All houses are running JBL 4675 stage speakers, 8340 surround speakers(8-per house), and 4645B subs. Each house is between 300 and 350 seats.

Thanks
 

Thanks
Glenn
 

4645B is listed at only 97dB

You say your auditoriums are either 61' or 63'

You have 3 units...

You will need somewhere between 1000-2000 watts

To be precise...

You have 3 97 dB speakers...doing logrithmic addition yields a system efficientcy of 101.77dB for closely spaced speakers.

Now, using that with a 63 foot room and a desired max spl of 113dB in the middle of the room, we get:

1223 watts

For the 61 foot room the power reduces to 1148 watts.

This presumes you are indeed running your fader at 7.0 for all films. Your QSC 1400 only has only 550 watts into 2 Ohms at a whopping 1% distortion and only 1KHz tone, unlike real world conditions. Since you are only at 2.67 Ohms (nominal)your real world wattage is closer to 350-400 watts maximum.

Thus, yes you are under driving your subwoofers. The 4645B uses the JBL 2242 driver, probably one of the best drivers made at the moment. It can handle 800 watts of continious pink-noise or 1600 watts of "program power"...always use the pink noise spec for theatre subwoofer applications.

To properly power you subs, sticking with the QSC line up, You would need something like a DCA-3022..run two off of one channel and one off the other or, use two DCA-1222 amps , both bridged and again two subs on one amp, one on the other. Cost wise, it is a wash so I would favor the two-amp scenerio. Alternatively, if you have the depth and the weight capacity, QSC's new ISA amplifiers can offer a lower cost solution using a pair of ISA-450s in bridge mode.

One last thing to consider for your 4645B (and "C") subwoofers is to B-6 tune them to yeild a substantially improved bass response. Use the QSC SF-3 module on either the ISA or DCA line. Using other amplifiers, RDL makes the CX1S that will also allow B-6 tuning.

BTW, you are fine on your surrounds but are a bit difficient on your stage amplification if you run your system at 7.0. Ideally, you should have just over 300 watts and you only have 200 watts available.

Steve

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"Old projectionists never die, they just changeover!"
 

One other thought -- placement is always a way of improving bass efficency. Placing subwoofer bins in the corner of the room if at all possible will show a marked SPL improvement, as will placing bins as close to each other as is physically possible so they "couple."

My theory -- never be stingy with the subbass system. There is nothing that gives the patron more of a kick and the perception that you have a breathtaking sound system as a deep, rich, CLEAN subbass response. Make 'em FEEL it, and they will come running back for more.
 

You are always precise and clear!! I've amazed many of my colleagues with our last "chat" on power needs.
You said:
--
One last thing to consider for your 4645B (and "C") subwoofers is to B-6 tune them to yeild a substantially improved bass response. Use the QSC SF-3 module on either the ISA or DCA line. Using other amplifiers, RDL makes the CX1S that will also allow B-6 tuning.
--

What is "B6"?

Also: in one of our theater, 4 4645B Subwoofer has been placed directly under the center channel, on the centerline of the auditorium. Can this improve the resonance of the room?

Bye
Antonio
 

Think of "B-6" tuning like you would slit loss for optical soundheads. A speaker designer can purposly design the low-end fall off of their speaker to conform to the B-6 criteria (kind of a gradual roll off actually). If a B-6 filter is applied to the signal, it will apply a complimentary boost to the signal and high-pass the signal above the unload point of the speaker. As such you will get an extremely flat response down to the cut off point of the speaker and then a sharp drop (again, just like on your slit loss of an a-chain). As such, a subwoofer like the JBL 4645B, and the 4645C can be ruler flat down to 22Hz rather than starting to roll off below 30Hz. The 4641 and 4642A also can take advantage of the B-6 tuning

Another popular theatre subwoofer than can take advantage of the B-6 tuning is the EV TL-880D.

Some speakers call it "step-down mode." The older TL-880D had a movable port plate so you could choose wether or not use use it with B-6 tuning or not. That way if you didn't have the appropriate boost, you would get a more extended bass response if you moved (I think removed) the plate.

