Recommended Batting and positioning.

Crashdot

Greetings,

I have been advised to put a layer of polyester batting in my RTA12Cs, and need to replace the batting in a set of 5jrs due to a previous owner tearing it into pieces, so I would like to ask if anyone can recommend a source. I didn't find any at Parts Express so far, and don't know if the kind that is sold for quilting is what I should be looking for.

Also, I've noticed that the batting has fallen down to the bottom of some of my speakers, and I wanted to confirm where this should go. On some speakers it seems to be folded in half and behind the main driver, and on others it is unrolled and seems to be placed as a single layer across the entire speaker. Where should it go?

Any suggestions are appreciated.

Outfitter03

Here is one source.

http://www.mcmelectronics.com/product/LS00385

http://www.mcmelectronics.com/product/LS00916

skrol

The batting usually goes above, beside and behind the mid-woofer. There usually is none behind the PR. However, I have a pair of Monitor 5A that are stuffed top to bottom including behind the PR from the factory.
Stan

drumminman

the batting should fill the area behind the mid woofers, with none behind the PR. When I recently overhauled my 12C's I saw that a big piece had fallen to the bottom of the cabinet.

I re-positioned it and then put a screw inside the cabinet on both side walls to which a tied a piece of twine. This should keep the batting in place. :cool:

Fred

Crashdot

What would be the effect of having the batting behind the PR? Mine was down there before I moved it back up today, and I am doing listening tests.

20hz

Crashdot wrote: »

What would be the effect of having the batting behind the PR? Mine was down there before I moved it back up today, and I am doing listening tests.

I pulled apart a energy EAC center it has 2x5.25 and a alum tweeter w/2x9" ports (basic stuff)
but..
it was also packed with a huge chunk of pink insulatin I figure it slows the bass wave down before it gets to the port thus making the cabinet appear bigger ( I guess ) crazy idea the speaker was not bass strong like my Polk
cs300 that cs300 is amayzing .

drumminman

Crashdot wrote: »

What would be the effect of having the batting behind the PR? Mine was down there before I moved it back up today, and I am doing listening tests.

I think it would diminish the output of the PR.

Joe08867

Having it down by the PR slows the response of the PR. The batting is slowing and absorbing the sound from reflecting off the back of the cabinet before it gets to the PR.

Crashdot

Okay, here is another question: On a model such as the 5jr, should the batting be rolled up and placed behind the driver (as it is on the 12C) or should it be unrolled and placed against the back of the cabinet?

Joe08867

The 5jr is ported yes?

On the ported 5jr models it is flat (Unrolled) along the back wall of the cabinet.

I don't remember how it is in monitor 7's or 10's anymore. I believe just along the top half behind the drivers but not behind the PR. But I could be wrong on this.

Crashdot

I'm pretty sure that by now most of my speakers have batting in the wrong location. From the significant effect that it has had to put the batting back where it belongs in the 12Cs, I am thinking it is time to open up all the speakers and make some adjustments.

What is a good way to attach batting to the cabinet? I was thinking of something like 100% silicone caulk or contact cement (something that will remain soft).

Thanks

skrol

There was some talk hear a while back about the use of silicone caulk out gassing corrosive vapor that attacks metals (ie. speaker drivers). There are some that don't. I believe the 3M bathroom caulk is OK.

You could go a more mechanical approach like staples or velcro with adhesive backing.

Jstas

The batting doesn't slow down the sound as much as it dampens air flow. In ported speakers, it helps reduce port velocity. Port velocity that is too high causes an audible whistling. In mid-bass frequencies, it can actually cause a resonance that creates high pressure areas inside the port itself which then restricts air flow, reduces port efficiency and creates an audible whistling sound. It's basically cavitation in the port.

Batting doesn't belong behind the PR because the PR acts like a port. Polk calls it a "Fluid Coupled Driver" which is fancy talk for a passive radiator. But the PR has to be weighted and unlike a port, it is not as susceptible to noise from airflow being too high. The biggest problem you get from PR's is cone breakup which sounds like someone flexing a sheet of poster board. To alleviate that, you build a really rigid PR and then add weights to the motor structure to add enough mass to the PR that the driver resonance drops to a frequency below the operational range of the loudspeaker that drives it. If you have batting behind the PR, you dampen that airflow that the PR was tuned to and reduce the efficiency of the PR thereby reducing output.

As far as silicone caulking, you can use it but you need to remove the drivers from the enclosure until the caulking has completely cured. Usually a few days. Otherwise, the fumes can act as a solvent on glues used to hold stuff like VC formers and surrounds attached to the speaker cone. It can also cause a kind of dry rot in certain kinds of surround material. It doesn't really affect the metals though unless it affects a finish that is applied to a metal.

But I wouldn't glue batting in place. If you need to dig around inside for a repair for whatever reason, you're going to regret gluing the batting in place. If you want to hold it in place, some stiff wire wedged in underneath the batting will keep it where it's supposed to be. You could even put like small eye hooks in on opposite side of the inside of the cabinet and string some twine through it or something.

