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Thread: An important discussion / evaluation on recent blind shootout.

  1. #71
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    Quote Originally Posted by wesley63 View Post
    When I posted that, I only had the evidence from the posts and believed that Dave was comparing the 340SE to the Acculine's by published specifications only. I didn't believe anyone was lying about their results. I was just assuming that they were different comparisons. Now that Dave has confirmed that he has taken his own measurements I am at a loss. Dave has taken his own measurements and I believe what he has observed. I also can think of no reason why Craig Chase would lie about attenuating the Acculines by .5 dB rather than the 340SE during the test.
    Jim,

    I am at a loss too but there are many possibilities for the discrepancy. If Craig measured his acculines as having higher sensitivity, and they were both positioned in the exact same position. then either his pair of acculines are different than my pair or his pair of 340 SE are out-of-spec, or there is a fundamental difference in how the sensitivity measurement is being performed.

    One thing that bothers me about Craig's response measurements is that with at least the one 340 SE that he measured (no attenuation, no screen), the tweeter level is down about 5dB on average compared to the 2k - 3k region. This could be due to measuring equipment (I am not a fan of Sound Card based measuring systems, too susceptible to noise) and many microphones roll-off highs. The tweeter level of the 340SE should be slightly higher than the upper mids, not lower. Craig purchased the recerts a few months ago, I am going to look up the response curves in our database this evening.

    Also, I appreciate the kind words
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    David Fabrikant
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  2. #72
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    Something is definitely strange about Craig's measurement of the 340SE. The upper frequency range is several dB lower than the midrange even with no attenuation on the switcher box.

    Here is my measurement of the 340SE that I used to own:


    Nice and flat.

  3. #73
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    Quote Originally Posted by Mike^S View Post
    Something is definitely strange about Craig's measurement of the 340SE. The upper frequency range is several dB lower than the midrange even with no attenuation on the switcher box.

    Here is my measurement of the 340SE that I used to own:


    Nice and flat.
    Yep -- that is EXACTLY how the response of the 340SE should look. Ever so slightly tipped up top end.

    Nice measurement by the way. What mic are you using?
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    David Fabrikant
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  4. #74
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    Thanks Dave! That was an ECM8000 by Behringer. Only $100 for the mic and phantom power.

  5. #75
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    Quote Originally Posted by Mike^S View Post
    Thanks Dave! That was an ECM8000 by Behringer. Only $100 for the mic and phantom power.
    I suspected it was the Behringer.. Slight roll off of the top end starting at about 14kHz, getting steeper as frequency increases. I have a few of them.

    You would have to spend several hundred to beat the performance of the Behringer. Not really suitable for engineering grade work, but for the hobbyist it is perfect, there is no reason to spend more.
    Last edited by davef; 10-12-2007 at 02:35 AM.
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    David Fabrikant
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  6. #76
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    Default Going too far!

    Guys,

    This is getting way out of control. We now have a competitor making accusations regarding "anonymous" forum posters etc. etc. I posted this discussion on our forum to avoid this because I thought it was an interesting and informative discussion, worthy of a good read, information worthy of publication.

    The competitor in question does quote some good technical info regarding series resistance vs. series-parallel resistance (an L-pad). If the switch box in question uses series-parallel resistance, the net effect of the attenuation would be different as impedance can remain constant, however an L-pad introduces other anomalies but these would not concern me nearly as much.

    I did NOT want to have to get into this even deeper. To be quick, I am going to use an example here. To determine the cut-off frequency for a simple 1st order RC high-pass filter (the building block of the tweeter section of a crossover) the formula is F= 1 / (2*pi*R*C) where F = cut off frequency, R = total resistance, C = capacitance). As you can see from the formula, when resistance is increased, the cut off frequency decreases. The more resistance, the lower the cut off point. Let us assume a 6 ohm tweeter, using a capacitor value of 6uF (.000006 Farad). Doing the math, we get a cut off frequency 4423 Hz. If we add even as little as 2 ohms of series resistance (resistance now sums to 8 ohms), the cut off frequency changes to 3317 Hz, considerably lower.

    The opposite is true with the woofer section that uses series inductors. As resistance increases, the cut-off frequency increases. Adding series resistance to a parallel crossover network (which is the design of the majority of crossovers out there) will lower the tweeter cut-off frequency and raise the cut-off frequency of the woofer. Additionally, the slope and Q of the filter will change as well -- these formulas also depend on the resistance (impedance) of the circuit. I should mention that it is more complicated than this as most crossovers use higher order filters, but you can clearly see the effect of resistance changes.

    The net result of this is interesting actually and it relates to speaker sensitivity as well. I will explain -- the design of a crossover will call for the crossover point (the summation point of the filters we are discussing) to be at a specific level compared to the response when the filter is not engaged. For example, the crossover point might be -9dB down so that both filters will sum to a flat response. If series resistance is added, thereby raising the woofer cut-off frequency and lowering the tweeter's -- that -9dB crossover point might now be -6dB or less so that instead of both filters summing to "flat" -- there is now a 3dB "bump" that will typically span at least two octaves. Look at the various frequency response graphs that both I and Craig measured, notice that as attenuation increases, the range between 1 kHz – 3 kHz becomes exaggerated with respect to the rest of the range.

