Altec 755a's
- Thread starter scoville
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Joe Roberts
Agent Provocateur
Hope you gots a big stack of Korean Won, sucker.
bowtie427ss
Lunatic Member
You ain't dealin' with no Hoochie Mommas! 
Joe Roberts
Agent Provocateur
Redboy, you are way down on my list of potential Hootchie Mamas.
In fact, I would have to add a considerable extension at the bottom before you would fit on it....and even then you would probably just barely beat out Donald Rumsfeld, Caitlyn Jenner, and Al Sharpton.
I have standards!
In fact, I would have to add a considerable extension at the bottom before you would fit on it....and even then you would probably just barely beat out Donald Rumsfeld, Caitlyn Jenner, and Al Sharpton.
I have standards!
jeb98
Well-Known Member
I agree with this. I look forward to building a pair of those Silbatone designed boxes.
Redboy, I'm interested to hear what you think of the 755a's as I know you had mentioned in the past you were using Feastrex single driver full range speakers. I guess it will be a while since you don't have a 4 ohm amplifier right now.
Joe Roberts
Agent Provocateur
4 ohm tap is nice but non essential. I doing the 8 ohm on the SCA35 right now.
The ultimate effect of a higher tap depends more on the amp design than the speaker and is another of those things best evaluated by ear in use context rather than the textbook or forum scholarship.
These have a super flat 4 ohm impedance except at the 90hz resonant frequency. I think they are 4 ohms to get a low inductance vc to moderate Z rise at high frequencies.
The ultimate effect of a higher tap depends more on the amp design than the speaker and is another of those things best evaluated by ear in use context rather than the textbook or forum scholarship.
These have a super flat 4 ohm impedance except at the 90hz resonant frequency. I think they are 4 ohms to get a low inductance vc to moderate Z rise at high frequencies.
Dang, and to think that I don't even have a list!
I'm still using those Feastrex, but I'm noodlin' on horns, too... If Joe'd quit distracting me with 755A talk and stacks of Korean Won, they might be finished already!
I have other amps too, but triode-strapped 46s might be deficient in other ways. There's a Pilot SA232 around here somewhere that needs to be buttoned up - methinks it'd do just fine with these!
Joe Roberts
Agent Provocateur
Well, to be honest, mine is somewhat unrealistic. If I tried to talk to any of the "mamas" on it, they would instantly dial 911.
Although 755As will work on low power triodes, they do respond well to power. The standard WE amps that went with these were PP 6L6. WE 124s and 755As was my hot snot setup back inthe 80s.
I hear these all the time with Silbatone 300B SE amps and that works too, but the Silbatone amps have exceptional bass control and drive for SE 300Bs.
I think a Pilot 232 would be an excellent combo. i remember that amp being much better than the SCA35 I'm using at the moment and this Dyna is really clicking with the 755As. I tried the same amp on 756B and 728Bs and it is not quite as effective on the 10" and 12" members of the WE PM family. Why not? Who knows?...hence the precedence of experience over abstract speculation.
bowtie427ss
Lunatic Member
Joe Roberts
Agent Provocateur
Hey! That is the defroster vent from my 2008 Volvo V70. How did you get it?
bowtie427ss
Lunatic Member
Front or rear?
Volvo builds the safest, most reliable, rectangular box i have ever seen.
In another life i have a genuine fetish for small Volvo Penta marine engines. But, i think that's a different thread on another forum.
Hey, I recognize that...Ask Joe his thoughts about this here hunk a plastic, i dare ya.
Nope, that's a catch filter for oil changes! I have a couple, but mine are aluminum.
elitopus
Addicted Member
Damn that car just keeps on going
Wow, good to know that my 2004 Volvo XC70 has a good heritage. I never expected that thing to keep going, crash after crash, that would have killed most cars after the first few.
I have a few of the metal 32B and one plastic 32B. Haven't played with them yet but I can tell you that the 90 degree transition is a lot smoother on the plastic one. I suspect it's the reason folks say it's a little bit better. I also suspect that the playing field could be leveled with a small die grinder or some rifler files, the short curved ones that look like the bottom of a narrow spoon, they used them in mold work to blend. Clean up the transition and I'm pretty sure they will sound the same.
BillWojo
I have a few of the metal 32B and one plastic 32B. Haven't played with them yet but I can tell you that the 90 degree transition is a lot smoother on the plastic one. I suspect it's the reason folks say it's a little bit better. I also suspect that the playing field could be leveled with a small die grinder or some rifler files, the short curved ones that look like the bottom of a narrow spoon, they used them in mold work to blend. Clean up the transition and I'm pretty sure they will sound the same.
