AudioCircle
Audio/Video Gear and Systems => The Lab => Topic started by: Charles Calkins on 7 Nov 2018, 07:23 pm
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Hi Guys:
I've been listening to talk about using two stereo amps in a system.
Suggestion is have a solid state amp to drive the bass and mid range.
Have a stereo tube amp to drive the tweeter. I can do that. My pre has
two pair of inputs. They run parallel.
Has anybody tried this? If so what were the results. Good. Bad. No difference?
Cheers
Charlie
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Sure lot's of audiophiles do that. Only if each loudspeaker has four terminals. The two problems are matching woofer & tweeter levels and polarity.
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Sure lot's of audiophiles do that. Only if each loudspeaker has four terminals. The two problems are matching woofer & tweeter levels and polarity.
By four terminals on each loudspeaker do you mean L+R for the bass and L+R for the tweeter.
Cheers
Charlie
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whoops, double post
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We often use our DVA 4/2 amplifier for this purpose. It can do either four independent channels or two very high power channels.
We simply use all four channels to bi-amp speakers with separate top and bottom speaker terminals. Two channels of the amplifier per speaker.
Make sure you remove the links between the top and bottom speaker terminals before trying this!
It does make an obvious difference in overall system performance and since the four channels are identical, no gain matching is required.
Frank
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This is possible as long as the speakers have separate terminals for the tweeter and the bass / mid range.
I have done this in the past but only using 2 identical stereo power amps. I did this years ago when I had Roksan L2.5 pre and 2 x S1.5 stereo power amps, it worked nicely I got cleaner more refined sound.
What you are proposing doing is completely different type of amps, sounds you like you may have problems first you will need to find different amps with the same gain. Also if one amp is slow and the other fast, I don’t know how that will play out. Example my Spectral is very fast if that is what is called for, I can’t imagine how the sound would be if I pair it up was say a slow amp driving the tweeters.
I guess only one way to find out, give it a try.
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This is possible as long as the speakers have separate terminals for the tweeter and the bass / mid range.
I have done this in the past but only using 2 identical stereo power amps. I did this years ago when I had Roksan L2.5 pre and 2 x S1.5 stereo power amps, it worked nicely I got cleaner more refined sound.
What you are proposing doing is completely different type of amps, sounds you like you may have problems first you will need to find different amps with the same gain. Also if one amp is slow and the other fast, I don’t know how that will play out. Example my Spectral is very fast if that is what is called for, I can’t imagine how the sound would be if I pair it up was say a slow amp driving the tweeters.
I guess only one way to find out, give it a try.
Well it was just something I've heard about doing. I don't think I will. I have a mac 352 amp. Van Alstine hybrid pre
And a pair of Von Schwikert loudspeakers. Sounds pretty good to me. I'll just keep things like they are.
If I got into this it would be like opening a big can of worms.
Cheers
Charlie
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By four terminals on each loudspeaker do you mean L+R for the bass and L+R for the tweeter.
Make that Plus & Minus for the bass and Plus & Minus for the tweeter.
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first you will need to find different amps with the same gain. Also if one amp is slow and the other fast, I don’t know how that will play out.
If one of the amps has a volume control, you can deal with the gain differences.
For all practical purposes, all amp have the same thru-put speed.
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In order to get optimum results for two amps, a active crossover is strongly recommended so the mid-treble amp is matched up to reproduce the intended frequency band. Secondly, gain matching is crucial to get a flat response. A small gain difference can make the playback sound off kilter.
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True an active crossover is a much better path, but it's an engineering challenge. There is more going on in a passive crossover than meets the eye. You often can't just plug-in frequency and slope and get the same transfer function.
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I could always hear the difference between the tube amp and SS amp in horizontal biamping. I find it distracting so I stopped trying. I wasn't happy with the treble sound of any of the AB amps of the time that I could afford so I used tube amps to get good treble tone. But a couple years ago I tried Modulus86 chip amp and found that it had treble as good or better than my tube amps. Then I needed more power so I tried ICE Edge and found it to be "the answer" (for me :) ) to perfect treble, low impedance and unlimited power, and it's cheap compared to ultra high end class AB amps that have good enough treble.
