How stuffing affects bass in AR Speakers

[harry398]

I would like to open a thread and have people discuss their opinions,experiences with different types of stuffing.   ( original fiberglass, commonly available pink fiberglass, and they later Poly fill ),  and what they prefer and why.

 

Secondly,  I would like to know how people have tailored the amount of a particular stuffing and it's result.

It's fairly common to find the poly filled speakers overstuffed.

I have experimented a bit, and found the AR9LSI improved BASS output  with swapping out polyfill, to pink fiberglass from my attic.  (I reduced the amount of stuffing by half or 2/3 !)

Share your experiences......

[ar_pro]

Due to the nature & location of the polyfill batts in the AR-9, I thankfully never found a need to remove them for a restoration/rebuild.

The AR-91 systems that I refinished a couple of years ago had the stuffing temporarily removed, and then replaced exactly. On the other hand, using the same amount of tightly-stuffed AR-91 polyfill (27 ounces) in this past year's AR-3a/91 project resulted in what I felt was a subtle loss of articulation in the reproduction of certain acoustic bass notes.

Members genek and ra.ra advised the substitution of 20 ounces of fluffed-out Home Depot fiberglass insulation for the polyfill. After making the switch, the difference was not subtle, and after a few more months of listening, I consider everything to be essentially perfect.

This back-and-forth can be found toward the end, here:

 

[harry398]

I have thoroughly reviewed your project in the past, and You did some great work there AR_PRO.

 

[ra.ra]

Can't offer anything specific regarding the pros and cons of stuffing types and quantities, etc., but I am pleased to see ar_pro chime in so soon - - it was his 3a/91 project that first came to mind when I read the OP's post. - - that was an interesting project.

This could become an insightful discussion, and I hope contributors can be specific with regards to measurement terms: weight, density, volume, etc.  Also, it would be interesting to hear thoughts about the evolution from mineral wool to fiberglass to polyfill, as well as that multi-colored synthetic fill that is often found in Euro cabinets. 

[ar_pro]

I'll add that I've seen what might be a degradation in the AR-9-series' original poly stuffing over the past few years, with a more noticeable amount of particles escaping into the air when things are moved about. Not sure how this could affect things.

[amanteyzapata]

I have had a number of speakers pass in and out of my house and will concur that polyfill seemed to bring out the stupid in some people.  In a pair of AR91s I restored, one speaker simply had a roll tossed in.  The other was laid out better.  In a DCM Timewindows speaker, one had an empty soda can thrown in.  I did not alter anything with the Timewindows (son owns it now) because it was the most poly stuffed speaker I have ever witnessed.  I also never messed with that pair because they sure had some low notes that I was not expecting...sounded great with jazz articulation which they are known for.

In general, I copy the AR3 lay of filling.  Spread out but cupped a little around the woofer.  In fact, AR3 woofers usually had a very light cheesecloth wrapped around the woofer frame.  And then, if there's room I put a little of the opposite filling.  So, if it's fiberglass then poly, and vice verse.  I was told the two materials are cut differently and both are mightier than one to handle LF waves.

Finally, the two speakers I noticed immediate sound differences with regard to filling were anything Bozak and Boston Acoustic A series.  I own BA100s that sound amazing and better than other pairs I've heard once I recapped and played a little with the filling.  It's not scientific, my opinion, but I've had the BA100s in all sorts of locations and still wow!  Those are going to my daughter but sometimes I think....  I also have a pair of Bozak 301s placed in a much larger and beautiful University case.  THAT ONE...if you adjusted the Bozak filling one way or another the sound would be glorious or crappy.  I spent considerable summer hours on that pair because it was an interesting listening test.  I still have them and they ain't going anywhere.

[genek]

With regard to different colors of fiberglass, fiberglass itself is more or less transparent (because it's glass). The resin binder that keeps the fiberglass from splintering into dust is naturally yellowish in color. Some manufacturers add colors, but it's all just branding. Pink fiberglass is made by Owens Corning. Green or white is Johns Manville. Functionally, it's all the same stuff.

[harry398]

On 5/31/2017 at 10:16 PM, ar_pro said:

I'll add that I've seen what might be a degradation in the AR-9-series' original poly stuffing over the past few years, with a more noticeable amount of particles escaping into the air when things are moved about. Not sure how this could affect things.

In the ar9 manual, it specifically states they chose that polyfill and left the woofer area empty for a reason.

The polyfill is easier to work with, however I already experienced replacing it from the ar11 and refilling with pink glass, much better bass response.

Wonder if ar9 owners tried swapping out the polyfil.

 

My ar9lsi benefited as well with the swap, However I wonder why they did not leave the woofer area open on this series?     

[Carlspeak]

It's common practice with tall, slim line speakers to put polyfill up towards the top of the cabinet behind the tweeter and mids. The reason being to dampen reflections of the bass sound waves from bouncing back and forth from top to bottom. That type of speaker typically did not require the standard AS stuffing protocol like that used in the 3a and many similar designs. Evidently, after much testing and listening, engineers found the cabinet top stuffing was the best solution for tall, slim line speakers.

Personally, I highly doubt replacing the top of cab polyfil with FG will improve anything. FG does its job best in fully stuffed situations like the 3a, etc....

