Replacing sound proofing in cabniets

I have an old set of speakers I am bring back to life. I have replaced many of the drivers. My next step is replacing the thick cloth material inside the cabinets. Must be used for sound proffing, keeping the sound from bouncing about.
Just curious what people use for this. Carpet pad? Any suggestions sure be appreciated!

Thank you.
Home insulation works well
As the above poster stated, home insulation fiberglass works very well. I've seen many charts from tests of various speaker stuffing materials and good ole fiberglass holds it's own quite well.
Are these speakers vented or sealed? At what frequency does the woofer cross over to the mid? Sean
These speakers are vented. Someone suggested home carpet felt pad. As far as what frequency, I have no idea??
After doing some research, I see there is acoustic foam. I also see some sort of egg carton liner.
Has anyone used these?
I was told that some felt carpet pad would do the trick.
I like the insulation idea, but would thing that the fibers might eventually come out the vent holes.

NO fiberglass in a speaker with open vents.

Acoustic foam can work very well, especially since you can easily adhere it within the cabinet and vary the density through-out it. I would suggest covering the entire inside of the cabinet with a layer of low density foam and then stuffing the open chamber in the top end of the cabinet using the same material. That is, if the port is located in the bottom section.

From there, you can vary the amount and density of stuffing within the open area between the woofer and the port. Don't go crazy here as all you want is just enough to very loosely fill the open space.

Not only will this provide what is probably a far more natural sound, you may actually experience a slight increase in bass extension. If you find the presentation to be lacking mid-bass ( warmth ), reduce the amount of foam between the woofer and ports. Most people will tell you not to block the area between the ports and the woofer at all, but that is because they don't know what good sound is and are used to high levels of sonic colouration. By placing a small volume of low density foam between the woofer and the port, you minimize the contribution of the port above its' tuned frequency. In effect, the port works as a port and not as a "leaky hole" radiating sound above the frequency it was designed to work at.

As a side note, carpet pad can work, but there are quite a few different types and densities available. This can be really hit or miss, depending on the materials and densities used. Dacron, polyester fiberfill, "acousta-stuff", etc... can all be used, but low density foam is by far the easiest to work with. Sean
I stand corrected. With a port design, I wouldn't use fiberglass either.

Richard: I agree that Fiberglass is typically a GREAT insulator inside of sealed speakers, but due to all of the health hazards and variables involved, i'm hesitant to recommend it unless i know exactly what's going on. After getting "bit" a few times, i've learned to ask questions before responding with answers. Not all dogs ( or questions ) are as friendly as they seem : ) Sean
For a vented system you should only have material lining the cabinet walls. In a sealed system you would have the filler material filling the entire cabinet interior (the amount of stuffing will depend on a number of design goals). Placing any type of material in the vent tube or vent hole will change the "Q" of the speaker system alignment. If we assume that the speaker's designer knew what he/she was doing, changing the alignment will probably not improve things.

Barry Kohan
I like the idea of adding Acoustic foam/low density foam.
Can anyone tell me the best place to buy this? My replacement drivers should be on their way soon and am hoping to replace the old material ASAP.

Agree with above posts, but will add a couple of other suggestions...

You can try to completely stuff the box with foam - the type Sean recommended exactly. While it goes against the conventional wisdom to stuff a ported box, this is what the Fried Line Tunnel or the Von Schweikert Transmission Line(I disagree that it is a TL) do.

Or, you can use polyester batting, loosely filling up the box.

Both of these things can relieve a speaker of its boxiness in many, many instances, turning wheezing bass into more natural sound. As in all cases, experimentation is needed to see if it works for you and/or your speakers.

I bought some acoustic fill from them. They have a few selections including eggcrate foam, stuffing, and dampening sheets.
As Barry aka "Bright Star Audio" mentioned, i typically do not advocate stuffing the port in any way, shape or form. That is, unless one is "experimenting" and does so in a fashion that is easily reversed.

Having said that, most mass produced and even many "audiophle approved" and "hand built" vented designs will benefit from what i've mentioned. As mentioned in another thread, i just got done doing this to a pair of speakers that currently retail for over $3K. The results were quite obvious and highly beneficial. For the record, these speakers were HIGHLY under-designed to begin with in almost every aspect. Even though they were poorly designed, lacked proper implimentation of the design, which resulted in them sounding like crap, they get rave reviews all the time. Sean
Sean, I take it that you are referring to the Legacys you have been working on?

As you know, I am not such a big fan of their speakers. I will say that the Focus and the minimonitor sound the best in the lineup to my ears. Legacy is my biggest disappointment in audio, where the whole definitely does not add up to the sum of its parts. Of couse, I am speaking "on paper", and your recent exercise probably proves that the sum of the parts isn't all that much to begin with.

