me the straight horn though which was in the basement beneath the auditorium.

Posted by Eric Robinson (Member # 2966) on 03-29-2012, 12:14 AM:

What effect would a straight horn have on subwoofer sound?

Posted by Mike Blakesley (Member # 26) on 03-29-2012, 12:36 AM:

I might have missed it, but I don't think anybody has addressed the issue of wall-to-wall screen. Currently our L-R speakers are way out to the edges...should we move them in somewhat when we do the baffle wall? How far in? Screen is 30' wide.

Posted by Cameron Glendinning (Member # 3516) on 03-29-2012, 01:25 AM:

Mike I addressed your question above, the THX cinema that I use to work in the baffle wall was floor to almost ceiling. More info two posts up.

No need to move the speakers I suspect.

Posted by Brad Miller (Member # 2) on 03-29-2012, 01:40 AM:

Leave the speakers where they are.

Posted by Chuck McGregor (Member # 6826) on 03-29-2012, 01:41 AM:

Cameron

I said: "The logic behind it does matter in understanding the impact on the sound projection and therefore what to expect."

You said "I disagree" followed by your discussion how you went to considerable effort to figure out the "logic" so you would know what you were doing!! [Razz]

Here is where you get five gold stars plus for saying a truth that is pretty much ignored by all manner of audio people [thumbsup]

quote:
On my next generation of cinema loudspeakers I dropped the bass refex port and its inherant distortion.

Years ago Altecs had a THX aproved cinema speakers that were large sealed boxes, its a shame that the other manufactures did not take note...

A box with a hole in it is a resonator. Excite the air in the box and it resonates. A big "selling point" for ported loudspeakers (more so some years ago) is that the cone movement is greatly reduced at the port tuning. Well, if the loudspeaker cone isn't moving very much it should be quite obvious the cone isn't "moving" much air, so where is all that low frequency energy coming from? Answer: a box with a hole in it that is resonating. It doesn't take much to get a resonant system going. That is not reproduction. Call it distortion or whatever and it may be sonically convincing but, again, it is not reproduction. It would be more accurate to call it something like a low Q organ pipe driven by a vibrating piston.

The joys of infinite baffles have been well-known for the better part of a century. Loudspeaker designers do know this. However, the economy, practicality, and "ported efficiency" of smaller enclosures drives the designs. Rudy Bozak, was one of the last champions of the infinite baffles and their practical equivalent of enclosures large enough to not appreciably load the rear of the cone. He hated ports for the very reason you cite.

Whether to center the loudspeaker or not depends. With an off center loudspeaker, the effectiveness of the shorter side will be limited to a higher frequency. As well the radiation pattern will be asymmetrical. One only needs to figure out if these things matter or not. As to implying it "must" be centered, I was thinking about my own situation when I wrote that where the wings have be about equal, but for other than acoustical reasons.

"You have never built a set of wings?" Based on your picture, I was designing loudspeakers (professionally) before your were born so let's leave it at that. You are right that the science is easy...at low frequencies. For example however, the screen/baffle reflections can make the science more difficult at high frequencies for high resolution HF horns. Then again, such horns are not at all common so this is more of a moot point.

"Secondly a usable response closer to 30hz in the real world.." 50 Hz was presented only as an example not as any kind of goal if that is what you thought I meant. I should have made that clearer.

Posted by Cameron Glendinning (Member # 3516) on 03-29-2012, 06:55 AM:

quote: Eric Robinson

What effect would a straight horn have on subwoofer sound?

Horn loading tends to increase efficiency, whether its folded or straight they tend to be very big beasts. Ultimately its purpose is to recreate sub bass frequencies which if well designed and well built, will in my opinion out perform a smaller bass refex design in terms of realism.

Posted by Paul Stevens (Member # 4016) on 01-07-2013, 07:02 PM:

I have torn two HF diaphragms from two auditoriums playing Les Miserables this last few weeks. New amps with new diaphragms and torn again. Could the Component Engineering crossover cards be failing?

Posted by Sam D. Chavez (Member # 1841) on 01-07-2013, 08:57 PM:

Hello Paul,

I don't see a previous posting from you on this topic unless I overlooked it.

So, I would look elsewhere first other than the THX monitor with CE made crossovers.

What is the model of the amps, brand and model of speakers? How big is the cinema?

It does sound alarming to blow 2 HF drivers in one week.

