Replacing Fiberglass in Speakers

[sholling]

This thread is a classic example of

If it ain't broke, don't fix it!!

If the manufacturer chose to fill a ported bass reflex cabinet with fiberglass, so be it, even it is not considered the standard way to treat a bass reflex cabinet. This has been done before, with success.

If you replace the fiberglass with polyfil or any other material with different acoustic absorbance properties, you risk changing the bass performance of the woofer/cabinet combination. Assuming that the manufacturer knew more about it than you do (more often than not, this is a safe assumption) you risk degrading the performance of your speakers. Fiberglass and polyfil do not absorb sound waves the same amount. Usually it requires more polyfil to accomplish the same amount of absorbance as it does for fiberglass. So replacing fiberglass with an equal amount of polyfil will fail to perform the same as what the manufacturer originally did. To do this, you would be in essence retuning the bass performance of your speakers. If you have no experience in doing this, just remember that your speakers are not broken, and as such you should avoid trying to fix them.

This is exactly way I would leave well enough alone. You'll accomplish nothing toward making them safer and quite likely degrade the performance. One thing that you can count on is that the manufacturer spent hundreds, if not thousands of hours testing with various stuffing materials/configurations and chose what they chose for a reason.

 

[Swerd]

It took me only a few minutes to realize that you've managed to press my buttons again .

I should have noticed when you said "it causes cancer... and just any cancer, but brain cancer."

Nice job Alex .

 

[jostenmeat]

That looks like the non-itch fiberglass.
Some insulation companies wrap it in 4-mil polyethylene that's perforated. Owens-Corning has one called Miraflex that feels soft to the touch and isn't wrapped.

I would bet money that Rickster is right on the money here. My experiences with handling fiberglass are extremely limited, but I usually hate it. Well, I've been somewhat playing with this stuff in my T55 project, and it is completely non-itchy, and surprisingly so.

 

[Alex2507]

It took me only a few minutes to realize that you've managed to press my buttons again .

I should have noticed when you said "it causes cancer... and just any cancer, but brain cancer."

Nice job Alex .

I had jokingly been suggesting that he give me the speakers in order to protect his baby and facilitate the acquisition of speakers that TLS Guy approves of. Then when you chimed in I was helpless to resist saying something beyond stupid considering your field and still running the 'give them to me' joke. That's what the address part was about. I had hoped that would have tipped you off to the nature of the post. I'm aware of what you do and maybe you don't know but we (carpenters) install more insulation than most people have ever seen. I didn't mean to push your buttons but I'm amused to see you irked by ignorance. Thanks for giving me the satisfaction.

 

[TLS Guy]

What would you recommend here TLS?

First of all fiber glass is a not the optimum damping material. Like most things to do with loudspeakers nothing is ideal. But G.L Ausperger in an AES paper investigated damping materials. Fiber glass unfortunately has holes for absorption at 75 and 200 Hz. Polyester fiber stuffing gives the most consistent results. I use Polyfill available in the pillow/quilting dept. of Walmart stores. It is very cheap.

Whilst polyfill and the other commonly used products control Fb and absorb other unwanted internal resonances, it does little to control back reflection.

Now lets change gears a little and talk about the damping of ported enclosures in general. The whole basis of the Qb 4 ported box is the controlled interaction of the driver free air resonance Fs and the box resonance Fb. Now you can not make a Qb 4 box highly damped and essentially non resonant. That is why I personally think a Qb4 ported box is not the optimal choice of loading for a center speaker where the need is great for uncolored dialog.

So this issue becomes how much to tame Fb. The usual thinking for Qb4 ported boxes is to give a light covering of damping material to 50% of the internal surface of the box. For music that usually works out, but in my view for a speaker, or speakers handling a lot of dialog I don't think that is enough. So I over damp Fb. This does reduce bass output but increases speech intelligibility.

So if the speakers are going to be used a lot for speech, I give a light covering of all surfaces with polyfill and place mineral wool on the back wall of the enclosure to reduce back wall reflections which upset driver response due to interference from the back wall reflection.

Now polyfill tends to settle and glue makes it stiff. So I go to gardening centers that sell Christmas trees in plastic netting. I place the netting over the polyfill and staple the netting to the enclosure. I make sure the polyfill is not compressed. You can see the netting in this photograph.

So I would get rid of the fiber glass.