When I was about 19, I finally had enough money to buy a pair of Legacys, and a used pair popped up in a nearby audio salon. After receiving their catalogs for years, I just "knew" they were the best speaker out there. Especially, at the price point.

I mean, come on, all those woofers are drivers, in a big, beautifully finished, well braced box. The testimonials were jammed with people who had moved to them from all of the respected brands - Thiel, Wilson, Mirage - let's just say that from this and all of the other "wonder products" I have encountered, I have zero faith in testimonials these days.

Fortunately, or unfortunately, I decided to go to the store to listen to my Legacies. It was a foregone conclusion that I would be buying them. The audition was simply a formality. Credit card in hand(if they were at a distant dealer, I would have just had them shipped), I drove on over.

Wow! All I can say is that there is no other product that I have encountered in audio that failed to live up to its hype like these babies. The overwhelming feeling I got was that it was impossible for a speaker this big and bold to come across this small and weak.

I won't go into all of the other details, but in a Legacy show, at the Allen Organ Company, which seems to have bought the line from Bill Duddleston, along with his services, I got the same exact impression.

There are formula's for the very thing your wanting to do.

The best investment you could make, would be to purchase the 'The Loudspeaker Design Cookbook'.

If you line the walls of the speakers with a dampening product, that will cut down on externally transmitted cabinet vibes. But, if the speakers was designed with that taken into account, then leave it alone.

I'm surprised, but I shouldn't be,that no one here has mentioned the difference in lining the walls and using a fill of some sort in the cabinet, will have two very different out comes.

Filling the cabinet with some sort of fiber fill, depending on the amount used, will change the QTS of the speaker. Changing it dramatically is possible. The more fill used, the larger a cabinet the driver sees, thus changing the sound.

The more fill used, the higher the QTS will be. The higher the QTS, the boomier the speaker will sound, most of the time. There are a million variables, but this is the
general rule.

Whatever the cost is of the book now, it was $30 when I purchased it several years ago, will be your greatest investment. It's writen in a way that most people can understand the concepts. Not rocket science.

Good luck.
Trelja: Yes Joe, these were the Legacy's we were working on. We just got them finished tonight and are pretty happy with them. That is, considering what we started off with. They are like a completely different speaker now i.e. MUCH better sounding. They still have a "ported" sound to them, but you can't get rid of that without sealing them or using a more advanced bass alignment. This type of problem is especially hard to conceal when the designer crams TWO woofers into a box that is too small for just one of the woofers!!! All of these designs use a box that is just too darn small for the drivers being used, hence the bloated bass that lacks definition. Believe me, this is only a very small part of the problem too. I took pictures of the crossover network before and after. If i can figure out how to transfer these pics from my camera to my puter, i'll forward them over. As i mentioned in what was probably another thread, we were able to go from a total of 122 connections in the pair of crossovers down to 46 connections total!!! All of this by paying attention to how the crossover was laid out on the board. There were NO circuit changes made, so it's not like we changed the parts count in order to reduce the number of connections. Then again, i'm "preachin' to the choir" on this one, so i'll save it for a more appropriate time : )

Steveallen: Most vented designs can be drastically improved by adding damping materials internally. Very few vented designs make use of optimally sized boxes, so adding internal volume via damping material typically helps to reduce the output peak at resonance and smooth the overall response. This is because internal reflections are damped and the box appears to become "bigger", bringing the alignment closer to what the driver would optimally like to see. To top it off, this approach will typically produce increased clarity and definition due to the reduction of the aforementioned internal standing waves being reproduce and less leakage from the ports.

While i do agree with your suggestion to read this book, many people have read hundreds of books and even graduated from schools with a degree. Reading textbooks and passing tests vs knowing how to properly interpret and apply that information are two very different things. This is why we have so many speakers that sound like crap but look so good on paper. Even those that know how to talk the talk end up not knowing how to walk the walk due to a lack of understanding and experience. If this were not true, Trelja and i wouldn't have initially been impressed with what we read and saw about Legacy's, but we were. Wanting to believe and being able to believe are two different things, especially if you are honest with yourself. Sean
Sean, excellent job on those Legacys!!!

I have absolutely no doubt in my mind that you have taken them at least two levels forward. Your diligence in reducing the number of connections in the crossover would pay enormous dividends, at least to me. You obviously know much better than I how things improved, but if I would venture to guess, I would predict the dynamics and clarity improved audibly, while also realizing gains in liquidity and smoothness at the same time. The audio Holy Grail!

Did you go with the Solen caps in this project that we have talked about in the past? If so, I know you have great sound. I think these caps really get shortchanged when it comes to how good they sound. Full sounding and smooth, again, with great detail. The BEST everyday cap out there(well, actually the thicker film SCR/AXON made on the same line is a bit better, but they're both close). And, did you give those wirewound resistors a shot, Ohmite or otherwise?

