AL-III Woofer Tweaks

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Robert R
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AL-III Woofer Tweaks

Post by Robert R » Sat Jun 27, 2015 7:24 pm

For those not familiar, the stock AL-III woofers are down-firing, in a ported box. And they have a pair of little weights stuck over their dust covers, presumably to add some extra mass to the cone/piston. The effect is to lower the resonance frequency, and that should have the effect on extending low-end response but I'm pretty much a blank about the details.

It occurred to me that since I use a TrueSub with mine, crossed over at 50Hz, why do I need these weights? The cone would be lighter without them, and that sounds advantageous, at least for the two octaves I want from them.

Also, that same lack of needing the lowest response suggests that sealing up the port might have a positive effect as well, especially if followed by some DSP EQing, as needed. Sealed boxes in general are considered to be smoother and better sounding. They're less efficient, but again, in this setup that doesn't matter.

So, my question would be, has anybody experimented with this sort of tweaking, or even considered doing so? It would take some fiddling, and if somebody already knows some pros or cons I'd love to hear.

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Re: AL-III Woofer Tweaks

Post by radioeng2 » Sat Jun 27, 2015 8:36 pm

I'm a big fan of the sealed enclosure. The transient speed is so quick that way. Should do a better job yet of keeping up with the ribbon.

The questions I come up with...
Will you still get it low enough to mate with the sub...and how well does the sub mate up anyway?
How well does the driver parameters work with a sealed enclosure...before or after removing the added weight?
Does the digi eq fix it all up? Likely yes.

Seems like a some measuring would be in order. Or cheat and ask if anybody else has done any of this! You already did that though... :lol:

Enough guys running AL-3's to make some effort interesting.

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Re: AL-III Woofer Tweaks

Post by Robert R » Sun Jun 28, 2015 8:00 am

Mark - I'm with you on the sealed box issue - never even liked the idea of boxes at all, but if you must have one it should be sealed. The idea the idea of ports always struck me as sort of a cheap trick. Great advantage on budget speakers, but if one aspires to something higher, no so good.

It's easy enough to plug the ports for experimenting, and no lasting harm done. So guess I'll start there.
Might hear no difference at all, since the lowest notes aren't even present. But maybe in that certain range on pianos, drums, low strings, bassoons, trombones...

On the other hand, I don't want to mess with those weights unless I'm pretty sure of some noticeable improvement. The surgery required is kind of risky. They are basically part of a second dust cap that's glued over the main one. Maybe wait for the Fest and ask Bob about the weights. It's not that far off.

Quite a few guys have gone to other drivers, often by necessity when their originals crap out. Love to hear something from them.

As to room measuring, my plan is as always: do it by ear from the exact listening position, with downward tone generator sweeps. Works for me. It better work - I have two 3-channel systems to deal with - one here in Rochester and the other in Florida. So with 3 pairs of IIIs in all I'm pretty committed (hmm - maybe should be committed).

Since I'm bi-amped with mini DSPs, I can delay just the ribbons, giving the bass as much lead time as desired. But that's another bunch of tweaking experiments, of course. The fun never ends.

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Re: AL-III Woofer Tweaks

Post by pmat » Mon Jun 29, 2015 12:26 pm

Bump, I have two pairs so I am very interested in this topic.
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Re: AL-III Woofer Tweaks

Post by TNRabbit » Mon Jun 29, 2015 3:09 pm

So, the purpose of the weights is to slow down the woofer to change it's resonant frequency. I know this is done with passive woofers, but come on, how much can it actually affect an active driver?

I can't imagine you be able to hear any difference. I suggest crossing over at 40 hz & let the sub handle anything below that.
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Re: AL-III Woofer Tweaks

Post by radioeng2 » Mon Jun 29, 2015 4:13 pm

It's actually a pretty common manipulation to lower the drivers resonance. I know a number of drivers that have some obvious add-on. And many may not be so obvious, like heavier cone material. I don't know how much the change is. I should try sometime measuring a driver and then add something and see how much it changes. Be informative.

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Re: AL-III Woofer Tweaks

Post by Robert R » Mon Jun 29, 2015 8:34 pm

My plan with the weights is to ask Bob first - maybe save a lot of bother.
Messing with the ports is something I can start on right now, as soon as I get a few more pressing things done around here.

Gary, I agree - it shouldn't make much difference. But Bob is very fussy, and, as he says, the difference between a very good speaker and a great speaker might not be dramatic, but it's worth the effort, if you have the ability to make it happen. Hope you are there - if you're coming at some point I won't even mention it to Bob until you get there. Do you use the stock drivers in yours? I thought you had replaced them, but that memory is from 2009.

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Re: AL-III Woofer Tweaks

Post by TNRabbit » Tue Jun 30, 2015 10:52 am

I did replace mine with infinity perfect 10 woofers. Sold the old woofers to Angelo.

The infinities are a great way to beff up power handling and the lowest notes, but since I'm using a sub for the lowest notes , I could probably have stayed with the original woofers.

Hope to be there the last weekend~
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From FrankieD's lips to your ears: Sunfire - a quiet box of endless power.

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Main: HotRodded AL-IIIs
Sub: Klipsch RT-12d
Center: Sunfire CRS-3c
Surround: Sunfire CRS-3 (x 2)

OconeeOrange wrote:"Gary likes to play it 'loud' as do I. His system begs you turn it up until you die"

RIP WIlliam B. Dibble, 1948-2012. I'll miss you my friend.

