Ultimate baffle material

Daygloworange · « **Reply #20 on:** 23 Jan 2007, 05:56 pm »

I have some solid 18mm thick (4'X8') phenolic in my shop that I got a while back. It's killer expensive. I believe it's mass is something like 80lbs per cubic foot. I've been thinking about using it in some speakers. I got it at a bankruptcy sale, a while back.

Cheers

Rafal · « **Reply #21 on:** 23 Jan 2007, 07:54 pm »

Quote from: mcgsxr on 23 Jan 2007, 05:46 pm

Hmmmmn, at the quoted $200 for a 2 foot, by 8 foot, at 18mm thickness, I think I will rethink my strategy!

I will likely turn to baltic birch, for roughly $50 or so, for a similar quantity...

Oh well, either that or hound Paul at Nomad for some scraps!

That's a bit pricy. There is a place here in town where you can get solid wood table tops that look like butcher's block. they are quiet large. I'll check their prices and report back. Those would look really cool.

sulis · « **Reply #22 on:** 25 Jan 2007, 03:58 pm »

Hi there,
For anyone aiming to make non-resonant baffles, i would suggest looking into constrained layer damping using Green Glue www.greengluecompany.com/
I've just made a baffle using 15mm birch ply and 12mm Viroc ( a cement wood fibre board) using Green glue and it's remarkably dead, even seemed to suck the noise and vibration out of the finishing sander.
I had tried using cld pads for box speakers before using silicone and water based contact cement but this green glue stuff does seem to be in another league. Commercial cld products seem to be expensive and mostly aimed at damping metal sheet like dynamat for cars. Nice to see something new on the market that does seem to work as well as the manufacturers hype suggests.
Downsides?
Well, It ain't cheap, particularly as it comes in non standard size tubes so I had to buy a applicator gun as well,
and make sure you find something to clean up any glue that gets squeezed out as it never completely dries stays tacky and really difficult to remove.
Khush

JohninCR · « **Reply #23 on:** 25 Jan 2007, 04:55 pm »

I'm a bit confused about the talk of non-resonant materials or adding damping if we're talking about flat baffles. They just don't have anywhere near the same forces on them as the panels of a box speaker. I don't recall ever hearing one resonate. I hear diffraction at the edges as a separate sound source. For large baffles, damping reflections off of the baffle surface makes sense, but the front is probably more important than the back.

Baffles vibrate, but it's not from resonance. It's primarily the mechanical forces of the drivers. To me there are 3 ways to address these vibrations.
1. Decoupling the drivers from baffle.
2. Using enough mass to make the forces immaterial in relation to the baffle.
3. Structural rigidity which still requires mass and affects dispersion of the rear wave.

If you're talking about folded baffles, it's a different story, and everything related to box construction applies.

Rafal · « **Reply #24 on:** 25 Jan 2007, 05:01 pm »

In my case, I want not so much eliminate the baffle vibration but reduce the echo (reflections) between the baffle and the wall behind it. I hope you know what I mean. I may not be expressing myself eloquently enough.

JohninCR · « **Reply #25 on:** 25 Jan 2007, 05:44 pm »

Quote from: Rafal on 25 Jan 2007, 05:01 pm

In my case, I want not so much eliminate the baffle vibration but reduce the echo (reflections) between the baffle and the wall behind it. I hope you know what I mean. I may not be expressing myself eloquently enough.

That makes perfect sense.

JoshK · « **Reply #26 on:** 25 Jan 2007, 06:23 pm »

Quote from: Rafal on 25 Jan 2007, 05:01 pm

In my case, I want not so much eliminate the baffle vibration but reduce the echo (reflections) between the baffle and the wall behind it. I hope you know what I mean. I may not be expressing myself eloquently enough.

In that case, I'd get ahold of some thick (>3.8") industrial wool felt (ala McMaster-Carr) and line the back of the baffle with it. This should eliminate echo.

Brad · « **Reply #27 on:** 25 Jan 2007, 07:17 pm »

Is that 3/8" Josh?

Either way - good idea for eliminating the back of the baffle as a problem point.

tminus · « **Reply #28 on:** 31 Jan 2007, 12:45 am »

I got around to looking at the huge slab of soapstone my marble tops guy has languishing in the back of his shop. I was interested because of the mass - 25lbs sq ft. I would need that kind of mass if I used the long throw 15" on OB. Soapstone is about the softest natural stone around and can be shaped with a router using multiple passes for large roundovers. Then sand and finish to high luster w/ mineral spirits. Sounds like a plan, except for.......

Nix idea @ $200 per baffle. While I'm at it, nix idea of long throw driver on OB. I mounted it on a test baffle on a base w/ lagbolts for "spikes". Even with my 220 lbs standing on the base, it "walked" around the garage floor while making next to no bass.

I'm back to wood - even MDF - as ultimate baffle material, maybe covering w/ sound absorbing material where benefits could be derived, such as backside of OB - or frontside too.

markC · « **Reply #29 on:** 31 Jan 2007, 12:56 am »

Try some cork on the back of the baffle-as thick as you can find, (at least 1/8"), I bet you like it.

tminus · « **Reply #30 on:** 31 Jan 2007, 01:09 am »

Naw, it's too cheap, effective, aesthetically pleasing, and readily available at any hardware store. That just couldn't be good.....

Rafal · « **Reply #31 on:** 31 Jan 2007, 04:09 am »

What do you guys think of Convoluted Open Air Cell Acoustic Foam for the back of the baffle?
First item at:
http://www.solen.ca/damp.htm

D OB G · « **Reply #32 on:** 23 May 2007, 05:04 am »

Hi Rafal,

This may be a dead thread, but for what it is worth, here goes.