Posted by Louis Bornwasser (Member # 3063) on 01-08-2013, 06:13 AM:

First: put pink noise into crossover. Then go to amp output and be certain that nothing below the crossover frequency is present. It is helpful to know the make/model of the hf driver. Louis

Posted by Paul Stevens (Member # 4016) on 01-08-2013, 04:09 PM:

The original power amplifiers were QSC 1500C. The HF driver is an EV 81256. Both rooms are fairly large 72 X 53. Three new Crown T5000 HD replaced the QSC's in one auditorium. The crossover cards correctly isolate HF and LF components. Equalization does not involve any corrective HF spectra and sound pressure levels are to spec. Everything appears right under stand test criteria. Oh by the way, the duration to failure has been about a month. The domes are shattered. Very strange.

The common thread between the two auditoriums the 7.1 version of Les Measurable.

I have not sat through the nearly 3 hours feature in an attempt to locate any special spots in the sound track to directly analyze. However the highly energetic and compressed sound tracks of several releases in the last six months that something damaging my be blasting past all limiting factors that keeps parts from flying through the screen.

Thanks for any idea's you may have.

Posted by Sam D. Chavez (Member # 1841) on 01-08-2013, 07:34 PM:

It sounds like you have no lack of power from the Crown amps. The DH 1 driver that goes with the HF diaphragm you mentioned is used all over the place.

We don't know the horn type but this should not be the problem.

So this leaves all the other possibilities.

Cinema processor type might give a clue to likeliness of internal clipping.

Oscillation?

I have had problems with the 3417 crossovers and other monitors if there is no ground return from one of the power amp - terminals to the crossover -. Under certain conditions, it will break into ringing and the shattered HF units make this a likely cause.

LF leakage into the HF?

So you never had this problem before replacing the amps? How long ago were the amps changed?

Posted by Paul Stevens (Member # 4016) on 01-26-2013, 01:11 PM:

Thank you your thoughts. This is the strangest thing I have ever encountered. Will look into the ground return possibility. I suspect it may be a destructive octave that is just perfect for the diaphragm to shatter. If I can find out what it is I can filter it out.

Wish me luck!

Posted by Chuck McGregor (Member # 6826) on 01-29-2013, 10:58 AM:

quote: Paul Stevens
blasting past all limiting factors that keeps parts from flying through the screen.

As they are bi-amplified, are there "protection" capacitors in line (i.e. in series) with the HF driver on the amplifier outputs?

Typically HF diaphragms shattering is almost always the result of the diaphragm bottoming out against the phase plug. HF oscillations or excess higher frequencies will burn out the coil not shatter the diaphragm.

It would seem some kind of low frequency energy got to the drivers. This could be from a dc pulse, a low frequency oscillation, SW or LF signal bleed. Very hard to say.

All it takes is one good slam to the phase plug to cause damage. This is especially true for titanium diaphragms, not so much with softer aluminum ones, and very rarely a problem with phenolic-type (like polyamide), or carbon fiber diaphragms. One such HF driver made of the latter was tested for around 24 hours of hard slamming against the phase plug using an LF sine wave. The result? An abraded poly-carbonate phase plug. But I digress.

Bottom lines:

You almost assuredly had an "LF event" that occurred in or from something between the output of the electronic crossover and the drivers.

If you don't have them you (anyone actually who is bi-amplified) should have protection capacitors on the HF drivers to protect against both dc voltage and below crossover LF from getting to the drivers for whatever reason.

After the electronic crossover there is usually no such protection, hence the use of "protection" capacitors. This likely would not have happened had they been in place.

Such capacitors must be non-polarized "by nature," like metallized polypropylene (i.e not electrolytics back-to-back), have a low ESR (equivalent series resistance), and an ac voltage rating 3 times (for reliability) the maximum voltage capability of the amplifier (not driver). This should be the peak voltage aka clip voltage, not rms. A 250 V rating is usually sufficient and is a common specification.

Their value must be small enough to block as much low frequency energy as possible without substantially affecting the crossover response. This means measuring or modeling the crossover response with and without the capacitor. For a 500 Hz electronic crossover this would end up in the rough ballpark of 50 uF to 75 uF, but it depends. Higher crossover points mean a smaller value. Lastly they should be soldered in in-line right at the driver. I normally connect one lead of the capacitor directly to the driver.

This all means they could be big (inches in size) and cost way more than your your "average" capacitor. Sources are limited and after much research I settled on "Pulse-X" from ERSE Audio. It's "audiophile" oriented ($$) but the product has the right characteristics and thus worth the price.

