# Mod question



## TypeA (Aug 14, 2010)

Ive been removing this grey blanket material Infinity used to dampen the cabinets and replacing with a couple of layers of seam tape and quiet board material. It works much better for dampening the cabinet and is an obvious improvement. My question, should I be putting the dampening blankets back in the speaker after I apply this modification?


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## bambino (Feb 21, 2010)

I would try would put it back in one of the cabinets and compare the sound of each one then if you like it one way or the other you can go from there.:T


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## TypeA (Aug 14, 2010)

Well I know I lost some displacement, so much so that I decided against 1" of the board material and just went with 1 layer (1/2")...


Thanks for the reply. Im assuming my mod has replaced (and improved upon) that grey fiber blanket, but I might compare just for giggles.


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## bambino (Feb 21, 2010)

No problem.:T I think if i were at it i would try it too just for giiggles.


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## Lucky7! (Jan 7, 2008)

A, there are two types of damping in a speaker. One relates to the reduction of flex, vibration and resonance in the enclosure panels themselves which it looks like the hardboard is trying to address, however bracing would be more effective. The other type of damping relates to the _acoustic_ modes inside the box, which materials such as fibreglass and polyester batting or cotton wadding aim to minimise or eliminate.

It seems you are confusing the two.

Is the speaker ported?


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## TypeA (Aug 14, 2010)

I wouldnt be surprised at all if I were confusing the two. Im not familiar with bracing, how to do it or where to begin. Can you point me in a learning direction? Yes the hardboard seems to address the resonance of the cabinet, to the point that there is little to no echo within the enclosure post treatment. The bookshelf 162's, which is pictured and is the only one I have done thus far, is ported. Also the tower 362 model is ported, which I also intended to mod. The center pc350 is not ported, I had plans to do the same to it. Thanks for the help.


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## TypeA (Aug 14, 2010)

For those interested, my personal research on this has lead me to a few internet sources. Good info on the 'constrained layer', one that recommends a few printed sources of knowledge as well, is this one.











This thread references the same article, also has info on what folks use for batting in their enclosures...


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## Lucky7! (Jan 7, 2008)

TypeA said:


> I wouldnt be surprised at all if I were confusing the two. Im not familiar with bracing, how to do it or where to begin. Can you point me in a learning direction?


The efficacy of various bracing methods relies on building and measuring with a variety of materials. Because I don't have the time to try a whole variety of designs, I personally have settled on copying how B&W do it with their Matrix. the idea is to make each 'sub panel' within the bracing small enough so that each panel's resonance will be high enough in frequency so that it is not easily excited, and if it is, then it is easier to damp than at lower frequencies.










This is closer to how I do it though this is a pic from Tony Gee's Serious Sub build. For sealed I'd fill it with fibreglass, and for ported I would do the same, but leave a clear path from the driver to the port. Current builds are sealed mains and ported surrounds using similar bracing.


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## Lucky7! (Jan 7, 2008)

TypeA said:


> For those interested, my personal research on this has lead me to a few internet sources. Good info on the 'constrained layer', one that recommends a few printed sources of knowledge as well, is this one.
> 
> 
> 
> ...


I'm on the fence WRT constrained layer damping. It's not my field of expertise, but I have read from engineer's whose it is on diyaudio in threads on the subject, whom question its effectiveness in speaker enclosures. I've seen few measurements on braced panels so not ready to yay/nay. Note the pic in the previous post uses both extensive bracing and CLD.


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## TypeA (Aug 14, 2010)

While bracing could well be the better option over dampening, it would seem that for me; my lack of tools, time, and shear lack of carpentry skills prevent improved bracing of 11 speakers being a viable option. Im sure it makes an amazing difference tho.

