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Thread: What measurements matter to you?

  1. #11
    Big Daddy Chad's Avatar
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    There is a lot to be said about a MATCHED set of preamps (tits on) that has a tight tolerance between channels..... and a polarity swap.... and a set of ears.

    It's not "Science" but you can HEAR what's "not."

    Especially when it shits the bed, it's unique to hear a "difference" in the cumzinta versus the goezouta sans gain.

    It's how we test/build mic preamps.

  2. #12
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    Along the lines of what cvjoint said, I'd be more interested in evaluating the real output capabilities of drivers. We all know that when we push speakers beyond their limits, this is where the bulk of the distortion and nonlinearities come from (relatively speaking). But what measure do we use to determine where those "limits" are? Most people simply judge xmax, and compute how much power can be delivered before you exceed it (and sometimes, but not often, compute output levels). But it's not often that people outright test the thermal capabilities of drivers, and how they affect responsivity.

    So I echo cvjoint's points about:
    1) power compression measurements to determine:
    .. a) output attenuation
    .. b) FR
    2) thermal power handling capabilities (for cheap drivers, anyway ;) )
    3) distortion performance as a function of output (I'd be interested in comparing underhung/overhung technologies... I'm sure this has been done...)

    It also seems to me that some polar measurements could be useful for a lot of cases where more sophisticated dispersion techniques are used. I'm still not sure there's a consensus on that, and I'm sick of looking at FR plots with two data points. Once upon a time, Andy W provided real polar plots for some driver, I forget...
    Last edited by MarkZ; 09-22-2011 at 03:15 PM.

  3. #13
    Founding Member Subwoofery's Avatar
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    Quote Originally Posted by MarkZ View Post
    Along the lines of what cvjoint said, I'd be more interested in evaluating the real output capabilities of drivers. We all know that when we push speakers beyond their limits, this is where the bulk of the distortion and nonlinearities come from (relatively speaking). But what measure do we use to determine where those "limits" are? Most people simply judge xmax, and compute how much power can be delivered before you exceed it (and sometimes, but not often, compute output levels). But it's not often that people outright test the thermal capabilities of drivers, and how they affect responsivity.

    So I echo cvjoint's points about:
    1) power compression measurements to determine:
    a) output attenuation
    b) FR
    2) thermal power handling capabilities (for cheap drivers, anyway ;) )
    3) distortion performance as a function of output (I'd be interested in comparing underhung/overhung technologies... I'm sure this has been done...)

    It also seems to me that some polar measurements could be useful for a lot of cases where more sophisticated dispersion techniques are used. I'm still not sure there's a consensus on that, and I'm sick of looking at FR plots with two data points. Once upon a time, Andy W provided real polar plots for some driver, I forget...
    You're looking for some 3D ACTION I suppose... :p

    Kelvin

  4. #14
    Tester Extraordinaire ErinH's Avatar
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    HD at intervals will tell you a speakers performance in relation to nominal and max levels. FR won't show a change in response by default (linear distortion). I tested this myself multiple times. The only difference I ever had was the output level tested. As far as polars, I still haven't seen a valid reason why it's needed for us folks in car audio. I think the basic FR and HD testing suffice. We understand the implications of that data. IMO more than that broaches unnecessary. if you add IMD to the testing, though, I think you've got a very well rounded test.
    Your ears: The best tools you have... and they're free, too!

  5. #15
    Tester Extraordinaire ErinH's Avatar
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    I'll also be happy to klippel every driver Adam tests. that was my original goal and I think Dickason's approach of doing that is a solid one. That way you have real driver parameters in addition to linear and nonlinear dolistortion measurements.

    And again, while it's nice to toss out ideas, let's be practical about why we want. It takes a while to test drivers and report the data. As a favor to the person testing, consider just how much info you really need to make your purchase decision.
    This is where I think education really comes in to play. If we understand what the data means, we'll have a better grip on just what we need for it to be useful and what might be considered overkill. Time/value aspect, I suppose.
    Last edited by ErinH; 09-22-2011 at 05:03 PM.
    Your ears: The best tools you have... and they're free, too!

  6. #16
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    Quote Originally Posted by ErinH View Post
    HD at intervals will tell you a speakers performance in relation to nominal and max levels. FR won't show a change in response by default (linear distortion). I tested this myself multiple times.
    This is surprising. Increase R while not modulating L and C (much), and the electrical filter parameters of the speaker should change. Alternatively, change L (depending on the motor), and the same thing would happen.

    The only difference I ever had was the output level tested. As far as polars, I still haven't seen a valid reason why it's needed for us folks in car audio.
    Why isn't it useful?