    Depending on the method used to measure sensitivity, it is often calculated by averaging the frequency range of say 1 kHz – 5 kHz. Since the crossover point will be in this range, a 1dB drop in sensitivity (if using this method to determine sensitivity, which is the most common), will cause a far greater drop in sensitivity below this range and above it, since this range becomes bumped up with respect to the rest of the range by adding resistance. While it might appear that sensitivity is only dropping by 1dB, the range above and below the summation range will be attenuated by a much larger amount. In other words, with this method -- what might appear as a 1 dB drop in sensitivity will only be a 1dB drop in perhaps a 2 octave range while the range outside of this will be attenuated much more. In other words, this is not equal attenuation; it does not drop the complete bandwidth by 1 dB. The delicate balance of the speaker is changed.

    All of this is easily evidenced by examination of the response measurements, the measurements that I took and third party.

    Back to my original point, if attenuation was achieved by use of variable series-parallel resistance, the effect on frequency response would be much less evident and in fact, I would not have been all that concerned with the attenuation device. While still not all-fair, use of an L-Pad would have been acceptable to me. However, the measurements taken by Craig clearly show the same affect as I measured using series resistance. And please lay off Craig -- he did not do anything wrong.

    Additionally, I mentioned that I do my due diligence. The question was indeed asked of the manufacturer of the switch whether attenuation was achieved by use of series resistance or L-Pad. The answer was straight series resistance, which corresponds exactly with the frequency response graphs taken by Craig when using attenuation on the device.

    My discussion here has resulted in complete upheaval -- mud being thrown all over the place. Truth be told, I even tried to handle this off-line with various parties but my emails were conveniently ignored. I am not here to make enemies of people who don't even know me, or what I stand for. I have not called for a retraction of any of the now widely published results and I most certainly can (and probably should), SO GET OVER IT.

    If someone can argue that series resistance, even as little as 1 ohm, will not change crossover performance, please proceed. It will be difficult though as they would have to re-write a whole lot of circuit analysis books. Otherwise, there is absolutely nothing more that can be discussed regarding this.

    Instead of all the different sides fighting about it, do the listening session again. What better excuse to have another good time? If given enough time, I would even build the appropriate level-matching low-level switcher at my expense that can be used for this, although it would not be remote controlled, but there are other methods. Even better, just do the comparisons in your own home and draw your own conclusions.

    I have said my peace regarding the attenuation device. If someone can re-write the laws of physics, please do let me know.... I have several urgent requests at this time.
    Last edited by davef; 10-12-2007 at 02:37 AM.
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    David Fabrikant
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  7. #77
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    Sorry, one last but important point...

    Nowhere in any of this have I discredited any product or any manufacturer. Don't let what is being posted cause you to think otherwise.

    I have not placed blame on anyone but myself, for not looking into any of this deeper, beforehand. No *permission* was ever asked of us to use any of our products for this listening session, yet from public postings, it is easy to conclude many conversations occurred well beforehand with the other ID companies. Other companies graciously declined when asked to submit product. I repeat, nothing was asked of us... There were products present from competing companies that aren't even in production yet, I would have loved to have a new product there too -- something that is in limited production right now but has not been discussed at all by me. In all fairness, is this "fair"?

    Had conversations between myself and involved parties occurred, I would have looked deeper, changed a few things, made some requests. We produce only 4 loudspeaker models and 3 of ours were at this event. 2 of which were the subject of 3 published comparisons (more than any other brand). Every one of these models being either B-stock or recertified. Not that any of this should matter because I let all of it pass once I started to pay attention. I let all of it go. I didn't want to mention any of this because THIS information would start a war. But now it has gone too far.

    Seriously, what manufacturer would want B-stock product at such a large event, being inspected and evaluated by so many people? Performance aside, we all know looks and build quality matter too. I also let this go…

    I wasn't even aware of the dates of this event... too much going on in my personal life. It was my friend Mark Schifter who told me he was flying to Craig's house in a few hours that prompted me to start reading that forum. He called me only a few hours before he left, just to see how things were going in the mess that has become my personal life.

    I publicly mentioned that in the comparison between the Sierra-1 and a competing product that has higher sensitivity, in which the Sierra-1 scored higher, I consider this invalid -- and it is.

    Now, because I published a perfectly respectable study on the effects of series resistance, I am being attacked. I would have conducted the study on the Sierra-1 instead of 340SE, if only I had available inventory (which I don't).

    For those slinging mud my way -- please take a deep breath, read everything that I posted, consult with ANY electrical engineer, and then please take a closer look.... at everything.


    I have had enough -- and I thank you for your time.
    Last edited by davef; 10-12-2007 at 03:43 AM.
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    David Fabrikant
    www.ascendacoustics.com

  8. #78
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    Hi Dave,

    I read all the results of the blind test while they were being posted. I still ordered a 340 center because I liked what I heard out of the 170's I purchased a while back. It should be here Tuesday, I can't wait LOL. They can post all the blind test they want I'm sold on your product. IMO one of the biggest bargains in audio!

    Later, Daman

  9. #79
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    Ok now let's move on to something fun...like:

    I would have loved to have a new product there too -- something that is in limited production right now but has not been discussed at all by me.

  10. #80
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    I agree with Chas.

    Dave what could this product be?
    "I would have loved to have a new product there too -- something that is in limited production right now but has not been discussed at all by me. "
    You could email us loyal customers privately, I for one promise to not say a thing!
    Just a small note to let you know that my Sierra's sound fantastic in my McIntosh two channel rig. A huge Thank You!!

    Peace,

    Jim

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