Wood for OB speakers

oldgears · « **on:** 21 Mar 2009, 05:38 am »

I've read somewhere that Baltic Birch plywood are material of choice for building speaker cabinets. Does that rule also apply for open baffle or would MDF sound just as good since this is OB. Thanks.

Mr Content · « **Reply #1 on:** 21 Mar 2009, 05:56 am »

Hi oldgears, well I have seen OB's baffles made out of just about anything. After about 3 years building and owning OB's I have found that the most inert baffle is the best baffle. I use 3 laminated substrates in my baffles. 16mm of MDF, 16mm chipboard, 16mm HDF. I find that this is best I have heard, not storing energy, and thus smearing imaging and micro detail. A lot may talk about the tone of the baffle, but I prefer to just hear the drivers tone. But I encourage you to experience with different material, as we all have different ears, and hear the music differently.

Mr C aa

Telstar · « **Reply #2 on:** 21 Mar 2009, 09:39 am »

There are two schools, like in normal speaker designs.

One, to use the least resonant material. Here u go with multi layers of mdf, plywood, acrylic, marble, filled with sand etc. IMO this is the best approach for the bass. When there is still quite much resonance, this is of a not nice type for our ears.

Two, to use woods that have good resonances, such as the one used in musical instruments (violins, guitars, cello erc). Spruce, Birch and Mahogany. Red Spruce is my favourite because used in violin manufacture and violin is one of my favourite instruments. IMO this is the best approach for midrange and highs reproduction.

I will add that in OB the impact of the material is LESS than a boxed speaker, but you cannot damp it.

Mr Content · « **Reply #3 on:** 21 Mar 2009, 09:50 am »

Hi Telstar, yes there seems to be 2 very distinct camps with this. The problem I have with the this wood or that wood is, when wood is used in an instrument, it is chosen well for that particular instrument, and made quite thin, so it will resonate, but is also tuned by volume and porting. I don't see much of a use for any of these things in an OB baffle. I could see some sort of similarity with a box speaker, but all "High End" box speakers are still built very inert

Mr C aa

Telstar · « **Reply #4 on:** 21 Mar 2009, 10:05 am »

Quote from: Mr Content on 21 Mar 2009, 09:50 am

I don't see much of a use for any of these things in an OB baffle. I could see some sort of similarity with a box speaker, but all "High End" box speakers are still built very inert

Mr C aa

Well, not all. Check Bosendorfer.

My idea is to still choose wood but make it not very much resonant (which means very thick plywood), but when it does, the resonances are pleasant to the hears.

sch · « **Reply #5 on:** 21 Mar 2009, 12:58 pm »

Using silica sand with a special resin plus MDF produced, at least in our case, a very inert open baffle without apparent resonances.
Once in black they are not that ugly as you can see. Not commercially available at this time but "it is cooking"

http://www.badongo.com/pic/5537508
http://www.badongo.com/pic/5537510
Happy weekend,
Santiago

Bob in St. Louis · « **Reply #6 on:** 21 Mar 2009, 01:34 pm »

All reports I've heard from fellas that have sand filled their ³/₄" plywood baffles have been very positive.

Which reminds me...That's what I should be doing right now; Building some new sand filled plywood baffles. aa

Bob

JoshK · « **Reply #7 on:** 21 Mar 2009, 03:42 pm »

Quote from: Telstar on 21 Mar 2009, 09:39 am

There are two schools, like in normal speaker designs.

One, to use the least resonant material. Here u go with multi layers of mdf, plywood, acrylic, marble, filled with sand etc. IMO this is the best approach for the bass. When there is still quite much resonance, this is of a not nice type for our ears.

Two, to use woods that have good resonances, such as the one used in musical instruments (violins, guitars, cello erc). Spruce, Birch and Mahogany. Red Spruce is my favourite because used in violin manufacture and violin is one of my favourite instruments. IMO this is the best approach for midrange and highs reproduction.

I will add that in OB the impact of the material is LESS than a boxed speaker, but you cannot damp it.

IMHO, the rational behind the second school of thought isn't quite explained right. No offense intended. Take MDF versus birch. Both have resonances, its a matter of where. MDF's resonance is very low in frequence, iirc, and the idea is that because it is low it isn't very audible. Its outside the sensitive hearing range.

Birch's resonance is in the audible range. However, MDF's resonant decay is slow, while birch's is very fast. So birch has the ability to dissipate its resonance much quicker. This is referred to as stored energy and the MDF has more stored energy.

