snapsc
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I have no numbers to prove this but I’m reasonably certain that the distortion from subs made by the big 4 independents... rythmik. Power Sound Audio. SVS. and HSU are very close ... and 3 of them are not servo.
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Do servo subwoofers actually lower distortion?
- Thread starter Joseph Crowe
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Kind of a strange assertion to make with no data, no?
snapsc
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Not strange at all... if servo subs were considered to be sonically superior, these companies would either adopt the technology or suffer sales declines... neither seems to be happening... why? They all make great sounding subs suggesting that the servo difference is small.
I don't think servO sub systems solve it all. I've pounded the crap outta Velodynes and it was no better than a good pair of good big bore speakers.
snapsc
Active Member
This is a really good interview with a number of the key sub designers. As you will see, they all site keeping CEA measured distortion levels low, below 10%, as a key ingredient in sound quality. When you get to the last page... click on each of the designers for more detail.
https://www.soundandvision.com/content/subwoofers-guts-and-glory
https://www.soundandvision.com/content/subwoofers-guts-and-glory
i believe brian is sending one of his subs to amir for testing.In the past, Brian Ding refused to divulge or discuss any of the techniques utilized in his products. I don't know if he still holds to that.
The basic concept is he uses a separate coil on the woofers for voltage feedback and also a current monitor on the driven coil. Those two parameters are inputs to the servo mechanism that's adapted into the amplifiers.
But, as mentioned by pozz, he provides next to nothing regards any objective data for his products.
If you want to get into a discussion where you ultimately throw your hands in the air......he's your guy.
Dave.
snapsc
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Another great site because the tests include the distortion numbers... although for music it is unlikely that we ever hit these levels.
https://data-bass.com/#/systems?_k=y8ew37
https://data-bass.com/#/systems?_k=y8ew37
You do know this forum is heavy on numbers and not unfounded assumptions, yes?
I don't know the distortion levels but there are plenty of great subwoofers around these days and many ways to achieve low distortion. As for not using servo, it costs money -- you need a sensor (in Rythmik's case a special driver) and amplifier plus R&D to develop the systems. Velodyne still does, or did, use a servo design, and there have been a few others over the years. There are some things a servo can help (e.g. driver control to reduce distortion and "ringing", thermal issues in the voice coil) that are difficult to solve without a feedback loop. But a lot of that will go unnoticed at sub frequencies and of course optimized conventional designs may provide equal or better performance for the dollar.
Always trades...
What? To make a subwoofer, the box must contain a live monkey! Geez...
That does remind me of an old joke about creatures in boxes:
thewas
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Yes, by a more symmetrical driving force vs displacement you reduce the amount of even harmonics like K2.
thewas
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By the way to reduce distortion on woofers you don't necessarily need closed loop feedback control, but if you know your system well and it doesn't drift much you can even use open loop control like Harman/Samsung does for their newer soundbars
(from https://www.areadvd.de/tests/xxl-sp...nien-zu-besuch-im-samsung-audio-research-lab/)
By the way they also did blind listening tests compared to some small Genelec monitors and the soundbars did comparably well, quite impressive.
(from https://www.areadvd.de/tests/xxl-sp...nien-zu-besuch-im-samsung-audio-research-lab/)
By the way they also did blind listening tests compared to some small Genelec monitors and the soundbars did comparably well, quite impressive.
Its simpler version is also called pre-distortion(oh it's in the picture). The complexity is also quite high. You have three degrees of freedom: Different frequency, different level, and different distortion phase. Only a complex digital processor can do it.
Closed loop control normally is implemented in analogue circuits (at least preferably), these control systems are more accurate, have less delay, performance is more consistent and is immune to component aging. Small loop gain is going to have a lot of benefit. It's ideal for subs (low frequency).
thewas
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Closed loop systems have of course several advantages, but not everything you mention, like for exampe they have more "delay" as they can only correct when deviations already have happend. Also component aging is a problem in their feedback sensors, like for example piezos, myself I have a pair of lovely Philips MFB loudspeakers with such.
MFB can give you less delay, the feedback will make the speaker actually move faster to its 'wanted' position.
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Wouldn't an accelerometer measure woofer motion and send corrective signals far faster than the time it takes to complete a period of a single bass wave?
thewas
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With a well implemented feed forward controller you don't need to have any waiting of feedback as your pre-compensate any deviations so the output signal is already optimal from the start.
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It's a good point. Are you saying that feed forward would be be superior to servos for sub design? Are there any examples of subs like that yet?
I would be impressed if there's analogue realization of such compensator.
thewas
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Often the combination of feedforward control for speed and feedback control for error reduction and parameter drift is the optimal way, I don't know of such an implementation on loudspeakers though, only the known feedback woofers and the feedforward on the new Samsung soundbars.
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