Lining dedicted midbass cabinets

[mitchyz250f]

What would you line dedicated midbass enclosures with? Open cell foam, closed cell, poly fill, jute..

frequency range is 100hz to 200hz.

[critofur]

Some sort of padding made from natural fibers, if the material you use is good, then when you put your ear up to the opening where the speaker goes there should be a very "dead" quiet sound, and when you talk into there it should sound muffled.

If you don't have some good thick 1"-2" thick sheets of padding made from natural materials such as this: http://www.bondedlogic.com/ ("ultratouch" insulation made from scrap denim) then your other alternatives are fiberglass, or, expensive sheets of damping material such as "black hole", or "sonic barrier". Sonic Barrier is available at parts express, though, to me, it's not a good value and I don't believe it's nearly as effective as some of the natural fiber materials I have used (the performance of these vary widely).

EDIT: closed cell foam would typically be useless, except, perhaps, in a multi-layer composite, most other foams are also mostly ineffective.

Insulation made from denim:

Here's the first link I found to a place that sells this stuff: http://www.naturalbuilthome.com/prod...tion_2676.html

If anybody wants to split an order (kind of a mini-group buy) I might be interested, I'm in Columbus, OH.

[mitchyz250f]

Thanks for the reply. Do you think natural fiber (Carpet padding)jute would be usefull for this application?? Not the stuff made from foam but the stuff that looks like it is made from fibers??

[critofur]

If the fibers are course (thick stiff fibers) then no, can you send a closeup picture?

If it's somewhere in between a cotton ball and felt, then it may be good. (Cotton (as in a fluffy cotton ball) seems too light and felt seems too dense, just my guess)

If this is something you have on hand, or, if it's cheap and easy to get, then just try it (stick it in w/o glue) temp. and you will be able to hear an obvious difference between the lined box and the unlined box simply by sticking your ear up to the opening (if it is effective).

You could start with fiberglass as a base then try to find something better by comparison.

How thick is the natural fiber carpet padding you're talking about? I think you want at least an inch (about 2.5 - 3 cm) thick.

This type of material lining the walls may not help to dampen vibration of the cabinet walls themselves, but it can certainly help reduce reflections, and, when placed properly (in the right places suspended in between walls) can reduce standing waves in the cabinet.

[critofur]

Oh, BTW, in the range 100 - 200 Hz damping the walls would be more important than the effect you would get with the sort of lining I've talked about here, which, would prob. be most beneficial for frequencies above 1 Khz?

Figure out the wavelength of sound in the material that you're building the walls out of then you can calculate approximately what the resonant frequencies of panel sections will be. Whenever you apply braces to the cabinet walls you don't want to put them right in the center, you want them offset some so that you don't create two panels with the same resonant freq, you also want to avoid sections that will resonate at a freq. within the pass band, if possible.

"Constrained layer damping" is one effective method, dual walls with sand in between is another good method. Irregular bracing can be very helpful. Building the walls out of layers of different materials is good as energy is lost at each transition between different materials (materials of different "impedance"?) I would call it materials with different "Q"s.

If you hit the cabinet with your knuckle, the more "dead" it sounds the better, should just be a dull thud and not a nice clear "lively" resonant sound.

[mitchyz250f]

Thanks,

[SGD]

ok before iam shot down in flames, iam fairly new to DIY speakers, last pair i made was close to decade ago and i havent tried my hand since.


i have heard of sandwichs between 2 enclosures with sand (and lead etc), i am myself at the concept stage of designing a pair of nearfield monitor and like the idea of this but dont want to create anything weighing so heavy.

my idea is to use paper mache inner enclosure (!), a sandwiched layer of bubblewrap (!!) and outer enclosure of ply and/or mdf.

i figured bubblewrap wouldnt store much energy, as for the papermache i suppose you could build up layers of different materials.

am i talking rap with a silent C and is my idea hit with a silent S?