Now to the powered subwoofer stuff. There really is no advantage to them and in fact a disadvantage. There isn't any trick to matching amps to their application, subwoofer or otherwise. A good speaker manufacturer may not be the best qualified to make amplifiers and vice-versa. The damping factor arguement has long been exposed as sheer marketing. What is the biggest resistance in virtually any amplifier/speaker run? Why the voice coil, naturally (unless you are using 22awg speaker wire over 100 feet). Now if an amplifier has very poor damping then yes it can be heard as mushiness in the bass (anyone wanting to experiment, take a series resistor on their speaker line, some actually prefer the tubbiness).

If the amplifier is down by the screen and the processor is in the booth, you have a grounding situation to consider. It is unreasonable to expect that the path to the building ground rod is identical between the two desperite power sources (now you could have two ground wires go from the ground rod, one to each system and make sure both are of equal length, irrespective of how far they are away from the ground rod). As such you WILL have some form of ground loop if the grounds of the two systems are tied in any way. Since most balanced systems nowadays are active balanced, their will be a ground reference so even if you lift the shield at one end (as most people do) you will still have two different points on the ground system tied together. So now, if you want to keep the grounds interacting, then the best solution is to have a transformer in line. Now one should have a good audio tranformer to keep the frequency response good.

Then there is the service aspect, who would want to climb behind a screen to service electronics? Also one must power it and switch that power to avoid whomps and such as the system is powered on and off.

I trust your explanation of adding units until the power requirements were met was a joke. Since both powered and passive subwoofers follow the same laws of physics and performance can be predicted without too much hocus pocus.

As to placement...there are advocates of corner placement as well as directly center. The corner people try and take advantage of the interaction with the boundries so as to get an exaggerated response, the center people seem to go for "equal." Most of the theory I've read and experienced is that placing subs slightly off center will yeild the most uniform response. I don't run away in terror from corner placement nor center placement as if all is lost if it is done. My personal preference is to use two subwoofer arrays (or merely two) such that they are a little off center to the left and a little off center to the right. I have always found that if there is only one sub location, I can localize on it...I much prefer distributed subs, despite the omnidirectional claim. I think in theatres where the sub frequencies can get above 100Hz allows for perceived directionality.

There are programs such as EASE that will allow a designer to design subwoofer (and any other speaker) placement for optimal uniformity.

Steve

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"Old projectionists never die, they just changeover!"
 

Thanks for the response. We are currnetly only running one sub in those houses and not two. Im hoping to convince the new tech to add two. Sorry for the confusion. Im not sure what amps we will be using probably the QSC MX series amps. Can you explain series and paralell wiring configurations and how this effects the amp. As Antonio explained your explanatons are clear and concise and this has always confused me.

Thanks,
Glenn
 

I will read again your reply, I want to understand it very well.
In the meantime, one thing is not clear to me: how can be realized B-6 tuning with 4645B?
Do we need a particular type of amplifier?
Bye
Antonio
 

I guess I have just been listening to much to all the marketing hype about the ease of the packaged subwoofer system. And although BGW has been making high powered amps for decades, you are right, that doesn't mean that any company will necessarily excels at both speaker and amp design. Then, all you really needed to do was to say the words "ground loop" and all of a sudden I am running in the other direction. I know how difficult that nemisis can be. In our big house, the amp racks are unfortunately in an amp room off the side of the stage -- a good 200 feet from the booth. Grounding issues were a nightmare when we first started and ikt took lots of money for installation of a single point earth ground and lots of transforer swapping to get good sound and no loops. Now whenever I hear "active ballanced" or "electronically ballanced," I think, yah, that's fine, but buy the REAL transformer accessory anyway.

When I first started working in a small studio in another part of our complex, I found a ground potential difference WITHIN THE SAME ROOM of 17v between grounding pins on outlets with less than five feet between them. Try and get an active ballanced piece of equipment to null THAT out.

And yes, I was kidding about just keep adding subs, Although,that's the way I heard a cinema supply guy here in NY explain it -- funny thing is, he also said you could leave Dolby A in for SR prints and no one will know the difference. So much for cinema supply personnel. I sure wish you had a New York City office.
 

Glenn, I misread your post, you have 3 auditoriums each with only ONE subwoofer, not three, right?

