Measuring the electronics inside active monitors

[tuga]

The topic is measuring the electronics inside active monitors.
Has this been done?
Is it even possible?

A 3-way DSP'ed active monitor will house an ADC and a DAC, a SRC, 3 amplifiers, power supply.
It'll perform processing at a particular bit-depth and sample rate and use particular upsampling, filtering and noise-shaping algorithms.

Yet the only way to evaluate the performance of the on-board electronics is to measure the electrical signal before it reaches the transducers, which would probably mean tearing the speaker apart.

Soundstage's measurements of the Devialet Phantom are impressive (though the THD+N plot are missing).
Yet according to ASR's the measured performance of the Devialet Expert isn't particularly stellar.

This subject is related to the ongoing discussion taking place in the follwoing thread:

So we now have a speaker with >5% distortion which isn't audible subjectively. Is a SINAD of 96dB poor?

 

[RayDunzl]

Has this been done?

Not that I recall.

Is it even possible?

Put test leads on the speaker terminals, at least.

But...

It's a unit. Unless you are planning to replace the drivers or modify the electronics (or both as necessary), I'd just consider it a speaker and measure the output.

Yes, I'm a spoilsport.

 

[KSTR]

It's been done, in-house at the speaker companies. I've done only all-analog signal chains, and some of them sport VCAs (for limiting) which spoil measurements ("significant" amounts of low-order harmonic distortion) even when measuring only the preamp section... but "they do sound good" and save your speakers.
The integrated electronics of many commercial active speakers expose the full fallacies of the hunt for best performance as those are using mostly cheap and bog-standard parts (like tons of lowly MC33078 opamps, LM3886 or TDA7493 power chip amps or even lesser PWM chips etc, let alone "standard cabling" etc), typically for good reasons apart from BOM cost alone (availability, long service life etc).

 

[tuga]

It's been done, in-house at the speaker companies. I've done only all-analog signal chains, and some of them sport VCAs (for limiting) which spoil measurements ("significant" amounts of low-order harmonic distortion) even when measuring only the preamp section... but "they do sound good" and save your speakers.
The integrated electronics of many commercial active speakers expose the full fallacies of the hunt for best performance as those are using mostly cheap and bog-standard parts (like tons of lowly MC33078 opamps, LM3886 or TDA7493 power chip amps or even lesser PWM chips etc, let alone "standard cabling" etc), typically for good reasons apart from BOM cost alone (availability, long service life etc).

What I would like to determine is how using mostly cheap and bog-standard parts put together according to the application notes compares with the mirabulous topologies of hi-fi separates.

Transducers are far less accurate than electronics so we probably can agree that the performance of the later cannot be judged with acoustic measurements.

 

[Senior NEET Engineer]

My manual only says "Amplifier system THD at nominal output <0.05%" I think most active speaker electronics will fall in the "yellow" or "red" zone.

 

[KSTR]

Another point to consider is that active speaker electronics are "endpoints". Any error here does not propagate further, unlike, say, a DAC or PreAmp where the output may get recorded. That's why contraints in fidelity, if any, are much less of a compromise here -- as long as the transducers and the overall acoustic design dominates performance.

 

[tuga]

as long as the transducers and the overall acoustic design dominates performance

Is that an excuse for not excelling in the electronics half of an digital-active speaker?

 

[maverickronin]

Is that an excuse for not excelling in the electronics half of an digital-active speaker?

Yes it is.

Although it also demonstrates that the "need" for better measuring electronics is pretty much just psychological...

 

[tuga]

Yes it is.

Although it also demonstrates that the "need" for better measuring electronics is pretty much just psychological...

It might be.
Prove it then.

I don't know of any discussions around optimising/modifying active monitors (Genelecs, Neumanns, etc.), there may be one or two at DIYAudio.

 

[Juhazi]

If it's a commercial active loudspeaker, acoustic response measurements should be just fine. But I know that among hifi aficionados we have herds of neurotic pessimistic people...

If it's about dsp units or multi-ch dsp-plate amps, I'm interested! Diy people are mostly realistic and practical and can read/understand measurements. But I personally have blind trust in the friendly engineers of minidsp, Hypex, etc. "good " brands. Finally, the acoustic response is what we hear anyway!

 

[sergeauckland]

Is that an excuse for not excelling in the electronics half of an digital-active speaker?

