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Author Topic: Sound and acoustics Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 05-02-2016 08:01 PM                     Exactly, In the 1980's I had a customer in Wisconsin that liked to experiment. We finally ended up with individual roof decks, floors that were not attached to the walls and had expansion joints, and at least several "S" turns in the HVAC duct and floating roof units. All this combined could usually produce ~NC-28. Mark  |  IP: Logged Ted Uzzle Film Handler Posts: 19 From: Chicago, Il., U.S.A. Registered: Oct 2015 posted 05-03-2016 12:57 AM                     And so, we're off to the races! The problem of sound transmission from auditorium to auditorium has engaged me since the 1970's, when everybody was building walls down the middle aisle to convert to twins (or two walls, for triples). But, the first rule of troubleshooting is, don't try to fix it until you know what's wrong. There are three ways sound gets from one room to another: structure-borne vibration, panel re-radiation, and flanking paths. You need to know which it is before you initiate a solution. Structure-borne. Wow. Floating floors? Room-in-a-room? That's as costly as adding a second story onto your house. Well, okay, if the problem were a tap-dance studio on the second floor above a cinema. In real cinemas the problem is a vibrating loudspeaker cabinet attached to the structure somehow, even if only sitting on the floor. Here's what I'd do: set the loudspeaker on springs, or suspend a surround loudspeaker from springs. Not the springs you get from a hardware store, the kind you get from a vibration-damping company. You tell them the mass (weight) of the loudspeaker, they calculate the spring compliance needed for the system to resonate at a subsonic frequency, then make and ship them to you. The loudspeakers still set the structure in vibration, but nobody can hear it. The audible frequencies are dissipated as heat in the internal friction of the spring movement. A multiplex can be retrofitted in one day. (These systems can be more complicated than steel coil springs, and often include dissipative elements of neoprene or butyl rubber, to widen the quality factor of the band-pass filter. If you know the physics and want to do homebrew, Amazon has automotive coil springs for $44 the pair. The formulas take about 20 minutes on a pocket calculator.) These companies do this for virtually every big rooftop air-conditioning unit in places of public assembly. Got a huge rooftop unit? Climb up and go roofwalking. See how the units are connected to the roof. Usually the spring will be internal to the unit; bring a screwdriver to remove the side panel next to the leg. The air-conditioning industry understands vibration damping. We haven't twigged to it yet. Don't implement this, however, until you have tested and eliminated panel re-radiation and flanking paths, which are far more likely the cause of the problem. Yup, we're underway. I'm so energized. Let's hear your ideas, war stories, and solutions.  |  IP: Logged Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 05-03-2016 08:28 AM                        1974. Customer said I had the job IF I could fix his problem. He located on the ground floor with a tennis court above. The offices next door had horrible noise that was the sound of tennis balls. I brought in an acoustic engineer. The frequency was isolated and a ceiling was designed to stop the sound. The ceiling had lead sheet in it to impart a mass. This was hung using vibration dampers: expensive. That theatre is still open; 8 screens in Louisville KY: The Village 8. We did not do the lobby or bathrooms. Quiet, though in the cinemas. Also did staggered stud walls with massive thicknesses of drywall on both sides. Only sound leakage is sub-bass due to the one piece floor.  |  IP: Logged Christopher Lani Film Handler Posts: 62 From: Ely, Nevada, USA Registered: Nov 2013 posted 05-03-2016 11:35 PM                        I think this would be an excellent idea !  |  IP: Logged Ted Uzzle Film Handler Posts: 19 From: Chicago, Il., U.S.A. Registered: Oct 2015 posted 05-04-2016 01:49 AM                     Oh, Louis Bornwasser, you've been around the block a few times, I wish I could bring you to Columbia College Chicago to co-teach with me a couple of courses in architectural acoustics and noise control. My theory, your practice, we'd conquer everything!  |  IP: Logged Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 05-04-2016 08:04 AM                        Remember, Ted, this was the dark ages before thx and Dolby educated us some.  