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Thread: Differences between compression drivers

  1. #46
    Senior Member pos's Avatar
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    Quote Originally Posted by Robh3606 View Post
    Hello pos

    Do you know what software or tools he was talking about? I have always been curious why HOM's are not lets say obvious in Group Delay and CSD plots.

    Unless of course they are there but are difficult to see. Like the Step vs Impulse where the Step is easier to see actual delay between the drivers.

    If I remember he uses Mathlab? And he has several applications he developed like his polar maps as an example.
    Hi Rob

    I wouldn't know! I have never seen those elusive HOMs myself.
    The M2 waveguide is surely packed with those, so much so that they stop being a problem in the end

    Funny to think that Earl Geddes took two opposed routes for dealing with HF and LF problems: trying to suppress any defect for the HF (and ending up with a big one on axis, that he deemed irrelevant in his preferred listening scenario) while trying to mix and compensate different modes together with his multi sub approach in LF.
    The M2/sub18 system is the exact opposite

    I guess both approaches can work, as well as many others probably, as long as the system is coherent and well thought out.
    I think the same goes for measurements: you can look at them in many different ways and representations, but this is still the same info. No need to fight over this.

  2. #47
    Senior Member pos's Avatar
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    Quote Originally Posted by 1audiohack View Post
    If recall correctly Dr Geddes has interest in the phase relationship of the higher harmonics with the fundamentals? I do. This is where for instance if a diaphragm is ringing, the sound is no longer correlated with the fundamental and is just noise. This is what we see with the diamond surround drivers. The extra HF is not signal correlated, its energy seen in many frequency domain measurements is energy dispersed in the time domain.
    Oh I see, interesting!
    Is there any specific representation he is using for that?

  3. #48
    Administrator Robh3606's Avatar
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    Quote Originally Posted by pos View Post
    Oh I see, interesting!
    Is there any specific representation he is using for that?
    Hello Pos Barry

    I remember Wavelets used in the Truextent PDF. I was looking at CSDs and Wavelets to look for correlation's and differences.

    https://www.audioheritage.org/vbulle...mat-Diaphragms

    Here are the plots Ribbed Ti Smooth Ti Aluminum and Berylium

    Also Joseph Crowe reviews

    https://josephcrowe.com/blogs/news/1...er-test-review

    Looking at Wavelets they seem to highlight the resonances better than the CSD's

    Rob
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  4. #49
    Senior Member pos's Avatar
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    Quote Originally Posted by Robh3606 View Post
    I remember Wavelets used in the Truextent PDF. I was looking at CSDs and Wavelets to look for correlation's and differences.
    Hi Rob

    Oh ok, I read Barry's comment wrong and thought he was talking about harmonic distortion. It appears it was just the HF itself.
    Sorry for the confusion.

  5. #50
    Administrator Robh3606's Avatar
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    Hello pos

    I did as well he mentions Geede's Metric and assumed it was the distortion metric. I thought his second post was a new topic. I sure when he see's this he will clarify,

    Rob
    "I could be arguing in my spare time"

  6. #51
    Senior Member 1audiohack's Avatar
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    Hello guys;

    I am re-reading a couple of Dr Geddes’ papers to refresh my memory as it has been a decade or more since I last read them. I am pretty fuzzy on exactly how his metric scores a device.

    Very basically it says all distortions are not equally egregious to our perceived sound quality and some distortions become more unpleasant to our perception with increased SPL. An example (mine and not to be construed as certain) could be that second harmonic is not even noticeable until say 6% and carries a very low score with increased SPL but diffraction which may be inaudible at low SPL becomes very objectionable at high SPL would carry a much higher score in the metric.

    I will come back with a better understanding of this metric after some reading. GedLee.com has all of his papers for reading if you are interested.

    As I said before, a metric like this is a step forward in the attempt to measure the “why this one sounds better than that one despite what some of our normal measurements tell us”.

    I think that’s the essence of this thread yeah?

    Thanks all.
    Barry.
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  7. #52
    Senior Member pos's Avatar
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    Earl Geddes did bring a lot of interesting topics to the table for sure!
    One I find very interesting is the instantaneous thermal compression that he classifies as a distortion, calling it "thermal distortion".

    Although the 2.7sec he is using is way too long to fit Earl Geddes' definition, Erin's "Instantaneous Compression Test" is pretty discerning already:
    M2: https://www.erinsaudiocorner.com/lou...mpression-test
    708p: https://www.erinsaudiocorner.com/lou...mpression-test
    305p: https://www.erinsaudiocorner.com/lou...mpression-test

    That is an area where compression drivers and big woofers do shine

  8. #53
    Administrator Robh3606's Avatar
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    Hello pos

    I found his thermal distortion interesting as well.

    Those are interesting plots! I have a pair of 308 Mk 2 that I have next to my passive M2's and they definitely run out of gas. They don't obviously break-up they just compress like a limiter.

    Agree lively is the way to go!

    Rob
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  9. #54
    Senior Member pos's Avatar
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    Quote Originally Posted by Robh3606 View Post
    Those are interesting plots! I have a pair of 308 Mk 2 that I have next to my passive M2's and they definitely run out of gas. They don't obviously break-up they just compress like a limiter.
    Indeed, on Erin's measurement you can see that the 305p has a limiter set somewhere between 96 and 102dB SPL at 1m, as the 102dB SPL curve is buried down low.
    I bet the 308p can go a few dB higher.

    I'd be curious to see similar measurements for the LSR32 as its woofer has an integrated brake system.
    But that is utterly off topic, sorry for the digression

    Back on the topic of compression drivers, did you ever measure a difference between the different 1.5" cores?
    When I compared a few of these 12 years ago I remember that the 2452 core sounded way worse to my hears compared to the 2450SL one (less "realistic" dynamic), both equipped with the exact same diaphragm.
    I don't know if this was due to the magnetic field ("optimized" at half the weight, both neo), the smaller back cap or the somewhat shorter phasing plug.
    That might also just be my personal bias (bigger=better)... or my failure to reliably/consistently install diaphragms

  10. #55
    Administrator Robh3606's Avatar
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    Quote Originally Posted by pos View Post
    Indeed, on Erin's measurement you can see that the 305p has a limiter set somewhere between 96 and 102dB SPL at 1m, as the 102dB SPL curve is buried down low.
    I bet the 308p can go a few dB higher.

    I'd be curious to see similar measurements for the LSR32 as its woofer has an integrated brake system.
    But that is utterly off topic, sorry for the digression

    Back on the topic of compression drivers, did you ever measure a difference between the different 1.5" cores?
    When I compared a few of these 12 years ago I remember that the 2452 core sounded way worse to my hears compared to the 2450SL one (less "realistic" dynamic), both equipped with the exact same diaphragm.
    I don't know if this was due to the magnetic field ("optimized" at half the weight, both neo), the smaller back cap or the somewhat shorter phasing plug.
    That might also just be my personal bias (bigger=better)... or my failure to reliably/consistently install diaphragms

    Hello pos

    No I have never compared the cores. Never had the opportunity. I only own 2 pairs of large format drivers the 476Mg's and a pair of 2453Sl's. I got them at different times and never compared them one on one. The way the 2453Sl's are built you can't swap as the the back cap and diaphragm are one piece. The ultimate cost savings I would guess. Use them from 1.5K and up and they sound great.

    Rob
    "I could be arguing in my spare time"

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