"An amp" is a bit broad. "An amp with insufficient drive capability for low impedances," sure. And this is massively not the case for the ridiculous claim made here.
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Class A vs AB vs D amplifiers
- Thread starter boomtheroom
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I understand that is a common saying. However it is hard to do an apple-to-apple comparison between bridged and non-bridged in order to make the statement valid in practice.
Mostly because how are you going to transform a SE amp to a bridged? Not without adding a lot more components. That "half impedance" statement is true in the sense when you compare it to an SE amp with the speaker's negative terminal tied to ground; in a bridged amp the virtual ground will be at the halfway point of the load. Thus, half impedance.
However, also consider how did you get to a bridged amp from the original SE amp. If all you did is taking the first SE amp, clone it and flip it upside down, then effectively you have the same current capability. You don't need as much voltage to reach that same current because "half impedance". But your amp x2 will never get less total output power from having two amps compared to one. It may get the same output power into a current-limited scenario, and more output power in others.
And if you're talking two amps of similar total cost except one is designed bridge and the other not, or one amp that can be configured for bridged or not, then it is no longer an apple-to-apple comparison.
And if we're talking about an amp that is fixed to bridged mode only, then the designer can simply design for half the load impedance to begin with. Like car speakers are 2ohms and car amplifiers are design for that, no biggie.
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Sokel
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I have tried icepower 300a (the Edge version) both mono and bridged (it doesn't matter if it's the stereo or mono version,they work identically as mono),I also measured them acoustically too.
Zero difference with the mid-high passive section of my speakers with their 3.2 Ohm min impedance according to the measurements.
Same FR,distortion,etc.
I just let them mono for peace of mind as they can handle lower impedance better by specs.
Edit:for those (rightfully) confused by the configuration,a stereo 300a2 can be used in three ways,stereo - mono - bridged )
Zero difference with the mid-high passive section of my speakers with their 3.2 Ohm min impedance according to the measurements.
Same FR,distortion,etc.
I just let them mono for peace of mind as they can handle lower impedance better by specs.
Edit:for those (rightfully) confused by the configuration,a stereo 300a2 can be used in three ways,stereo - mono - bridged )
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Because the noise from switching amplifiers is much higher than 20khz or even 40khz, it's more like 200khz. So, maybe the noise does reach the tweeter, but tweeters are generally not responsive in that frequency range to begin with... so it's sort of irrelevant, I believe.
Petrushka
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Noise that a speaker cannot convert to pressure waves has to be dissipated as heat, but it will be in the range of micro watts.
MAB
Major Contributor
None that I have seen Pogo ever demonstrate. Particularly odd since they are singularly obsessed with these specific NAD in bridged configuration... while simultaneously obsessed with damping factor, or 'dampening factor' as stated some of the discussions and videos they claim as evidence.
But certainly no proof. Quite the opposite.
I hesitate to call this out, except there is a long track-record of nonsense and non-physical discussion on this, with misquoting or made-up product specifications and measurements thrown in for good measure.
Blenderguy
Member
Going to try this now.
It is 3 uH that way using AWG zip cord. My Kimber Kable measures 0.3uH, but it is a lot of wound wires.
Zip cord is 300pF, Kimber Kable is 2.3nF. No wonder back in the days, it blew up unstable amplifiers
Blenderguy
Member
After looking at it closely, I noticed that the frequency scale was logarithmic, did not notice this before. So all the spurious distortions are the cumulative addition of all third order components.
Even the Dynaco that has the worst looking distortions are still at the threshold of inaudiblity according to lots of articles that claim you can't hear distortion lower than 0.2%. Is that generally so? So the takeaway is that even though new designs are better, the differences maybe inaudible, right?
Blenderguy
Member
I did another spectrum analysis on a second song. It looks completly normal. I can't explain the high frequency spectrum, so far no other song has it. The other thought was that a mic or mixer amp was clipping, but when taken any short samples you end up with the same spectrum. Interesting.