Edit:Be aware that most tube amps are AC coupled (input cap,) while most SS amps are DC coupled (no cap.) The cap rotates the phase by 90 degrees. If your SS amp is DC coupled then the input cap of the tube amp will cause a time misalignment between whatever bands are assigned to each amp. If tubes power treble only, you'll have a 1.5" time misalignment at xo freq of 2kHz which will ruin vertical directivity and tone. If tubes power mid and treble, then you'll hear a time misalignment of 12" at 300Hz between mid and bass. If your SS amp doesn't have an input cap you can add one if necessary, it can easily be added to the interconnect in the RCA plug. Some tube amps use cap coupling between multiple stages in the amplifier, each one rotates phase by 90 degrees. This is what determines whether an amp is "inverting" or not. Coupling caps can also be used in SS inputs or between SS stages. The point is that the output signals must be aligned in time. This is why active speaker proponents like Linkwitz stress using the same amplifier on all drivers of the speaker. But you can work around it. A cheap little USB scope for your phone can display the phase difference between the amps. I don't think most audiophiles know about this and this is why horizontal biamping with tubes and SS often fails to sound as good as either one amplifying the whole speaker.
Another thing, commercial 3way speakers have dual input speaker posts that are wired one set to bass and the other set to mid/tweet. So if you wanted one amp to drive bass and mid, while the other drives tweeter, you would need to rewire the speaker at the crossover board to move the mid driver crossover input from the upper post to the lower bass posts. But usually what people do in horizontal bi-amping is to use the tube amp on the upper posts to drive both the mid and tweeter together while a separate SS amp drives the bass only.
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A coupling capacitor does not rotate the phase. But a cross-over cap does.
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A coupling capacitor does not rotate the phase. But a cross-over cap does.
Yes, thanks for the correction. :)
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For all practical purposes, all amp have the same thru-put speed.
Maybe in theory, but in real life speed is different unless you have heard what I am taking about you will not know. I too was surprised the first time I heard it.
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What differences you heard were not amplifier speed in any engineering meaning of the word.
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Audiophiles have been mating solid state and tube amps together for decades without this 'speed' problem.
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What differences you heard were not amplifier speed in any engineering meaning of the word.
* * * * * * * * *
Audiophiles have been mating solid state and tube amps together for decades without this 'speed' problem.
Maybe and maybe not. Comparing a Leben to a Spectral Audio we went from playing a record, switch from the Spectral Audio to the Leben we all thought we had started the record at the wrong speed. It’s like when you accidentally play a 45rpm at 33rpm, no kidding it was that dramatic.
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A coupling capacitor does not rotate the phase. But a cross-over cap does.
Granted, I'm still learning, but I don't understand how this can be.
All capacitors introduce a 90 degree phase shift into a circuit. However, when this phase shift is added to the phase shift of the load, the phase shift changes with frequency.
Example, a 1uf capacitor in series with a 24K amplifier load will give you a 45 degree phase shift at 6.63 hz. As the frequency doubles, the phase shift is halved, eventually approaching zero. A capacitor in a crossover cannot behave any differently.
As far as amplifiers are concerned, is it not true that the output of some amplifiers is inverted and others not? If you were to feed a non-inverting signal to the low pass and an inverting signal to the high pass, the summed voltages at the crossover point would tend cancel each other out.
What am I missing?
Mike
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What differences you heard were not amplifier speed in any engineering meaning of the word.
I think TooCool is talking about rise time. Many use this non scientific term, being knowledgeable in other fields.
Yes, TooCool, the ear perceives rise time differences of at least 5 us (microseconds), some claiming as low as 2 us.
cheers
steve
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I think TooCool is talking about rise time. Many use this non scientific term, being knowledgeable in other fields.
Yes, TooCool, the ear perceives rise time differences of at least 5 us (microseconds), some claiming as low as 2 us.
cheers
steve
The people that say that were confused by Kunchur. What you can hear is if one channel of a mid-range sound is suddenly delayed by 10 us, the sound will seem to move laterally a small amount. It's about one channel time delay, nothing to do with rise time.
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Example, a 1uf capacitor in series with a 24K amplifier load will give you a 45 degree phase shift at 6.63 hz. As the frequency doubles, the phase shift is halved, eventually approaching zero. A capacitor in a crossover cannot behave any differently.
The same rules apply. But we have to look at the ratio of capacitor impedance and resistor impedance at cross-over frequency.