It cost me about $60 each (with shipping) to outfit the 3 screen channels. Several times since then a pulse has been accidently sent to the drivers at the full output voltage of the amplifiers > 55 V, which was generated AFTER the electronic crossover. The driver is rated for 40 V peak, but only ABOVE 500 Hz. Because excursion quadruples for each halving of frequency this pulse with a lot of LF energy in it should have caused instant catastrophe = diaphragm dust. They're fine.

Just my $0.02

Posted by Paul Stevens (Member # 4016) on 02-09-2013, 08:21 AM:

Thank you very much for the 2 cents. I had very little knowledge of the material composition of the diaphragms, or that alternatives were available.

The EV replacements for both auditoriums center channels lasted only about three weeks before shattering. I received a generic version of the same diaphragm and noticed immediately the rigidity was much greater. I would guess that it was of a different metal composition. So far the generic versions are holding up.

Literally every component in the chain including active crossovers were changed out and levels meticulously measured. What leaves me more perplexed than anything is this has not be reported happening anywhere in the company system, and only two of the 17 auditoriums I maintain.

Thanks again for the recommendations.

Posted by Louis Bornwasser (Member # 3063) on 02-09-2013, 08:27 AM:

My experience with EV diaphragms is that they are very fragile. I am 98% JBL diaphrgms. I sold 10 times the EV diaphragms to the 2%. You do the math. Louis

Posted by System Notices (Member # 2357) on 03-23-2014, 12:27 AM:

It has been 406 days since the last post.

Posted by Bob Ezra (Member # 841) on 03-23-2014, 12:27 AM:

Old thread but

Mike- what model QSC screen speakers did you get and do you hear an improvement in dialogue?

Posted by Mark Gulbrandsen (Member # 72) on 03-23-2014, 11:51 AM:

They are three SC-423C's in biamp config right now, and two SB-7218's. I don't remember which surrounds or how many but it was quite a few. Fourteen comes to mind but that may have been another system...

Mark

Posted by Marco Giustini (Member # 4544) on 03-23-2014, 01:20 PM:

Nice. It's a shame nobody installs the THX wall anymore these days.

Posted by Bob Ezra (Member # 841) on 03-23-2014, 01:45 PM:

any opinions or experience with the 322xc ?

http://qsccinema.com/products/?family=Loudspeakers&series=DCS%20Series

Posted by Mark Gulbrandsen (Member # 72) on 03-23-2014, 01:46 PM:

This location is about 900 seats and we couldn't build a full wall because the stage is multipurpose. So we re-utilized a set of old Simplex Voice Of The Theater Speakers that were there as partial baffles and they were already on roll around stands. We reinforced the old stands and extended the baffle both up and down. Then covered it with the appropriate Johns Manville liner. The response was excellent in this room. There are four QSC subs not shown in these pictures. And these are fully triamped with four channels of amplification per channel. There are pins that go through the bottoms of the stands into the floor to properly locate each speaker when they are rolled back into position. Note that this theater is in a town of just 3000 people.

Posted by Bob Ezra (Member # 841) on 03-23-2014, 05:01 PM:

Is this Mike Blakesley's theatre?
It was his situation (at the start of this thread) that I was inquiring about.

Posted by Mark Gulbrandsen (Member # 72) on 03-23-2014, 08:12 PM:

Yes, the picture right below your question is.

Posted by Mike Blakesley (Member # 26) on 03-23-2014, 08:39 PM:

quote: Bob Ezra
Mike- what model QSC screen speakers did you get and do you hear an improvement in dialogue?

Yes, definitely a huge improvement. Plus the bass and directionality is improved with the baffle wall added. I love that we can play it nice and loud and people don't complain.

Posted by Bob Ezra (Member # 841) on 03-23-2014, 09:57 PM:

Mike

size of your room and # of seats?

thanks

Posted by Mike Blakesley (Member # 26) on 03-23-2014, 10:37 PM:

35' wide, about 100 feet long and has 194 seats (44 of which are in the balcony).

Mark - there are 12 surrounds (2 in the balcony) and they are the QSC wedge shaped ones.

To be clear - the picture just below Bob's question is my theater and the one below that is the Hyart in Lovell, WY.

Posted by Buck Wilson (Member # 5885) on 03-23-2014, 11:41 PM:

That baffle wall has me thoroughly aroused. Glad to hear it made a big difference

Posted by Jarod Reddig (Member # 6363) on 03-24-2014, 03:37 AM:

Got me aroused too. Agreed more theaters need to be doing this. Cheer Mike and all others who made the right choice.

