I have Jensen Imperials that I enjoy greatly (with 18" DIY subs, 5 amps actively crossed when all is working). One of my mid horns gave up the ghost. I bought some Great Plains Audio 909 and paired them with Altec 511B. Oddly, compared to the remaining Jensen RP201 horn, the MUCH larger Altec/GPA has significantly less presence in its lower range, say 500hz-900hz. They are almost unlistenable if I cross to them much below 1khz . I haven't actually tested response with signal generator and mic, but it's pretty easy to make relative evaluation since all drivers are actively crossed over. I put the GPA drivers on the Jensen horns and the result was similar. These were my first "vintage" speakers, so I have very little actual experience with horns. I'd appreciate suggestions. Which (relatively inexpensive) drivers might be better suited than these GPA? Or if anyone knows where to get a replacement diaphragm for RP201 that'd be swell...
Last edited:
It may be that some drivers are not suited to the horn, but that doesn't mean that a change in response means the driver isn't right. If you think the driver should work I think you should consider changing the crossover to return to the original response, that might get you most of the way there.
Maybe it has to do with phenolic diaphragm on Jensen having restricted HF and in consequence sounding fuller in a lower range . altec 1" should be crossed over 1 kHz.
I've toyed with xover frequencies extensively - pretty easy with active variable xovers. I turn on only midrange power amps, apply signal, and turning xover frequency pot reveals where response starts to kicks in or fade out. These GPA drivers clearly have issues below 1k regardless of which of my two horns they're mounted to.
OK, didn't know that. 511B's are spec'd at 500hz, but suppose that doesn't mean much - with what driver? at what slope?
Don't think my woofs will wanna go to 1k smoothly, think I need to ditch the altecs. Have any recommendations for modestly priced driver I could mount to my original Jensen horns? Horns are threaded, but I already have 1" adapters if needed. Original Jensen specs call for 600Hz - 4kHz.
Altec crossed 802 B drivers at 500 Hz .I have 288c 1.4" and they are really much happier at 800-1 kHz than at 500 Hz and its a big driver
The 909 spec sheet calls for 1,200 hz to 5,000 hz. You are expecting WAY too much from that driver.
http://greatplainsaudio.com/wp-content/uploads/2016/06/909series.pdf
http://greatplainsaudio.com/wp-content/uploads/2016/06/909series.pdf
fwiw - here's a cheap phenolic diaphragm driver on a 511b - no baffle. That horn works fine as a midhorn for 3-way Klipsch setups
Yes, my experience has shown that I'm expecting way too much from this driver - that's why I'm asking for advice seeking a new driver. That being said, I'm guessing you didn't read the pdf you referenced too well? Quoting from the "ARCHITECT’S AND ENGINEERS SPECIFICATIONS":
"Frequency Response:uniform from 500 - 20,000 Hz"
Either way, I know better than to expect all speaker specs to be actual, and the intent of my post wasn't to dis GPA, but to get steered towards a driver better suited to my needs (best bang for buck that covers 600Hz - 4kHz).
Here is a response I got on another forum:
Below 1k the 511 doesn't provide enough/proper acoustic load for the 1 inch Altec drivers.
The only factory Altec speaker systems(1233C, 1235C, 1236C, and the last runs of slapped together model 19's, but they're another story completely) that mounted a ferrite driver on a 511 were de-refined sound reinforcement systems with 1.2khz XO's at the time Altec was under the same parent ownership as Electrovoice, and the EV engineers were essentially trying to put the Altec brand in it's grave. The earlier versions of these models used alnico 808's crossed at 800hz and genuine Altec woofers, they'd play at nearly the same SPL's while sounding much better doing it.
Further, the small format ferrite drivers from Altec(which the GPA driver is a close facsimile of, but NOT exact copy) all exhibit a frequency response that is shifted upward nearly an octave from their alnico predecessors. GPA 902 uses a different phase plug than the original Altec 902.
In a nutshell, the newer style ferrite Altec drivers don't belong on a 511. The throats don't even match with a 902 as it has a 7/8 inch aperture while the 511 and 811 throats are a nice even 1 inch.
First choice for a small format mid driver from Altec would be an 808-8A with the original symbiotik diaphragm.
Below 1k the 511 doesn't provide enough/proper acoustic load for the 1 inch Altec drivers.
The only factory Altec speaker systems(1233C, 1235C, 1236C, and the last runs of slapped together model 19's, but they're another story completely) that mounted a ferrite driver on a 511 were de-refined sound reinforcement systems with 1.2khz XO's at the time Altec was under the same parent ownership as Electrovoice, and the EV engineers were essentially trying to put the Altec brand in it's grave. The earlier versions of these models used alnico 808's crossed at 800hz and genuine Altec woofers, they'd play at nearly the same SPL's while sounding much better doing it.
Further, the small format ferrite drivers from Altec(which the GPA driver is a close facsimile of, but NOT exact copy) all exhibit a frequency response that is shifted upward nearly an octave from their alnico predecessors. GPA 902 uses a different phase plug than the original Altec 902.
In a nutshell, the newer style ferrite Altec drivers don't belong on a 511. The throats don't even match with a 902 as it has a 7/8 inch aperture while the 511 and 811 throats are a nice even 1 inch.
First choice for a small format mid driver from Altec would be an 808-8A with the original symbiotik diaphragm.
Thanks a lot for that. I just posted a quote from another forum where guy says below 1k the 511 doesn't provide enough/proper acoustic load for the 1 inch Altec drivers. So, I was specifically wondering if 511 might get near mark with smaller magneted (typically cheaper) drivers.
The driver you've charted is discontinued, but its replacement, Selenium D250-X, seems to be a popular choice. Do you (or anyone else) have a standout favorite among inexpensive drivers? Could probably afford up to $100/driver...
For the last 30 years or so my living room has had build-in speakers flanking the fireplace with old Altec 15" woofers and 511b horns (plus a tweeter horn). An original 808-8A proved ratty under tone sweeps and they weren't growing on trees back then either. I bought a pair of Peavey drivers and screw-on adapters at a now-defunct music shop. I don't recall the model # offhand for a couple of reasons, the first being that I knew years ago they were no longer available, the second being that I've never had reason to change them. I cross the horns at 450hz (18db/oct, the horn unloads at 400hz I believe) through a diy (of course) active xover I made at about the same time, and cross over to the tweeter at 4500hz. The 511s are as clear and clean as anything I've heard. If I somehow managed to blow the drivers (and I've tried, inadvertently) I would go first to the Peavey catalogue, though truth be told I find that many modern compression drivers seem to be more durable than their venerable and far more expensive (original price in real dollars) predecessors.
It does. 😉 Only for high power apps, then really needs 1200 Hz, hence the limited 1200 - 5000 Hz test BW for high speech intelligibility.
GM
The Selenium D250-X is a potential solution for a driver to use with your Jensen horn and is inexpensive. Spec wise, it should cover 600-4K Hz. It's a 1 inch threaded driver with a phenolic diaphragm. I have no experience with it to know how it might sound.
Last edited: