Altec 511B horn compared to the GPA MR931

[Alien_Shore]

Why would you measure below 300hz? Seems like it would be easy to damage them.
Can you detail your test setup for us?
And, because I'm lazy, what is the MR931? The little guy used on the model 14?
Edit: I went and looked...I never did like those.
I have a pair of MR994 that I like quite well but have never really built into a system for critical evaluation. Small format 500hz, they are huge!
Ron

Bear in mind, I'm an utter noob with measuring, but I really am interested in getting better and putting up some more quantitative info about Altec gear (I'm inspired by the work of Zilch, Earl, Vin, and others here). Taking some advice I've received, I did a full-sweep with low SPL to avoid any damage.

My test setup is pretty simple:
ECM-8000 $55
Blue Icicle USB preamp $40
Creative Labs SB1095 X-fi Pro USB external sound card $60 (this has a highly rated DAC for the money and doubles as a great replacement for my crappy laptop integrated sound)
Old laptop w/ windows XP
Mic Stand $20
XLR Mic cable $4
Holm Impulse Free
Mic and pre-amp calibration by CSL $75 (includes off-axis and polar response measurements)

I did the measurements with no filters inline whatsoever, just the test rig hooked up to an old Onkyo SS amp and straight to the 902.

Thanks for the plots, very nice reference.

As a long time user of HOLMImpulse here are some tips to give you cleaner results:

• Keep the volume up. It looks like you are not running these very loud, at least not compared to the noise floor. You want a good S/N ratio.
• Use the high pass filter. If you look down just to the left of the impulse window, you'll see High Pass and Low Pass filters. For horns and drivers, a 200Hz HP is a good idea. No low frequencies going into the driver and HOLM won't pick up junk down there
• You can start your sweep at 100Hz or higher. That's in the first tab. It's handy, but the high pass filter is the real tool you need.

I'm a little surprised to see how similar at least two of plots are. That's encouraging.

Thanks Pano - I'll use your tips to rework a couple of the measurements. The pre-amp I'm currently using is pretty much useless below 100Hz anyway. I welcome and appreciate any other tips - I have done a ton of reading, but again, pretty new at this. I had used the filters in Holm on an earlier set of measurements on my M14s, and will try that again. It's probably best to also use a series cap to protect the driver if I up the SPL. I probably won't pull the 511 down from the garage - it's a heavy bugger to carry up there to my man cave

Earl - thanks for posting those graphs and the link to your gallery - there's some great info in there I've not seen yet. I will definitely be looking through that in some detail.

Edit: Here's an updated measurement. This is from the same driver; OEM 902 (PN 34635), manufactured in May 1980, with the original diaphragm (PN 34647). For these two measurements, I adjusted the sweep range to start at 100 Hz, added a Hi-Pass electronic filter (200 Hz) in Holm, and added a 49uF cap in series. I cranked up the SPL considerably and plotted the graph using 2dB amplitude scale.

[RonSSS]

Good work Mike. This is how we learn!
Too bad you don't have a 511 and a MR994 to throw that driver on.

Ron

[theophile]

That addition to your last post is interesting.

It shows me why Altec crossed the 416 over at 1200Hz in the Model 19. It also shows me why I cant put a 902 into my Valencia at the 800Hz crossover point.

[RonSSS]

I'm confused. The 902 does fine at 800hz on the 811 horn. Scale is 2dB/div. It doesn't look so hot at 800hz on the MR931, but that is a 1500hz horn.
There is no data here for an 802. So ?????

Ron

That addition to your last post is interesting.

It shows me why Altec crossed the 416 over at 1200Hz in the Model 19. It also shows me why I cant put a 902 into my Valencia at the 800Hz crossover point.

[theophile]

Well to my eye, on that graph the response at 800Hz is 5dB down from approx 1200Hz on the 811. If I was using a 902(which I have the GPA version of), I wouldn't put it on the Valencia using the 811 and the conventional Valencia 800Hz XO point. With an active crossover (like I use) it is a simple matter of adjusting the XO point and getting the output levels to blend with the 416Z. I wouldn't cross over at 800, given what I see in that graph. I'd be more inclined to use the 1200Hz crossover point that the Model 19 used.

Does that explain my statement, to you? That's my reasoning anywho.

[RonSSS]

If an 802/6 were measured and on the same graph and showed 5dB better at those frequencies, then yes, I would agree.
I suspect however that an 802/6 would look quite similar.
Remember that the model 19 used both 902 and 802 drivers depending on the year produced.
I think Altec switched to 1200 hz to keep the frams from blowing up. I may be wrong.

Ron


QUOTE=theophile;1841402]Well to my eye, on that graph the response at 800Hz is 5dB down from approx 1200Hz on the 811. If I was using a 902(which I have the GPA version of), I wouldn't put it on the Valencia using the 811 and the conventional Valencia 800Hz XO point. With an active crossover (like I use) it is a simple matter of adjusting the XO point and getting the output levels to blend with the 416Z. I wouldn't cross over at 800, given what I see in that graph. I'd be more inclined to use the 1200Hz crossover point that the Model 19 used.

Does that explain my statement, to you? That's my reasoning anywho.[/QUOTE]

[Old Guy]

Frams blowing weren't so much an issue in HiFi. Live, yes. The 902 is a lighter driver, so is gonna resonate. I am speaking of the driver body, at lower freqs. The lower you cross any small Altecs, the less loudly you can play them. The heavier 802 does better than 806 and 900's. At 500 I REALLY suggest large format.

[GM]

Or use dual 802s which yields more performance overall at less cost.

GM

[Alien_Shore]

I went by my storage shed and grabbed a 511b - ran a few more tests. These are all using the same 902 driver, on-axis, at 1m. Compares MR931 (blue), 811b (green), and 511b (red):

[Panomaniac]

Thanks for the graph. Kinda unexpected. I'd have guessed the plots for the 511 & 811 the other way, Hmmm....