This is what a sandwich of 18mm fiber board and 18mm birch ply does. Main resonance at about 500Hz. More flexible boards (thinner) have lower resonances, but my point is: your construction will have pretty high resonance frequencies anyway (above 500Hz). So better build a small midrange enclosure with CLD and a stiff lowrange enclosure with high enough panel resonance frequencies to put them outside the passband.
The resonances of your setup will not be in the range 80-200Hz and modal behavior in the room would render possible resonances in that range beyond perceivability. So don’t bother, however ingeniously your plans are.
The resonances of your setup will not be in the range 80-200Hz and modal behavior in the room would render possible resonances in that range beyond perceivability. So don’t bother, however ingeniously your plans are.
That's actually a pretty clean plot. I've never used baltic birch plywood before because I can not afford it. In my area small sheets are over 100 USD and only large enough to cut one sidewall of an enclosure of the size I am planning. I've also noticed the quality of MDF is terrible now. I cut a lot of it at work and the stuff just flakes apart. 30 Years ago it was much better and stronger quality. I'm almost tempted to make the entire lower enclosure out of EG or UHPC reinforced with rebar.
I know the resonance in my setup will be much higher than 80-200Hz. that was the whole idea. To drive the resonance high enough so that it can more easily be damped by the core material.
Now this is a lot cleaner, 18mm birch ply, 11mm mass/lossy plate, 18mm MDF, glued together and braced. CLD really works well. But even MDF with only mass plate and bracing works pretty well, with resonances above 300Hz. Courtesy of Martin van der Hoff, who published these years ago.
Here is an example of what I'm saying. You take the motor in your car assuming you have one and you are concerned about something going wrong internally and you need to listen to it but you cant hear it over the noise so you grab a dowel rod and place it against the engine at the point of concern and put your ear up to the other side and suddenly you can hear the inside engine. Now if you place a flat panel against the dowel rod instead of your ear the sound will broadcast. The dowel rod acts as a bridge for the sound to jump the air gap that is the constrained material in this example. The bolts will act in the same manner in your case. The thing to do is to adhere the layers together with out the use of the bolts. A general purpose carpet glue applied with a notched trowel works well for this or contact cement works too. But in any case you are likely not going to gain much noticeable improvement in sound quality either way and that's a lot of extra work to go through just to gain so little. But then again if you have a bunch of small advances when combined as a whole you might come out a head of the game so have at it.
No kidding. I'm building a set of speakers right now and came across a small scrap piece of MDF I had left over from a box project in one of my vehicles from years ago and I was actually surprised to see just how much difference there was between the two. Mind you I live in California so it might not be so bad else where in the world but here where anything that works well or lasts a long time is outlawed working with crap is just part of deal you make to live here. Kind of sucks though.
Mark, on the 11mm lossy mass plate. What kind of material is this exactly. Thick rubber type material or something like that.
To be more precise, it is Isomat TS24 by Merford — a flexible synthetic panel made from thermoplastic, unvulcanized rubbers (EVA copolymers), and mineral fillers. It has a weight of 24kg/m² and a thickness of approximately 10-11 mm.
Specifications:
https://media.pim.merford.com/uploads/pdf/1/6/167_isomat-ts.pdf
https://www.merford.com/nl/producten/isomat-ts+29
Example configurations:
- 18 mm MDF + Isomat TS24 + bracing:
Note: Without bracing, it has much worse results, so it’s not recommended.
- 18 mm Baltic bearch + Isomat TS24 + 18 mm MDF without bracing:
- 18 mm Baltic bearch + Isomat TS24 + 18 mm MDF with bracing:
- 18 mm Baltic bearch + Isomat TS24 + 18 mm MDF with bracing + 80 mm fiberglass:
Can anyone tell me whether the MDF was used as the inside layer and the Baltic birch as the outside layer?
Also, are there any similar products like Isomat TS24 available for purchase in Canada?
Thanks!
Martin’s site is no longer active, I think he’s retired his business. So who knows? But I don’t think it matters. Sound transmission works both ways.
I have no clue about Isomat alternatives across the pond. Check out specialized companies that do noise reduction.
I have no clue about Isomat alternatives across the pond. Check out specialized companies that do noise reduction.
I don't think so... The driver installed in the cabinet vibrates in response to the input signal from the power amplifier. These vibrations are transmitted through the driver basket to the cabinet. Simultaneously, the air inside the cabinet is rapidly compressed and expanded in sync with the driver’s motion (the piston effect). Together, these factors cause vibrations throughout the entire box. Therefore, the material of the cabinet plays an important role in the overall sound of the speaker. Birch is harder than MDF and resonates more loudly because it doesn’t dampen vibrations as effectively as MDF. With this in mind, I believe the innermost layer should be fiberglass (or another material like wool cotton), followed by MDF, then a sheet of Isomat, and finally birch on the exterior of the box.
Please correct me if I'm wrong. Thank you!
