Soffit Construction

Frontman · Post by **Frontman** » Sat Oct 02, 2004 11:02 am

I was wondering if anyone out there had some pics of there in progress or finished soffit designs they would be willing to share. I'm to the point that I understand how the basic design works, I'm just running a little low on the creative juices for a snazzy front about now. I've seen a few that are around in the forum, I just want to kind of come up with something that will get people to kinda look and say "cool". Only at the same time have it functional. I promise I wont steal anyone’s ideas I just want to get some visuals of what some others have done to maybe spark my own thoughts. Any help would be greatly appreciated. Thanks in advance.

AVare · Post by **AVare** » Sat Oct 02, 2004 2:55 pm

Have a look at the studios under the "Studios Under Construction" off the main page. Several soffits built, and possibly ideas that will help you in other areas.

Enjoy!
Andre

barefoot · Post by **barefoot** » Sun Oct 03, 2004 3:34 am

Here are some nice soffits that -=glEnn=- built: http://johnlsayers.com/phpBB2/viewtopic ... c&start=15

dbluefield built my decupled bezel design here: http://www.johnlsayers.com/Studio/Mainp ... efield.htm

Thomas

Paul Woodlock · Post by **Paul Woodlock** » Sun Oct 03, 2004 8:57 am

Greetings Frontman

I've recently designed a soffit wall/soffits for my Genelec 1037B's for my currently under construction studio build.

You want the soffit wall( and soffits ) to be as sturdy and as stiff as ossible to prevent as many frequencies as possible from being radiated backwards through this wall.

In keepign with my walls and ceilings I@M using 6 layers of 12.5mm drywall and 1 layer of 18mm MDF.

The front of the speaker cabinet must be exactly flush with the soffit wall to aviod diffraction distortions. ANd the bezel aroudn the speakers must be close 3 or 4mm or less WITHOUT touching the speaker cabinet of course.

Also, you need to decouple the speakers from the soffits by placing them on elastomer pads. This stops the soffit wall from also resonating sound, so that what you hear coems from the speakers and onyl the speakers. These pads MUST be calculated to get the resonant freqeuncy of the soffit-pad-speaker ( mass-spring-mass ) system well below your lowest freqeuncy. 9 to 10Hz is what you should be trying to achieve.

Placing speakers on soft pads to get the right decopling can make the speakers MOVE causing audible distortions, so the way around this is to place the speakers on a HEAVY weight before putting them on pads.

I'm casting concrete blocks that are around 70Kg (154lbs ), and are twice the weight of of the speaker sitting on them. These blocks should also sit inside the soffit of course.

The other benefit of using concrete blocks is that it is easier to get the natural freqeuncy of the elastomer decoupling system down to 10Hz.

See Paul's Studio Build Diary at the StudioTips acoustics forum

http://forum.studiotips.com/viewforum.php?f=1

, as I'll be showing how to buidl the soffit wall soon. It's one of my next jobs.

ALso take a look at the Genelec Papers on soffit design at these links.....

Genelec - Soffit Mounting
Genelec's how to build a soffit wall
Genelec's Why have a soffit mounted monitor system?

HTH

Paul

Arthur Rice · Post by **Arthur Rice** » Mon Oct 04, 2004 8:37 am

Howdy,

I was just going to set my speakers on stands but the more I dig into this matter makes me rethink the soffit idea, but my main concern about soffit mounting my monitors is how do you deal with the heat and ventilation issue with powered monitors? Event 20/20 bas, I can't figure this out.

Thanks,
Arthur

cfuehrer · Post by **cfuehrer** » Mon Oct 04, 2004 8:49 am

Arthur Rice wrote:how do you deal with the heat and ventilation issue with powered monitors?

Ditto: 20/20BAS and Genelec 1031s

knightfly · Post by **knightfly** » Mon Oct 04, 2004 11:02 am

Nothing says soffits need to be sealed - their main purpose is to extend the baffle size for the LF driver so that it's forced to radiate in half-space instead of full space. This means that the effective baffle needs to be 4-5 times the woofer diameter, with the woofer NOT centered in the overall flat plane that's comprised of the speaker baffle and the baffle extension (AKA the soffit face)

Another requirement to avoid high frequency diffraction around the face of the speaker's box itself, is that you have as narrow a gap as possible between the edge of the speaker box and the soffit face, or bezel - less than 1/4" is needed, and this should be filled with insulation.