(they will both have the same impedance)
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Here is what the response plot of a single pole RC high pass crossover looks like. The response scales with frequency were Fs is the center of the plot in this case at 1KHz. Same for the coupling capacitor into a resistive input like most preamps/amps.
The phase response is about 5 degrees at 10x Fs and decreasing. So in the example of Fs = 6.63Hz with phase shift at 45 degrees, the phase shift would be about 5 degrees by 66.3Hz.
(https://www.audiocircle.com/image.php?id=186591)
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The people that say that were confused by Kunchur. What you can hear is if one channel of a mid-range sound is suddenly delayed by 10 us, the sound will seem to move laterally a small amount. It's about one channel time delay, nothing to do with rise time.
That false conclusion was initiated by JJ some nine years ago over on Stereophile forum. JJ falsely claimed one could use a cd and delay one channel by 5 us (microseconds), not 10us, and the individual could perceive the difference. However, Dr. Kunchur's work involved one ear, not both ears. After being confronted, JJ admitted he was incorrect and had posted false information about the study.
Not one of the hundreds of 3rd party eminent individuals, national organizations, hospital staff, university professors etc made the observation that Dr. Kunchur was dealing with both ears, as JJ had claimed. Not one concurred with JJ in 5 years of this study. However, JJ and others have some patents and businesses, and Dr. Kunchur's study, may have brought some of those patents and business claims into question.
Here is Dr. Kunchur's comments concerning some false information posted.
Thank you for your query about my papers on auditory temporal (time) resolution in humans (posted on my web site: http://www.physics.sc.edu/kunchur/Acoustics-papers.htm) and for forwarding the forum comments to me. I would like to respond to some of the assertions and comments that were presented.
First of all, an internet forum is a dangerous place to obtain information -- instead one should go to an authentic original source such as a published scientific paper in a refereed journal. On an internet forum, a writer can post completely arbitrary, unproven, and indeed totally wrong statements with no backing or oversight whatsoever. Normally this would be a laughing matter, except that sometimes people obtain their "education" through such forums and this can therefore cause further harm to the scientific understanding held by the general population, which is already in a national crisis.
In science, assertions must be properly backed up and verified. I don't know who made up this nonsense of dividing the sampling period by the vertical bits to obtain a temporal resolution. The bits give the shades of intensity (related to sound pressure level) that can be differentiated, whereas the sampling period gives the frequency at which the information about these levels is updated. They have no direct connection! In digital photography, the angular image resolution is governed by the number of pixels of a digital camera sensor, whereas the shades light intensity that can be discriminated is governed by the number of bits (about 14 bits in current digital SLRs). If you do not have enough pixels to resolve a certain angular separation between points in an image, no number of bits can fix this.
Similarly, if you have two sharp peaks of sound pressure separated by less than the sampling period, the two will become blurred together: the temporal density of digital samples is then simply not enough to represent the two peaks distinctly and nothing you do with the bits can change this. Unless a different interpretation of minimal temporal separation is taken, it is completely fallacious to assert that a CD can resolve less than 5 microseconds when its individual samples are separated by periods of 23 microseconds. (Note that it is true that small alterations in temporal profiles can be indirectly encoded through variations in adjacent levels and that this is certainly aided by having more bits; however, a true translation in time of a temporal feature can only take place in quantized sample periods.)
Just to give a clearer idea of how formal science and the (incredibly rigorous) scientific process is conducted, I thought I would explain what went into publishing the two above mentioned papers that have apparently generated controversy among lay readers (interestingly there has been no controversy whatsoever in all the professional circles, which include
audiologists,
otolaryngologists,
acousticians,
engineers, and
physicists ).
An experiment has to be carefully thought out and then submitted as a proposal to an Institutional Review Board (IRB) and approved by them before it can even begin. Then optimum equipment, methods, and a multitude of cross checks must be developed (my papers give some details to help appreciate what went in). It takes about half a year to conduct each sequence of controlled blind tests.
Consent forms (legally approved and certified by the IRB) must be signed. The results, analysis, and conclusions are then carefully considered and discussed with colleagues who are experts in their related inter-disciplinary fields;
for this I went in person to various universities and research institutes and met with people in departments of
physics,
engineering,
psychology,
neuroscience,
music,
communications sciences,
physiology, and
materials science.
After that the results and conclusions were presented at conferences of the
Acoustical Society of America (ASA),
Association of Research in
Otolaryngology (ARO), and
American Physical Society (APS).