I would place mineral wool on the rear wall behind the drivers. I would put a layer of uncompressed polyfill over the entire internal surface leaving plenty of cavity unobstructed by polyfill. That is where I would start. If I wanted speech a little less chesty still I would put a little polyfill in the cavity. I would experiment and let the ear be the arbiter.

I followed the advice I have just given you with these Qb4 boxes, and speech intelligibility is good, while the bass is not a forceful as you can get from a KEF B139 it is by no means bass deficient.

I give them gentle support from these two isobarik Qb2 coupled cavity subs with a low system Qt of 0.5. The movie experience is actually very good although it is only a two channel system. The absence of a center channel does not seem to matter one bit.

And yes, the subs are mono!

By the way is there any internal bracing in those speakers?

 

[jostenmeat]

By the way is there any internal bracing in those speakers?

Yes, there are at least two braces like these. My speaker isn't identical to Ares', but it's the next closest thing, and I presume the construction is near identical.

You will see that it's not just fiberglass, but I don't know what the dark gray material is called.

If you have ideas for modifying my speakers, I'm all ears. If Swerd agrees with anything you propose, the odds that I follow through on my 4x T55s are very high. This would be a better compromise as I'm shying away from a full blown DIY upgrade, which I don't feel up right now, in all the senses including time, energy, and money. I am already attacking multiple learning curves on multiple fronts, if only from a neophyte level.

 

[TLS Guy]

Yes, there are at least two braces like these. My speaker isn't identical to Ares', but it's the next closest thing, and I presume the construction is near identical.

You will see that it's not just fiberglass, but I don't know what the dark gray material is called.

If you have ideas for modifying my speakers, I'm all ears. If Swerd agrees with anything you propose, the odds that I follow through on my 4x T55s are very high. This would be a better compromise as I'm shying away from a full blown DIY upgrade, which I don't feel up right now, in all the senses including time, energy, and money. I am already attacking multiple learning curves on multiple fronts, if only from a neophyte level.

That looks like a microfiber product that has quite good properties.

I guess if the speaker sounds OK without chesty speech, you won't improve it. However if you think speech is chesty and unnatural, you have nothing to loose by experimentation. You can easily put things back the way they were.

I personally have not had good luck with bats of fiber glass in speakers.

 

[jostenmeat]

That looks like a microfiber product that has quite good properties.

I guess if the speaker sounds OK without chesty speech, you won't improve it. However if you think speech is chesty and unnatural, you have nothing to loose by experimentation. You can easily put things back the way they were.

I personally have not had good luck with bats of fiber glass in speakers.

Voice from the towers are very good considering the price point, IMO. The center speaker, the voice can* be chesty to me, but I attribute this to horrible speaker placement (which I hope to soon remedy with AT screen). And after all, the center speaker design is fundamentally different too.

I have found at times some midbass bloat (I mean, compared to other towers costing much, much more). The offaxis response could definitely be better to me, subjectively, but in the general price range, I only have heard significantly better with bookshelves. There is no way to know if it was the layout or placement, so take my impressions for what they are.

To me, they have very good power handling and/or efficiency for what they are, and in a multirow HT setting, this is a good thing. They won't please commercial speaker users by any means, and that's why I said "for what they are".

People rave about the sound all the time. No one I know has heard better in an HT environment, but they don't know any AHers except myself. I believe it might* be the same case for Ares, but the fundamental use of these speakers for me is for movies. Music BDs get played about once every 30 movie viewings as a guess.

If I ever my HT upgrade speakers, I do sincerely hope I will go with DIY. My only concern would be the mismatch with my 4 surrounds speakers, the sides being PSB bipoles.

 

[Swerd]

I didn't mean to push your buttons but I'm amused to see you irked by ignorance. Thanks for giving me the satisfaction.

You'd be surprised how often I can irk myself with my own ignorance

 

[jostenmeat]

Hello Josten,

I was thinking of wrapping the glass since they are in rolls, I thought the tuning difference that Highfigh was referring to had to do with placing fabric over the port. So an other material let's say like cotton can possibly effect the enclosure's tuning? reason I ask is the wife likes to make pillows and things of that nature and the fabric she uses is the same stuff that T-shirts are made out of she has yards of that stuff lying around.

Ares, sorry I failed to address your post here. I also read highfigh's input as it pertains to right on the port. Honestly, I would go for THE most acoustically transparent fabric I could find. I am "sure" (not really) cotton, if breathable, loosely woven or something would work fine, but you don't have any need for aesthetics, strength, visual projector performance, light blockage, light absorption, or anything else, just AT performance. The Joann fabric that highfigh pointed me to is only $10 for 54" x 36". I don't know if this is the best . . . but I'm sure it may be better than cotton?

