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Thread: Tower speaker help

  1. #31
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    Default Re: Tower speaker help

    Quote Originally Posted by robpar View Post
    As a follow up, I know there a lot of misinformation regarding bi amping but here is one article that is interesting:

    https://www.qacoustics.co.uk/blog/20...tion-benefits/
    That article is about bi-wiring, not bi-amping. The two are very different.

  2. #32
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    Default Re: Tower speaker help

    Well, sorry, my bad. I thought the findings would be interchangeable with Bi-amping?
    Anyway, Thanks!
    Now, on another related subject that actually may be more beneficial for me, I am considering placing monitors or good sounding speakers (small though-TWF) in my upstairs living room. I currently have medium in-wall B&W (I can't remember the model but they were very expensive about 10 years ago, around $1000/pair) with a "hidden" sub. If I like the sound, I may be able to convince her that a good, small speaker, that puts more/better sound than the B&W's is the way to go (Sierra 1?). The Sierra 2 may be an overkill?
    Would be great if the Sierra's would be available in white though, otherwise piano black would have to do...

  3. #33
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    Default Re: Tower speaker help

    Quote Originally Posted by robpar View Post
    As a follow up, I know there a lot of misinformation regarding bi amping but here is one article that is interesting:

    https://www.qacoustics.co.uk/blog/20...tion-benefits/
    Sorry, but why did you note that there is "a lot of misinformation regarding bi amping," only to post an article that is nothing but misinformation about bi wiring?

    That article is misleading garbage. I say that as an electrical engineer who spent much of my career testing audio electronics and cables. Cables are linear, not nonlinear. They don't introduce nonlinear distortions like intermodulation distortion.

    Shame on qacoustics for presenting such a misleading and downright false article.

  4. #34
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    Default Re: Tower speaker help

    Quote Originally Posted by Beave View Post
    That article is misleading garbage. I say that as an electrical engineer who spent much of my career testing audio electronics and cables. Cables are linear, not nonlinear. They don't introduce nonlinear distortions like intermodulation distortion.

    Shame on qacoustics for presenting such a misleading and downright false article.
    I have to agree with Beave here, this article is pure pseudoscience and the measurements don't prove their hypothesis, just the opposite actually.

    It brings back some interesting memories for me. At a previous employer, I had to – on occasion – generate various publishable test results to “prove” marketing hype of various technical features (often that were more marketing than anything else). The simplest way to do this? Use inherently inaccurate test gear, take the measurements dozens of times, and use screen shots of the tests that best prove what marketing was asking me to “prove”. Simple to do if there is no control. I never felt good about doing this, but sadly, it was and still is part of this industry.

    This test setup uses hobbyist measurement gear at best. An electrical engineer would never use this same gear to run such a test.

    After my 10 yr run as an engineer at M&K and as Ascend Acoustics was getting underway – to pay my bills, I did quite a bit of consulting. One such job was working for a venture capitalist who hired me to prove / disprove a company claiming they developed an external “treatment” for CD’s that “dramatically” improves audio quality.

    They provided this venture capitalist with all sorts of measurements that someone without much knowledge would assume proves the viability of the device in question. The venture capitalist was ready to invest – but wanted a professional second opinion, that’s where I came in.

    I quickly recognized the equipment used for these measurements, which just happened to also be TrueRTA software combined with a USB Audio Interface and I was able replicate the same test results – problem was, every test I took had slightly different results – about half proved the viability of the device, the other half proved the opposite – all based on a few dB difference in the noise floor (which is inherently inaccurate using this type of test setup)

    The next step was to use reference grade testing gear, including proper low distortion oscillators, a digital oscilloscope, and my MLSSA system. Every test I took was 100% repeatable, and every test I took showed absolutely no difference between the “treated” CD’s and non-treated CD’s.

    The creator of the device was rather upset, and argued to the venture capitalist that my tests were flawed – but when he read my evaluation and presented it for peer review, it was accepted and as such, the creator of this device never saw a dime (at least from this venture capitalist)

    This bi-wire article would never stand up to peer review, and I am going to break it down.

    First off, this is not a measurement of intermodulation distortion (this isn’t how one would even going about measuring it, if it even existed in cables, nor could TrueRTA even detect it) This is simply a measurement comparing the noise floor.

    The interesting thing here is that the publisher's posted measurements actually prove the opposite of their claims…

    They are claiming “IMD reduced dramatically”… Let’s take an actual look… Some minor Photoshop work placing one graph on top of the other and applying some opacity, and using the replace color feature so you can see both graphs – it is easy to see that the noise level - what they claim is IMD - (the blue line on the single wire measurement, green line on bi-wire measurement) - - is actually the exact same between the bi-wire measurement and the single wire measurement.