Seminars were also made at numerous universities and research/industrial institutions (please see the list on my web site). After each presentation, the audience is free to tear apart the conclusions and ask all possible questions.
Eminent people such as presidents of the above mentioned societies and corporations were present at my presentations and engaged in the discussions.
After passing through this grueling oral presentation process, written manuscripts were then submitted to journals. There, anonymous referees are free to attack the submission in any way they want. More than a dozen referees and editors have been involved in this journal refereeing process. Only after everyone is satisfied with the accuracy of the results and all statements made in the manuscript, are the papers published in the journals.
The entire process took around 5 years from initial concept to refereed publications. (Note that an article in a conference proceeding does not go through the rigorous refereeing process of a formal journal. Essentially anything submitted there gets accepted for publication. Contents of books are also not rigorously refereed. When possible, reference should always be made to an original journal article.)
I would like to add some other observations:
(1) One should be wary of drawing conclusions based on an “intuitive feelings” or because something “makes sense”. This has its role in adding plausibility to the understanding but can sometimes be contrary to fact. Thus qualitative statements based on survival and evolution cannot lead to a quantitative estimate of temporal resolution. One has to gain a detailed understanding of the physiology of the ear followed by all the neural processing steps in the ascending pathways of the brain. This knowledge can take years to acquire. (I give some references below for further reading.) On the other hand something that cannot be understood or explained (at the moment) isn’t necessarily false. It can be dangerous to dismiss claims just because they don’t make sense. Science should deal with properly authenticated facts.
(2) Listening tests can be notoriously unreliable unless properly designed. This is why the proposal and consent forms for tests on human subjects have to approved by the IRB, otherwise no journal will consider an article for publication. The tests have not only to be blind but also must be absent of extraneous cues (such as the switching transients discussed in my papers). I would therefore be wary of informal listening tests conducted at home – these can be useful in helping you decide which component works better in your system but not rigorous enough to establish a scientific fact.
(3) There is an erroneous statement in one of the forum posts “Such temporal resolution depends on the "coincidence detector" circuitry of the medial superior olive … mostly effective below 3kHz.”
Actually the bipolar cells in the MSO (medial superior olive) encode relative delays between right and left ears which are used in azimuthal localization (left-right location determination). This has nothing whatsoever to do with the monaural temporal resolution being discussed. Coincidences between different frequencies arriving at each ear are encoded by octopus cells (which act like synchronous AND gates with a huge number of inputs) located in the PVCN (postero-ventral cochlear nucleus). This slew-rate information from the octopus cells then feeds bushy cells in the VNLLv (ventral subdivision of the ventral nucleus of the lateral leminiscus) which contributes to elements of pattern recognition.
I hope this clarifies the meaning of temporal resolution in the context of sound reproduction systems. For further insight into psychoacoustics and the neurophysiology of hearing, I can recommend the following books: (1) “The psychology of hearing” by Brian Moore
(2) “Integrative functions in the mammalian auditory pathways” by Oertel, Fay, and Popper
(3) “Neuroscience” by Purves et al.
I have personally met with and discussed my results with the authors of the first two books. All of these books are used as texts at universities. The last one is used in introductory neuroscience courses and is relatively easy to read.
Sincerely,
Milind Kunchur
*********************************************************************************
Milind N. Kunchur, Ph.D.
Professor of Physics
Department of Physics and Astronomy, University of South Carolina
Web: http://www.physics.sc.edu/kunchur
Again, not one of these eminent individuals, medical entities, national organizations, university professors etc. made the observation that Dr. Kunchur was dealing with both ears as was falsely claimed. Some of these dissenters not only have "patents", but also businesses that depend upon their pseudo science. As mentioned above, JJ already admitted he posted false, incorrect information, so if he is again posting false information, well.....................
Jneutron stated he read a study that demonstrated one can perceive 2 us. (Jneutron has worked at FermiLab, Cern, now Brookhaven National Laboratory, teaches scientists in classroom setting, procedures in scientific testing/experiments/studies etc. He has also been a music lover for some 25 years +.)
I have tested altering the -1db point from 200khz to 150khz for some months back in the 80s, and the ear is extremely sensitive to rise time changes in the stereo system, as such tonal balance changes.
Speedskater, you have been taken advantage of. I always recommend sticking with 3rd party, major national organizations.
cheers
steve