Lining a Speaker Cabinet

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We are building an entertainment unit for a client. He designed it himself and did a nice job. He wanted the boxes that hold the speakers to be lined with MDF. Now that we have built the unit we have found that here is room at the top, bottom and back of boxes (cabinets) for 3/4" MDF but because of the size of the speakers there is only room for 1/8" (if it's even available) for the sides. Is 1/8" MDF going to make a difference? Is there another material to use? Or the broader question, is MDF required / desirable at all. Thanks, JG
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MDF is difficult, if not impossible, to get to resonate. That is the reason for it's use in speaker boxes. Little is better than none. How much difference it actually makes is dependant on may factors. Couldn't hurt.

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What are the boxes made of? Plywood? Plywood will resonate more in the midrange frequencies than MDF, MDF will resonate more in low frequencies. Adding layers of MDL to stiffen the enclosure sounds like it makes a lot of sense. I am not certain where to get 1/8" MDF and I don't think it will stiffen appreciably.
I wonder, though, if you can add thicker MDF in part of the side panels.
You can do a couple of other things. You can run bracing along or between the side panels. I suggest NOT at 1/2 the height or width; using a different spacing will effectively break up the panel into smaller less resonate sections and the amount of resonance will be reduced, and the resonance frequencies of each section will be different and so not combine to a larger peack.
You can check out antiresonant Deflex panels from a source such as Madisound (http://www.madisound.com/cgi-bin/index.cgi?exact_match=yes&product=SD&cart_id 2268.22629), or perhaps Sorbothane (reputedly not as effective).
By the way, I see Madisound is selling a 1 edition-old issue of "The Loudspeaker Design Cookbook" for $11 (normally $30) and if you purchase some Deflex, I suggest you get one of those. It will no doubt have some very specific info on speaker cabinet construction.
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JGS wrote:

Speaker enclosures are usually designed from the inside out rather than the converse. MDF is used for its density (damping ability) and rigidity, properties that keep the box from vibrating along with the driver (speaker). The box is also usually air tight unless there is a port that is tuned as part of the design.
At this point I would question the lining of the sides with only 1/8" MDF unless it is securely glued to the existing sides, which are hopefully already pretty substantial.
As an alternative I would suggest a sheet damping material similar to this:
http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber &8-035
Good luck.
Wes Stewart
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JGS wrote:

This subject is close to my heart.
"the boxes that hold the speakers"... please clarify. Are you talking about an enclosure that will house a completed speaker box...or the speaker box itself, containing only the drivers?
I need more information in order to give you an accurate asessment. MDF 'can' be a solution. 1/8" MDF is not going to be a solution to any vibration as it will act like the skin on a drum and will start to behave as if it was a transducer on its own (passive radiator-like behaviour with all its phase complexities.) Stiffnes and mass plus internal volume will create the box's "Q". MDF has good mass, but is not very stiff. Balic birch has lower mass, but more stiffness. A sandwich of baltic and MDF with adequate internal bracing can make a nice speaker box. Internal reflection has to be dealt with via dampening/non reflective material as the sound comes off the back of a woofer with as much vigor as the front. When adding stuffing, keep in mind that the woofer then thinks the air behind it is actually heavier than it is changing the resonant frequency of the enclosure. Thin walls then add to the dilemma by allowing the woofer to think the box is yet bigger again. Insulation on the enclosure inside walls are only effective up to the wavelength i.e. a 1" pad will do nothing below 1KHz.
All speaker enclosures are a compromise. You want deep bass or tight bass? Can't have both with the same driver (woofer). There is only one way to stop transmitted sound: mass/stiffness. HDF is a nice product, so is HDPB. Two 1/2" skins of BB with 1" sand in between is VERY effective, but a bitch to build.
For a solid engineering reference: http://www.colloms.com/pages/works.aspx
Electroacoustics was my favourite subject, btw.
r
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Hi Robatoy, I am talking about effectively a box which holds the completed speaker. Thanks, JG