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Re: AL-III Woofer Tweaks

Post by radioeng2 » Tue Jun 30, 2015 2:02 pm

TNRabbit wrote: Hope to be there the last weekend~
Wouldn't feel like the fest if you're not Gary! Hope it'll work out!

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Re: AL-III Woofer Tweaks

Post by Robert R » Tue Jun 30, 2015 6:25 pm

Gary - Hope you make it. I remember your lowest notes as impressive. Maybe less doubling than the stock ones?

Without the sub, I tried alternate playings of a track with a lot of 8-string bass guitar (lowest note is the F# at 46.25 Hz). With the hole plugged or not, not a lot of obvious difference. Both ways it's noticeably dropping off below 50, but that's the DSP doing its thing. Need to try a variety of other tracks. Drums, piano, etc.

The step after that will be a downward sine wave glide, from 300 down to under 40 Hz. The crossover is set for just 200-50, but of course the woofer contributes outside those numbers, albeit at a reduced level - I cut it off pretty sharply. So I'll be checking an extra half-octave beyond the designated range.

My sub is a Hsu ULS-15, another sealed box. I hate running the rig without the sub, and in mono at that, but this is war.

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Re: AL-III Woofer Tweaks

Post by Robert R » Wed Jul 01, 2015 9:00 pm

It has rained every day here lately - on and off - at least five in a row. But I've finally finished beheading my pickup, and that gory mess is now in the shop for milling and valve job and stud repairs. Got the radiator into another shop today, and fixed the starter myself. So not much more I can do, except scrape off some gaskets, practice my cussing, and wait.

Time to get back to the AL-IIIs. Did some downward glides with sine wave tones, running just the center speaker. As usual, the room played a role - there always seems to be some frequency that is way too strong, and another that's quite weak. It's easy to cut the over-loud peaks with the DSP, but boosting the weak notes is not so productive. In this case it's around 83 Hz, +/- 2 or 3 Hz. If I lean forward half a foot it fades even worse - sounds about like the generator got turned off. But move a couple more feet in any direction, and the problem goes away, though maybe some other note disappears in that location. In practice this is not so bad, since I get a good amount of that freq. from the two other channels. I find for smoother response it's really best to have bass coming from several places. The DSP lets you tune each amplified signal independently - that's especially useful in the bass range.

Anyway, with the cabinet port open or plugged there seems to be no obvious difference in this problem at 83Hz, and furthermore no audible change at any frequency I'm trying. Can't even swear that it's louder overall with the port uncovered. I imagine the lowest frequencies would be noticeably affected, but I'm not using those, so no matter.

This whole deal is turning into a non-event. Would need a microphone and analysis program to run and record a response test with differences so small.

Of course sine wave response is an oversimplification of what audio is all about - 'taint that simple. There's stuff like interference and phase shifting to consider, so before I write this off as a dumb idea I want to listen to some music, but with the full array of speakers playing, with and without the ports blocked. Can't try that tonight because I first have to make up a couple more little port covers to block the holes, and I'm worn out.

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Re: AL-III Woofer Tweaks

Post by angelod307 » Thu Jul 02, 2015 12:43 pm

All the port does is double the output at the tuned freq. below that, it drops off like a cliff.for a difference that you seek, you want half the air volume on average for sealed to ported woofer boxes. The weight on the driver does not slow the driver down one bit. It does however change the freq that the driver has the most output with the least input for a lack of a better description. So, when bob lowered the resonance by adding weight, what he did on the negative side was made the driver less efficient, needing more power to do the same job. Again, I can not explain my thoughts with the proper words, but the woofer setup in a al3 is a exact science that bob did. I think that when I took out the regular eminence woofer and used Jls , the speaker had a midbass notch, as bob put it a clarity notch as the bass seemed cleaner and less muddy. After years of this. The speaker sounde thin when I added a dedicated sub. The infinity that Gary spot of, is great when al is crossed over electronicly, but passively the infinity woofer does not match as well as say a replacement paper, not plastic driver. I find paper drivers have a warmer tone to them than plastic, but that's my observation and not to be taken literally for every driver out there.
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Re: AL-III Woofer Tweaks

Post by TNRabbit » Mon Jul 06, 2015 12:15 am

The Infinity driver is aliminum, not plastic.
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From FrankieD's lips to your ears: Sunfire - a quiet box of endless power.

Sunfire TG-IV/400~7 Amp
Carver SD/A-360 CDP
Benchmark DAC-1
Sony SACD/DVD-A
Active bi-amp: Ashly XR-1001 & 2 Rane PEQ-15s
Main: HotRodded AL-IIIs
Sub: Klipsch RT-12d
Center: Sunfire CRS-3c
Surround: Sunfire CRS-3 (x 2)

OconeeOrange wrote:"Gary likes to play it 'loud' as do I. His system begs you turn it up until you die"

RIP WIlliam B. Dibble, 1948-2012. I'll miss you my friend.

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Re: AL-III Woofer Tweaks

Post by hewlew1 » Mon Jul 06, 2015 12:54 am

Gary, other than increased power handling I saw no advantage to the infinity driver what so ever.Mark and I A-B compared the two drivers and the stock woofer had much better bass.
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