Film-Tech Forum ARCHIVE: Baffle Walls

This is topic Baffle Walls - Need them or Not? in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by William Bunch (Member # 1040) on 03-23-2003, 07:56 PM:

I have searched the history threads here on the subject of baffle walls and only find the term mentioned indirectly with speaker topics.

My question is: Does a baffle wall offer significant improvement in sound dispersal/fidelity or is it a nice-to-have in only really LARGE auditoriums?

I will be rebuilding one of our older military theaters soon. New projector, new processing, all new JBL speakers along with a new screen. Now is the chance to add any extras that can set us apart from the others.

The building is constructed of all wood. Acoustics are good and the only hard surface is under the seating. There is a sloped floor (not stadium) with 500 seats. Room is a little wider than the screen is wide. Screen is on a stage made of hardwood flooring and is 16 x 35 ft. There is about 10 feet of blank space behind the screen and then a blank wall. Lots of border and bracket curtains. This room is often used for briefings and such but never for theatrical so the screen and speakers never move.

I could easily afford the labor and building materials. Is this an effort worth having or not?

Thanks a BuncH

Bill BuncH
Misawa, Japan

Posted by Gordon McLeod (Member # 33) on 03-23-2003, 08:26 PM:

The baffle wall effectively increases the radiating area of the speaker extending the lowfrequency response
It also stops secondary sound reflections from the back of the screen reducing the loss of inteligablity of dialogue

Posted by William Bunch (Member # 1040) on 03-23-2003, 08:30 PM:

I forgot to mention that my screen channels will be comprised of JBL 4632T speaker arrays.

Bill BuncH
Misawa, Japan

Posted by Phil Hill (Member # 371) on 03-23-2003, 08:31 PM:

I agree Gordon, I always push to use baffle walls in all installations. Be sure to put sound-absorbing material on the wall as well as the speaker boxes. Ummmm...Don't cover the radiators!

>>> Phil

Posted by Mark Gulbrandsen (Member # 72) on 03-23-2003, 11:23 PM:

Baffle walls make a huge difference, but be sure to build them to THX standards or better. Building to less than their specs may get you more bad results than more good. Stick with the reccomended baffle wall acoustic covering too. There is a big difference in available coverings there. Just because its black doesn't mean it will work appropriately. Use of good quality acoustic panels or acoustic treatment of some sort for the auditorium is also a very necessary item. The back wall is the most important and usually requires at least double the thickness, or more, of the side wall coverings...assuming you're doing an average auditorium.....
Mark @ CLACO

P.S. I forgot to mention that doing all of this the right way is VERY expensive....just to prepare you.....

Posted by William Bunch (Member # 1040) on 03-23-2003, 11:52 PM:

Where would a person find a list of materials that would be considered suitable acoustical surface material for the baffle wall? If you are talking low or high density fiberglass wool then, I can get that readily here.

The wall itself would not be a major cost for me but when you start talking about covering the building itself then that would be prohibitive since the building does not belong to my company. Only the projectors, screen and sound system are in my control. (It's a government/military thing)

Could I build a decent wall only and reap a significant benefit?

Did I forget to mention that the screen is slightly curved? That should not be a major finding, right?

Thanks for your inputs! I'll digest any and all.

Posted by Antonio Marcheselli (Member # 373) on 03-24-2003, 03:45 AM:

A question about baffle:

Reflections: If I have no sound wall but I put the sound treatment stuff on the back wall (that is, say, 2 meters behind the screen) shouldn't I have the same result?

Bass frequencies: If I correctly understood put the, say, subwoofer against a wall increase the SPL response because since bass frequencies are omnidirectional, I take advantage of the rear emission without having them out of phase in the seating area. Right?

But if I put the subwoofers on a sound wall, what is the end of the bass frequencies that come from the rear of the speakers? They're trapped in the wall-soundwall space and not useful?
I'm sure that I didn't understand something! [Smile]

Bye
Antonio

Posted by Darren Briggs (Member # 1071) on 03-24-2003, 06:51 AM:

THX mentioned the introduction of a Bafflete, which just goes around the speaker array, this is a cheaper way of doing things, probably to try get the cost of installing THX cheaper?? Ill try dig out some more details on it.

Darren

Posted by Gordon McLeod (Member # 33) on 03-24-2003, 08:36 AM:

The baffelet design requires a cross over that does bass management like the new THX one

Posted by Steve Guttag (Member # 268) on 03-24-2003, 08:37 AM:

Consider using the JBL 4675C/4LF (or 8LF if want) over the 4632. To my ears, the 4675 is significantly better. If you want a 3-way, look towards the JBL 5000 series.

