new surrounds

[Guest rickcee]

Hi just curious - since most models of '60's - '80's speakers have the falling apart foam , why replace with more foam ? is the new foam an improved material ? How about rubber surrounds, as good ole Dynaco ? ?

seems to me new foam kits probably are at least a little different than the original, so if they were avail., much longer lasting rubber surrounds would be much better choice. . . . Rick , who has cloth surround KLH 17 ( sealed a few years ago with kids 'rubber cement') plus rubber surround Dyna 25's, Cloth surround mid '70's Koss 1020, my main spks., and fairly new as things go AR 302 with rubber surrounds, I think.

[Guest dogmeninreno]

>

>Hi just curious - since most models of '60's - '80's

>speakers have the falling apart foam , why replace with

>more foam ? is the new foam an improved material ? How

>about rubber surrounds, as good ole Dynaco ? ?

>seems to me new foam kits probably are at least a little

>different than the original, so if they were avail., much

>longer lasting rubber surrounds would be much better choice. .

>. . Rick , who has cloth surround KLH 17 ( sealed a few

>years ago with kids 'rubber cement') plus rubber surround

>Dyna 25's, Cloth surround mid '70's Koss 1020, my main

>spks., and fairly new as things go AR 302 with rubber

>surrounds, I think.

Well I guess foam lasting about 30 years and relitively cheap is a start? That's pretty good (in my opinion). I don't know about rubber or butal surrounds (let alone how to get them) and what (if any) effect they would have on the AR "voice" as designed and I agree that we don't know how the new foam surrounds compare either. Cloth surrounds last a long time but in my experience get weak and dimple putting additional work on the spiders. Maybe someone else can comment? Dale

[Guest Bret]

>and I agree that we don't know how the new foam surrounds compare either<

As I read the results of Ken's free air resonance tests, the speakers that were refoamed by Tri-State, and even one of the reconed woofers, kept their <20Hz resonance numbers. The speakers resurrounded at Simply Speakers suffered a large rise in their free air resonance numbers.

But what I don't know, and we will likely never know, is if it is the material or the application.

As I've commented before, I now have a *big* question about the "Edge-It" materials and/or Simply Speakers' application.

Bret

[Guest Bret]

I went back and looked at this again. Either I was reading the wrong numbers or the numbers changed.

Bret

[Guest SteveG]

Bret,

Hoping to take advantage of your read of the data from ken, how are you now seeing it? I have 1 pair of 12" refoamed by Simply Speakers, another pair refoamed by TriState, and another pair reconed by TriState. All sound fine to my ear, but have not been "tested". Did your reread of the data indicate that Simply Speakers is also doing well (like TriState)? Or did you discover all showed degradation?

Thanks

SteveG

[tysontom]

>

>Well I guess foam lasting about 30 years and relitively cheap

>is a start? That's pretty good (in my opinion). I don't know

>about rubber or butal surrounds (let alone how to get them)

>and what (if any) effect they would have on the AR "voice" as

>designed and I agree that we don't know how the new foam

>surrounds compare either. Cloth surrounds last a long time but

>in my experience get weak and dimple putting additional work

>on the spiders. Maybe someone else can comment? Dale

Dale, I think you are exactly right here: the new foam is relatively cheap and supposed to last a pretty long time, but I have not heard that it would last thirty years. The original urethane-polymer foam can last a pretty long time depending on where you live and the condition under which the speaker lived out its "life." Urethene-polymer foam that AR used in the 1968 ARs (the AR-5 was the first, or one of the first loudspeakers to ever use foam surrounds) was mainly used because it significantly improved the performance of the woofer by damping the reflections moving down the cone -- the old "cone cry" as they used to call it -- that occurs in the higher frequencies. It was also more supple and quieter than the impregnated cloth surrounds, and significantly more uniform in performance from speaker-to-speaker. AR also treated the surrounds with a butyl-rubber compound. So it is safe to say that the surrounds used on the AR woofers had some effect on the frequency response of that speaker.

The new foam replacement surrounds, at least those used on the AR 12-inch woofer, are a different compound and have a smaller half-roll cross section. They are not the same as the old ones, but I guess they are the next-best thing. I still have a boxed NOS AR-3a woofer that I looked at a couple years ago and it was still fairly intact after thirty-four years or so. It was beginning to show signs that it was going to deteriorate, but it had not crumbled. My Allison: Ones still have the original surrounds, as do my AR-6s and AR-7s. On the other hand, I have seen deterioration as early as seven years after the product was built, so it varies widely. Butyl-rubber surround certainly work well, but do not dampen resonances nearly as well as foam. On my cloth surrounds, I began putting ArmorAll "Protectant" polymer stuff on them years ago, and most of them have remained very supple and compliant, and have not dried out. It is the latex or whatever that was used on that surround originally that dries out and caused problems for the cloth surround, and ArmorAll seems to work pretty well.

