3-5 mm bitiminous felt ?

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speakerbug

Member
2008-01-10 4:02 pm
Hello all

The plans for the speaker I am finishing call for this as lining. I live in the US and can't find anything this thick. All the audio dampening products get very expensive when you consider I probably need about 20 sq feet.

Any recommended economical alternatives or anyone know where I can find roofing felt this thick?

Thanks

Scott
 
Hi bug, I moved this over the loudspeakers.

Either at a roofing supply or home depot type store will have it. It's known as #90 or 90 lb. felt. That is assuming you do mean felt (organic) and not fiberglass. If it is the fiberglass based products, you may have to double up on some #40 underlay type sheet.

Either way, I don't consider it first when thinking about damping materials. Can you tell us more or show us a pic of what you are trying to do and maybe someone can help?
 
Quote:

"Cabinet lining is 3-5mm bituminous felt damping or similar mass loaded material, 30-50mm polyester (Dacron 200g/m2 density) stuffing/lining. Wall lining and damping is added to all internal walls, except the front wall. It is important not to over specify or use too much lining so the correct amount and density of lining is used in order to maintain the same voice balance of the speaker. This can have more effect on the sound than other over specified and expensive crossover parts (capacitors and inductors). Over stuffed cabinets will result in undesirable and constrained sounding speakers with less bass and midrange voicing. If you cannot find the correct density or thickness, simply peel away estimated amounts of lining."


It gives you the option of polyester lining so I would either head to my local fabric store and get some pillow stuffing or the local hardware store and use rock wool insulation. The nice thing about damping is that it can be tailored to your requirements simply by listening and making adjustments to suit. I hop they're not talking about a bituminous membrane that adheres to the walls and acts like a panel damper rather than the more traditional means of damping the internal waves.
 
OK, it looks to me like the felt is stapled to the walls and the polyester is added for internal resonance. I wonder how effective the panel damping is when it's not fully adhered, just stapled in place over the wood. Either way, don't be afraid to experiment. Try using whatever thickness you can get and multi-laming to get to 5 mm. If you want to get really fancy, consider using vinyl floor tile fully adhered to the walls. That will help with panel damping better than any felt would. Even the peel and stick kind work well if the inside surface is good and clean.
 

speakerbug

Member
2008-01-10 4:02 pm
Thanks a lot

I am heading over to Home Depot now to see what I can find. I'm told there is is a heavy felt that is used in roof valleys and rakes that is sticky on one side. However, what ever I end up using, I will glue it securely to the MDF.

PS I am envious of your big speakers. Perhaps my next project...
 
Whoa grasshopper, not so fast. That peel and stick stuff has a high solvent content which can have detrimental affects on the drivers. It also stinks. I wouldn't use it unless you are able to install it and leave it for a month before closing up your box.

EDIT: The peel and stick I was referring to was the floor tiles, not the roofing.
 
First, I'm not real eager to put anything in my speakers with 'bitumen' in the name, which basically mean tar or asphalt.

I think a dense carpet (felt or foam) underlayment would work just as well, with no potential for becoming an environmental disaster area (he said somewhat sarcastically).

As for vinyl tiles, I think they are too dense and smooth to be effective - that's just me.

Personally, I've always used fiberglass, though if I were to use it now, I would put down the fiberglass and cover it with a thin layer of polyester batting.

Also, keep in mind that there is a new product on the market. It is flame retardant cotton house insulation that is made primarily from recycled fiber and comes in rolls just like fiberglass. It's called 'Ultra Touch' -

http://www.ultratouch.net/

Again - this is just me - I don't feel real comfortable putting petroleum impregnated fibers in my speakers. There are just too many other fibers and foams to not use them.

Steve/bluewizard
 
By 'damp the panels' I assume you mean prevent the side and back panels from vibrating rather than prevent reflected waves inside the cabinet.

Still, I don't see how vinyl tile can accomplish either of those things. Wouldn't some serious bracing do a better job on the sides and back, then use 'soft' damping to prevent reflected waves.

Actually, just curious about what you mean by 'damp the panels'.