Just, whatever you do, try not to add too much mass or anything too loose because it will change the characteristics of the loudspeaker and/or vibrate. Large chunks of wood or metal and such not only change cabinet volume and skew the tuning of the enclosure but they change airflow. Changing airflow will affect how the port performs and can cause enclosure effects that artificially truncate frequency responses of certain drivers and will change the sound of the speaker. It's a method used to create a physical crossover in subwoofer enclosure such as band-pass and iso-baric enclosures which emphasize a certain frequency range at the expense of others. It works well in a sub because it's already working in a limited frequency range. In a full range loudspeaker enclosure though, it can cause things like excessive sibilance from tweeter cone breakup or a nasty mid-range hump that no amount of capacitors, resistors or inductors will tame.

I do like the velcro idea though.

Joe08867

Jstas, Thanks for clarifying what I meant. My head was in the right place but the words weren't coming out. I think my allergies have dropped my IQ by at least 50 points in the last day or two.

Anyway, Like Jstas said, The batting slows airflow not the sound waves. Although batting can and does absorb lower frequencies but the absorption would be minimal with the amount of batting we are talking about.

As far as securing goes, I prefer using Velcro myself. But I have used glue in the past. I think it depends on whether or not you plan on opening these up several times.

skrol

When I reworked my RTA11TL's I found that the material had fallen out of place. Since I clear on the proper batting position, I asked Polk Customer Service.

The 1st drawing is the original placement
The 2nd drawing is my upgraded damping
The 3rd is a more traditional batting position

Stan

Crashdot

He-heh-heh! This is interesting, so your batting is above the drivers only, and not behind, but with sonic barrier behind?

skrol

Yep. I don't know if this the best configuration but the bass is more defined than stock and sounds pretty good.

Crashdot

I would appreciate some feedback on the placement of damping material in my speakers. I have noticed that it is inconsistent from one speaker to the next, and would like to know what is appropriate for best sound.

For example, the polyester batting in my 12C's consists of one flat piece to line the back of the cabinet, split down the middle to go around a cabinet brace, and also two rolls of batting. The two rolls were behind the drivers, while the flat part had fallen down behind the passive radiator. When I moved the flat part back behind the drivers and also placed the rolls behind the drivers, the bass was greatly improved, but the mid range seemed to become stifled and is nowhere near as detailed as it was before.

The material in each set of 5jrs was placed differently; some rolled, some flat, some packed completely full. The 5B's have a roll of damping crammed just above the main driver only, rather than behind the driver or lining the back of the cabinet.

It was my understanding that it is appropriate to have the back of the cabinet covered to prevent sound from bouncing back out through the cone. I don't know what the purpose would be of an additional ball or roll of batting directly behind the driver, or why it would be at a 45 degree angle above the driver as it is in the 5B.

It is clear that the position of this material makes a significant differnence in sound, so I would like to know what the current positioning may be doing, and whether something may need to be moved in any or all of these speakers. Once I determine the best way to affix batting, I plan to line several sides of each speaker if this isn't going to cause undesired effects. I still would like to know what the rolls of batting are intended to do.

I have attached images showing the current positioning of the material in each of these speaker types.

Thanks for your consideration

20hz

Crashdot wrote: »

I would appreciate some feedback on the placement of damping material in my speakers. I have noticed that it is inconsistent from one speaker to the next, and would like to know what is appropriate for best sound.

For example, the polyester batting in my 12C's consists of one flat piece to line the back of the cabinet, split down the middle to go around a cabinet brace, and also two rolls of batting. The two rolls were behind the drivers, while the flat part had fallen down behind the passive radiator. When I moved the flat part back behind the drivers and also placed the rolls behind the drivers, the bass was greatly improved, but the mid range seemed to become stifled and is nowhere near as detailed as it was before.

The material in each set of 5jrs was placed differently; some rolled, some flat, some packed completely full. The 5B's have a roll of damping crammed just above the main driver only, rather than behind the driver or lining the back of the cabinet.

It was my understanding that it is appropriate to have the back of the cabinet

It is clear that the position of this material makes a significant differnence in sound,

If the cabinet is perfect volume for the port batting will hinder performace , a PR is a port so if its loaded properly and the cab is perfect it wont need batting .
in a big sealed sub once the cabinet is correct 2" of insulation will help deaden the walls if you want the sub to go real low but if you build it like a prosound sub (30hz up) you probebly dont want insulation just loud .
In a center ch I built it had a 4 db peak around 100 hz even though all was perfect size cabinet I guess that single 5" just did that, I figured it coloured the midrange so I added polyfill untill it evened out , but a decrease in freq here added something elsewhere (as you found), so it all comes down to what you like your speaker to sound like aside from what the manufacture builds it as .I was told adding polyfill (1 lb per cu foot) adds 10% to cabinet volume but I dont think so 10% is not worth the effort and all sealed subs I stuffed had less output and did not go lower w/stuffing .
maybe on a graph you can gt 2 db lower in a stuffed box but I think you loose the 40-80 hz a bunch .if you want to use polyfill I suggest you spray some adhesive on the wall and glue it on , as far as internall resonances you need parallel walls for sound to bounce so a tube or curved walls will sound best ,I run a stryke disc (signal sweep 15 hz-20khz) with a radio shack decible meter and draw a graph this tells you exactlly how flat the speakers response is if it has a big hump it can be tammed w/polyfill . Also my ls50's have this dense polyfill ( i call it camel hair) it can never seperate or move .

Joe08867

20hz, Crashdot is just trying to get the speakers he has back to factory spec. They came with polyfil in them he is trying to determine where it should be located in the cabinet and if there is a benefit to adding it to any other surface of the cabinet.