Steve

Posted by Mark Gulbrandsen (Member # 72) on 03-24-2003, 09:26 AM:

Whoa, I missed that he was going to use the Screen Dissaray speakers.......Definately go with Steve's reccomendation.....it will be ALOT better overall!!
Mark

Posted by Per Hauberg (Member # 529) on 03-24-2003, 10:36 AM:

I'm about to do something to my front in Screen #1 this summer, too. For my only 88 seats, and from what i read in brochures, i believe JBL 3632T would be a top-investment, together with a baffle-wall. -Any of You familiar with this particular model ?
As far as i understand, the 3632 can be ran bi as well as tri coupled. -Just how big a plus will the expense for extra amps and wiring give...?
I have enjoyed those great pictures from the Film-Tech Screening room. This must be exactly to do it right, i guess - but the THX specs, Mark is mentioning -- can they be seen anywhere without being THX custumer ? -And anything else on print about the proper bafflewall installation ??

Thanks for any advise on this.

Per

Posted by David Stambaugh (Member # 1102) on 03-24-2003, 10:38 AM:

There's a formerly-THX-certified theatre here in Eugene that uses the bafflette (sp?) design. From a listener's perspective, the results seem to be very good, and low-end articulation is excellent. (Happens to be EV speakers though.)

Posted by Darren Briggs (Member # 1071) on 03-24-2003, 01:00 PM:

I Can highly recomend Martin Audio systems

Darren

Posted by William Bunch (Member # 1040) on 03-24-2003, 06:23 PM:

Steve, Too late. Already locked into the JBL 4632T with SST modules. Just unloaded the truck last week. Only took ten months to get here. Guess I'll just have to make them work somehow. Anything will be an improvement over what we have existing.

Does anyone remember the Jim Lansing Ampex theater speaker Model 5050? That unit used what could be called a "bafflette". It was a small 2x4 and plywood wall that surrounded the entire enclosure. This speaker system is still in use in some of our older theaters running mono. My shipping documents say they were shipped over here around 1954. This is a horn reflex type box. Many twists and turns. A small person can actually sit inside the port. But they better have hearing protection.

Posted by Mark Gulbrandsen (Member # 72) on 03-24-2003, 06:56 PM:

Bill, There are baffeletts available for many of the JBL speakers. You could also fabricate yourself them on-site as well. Use the same duct liner THX uses and make them extremely rigid. I've used layers of Drywall in past projects same as in the full scale baffle wall. The stuff is extremely dead.

My condolences on being stuck with the screen dissaray speakers. JBL makes much finer products than those!!
Mark

Posted by Steve Guttag (Member # 268) on 03-25-2003, 12:03 AM:

RE: 3632...Consider the 4675C or the 4670D (2-ways) or if you insist on a 3-way...the JBL 5000 series is out there.

Remember this...a good 2-way beats the heck out of a middle-of-the-road 3-way. If you aren't willing to spend $3000 or more a speaker on the 3-way, you should probably consider 2-way speakers.

Now whereas you got the SST modules...you will have ALOT of work ahead of you. The SST is a basic 3-way crossover to be used in the Crown CE or CL series of amplifiers.

My most successful 4632T (or 3632s for that matter) have been with DSP based crossovers (RANE RPM 26V). Being able to apply appropriate parametric EQ, and custom crossover points and such minimized phase anomolies. I don't think you can tune a 4632T with 1/3-octave EQ and not introduce substantial time-domain errors. The midrange horn is the trickiest part of it.

Good luck and listen often as you attempt to tune them.

Steve

Posted by William Bunch (Member # 1040) on 03-25-2003, 03:55 AM:

Egads and Ommigosh! Please don't tell my bosses.
Steve, I greatly value your opinions on this forum. But now I wonder what sort of monster I've moved in with. It is like a bad dream.

If this system is so terrible why would they still make it push it on the market? I'm sure your opinions are based on solid experience.

Well, there will be no turning back now. Just gotta dive in and make it work somehow. I do have experts in Tokyo that I can call in if the going gets tough. But they are partial to EAW systems.

I did get the proper amps to go with the crossovers.

This thread is supposed to stay on the topic of baffle walls so I will now go elsewhere to study up three way speaker systems now.

Posted by Steve Guttag (Member # 268) on 03-25-2003, 07:14 AM:

Who said anything about being terrible? If you read around the threads you will find that speakers/sound is VERY subjective. What I personally may like has nothing to do with what is best, persay.

