Woofer choice : maple or mdf ?

[Scott L]

this wood vs that wood, these posts always the same

Go back and read post #25. This echos what I posted even earlier than that about using a composite.

Single 3/4 inch anything just will not work for any enclosure of considerable size.

What I mean by "not work" is that it will ALWAYS impart a sonic signature.

I just completed a double walled push-pull slot loaded enclosure. It sure was a LOT of work, and I ended up purchasing 4 @ 4x8 sheets of mfd. For some panels I used mdf+ply, others just mdf+mdf. It's pretty much a neutral enclosure. Between the opposed-force-reaction canceling and dbl thick walls (plus bracing) the results are outstanding !

 

[twinter]

You guys are correct, chipboard (European speak) is particle board in North America. The author and administrator of the Qualia website, username Cat's Squirrel, is from the United Kingdom. Link About Me - Audio qualia

"......MDF is very well damped acoustically thus making it an ideal material for speaker enclosures....."

A number of audio sites will say MDF is well damped. As far has engineering products are concerned, MDF is not well damped. And yes, the data listed shows that lowly particle board is better damped than regal Baltic birch plywood or MDF. I have yet to find data that states otherwise. MDF and Baltic birch plywood like to resonate around 280 to 500 Hz. Using MDF or Baltic birch plywood requires extensive bracing for high performance loudspeaker applications.

 

[planet10]

... requires extensive bracing for high performance loudspeaker applications.

Any quality speaker requires bracing.

dave

 

[twinter]

Scott L, "Single 3/4 inch anything just will not work for any enclosure of considerable size." That's a similar conclusion to one stated by Cat's Squirrel after several years of testing materials for good damping. Some times two different materials with low damping can be used together to achieve good damping, such as aluminum/ MDF /aluminum sandwich.

 

[jReave]

diypass, if you have time to do some reading, much of what you are asking re best materials to make cabinets out of, has been covered before. Try these 2 threads:

http://www.diyaudio.com/forums/multi-way/138111-what-characteristics-better-material-enclosure.html
http://www.diyaudio.com/forums/construction-tips/98834-discussion-what-materials-build-speakers-out.html

 

[nigelwright7557]

I use 18mm plywood for my speaker cabinets.
Its more robust than chipboard.
I finish my cabinets with thin carpet. Its hard wearing.

 

[Eldam]

What about the bracing architecture ? Is the bracing need to be very resistive ? What about balls suspended by a threads in the middle of the load : with their little mvt due to air can they brace ? Multi balls with different diameters/weight + cleats ?

Is it possible than a very hard wood having a good internal damping ?

 

[Scott L]

What about the bracing architecture ? Is the bracing need to be very resistive ? What about balls suspended by a threads in the middle of the load : with their little mvt due to air can they brace ? Multi balls with different diameters/weight + cleats ?

Is it possible than a very hard wood having a good internal damping ?

Solid wooden dowels work best; the trick is just how to affix them to the cabinet walls. Building a proper speaker enclosure is not cheap, and it is not easy. That's why it's rarely done correctly.

All the information on "how to" has already been offered in these threads.

 

[Eldam]

It's my understanding indeed... and more expensive because experience stays important for the final result.... the first enclosures must be....🙁

Well not speaking of the price, all are said about Yung module and damping ?😕 Or is it enough for the result needed ! (my understanding to your answer...) ?

 

[planet10]

Solid wooden dowels work best

The study behind the image on this paper published in the AES Jouranl seriously disputes that assertion.

The higher the brace pushes the panel resonance the better.

dave

 

[jReave]

Dave, I'm curious on the conditions of that study.

Is there anything on the other end of that single dowel, like another panel, that would help to stiffen it making it more applicable to how cross-bracing is used in cabinets?

Typically in these diagrams based on plate theory, the diagonal fill on the edges denotes a fixed edge, but the first condition doesn't show this for the center dowel but does for the other bracing conditions. Whether the edges are fixed, simply supported or free will definitely make a difference in the results.

 

[planet10]

I believe so. But it has been a long time since i read that paper.part of the AES loudspeaker anthologies. i have put it into use very successfully.

dave

 

[twinter]

Is it possible than a very hard wood having a good internal damping ?

Eldam, yes as I stated in an earlier post:


"I believe there is promise for several of the tropical woods such as Ipe, which has a very high stiffness, around 3,500,000 psi modulus of elasticity (three times the stiffness of Baltic Birch Plywood and seven times that of MDF), and has high internal damping, maybe 4 times that of Baltic Birch Plywood or MDF. Even if only used for the front baffle or bracing. Most Ipe imported is air dried and used for higher grade decking. Some kiln dried Ipe is imported, which would be required for indoor use."

Qualia tested ipe to have a damping factor of 0.5.
Qualia tested MDF and Baltic Birch Ply to have damping factors of well less than 0.1.

As Jcx pointed out, the stiffness of wood is very grain depended.
For the stiffer American woods such as ash, maple, oak, tangential to the grain rings is about 1/15 the stiffness of along the grain. So, I not sure how much this will effect the vibrations.