If you mean to isolate the inside from the outside, as in sound proofing, which in turn is really just preventing the cabinet itself from vibrating. I would think some dense carpet padding foam glued to the sides and back, then covered with a fair layer of Poly would get the job done.

In my mind, I can picture tar impregnated felt doing an excellent job of preventing the escape of internal vibration. It would seem to have both energy absorbing mass as well as sound absorbing qualities, but neither changes the fact that you are putting a petroleum product in your speaker cabinets.

Though I confess I may have a misunderstanding of what 'bituminous felt' actually is. Based in my understanding, I would want something a little less toxic for my speakers.

Just curious.

Steve/bluewizard
 
Hi,

I have used self adhesive vinyl floor tiles for damping panel resonances
and they are very effective - as long as you have the solid vinyl types -
not the foam with vinyl surface layer types.

The mass + viscoelasticity wall damping appraoch is to drop thin
wall panel resonances below the critical midrange frequencies
and to damp (via hysteresis) the Q of the lowered resonances,
an approach typified by the UK BBC and the material used was
bitumen impregnated felt panels, still used by Harbeth.

The main effect of adding panel damping to most thick wall speakers
is to moderate the Q if the main high Q panel resonances, it does not
remove them. It will lower frequencies, lower overall flexure due to
mass but resonances will remain, thewy are not completely damped.

It suits thin walls best and is restrained layer damping.

For thicker walls constrained layer damping is better, this can be
achieved by laminating two layers with a suitable constrained
layer between them, but good info on this is hard to find.

:)/sreten.

edit :
All carpet damping stuff I've seen is not heavy enough or lossy
(i.e. its too bouncy/elastic) enough to be particularly effective,
though its better than no lining at all.
 
Wow - too much information

OK. Thanks.
What would you use if you were building these? Can you recommend an alternative to the 3 - 5 mm bitiminous felt? Even the #90 "tar paper" stuff I looked seemed barely 2 mm. The walls in the speaker are 18 - 25 mm and I plan on putting additional poly batting stuff over the first layer of dampening.

I was hoping to avoid paying for dynamat or similar product, but I don't want to mess it up at this point
 
I guess it depends on what your goal is. The speakers you are looking at are (1020mm) 40" high and (225mm) 8.86" square on the ends. The drawing shows one cross-section brace. The cabinet is for a 6" woofer with a rear port.

If you are building this out of cardboard, the you are most certainly going to need to 'damp the panels'. However, if you are building it with the side of 1" MDF and the fronts and backs out of 3/4" MDF as specified, I don't think the problem is going to be as great.

If you can find 1" MDF, build it all out of that, and adjust your dimensions accordingly. If you are concerned, add another brace.

Now line the walls with some type of 'fluffy' material. You can use house insulation (3" to 4") and over that with a thin layer of Poly batting.

If you insist on some heavy dense material on the wall, I've seen roles of recycled rubber mat about 1/4" to 3/8" thick that are at the same time soft to walk on, but still hard and dense. Glue this to the walls. (saw this at Menards home building supply store).

I've also seen roles of thin soft rubber mat to be used as carpet underlayment. I'm guessing the thickness was about 1/16" though it may have been slightly thicker. You can build up layers of this. I saw this at Fleet Farm Supply in the carpet section.

You can try Sreten's idea of solid vinyl floor tile, but I don't personally see that it really buys you anything. If the walls/panel are flimsy, then a floor tile isn't going to matter, and if the walls/panels are thick, solid, and braced, I still don't see how tile helps.

As to the bitiminous felt, if you must, then find a thick dense layer of felt, but skip the bitiminous part.

Also consider, soft foam or convoluted foam, you can even use that in combination with Poly batting.

Here is a link to the cheapest convoluted foam I've found anywhere.

http://www.uline.com/Browse_Listing_8002.asp?desc=Convoluted+Foam+Sets

http://www.uline.com/Browse_Listing_865.asp?keywords=foam

http://www.uline.com/Browse_Listing_863.asp?keywords=foam

But if you want to 'damp the panels' I would suggest just doing a better job of bracing them.

Hey...it's just one man's opinion.

Steve/bluewizard
 
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