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In Reply to: RE: Speakers with lowest THD posted by eyedrop on September 04, 2016 at 21:32:59
nt
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I'm not a technical expert, but I believe that THD is measured under conditions that bear little or no resemblance to actually reproducing music. I've found no correspondence between THD and how much I enjoyed a component.
I on the other hand have found a quite close correspondence between a speakers THD and how much I enjoy them.
IME > 1% THD in the mid and treble is quite audible and annoying.
Luckily it is very easy to keep THD of the other components one or two orders of magnitude below 1%.
"Correlation", not "correspondence".
THD is just that: Total Harmonic Distortion. It says nothing about the spectral make up. A lot of 2nd and a little 5th sounds way different than a little 2nd and a lot of 5th.
Also, the difference in sound character from, say, one trumpet to another, or one saxophone to another, is highly dependent upon the relative strength of the various overtones of the fundamental, i.e., the make-up of the distortion produced by the instrument! This is why it's humorous when a person says that this-or-that speaker or system sounds "just like the real thing".
:)
The only people who could have any substance with a statement like that are recording engineers since they are usually the only ones who get to compare the real thing to what comes out of their speakers.
Unfortunately digital has democratised the recording process to such an extent that there are now a large number of 'engineers' and 'producers' who know very little and are seemingly deaf.
Are the real people that effect what we hear is stereo reproduction: They compile the recorded tracks from artists, musicians and performers in a listening room that doesn't muck resemble any room audio enthusiast listen in, played through loudspeakers and equipment that similarly doesn't reflex audiophile gear, onto a two or more channel "soundscape" they they create while adjusting "imaging", phase, tone, dynamics, and several other parameters to create the "Art" that becomes a pair of digital or Analog signals that reside on the "software" we send into our playback systems.
It is the miracle of desire and fallibility of human perception that allows us to emotionally respond to the playback as if it sounds "Real".
The fact that most of us do not recognized this, or if so, minimize this fact as "out of our control", is also a miracle - in a fashion - as it created the industry of hi-fi that we know and love.
Could you imagine perfect recordings? Standardized studios and environments with optimized mics and diffusion in the spaces to capture the essence of the wave forms that are then processed in a way to provide a consistent soundscape appropriate for the music performance - a listening position preferred by the engineer? The tracks also include metadata that will allow your home playback system to recreate that environment - based on a pre-assessed impulse response of your loudspeakers and room and stored in your equipment.
Actually the technology exists now for the implementation of such a process. We will likely see it in home theater reproduction first probably from Sony - in partnership with Dolby or DTS.
Personally, I like to spin my own - as a little rear reverb or presence boost on a track - Set the playback of my system so it is optimized for my preferences and pleasure. A little EQ to move Diana Krall and her piano a little further away in my living room - same for Frank S. but I can't get the band up front enough to be live with Frank. I'll add a little delay or reverb as needed - or I can spread the image a little, though that can be a little dicey if there is anything panned hard left or Right in the recording - or worse, when the engineer had already speread the image beyond left and right (think "dark side of the moon" synthesizer "helicopter".
"The hardest thing of all is to find a black cat in a dark room, especially if there is no cat" - Confucius
You missed the point.
The point being that when it comes to people judging speakers recording engineers are usually the only ones who ever get to compare their speaker's output to the actual live voice/instrument.
Unlike recording engineers mix/mastering engineers and producers care little what the original performance sounded like, it is not even necessarily in their job description.
Their job is to make the recording sound like they THINK it should sound like.
When it comes to THD of any speaker no manufacturer will ever give you the number for the lowest octave, just check any speaker specs.
The reason is obvious, at the lowest octave the THD is HUGE.
Vahe
many folks like added woofer distortion.
Why? Because it is primarily doubling distortion - simply more bass at twice the fundamental frequency. :)
I think in your rush to type you missed an 'n'. ;-)
Many moons ago I came across a test of high-$ subwoofers including THD measurement.
Only two of the eight or ten subs tested stayed below 10%THD at normal volume.
Both were studio-grade subwoofers, one from PMC and the other Genelec.
Here is one compendium:
http://www.data-bass.com/systems
And another:
http://www.hometheatershack.com/forums/subwoofer-tests-archived/
Unfortunately, a lot of the more recent tests start at 105 dB and go up to 115 or even 120 dB. So the distortion they're measuring is almost entirely dynamic compression. I don't think that's very useful since most people will never play them that loud.
I look more at the 90 dB and 95 dB results (where I can find them) since that's about the loudest I play them. At 95 dB, there are a lot of subs that can hit 20 Hz at 10% THD or less, even some sealed 12 inchers. Some of the biggest subs are at 2-3% THD at 20 Hz and 95 dB.
Take a look at the sidebar on "page 90" of the Polk SDA-SRS review linked-to. Julian Hirsh reports "we have never measured a low-bass distortion level as low as that of the [Polk] SDA-SRS."
Specs are 0.7% THD from 70 to below 20 hz except for a rise to about 2% that was traced to a measurement anomoly ("hum picked up by the system") The THD was primarily second-harmonic.
This seems...spectacular...compared to the ~10% THD of the subwoofers mentioned.
Now, being a vented (passive-radiator) box, of course the bass became increasingly out-of-phase below 53 hz; and I wouldn't place any bets on how, exactly, the THD measurements were taken. At 2.5 volts--supposedly 90 dB in the midrange--the bass output seems shy on volume. I have the sense that the article was written to appear all scientific and thorough, while in fact presenting "best-case" info. But I've been wrong before.
0.7% THD at 20 Hz is extremely low, even at 90 dB. Almost seems too good to be true.
The big Funk Audio subs might be able to equal that. Unfortunately, the distortion measurements made on the FW18 and FW21 started at 110 dB. The FW21 stays under 1% THD through the middle and upper bass at 110 dB, and it has a relatively slow rise in distortion at lower frequencies. So it's conceivable that it could remain flat at 1% or less down to 20 Hz if tested at 90 dB. Nothing else I've seen comes close. You're doing well if your sub can stay under 2-3% THD at 90-95 dB over most of it's range above 30 Hz. And all but the biggest subs show a sharp rise in distortion below 30 Hz.
Cheers!
Thanks for those, quite interesting.
Seems ported subs are on average quite a bit better than sealed when it comes to distortion.
If I remember correctly drivers start to produce more 3rd order once they run out of linear excursion so that would be something to look for.
I was hoping to find some incarnation of my woofers but no luck so far.
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