Excelling is a value judgement. What any sensible active loudspeaker manufacturer will use is what's adequate. It has to be 'Good Enough' for transparency such that the drivers and enclosure become the limiting factors, not the electronics. That means that pretty much any modern chip amplifier or Class D module will be fine for the application. Bear in mind that the manufacturer has complete control over how the electronics gets used in terms of load and levels, so as long as the electronics can drive the loads adequately, that's all it needs.

Having said that, there may be commercial reasons why they might want to advertise that their electronics have 0.00001% distortion or whatever, but there's no technical reason to do so and active loudspeaker manufacturers who don't see themselves selling to the lunatic fringe won't bother.

S.

 

[RayDunzl]

I don't know of any discussions around optimising/modifying active monitors (Genelecs, Neumanns, etc.), there may be one or two at DIYAudio.

I have a pair of JBL LSR 308, active, using ADC for analog inputs, using two (of 3) channels of amplification, with dsp.

The amplifier and DSP:

It's an STA350BW amplifier/dsp fed I2S from a Cirrus CS5341.

Rated 50W, but that's at 10% distortion.
Rated (maybe) 0.05% at 1 watt.

They sound fine at lower levels. Room-filling but not room-shaking (unless you don't mind their THD/IMD).

The woofer is a not very stiff (easily deformed with a finger on one edge) thin plastic thing.
Harmonic distortion is evident and increases quickly above about maybe 75dB in-room.
Given the specs of the amp I'd blame the driver.

The tweeter is a soft-looking (no touch) dome in a fancy waveguide.
I don't remember it distorting as early as the woofer.

Optimization?

I suppose you re-flash the STM8S005K6 microcontroller if you can figure out how and with what.

 

[wwenze]

I've done it when repairing speakers. Not really out of that. Frequency response is an interesting adventure.

 

[tuga]

If it's a commercial active loudspeaker, acoustic response measurements should be just fine. But I know that among hifi aficionados we have herds of neurotic pessimistic people...

If it's about dsp units or multi-ch dsp-plate amps, I'm interested! Diy people are mostly realistic and practical and can read/understand measurements. But I personally have blind trust in the friendly engineers of minidsp, Hypex, etc. "good " brands. Finally, the acoustic response is what we hear anyway!

I agree regarding acoustic response. A frequency response measurement does not fully characterise it.

 

[wwenze]

My manual only says "Amplifier system THD at nominal output <0.05%" I think most active speaker electronics will fall in the "yellow" or "red" zone.

Yellow zone probably or even green zone for amplifiers. TDA7294 when done properly can reach 0.01%

Now let it sink in that there are boutique amplifiers in the red zone.

 

[tuga]

Yellow zone probably or even green zone for amplifiers. TDA7294 when done properly can reach 0.01%

Now let it sink in that there are boutique amplifiers in the red zone.

Let's leave poorly designed and intentionally tailored sonic signature equipment and stick to high measurable performance.

 

[RayDunzl]

Let's leave poorly designed and intentionally tailored sonic signature equipment and stick to high measurable performance.

If they're already high performance why do you want to mess them up with modifications?

 

[wwenze]

Swan M50W to confirm no issues after a repair. At 1V & 2V rms output voltage. Ignore the 7kHz and 21kHz, that's from my apartment.

 

[maverickronin]

It might be.
Prove it then.

I don't know of any discussions around optimising/modifying active monitors (Genelecs, Neumanns, etc.), there may be one or two at DIYAudio.

With passive speakers people can rarely differentiate any upstream electronics that measure half decent so that's why I say it's mostly psychological. From a performance standpoint it doesn't make much of a difference how many separate boxes there are.

Some people worry about the built in components they can't (easily at least...) change out.

Some people worry about about the individual components they can change out.

Some people worry about everything.

It's only the acoustic output that matters so that's why I say the concern about the electronics measuring many orders of magnitude better than the transducers is mostly psychological.

-

Personally my concern about active monitors (at least the really expensive ones...) is reliability and repairability. What are you going to do in 10 or 15 years when tin whiskers or a blown cap take out a DSP chip or microcontroller? Are Kii or D&D even still going to be around? Genelec and Neumann probably will, but will they even sell you a new board?

I have a pair of JBL 305 MKII's but given their price I can at least treat them as the disposable consumer electronics they are.

 

[maverickronin]

But at least they have replacements.

That's the important part.