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Author Topic: Making small speaker baffles John Walsh Film God Posts: 2490 From: Connecticut, USA, Earth, Milky Way Registered: Oct 1999 posted 02-14-2004 10:31 PM                     Our company is going to refurbish one of our theater complexes. It this location, there are no baffles or bafflettes behind the screen. The area behind the screen has an exit hallway, so the speakers are on top of the exit ceiling. I don't have much of a buget, but I was thinking of making small baffeletts for each speaker. The idea is that the exit hallway facing the screen could be part of the baffle; I would just place a pre-made section around the speaker, even with the existing wall. Would there be any advantage in placing a 2ft wing on each side, and top of the speakers we're using (JBL4675's)? I'm wondering: Is a 2ft wing is too small to do any good? I'm thinking of this size because I can use one sheet of 3/4" plywood, with not much waste, for each speaker. I'd make a frame, put ductliner on the face, and bolt it to the speaker decking. Opinions?  |  IP: Logged Adam Martin I'm not even gonna point out the irony. Posts: 3686 From: Dallas, TX Registered: Nov 2000 posted 02-14-2004 11:40 PM                     You mean something like this?  |  IP: Logged Ian Bailey Master Film Handler Posts: 317 From: Nambucca Heads, Australia Registered: Jun 2003 posted 02-15-2004 05:50 AM                     Ok I haven't seen these wings before can I get a bit more information on what they do.What they are made of-"duct liner" is that like fibre-glass insulation? And when installed can you hear the difference?  |  IP: Logged Ian Price Phenomenal Film Handler Posts: 1714 From: Denver, CO Registered: Jun 99 posted 02-15-2004 12:36 PM                     I tried to find a paper on the use of baffles for cinema speakers but I couldn’t find anything written. So I’m going to give it a whirl off of the top of my head. Bass waves are very large. A 30-Hertz bass note is about 30 feet long. When Altec Lansing first came out with their cinema speakers they were all horn loaded. The size of the horn has an effect on how low that horn will play. Klipsch used the walls in the corners of the room to increase the horn size with their Corner Horns. Altec used Baffles on their A1 through A5 cinema speakers to increase the bass energy coming from what were very small excursion drivers. Also when bass energy goes around the speaker it tends to cancel the signal at the back of the speaker. If you can stop the bass energy from going around the speaker, you can subjectively increase the perceived bass energy. So why doesn’t every home speaker come with a big old flipping baffle? Baffles tend to propagate the sound energy along the baffle and destroy imaging. The entire concept of stereo speakers is imaging. The idea is to sit in the sweet spot and close you eyes and “see” each instrument in its proper position on stage. It is very hard to get proper stereo imaging in a movie theatre because you have people sitting everywhere at once. So the first thing you can get rid of is proper imaging in favor of increased bass energy. Now how do we get proper stereo imaging for all these people? Well first we add the center channel, which has always been there to anchor the dialogue behind the screen. Then we add surround speakers to place sounds coming from discreet locations. Then the speaker manufactures discovered that you could increase bass energy by using larger excursion speaker cones. Then you can port the speaker or add some sort of sympathetic vibrating device like a passive woofer to increase bass energy. All of these approaches have the problem of introducing various types of distortion to the sound. So the problem in picking speakers for any room is how big is the room? How many people will be sitting in the room? What is more important to you, efficient, copious bass or proper stereo imaging? If you have 1-3 people sitting in a room listening to pop, jazz or classical music then a small speaker without a baffle and with proper imaging might be good. If you have 100-1,000 people sitting everywhere in a room and you need to hear clear dialogue and thunderous explosions, then a nice horn loaded speaker with proper baffles will help. Baffles in a theatre tend to increase bass energy and limit room interference problems to more focus the speaker for clear sound. In-wall speakers give you that baffle but with thin flexible speaker frames and very resonant walls. A theatre baffle is usually an inch thick partial board or plywood with a layer of duct liner on the face to control slap echo and to limit high frequency smear. The best kind of baffle is a baffle wall that is continuous from speaker to speaker and to the sidewalls. But they have discovered that you can get 80% of the effect from small baffles or wings attached to the speaker. Usually these are as tall as the speakers and 3 feet wide. Yes you can make them yourself with inch-thick plywood or MDF and black duck liner on the face.  |  IP: Logged Adam Martin I'm not even gonna point out the irony. Posts: 3686 From: Dallas, TX Registered: Nov 2000 posted 02-15-2004 01:14 PM                     Wow. And here I thought the only purpose of the baffle was to reduce echo by absorbing some of the sound bouncing back at the speaker from the rear of the screen.  