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Performance of Amps in Active Speakers

Ron Texas

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Around here members make a big deal about amplifiers with a SINAD over 90db. They also make a big deal about using active studio monitors in home systems. I wonder what the measured performance is of the Class D amplifiers (and related DSP) in active studio monitors. Has this been tested anywhere?

Due to the relatively high noise floor in inexpensive active studio monitors I would expect the electronics would not measure all that well.
 

Cahudson42

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Hopefully not to divert at all from the OP observation and question but to add to it, It has always seemed to me that perhaps the one advantage of active speakers is that you could optimize the actuator and the amplifier as a system together. Not just 'paste on ' a conventional amp to a conventional actuator.

For example, there is an old saying 'Current is your enemy. Voltage is your friend'. The actuator could be designed with an odd impedance, say 250 ohm. The amp with high voltage to match, with low output impedance. You get the advantage of lower i2r with less heat for the power. Higher damping factor. Thinner cabling. etc. Reminds why cars changed from 6v to 12v..

Are there active speakers actually designed this way?
 

KSTR

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Are there active speakers actually designed this way?
None that I'm aware of.
Sometimes the impedances of the transducers are selected from the typically available 4/8/16 ohms versions to give a better match to the power amps wrt to noise and headroom, notably of the amp are all the same type and run off the same supply. So, low impedance woofers and high impedance tweeters (notably when they are very sensitive compression drivers).
 

q3cpma

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KSTR

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Around here members make a big deal about amplifiers with a SINAD over 90db. They also make a big deal about using active studio monitors in home systems. I wonder what the measured performance is of the Class D amplifiers (and related DSP) in active studio monitors. Has this been tested anywhere?

Due to the relatively high noise floor in inexpensive active studio monitors I would expect the electronics would not measure all that well.
Since the amps are hidden to the user only the designer/manufacturer ever test them, and published specs are usually thin.
Many very well regarded active monitors run less-than-stellar amps.
For example, all Neumann monitors except maybe the subs run simple TDA7293 chip amps, and many Genelecs also run chip amps (LM3886). A well implemented chip amp has "just OK" measurements and would not fare well in the ASR power amp rankings but the speaker designers found that they are good enough for the job. The designs I was involved in used anything from simple chip amps (TDA7292 and TDA7294), simple PWM amps (TDA8920 etc), PWM modules (ICEpower AS and ASP series), composite designs (with a chip amp as the slave in the loop of a good opamp), and even old-fashioned fully discrete amps. Non of that really had any prominent impact on sound, maybe a bit of "fine-print" on the sound. With some exceptions, for example a TDA8950 design is not going to ever sound good on a tweeter.....
 

q3cpma

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Since the amps are hidden to the user only the designer/manufacturer ever test them, and published specs are usually thin.
Many very well regarded active monitors run less-than-stellar amps.
For example, all Neumann monitors except maybe the subs run simple TDA7293 chip amps, and many Genelecs also run chip amps (LM3886). A well implemented chip amp has "just OK" measurements and would not fare well in the ASR power amp rankings but the speaker designers found that they are good enough for the job. The designs I was involved in used anything from simple chip amps (TDA7292 and TDA7294), simple PWM amps (TDA8920 etc), PWM modules (ICEpower AS and ASP series), composite designs (with a chip amp as the slave in the loop of a good opamp), and even old-fashioned fully discrete amps. Non of that really had any prominent impact on sound, maybe a bit of "fine-print" on the sound. With some exceptions, for example a TDA8950 design is not going to ever sound good on a tweeter.....
I'm curious, do you have a source for Neumann's use of such amp? I know Genelec uses a lot of class D in their newer designs (8030C and 8020D, for example), but I didn't know about their use of chipamp.

Oh, well, not like it's a problem. The LM3886 has a SNR > 92 dB, which is good in my books.
 
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Ron Texas

Ron Texas

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Since the amps are hidden to the user only the designer/manufacturer ever test them, and published specs are usually thin.
Many very well regarded active monitors run less-than-stellar amps.
For example, all Neumann monitors except maybe the subs run simple TDA7293 chip amps, and many Genelecs also run chip amps (LM3886). A well implemented chip amp has "just OK" measurements and would not fare well in the ASR power amp rankings but the speaker designers found that they are good enough for the job. The designs I was involved in used anything from simple chip amps (TDA7292 and TDA7294), simple PWM amps (TDA8920 etc), PWM modules (ICEpower AS and ASP series), composite designs (with a chip amp as the slave in the loop of a good opamp), and even old-fashioned fully discrete amps. Non of that really had any prominent impact on sound, maybe a bit of "fine-print" on the sound. With some exceptions, for example a TDA8950 design is not going to ever sound good on a tweeter.....

Lots of insight there. Could you round up some data on any of these chips and convert it to SINAD?
 