If so you have a 97dB speaker...in the 63 foot theatre you will need 3670 watts! Got that much? Your amplifier, the QSC 1400 using just one channel into 8 Ohms has only 200 watts/channel. Hmmm sounds like it isn't going to work! Not to worry, you only need 3441 watts in your smaller 61 foot rooms! Again, this all presumes you run your fader at 7.0 and have tuned your system "to spec." If you are like most theatres, you probably are running at about 5 or so so you may take off 5-6dB...that brings you down to 860 watts for the smaller theatres and 917 watts for the larger one....hmmm still not enough.

The biggest bang for the buck any subwoofer system can get is the 2nd subwoofer...it brings with it normally a 6dB increase in output. This is due to the mutual coupling effects of the two units, and that most amplifiers will give you nearly double the power into half the impedance. So in your case, adding just one subwoofer to each system, will take you from 97 dB Sensitivity to 100dB and your power will shoot up from 200 to about 400 watts. You power requirements with two units will be cut in half (1835 watts, and 1721 watts respectively). And if you only run at 5.0 on the fader, you are practically there! This isn't the way to set up a system. You should set it up so at 7.0, everything is just fine. Since you have 800 watt speakers, the two sub senerio really isn't sufficient if you want to set it up to spec (though it will probably work fine). You would want to have at least 2000 watts into 4 ohms though. With the MX line of amps, that would be the MX-3000a (an excellent amp by the way, one of my favorites). Add the SF-1 subwoofer filter card to get the B-6 tuning and things would be nice. If I were designing the system, I would probably go to 4 subwoofers (using the 4645C). This would drop the power requirement to a reasonable 922 watts and using the MX line of amps a single MX-1500 would do the job with two units on each half of the amplifier. Now if cost is a concern (and when isn't it?) you can consider using the JBL 4642A...it is a 101 dB sub (double 18") you would only need 1461 watts in your larger house and it can handle 1600 of continous pink noise. A single MX-1500a bridged could barely handle it (1500watts @ 1KHz 1%THD). The 4642A's bass response is not quite as good as the 4645C's (or 4645B)...with speakers, one is always trading off efficientcy, response, sensitivity and size. The 4645C is JBL's best subwoofer at the moment in terms of performance (response/power handling). The 4642A is JBL's most efficient and often the less expensive solution though not quite as good bass (same with the 4641).

Now ignorance is bliss, I believe the Dolby nomographs cheats the subwoofer chart by 3dB (only requires 110dB instead of 113dB). I've never blown a speaker using the 110dB figure.

Antonio,

The B-6 filter can be realized by a variety of manufacturers of electronics. For instance, QSC offers a subwoofer filter module for their cinema amplifiers (SF-1 or the SF-3 depending on the model of amp), they also incorporate the option on their DCM line of monitor/crossovers. Radio Design Labs (RDL) also makes a cute little piece called the CX1S module that will provide the required boost (JBL used to sell it under their name briefly when the 4645B came out). I'm sure there are others out there as well.

Back to Glenn,

Wiring anything in series with the amplifier to the speaker, will kill it's damping factor (the amp's ability to control the drivers)...as such it normally will show up as a mushy bass response. Amplifier manufacturer's often use this spec (expressed as a ratio with the higher number being better) to show off their superiority. So even speaker wire can be considered a series resistance. However, it often is negligable in the over all scheme of the system. The driver's voice coil which often has impedances of 8-16 Ohms is much more significant unless you use really tiny wire over a long distance (to wich current limiting may come into play, if not fire hazards). Now an often overlooked aspect of this is in the surround arrays...many of us (me included) have used series/parallel connections on the surrounds to present a usable load to the amplifier. Not too long ago, anything below 8 Ohms was pushing it. Nowadays, most good amps will go down to 2 Ohms. Whenever possible, one should never wire speakers in series. The solution? Get more amplifier channels or an amplifier that can handle the load. With modern amps, a 5.1 sound system can use a single amplifier channel for up to 4 speakers (presuming 8-Ohms). What to do with a 10 speaker surround array (5 each side)? This is a sticky one and comes up a bunch. QSC makes the DCA-1222 that WILL run into 1.6 Ohms (5 8-Ohm speakers) all day long and not mind...it was designed to do that. Even series/parallel doesn't work well for 10-speakers since one group on each side will be louder.