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 02-15-2004 02:06 PM                     John, Actually its better to stick to Drywall for baffles because of its deadness. With todays high reproduction levels and bass energy a simple plywood baffle might be more likely to rattle and squeek unless its reinforced by a very well made frame. You can make a lesser frame, cover it with 5/8 drywall and then duct liner of what ever you normally utilize for absorbtion. be sure to go up at least a foot above the mouth of the hf horn and figure the baffle size by eigth wavelength, quarter wavelength or half, etc. depending on your size constraints. Any decent baffle around a screen speaker will be a benefit though. Also be sure to completely cover the entire back wall behind the screen and the reear wall of the room with at least 2 to 3" of material. Adam actually hit a much more important point of a properly designed baffle, or baffle wall. It does a big job of limiting the relfected high frequency waves bouncing back and increasing distortion and uninteligibility levels. The other important function a baffle wall does is to reinforce the low frequency end of the spectrum. Typically it will increase the bottom octave 2 to 3 db. This is actually a benefit as one can cut back the lowest 1/3 frequency adjustments a bit and lower the normally high harmonic distortion produced by woofers. I normally dump the 30 and 40 hz adjustments completely in any installation that has a sub woofer as this is normally(but not always) the highest point of distortion produced by a woofer. Extreme LF distortion is usually measured in the tens of percent!! We will also be building quite a few smaller baffle assemblies for several upcomming jobs. I've seen over the last 25 years that way too many techs think that placing the speaker up on a shelf is all there is to installing screen speakers in a room. This is absolutely NOT true. Mark @ CLACO  |  IP: Logged Jeff Stricker Master Film Handler Posts: 481 From: Calumet, Mi USA Registered: Nov 1999 posted 02-16-2004 05:54 AM                     The way I had it explained to me a baffle keeps the sound waves produced by the rear of the speaker cone from reaching the waves produced by the front of the cone. At low frequencies, these waves combine out of phase and limit the low frequency response. The demonatration I saw was using a 2ft X 2ft piece of plywood with a 6" hole in the center. The person doing the demonstration held an operating 6" speaker in his hand, then he placed it on the baffle at the hole. What a difference in the sound!  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 02-16-2004 09:00 AM                     Thats exactly right Jeff for an unbaffled or unenclosed driver. The drivers that are being installed in cinemas are already enclosed and on a baffle though so the baffle wall serves to reinforce the LF energy and helps couple it to the room in a more efficient way. Mark  |  IP: Logged Manny Knowles "What are these things and WHY are they BLUE???" Posts: 4247 From: Bloomington, IN, USA Registered: Feb 2002 posted 02-16-2004 11:06 AM                     What are the odds that all of these reasons are valid?  |  IP: Logged John Walsh Film God Posts: 2490 From: Connecticut, USA, Earth, Milky Way Registered: Oct 1999 posted 02-16-2004 11:25 AM                     Thanks everybody! This is a drawing of what I'm thinking of (hope it comes out OK...) The idea is, well, I can't spend too much money, so I was thinking of using just one sheet of drywall(thanks, Mark!) per speaker; I'll need a total of 27. I wasn't planning so much of increased bass, (Ian P's idea) which is a good one, but I figured the baffle was too small. It was the reduced 'screen reflection' (Adam's idea) I was going for. We will have a subwoofer here, but I can't have too much power, because the walls at this theater are not too well isolated; sounds can be heard in the next auditourium. Thanks for several good ideas! If you think of anything else, please post it. If we do this, I'll take pictures and try to get an idea of if it was successful.  |  IP: Logged Gary Crawford Expert Film Handler Posts: 200 From: Neptune NJ USA Registered: Nov 2003 posted 02-16-2004 03:03 PM                     I was curious as to how high your speaker(s) would sit off the floor. Thanks for the drawing, I saw it would be centered at 4'8". Keep in mind the accoustics of the room. In the older theaters (with stages that is) the rooms were designed for a speaking person's mouth, somewhere near 5' off the floor. We did a restoration some years ago and just parked a speaker on the stage floor while we worked on the sound system. It sounded flat, actually awful. One of us remembered about the accoustics, and the normal height of a person's mouth onstage, and placed the speaker on a table and a small wooden platform so it was centered at 5'. It sounded great all of a sudden.  |  IP: Logged John Walsh Film God Posts: 2490 From: Connecticut, USA, Earth, Milky Way Registered: Oct 1999 posted 02-16-2004 03:28 PM                     Gary; The speaker(s) are on top of an hallway, like in this picture: On the right, you can see the screen is placed in front of the hallway wall; there is no classic stage, just a area for speakers. There is a SMPTE standard that suggests to place the HF horn at 2/3 the screen height. This means that, at least for close ups of actors, most of the sound will seem to be comming out of their mouths.  |  IP: Logged Manny Knowles "What are these things and WHY are they BLUE???" Posts: 4247 From: Bloomington, IN, USA Registered: Feb 2002 posted 02-16-2004 05:12 PM                     How sturdy is the construction of that "hallway"? Any concerns about that platform vibrating? Are the speakers sitting bare on that plywood or are they decoupled? Is wall-treatment still required (or recommended) behind the screen even when baffles/bafflettes are present?  |  IP: Logged John Walsh Film God Posts: 2490 From: Connecticut, USA, Earth, Milky Way Registered: Oct 1999 posted 02-16-2004 05:38 PM                     Hi, Manny; Good point about the hallway construction.. I'll have to look at it when I'm there again. All speakers will have the Mason "Super W" pads, so at least there's a little isolation. Again, the wall isolation is not so good, so we're sort of stuck not being able to turn the sound up. We have THX approved auditoriums that have no ductliner/insulation of any kind behind the baffle wall, neither on the baffle backside, or on the rear 'demising' wall. But those are full baffle walls, not 'bafflettes.' So the thinking is there's no way for the sound to get back there (to echo) in the first place. I did a theater recently (non-THX) and was afraid to do that, so I did put regular insulation on the rear wall just in case.  |  IP: Logged System Notices Forum Watchdog / Soup Nazi Posts: 215 Registered: Apr 2004 posted 03-05-2007 11:45 PM                 It has been 1113 days since the last post.  |  IP: Logged

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