I concur with your assessment of the bass alignment. You can only get so much from a box, and that makes me realize why I have been so underwhelmed by the Legacy bass in the past. When you see that kind of artillery, you expect to be blown back. When it doesn't happen, you are left with a lot of disappointment.

I will say that my last encounter with Legacy, at a demonstration they put on locally was by far my best time with them. Again, I found the Focus and the minimonitor to be the best in the line, and even quite good in some areas where a lot of (most) audiophile speakers fall down. My biggest complaint was that the metal dome tweeter was woefully out of date, and its piercing sonics bore this out. They have addressed this since, and I would like to give them another listen.

Their headquarters, in Allentown, are only about an hour from my home, or less.

I also agree with your statements to SteveAllen. While the books(and I have the utmost respect for Dickason's Cookbook) say what they say, I had to say what I have outlined previously goes against conventional wisdom. Like you, I have found that stuffing the ported box often has the opposite effect of producing a more boomy sound. As Fried and Von Schweikert show, it actually produces a less boxy sound. I know I am going to have a bunch of people jump on me here, but I consider the bass of my Fried A/6 Line Tunnel to be superior to my buddy's Von Schweikert VR2.
I agree that we live in a free society and that we have the right to experiment with modifying speakers as much as we want, but if making a change as large as stuffing a vent hole actually IMPROVES the speaker, I contend that it's time to sell the speakers and buy something from a company/designer that actually KNOWS what they are doing! If the woofer section had been (apparently) designed so poorly, how much more well designed could the mid/high section be?!

Barry Kohan
Barry: Neither Joe or myself are encouraging anyone to "stuff" their ports so much as we are encouraging additional damping material inside the cabinet.

Having said that, most vented boxes are pieces of junk and closing the ports completely could quite possibly produce better quality, albeit less quantity of sound. As such, yes, most people would be better off with different speakers than what they have, especially given the majority of under-designed, poorly executed, over-priced products that are currently available. Like most changes in society that have taken place over the years, the public seems to desire greater quantity, even if it is at the expense of quality. As such, the designers / engineers / manufacturers have responded to those desires and given the consumers higher sensitivity and greater extension at the expense of linearity and over-all quality. There are exceptions to this generalization, but that is why they ARE exceptions and are far and few between. Sean
Hi Sean,

After re-reading these posts I see that you are right - stuffing the ports was not specifically mentioned. Although filling the interior with foam to replicate a transmission line does prettty much fall into the catagory that I'm describing - that by making a significant change to the speaker's basic design actually improves performance does call into question whether buying an intrinsically well designed speaker would be more appropriate.


Barry Kohan
You can't replicate the response of a transmission line with anything other than a transmission line and even then there are variables involved. Other than that, i try to avoid vents of any type as much as possible. If i had to choose out of what is commercially available, i typically prefer sealed low Q designs. Second would be an IB ( Infinite Baffle ) and third would be a stuffed or partially stuffed T-Line. Bringing up the rear in a very distant fourth place would be an aperiodic ( vario-vent ) design. Anything else would be WAY down the list. Sean
Hi Sean,

I generally agree with your post. The reality for a designer of a commercial speaker is that they are always walking a tightrope and doing a balancing act. No matter what the price point of a speaker (even the relatively new breed of extreme megabuck speakers) the designer is constrained by cost of parts, manufacturing and marketing versus the quality and performance of the parts available versus the size of the speaker system and its practicality for shipping and placement within the customer's home.

In the speakers that I have designed for commercial sale, maintaining a moderate size was a siginificant factor and an aperiodic loading chamber was employed to provide the target response for the system.

In my personal speaker system I do use a low Q sealed system for the dynamic woofer section.



Disclaimer: I am a manufacturer of loudspeakers and vibration control products.
Sean and Bright star...have you ever heard of anyone using the black undercoating in a spray can that can be bought at any of the larger auto parts stores for damping? I really think that would work very well..whatcha think?
Hi Tunes4me,

The spray may be useful to damp the interior of a component's chassis. It would mainly damp gross ringing of the chassis but it can't absorb a large amount of vibration or even damp ringing as effectively as some other applied coatings or materials. The damping spray would be considered only PART of an overall scheme to eliminate vibration.


I have used it in a few cabinets. In the grander scheme of things, it is just about useless on a well designed cabinet. Other than to help seal any seams / cracks and help keep the cabinet "air-tight" if sealed, the benefits / results are far out-weighed via other simpler and less messy methods. Sean
Hi Tunes4me,

Bright Star speakers did use multiple layers of compliant ceramic and a special damping compound that I developed that were quite effective when applied correctly to cabinet panels, driver baskets and crossover components.

Plus, I also agree with Sean's post above.