View Full Version : Best Speaker Damping Materials?


styler
02-26-2005, 10:49 PM
what are the best materials to line the inside of a speaker cabinet? :scratch2:

jerrymrc
02-27-2005, 07:07 AM
What kind of speaker, sealed or ported?

axel
02-27-2005, 08:16 AM
Deflex panels: http://homepages.enterprise.net/smason/Pages/spectrdp.htm

really effective and unbelievably so.

BillEpstein
02-27-2005, 08:56 AM
This article:
Art Ludwig on Speaker Building (http://www.silcom.com/~aludwig/Loudspeaker_construction.html#Panel_vibration_expe riments)
Makes a lot of sense and offers easy and inexpensive methods. Bob Brines:
Brines Acoustics Forum (http://audioroundtable.com/Brines/)
advocates the use of an underlayment called Hardi-Backer which is ukltr-dense. My next speaker will have 30 lb roofing felt and Hardi-Backer sandwich inside.

http://www.audioheritage.org/vbulletin/images/smilies/band.gif

ilimzn
02-27-2005, 10:19 AM
Depends on what you need, damping of the walls or the internal volume.
For the walls, I've been using tar foil (about 4mm thick), also, to reduce reflections, some sort of profiled polymer or sponge is needed, like Deflex or just the 'eggcrate' foam. Felt over tar works great too - in general, sandwich materials provide better damping. Out of the less orthodox things I've used, I'd mention ceramic tiles. They need to be 'glued' on well, and this is not easy. I've used all sorts of tricks, from molten tar to epoxy resin. If you use something that hard, you absolutely need to guard against internal reflections.
For volume damping, the best bang for buck has proven to be Miraflex - a super thin glass fiber material, normally used for insulation. I've also used polyester pillow stuffing, but it is less efficient. You need to take into account that treating the walls of the enclosure and the internal volume with acoustically semi-transparent materials tends to act as an increase in the apparent volume of the enclosure, as far as the speaker is concerned - which can be a great bonus - 6-8% apparent increase is not at all uncommon...

WhiskeyRebel
02-27-2005, 10:20 AM
That is the stuff you use behind or under ceramic tile. It is practically a sheet of concrete. On that same token it seems like gypsum board, maybe in multiple layers, would make a good enclosure material as long as you didn't need to move it once it was finished.

styler
02-27-2005, 05:10 PM
great suggestions all! i am wanting to increase the bass in an enclosure... i hear alot about dynamat and similar materials, other than being overpriced, is this stuff any good?
Tyler

dbwinger
03-01-2005, 02:28 PM
Would adding deflex pads to my Large Advents make a difference in sound? If I did add them would I leave in the foam bricks?

axel
03-01-2005, 02:44 PM
Deflex panels will lighten up your bass.
That is, put properly: it will allow the driver(s) to "breath" better, sort of. It's extremely effective on sealed enclosures, not as much on ported systems. What you will get is more bass because it is cleaner.

What it will do anyway is deaden the cabinet because of its high mass (but not make it weigh 100kg either :-)

I've installed panel on three sets of 'speakers and it was almost a miracle every time. Normally, Deflex advises to take all original damping material away and put only Deflex but on my own experience, a measure of both can work, too. If you don't cover the inside completely with these panels, place them right behind the drivers.

ilimzn
03-01-2005, 06:45 PM
In amny cases the original dampening material was used to do a virtual increase of the enclosure volume, and it is best not to completely remove it. The telltale would be that the enclosure is filled completely. As I outlined in the post above, foam bricks would probably be used to dampen reflections - similar (as full filling also accomplishes some of that) but not exactly the same.

Perhaps it is prudent to mention that speaker enclosure damping is anything but an exact science. Changes in enclosure wall damping may well warrant changes in volume damping. Also, speakers do age - I mean this in a technical way, their characteristics change as they are used (they are worn in, so to speak), which can lead to them requiring adjustment in the amount of filling.

