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Multi-Way Conventional loudspeakers with crossovers

Rod Elliot's test box for impedance flattening - starting point?
Rod Elliot's test box for impedance flattening - starting point?
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Old 16th April 2018, 06:55 PM   #1
KVSV is offline KVSV  United Kingdom
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Default Rod Elliot's test box for impedance flattening - starting point?

Hi,

Started on my first two-way project (SB12PFC25-4 + SB19ST-C000-4 in a 7L vented box).

I just built Rod Elliot's "test box": Loudspeaker Test Box

As he describes it "No maths, no spreadsheets, just a quick frequency scan and twiddle a couple of knobs to get the values needed".

First I need something to generate a sweep. I found this tutorial by Claudio Negro (Claudio Negro's home page, how to project and test a loudspeaker using Speaker Workshop) which I guess I can follow not only to generate a sweep but also to capture impedance graph. Is it a good option or there is an easier one?

Second question is where to start with cap/resistance knobs. I think there are way too many combination for the process to be be "quick". Any suggestions for the initial settings for the knobs? Should I use some online calculator, and then twiddle a bit to see how it affects the curve?

Third question. Is it actually worth doing it? Can I just measure impedance curve and frequency response and then model zobel and crossover in XSim?

Oh, and one last question! Should I measure impedance in free air or in a box?. Basically should I build test box close to final dimensions before attempting to measure?

thanks

Vladimir
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Old 16th April 2018, 07:46 PM   #2
eriksquires is offline eriksquires  United States
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Third question is most important.

No, not worth doing.

For T/S values, use free air. This is what you use for box design.

For impedance, you should design your crossover with the in-box measurements, but for tweeters and sealed midrange drivers this is essentially the same as free-air. This is part of what you will need for crossover design.

If you wish to buy, DATS or OmniMic+DATS is a great choice. Otherwise, you can use Room EQ Wizard with a home made jig to get the necessary measurements.

Best,


E
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Old 16th April 2018, 07:58 PM   #3
KVSV is offline KVSV  United Kingdom
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Thank you Erik. I didn't realise REW can measure impedance. Will start building boxes and will try measuring impedance and frequency response with REW. Might also try to work out crossovers using AllenB tutorial as an alternative approach.
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Old 17th April 2018, 04:05 AM   #4
eriksquires is offline eriksquires  United States
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More on REW and impedance:

Impedance Measurement
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