However, the REAR of the speaker box does NOT need to be sealed - so, with rear mounted amps you could just leave an air channel from floor to ceiling behind the soffit, with vents open on both ends - this would allow natural convection to cool the amps, and it would also keep heated air from escaping out the bottom FRONT of the speaker, thus not allowing the unevenly heated convection currents to disturb the air in FRONT of the speaker, which can cause really wierd phasing problems.

As Giles pointed out, if this isn't enough some of his really quiet fans (not the ones who SHOULD be loud and proud

) would assist in getting good (but quiet) air flow.

Check out these soffits (not sealed but work REALLY well)

http://www.johnlsayers.com/Studio/Pages/Sjoko_2.htm

Hope this helps some... Steve

dymaxian · Post by **dymaxian** » Tue Oct 05, 2004 12:42 am

Greetings!

I've been toying with the idea of soffit-mounting my Mackies on-and-off for a while now. It's just a matter of getting the right design. For me, the biggest concern will be heat build-up; I have small sheets of cotton cloth that I use for dust-covers when my speakers arent in use, and sometimes when i'm just listening to music and not working I'll just peel back the front- but I've got to make sure that the back of these cloth covers don't contact the back of those speakers, because the amps will overheat and shut down the speakers within an hour, guaranteed- and this isn't even at serious volume. I've emailed the guys at Mackie to see if it was something wrong with the speakers, but they say that'll happen every time. They don't recommend they be soffit-mounted, and that's their primary reason (there's other things, too, I'm sure...)

The computer-geek world has a sub-set of people that are obsessed with silent computer case fans. I'm sure that getting a pair for each speaker (intake and output on opposite ends) would push enough air past your speakers to keep them operating.

But I got some questions for Knightfly, now that he's thinking about it... You mention that the soffits should be 4 to 5 times the size of the woofer- is there anything we can do with that wall space without messing up the effect or inadverntently horn-loading the speakers? With my stand-mount designs, I was planning to use the front wall for panel-traps and other low-freq absorption- could I mount a panel trap on each side of the speaker as part of the baffle? I'm concerned that the front membrane of a panel trap wouldn't be heavy enough to serve double-duty as the front face of a speaker soffit. If I did this, I'd use the isolated double-frame design, just with a thinner construction to serve the panel-traps. Should I just leave it alone, and make that face heavy?

knightfly · Post by **knightfly** » Tue Oct 05, 2004 3:35 am

Yeah, heavy is the ticket - you want the baffle extension to be massive enough NOT to vibrate sympathetically, or it acts as a sort of passive woofer design - unfortunately, not very linearly though. A good soffit face would be something like 1-1/8 flooring ply faced with 3/4 MDF, then laminated to your veneer ply of choice -

The horn loading effect comes into play if you have a smaller than 4-5 times woofer size baffle, then continue the side walls/center front at the angles necessary for RFZ - this "focusses" the sound from the woofer into a narrower "beam" and can narrow the coverage for the producer's position; it will also change the reflection patterns and strengths after this narrower "sound beam" hits rear and side walls, which would tend to make the whole room "quirkier", or in other words harder to get an even sound field.

In choosing a position within the area of the baffle extension for your speakers, you want to pick a point where the woofer will NOT be exactly centered from edge to edge of the extended baffle; a couple inches offset is enough to eliminate the chance of the same frequencies being diffracted by the edges of the extended baffle (also known as the soffit face)

Hope that helped... Steve

Frontman · Post by **Frontman** » Sat Oct 09, 2004 1:22 pm

Thanks for all the replies, advice and links. Another question has anyone soffit mounted resolve 65a active monitors, or heard of anyone who has? I've seen a lot of posts for Mackies and event but not one for the monitors I have. I'm beginning to wonder if it will be beneficial.

knightfly wrote: In choosing a position within the area of the baffle extension for your speakers, you want to pick a point where the woofer will NOT be exactly centered from edge to edge of the extended baffle; a couple inches offset is enough to eliminate the chance of the same frequencies being diffracted by the edges of the extended baffle (also known as the soffit face)

A couple inches offset?? Both sides offset different directions? As in the left side and inch and a half to the left and the right two inches to the right. I'm not sure I'm following.

knightfly · Post by **knightfly** » Sat Oct 09, 2004 7:19 pm

No, I meant that each speaker should not be centered in its soffit - if you offset the left speaker 1-1/2" to the inside, then the right speaker should also be offset 1-1/2" to the inside - then, if the left speaker is offset so the woofer is 2" above center of the soffit, so should the right one. By differing amounts, I meant that you should NOT have the same distance from center of woofer to any two edges of that speaker's baffle extension (soffit) - in any case, whatever you do to one, the other should be done the same (except mirror imaged left-to-right)

What this does, is make it so that any diffractions caused by the baffle extension happen at different frequencies at one edge of the baffle extension as compared to any other edge. This just spreads out the effect of diffraction to make it less pronounced.