--Tom Tyson

[Guest Bret]

>Did your reread of the data indicate that Simply Speakers is also doing well (like TriState)?<

Look at Ken's summary spreadsheet at http://www.aural.org/ar_hist/data

Looks to me like Fs is high on both the Edge-It speakers. Like 20-24% high. Can that be good?

From reading a post from Tom, it looks like there is a serious transition to "compliance control" below cabinet resonance. That's going to cause (if I read Tom right) a very quick roll-off from cabinet resonance to Fs.

What I don't know is what the usable bottom (say 6db down) is, given:

1) In a cabinet with a resonance of 42Hz and a driver with Fs of 18Hz

2) In a cabinet with a resonance of 42Hz and a driver with Fs of 26Hz.

Could it be that it doesn't matter and the "bottom" is about 30Hz either way? I don't know. I'm ignorant.

I struggle with the numbers. I know that one needs a clue to interpret all of this. I don't have a clue.

This might help:

http://sound.westhost.com/tsp.htm

but I don't see how! :-)

Bret

[tysontom]

>>Did your reread of the data indicate that Simply Speakers is

>also doing well (like TriState)?<

>

I glanced at Ken's numbers there at one time, but I didn't study them. I left that for you. However, I think he ran his driver test in free air, and I didn't see where he applied the box compensation for a 1.7 cu. ft. sealed enclosure with the proper amount of fiberglass for a Q of 0.7 to 1.0, which is the normal range for say an AR-3a. It appeared to me that he was more interested in seeing what the variances in the drivers would be from driver-to-driver rather than how each would measure in a real closed box. His program can compensate for the box, but I did not see where he applied that to his tests.

>Look at Ken's summary spreadsheet at

>http://www.aural.org/ar_hist/data

>

>Looks to me like Fs is high on both the Edge-It speakers.

>Like 20-24% high. Can that be good?

Let me say this: the fs for the 2000003 woofer, the "12W" as it was known at AR (or "the 11-inch woofer," as it is known to Layne Audio and some others), is going to be somewhere in the 14-18 Hz range, probably closer to 18, and if a re-coned/coiled or re-surrounded woofer is up in the 23-25 Hz range, there are some serious compliance or diaphram-mass issues there.

>

>From reading a post from Tom, it looks like there is a serious

>transition to "compliance control" below cabinet resonance.

>That's going to cause (if I read Tom right) a very quick

>roll-off from cabinet resonance to Fs.

Well, here's the deal as I understand it: air-load resistance is the thing that determines how much energy is permanently transferred to the air for a given cone velocity. This resistance (radiation resistance) increases with the square of the frequency up to the frequency of "ultimate air-load resistance," or about 900 Hz for a 12-inch driver. Above that frequency, it remains constant. If you look at the published frequency response curves on an AR-3 woofer measured with the woofer flush with a 180-degree, solid-angle baffle, radiating into space, for example, you can see this effect -- the woofer's output is flat and uniform above system resonance (fc) out to about 800 or 900 Hz. The speaker is mass-controlled above resonance, and the cone velocity and is cut in half for each higher octave. Below resonance, as you say, the moving system is compliance-controlled, and the velocity of the diaphram is cut in half for each lower octave, and since the radiation resistance is still falling, the total drop in speaker output below resonance is 12 dB-per-octave. Excursion, of course, quadruples for each lower octave below resonance, for constant acoustic output. This is why you cannot have a practical fc in the 20 Hz range for most speakers: the excursion would be horrendous, and power-requirements for such devices would also be very large. This is where Henry Kloss went wrong with his Small Advent Loudspeaker. He tried to have a resonance as low in this small speaker as in the Large Advent, and the smallish woofer had to make extra-long excursions to do it, and it had high harmonic distortion at anything above a whisper. Enter subwoofers.

>

>What I don't know is what the usable bottom (say 6db down) is,

>given:

>1) In a cabinet with a resonance of 42Hz and a driver with Fs

>of 18Hz

>2) In a cabinet with a resonance of 42Hz and a driver with Fs

>of 26Hz.

>

Neither (1) nor (2) shall meet. Number two is not a reality, since the system resonance will be significantly higher than 42 Hz, all things being equal, since the driver resonance is higher than in Number One. This was the issue with the AR-10Pi from our long-lost friend from England who routed out the 12W hole and put in the Eminence guitar driver. That driver has a 55 Hz fs, and mounted in the AR sealed box, the system resonance would be too high. The speaker would sound thin and lack low-bass output, unless you added huge amounts of bass boost.

