Altec 2 Way Build ala JELabs - 802/32/414

Salectric

Senior Member
I bought two rolls off Ebay or Amazon, I don't recall which one, a few months ago. I haven't tried it in my Jensen/Altec vented cabinets yet, but I did try it with my Jensen/YL open baffle speakers to dampen the rear wave from the Jensen woofers. In that application I preferred the sound without damping. A box will probably give different results.

The last time I listened to my Jensen/Altecs (3.2 cu ft vented cabinet) I had no damping in the boxes at all. That gave a very lively but rather boomy sound. Previous to that my favorite arrangement was a piece of 1" memory foam stapled to the rear panel and no other damping in the cabinet. Even earlier I started with 1" memory foam stapled to all surfaces and the sound was much too dead. Each time I removed a panel the sound got better, more lively, but I stopped with the rear panel foam still in place. The next time I listen to them I want to try the "curtain" of felt or some other material; that might give the best of both worlds. I also want to try internal bracing with no damping on the plywood panels. Lots of possibilities. The cabinet walls definitely need to flex and vibrate.
 
The cabinet walls definitely need to flex and vibrate.
My favorite "corporate designed" speakers are ones w a live cabinet design, Harbeth, Shindo, and other BBC derivatives.
But, for me, trying to emulate those designs in a DIY speaker was a bridge too far. Speaker design is definitely one of those subject that proves the saying, "the more you know, the more you realize what you don't know."

The resonance in the cabinet walls is a distortion in a particular frequency range and can really muddy other frequency ranges. Shindo, Western Electric, Harbeth know how to manipulate that distortion to a region that does less harm to the other frequencies but still keeps the "ringing" or liveliness quality. Very few designers do this... I assume because its not easy and it probably doesn't measure well.

Anyway... heres a good read by Alan Shaw of Harbeth:

"What underpins the BBC's thin-wall cabinet philosophy (and I was surprised to read that exact word in one of Harwood's papers recently) is the observation that a perfectly cast bell will ring on for many seconds. Conversely, a bell with a hairline crack will sound leaden and hardly ring at all. It's the same with cabinets: if the panels are all rigidly glued together then at some critical frequency or other a note or notes in the music will trigger the cabinet's natural structural resonance. In such a rigid structure, there is nothing that can be done to suppress the ringing - and each time that note reappears, it tops up the ringing which then becomes a permanent drone underneath the music.

Conversely, in a thin-wall cabinet, the lossy joints (i.e. removable baffle/back and the generally 9-12mm thin panels used throughout the box) each act as an acoustic hairline crack. They inhibit the build-up of resonance. Simple as that really!

Now, let's not kid ourself that it is possible to kill cabinet resonance stone dead. It isn't. Not with any approach to cabinet design because the sound pressure inside the cabinet is huge. What the thin-wall approach does is to move unwanted resonances downwards in amplitude and frequency so that they are adequately buried below the music and then pushed down in pitch. Note that I said adequately.
Providing that the resonance, be it from the cone, cabinet or even recording - whatever the source - is x dBs below the fundamental, the BBC proved that it was completely inaudible. Once inaudible to trained listeners on all types of music/speech, that is the end of the matter. Inaudible to the trained listener is as good as the solution needs to be. It is neither necessary nor cost effective (nor good engineering) to continue pushing for a degree of theoretical excellence that nobody can appreciate but everyone must pay for. That pragmatism keeps our speaker affordable - and sounding natural.

What we seem to be lacking in the industry today is the good old fashioned common sense that was abundant when serious researchers with zero commercial interest (i.e. the BBC) had their hands on the tiller. Thank goodness that they thoroughly documented their efforts for posterity since physics, acoustics and our hearing are the same now as fifty years ago. Now it seems we are all conditioned by marketeers to chase theoretical perfection which is far, far beyond what our ears can reliably resolve."
Alan A. Shaw
Designer, owner
Harbeth Audio UK
 

Salectric

Senior Member
Conversely, a bell with a hairline crack will sound leaden and hardly ring at all. It's the same with cabinets:
What a great analogy! That makes sense on some intuitive level. I don't doubt for a minute that a BBC-school manufacturer devotes considerable attention to the cabinet construction and type of damping material as well as its location. And this is something we amateurs need to do as well to get the best sound quality even though we are only making one pair of speakers, not 10,000 pairs.
 
Felt Curtain detail.
The felt curtain I'm using half way in the box is 5 mm thick. Total thickness is 7 mm with the think sewn material on each side adding 1 mm to create the 7mm total. So its very light. Next trial will be to have the 'curtain' hanging on a 45 degree angle more similar to what Joe Roberts has done. But my material looks far thinner than his. I found thicker in my installation harmed the sound over the thinner 7 mm material used.
Western Electrix
 
Felt Curtain detail.
The felt curtain I'm using half way in the box is 5 mm thick. Total thickness is 7 mm with the think sewn material on each side adding 1 mm to create the 7mm total. So its very light. Next trial will be to have the 'curtain' hanging on a 45 degree angle more similar to what Joe Roberts has done. But my material looks far thinner than his. I found thicker in my installation harmed the sound over the thinner 7 mm material used.
Western Electrix
Are you going to build a frame of sorts? It seems like this thin material would be flapping around inside the speaker. Not sure if that's a terrible thing, but it seems kind of odd.
 