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Blenderguy
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@Doodski
Not sure what to do with that video. I am at my desktop computer using creative lab speaker. Certainly not a reference. I also don't know what codec Youtube is using or how the guy encoded the audio on the video. I guess this video is a curiosity, a method for some people to get clicks.
It would be useful to get a high res flac file to eliminate all the variables.
Not sure what to do with that video. I am at my desktop computer using creative lab speaker. Certainly not a reference. I also don't know what codec Youtube is using or how the guy encoded the audio on the video. I guess this video is a curiosity, a method for some people to get clicks.
It would be useful to get a high res flac file to eliminate all the variables.
Use headphones.
Blenderguy
Member
Using the reactive resistance of the 3uH speaker cable, we can calculate what it is at 10kHz and 20kHz. We get 0.3 Ohms and 0.6 Ohms. Hardly negligible. Most Martin Logan ESL speakers have 2 Ohm impedance at 10kHz -20kHz range, some models are even lower. Doing the arithmetic to calculate frequency response deviation we get
20log (2/2.3) = 1.2dB at 10kHz
20log(2/2.6) = 2.3dB at 20kHz
I would say this is significant, but only to people who have not lost their high frequency hearing. Mind you some people may consider those speakers edge cases, but they do exist. So not for all conditions is just the pure cable resistance important. The other inductance not taken into account, is the Zobel output inductor on most class AB amplifiers. This could be 1.2uH to as high as 2uH what I have seen on schematics. I would be interested to see from people who have amplifiers that do not have the output coil.
20log (2/2.3) = 1.2dB at 10kHz
20log(2/2.6) = 2.3dB at 20kHz
I would say this is significant, but only to people who have not lost their high frequency hearing. Mind you some people may consider those speakers edge cases, but they do exist. So not for all conditions is just the pure cable resistance important. The other inductance not taken into account, is the Zobel output inductor on most class AB amplifiers. This could be 1.2uH to as high as 2uH what I have seen on schematics. I would be interested to see from people who have amplifiers that do not have the output coil.
Blenderguy
Member
Still does not eliminate the distortion introduced by the codec. Plus the music he chose is just distorted noise, really bad test. There are music sections on the video game Nuke Dukem composed by Nine Inch Nails. I like the pieces, but no amount of added distortion is going to be noticeable. Like no amount of perfume is going to make sewer water appetizing.
The video certainly suffices for newbies that expect 0.001% compared to 0.05% distortion should sound different when they don't.
If you prefer another test, one with real music, and proper ABX testing.
Listening Test
I would agree - but probably swamped/masked by the actual in room response of the speaker in a typical listening room. Further, for anyone applying room equalisation, it would trivially be compensated for there.
Blenderguy
Member
I still have issues with tests like this. How do you do the math eliminating the distortion produced by your own equipment? To really get the right results, and not "how much added distortion can you hear added to your already distorting equipment". I did try the the video using my Topping DAC and some $500 headphones I chose for extremely low midrange distortion, but the low frequency distortion is significant. So how do you calculate what your distortion sensitivity is say at 100Hz, when the headphones already are at 1%? To get the real numbers maybe impossible, you would need an anarchic chamber with specially designed transducers that have lower distortion than what scientist believe a person can hear. The other thing that bothers me is when you have a codec that is designed to throw away signal it thinks you can't hear, then does it throw away the harmonics the test has added for you to detect the threshold. Maybe from what I read in the comments, is that at a certain threshold it puts back those low level signals, and you get an abrupt increase in perception. I don't know enough how the internal working of any of those codecs work and which one YouTube uses.
So lets just say all the commonly available tests are based on added distortion to an already flowed reproduction system.