My next step has been to find a reasonably-priced answer to the batting question. Id like to avoid fiberglass as these are ported speakers and I dont want to introduce glass fibers into the listening area. Granted this could be prevented by a light cloth wrap to hold the fibers in, but that makes fiberglass a pain to use. My first product try is a poly fiber, though cotton is recommended over poly. $11 at walmart, enough for maybe three or four 162 speakers...










Thanks for the input


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## Lucky7! (Jan 7, 2008)

TypeA said:


> While bracing could well be the better option over dampening, it would seem that for me; my lack of tools, time, and shear lack of carpentry skills prevent improved bracing of 11 speakers being a viable option. Im sure it makes an amazing difference tho.


I would still add something. A couple of oak 1x3" side to side and one front to rear and top to bottom would me ake a well worthwhile difference for minimal expense and effort. I've seen photos similar recently but I can't recall where at the moment and will post when I do.

My woodworking skills are not that great, but with a bit of patience and care the set up I use is easily achievable, even for a klutz like me.



TypeA said:


> My next step has been to find a reasonably-priced answer to the batting question. Id like to avoid fiberglass as these are ported speakers and I dont want to introduce glass fibers into the listening area. Granted this could be prevented by a light cloth wrap to hold the fibers in, but that makes fiberglass a pain to use. My first product try is a poly fiber, though cotton is recommended over poly. $11 at walmart, enough for maybe three or four 162 speakers...
> 
> 
> 
> ...


Lots of people have used the Wallmart poly before, it'll be fine. Shredded cotton is also good, like futon filling and can be cheap if you can find a commercial source. It does tend to settle over time so I have seen people staple in cloth dividers to hold it in position.
This stuff is supposed to be excellent, but it's not available here or I would try it.


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## TypeA (Aug 14, 2010)

Ive searched high and low, cant find the answer Im looking for. Will batting produce the best results installed on all five sides? Should I be covering the interior completely save the port area? 

Heres a shot of the stock batting as installed by manufacture, manufacture did NOT install on the back, bottom OR the bottom section side closest to the port (you can see the beginning of the port in the bottom right of this photo)









External dimensions are H 14-3/4" x W 8-1/4" x D 11" if that helps at all. My experiments will begin with 1" thick, any input on this starting point as far as thickness? I know to keep the port and drivers clear of batting.


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## 1Michael (Nov 2, 2006)

"My next step has been to find a reasonably-priced answer to the batting question. Id like to avoid fiberglass as these are ported speakers and I dont want to introduce glass fibers into the listening area"

Fiberglass will Not go into the listening area threw the port. Many of us use it in our subs which have a much more violent air movement:T


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## TypeA (Aug 14, 2010)

Thanks for the info buggers, its much appreciated. Suppose Ill have to install the batting the hard way (unscrewing the drivers multiple times and experimenting with what configuration and amount of batting sounds best). Strange I cant find a general consensus on a good starting point beyond what the manufacture installed for batting and the general reply that 'you should experiment to see what sounds good to you.' Im pleased with the results of the mods thus far so I would imagine it will all be worth the effort


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## southworth (Oct 7, 2006)

Looking at your photo, it's strange that they didn't put any batting directly behind the woofer to mitigate the reflection of sound waves from the rear wall back to the woofer cone. Tell me I'm wrong here.


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## fbov (Aug 28, 2008)

TypeA said:


> Ive been removing this grey blanket material Infinity used to dampen the cabinets and replacing with a couple of layers of seam tape and quiet board material. It works much better for dampening the cabinet and is an obvious improvement. My question, should I be putting the dampening blankets back in the speaker after I apply this modification? ...


Yes. 

If quiet board is what it sounds like, it's a surface treatment that damps vibrations in the surface. The blanket-like material is surface-mount acoustic absorber. It absorbs energy from the air whenever a wave tries to bounce off the surface it covers. Once you stiffen the panels, you still need to absorb energy within the enclosure, so put it back in. Then you can think about the volume fill, which you may want to adjust to your liking.

