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A taste of vintage German coaxials: Isophon PH2132E

audiozaz

audiozaz

rtfm!? - tl;dr
The thrift had a couple of monkey coffins around the place - I was looking for a box of suitable dimensions for some wintertime experimentation. There was a pair of Noresco-labelled, Isophon-badged medium boxes. Even without the Isophon badge, I highly suspected these held this brand drivers, perhaps a 8" fullrange/midbass and a 4" cone tweeter. Upon opening these back at my place, I was surprised by the reveal, the somewhat sought-after PH2132E coaxial. A 12.5"x8.25" oval fullrange/mid-bass, bra-strapped by a 4" cone.

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These are in pretty good shape and are the 4ohm version. There is a single cap for the tweeter, likely tired after all these years. I'll try measuring the T/S parameters, but suspect a high Qts and OB-suitability. One tweeter does not work because a wire is broken on the fullrange's terminals, but I'll try to give a listen in mono to the one that works, in the Noresco reflex cab it came in.

az
 
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Always thought those were kinda cool for some reason. Look forward to reading what you think of them.
 
Interesting. I'm inclined to think those have a nice warm tone considering the sound I've heard from German consoles.
 
Tom Brennan said:
Interesting. I'm inclined to think those have a nice warm tone considering the sound I've heard from German consoles.
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I might say they have such a tone. Likely there is a better enclosure for them as well. Sitting straight on-axis makes for a bright presentation, which becomes bearable with not too much toe-in or being off-axis from the mono unit.

az
 
audiozaz said:
Sitting straight on-axis makes for a bright presentation, which becomes bearable with not too much toe-in or being off-axis from the mono unit.

az
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A quick measurement revealed just that, a dip at 5kHz, followed by a broad peak at 7kHz - either the tweeter's own idiosyncrasy or interaction with the fullrange. Perhaps phase inversion might alleviate this, or a better crossover. The peak settles down with only a few degrees of movement. The tweeter has good output up to ~12kHz. I'll see about measuring drivers individually.

az
 
I've measured the following parameters for these:

Re: 2.9ohm
Fs: 58Hz
Qms: 6.3
Qes: 1.05
Qts: 0.9

Glad to see Fs is not too high, meaning 75Hz+. Qts makes them suitable for infinite baffle or an aperiodic enclosure with somewhat less bass - I don't like Qtc>0.9 - and open-baffle of course. I might try them on OB if I can get some cheap panels and courage to make odd-shaped driver cut-outs in the cold. :)

I like this Philips design, meant for the AD4200 and AD5200 fullrange drivers:

Philips-AD5200-AD4200-Open-Baffle-Plans.jpg

It is quite large though. The JE Labs OB is somewhat smaller:

JE_Labs_OB.jpg

Practically though, it may end-up being 24" square panels, much easier to procure, transport and cheaper as a simple test mule.

az
 
Those look like they would be a lot of fun to play with. I love opening up a nondescript box and finding a surprise like this:)
 
Vaughn said:
Those look like they would be a lot of fun to play with. I love opening up a nondescript box and finding a surprise like this:)
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I've been lucky to find a few gems through the years in such boxes, some of them home-built - shoddily so. :)

az
 
audiozaz said:
...

It is quite large though. The JE Labs OB is somewhat smaller:

View attachment 411181

az
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I have tried my set of 2132Es out in a couple of OBs like that:

OB-001.jpg


The sound was very good, detailed and with a extraordinary accurate image; the speakers were driven by a small Sansui AU-101 solid state amp - not the one in the picture; it is a au-9500 - since my Siemens (2000 film projector) amps doesn't like speakers with impedance below 8 ohms.

PQR
 
Very nice pqrannes!

Are you using the "stock" crossover, meaning the single tweeter capacitor? Have you tried the drivers oriented vertically as well? I have yet to try mine in anything serious, not much room for that as well.

az
 
audiozaz said:
Very nice pqrannes!