    Here are the 2 measurements positioned on top of each other, and then with heavy zoom:


    m1.jpg

    --

    m2.jpg

    The noise level is exactly the same between the bi-wire and single wire measurements. There is no reduction of anything - not even a reduction in noise at the fundamental bass frequencies (which have been attenuated) -- this is exactly opposite of the claims bi-wiring promotes.

    The second part of their claim is that there is a reduction in the measurement of low frequencies in the bi-wire test.

    This reduction is actually clearly evident in the measurement they posted. Basically, what they are doing is sending a specific set of tones consisting of 5 low frequencies and 5 high frequencies to a speaker, with one set of measurements with the speaker properly bi-wired, and the other with the speaker not being bi-wired.

    In the bi-wire measurement, the bass is reduced by approximately 30dB measured at the tweeter speaker cable, while in the non bi-wire measurement, bass is not reduced in the single cable. This alone proves bi-wiring does not work as claimed as the claims made are that the bass signals would not travel in the tweeter speaker cable. Clearly there is still bass frequencies in the tweeter cable – but the question is, why are they attenuated by 30dB?

    The answer is very simple… When you bi-wire, you isolate one filter network from the other. Current must be flowing between the + and – amp outputs to form a complete system. The reason the bass is attenuated is because they are measuring the tweeter cable, which only feeds the tweeter filter network when a speaker is bi-wired. And what does the tweeter filter network in a crossover do? It is a high pass filter, thus it dramatically attenuates the bass. And with the bass being ~30dB down at 200Hz, this is basically what I’d expect with a crossover high pass filter.

    What is actually happening here is not that bass is being reduced in the tweeter cable due to bi-wiring, it is that the bass is reduced due to the high pass filter in the crossover, which is exactly what should be happening if one isolates the high pass filter network from the low pass filter network.

    The reason bass is not reduced in the single cable connection is that the bass frequencies are flowing through the low pass filter network – exactly as it should be since the 2 filter networks are no longer isolated from each other. With bi-wiring, there is no low pass filter network attached to the tweeter cable for the bass to flow freely through - of course it is attenuated because is trying to flow through the high pass filter.

    What is a bit alarming though, is that the fundamental in the bi-wire test is different than what is applied to the single cable test.



    The fundamental is the red line… See that spike at 50Hz?

    That same spike doesn’t exist in the fundamental on the single cable measurement, nor does it exist in the original graph of the fundamental which is the generated test tones on the CD (fundamental is yellow):





    In fact, the original CD test signal perfectly matches the fundamental applied to the single wire speaker test but it looks completely different in the bi-wire measurement. Why is this? -- what is that spike? Could be port tube resonance, but if it is - it would also show up on the single wire measurement... hmmm....

    So why would a speaker company go through all of this trouble? Promoting claims of bi-wiring benefits allows cable companies to sell a lot more cable at already huge margins. A quick peak at their website indicates they not only sell speakers, but also sell QED cables. Further investigation reveals that Q Acoustics:

    https://www.qacoustics.co.uk/contactus

    and QED cables are the same company…

    http://www.qed.co.uk/contact-qed.htm

    Or at least share the same exact office…..

    I'm not arguing against bi-wiring (to each his own), but this article proves zilch...
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    Good Sound To You!

    David Fabrikant
    www.ascendacoustics.com

  5. #35
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    Default Re: Tower speaker help

    Quote Originally Posted by robpar View Post
    Well, sorry, my bad. I thought the findings would be interchangeable with Bi-amping?
    Anyway, Thanks!
    Now, on another related subject that actually may be more beneficial for me, I am considering placing monitors or good sounding speakers (small though-TWF) in my upstairs living room. I currently have medium in-wall B&W (I can't remember the model but they were very expensive about 10 years ago, around $1000/pair) with a "hidden" sub. If I like the sound, I may be able to convince her that a good, small speaker, that puts more/better sound than the B&W's is the way to go (Sierra 1?). The Sierra 2 may be an overkill?
    Would be great if the Sierra's would be available in white though, otherwise piano black would have to do...
    Bi-wiring and bi-amping are very different. With bi-amping, especially active bi-amping, there are definitely performance benefits. What you are doing is passive bi-amping, powering your speakers with 2 different amplifiers, one amp powering the highs, another the lows. This essentially adds more available headroom, and - as you have found out, you can add (or reduce) the balance of the bass to the mids & highs by adjusting the gain of the amp.

    We can do a very nice custom white finish on Sierra cabinets Best to contact us directly.
    .
    .
    .
    Good Sound To You!

    David Fabrikant
    www.ascendacoustics.com

  6. #36
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    Default Re: Tower speaker help

    I reread my post from above and felt it came across rather rude to robpar, so I'd like to apologize for that.

    As I said above, I worked as an engineer doing audio for many years, so I get really frustrated with the amount of misinformation propagated by the industry. I got annoyed with that and reacted too strongly to robpar's post. I have to remind myself that not everybody has the background that allows them to distinguish what is good information and what is misleading bs. So my frustration should be directed at q acoustics and not at all at robpar.

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