  7. #17
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    Quote Originally Posted by Subwoofery View Post
    You're looking for some 3D ACTION I suppose... :p

    Kelvin
    Sounds hot.

    Thinking more about polar plots binned across different freq bands (only some bands would show directivity, and so this can first be established using the routine ways...).

    Or yeah, hot 3D action.

  8. #18
    Tester Extraordinaire ErinH's Avatar
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    Quote Originally Posted by MarkZ View Post
    This is surprising. Increase R while not modulating L and C (much), and the electrical filter parameters of the speaker should change. Alternatively, change L (depending on the motor), and the same thing would happen.
    I tested mine at some pretty wicked levels and never noticed a change in FR. However, I wasn't viewing the scale at 1dB; typically it was 3dB scale. If there were changes, they had to have been subtle. I've never seen discussion or anyone stating that FR is dependent on volume. I'm not going to say there certainly isn't... I'm saying if there is, I'm not aware of it and my tests, ranging from 85dB to 105dB (in some extreme cases) never showed this.


    Quote Originally Posted by MarkZ View Post
    Why isn't it useful?
    Alright, maybe useful is a relative term. To me, though, for car application, it's just not useful enough for me to ask Adam to go through the lengthy process of creating it. I thik as a science project it'd be cool to see, but to take the time to accurately measure the response at such small increments (imagine 5* increments would be pertinent; any less and the curve fitting wouldn't be as accurate) isn't really worth it to me. I can get a good idea of what I want to know from FR; beaming, ringing, response off-axis, etc...
    Of course one can easily reply "well, if your stance is the car makes it moot, then why bother with FR" and that's a valid reply. My reply to that would simply be that some sort of FR curve is useful to me to get the aforementioned characteristics which will help me to determine in what bandwidth I can expect to play the driver in. I'm not as concerned about the incremental changes between 0 to 60*. I'd rather Adam focus his efforts on the other tests.
    That reply is based on my own initial desire to provide polars. After a few goes at it, I didn't find it worth the trouble.
    Your ears: The best tools you have... and they're free, too!

  9. #19
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    Quote Originally Posted by ErinH View Post
    I tested mine at some pretty wicked levels and never noticed a change in FR. However, I wasn't viewing the scale at 1dB; typically it was 3dB scale. If there were changes, they had to have been subtle. I've never seen discussion or anyone stating that FR is dependent on volume. I'm not going to say there certainly isn't... I'm saying if there is, I'm not aware of it and my tests, ranging from 85dB to 105dB (in some extreme cases) never showed this.
    Yeah, I'm trying to figure out why they weren't there. Did you make power compression or inductance (v. power) measurements in these drivers as well? Those would be the two major culprits responsible, it would seem. So, it would be something that would be prominent in speakers that exhibited large swings in those parameters.

    Alright, maybe useful is a relative term. To me, though, for car application, it's just not useful enough for me to ask Adam to go through the lengthy process of creating it. I thik as a science project it'd be cool to see, but to take the time to accurately measure the response at such small increments (imagine 5* increments would be pertinent; any less and the curve fitting wouldn't be as accurate) isn't really worth it to me. I can get a good idea of what I want to know from FR; beaming, ringing, response off-axis, etc...
    Of course one can easily reply "well, if your stance is the car makes it moot, then why bother with FR" and that's a valid reply. My reply to that would simply be that some sort of FR curve is useful to me to get the aforementioned characteristics which will help me to determine in what bandwidth I can expect to play the driver in. I'm not as concerned about the incremental changes between 0 to 60*. I'd rather Adam focus his efforts on the other tests.
    That reply is based on my own initial desire to provide polars. After a few goes at it, I didn't find it worth the trouble.
    Fair enough, but I don't think 5 degree increments would be necessary at all. I was thinking more along the lines of ~22.5 (I'd actually probably do a logarithmic scale with ~1.2 multiplier, off the top of my head). The point is to get an accurate picture of the off-axis response profile, which I think can be difficult to reconstruct with only two points.

    In terms of investment -- you're the expert here, so tell me if this is practical -- but an array of mics in set positions feeding a multichannel acquisition board would seem to me to reduce the issue of it being a PITA to record. The money spent would be on mics, but I can think of a couple other uses for that as well. I just don't know how much individual adjustment would be required after the initial rig is built.

  10. #20
    Devil's Advocate Adam_MSS's Avatar
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    Does measurement software exist that allow simultaneous capture from multiple mics?
    You don't use science to show that you're right, you use science to become right. - R.Munroe

    The important thing in science is not so much to obtain new facts as to discover new ways of thinking about them. - W.L.Bragg



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