32B Lover's Tale

[mah]

Any 32B fans here?

JE Labs: Altec 2-way horn system redux

[VolvoHeretic]

I am now doing an un-scientific A/B comparison of a 32B aluminum bent horn and a 511B sectoral horn, both in front of 802-8D compression drivers w/ Symbiotic diaphragms. It is not a fair comparison since the 32B is 38" high, and 511B's are 52.5".

The room is not perfectly symmetrical and is 13.5' x 35.33' with an enclosed stairwell jutting out on the sidewall of the rear kitchen area. Any way, I listen sitting 14' away or standing 24' away. Both speakers sound like Altec 802-8D's behind horns.

I like the 32B close up and the 511B farther away but wifey says the 511 sounds clearer no matter where. My hearing drops off like a stone at 14khz and hers at 15khz. They both sound great on top of 418-8H II guitar woofers in 8cu. ft. boxes.

I also have two piezo super tweeters above each horn, but still haven't hooked a resistor and two caps to cross them over at 8khz.

Edit: The 511 is definitely louder and I have lately set the ele. Xover to 1khz Vs. 1.2khz for the 32B. I can't tell....

[lokie]

I think there is something "going on" with the effect of the bent horn and it's ability to integrate with the mid/woofers.

The physics of speaker design gets away from me very quickly, so, please excuse my rudimentary theory. I'm guessing a bent horn slows down the velocity (less efficient??) and enables a better "match" with lower frequency drivers.

So, while the 32b may be a few points less efficient (which doesn't matter because you have to match the woofer's efficiency anyway), the big benefit is it's integration with the other driver. The downside is that it's lower frequency range is limited, forcing one to use the woofer above 1khz... which is less than ideal- but still sounds fantastic on my diy 32b/802B/Jensen15PLL speakers.

The big Western Electric horns do the same thing (whatever that is??) with a broader frequency range and one driver.

I would be very curious to a bent horn that goes down to 700hz and a 1.4" throat. I don't think it exist.

[bowtie427ss]

The 32 horn is unique in that it's acoustic axis is not perpendicular to the horn's mouth or the baffle it's attached to.

It has a HF advantage over the 811 and 511 horns due to it's shorter horn path. The higher the frequency, the faster acoustic energy dissipates.

[GM]

I'm guessing a bent horn slows down the velocity (less efficient??) and enables a better "match" with lower frequency drivers.

The downside is that it's lower frequency range is limited, forcing one to use the woofer above 1khz...

I would be very curious to a bent horn that goes down to 700hz and a 1.4" throat. I don't think it exist.

Well, acoustically tight bends can lower efficiency due to causing reflections back to the throat, reducing output in this BW, but the SoS stays the same, though AFAIK the 32B suffers no such problem.

Note that the 32B horn was designed for mating to a 12", which is ~90 deg around 1356 Hz, so a 1400-1500 Hz XO is desirable for a nominally 90 deg horizontal horn.

Before there was a 32B horn there was the 32A PA horn with a 300 Hz cut-off: http://www.lansingheritage.org/images/altec/specs/components/sectoral-horns/page2.jpg

GM

[lokie]

"Note that the 32B horn was designed for mating to a 12"," Not so sure about that.

Before the Altec Model 15 was the Western Electric 753c. I think this was the first application for this horn.

We 713 back.jpg

753 beutiful example.jpg

- - - Updated - - -

Before there was a 32B horn there was the 32A PA horn with a 300 Hz cut-off

If I had to pick a predecessor to the 32b, it would be the Western Electric KS12024.

http://https://quintusaudio.wordpress.com/2014/05/

[GM]

??? The 728B woofer in the 753C studio monitor is a 12". Indeed, ATM I can't recall any W.E. [studio] monitor or even small venue horn systems with any of the KS or small 32 series horns that used a 15"; they just doubled up woofers for higher [acoustic] power apps.

WRT the 32A, I didn't say it was the B's predecessor, just that it predates it AFAIK as supposedly all the large format horn systems were developed for large PA/cinema sound systems before much effort was directed towards providing for the emerging smaller venues, studio and HIFI markets.

AFAIK, the direct predecessor to the 32B was the KS12027, which looks ~ like a cross between a mini-32A and the later 32B.

GM

[VolvoHeretic]

And let's not forget the 15" 416A/802/32B Altec A8 that I would love to actually hear in person.

[GM]

It's OK sounding, but too compromised for me and relies heavily on being behind a large cinema screen to get the most out of it, then needs a super tweeter to fill in the extreme highs. Needs a lot delay too, though with 416a's fairly wife HF BW I imagine the XO could be gapped quite a bit, allowing the use of a 1st order XO on the HF for HIFI apps.

Still, unless a very shallow cab is a primary goal, it seems more trouble than they're worth.

GM

[lokie]

The 753C has a 15" Western Electric/Jensen KS-12004 15" Woofer.

Maybe you are thinking of the WE 757?

757 WE back.jpg

we 757.jpg