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message
product like 1/4" oak plywood. 1/4" MDF would be like spagetti, not a good product so they don't make it AFAIK. You can get 1/4" masonite of course, and that is pretty stiff and paintable smooth.
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I never understood why electrostatics cost so much - $10K for a headphone and a few X more than that for full panel speakers. Years ago I build one with some spare parts laying around and I'm sure I could make the sound more "hi-fi" if I play with it some more. Those spare parts wasn't worth more than $10 at the time.
I suppose that's the same reason why a local custom wood shop charge over $20K for a table - custom design with exotic wood.
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# Fred # wrote:

Electroacoustics is a subject that deals with the conversion of electrical energy to acoustic energy via a transducer, or backwards (as in microphone)
Electrostatics on the other hand, are a form of transducers which do not operate on an electromagnetic motor, but operate on a totally different principle. The $10K headphones (I'm assuming you're talking about Stax Earspeakers?) are simply the most incredible experience for $10K you can have...with a few caveats like you need to sit on a subwoofer for the tactility of the bass, and the recording should be made with the Sennheiser Kunstkopf microphone method. I have a Stax tone-arm which has never been equalled in any way, shape or form. That used to be one crazy little company.
Full-range electrostatic loudspeakers have a myriad of problems in terms of physics limitations as well as reliability issues when pushed to sound pressures we expect from today's dynamic range-heavy sound sources. Many need to be sub-woofed, which totally screws any ideas of a single sound source.
If all you listen to is harpsichord or cello, a pair of Quad ESL63's will make you weep. (with the right amps, in the right room, yadda, yadda....)
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You mean a moving capacitor.

I could have gotten a new Stax for $500 - ah, inflation over the years.

Is that like the Japanese laser turntable? I've donated all my vinyl's when the first generation CD players came along in the early 80's and never look back.
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# Fred # wrote:

Uhhh...sure.
Baseball cards, My Marklin train collection. Yup.

No. Beryllium shaft, rolomite bearings, gobs of platinum everywhere. It is worth more than the mortgage of 3 of my houses.
r
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You mean the speaker diameter plus 1/4" is all you have for the side space? If so, could you route out the two front part of the sides on the 3/4" MDF - the left and right side front edges where the speaker goes into it? Looks like a common practice for speaker construction where the outer edge or the speaker comes almost next to the outer box edge if I'm not mistaken.
Assuming the box is not very big, I don't think too many people will notice the sound quality difference between 1/8" and 3/4" for the side panels after you fill up the box with insulation material.
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Why not just cut the side panels back enough to just clear the speaker cones in the area of the speakers and complete the lining that way. The MDF is used in this manner to increase the mass of the surfaces of the speaker boxes; so, as long as it is mostly there it should do the job nicely - 1/8" thickness will not do an effective job of increasing the mass of the box side panels. BTW, to do this job effectively, the MDF liner should be surface glued to the sides of the box. Jim Seelye

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Years ago I built cabinets for a pair of 12" Wharfdales (you old guys will remember them) driven by a McIntosh amp. The resonance was enormous. My solution was to line the insides with ceramic tile. Cheap, easy, and about 1/8 thick. If you have more room you could put a natural stone tile inside. Of course they would end up pretty heavy to move around.
Joe

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Joe Bleau wrote:

I have old tag-sale Wharfdales hanging from my shop ceiling. <G>
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Wharfdales put sand in their speakers.
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wrote:
. <G>

They only put sand in those speakers created to play "Beach" music.
However, some cabinets were made with encapsulated sand panels for the reasons being discussed in this thread.
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But as any serious audiophile will tell you, Sumatra beach sand has better clarity in the upper mid-range than Punta Cana beach sand. I prefer the Zandvoort beach sand (sifted of course).
r
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"Robatoy" wrote in message

Speaking of sand ... it is immutable fact that the first words to a soundman, out of the mouth a musician buried up to his neck in sand, will be: "Could I have a little more sand, please?"
--
www.e-woodshop.net
Last update: 1/06/07
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Only if it's his own sand in his own sand monitor.
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