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Old 7th April 2014, 11:57 PM   #41
xrk971 is online now xrk971  United States
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GM,
I think I was referring to amplitude ratios while you are referring to power ratios which is square of amplitude as P=V^2/R?

In amplitude signal world dB = 20 log(Vhigh/Vlow)

Last edited by xrk971; 7th April 2014 at 11:59 PM.
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Old 8th April 2014, 12:09 AM   #42
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BMS,
I wonder if rectilinear cabinets tend to have more of a problem with internal reflections. In my curvy walled DCR, the impulse looks pretty clean and free of reflections. Not a A7.3 but here to demonstrate effect of non rectilinear walls on IR.

Click the image to open in full size.

And here is same driver IR in an open baffle.

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Old 8th April 2014, 02:04 AM   #43
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In my experience the only way a cabinet tends to mar a drivers distortion performance is if the rear of the cone is extremely covered up by the cabinet. If it's free to breathe then the box wont typically cause any issues.

Normally though, if box resonances or reflections are the culprit they tend to show up only at specific frequencies, rather than being broadband. They also show up in the impedance plot as wiggles or bumps, deviating from what you'd expect from a purely inductive rise. Of course you'd need to compare the driver measured in free air vs in the cabinet to see if any bumps were showing up. Full range drivers typically display a number of these anyway as exploiting resonances is inherent to their design as a way of extending the high frequency response. Getting this effect comes at a price though because lightening the cone causes it to be less pistonic further down in the midrange, so you get issues occurring there too. Now full range drivers aren't the only ones that succumb to these mid band resonances, as other heavier soft cones do too. Heavy, very rigid cones, like the SEAS excel drivers, are completely free from any resonances, except of course for their bell mode resonance high up in frequency.

Nevertheless, if you wanted to pin box resonances/reflections on the problem, you'd need to make sure the bumps you were seeing in the impedance were actually being caused by the box and not the driver.

The dip encountered at 1.2kHz is unlikely to be box related as this is present in Mark's own measurements, but the box could quite easily be designed to reduce its effect. 1.2kHz is smack bang in the frequency range where the primary diffraction peak can show up for cabinets with the range of widths we're talking about using with these drivers. If you designed the width accordingly it would compensate quite nicely for the inherent dip. Also some internal cabinet reflections/resonances could help to reduce its effect too, or make it worse, but this would be incredibly unpredictable and getting the compensatory effect from cabinet diffraction would be a much better choice - this could explain why some peoples measurements present with the dip and some don't.

In any case the simplest way to confirm measurements, one way or another, would be to get a 50x50cm baffle of MDF, flush mount the driver in the centre of it, chamfer the rear of the cut out and do some gated far field measurements in a properly configured room (ie one that's had all reflective surfaces from furniture etc removed). I would also suggest using STEPS to perform distortion measurements, that is rather than swept sine stimuli as it tends to give better end results.

Yes the 50cm baffle wont be large enough to give low end accuracy and no doubt your room wont be either. But it should be good enough to satisfy anyone's doubts as to the measurements usability from around 400Hz and up.
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Old 8th April 2014, 01:59 PM   #44
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Quote:
Originally Posted by xrk971 View Post
GM,
I think I was referring to amplitude ratios while you are referring to power ratios which is square of amplitude as P=V^2/R?

In amplitude signal world dB = 20 log(Vhigh/Vlow)
What I posted are power ratios, yours are voltage ratios, so must be converted back to power ratios for response plots as I understand such things.

GM
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Old 9th April 2014, 07:30 PM   #45
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Something about mesurments, it isn't that simple!

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Old 9th April 2014, 07:52 PM   #46
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gee, if we were looking for something simple and absolute, we probably need to find another hobby
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Old 9th April 2014, 08:02 PM   #47
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That's why I have two hobbies. Speakers and drinking. If one isn't working at the moment, the other probably will. See? It's not that hard.
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Old 9th April 2014, 08:08 PM   #48
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yes, of course, the second one does easily encompass Absoluts - nicely done Cal
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Old 10th April 2014, 12:22 PM   #49
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Originally Posted by pk2carlos View Post
Something about mesurments, it isn't that simple!

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True. I haven't measured my MA A5, and I'm not slighting the brand either, BUT mine exhibit an AUDIBLE resonance at almost exactly 400hz, which isn't obvious on the published specs.

These plots could be inaccurate, hesitant to say that.

OR the resonance isn't easily found through a FR plot alone.

There is alot a measure excludes as well as the info it shows
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Old 10th April 2014, 01:10 PM   #50
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Originally Posted by tuxedocivic View Post

Click the image to open in full size.
What was exact measurement conditions? Did you merge near and far field data?
Gating and so on?
Is this only one automated gating and no near field splice?

Measuring Mark Audio Alpair-10 gen-2
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