Are you using the "stock" crossover, meaning the single tweeter capacitor? Have you tried the drivers oriented vertically as well? I have yet to try mine in anything serious, not much room for that as well.
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I never got to change the stock crossover (capacitor?) - it is still on my very long vintage-hifi-to-do-list.

The speakers were mounted sideways when I first got them:

ikea-ben%20010.jpg


NB: I took the backside off the cabs they came in.

It never occurred to me that it is worth trying turning them 90 degrees; this must on the to-do-list too.

PQR
 
To preserve them it is usually recommend to rub clear calk on the paper surrounds to remain elasticity and for them not to deteriorate.

IMO those should sound much better in large boxes, than OB. They were designed for that.
 
Pandovski said:
To preserve them it is usually recommend to rub clear calk on the paper surrounds to remain elasticity and for them not to deteriorate.

IMO those should sound much better in large boxes, than OB. They were designed for that.
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I've had a few old Philips fullrange drivers around, with pleated paper surrounds. My AD9710's looked a bit worn, no tears or anything, still solid, but a bit fuzzy. I applied some rubber cement to help that one last longer and it looks good to this day. My PH2132E have their surround in exceptional condition, not even dried out or anything, so I would not consider doing this just yet.

pqrannes' original box is similar to the Noresco box these came in for me, though the vent hole was larger on mine. I would not use these in any kind of reflex enclosure, but a large sealed box should be good. We're probably talking 200L+ here. ;) It was not too bad on the original box with the back panel off actually, but it probably was hurting the midrange with reflections.

I'd venture a guess that dispersion will be broader on the 8.25" dimension on these, so it's a matter of how you want sound to project in your room. I suspect I'd prefer them vertically, to have broader horizontal dispersion, but practice may prove otherwise.

az
 
audiozaz said:
I've had a few old Philips fullrange drivers around, with pleated paper surrounds. My AD9710's looked a bit worn, no tears or anything, still solid, but a bit fuzzy. I applied some rubber cement to help that one last longer and it looks good to this day. My PH2132E have their surround in exceptional condition, not even dried out or anything, so I would not consider doing this just yet.

pqrannes' original box is similar to the Noresco box these came in for me, though the vent hole was larger on mine. I would not use these in any kind of reflex enclosure, but a large sealed box should be good. We're probably talking 200L+ here. ;) It was not too bad on the original box with the back panel off actually, but it probably was hurting the midrange with reflections.

I'd venture a guess that dispersion will be broader on the 8.25" dimension on these, so it's a matter of how you want sound to project in your room. I suspect I'd prefer them vertically, to have broader horizontal dispersion, but practice may prove otherwise.

az
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If I may add large boxes and almost no dampening material, just on the walls to reduce reflections. Or even just a single layer on the internal back side of the box. Too much damping material will significantly reduce LF SPL.

Having them in vertical/horizontal mode and in the room corners might be interesting to experiment with.

EDIT: Cabinet size - the bigger the better. Forget calculating Ts etc. :D Large fridge packaging boxes would be good start for experimenting.
 
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Pandovski said:
EDIT: Cabinet size - the bigger the better. Forget calculating Ts etc. :D Large fridge packaging boxes would be good start for experimenting.
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That's what I'm talking about. :)

They may be decent in a "ResonanZ" enclosure. I'd only be concerned about the low-ish (relative) Fs over-exciting the thin cabinet walls.

az
 
What is the original single crossover capacitor's value?

I have a pair the have a non original cap installed, which prompts the question
 
Steve Riley said:
What is the original single crossover capacitor's value?

I have a pair the have a non original cap installed, which prompts the question
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AZ also posted about these at DIYAudio: http://www.diyaudio.com/forums/full-range/228505-noresco-isophon-sr-2-a.html

At post 3 he states, "The crossover cap is a 5µF, which suggests ~8kHz nominally for the 4ohm tweeter."

I've got a few of the smaller Isophon ovals and some tweets. Very nice sound. Would love to pick up a pair of the co-axials.
 
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