Edit: If you want to read about the science behind the stuffing protocol for tall, slim line speakers click on the linked (below) Wikipedia article about the Kundt tube. I unwittingly made one once in an attempt to fabricate a closed up test chamber for small drivers like tweeters and mids to keep the noise down in the house. Made it out of 12 inch cardboard tubing normally used to pour deck foundations. Lined it with thick mattress foam, capped each end. One end had a mic mounting plate and the other a wooden plug with a nose sticking into the end of the tube that narrowed down to the flat mtg. surface for DUT's. IIRC, it was about 3 ft long. The narrowing was intended to create angular reflections down the tube that would become absorbed by the foam. Nice in theory, but it didn't work because of the Kundt tube principle that created peaks and valleys in the sound waves internally the lined foam could not mitigate. Here's the Wikipedia link.....  https://en.wikipedia.org/wiki/Kundt's_tube

[harry398]

Interesting, however my ar98ls are packed just like the ar9lsi was.  1/2 the height.

 

Also, I did get better bass response removing the polyfil from the 9lsi, replacing with 1/2 the amount in pink panther special. .......however why did they leave the ar9 and ar90 woofer chamber empty, and leave the ar9ls,a 9lsi Stuffed??

I will repeat that I find the late model ar's are overstufffed.

 

[Carlspeak]

The density of polyfil is much lower than FG. Thus the seemingly overfilling to attain Fs and Q targets comparable to FG. I suspect the switch from PF to FG was done for worker safety and compliance. 

A similar situation occurred when Advent stopped using FG and switched to 12 X 12 X 2 inch thick open cell foam blocks. I've written about the Fs and Q improvement when replacing the foam blocks with FG in the Advent forum.

[harry398]

Well that makes sense.   So any advantage to removing 1/3 of the polyfil in a cabinet?

Yes, the fiberglass is a PIA to work with.

 

[harry398]

Carl,  

Any idea why they stuffed the woofer area on the ar9lsi, but left the ar9,ar90 empty?

[Carlspeak]

No idea. I don't know enough about those models to be able to hazard a guess. Where's T.T. when you need him?  :-)

[harry398]

Haha........welcome to ALL.

I did read a good amount of the ar9 manual,  Tim Holt.   Seems that was the only technical paper I have seen from AR.  

yes it's very nice some of the Former AR People join in here......it's awesome for the hobby.

The manual addressed some of the reasoning to cut off the woofer at 200hz.....which has had my brother and me baffled for a while, whereas we do enjoy the 3a/11 extra freq through the woofer.....makes a nice thicker sound, but I do realize the 4 way driver speaker produces a more accurate sound by dividing up the work more.

The ar9lsi may not get the fans the ar9 gets for a few reasons.  My experience is, even after the lsi modification that ar did, it still needed a touch more modification.     I found adding 1 ohm more resistance to the mid highs and 1.5 ohm to mid woofer has now made it smoother to my tastes.   

I also found it about the same on my 98ls, even after the lsi mod, it needed a tickle more resistor on mid highs...and it's as smoooth as can be now.  Awesome speaker.    Also overstuffed, but I have left that alone for now.   The LS,LSI series are under rated, are exceptional in sound , detail is outstanding.

 

[tysontom]

On 6/3/2017 at 1:05 PM, Carlspeak said:

No idea. I don't know enough about those models to be able to hazard a guess. Where's T.T. when you need him?  :-)

At your service, Carl!  

The difference between the AR9/90 and the AR9Ls/i is the separate 10-inch woofer chamber in the bottom of the AR9Ls and the upper chamber for the 12-inch woofer, necessitating a difference in the way the material is placed in the cabinet to maintain proper output flatness.

One caveat here: the amount of fiberglass will specifically affect the "Q," or woofer damping, of the speaker at resonance and a little above and a little below that frequency.  The exact amount of fiberglass or Polyfill in the cabinet of an acoustic-suspension woofer is critical to flat response at resonance.  Ironically, too little fiberglass will not only affect the peak at resonance, but it also can affect the actual resonance frequency in that a certain amount of it in the cabinet makes the woofer sense that it is slightly larger than it actually is.  

Using the AR-3a as an example, if one were to remove the existing fiberglass material and replace it with Polyfill, determining the exact amount to keep the "Q" at 1.0 in the speaker would be difficult without making an actual frequency-response measurement of the woofer.  Of course, this could be done by close-miking the woofer with good-quality equipment, and then determining the shape of the rise at resonance.  If that speaker were to be placed at or near a corner, over-damping might be desirable, but it's usually best to stay within the speaker's original guidelines.  It's possible that fiberglass is a bit denser than Polyfill, and the speaker might then become slightly under-damped, maybe 1.2 or higher, giving a slight peak at around 45 Hz or so.  Too much fiberglass or Polyfill in the cabinet will over-damp the woofer, causing the speaker to have a slightly "dry" sound with a reduction of output at resonance.

--Tom

 

[Carlspeak]

LOL! Thanks Tom.

It's also worth noting that the Sg of FG is 2.5 and Polyester fibers is 1.38. Quite a difference that contributes to the differences seen in stuffing AS speakers with each.

[Finjima]

When I replaced the old broken up fiberglass in my AR-3's I went with the Johns Manville from Lowes and found them to be clean smelling and a very low itch factor while using them. I had no irritation working with this brand. didn't have to wear a mask like i did with the old crap in the speakers. A fish scale is a must have when weighing the insulation. 

[Carlspeak]

22 minutes ago, Finjima said:

When I replaced the old broken up fiberglass in my AR-3's I went with the Johns Manville from Lowes and found them to be clean smelling and a very low itch factor while using them. I had no irritation working with this brand. didn't have to wear a mask like i did with the old crap in the speakers. A fish scale is a must have when weighing the insulation. 

What stuffing density did you use for the JM glass? I hope it wasn't the same wgt as the much denser stuff you took out. 

[Finjima]

it was around 30oz, you have a idea if that should work?

[Carlspeak]

The 3a restoration doc. calls for 28-30 oz. of new FG. So I guess you are good to go in that department since you have an early woofer IIRC. 

[Finjima]

good i was going by that doc.