Since the Resolve 65a's are front ported, you won't have any problems with soffit mounting them - the only downside is if your room is pretty large, you would have a problem filling it with these speakers; this would happen whether they were soffited or not.

Soffit mounting nearly ANY speaker improves the sound field in the room - this is because the larger baffle forces the speaker into "half space" mode, where it only radiates in the forward direction - this in itself reduces a lot of the early reflection problems caused by nearfields and midfield speakers interacting with the front and side walls.

Genelec says this better than I can, so I'll let them -

http://www.genelec.com/support/soffit.php

Hope that helps you decide... Steve

AndrewMc · Post by **AndrewMc** » Sun Oct 17, 2004 7:16 pm

Per the request for soffit photo's - here are some attached. The design is the barefoot design. Overall this was probably the hardest thing to construct in the studio, but all the info I needed was found here at this site. The only addition is I formed up concrete blocks to wrap the monitors in.

They sound incredible. Monitors are event 20/20bas

I've had a few 'non audiophile' people listen to them and they are blown away - the question is always - "this is coming from those 2 speakers right...?"

cadesignr · Post by **cadesignr** » Mon Oct 18, 2004 3:46 am

Hello Andrew, I have a couple of questions for you.

The only addition is I formed up concrete blocks to wrap the monitors in.

It is hard to tell from your photos, so could you describe these concrete block "enclosures". Are they to isolate vibration via mass, and do the speaker boxes "rest" on these also? Are they built from the floor, and if so, are they too isolated on pads or something? In the pics, all I see is something that looks like a concrete "rest" for the speaker boxes. In barefoots drawings for his concept, he shows some kind of isolation straps or something to keep the speaker box vibration from transmitting to the baffle itself, which if the framing for the baffle were fastened to the iso wall, would transmit to the iso walls, no?. How did you isolate the concrete from structural transmission IF the speakers are directly connected to the concrete blocks?
Also, when you built the framing for the baffle "extention" planes, is this framing fastened to your "islolation" walls, or did you decouple the framing also?

Thanks.
fitZ

AndrewMc · Post by **AndrewMc** » Mon Oct 18, 2004 4:09 am

It's a little hard to tell on the photo's - but if you look at the 1st photo you can see the speaker stands that sit behind the soffit wall. These do not touch the soffit framing. The speaker stands have an MDF top angled at 10 degrees down. A concrete pad was then glued to to the MDF and a thin layer of rubber on top of the concrete. The speaker stands on that and then concrete blocks on the sides and top of the speaker. This is then tied down to the stand with cable ties running over the top and through holes in the stand platform.

The speaker is sitting forward so that when the baffle is placed on the front of the speaker is flush with the baffle, but there is no connection between the sepaker and the soffit wall/baffle - except for the concrete floor. There is about a 1/8th inch gap between the speaker & the baffle. Getting the angles perfect on this framing was probably the most challenging thing.

The purpose for the concrete is to dampen vibrations, and help prevent sound going into the back of the soffit & beyond that - I'm no expert, but in a post a while back Barefoot concluded it would be a good addition. To make the blocks I just made up some forms from 2x2's and used a few bags of quickcrete.

knightfly · Post by **knightfly** » Mon Oct 18, 2004 4:32 am

Good plan, Andrew; obviously it's working, judging from your listeners' comments.

One of the main things that concrete above your rubber pads is doing is lowering the m-a-m resonance of your speaker/stand combo - this is not something I've figured out how to compute, but ideally (same as walls, etc) the lower frequency the better, below 10 hZ is a good target.

Paul woodlock has more and better info on this than I do, since he's in the middle of doing this very thing with his speakers/soffits - you might check out his "book" on studiotips if you've not already

http://forum.studiotips.com/viewtopic.p ... a50e2c59ce

since this is (so far) a 36 page thread (??!?) you might wanna start at about page 34 for this particular subject... Steve