I agree wirh JohninCR (and Linkwitz!), that rigidly and massively mounting the magnet is a desirable way to go.

I've tried a few techicques- hard to describe, but basically building a narrow box (to reduce rearward reflections), with a cross foot so it doesn't tip sideways, the protruding ends embracing the magnet(s), and bolting together, being careful not to chip/crush the ceramic of the magnet.

The "box" is filled with a mixture of lead shot and dry sand.

The baffle can the be virtually any material that suports its own weight and shape, so long as it rests lightly on the rim of the driver (even by its own weight- if the system is tilted back a bit, ot with a bit of velcro- the possibilities are endless), and is as non resonant as possible.

I've had great succes with baffles as simple as three ply COATED BOTH SIDES, AND ESPECIALLY WRAPPING AROUND THE EDGES with compressed chunk foam (carpet underlay). Others have had succes with polystyrene foam.

The resulting baffle can be wrapped in a WAF approved fabric, cut out for thr drivers, and maybe even covered again with an acoustically transparent fabric.

If possible, the full-range/mid should be on a separate magnet retention system to the woofers (Linkwitz uses the woofer baffle to retain the mid magnet which I think comprimises the principle a bit).

David

oldtimer · « **Reply #33 on:** 23 May 2007, 11:27 am »

Having built countless OB's over the last 2.5 years, a dense, rigid baffle will ALWAYS win over a flimsly baffle. I now use a comsopite board, made up of 3 different materials totaling 30mm thick, and then I put a steel brace behind the baffle. I have been magnet mounting for the last 18 months, and this has real world benefits, in imaging, focus, detail......... I wouls always recomend a baffle that is rigid, and that has mass. Decouple the driver from the baffle also aids things.

Be well
Nig.

D OB G · « **Reply #34 on:** 23 May 2007, 12:42 pm »

Hi Nig,

I agree to a point.

Over the years I have used baffles such as mdf (for mounting, and ensuring flaring to avoid cavity resonances) glued (lots of glue!!) to stone (I have access to a computer controlled water jet cutter) glued to mdf- about 60mm thick.

I've used two layers of 17mm plywood either side of a 90mm thick frame, with multiple bolts bringing both sides together under tension, and then filling the cavity with lead shot and sand.

But I've made three discoveries (really discovered three things that many folk know):

-Virtues of magnet mounting, and I mean massive magnet mounting, so that the driver can work without a baffle at all.
-The importance of stopping vibrations from exiting the baffle at the edges i.e. at 90 degrees to the baffle plane, which leads to the third thing:
-The virtues of using something like thick felt, foam carpet underlay (easy to get and to cut), or any similar material that transforms vibration, by self-damping, into heat (not much admitedly) as the "fundamental" material of the baffle. Of course this assumes magnet mounting, and a rigid means of holding the "foam" against the driver frame, against the floor, with no air gaps, and able to hold its own weight. And the foam must wrap around the edges.

I've tried both techniques and the massive baffle is the easiest, but not the only way.

GeoffH on diyAudio, in a different context (to describe the virtues of a medium mass baffle), described the thought experiment of using the 5 suspended steel balls. No matter how heavy they are, when one is released, the one at the other end is going to swing out.

Not if the outer two balls are foam, and only the inner ball is steel.

A bit of a quirky example, but there you go !!

David

scorpion · « **Reply #35 on:** 23 May 2007, 01:05 pm »

There are two schools for this, may be both are more relevant to the IB case. The first one advocates as dense a baffle as possible, so that you can bolt a speaker to it without any harming effects. Build yourself a brick-wall. The other school says: Try to make as resonance-free baffle as possible by choosing some light material so that it will not swing by excitation from the speakers.

Going into the OB-sphere there are scope for much more research especially when we go into techniques which doesn't fix the speaker to the baffle !
I advocate that those who are in positions to do so should encourage scientific OB research. There are lots of interesting research to be done, besides what we all together can bring about. And it will benefit not only us.

/Erling

mcgsxr · « **Reply #36 on:** 23 May 2007, 01:35 pm »

I will defer to those with more experience, but in mine (over the last 2 years) I have found that the b200 attached directly to a baffle does not create severe vibration, if limited to 80Hz and down.

The addition of a woofer directly mounted to the baffle, did - and I was warned, but I did it anyway!

My next crack at this, will magnet mount the woofer behind the main baffle, but I will bolt the b200 into the main baffle. Just for simplicity.

D OB G · « **Reply #37 on:** 23 May 2007, 02:14 pm »

Hi mcgsxr,

For what it's worth, I reckon that sounds good.

But remember that Linkwitz specifically magnet mounted his "mid-range" driver.

David

scorpion · « **Reply #38 on:** 23 May 2007, 02:22 pm »

Mark,

I think you are right in that low frequency resonances are taken up and spread more easily than higher frequencies. I don't think that you are right in
that there are less benefits from isolating higher frequencies to spread resonances. Above 80 hz there is still a good deal of pressure, indeed above 150 as I go I still would like to isolate a little bit better than I do with my cord mount.

/Erling

mcgsxr · « **Reply #39 on:** 23 May 2007, 02:59 pm »

I don't/didn't mean to sound as though the 80Hz mark is the perfect spot - just that for me, the added complexity of the magnet mount for the b200 is likely to prove too much work for my next baffle - note the use of the word "next" as opposed to "final".

It is all a journey for me, and every year or so I refine the approach, and being bull headed, I have to do it my way, I just try to incorporate the excellent advice that I find here - try and try again!