I've tried to keep my comments relating to the factual aspect of my experience with the speakers. That is, be very careful how you tune the mid-range section and give yourself listening tests to see how well you can make the analyzer and your ears agree. When I'm done with them, the customer has always been pleased.

I've tuned them with all analog crossovers and digital crossovers without nar a complaint from the customer (after hearing them...he bought three more theatres worth of them). Another nice aspect of the digital crossovers is that now that I have sussed out the speaker...I can download my settings on any future installations and generally, without ANY 1/3-octave EQ...I'm already at the X-Curve. If you read JBL's spec sheets, you will find that they base their frequency response of the 4632T on using their DSC-260 digital crossover.

However, given a choice, I'll take the JBL 4675 over it every day of the week. To my ears, it is superior sounding and MUCH easier to tune.

So, wipe the sweat off your brow, go in with an open mind and take it slow and easy and let us know how you made out...preferrably with baffle walls!

Steve

Posted by William Bunch (Member # 1040) on 03-25-2003, 04:03 PM:

Thanks Steve, I feel better now. I just finished opening a new restaurant and am now working on a retail store renovation. Hope to take some time off on vacation before I start in on the theater project so it may be a while yet.

Your points are well taken. Thanks to everybody here for their input. I'll report back later when the smoke clears.

Posted by William Bunch (Member # 1040) on 03-25-2003, 10:48 PM:

Here is a picture of the 1954 Jim Lansing/Ampex model 5050.

Mark, I'm assuming when you speak of "bafflettes" it would be something like this?

The Army and Air Force still have some these speakers in operation. So simple they work.

Posted by Mark Gulbrandsen (Member # 72) on 03-25-2003, 11:06 PM:

Yea Jim,
That sort of thing will work fine. Just extend these up to and above the HF horn. Cover it all with appropriate black duct liner of the type THX reccommends. Going above the hhf horn helps to reduce reflections that come back off the screen and improves MF, and hf clarity alot. Use 5/8" drywall, in layers, its cheap. No less than 2 layers and preferably three. I don't think I'd use plywood as they did back then, or HD particle board either. those are not dense enough. I've seen em made form all sound panel material, but I thought they were too absorbative, and too much loss of hf.....

Sorry...I can't remember the liner number off the top of my head......anyone else here remember??

Mark

Posted by William Bunch (Member # 1040) on 03-25-2003, 11:31 PM:

I finally got hold of some decent construction plans for a full wall. I will breeze by my contractors with it to see what is feasable. Much rather have the full deal if possible. There is no such thing as 5/8" gypsum board in Japan so will just need more layers of the thinner stuff I guess.

Thanks, everybody. I'm learning alot in the past few days.

Posted by Rob van Ede (Member # 1457) on 03-26-2003, 03:17 AM:

Wasn't that Lansing speaker a frontloaded open baffle design? If so, the wings are for preventing dipole cancellation so there is some bass output.

Antonio, a speaker radiates only from the drivers and ports, not from the cabinet walls. If mounted in a wall, there is no output behind the wall. The output can still be omnidirectional, but pressure normally lost in the space behind the driver is now reflected into the auditorium.

Posted by William Bunch (Member # 1040) on 03-26-2003, 07:41 AM:

Rob, I have tested your theory. I have one of these very same speakers that we use for outdoor events. At first it was just the main box on wheels. Then I got smart and tried replicating the baffle wall with two large wood panels off to each side. What a HUGE increase in the lower frequencies and all directed forward. It is easy to fill a completely wide open soccer field.

Lansing knew what he was doing. The waves from the back of both drivers is first combined and compressed then is bent three times in an ever widening horn like channel until it comes out the bottom. Like a folded foghorn.

So what was happening without the wings was the the longer waves were exiting the throat and wrapping around the back and cancelling out. Now with the wings attached you can stand directly behind the box and "feel" very few sound waves.

This box produces some VERY low frequencies effortlessly. I had to make the wings out of 2x4 with 3/4 plywood. All members glued and screwed. They attach with long 3/8" bolts with extra large washers and LOCKWASHERS. Earlier versions of attachment just rattled loose.

Having learned all this before is why I came up with my original question about whether or not a baffle wall could improve auditorium projection the same as in an outdoor setting.

Posted by Gordon McLeod (Member # 33) on 03-26-2003, 09:23 AM:

Properly done the baffle will improve the low frequency reproduction and the intelligability of dialogue