 

[Greebster]

Ipe like most other unobtanium is out of contension IMO. The dampening coffecient may be theoretically optimal but is not dimensionally stable. This is where BB, quality ply woods rule. MDF if used must be completely sealed with Zinnser BIN (art grade shellac, etc.) to prevent moisture intrusion.
Using CLD construction methods, panels and bracing made this way rule the day. I have yet to hear a panel made where the Q was much higher than 0.5 and had a negative impact sonically. Careful placement of panel bracing along the longest dimension raises the resonance the highest. Prefer to place these at the 1/3 and 3/5 appear to be rule of thumb.
The importance of raising the resonance is two fold. First as the frequency goes up the amplitude decreases and secondly this frequency is alot easier to affectively dampen.
I prefer to CLD bracing of the motors. These are not connected to the panel braces but independent and connected to a corner eg junction of the back panel and side, not neccessarily the top, back, side junction.
Also by beveling the edges and mounting to a groove the bending forces are not transmitted through to adjoining panels further reducing box coloration.

Similar to force cancellation with woofers approach I've used since the 80's. Prevent it first, minimize it second and dampen what you can.

All in all have yet to find a better aproach. 🙂

 

[twinter]

I would not consider ipe as unobtanium, as it is easily found in the USA and not ultra expensive. Several lumber yards in my area carry it. As with any solid wood, dimensionally stable would be a major consideration. Purchase kiln dried, and place indoors for a couple of months before use. Any solid wood would not be my choice for an entire enclosure.

Damping factor is the reciprocal of Q.

 

[ogie]

Here's a quote from Audio Note Kits regarding AN Speaker cabinets:


"Despite what you might think the guitar like structure of our cabinets is not resonant sounding, what they do do though is greatly enhance efficiency, dynamics and sparkle and sounds less colored than the alternative methods, which generally just move the resonance frequency and amplitude of the energy lower down in the spectrum, which in most cases is more audible, mainly because this also increases the duration of the resonance, our belief is that the shorter the duration of the energy is the less likely it is to interfere with the immediacy of the original transient and disturb what comes after.
For this reason, we also use only a minimal amount of wadding, and it has to be a specific type, preferably well cleaned and carted sheeps wool, positioning is critical, and here experimentation is recommended, if you build the speakers yourself."


Other manufacturers in this camp are: Harbeth, Shindo and Spendor.


Related readings:

BBC Cabinets

Harbeth


DIY Audio thread

 

[twinter]

Here's a quote from Audio Note Kits regarding AN Speaker cabinets:


"Despite what you might think the guitar like structure of our cabinets is not resonant sounding, what they do do though is greatly enhance efficiency, dynamics and sparkle and sounds less colored than the alternative methods, which generally just move the resonance frequency and amplitude of the energy lower down in the spectrum, which in most cases is more audible, mainly because this also increases the duration of the resonance, our belief is that the shorter the duration of the energy is the less likely it is to interfere with the immediacy of the original transient and disturb what comes after.
For this reason, we also use only a minimal amount of wadding, and it has to be a specific type, preferably well cleaned and carted sheeps wool, positioning is critical, and here experimentation is recommended, if you build the speakers yourself."


Other manufacturers in this camp are: Harbeth, Shindo and Spendor.


Related readings:

BBC Cabinets

Harbeth


DIY Audio thread

There is some credence to the thin, stiff, and damped panel.

1) Resonances negatively impact the sound. They increase the amplitude and duration.
2) Resonances are excited by input at the same frequency or large panel impulses.
3) To reduce a resonance at an offending frequency, panel stiffness and mass can be modified to move a resonance frequency up or down to avoid the offending region. So yes, thin & stiff & damped can work. The resonance is still there, just maybe in a more benign frequency for the application.

Most of the thin wall stance references panel vibration testing in the 1970's. And I have the BBC article, "Factors in The Design of Loudspeaker Cabinets."
Other testing has occurred since then.

Check out websites and some of the postings for Magico, Rockport Technologies, Perfect 8 Technologies, Von Schwikert, and Ascend (Bamboo) speakers.

You have to look at the frequency and damping. Stiffness, mass, and damping have to be considered.

 

[diypass]

diypass, if you have time to do some reading, much of what you are asking re best materials to make cabinets out of, has been covered before. Try these 2 threads:

http://www.diyaudio.com/forums/multi-way/138111-what-characteristics-better-material-enclosure.html
http://www.diyaudio.com/forums/construction-tips/98834-discussion-what-materials-build-speakers-out.html

thank you indeed

 

[twinter]

Links follow to articles on high performance enclosures. When you have the means and determination to perform numerous vibration measurements and make the necessary modifications to develop better performing enclosures.

Magico
Magico Technology | Enclosures

Rockport Technologies
Rockport Technologies

Perfect 8 Technologies
http://www.perfect8.com/nav/pdf/EnclosureBaffleStudies.pdf

Von Schwikert
A Whitepaper: The Audibility Of Cabinet Panel Resonances and Pat. Pend. Method Of Reduction Of Audible Coloration - Dagogo | A Unique Audiophile Experience

Ascend (Bamboo Enclosure)
Sierra - The Cabinet