The second school of thought is that the stored energy is more offensive than the actual resonance. If the resonance is quick to dissipate then it only affects the frequence response and can be notched out if it is big enough (probably not). If the resonance is long in decay, you can't notch it out as it affects the time domain.

doak · « **Reply #8 on:** 21 Mar 2009, 04:08 pm »

Constrain layered, sand filled, suede covered:

Hawthorne Audio Sterling Silver Trios

panomaniac · « **Reply #9 on:** 21 Mar 2009, 04:25 pm »

Wow, nice baffles! I like the suede. Did suede over felt on mine. Not as pretty as yours, tho.....

Sand filled certainly works well for bass reflex and horns, no reason it shouldn't for OB. A lot less work on OB, too.

Quote from: Mr Content on 21 Mar 2009, 05:56 am

... 3 laminated substrates in my baffles. 16mm of MDF, 16mm chipboard, 16mm HDF.

That's quite a sandwich. Ought to be well damped. Short of doing a sand filled baffle, that should be great. But I wonder how well it fits with JoshK's line of thinking?

doak · « **Reply #10 on:** 21 Mar 2009, 05:48 pm »

Quote from: panomaniac on 21 Mar 2009, 04:25 pm

Wow, nice baffles! I like the suede. Did suede over felt on mine. Not as pretty as yours, tho.....

Sand filled certainly works well for bass reflex and horns, no reason it shouldn't for OB. A lot less work on OB, too.

Thanks. The Hawthorne crew built mine. Darrel's "been the route" on baffles and did a superb job on these - much better than I could hope to do - at a very reasonable cost too.

dweekie · « **Reply #11 on:** 21 Mar 2009, 08:59 pm »

Another interesting item of possible discussion is Green Glue.

http://www.greengluecompany.com/

There's a fairly large discussion of this product on the AVSforums for use as a soundproofing material in HT applications. Some people used this between layers of mdf/wood in OB baffle construction in the Hawthorne audio forums and found it to work well in that application as well.

Mr Content · « **Reply #12 on:** 21 Mar 2009, 11:13 pm »

Hey nice looking fire place doak....

Yes sand filling a baffle is a good way of reducing resonances, and you can be very creative in making curves as well

Mr C aa

oldgears · « **Reply #13 on:** 22 Mar 2009, 12:18 am »

Thanks all for your response. I guess I will go with MDF then since most seems to agree that " in OB the impact of the material is LESS than a boxed speaker". Thanks again.

ttan98 · « **Reply #14 on:** 22 Mar 2009, 01:34 am »

One reason I don't MDF is it too heavy completed to plywood and particle board.

dweekie · « **Reply #15 on:** 22 Mar 2009, 03:20 am »

Quote from: oldgears on 22 Mar 2009, 12:18 am

Thanks all for your response. I guess I will go with MDF then since most seems to agree that " in OB the impact of the material is LESS than a boxed speaker". Thanks again.

Oh, one other thing that should be considered in your decision: if you're not working in a very well ventilated area, please avoid cutting a lot of MDF

oldgears · « **Reply #16 on:** 22 Mar 2009, 04:10 am »

Thanks Dweekie for the warning. It will be out in the backyard when I do this.

Bob in St. Louis · « **Reply #17 on:** 22 Mar 2009, 10:59 am »

There was a fella on the Decware site years ago whos wife got very, very sick. Took the doctors a long time to diagnose the issue. Turns out it was the out gassing of toxins from MDF, OSB etc... It really got bad when he spent the weekend building speakers, that's what put her in the hospital.
She got so sensitive to it, they had to throw away every piece of furniture (including speakers) in the house that where constructed with "processed" wood. I cant recall what it did to her body, but he said the doctors said her body would never make a full recovery.

Since then I do all my cutting the garage, not the basement workshop.

Bob

Jibara · « **Reply #18 on:** 22 Mar 2009, 12:33 pm »

urea(cow urine)-formaldehyde particle board

The building science folks call it "Was Wood"

Alergic to cow urine now there's a surprise

They are working on alternative binders: http://healthybuilding.net/healthcare/Alternative%20Resin%20Binders.pdf

Bob in St. Louis · « **Reply #19 on:** 22 Mar 2009, 01:04 pm »

You're telling me that MDF contains cows urine?!?

Bob