my profile | my password | search | faq & rules | forum home

» Film-Tech Forum ARCHIVE   » Operations   » Film Handlers' Forum   » building a sound wall with A7's (Page 1)

This topic comprises 2 pages: 1  2

Author Topic: building a sound wall with A7's Jeff Else Expert Film Handler Posts: 125 From: Detroit, MI, USA Registered: Nov 2006 posted 10-28-2009 09:28 PM                     i am building a sound wall with altec A7's. the high frequency horn is set a few inches back from the surface of the cabinet. should i set the speaker a few inches forward in the wall so that the HF is fully in front of the wall? or is it better for the cabinet front to be flush with the all and not worry about the far edges of the horn (so long as there is an adequate opening for the sound to dissipate)?  |  IP: Logged Monte L Fullmer Film God Posts: 8367 From: Nampa, Idaho, USA Registered: Nov 2004 posted 10-28-2009 10:16 PM                     Usual rule of thumb with speakers beind a screen is to have the face of the cabinet as close to the rear of the screen as possible with the horns just as close so the HF's doesn't dissipate from trying to go through the holes of the screen. If you have your speakers too far back, most of the sound just bounces off from the rear of the screen and "rattles" around behind there .. and the same with the HF's from the horn: too far back and HF goes out the window since HF are more sensitive to reflection and will really reflect from the back of the screen. You want the sound to be actually "pushed" out thorugh the screen, not get bounced around. Thus, with the "baffle wall" usage, this really helps in getting sound OUT though the screen, but still have the units as close to the back of the screen as possible. Others might chime in on many approaches to this...but all I know is of this basics. ..and good luck with your project ... -Monte  |  IP: Logged Cameron Glendinning Jedi Master Film Handler Posts: 845 From: West Ryde, Sydney, NSW Australia Registered: Dec 2005 posted 10-29-2009 12:37 AM                     How thick and what materials do you plan to use for the sound wall?  |  IP: Logged Jeff Else Expert Film Handler Posts: 125 From: Detroit, MI, USA Registered: Nov 2006 posted 10-29-2009 02:03 PM                     i'm planning on building them out of 1/2" OSB on a frame of 2x4's, with 1" acoustic baffle on the face. i assume i cannot change the depth at which the HF driver is set due to phasing issues, right?  |  IP: Logged Cameron Glendinning Jedi Master Film Handler Posts: 845 From: West Ryde, Sydney, NSW Australia Registered: Dec 2005 posted 10-30-2009 07:30 PM                     The 1/2 inch thickness is no where near the THX recommendation and would probably be more likely to lower your sound quality. Also how do you plan to space the cross bracing? Now you say you are using 1/2" materials to make your baffle plus then you say your adding 1" materials so I'm confused. Are you talking about fiberglass dampening materials or extra timber? The weight of fiberglass tends to be more important than it's thickness. Personally I would be looking at adding wings rather than a baffle wall because it is better bang for buck and far easier to get right. Monte explains well why you want to mount the HF as close to the screen as possible.  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 10-30-2009 10:47 PM                     The wood studs are fine but use drywall on the face as it's very dead. THX usually specs 3-5/8" thick sheets but keep in mind the weights involved with that much dry wall. Some of the completed walls easily weigh in at a number of tons! Two layers of 1/2" drywall might suffice for A-7's. The other problem is the multicell horns. They don't work good at all in today's cinema applications so consider looking for some of the later manta Ray horns if you can find any... or some good used JBL stage speakers's ala 4675C. At any rate if you do use the Altec Multicell horns don't bring the wall up any higher than the top of the A-7 cabinet proper. Mark  |  IP: Logged Kenneth Wuepper Phenomenal Film Handler Posts: 1026 From: Saginaw, MI, USA Registered: Feb 2002 posted 10-31-2009 06:49 AM                     Mark, I think that the A-7 cabinets he has are configured with the horns inside the cabinet. I had a pair of those for my old stereo system and the horns on top were not a pretty option. Also there were two versions of the A-7, the crossover at 700 Hz and one at 500 Hz. The higher frequency horn and crossover were not good outside of the PA applications for the A-7 while the 500 Hz model was for cinema sound. KEN  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 10-31-2009 07:58 AM                     It's hard to tell form his post but I've also seen many a grey utility A-7 with horns sitting on top. Then he definitely won't need to run the wall any higher than the cabinets either way. I just don't find that multi-cell horns work well in todays cinema applications. You can plug up some of the side opennings with socks or fiberglass but then you may as well just change the whole horn out. Constant directivity horns work out much better overall.  |  IP: Logged Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 10-31-2009 09:05 AM                        Agreed about multicell. Remember that (among other problems) that the A7 bottom has a bump about 80-90 Hz with NOTHING below. It is hard to reproduce hum. . . most of what you hear is 120 Hz. For that reason only it is unnecessary (but not harmful) to build a very large or secure soundwall. I will barely mention the "ringing" problems with the metal horn. Louis  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 10-31-2009 03:44 PM                     Oh my god...STOP...if you don't know the speaker stop advising about it! The A7, by definition does NOT have a Multi-Cell horn! If it had a Multicell, it would be an A5! The only difference in the bass cabinet between the A5 and the A7 is the driver...with the A7 having the 803 and then later the 416. The A5 always had the 515. On to the Sectorial horns...which the A7 uses, exclusively. The A7 used two horns...the 811 which used an 800Hz crossover and the 511 which uses a 500Hz crossover. It is properly called the A7-500 and was the Cinema speaker, as Ken pointed out. The reason...the Cinema industry discovered it was best to keep the crossover as far away from the vocal frequencies as possible and 500Hz did this and it was possible to make equipment that could handle it. This is one reason that most any speaker (modern or otherwise) that has crossover points between 500Hz-8KHz have a real hard time with vocal reproduction. Particularly if the