If you must wire surrounds in series/parallel, minimize your series connections. For instance, if you have 6 speakers on each side (12 total) wire four groups of 3 parallel sets (two groups each side). This way each group is only 2.67 Ohms and that is the equivalent series connection to the other group. This will present a 5.3 Ohm load to the amplifier (each channel).

Lastly, I didn't want to imply that the powered subwoofers are necessarily bad, some, for instance, really think that the BGW unit is the cat's meow. I was just stating that just because they are packaged that they are somehow better is not necessarily true, and often isn't. I do firmly believe that in cinema applications, powered subs present more problems than they solve. The types of people that want the ease of powered subs don't normally think about the consequences.

I hope I answered all of your questions.

Steve

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"Old projectionists never die, they just changeover!"

Thanks for the info. That subwoofers are in a (Ted pls don't hear!) THX theater. I wonder if THX crossover will provide the B-6 filtering.
Can be these filters be applied to any kind of amplifiers? We have two JBL MPX600 driving 4 4645C.

Bye
Antonio
 

Steve

------------------
"Old projectionists never die, they just changeover!"
 

The ironic thing about this situation at my theatre with the subs is they have now spent more money on replacing drivers than they would have if they would have just put in the right amps in the first place. What is it with corporate thinking, it drives me up the wall sometimes !!!! Well i better stop now before i get on a rant.

Thanks again.
 

Thanks for the info. I saw that SF-1 on QSC website costs only 150$. We have 4645C subwoofer, why it wasn't installed a B6 configuration????

Bye
Antonio
 

I can't speak to other designer's or installer's methods. I do find that the majority of people tend to install stuff without really knowing what they are doing but rely on and/or copying what other have done. There is also the cost factor...often one can loose a sale to another simply because one was cheaper...the fact the end-user gets less is of no consequence. After all, the system worked when it went in, to some degree.

Glenn, what have you been doing with your drivers from your subs? I'm amazed by the amount of people that have never heard of reconing. When a speaker fails, it often can be repaired as good as or better than new. For instance, the 2242HPL driver used in the 4645B costs less than 30% to recone as to buy a new driver. There is NO difference between a reconed unit and the new unit. A driver recone basically keeps the frame and magnet structure and all of the rest is replaced with brand new components so all of the wearables are replaced.

E-mail me if you are interested in having your speakers reconed (or replacement diaphragms for that matter on Altec, EV or JBL).

Steve

------------------
"Old projectionists never die, they just changeover!"
 

I agree with you but... what about THX? As I said it is a THX theater and I have the original projects. There are no Subbass filters in the needed equipment.

Bye
Antoni
 

As to THX...I don't believe that THX would have a problem with the B6 filter as it would extend the bass response of the system. You can always ask them before doing it. To my way of thinking, if a speaker designer tuned their box to the B6 specifications (part of that whole Thiele-Small thing) then to not apply the complementary filter to the signal is to have an incomplete system. Kinda like encoding with Dolby NR but not decoding with Dolby NR.

Steve

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"Old projectionists never die, they just changeover!"
 

Now that I know what is B6 I agree with you that a filter has to be installed with B& compatibile speakers.
THX: Do you mean that THX will not "force" a B6 setup with 4645 and others b6 compatibile speakers???
On the THX's specs sheet I have there are wrote type and numbers of speakers, type and numbers of amps that has to be used for that cinema. Why does THX didn't write two B6 filters??

Bye
Antonio
 

You are asking me to try and figure out why THX does or does not do things? You are joking. Right?

Steve

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"Old projectionists never die, they just changeover!"
 

I will get back to you on the re -coning you mentioned. Im currently with UA and im part of the big mereger right now so im still uncertain about what Regal's procedures are for getting things repaired but im gonna mention it to the regional tech who is coming through to look at his new theatres. If we where still UA id get them fixed but stuff has been kinda on hold since the the whole merger started.

Thanks again.