Have fun,
Frank


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## TypeA (Aug 14, 2010)

Great info, I think I can be taught. Kinda lost me at "volume fill" tho. Just to make sure I understand what Ive learned thus far... :nerd:

1. 'Dampening' reduces sound _vibrations_ within the cabinet. Bracing is the method of choice tho lesser benefits can be had with a constrained layer.

2. 'Acoustic Absorbers' reduces sound _reflections_ within the cabinet. Surface mounted blanket-like material on ALL sides except near a port is the method of choice. Southworth touched on this with a good question, any input on that question?

3. 'Volume Fill', apparently this is different than acoustic absorbers. Correct? Same material, but installed differently within the cabinet? 

Thanks alot for the help and patience.


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## fbov (Aug 28, 2008)

I didn't do the full breakdown, but you're seeing the pattern.

Box structure
- damping of surfaces
- bracing 

Acoustical/porous dampers
- surface effects, high density 
- volume effects, low density

In any given speaker, you may damp box surfaces, link them with braces, line the walls and fine tune the bass with fill. It's up to you, and what your ears like. 

1) Damping reduces all vibrational modes, but eliminates none of them. Bracing eliminates some modes, but still allows modes with a null at the brace. Best is to do both if spans are long.

2) Acoustic absorbers on surfaces reduce reflections based on their thickness and relatively high density. The 1-2" lining of the box works best at higher frequencies, allowing the bass to resonate. Everywhere but the baffle and the port.

3) volume fill is the same kind of stuff, but at lower density, and as the name implies, located away from the walls. This works on all frequencies, and can tune both sealed and vented boxes, the latter away from the mouth of the port, of course, but perhaps around it's base. 

In general, there are 3 ways to absorb vibrations in air
- porous absorbers
- tuned (Helmholtz) absorbers 
- deflection (diaphragmatic) absorbers

2) and 3) are both porous absorbers that work by impeding the flow of air. Surfaces are displacement nulls, so there's no air motion to absorb at the surface. The surface type must be dense and thick to work, while the volume fill is right where all the air's moving, so it's sparse. 

Deflection absorbers work by allowing a surface to be deformed by the sound, then absorbing that energy instead of reflecting it. It's the same idea behind some bass traps and CLD, but in reverse; CLD tries to absorb the energy so the panel won't deform while a bass trap absorbs the bass energy that caused the panel to deform. 

And please note that this is all a matter of degree; one can pass the point of diminishing returns...

Have fun,
Frank


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## TypeA (Aug 14, 2010)

Thanks again Frank, real good info and makes it much more clear.


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## TypeA (Aug 14, 2010)

Ok, another couple questions from the rookie to anyone who knows... 

Since I have the drivers out of the cabinet during this mod should I be installing anything between the driver flange and the cabinet as I reinstall? If so what material would I use, some kind of rubber gasket material? Ill happily go through the extra trouble if it means improvement. Like I said Im already pulling the drivers on 11 speakers, dont want to miss any opportunities for even modest improvement while theyre out...

There is no existing gasket between the driver flange and cabinet, driver is reattached using the included standard wood screws. 



















What are my options for upgrading the cross over? Can I get something better with the same form factor, not alot of money? I think it will be out of the range of what Im willing to spend, but I still feel obligated to at least ask about the cross overs. Might just do better crossovers for the two stereo pairs of 162s, but I dont see myself doing the 7 speakers in the primary theater.


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## WmAx (Jan 26, 2008)

TypeA said:


> Ive been removing this grey blanket material Infinity used to dampen the cabinets and replacing with a couple of layers of seam tape and quiet board material. It works much better for dampening the cabinet and is an obvious improvement. My question, should I be putting the dampening blankets back in the speaker after I apply this modification?


OP, the material Infinity supplied has NO physical function in the primary bandwidth of the mid-bass driver. You would be hard pressed to hear any difference with the OEM material or with the cabinet empty. The material you placed inside is far superior. I would even recommend adding a second layer on the back wall and on bottom.