I know this is not audio related, but I used to brew beer and belonged to a brewclub. The club would buy kits that contained all the typical defects that can occur during beer brewing. But you needed a beer that was devoid of any of that and did not have enough flavor to obscure the taste of the defects. And the beer that was chosen was bud light. What was interesting is that during the testing certain defects actually improved the flavor of this beer, haha. But what I came to realize is the as you get older your taste buds and your hearing deteriorates. So a few of the defects I could not taste at all. A few year after I stopped brewing beer. So yeah it is a similar set of testing, you had to get a baseline and then add the defects, the same as in the audio distortion perception. I don't know know if others have experienced it, but when I was younger my hearing was not exactly the same everyday. On some days I could hear deeper into the music than other days. Before I was married, I used to come home from work, put on a record and then relax in a beanbag chair. Did this for several years. Another thing I have not read much about was I felt that my Dayton Wright speakers would sound different on certain days. I suspect it had to do either with the barometric pressure or difference in humidity.
So lets just say all the commonly available tests are based on added distortion to an already flowed reproduction system.
I know this is not audio related, but I used to brew beer and belonged to a brewclub. The club would buy kits that contained all the typical defects that can occur during beer brewing. But you needed a beer that was devoid of any of that and did not have enough flavor to obscure the taste of the defects. And the beer that was chosen was bud light. What was interesting is that during the testing certain defects actually improved the flavor of this beer, haha. But what I came to realize is the as you get older your taste buds and your hearing deteriorates. So a few of the defects I could not taste at all. A few year after I stopped brewing beer. So yeah it is a similar set of testing, you had to get a baseline and then add the defects, the same as in the audio distortion perception. I don't know know if others have experienced it, but when I was younger my hearing was not exactly the same everyday. On some days I could hear deeper into the music than other days. Before I was married, I used to come home from work, put on a record and then relax in a beanbag chair. Did this for several years. Another thing I have not read much about was I felt that my Dayton Wright speakers would sound different on certain days. I suspect it had to do either with the barometric pressure or difference in humidity.
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Not surprised at the test with 1 khz tone. It is just higher than the old -60 db THD threshold for 1 khz tones determined by testing. Harmonics end up right where our hearing is most sensitive. Speakers likely have very low distortion themselves at only 67 db SPL. Though what they have is 2nd and 3rd harmonic possibly adding to the distortion from the mis-biased amplifier.
Years ago one of the pro sound designers said when he did listening tests (this was blind on a group of people working there), he would not allow peaks of more than 75 db and results were much better if kept to 70 db. He never published details, but said when he allowed listeners to set volumes when volume passed 80 db or more distortion had to be very high for anyone to hear it. To the point such a test was meaningless. I thought that might have made sense for average levels instead of peaks as peaks of 75 db means an average level of only about 60 db with much music. He insisted this was most efficient at finding out if his amps were clean enough. I also wondered if it was partly because speakers would be distorting less with lower levels. It does however fit with the spl point at which our ears begin to limit loudness.
Years ago one of the pro sound designers said when he did listening tests (this was blind on a group of people working there), he would not allow peaks of more than 75 db and results were much better if kept to 70 db. He never published details, but said when he allowed listeners to set volumes when volume passed 80 db or more distortion had to be very high for anyone to hear it. To the point such a test was meaningless. I thought that might have made sense for average levels instead of peaks as peaks of 75 db means an average level of only about 60 db with much music. He insisted this was most efficient at finding out if his amps were clean enough. I also wondered if it was partly because speakers would be distorting less with lower levels. It does however fit with the spl point at which our ears begin to limit loudness.
MAB
Major Contributor
A large thing minus a small thing, in the limit where the large thing is much larger than the small thing, is approximately equal to the large thing.
The point is, most people can't hear the distortion until it reaches a level that is large.
Did you actually take the test? Or are you posing a hypothetical while informing us what you don't like? There are a bunch to take. In case you ask me to do this and that to prove things to you, yes I have taken these, among others, but don't go and repeat over and over. You need to go demonstrate what you can and can't hear for yourself.
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