 

[Ares]

The internal construction of mine and Josten's speakers are identical albeit that T55's drivers are larger, I agree that for the money I spent on them they sound good. They get used on a 50/50 split with music and movies.

Josten would you happen to have the name of the fabric on hand?

 

[jostenmeat]

Ares, my recent visits to Joanns might have been my very first time in a large "costco" style fabric store, but it was just a big roll (that you can have cut to desired size, but I just grabbed the whole thing). It's label next to roller was something very similar like "speaker utility clotch", or maybe it was "utility speaker cloth". I might PM b pape to see if he knows what the most transparent thing might be . . .

 

[Ares]

I tried using the t-shirt fabric to cover the port of one of the T45's and the other left stock and then used a rubber band to hold it in place, well it didn't workout to well. Played some music in 2ch mode no sub, music chosen to play Duffy's Warwick Ave Wav. which is on my PS3's HDD now there was a clear difference between the two speakers, now the screened T45 made Duffy's voice for lack of a better word.. soulless here voice had no presence.

So after that failed attempt I thought why not try what Josten suggested earlier and wrap the glass, went to go get some more t-shirt fabric and saw that my wife and her sewing club was using it Hmmmm what to do now. Looked in her sewing storage closet to try and find something and I came across some poly-batting I thought why not, got to work and one thing lead to another and this is how it ended up.

First woofer position as you can tell the glass is wrapped and the sidewalls lined and the port tube is wrapped, also the port tube opening is clear of any poly as well as a little section of the sidewall. (¼" Poly-Batting used)

2nd woofer's position some more wrapping and lining, if you look in the back you can see a cleared section the crossover sits underneath the bracing and wasn't to sure if I should cover that with poly. Many are wondering if removal of the glass was an option well it was til I found out they glued it really well to the walls so wrapping it was the easiest option at that point.

Now that one was done time to test it and make sure it doesn't sound horrible, same music but this time with a different result. The stock T45 sounded a little off to me not in a bad way, it seemed that the mid-range was slightly more present in the stock and adding the poly seem to tame it a little, which sounded more natural to me if that makes sense. I'm not sure how to explain it better than that but it accomplished what I wanted with an added benefit, I did the B15's and the C60 the 6i was left stock might consider doing something in the future but before that I will ask and show pics to get your guys opinions on what would work. Sorry about not taking pics of all the speakers being done, got caught up into the project that went into the wee hours since I started kinda late.

Thanks guys for all your help whether you were for it or against it, I appreciate the time you have taken to respond to this thread.

 

[riker1384]

Rockwool, aka mineral wool, is also used as both a thermal insulator and acoustic absorber. Patrick Hart from Infinity had this to say when asked about it in comparison to the 1" of fiberglass in the Primus speakers: http://www.avsforum.com/avs-vb/showthread.php?p=18730080#post18730080

If the airflow through the port is restricted it can possibly affect the intended contribution of the port. On Harman's and most other loudspeaker production lines insulation is usually stapled rather than glued to the inner cabinet side panels precisely to keep the insulation out of the way of the airflow through the port.

Re: fiberglass versus rockwool. Price is by far the most critical factor in the production of low cost speakers. Thus the 1" thick fiberglass utilized is usually of the 2lb/cubic foot variety whereas 1" rockwool is usually in the 3-4lb. or heavier range, depending on cost. The 3-4 lb. 1" rockwool will have a very slight measurable effect in damping the peaks of the reflections inside the cabinet starting at about 700Hz on up. 1" 2lb. fiberglass will have very slightly taller peaks (than 3-4lb. rockwool) , perhaps 0.25 to 0.75 dB higher in my measurement experience.

Fiberglass and/or rockwool are put into speaker cabinets to damp primarily the the inter-modulation effects on the cone caused by sound waves coming off the back of the speaker cone then reflecting off the inside walls of the enclosure then back again onto the back of the speaker cone. When the sound waves hit the back of the speaker cone out of phase, for instance when the cone is moving toward the inside of the cabinet as the reflected wave strikes the cone trying to push back against it, a type of acoustic inter-modulation distortion is caused. The two sound waves are crashing into each other out of sync . This distortion is usually picked on voice as a very slight loss of vocal clarity.

Is there any benefit to using more than 1 inch?

No.