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 05-04-2016 10:52 AM                     Alright Mr. Uzzle...I've been waiting to bust your...uh ask you about this high-tech spiffy graph you created for the Altec TAN-7 In particular, I refer you to the A8 in the graph above. Now I realize that throughout the discussion, the A8 was noted for being inefficient, least power handing, most restrictive (except on size behind the screen...its ONLY redeeming value), yet in the conclusion graph above...it sits alongside worthy Altec speakers like the A4-A7. Did you have to swallow hard and tow the company line to put A8 in the high value column?  |  IP: Logged Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 05-04-2016 01:04 PM                        Ahh! But that was low so many years ago. (Steve is right, though.)  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 05-04-2016 03:16 PM                     While I've always liked the Altec Sound and have installed A5s and A4s in the not-too-distant past (A5s more than A4s), I recognized that A8 for what it was...a VERY shallow speaker that allowed you access to the diaphragm from the top (later design) and side mounted crossover since you likely couldn't get behind the thing. I get all of that. But sound wise, it was not Altec's finest moment. Then again, I dislike MOST of the shallow speakers I've had to deal with. Truth be told, I'm not the biggest A7 fan out there either...the HF/LF sections just seem like such a mismatch in a theatre. Whereas I like the A5/MRII594 and I've even done them with the full sized MR94: I've never met an A7-500 system I particularly liked in a theatre application. Maybe for surrounds but for surrounds, the ultimate speaker was the 604/620.  |  IP: Logged Ted Uzzle Film Handler Posts: 19 From: Chicago, Il., U.S.A. Registered: Oct 2015 posted 05-05-2016 10:03 PM                     Yup, I wrote that. I forgot it entirely, had to dig it out of my closet, but I wrote that. I did. How clever of you to post that fragment. You didn't post the graph of "price." You didn't post the graph of "depth required behind the screen." You didn't post the graph of "coverage patterns available." You didn't post the graph of "electrical power required." You didn't post the graph of "electrical power handling." You didn't post the graph of "maximum acoustic output." You didn't post the graph of "size of theatre satisfactorily filled." Any of that information useful? The last graphic meant, each of these is the best for its individual use. I believed that then. I don't know about it now, because I haven't heard all the new cinema loudspeakers. Have you?  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 05-06-2016 08:02 AM                     No...in my post above...I did mention that you had noted its short comings throughout the paper. Without saying it was bad, you just made it seem merely restrictive and suitable to smaller rooms when, in fact, it doesn't sound particularly good in any sized room. Hence, it isn't really a good value. What the A8 does/did was FIT behind screens where one had foot or so of depth in an era where speakers were typically 18"-48" deep. I don't consider it good value but pretty much one's only choice (back then). Did you really think it sounded good or representative of Altec?  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 05-06-2016 08:35 AM                     Pretty awful speaker actually. I have a site with three rooms of them and we have been replacing them room by room with small QSC systems and gained much improved sound reproduction and better high frequency coverage. There is no comparison to those Altecs and even the tiny SC-1150 or the SC-2150.  |  IP: Logged Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 05-07-2016 09:18 PM                        OK guys, I agree that it was pitiful. Ted was a marketer, not the designer. He had a job to do. I would rather have him here as a contributor than to lose him because I don't like the a8. (I'll never buy an Audi A8, partly because of it..!!!)  |  IP: Logged Ted Uzzle Film Handler Posts: 19 From: Chicago, Il., U.S.A. Registered: Oct 2015 posted 05-08-2016 10:23 PM                     The A8 stank like shit. Lowest value in the VOTT line. Did I not say that? Right out? You charge me for saying that? It was designed, produced, and sold before I ever got to Altec Lansing. For those fools who thought a rubber loudspeaker could go into 18" behind a screen. You can verify this yourself, since you have materials from 30 years ago.You never met a theater-owner who engaged in magical thinking? I say I'm not a marketer because I never got one single penny commission on sales. Never in my entire freaky life (and much of it was freaky), did my pay depend on sales. Not one penny. I drove the acoustic engineering lab, and then the electronic lab. If this offends anybody, I'm, sorry,I never meant offense. But, FU!/  |  IP: Logged Sam D. Chavez Film God Posts: 2153 From: Martinez, CA USA Registered: Aug 2003 posted 05-09-2016 01:02 AM                       Tough crowd, eh?  |  IP: Logged

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