As for 'adding' bass, you CAN accomplish that by damping, but not per se by damping enclosure walls (i.e. damping wall vibrations), but rather applying some form of damping that makes the enclosure behave as bigger than it really is - but this cannot be done on all speakers. Damping walls against vibrations and using things like deflex to damp internal (and external!) reflections will usually clear up the bass (and can have substantially more dramatic effects on the rest of the audio spectrum). What euphonic effect that can have to bass perception is less defineable.

Thatch_Ear
03-02-2005, 01:42 PM
A great thing to use to avoid problems with standing waves is to use the small bubble-bubble wrap. Just use a spray adhesive to apply it directly to the inside of the box. Egg crate mattress can be cut to size and just pushed in without glue. Poly fill makes the driver act like the box is larger so expirementation is needed to get it right. The long fiber stuff you can get with speaker making supplies is supposedly the best, but I can't tell the difference between it and the pillow stuffing that is $5 a 5 lbs box at Wall-Mart.

If you have concernes about the rigity of the box, before you put it together take the sides and or top and bottom, carefully clamp them exactly flush and use a hole saw on your drill to cut out holes for the heavy ash dowelling used in clothes closets. Since it is round it won't cause reflections that can turn into standing waves.

The standing waves end up back on the cone causing extra vibration and distortion.

WhiskeyRebel
03-02-2005, 06:27 PM
Does the convoluted foam mattress pad seem to work well inside a speaker enclosure?

Thatch_Ear
03-03-2005, 01:05 PM
I have some isobaric subs that have it in them. It provides good damping and is supposed to help defeat standing waves. Using the thin stuff probably only provides a bit of damping while the thicker pad should act as a bass trap. I have seen it used in room treatments as well as inside cabinets.

theNoid
03-04-2005, 08:51 AM
Firt of all, what speakers are you using and what size, type, and tuning specs is your enclosure built to?

For sealed speakers I have always used "fluffed" polyfil from Wal-Mart with great results. Doing so lets the driver act as if it is in a slightly larger box. How much too use always depends on the person the speakers are being built for and what we end up tweaking it to. There is no perfect ratio but a good place to start is about 1lb per cubic foot of internal volume. From there, do some critiacl listening and tweaking with amounts of polyfill until you are happy. If you want to spend the extra money and go for the natural long hair wool or the likes then go for it, but I have never had the means, nor been able to hear the difference enought to justify the extra bones.

For ported enclosures, I have always used egg-crate foam to line at least the back baffle of the box. If the box and design allows, I will line the side, top, bottom, and the back walls with the thinner egg-crate foam. In a ported enclosure, this is primarily to help eliminate standing waves and to help eliminate reflecting waves from making there way back through the port.

Neither of the above mentioned practices are a replacement for a properly designed and built enclosure. If you use the proper materials and bracing techniques, you should end up with a resonant free speaker cabinet that doesn't need all the other mass-adding "band-aid" techniques. If however, you do find that you are in need of some resonant killing mass, then try plain old modeling clay. About .25" thick layer will do the trick. Also try using this on the frames of your speaker drivers as well. I am betting you like what you hear.

Hope all this rambling helps and feel free to hit me up with any questions or comments on the subjects.

Noidster

ilimzn
03-04-2005, 11:54 AM
For sealed speakers I have always used "fluffed" polyfil from Wal-Mart with great results. Doing so lets the driver act as if it is in a slightly larger box.


Actually, it does this quite successfully for ported boxes as well, and for transmission lines it adds to the apparent length of the line. The trick is just to use a material that will not go flying out the port ;)


If you want to spend the extra money and go for the natural long hair wool or the likes then go for it, but I have never had the means, nor been able to hear the difference enought to justify the extra bones.


I have to agree on this. And it's also prone to moth and similar insect infestation...


Neither of the above mentioned practices are a replacement for a properly designed and built enclosure. If you use the proper materials and bracing techniques, you should end up with a resonant free speaker cabinet that doesn't need all the other mass-adding "band-aid" techniques.


I wholeheartedly agree. Still, it's nice to know if you want to mod a stock box...


If however, you do find that you are in need of some resonant killing mass, then try plain old modeling clay. About .25" thick layer will do the trick. Also try using this on the frames of your speaker drivers as well. I am betting you like what you hear.


Yes, it works very well, but I have found it tends to drop off when the driver heats up!