Are you going to build a frame of sorts? It seems like this thin material would be flapping around inside the speaker. Not sure if that's a terrible thing, but it seems kind of odd.
Not flapping around at all. I made it slightly wider than the width of the cabinet and slightly longer than the bottom so its seated in a way against the side and bottom of the cabinet. Playing music with the back ajar shows no movement at all.
Why don't you try it if you have time and let me know what you think? There are probably better options. I just haven't heard any personally with the not exhaustive experiments I've done. The sound with this approach was fundamentally better than other approaches i tried and so i happily left it alone and moved on to other aspects of crafting the sound I'm after.
I would love to try the Kimsul and will try to track it down. Could be fantastic.
Western Electrix.
 
Not flapping around at all. I made it slightly wider than the width of the cabinet and slightly longer than the bottom so its seated in a way against the side and bottom of the cabinet. Playing music with the back ajar shows no movement at all.
Why don't you try it if you have time and let me know what you think? There are probably better options. I just haven't heard any personally with the not exhaustive experiments I've done. The sound with this approach was fundamentally better than other approaches i tried and so i happily left it alone and moved on to other aspects of crafting the sound I'm after.
I would love to try the Kimsul and will try to track it down. Could be fantastic.
Western Electrix.
Will do.

Ordering Kimsul today. I also need to let a some new Teflon Coupling Caps burn in for a week or so more. They're sounding thin and hoping they will round out a bit more. Nothing happens fast around here.
 

Salectric

Senior Member
new Teflon Coupling Caps burn in for a week or so more
What type of caps did you get and where are they located in your equipment?

I can sympathize with burn in frustrations. I am trying out different loading resistors in my phono preamp, different resistors in my speaker crossovers, and new power cord connectors. The Furutech IEC plugs supposedly need 500 hours. Nothing is easy!
 
Is that foam padding?
It looks like thin bed foam padding thats sounded terrible in builds where i have tried it before. Padding on all the walls like in this case has never really worked for me either.
I like that they'd didn't brace the heck out of the cabinets. And they look gorgeous.
Western Electrix
 
It looks like thin bed foam padding thats sounded terrible in builds where i have tried it before. Padding on all the walls like in this case has never really worked for me either.
I like that they'd didn't brace the heck out of the cabinets. And they look gorgeous.
Western Electrix
Agree. This stuffing strategy sounded horrible in my experience... Dull, muddy and lifeless.

But I was working w 6cuft not 17 1/2cuft (by my calculation... Im terrible at math so, please correct me if I'm wrong).
So maybe the extra space in there makes a difference? I dunno??

Very hard to tell the cabinet walls thickness, but it doesn't look more then 3/4". With the large surface area's and minimal bracing, I would definitely put this in the BBC Cab Design camp. Especially w an 18" woofer! I bet those walls are singing.

Something else about this speaker that is extremely interesting is the specs on the CD and Horn.

"The 1 ¾-inch motor mounted on the 8-cell horn offers a bandwidth ranging from 600Hz to 20kHz".

So, they have basically morphed an 808 Horn (1") into a large format Horn(1.5").

Sure would be cool to get one of the aftermarket wood Altec horn makers to make this 808 derivative compatible w large format Altec drivers. If it was designed correctly, me thinks it would be much more compatible than a larger format horn (1005, 805, etc..) w a bass reflex cab. Especially if you could get down in the 6-700Hz range. Also accommodates a smaller room and closer sitting position.

And then we need to get Truextant to make Beryllium 1.5" Altec Diaphragms to get the top end. Then we DIYers could have some fun!

upload_2018-11-8_8-41-26.pngupload_2018-11-8_8-41-26.png
 
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Agree. This stuffing strategy sounded horrible in my experience... Dull, muddy and lifeless.

But I was working w 6cuft not 17 1/2cuft (by my calculation... Im terrible at math so, please correct me if I'm wrong).
So maybe the extra space in there makes a difference? I dunno??

Very hard to tell the cabinet walls thickness, but it doesn't look more then 3/4". With the large surface area's and minimal bracing, I would definitely put this in the BBC Cab Design camp. Especially w an 18" woofer! I bet those walls are singing.

Something else about this speaker that is extremely interesting is the specs on the CD and Horn.

"The 1 ¾-inch motor mounted on the 8-cell horn offers a bandwidth ranging from 600Hz to 20kHz".

So, they have basically morphed an 808 Horn (1") into a large format Horn(1.5").

Sure would be cool to get one of the aftermarket wood Altec horn makers to make this 808 derivative compatible w large format Altec drivers. If it was designed correctly, me thinks it would be much more compatible than a larger format horn (1005, 805, etc..) w a bass reflex cab. Especially if you could get down in the 6-700Hz range. Also accommodates a smaller room and closer sitting position.

And then we need to get Truextant to make Beryllium 1.5" Altec Diaphragms to get the top end. Then we DIYers could have some fun!

View attachment 8705View attachment 8705
Sorry to disappoint you, but "the 1 3/4-inch motor" is the voice coil diameter. The CD throat diameter will be 1" to fit the 808 horn.
 
Sorry to disappoint you, but "the 1 3/4-inch motor" is the voice coil diameter. The CD throat diameter will be 1" to fit the 808 horn.
Oh, got it. Well... it seems like a good idea anyway.

600Hz- 20Hz w this combo seems "magical".
 
A quote from Lynn Olson buried in the Beyond Ariel thread:

"I hope Bill of GPA experiments with beryllium diaphragms ... I told him to get in contact with the folks at Materion, who can probably provide a sample 288 diaphragm if he provides an aluminum version as a template. How beryllium works with the traditional tangential surrounds ought to be interesting, since Be has much better self-damping than aluminum and should be resistant to fatigue cracking (the problem with the original 288's back in the early Seventies).

I also mentioned to Bill that the same folks in Asia and Europe who like drivers with Alnico magnets will also probably like field-coil magnets, and they should be easier to make than hard-to-source and hard-to-machine Alnico"
 
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