Posted by Bob Ezra (Member # 841) on 03-24-2014, 08:11 AM:

QSC 322XC ... anyone?

Posted by Steve Guttag (Member # 268) on 03-24-2014, 08:45 AM:

I can't comment on its sound since I have not worked with it specfically (SC-322). The LF box is the same as their 400 series so it is well made, tuned...etc. The drivers on the LF-3215 are lower power and are clearly used as a low cost alternative to their more powerful drivers used in the LF-4215). The odds that the T-S parameters are identical between the two drivers are very slim so one should not expect the same response between the two (you can't get something for nothing). The HF section is the same as the 400 series HF so you are getting a similar response there. The passive crossover in this day and age should be avoided on design principles...more often than not they lead to driver failure if the system is driven hard.

So, if are interested in obtaining a well made speaker that will work without bi-amping so long as it is operated with the specifications of the speaker (300-watts...which isn't very much at all), I have every confidence that QSC made a good quality product. Is your targeted room suited to this speaker? You haven't provided enough information to comment. It better be a smallish room though. Is it going to be as good as the SC-422 or the SC-423 (or the SC-424)...not a chance. QSC's 3-way and 4-way speakers are where they really shine. It seems that they started with the SC-423 and then modified that design down to create the smaller cousins.

Sound wise, someone else has to comment on this model, including how well it tunes up in a typical cinema. I have not worked with it.

Posted by Bob Ezra (Member # 841) on 03-24-2014, 11:09 AM:

Steve

Thanks for that.

Room is 24x70 (1680 sq ft)- baffle wall behind screen.

Currently JBL 4638 Lf with 2385A horn - Qsc 1400 amps.

Not looking for huge sound but better dialogue intelligibility

Posted by Steve Guttag (Member # 268) on 03-25-2014, 09:49 AM:

My suspicion is that turning is where your problem mostly lies (or bad room acoustics). The 4638 is a decent LF system. It is the low-powered version of the 4648...same box, lower powered drivers...if it has the "TH" in the name, then the crossover is cut into the box.

The 2385 is actually a decent choice for your room since it is a 60x40...you have a long-narrow theatre and the 60x40 horn will keep the energy off of your walls better than a traditional 90x40 horn. The downside is that it is the small format horn and it will have poor pattern control below 1000Hz. I was never a big fan of the 2380 series. The 2360 series did MUCH better but they also were 3-feet deep.

Before throwing money at a new speaker...I would really look at the tuning, crossover and room acoustics. If you are going to buy new speakers and dialog is an issue...consider saving a bit more and look into the QSC SC-423 ...they are 3-ways (good ones) and will be horn loaded down to the 300Hz range. You'll need to, at least, bi-amp them but you'll have a chance of improving the dialog with this speaker. Going to another passive speaker with a wider dispersion is likely to make things worse. In fact, if QSC made their MF/HF in a 60x40 version, I'd recommend that. Note too, you could save money by reusing your LF section since that is NOT where your problem is.

Note, at a 70-foot room, you should have over 650-watts available to the LF section alone (disqualifies the SC-322 and all SC-300 series immediately).

Posted by Mark Gulbrandsen (Member # 72) on 03-25-2014, 12:00 PM:

Bob,

Before you do anything you should get your self new amplifiers. If not DCA's then at least the RMX's. The 1400's are reliable but a very old design with old semi's and old IC's with poor slew rates. You would be amazed at the increase in definition as well as high frequency extension when you install new amplifiers. For many of my customers just installing new amplifiers was the equivalent of rolling up a window shade that was seemingly in front of the screen. You also won't really be taking advantage of any new speaker's full performance with those old 1400's. And for D-Cinema you really should have more headroom anyway.

I have installed four sets of the 322's that I recall so far and in rooms about your length but narrower. They work well however, the dialog on the three way systems is much better IMHO, even the dialog intelligibility of the little SC-2150 which I have installed a few sets of in small rooms would blow you away. When I opened the first SC-322 upper section and saw how small they are I shook my head thinking these will never work.... But they turned out to be awesome.

Mark

Posted by Bob Ezra (Member # 841) on 03-25-2014, 11:07 PM:

Steve-
The room has been tuned by a highly qualified guy and acoustics are a problem.

I am in the process of ordering acoustic panels for the rear wall, hoping for an improvement.

Your analysis of my speakers was interesting and helpful.

Mark-
thanks too for your input

Posted by Jarod Reddig (Member # 6363) on 03-27-2014, 08:34 PM:

Do you have any pics of the room?