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Multi-Way Conventional loudspeakers with crossovers

Some basic FR measurements
Some basic FR measurements
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Old 23rd January 2013, 08:35 AM   #11
wintermute is offline wintermute  Australia
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Some basic FR measurements
I use holmimpulse HOLM Acoustics for gated measurements and REW REW - Room EQ Wizard Home Page for doing pink noise (with RTA) in room measurements (also great for measuring impedance curves)

I like your thinking with using audacity, but I think that using REW with pink noise and some averaging in the RTA you will probably get a better in room representation.

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Old 23rd January 2013, 12:39 PM   #12
Alex M is offline Alex M  Europe
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Thanks for the helpful suggestions.

I still can't see any obvious source for reflection at that distance. I wondered whether it might be a front-back reflection inside the mid-treble cabinet, since the boxes are about 35cm front to back, and the ultra-lightweight HDA midrange cone is notorious for passing the reflected backwave. However the tweeter is closed at the back, and the crossover is at about 3.2 kHz, so you wouldn't expect any substantial internal echoes at higher frequencies than that. I will try measuring with the speakers further away from the walls, just to see.

Yes, I see that "size" in Audacity defaults to 512 - a quick test reveals that increasing this extends the bass response accordingly, but I haven't repeated my measurements with this setting.

I am definitely feeding my amp white noise: it is track 65 of the Hi-Fi News Test CD, marked "white noise". Pink noise sounds like a waterfall, instead of the "hiss" I hear with this track.

It had indeed occurred to me to measure the drivers individually with and without the crossover, to test whether they (the mid in particular) are working consistently with the published specs.

I will also measure with a different (solid state) amplifier to eliminate my 300B amp as a possible cause of the HF rolloff.

Finally I will investigate other software packages. Holm appears not to be available for a Mac, but I will try REW.


Last edited by Alex M; 23rd January 2013 at 12:41 PM.
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Old 23rd January 2013, 04:20 PM   #13
speaker dave is offline speaker dave  United States
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There are definitely strong reflections going on, as evidenced by the periodic ripple. The lower curve is worse and the 6dB peak to trough indicates that the reflection strength is about 1/3rd the direct sound strength. It could also be a reflection at the microphone end. What is your mic support/stand like?

White noise is correct for this type of analyzer.

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Old 23rd January 2013, 09:35 PM   #14
Alex M is offline Alex M  Europe
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I've now installed REW on my MacBook, and started to have a look through the comprehensive manual and FAQ. There are instructions for using an SPL meter to calibrate a microphone, which reminded me that I have an old RS analogue SPL meter (modded as per Eric Walin's instructions), which I dusted off after ten years in storage and put new batteries in. I had forgotten that it also has a fixing for a camera tripod, which I had never used, but might well be handy.

I'll experiment and report back!

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Old 25th January 2013, 08:14 AM   #15
Alex M is offline Alex M  Europe
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I think I have solved the reflection issue. I re-did the measurements on one of the speakers using the RS analogue SPL meter instead of my homebrew microphone, and used a higher data length for the FFT in Audacity, and got the result below, which looks much more encouraging: I don't see the ~800Hz repeat at all.

The mic I was using before consisted of the Panasonic capsule in the end of a 30cm plastic tube, which was wrapped in tape to suppress vibrations: my feeling is that the reflections occurred along the interior length of the tube (possibly through the cable), and would have been relatively undamped at high frequencies.

The overall response is much smoother through the midband too. I will experiment with REW over the next few days to try to improve the measurements.

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