KSTR

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For the linear amps, a LM3886 would give some good 80dB of SINAD (1kHz), TDA7294 I recall being a bit worse, something equivalent to 70dB.
TDA8950 (PWM) might also have some 70dB, but the distortion profile for very low level signals is nasty, sounds a bit like fluctuating crossover distortion, decaying notes having a "digeridoo" type of distortion signature. And the channel crosstalk, while numerically low, also consist mostly of spikey and wandering distortion. You'll hear the woofer signal as underlying buzzing noise in the tweeter channel. Some of that might have come from layout problems but we didn't have full control on that. OTOH, the obsoleted TDA8920 which we had to replace didn't show the modulation noise in outright annoying amounts as the 8950 in the same layout.
The linear composite we had would certainly measure best on the bench but in the actual arrangment where it replaced a PWM module I could not manage to coax the true performance from the design.
 

RayDunzl

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Examination of a JBL LSR 305. LSR308 is the same but has a little heat sink glued to the Class D (?) chip Amp.

http://rdimitrov.twistedsanity.net/blog/show.php?entry=JBL LSR305 Teardown and Analysis

Data Sheet: https://www.st.com/resource/en/datasheet/sta350bw.pdf

1571855671153.png
 

GrimSurfer

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0.09% THD+N = -60 dB. Audible @ 1 kHz.
 

RayDunzl

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KSTR

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I'm curious, do you have a source for Neumann's use of such amp?
Probably there is no official info but from educated guesses made from pictures of guts in reviews of KH420, KH310 and KH120 we can assume that the amps used are TDA7293/7294. KH120 I've inspected myself.
For KH420, see: https://www.fidelity-magazin.de/2015/12/16/neumann-kh-420-messungen/ , where a pic of the amp plate is shown. We can spot 8 pcs. of 15 pin chipamp, 4 on each board. The woofer is running most likely on a bridged-parallel config (4 amps) and the mid and tweeter from 2 amps each, either bridged or paralled depending on the driver impedances -- most likely bridged, though -- , which would match the published power specs. Together this is IMHO a strong indication for TDA7293 being used (and powered from SMPS's).
 
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GrimSurfer

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Yes, and for the (discounted) price, they make a goodly amount of other sound, too.

I wasn't making a value assessment, just an audibility one.

Any figures for something more expensive, like Neumann or Dutch&Dutch?
 

RayDunzl

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GrimSurfer

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Not from (cheapskate) me.

Ha ha.

I was interested in seeing if there's the same trend we see elsewhere in audio: no absolute correlation between price and performance.

Don't measure SQ while listening to the news. Politics dominates and the SNR and time coherency of such broadcasts are notoriously low. PBS might be better...

The distortion %s are similar between the JBLs and ML, but the former has much higher 3rd order distortion. Might be seeing a little more mains noise on the MLs, but the 2nd order harmonics are of a comparable level. Interesting.
 
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Ron Texas

Ron Texas

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Examination of a JBL LSR 305. LSR308 is the same but has a little heat sink glued to the Class D (?) chip Amp.

http://rdimitrov.twistedsanity.net/blog/show.php?entry=JBL LSR305 Teardown and Analysis

Data Sheet: https://www.st.com/resource/en/datasheet/sta350bw.pdf

View attachment 36744

Thd+noise of .09% should be equivalent to an SINAD of 61 db

http://www.sengpielaudio.com/calculator-thd.htm

Now if SINAD of 61 db is good enough for an active studio monitor, why do some think the Crown XLS 1502 is junk at 76 db. Or, why are folks around here celebrating when Bruno's latest pushes a few more db past 100 SINAD?

Really, how much is enough?
 

GrimSurfer

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Maybe the same person who thinks that -61 dB isn't very good is the same one that thinks -76 dB SINAD isn't very good either?

Just a thought, as you try taking us down a very illogical equivalency path... Again!
 

RayDunzl

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Don't measure SQ while listening to the news.


No... I still measure "Sound Quality" with my feeble ear/brain combo. When it is perceived as good enough the satisfaction neuron fires, when not, the do something neuron activates.

I do use measurements as an academic exercise to calibrate my biases and the good enough/do something toggle point.

For instance, the JBLs don't get played loudly. They're never used when Audio Buddy comes over for Beer Saturday.

How much speaker distortion will be audible when the levels are here?

1571858489630.png


That's barely above the ambient noise floor.

Besides, I'm paying attention to something else that makes no sound at all:

1571858830502.png


Some upness into the close would be nice, being a little early on my entry, and a toggle to fire my satisfaction neuron dedicated to this activity will pay for dinner. Looks like I'll be ok.

Ooh, yes...

1571859000209.png


Go go go...

Whoa, should have set a limit (exit) instead of chatting...

1571859238763.png
 
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Ron Texas

Ron Texas

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D&D 8c uses Pascal amps, data sheet with measurements here.

Looks fairly similar to icepower (suspiciously so, in fact).

D&D is an active speaker, but it's not a studio monitor and it is pricey. Same could be said for Kii and B&O. Then again, some of the Genelec speakers are expensive.
 
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