BillWojo
scoville
Active Member
Thanks for the info gents. I'd love to build that cabinet for this, I do have a garage full of woodworking machinery, but if I can't get this sweetie repaired properly... I've talked to a guy who can replace the cone and VC, but it's not orig. I've sent a shout out to Gordon. I will have to check some of the local businesses. All my tube gear is currently stereo, I sold a mono Bogen 6 months ago, that was a peach dammit! If I can get this repaired I will have no issues with purchasing a high quality mono tube amp.
bowtie427ss
Lunatic Member
Certainly, to many ears they will sound the same.
But, to more than enough ears the differences are clear.
Simple laws of physics demand that they sound different, and they do.
Much of it has to do with resonance, and that damn law of compromise won't be left out of this comparison. The two different materials resonate so differently from each other that they cannot help but have at least a small influence in the timbre/color of the sounds they reflect.
Consider that the plastic horn has much less mass than the aluminum horn. Horn mass coupled to the driver helps reduce and control the accelerating and decelerating forces of the moving assembly, it reduces distortion. The aluminum horn has an advantage here.
The aluminum horn has a much much higher tensile strength as well as surface tension and is exponentially more reflective to VHF energy with increasing frequency. These characteristics also contribute to undesirable resonance requiring that the horn be damped in some way. Fortunately the 32 simply need only to be mounted to damp any unwanted resonances.
The plastic 32 is actually self-damping across it's bandwidth and requires no efforts to control resonance/ringing.
Plastic is actually excited at the molecular level with high enough frequency and amplitude, increase it enough and it generates enough heat to melt. Dukane Corp. did much research and development in this field, probably starting with transducer technology they gleaned from JBL in the 60's, and refining it into what would make them a world leader in ultrasonic plastic welding technology. You can find plenty of transducers and horns on that auction site today from that technology, they don't look anything like the horns we deal with here.
Just a smidgen of my .02 on the subject.......................................
1000 watts @ 20khz, look at the damping inside that chamber:
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Joe Roberts
Agent Provocateur
I have tried both plastic and metal 32s but not in the same system at the same time.
One thing that should be noted is that the metal Altec 32 takes the WE 32 which was designed for the WE drivers which had a smaller throat aperture than an Altec 1" and very crudely drilled it out to 1". See pic of KS 12025 throat measurement. I don't have a WE 32 on hand.
![IMG_2268[1].JPG](https://audiokarma.org/forums/data/attachments/879/879298-3648e89c0ce738fbb37ed1e2b7dcdb88.jpg "IMG_2268[1].JPG")
Poke your finger in the metal 32 and feel it....don't get your finger stuck in the hole now! And don't use any other body parts!
I have had two specimens of metal Altec 32 in front of me with very different drilling depths and interior throat profiles. Not good.
This strikes me as a tragic flaw, along with the very rough interior surface that can be found in the throat of most Altec 32s. You do not want a rough surface and all sorts of sharp casting flash at this point of high compression.
If I remember, which is unlikely, next time I am at the Silbatone factory, I will inspect some old WE 32s to see if they are smoother inside.
The difference in path length between the metal and plastic might be explained by the notion that the longer metal one was designed to expand from a smaller aperture and hence must be longer. They kluged the metal to work with Altec by drilling it out, then came up with a truncated version in plastic.
32C plastics are not the world's greatest precision casting job either, but at least they are set up for a 1" driver natively.
My casual evaluation is that the plastic 32 is fatter and richer sounding and the metal one is perhaps a bit sharper and drier. Can't say that for sure, but I can say that both sound good and maybe the plastic Volvo model is more comfortable to listen to.
One thing that should be noted is that the metal Altec 32 takes the WE 32 which was designed for the WE drivers which had a smaller throat aperture than an Altec 1" and very crudely drilled it out to 1". See pic of KS 12025 throat measurement. I don't have a WE 32 on hand.
Poke your finger in the metal 32 and feel it....don't get your finger stuck in the hole now! And don't use any other body parts!
I have had two specimens of metal Altec 32 in front of me with very different drilling depths and interior throat profiles. Not good.
This strikes me as a tragic flaw, along with the very rough interior surface that can be found in the throat of most Altec 32s. You do not want a rough surface and all sorts of sharp casting flash at this point of high compression.
If I remember, which is unlikely, next time I am at the Silbatone factory, I will inspect some old WE 32s to see if they are smoother inside.
The difference in path length between the metal and plastic might be explained by the notion that the longer metal one was designed to expand from a smaller aperture and hence must be longer. They kluged the metal to work with Altec by drilling it out, then came up with a truncated version in plastic.
32C plastics are not the world's greatest precision casting job either, but at least they are set up for a 1" driver natively.
My casual evaluation is that the plastic 32 is fatter and richer sounding and the metal one is perhaps a bit sharper and drier. Can't say that for sure, but I can say that both sound good and maybe the plastic Volvo model is more comfortable to listen to.
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