 

Looking at the old JBL sheets...the MPX line of amplifiers did NOT accept modules...only the MPA line did...sorry. To the looks of it, the MPX feels like the legacy line of CX amplifiers. Had you had the MPA line, then the IM-11 module would be the subwoofer module. Not to worry though, there are other means, like the RDL device.

Steve

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"Old projectionists never die, they just changeover!"
 

Thanks! It's funny, I've wrote to QSC and answered me that MPX600 is similar to MX1500a so "perhaps" it should accept SF-1!

Since I didn't found any data sheet on JBL MPX amp, I trust you!

Thanks again for your time!

P.S. I found RDL filter you said at 89$. HOW can someone think to not install it with capable subwoofers????????
Also: I downloaded the PDF data specs. I saw that RDL make a boost of +5.5dB on 32Hz for 4645B. But... I never saw the frequency response of a 4645B without EQ. Shouldn't freq. response has to be flat?
How will be the final freq response of the 4645B with Dolby EQ + Boost filter?

Bye
Antonio

We are looking for someone to take care of are blown drivers also.

Thanks for the help !!!
 

Look at the JBL 4645B (or C) data sheet. It shows it's response with and without the filter. That should answer your question.

Glenn:

The USA line of amplifier was NOT a replacement of the Series 1 (eg 1400, 1700) but a lower cost, stripped down version. The USA line basically was the same amp though (internally). The USA line did not offer the octal plug in ports to use accessory items but the later generation of USA amps did have Neutrix "combo" jacks that were nice.

The USA-1300 would not be my first choice for you since it was probably QSC's most failure prone amplifier (sorry to say). It was eventually replaced by a nearly identical looking USA-1310. A USA-1300 or 1310 with four 4645 subs would work fine. (two per channel). I have never been a big fan of running either the USA or series 1 amps into 2-Ohm loads (4-ohm bridged) though they are rated to do it...they will run HOT.

It seems though that you are moving in the right direction though.

Steve

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"Old projectionists never die, they just changeover!"
 

Although I just sent two of them back for out-of-warranty repair, and I thought their repair rates were reasonable.
 

Yes, I saw the pdf and I finally understood what "WITH EQ" and "WITHOUT EQ" mean!! Thanks

However you told that 4242A does not support B6 setting. But on specs I saw that there is the same "with eq" and "without eq"... What does it means?

If 4645C freq. response w/o the filter is as declared I wonder why JBL doesn't sell the filter with the sub...

Final question: why "B6"? What does it means?

Bye
Antonio
 

Thanks,
Glenn
 

I've heard that the Mx3000a and the EX 4000 are the same thing but different front, but then I heard from another source that the Mx3000a is a scaled down version of the EX4000.

Where did I say the 4642A did not support B6? In fact, I said the 4642A DID support B6 as does the 4641 from the JBL line up...the older original 4645 (no suffix) and the original 4642(no suffix) did not support B6.

B6 is a Thiele-Small classification. There is a word to describe the class that is at the tip of my tongue. You should be able to find more about B6 if you do some research into speaker design and the works of Thiele and Small.

The USA-1310 was not as failure prone as the USA-1300. Running it bridged into 4-Ohms is indeed rated though it will run hot. Bridged into 4-Ohms is the same load to the amplifier as stereo into 2-Ohms. Good luck (I'd recommend pressurizing the rack with a filtered blower (on the bottom).

Steve

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"Old projectionists never die, they just changeover!"
 

You're right. I was dreaming...

THANKS for your availability. As I said we have 4 4645B without any B6 filter and with a poor EQ (they have a very poor sound ). Tomorrow night I'll check the polarity of the entire system. We were going to have our tech to fix the EQ but now that I know all about B6 tuning I'm goint to talk with my manager to have CX1S installed before new equalization.

It is always a pleasure to talk with you!!

Bye
Antonio
 

I explain the B6 filter to my manager. It seems that I've discovered "hot water"...

Seems that noone in Italy knows about the B6 configuration with JBL and Electrovoice subwoofers...

I have a question: 4645B has 97dB sensitivity and 800W pink noise power. The B6 filter give a boost of 5.5dB at 30Hz (+/-). When I'll apply the filter, should the power needs increase?
In other words: the 4645B/C can handle 800W with or without the B6 filter?

I would avoid to blow something...

Bye
Antonio