frequency is anywhere near 3KHz. MOST 3-way systems suffer from this. The better ones use the same type of driver (compression) between Mid and High to minimize the timber difference between the two. Furthermore a BIG mistake that most speaker companies make is getting the drivers spread too far in the vertical plane. Note on the Altec VOT speakers (any of them)...they bias the LF driver high in the cabinet...not to make it top-heavy but to keep the vertical separation to a minimum...it improves the imaging and reduces lobing. Look at some of the 3-way systems out there...the spread on the MF to HF systems are WAY too far and it really sounds like it. As to Multicells...they are NOT my favorite horn for MOST applications...anyone that has them still can do a simple test to see why they have problems...turn on pink noise (at a reasonable volume, it need not be high) and walk the auditorium...you will distinctly hear as you walk into and out of each cell. Each seat gets a different timber no matter how you EQ it. The best results are definitely from a multi-mic plex. The Multicell was magical in its day. It allowed very little power to be used over a very large area. The tonal quality of them are also just fine for vocals...the key element in soundtracks. We STILL use the Multicell horn on an A5 system in Baltimore, MD for the Little Italy Film-fest in the summer time. It is the only horn where we can create a single point source and cover about 4 city blocks with reasonable frequency response, with good dialog and also work within the constraints of the space (the speaker is only about 8-feet in the air). If the speakers could be flown higher (and we could use multiple speakers) it is one of the few cases where I would prefer a line-array...probably the most overabused type of speaker system. The Metal Sectoral horns do have a bit of a metallicness to them. They can be deadened though. Some wrap rubber aound their mounting flange. One solution I saw used expanding foam (on the back side). All you are really trying to do is dampen out the metal so it doesn't vibrate. ALL A7 speakers can mount their horns either internal or external to the cabinet. Download the A7 Instruction manual from this site. We've installed some of the last cabinets off the Altec line in Oklahoma (cabinets were made in Austin, TX, I think...and were the 828 series). They had the internal mounting bracket and the adjustable port board for internal/external horn mounting. Whenever possible MOUNT THE HORN EXTERNALLY. The bass response is going to be better that way. The cabinet was designed for the horn to be outside but accommodated inside. There is going to be a dip at about 125Hz on the 825/828 cabinet...DON'T BOOST FOR IT...you'll just rattle the driver. It is where the system transitions from horn to bass-reflex. You will then get a decent response down to 80Hz, and on later systems, down to 50Hz. If you put bass-wings on the system (and I agree...just to the height of the cabinet)...you should get a decent response down to 40Hz on a modern, properly tuned, system. New Mantaray horns are available, if you desire to go that route. I would suggest going to an A5 system though...put on a 288/299/399 type driver with an MR/594 horn or, if you can find them, an MR94 horn...they remain the best I've ever heard/measured..VERY smooth throughout the coverage area. Steve  |  IP: Logged Jeff Else Expert Film Handler Posts: 125 From: Detroit, MI, USA Registered: Nov 2006 posted 10-31-2009 05:01 PM                     thanks for the information! to clarify i have A7's with 511b horns mounted on top of the cabinets. i think i will go the route of building wings. will the OSB suffice? should it be covered in something to deaden the sound or just be plain wood?  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 10-31-2009 09:36 PM                     Honestly, I would follow the A4's lead. Just use 5/8 to 3/4" Plywood. Reinforce it with 2x3s in a ladder shape. By bolting this to the main cabinet, you will also reinforce IT too so it doesn't sound so tubby. Then cover the surface of the wings with black duct liner like a baffle wall would have. Again, watch out on the power when using an 802-902 driver...if you must use this in a room longer than say 40-feet...consider changing diaphragms to a 909 diaphragm...it will double your power handling without affecting your frequency response too much (much less than the screen will affect it). If you can, go for the upgrade to a 288-399 driver with the MR594 horn. Steve  |  IP: Logged Jeff Else Expert Film Handler Posts: 125 From: Detroit, MI, USA Registered: Nov 2006 posted 10-31-2009 09:45 PM                     sounds good, I will do just that. fortunately, the auditorium is pretty small, just shy of 40' long, only about 130 seats, so for now the speakers should suffice.  |  IP: Logged Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 11-01-2009 10:03 AM                        Steve has good advice. My personal experience that the less EQ the better (always. . . but especially on A7.) Small corrections only. Louis  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 11-02-2009 10:56 AM                     Years ago Lonny Jennings sent me a mod to the A4 cabinets to improve there bottom end and it worked well but I have long since lost those notes but would that work on the A5 A7 cabinet?  |  IP: Logged

All times are Central (GMT -6:00)

This topic comprises 2 pages: 1  2

Printer-friendly view of this topic

Hop To: Select a Forum: Category: Operations -------------------- Digital Cinema Forum Film Handlers' Forum Large Format Forum Ground Level Feature Info, Trailer Attachments & REAL Credit Offsets Category: Community -------------------- Film-Yak Film Handlers' Movie Reviews The Afterlife Bob Maar's Joke-A-Thon Category: Classified -------------------- Equipment and Supplies Wanted/For Sale Help Wanted/Seeking Employment Category: System -------------------- Software Beta Testing Forum

The Film-Tech Forums are designed for various members related to the cinema industry to express their opinions, viewpoints and testimonials on various products, services and events based upon speculation, personal knowledge and factual information through use, therefore all views represented here allow no liability upon the publishers of this web site and the owners of said views assume no liability for any ill will resulting from these postings. The posts made here are for educational as well as entertainment purposes and as such anyone viewing this portion of the website must accept these views as statements of the author of that opinion and agrees to release the authors from any and all liability.