Chris


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## WmAx (Jan 26, 2008)

TypeA said:


> Ok, another couple questions from the rookie to anyone who knows...
> 
> Since I have the drivers out of the cabinet during this mod should I be installing anything between the driver flange and the cabinet as I reinstall? If so what material would I use, some kind of rubber gasket material?


That is unusual. Usuallyl Infinity applies a thin foam tape to the back of the driver flange to create a seal.

If the seal is really missing, you can use closed cell vinyl weather stripping effectively and cheaply from any hardware store. It is the 'grey' stuff.

Another possible fix while you have the drivers out is to buy a couple tubes of LIQUID superglue. Generously apply this to the crack/seam between the rear magnetic shield can and driver. Usually, this can is only crimped around the base of the driver and glue is used only inside the can where it connects to the back of the actual motor(that you do not see). As a result, the open small gap has the potential to vibrate at specific frequencies. Using a generous amount of liquid super glue into the crack and allowing to harden will remove this potential issue.




> What are my options for upgrading the cross over?


There is not much you can do unless you want to rebuild the crossovers. One thing I would do is remove the electrolytic capacitors and replace them with mylar/polyester film capacitors if you plan to keep these speakers for the long term, as these will not eventually degrade/dry out like the stock electrolytics tend to do after a couple of decades. Madisound has some very low cost high quality mylar capacitors. However, realize the film capacitors will be much larger in size compared to the electrolytic of the same value, causing you to have to essentially rebuild the xover board or making some extreme changes to the existing one to mount the much larger components. As for other upgrades to the xover; this would require you to actually measure/design a completely new circuit to yield a more ideal overall response. However, one upgrade that does not require changes is to add an 8 Ohm L-Pad control(_you simply install it in parallel to the tweeter and cut a hole in back of cabinet to install it_.) Being able to control the tweeter's overall level is often very useful to help achieve your ideal sound. However, if you have a high quality paramateric/DSP EQ on your system, then the L-Pad would be pointless.

Chris


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## TypeA (Aug 14, 2010)

WmAx said:


> The material you placed inside is far superior. I would even recommend adding a second layer on the back wall and on bottom.
> 
> Chris



Two layers of seam tape plus the 1/2" of quiet board seems like a substantial loss of volume within, am I being paranoid? Is there a point that reducing the volume of air within a cabinet begins to affect things in a negative way? 

Is it important that I leave these holes in the brace clear? I only ask because a second layer anywhere within the cabinet will create complications in that regard.

















And you were absolutely right, there _was_ a gasket on the back of the driver installed by Infinity. Sorry bout that, but thanks for the answer, it still taught me something. Cross over advice was great as well, thanks for all the patience guys.


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## TypeA (Aug 14, 2010)

Intimately familiar with the unmodified bedroom pair installed wall high in the bedroom, lots of blu rays and some cd's, more listening time than even the primary theater. (Bose AM6 ceiling-mounted cube is gone now)










Completed this mod on BOTH speakers yesterday, took me six hours straight, and thats with all materials pre-cut and only minor adjustments required for install. Thats not counting pulling them off the wall and driver removal/reinstall and re-installing on the AM40s'. Exhausting to do them both in such a short period of time but still shocked at the difference it makes in performance. Many thanks to the blu ray Legion, as well as the bands Quiet Riot, Ratt, and Crystal Method for the help in reaffirming my convictions. :clap:


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## BrianAbington (Mar 19, 2008)

I can give some more insight into poly fill. I always used it for sub enclosures in my car audio days.
Polyfill basically helps to slow down the sound waves inside the enclosure tricking the speakers into thinking its in a larger enclosure. It can though help to reduce resonance.

I tried to use at least one pound per cubic foot. 

I found if it had a bit to much resonance I would stuff a bit more in and it helped. 

I think your poly fill is much better than the they stuffed in there from the factory.


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