In the AR-1/AR-3/AR-10Pi/ etc. cabinet, 1.7 cu. ft., an 18-Hz fs will give approximately a 42-44 Hz fc if all the parameters are correct, such as cabinet damping and so forth. This would be a normal AR parameter, and really what you want it to be. This is the reason the Tonegen replacement AR-12W woofer with its slightly higher fs (I think it is above 20 Hz, but I need to measure one) has a higher fc mounted in the AR boxes. And if those re-foamed/re-coned/re-coiled drivers have a higher fs, then it will show up in the mounted cabinet. On the re-coiled AR drivers, I would also be *very* cautious to be sure that the coil replacement had the same XMas of approximately 7.0mm (giving a one-half-inch linear excursion) as the original AR woofers.

--Tom Tyson

[Guest Bret]

Thanks for going through all that again, Tom. Do you have a good idea of at what Hz they are -6db in the "standard cabinet" everything else being equal?

So I do have a point about the Simply Speakers' resurrounding job.

I had this suspicion, but I wasn't really convinced that I might have experienced a measurable effect until I saw those resurrounded CV woofers.

You commented on the excursion of the woofer in the Small Advent and how distorted it could be. My impression of the CV 12" drivers was always that they were "sloppy" but I also remember them as having the ability to cause concussions and bruising. These Simply Speakers resurrounds were obviously limiting the excursion. I've never heard a pair of CVs that were so lacking in "thump."

When Ken finishes with the drivers he has, I'll probably send the Simply Speakers pair to Bill Miller for re-resurrounding. Too bad I don't have test facilities.

Bret

[Guest Bret]

>Did your reread of the data indicate that Simply Speakers is also doing well (like TriState)? Or did you discover all showed degradation?<

Steve, Re-reading my response I see I didn't explain my confustion.

When I looked back over all the "report.htm" files in each driver's subdirectory, I'm not finding the numbers that are in the spreadsheet.

Maybe I'm just looking in the wrong places or maybe I'm confused some other way.

But if the spreadsheet numbers are right, then the Simply Speakers pair have a problem and they both have the same problem and don't share it with the other five drivers tested whether resurrounded, reconed, re-spidered or all of the above.

Bret

[tysontom]

>Thanks for going through all that again, Tom. Do you have a

>good idea of at what Hz they are -6db in the "standard

>cabinet" everything else being equal?

>

Measured in anechoic half-space (a good analogy would be the old way AR speakers were measured: a hole dug in the ground with the speaker, flush with the ground, facing the sky) an AR-3a would be approximately 5-6 dB down at 30 Hz. In a real room, the effects of room gain and positioning can change the bass output, and mounted close to room boundaries, the -6 dB frequency will be lower; with the speaker out in the middle of the floor, the -6 dB point will be higher, so it really depends on location.

Also, I want to correct a mistake I made in my feeble description of radiation resistance and so forth in a previous message. I said excursion quadruples for each lower octave below resonance. I meant to say that since cone velocity for a given power output doubles for each lower octave *down* to resonance, the excursion of the cone quadruples for each lower octave, for a given power power output. Once resonance (fc) is met, the excursion does not continue to get greater, and as you go lower the acoustic output drops proportionately at the rate of 12 dB-per-octave. So in other words, the acoustic output of the woofer is basically flat down to resonance (discounting the effects of room gain and speaker position in the room), and drops out at a predictable rate of 12-dB-octave below that. Since the AR 12-inch woofer is so potent to begin with, compensating for that natural drop-off with equilization, such as with the Allison Electronic Subwoofer, can result in flat bass down to 20 Hz. with only marginal increase in harmonic distortion.

Mounting a speaker in a corner can have a similar effect of jacking up deep bass, but it also brings us mid-bass frequencies as well, which makes the speaker sound somewhat boomy or heavy, not so desirable.

--Tom Tyson

[Guest Bret]

>since cone velocity for a given power output doubles for each lower<

Can you expound on this just a little for me. You see, what's confusing me is that a cone must move faster to produce 1000Hz than 100Hz, so I get "lost" trying to wrap my brain around "velocity doubles. . . lower."

But I think I'm beginning to understand the idea of CV's using a cabinet that's entirely too large. Seems they were trying to move "fc" down so that they didn't experience the -12db/octave drop below fs.

That means that fs gets really important, eh? The mechanical control of the excursion gets to be really critical because it is essentially all there ever is.

Or am I confused again?

Bret