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Old 8th November 2010, 05:14 PM   #1
Kilroy is offline Kilroy  United States
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Default Designing enclosures for vintage drivers: Tests?

I recently picked up some vintage 15" drivers and 1" horns made by Oxford in the 50s or 60s. I have no idea what the specs are for them, but I liked how they sounded.
My original idea was to use them as a cheap way to mess around with Altec FLH or Onken designs. But the more I listen to them the more I like the sound... Only, I'm starting to think they may not be right the designs I had in mind.

To compound the problem, I've never built an enclosure for an unpublished speaker before and most of my builds I simply tuned to ear, using my little B&W bookshelfs as a goal. So I have no idea how to test speakers or how to interpret the results. And from reading through the forums, it seems like the value of much of the testing is up for debate.

So I'll put it to you... How should I proceed? What tests do I need to run on the drivers to determine what enclosure they are best suited to? What tools do I need?

All I know so far is that they're all between 6.7 and 6.9 ohms.

Thanks!
-Phil
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Old 8th November 2010, 10:14 PM   #2
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To measure drivers: Download ARTA: ARTA ARTA Download, Make this simple jig: ARTA Jig - AudioBlog: A simple loudspeaker measurement jig for ARTA
]
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Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency

Last edited by PeteMcK; 8th November 2010 at 10:17 PM.
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Old 8th November 2010, 10:38 PM   #3
Kilroy is offline Kilroy  United States
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Quote:
Originally Posted by PeteMcK View Post
To measure drivers: Download ARTA: ARTA ARTA Download, Make this simple jig: ARTA Jig - AudioBlog: A simple loudspeaker measurement jig for ARTA
]
Thanks!
I think I have most of that stuff lying around.
And judging from the parameters it can provide, that might be good enough to sim designs, then.

-Phil
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Old 10th November 2010, 08:56 PM   #4
Kilroy is offline Kilroy  United States
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Quote:
Originally Posted by PeteMcK View Post
To measure drivers: Download ARTA: ARTA ARTA Download, Make this simple jig: ARTA Jig - AudioBlog: A simple loudspeaker measurement jig for ARTA
]
OK, I made the jig and ran the test...
Here's the result.

What am I doing wrong?
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Old 10th November 2010, 11:51 PM   #5
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Setup is important - check you've got the correct in/out jack selected; make sure you've calibrated, and check the calibrate/measure switch is in the correct position....
(made all those mistakes...:-)
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Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency
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Old 11th November 2010, 12:41 AM   #6
Kilroy is offline Kilroy  United States
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Default Artas Limp graph? Closer?

Here's the latest graph...

I think I'm getting closer but this is supposed to be a relatively smooth curve right?
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Old 11th November 2010, 02:25 AM   #7
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re:'this is supposed to be a relatively smooth curve right?' - yep, might have to double check the wiring of your jig...; another setup thing to check, that you have set the value of the calibration resistor
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Old 11th November 2010, 04:37 AM   #8
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You should get something like this (done with Fuzzmeasure on a Mac)

dave
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Old 11th November 2010, 06:02 AM   #9
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There are two different basic curves.

An impedance curve shoves some kind of voltage through the speakers then measures the current. This could be with a sine wave or with a noise waveform depending on the analyzer. The output from the analyzer connects to the speaker electrically, directly or via an amplifier. Another set of leads goes directly into the analyzer. There is no microphone in this setup. Then you should get a curve like planet10 posted.

An SPL curve measures the sound pressure at each frequency. The amp runs the speaker with a sine wave or noise, the microphone picks up the signal and measures it.

I'm not familiar with ARTA; you might want to make a new thread "ARTA questions."

If you had a MLSSA noise-signal system, I would say your curves could be any of:
- Something disconnected
- Microphone is not powered (if it needs power), or microphone preamp is off.
- Time gating is off. Most systems have a noise gating function to eliminate/reduce reflections out of the measurement. But if the gating is too early or too late, you don't get any actual sound.
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Old 11th November 2010, 06:13 AM   #10
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From Pete's post#2 we are trying to measure impedance calculate parameters.

dave
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