Do servo subwoofers actually lower distortion?

[pozz]

My unscientifically backed uncited opinion would say that a servo helps when..

- you don't have any room correction (i.e. in order to extend or flatten the operating range which room correction could also do)
- you are operating within the "normal" range of the subwoofer, i.e. not significantly distorting. Potentially servoing can help reduce distortion at higher outputs by "pulling back" certain frequencies etc.

If you have an appropriately sized sub or subs and room correction for them then personally I don't believe servos are necessary.

According to the measurements I've seen in the resources cited above, servos generally show:

• Better linearity and FR smoothness.
• Better (shorter) decay times.
• Better distortion measurements.

This is beside the other, more technical advantages I have only a loose grasp of. They are an overall better design for handling bass reproduction.

I wouldn't say your points are relevant here @stren, unfortunately. Servo subs will not fix room modes and will not selectively reduce output to reduce distortion (I think you have a limiter in mind).

I'll just add that psychoacoustically we are incredibly insensitive to bass distortion. So it's not an audible factor.

 

[pozz]

I think there are two questions to ask. One is to what extent a servo reduces distortion and the other is under what conditions is this necessary. So the servo approach likely has merit, and there can be other ways to reduce distortion.

As far as I know, none of the big full range speakers have a servo as part of their designs, so it’s definitely an interesting question if they can address in some other fashion for passive speakers where it’s simply not possible.

The forthcoming PS Audio speakers and older Infinity models are the only ones I know of.

 

[q3cpma]

The forthcoming PS Audio speakers and older Infinity models are the only ones I know of.

There's also Psi audio (cf Adaptative Output Impedance in https://www.psiaudio.swiss/technology/) and KS Digital did with http://ksaudio.com/ks-digital/adm30/adm30.html.

 

[direstraitsfan98]

Does JBL's dual differential system have anything to do with lowering distortion?

https://jblpro.com/innovation-transducers

 

[q3cpma]

Does JBL's dual differential system have anything to do with lowering distortion?

https://jblpro.com/innovation-transducers

Pretty sure it's a remedy against power compression due to heat.

 

[Doodski]

There's also Psi audio (cf Adaptative Output Impedance in https://www.psiaudio.swiss/technology/) and KS Digital did with http://ksaudio.com/ks-digital/adm30/adm30.html.

That PSI product looks very intriguing. What kinda price range is that stuff?

 

[WesParker]

That PSI product looks very intriguing. What kinda price range is that stuff?

Looks like $11K/pair for the A25-M

 

[q3cpma]

That PSI product looks very intriguing. What kinda price range is that stuff?

Expensive to very expensive. They give measurements in their brochures, they're not incredible. Still, incredibly well made in Switzerland with a 5 year warranty is nice.
Due to their lack of real waveguide, the directivity always take a hit at the crossover point. Another company I put in the Focal/Dynaudio basket: good to great engineering, but not really science (this includes psychoacoustic) driven.

 

[direstraitsfan98]

These look cool. I saw them in the movie Straight Outta Compton and I looked them up right after. Interesting that they're a design thats been visually identical for over 25 years now.

 

[q3cpma]

These look cool. I saw them in the movie Straight Outta Compton and I looked them up right after. Interesting that they're a design thats been visually identical for over 25 years now.

Interesting isn't the word I'd use. "Worrying" is more like it.

 

[pozz]

Expensive to very expensive. They give measurements in their brochures, they're not incredible. Still, incredibly well made in Switzerland with a 5 year warranty is nice.
Due to their lack of real waveguide, the directivity always take a hit at the crossover point. Another company I put in the Focal/Dynaudio basket: good to great engineering, but not really science (this includes psychoacoustic) driven.

They have good on-axis and phase response (due to all pass filters), but directivity is as you would expect. That really doesn't make sense to me given how clear PSI is on other aspects of design.

 

[direstraitsfan98]

Oh believe me I know. I was being facetious. They're also discontinued now, recently I might add. I saw them listed on their page two years ago but they are now under legacy products on Meyer Sound website. About damn time!

 

[q3cpma]

They have good on-axis and phase response (due to all pass filters), but directivity is as you would expect. That really doesn't make sense to me given how clear PSI is on other aspects of design.

The other strange point is their insistance on phase while using a ported enclosure.

 

[pozz]

These look cool. I saw them in the movie Straight Outta Compton and I looked them up right after. Interesting that they're a design thats been visually identical for over 25 years now.

Classic Meyer monitors. They released the HD-2 five or so years ago. Another example where the lead designer, John Meyer, is a brilliant guy but hasn't done the same sorts of comprehensive psychoacoustic research as we have with Harman.

 

[Doodski]

The amplifier board a person was stuffing into a box really caught my eye. Looked very nice. The smaller models are claimed to be useful for portable broadcast applications. I would guess that is a saturated market.

 

[snapsc]

I'd like to ask a slightly different question....even if you could measure what is probably a small difference in distortion...could you actually hear it?

Have you ever turned off your mains and then set your sub crossover to 50 hz....if so, you will agree that you hear very little tone...mostly just thuds, bumps, growls and other sounds coming from the deep low end...which are themselves a critical part of creating pressurization and chest thump...so would you really notice an increase/decrease in distortion by switching from a sealed servo sub to an equally well designed non servo sub???

Now if you told me that the sub had to pull duty all the way up to 100hz....and that listening level was 100db and not 85db (which is much more normal)...then maybe the servo sub difference would be slightly audible....but not if the mains were running full range at the same time.

 

[DonH56]

I'd like to ask a slightly different question....even if you could measure what is probably a small difference in distortion...could you actually hear it?

Have you ever turned off your mains and then set your sub crossover to 50 hz....if so, you will agree that you hear very little tone...mostly just thuds, bumps, growls and other sounds coming from the deep low end...which are themselves a critical part of creating pressurization and chest thump...so would you really notice an increase/decrease in distortion by switching from a sealed servo sub to an equally well designed non servo sub???

Now if you told me that the sub had to pull duty all the way up to 100hz....and that listening level was 100db and not 85db (which is much more normal)...then maybe the servo sub difference would be slightly audible....but not if the mains were running full range at the same time.

The problem with sub distortion in general is that harmonics, being higher in frequency, are much easier to hear than the fundamentals. So high distortion at 50 Hz means audible components at 100, 150 , 200... Hz. So, yes.

 

[oldsysop]

JBL B-460

Specifications
Type: single driver subwoofer
Frequency Response: 24Hz to 70Hz
Recommended Amplifier: 800W (maximum)
Crossover Frequency: 63Hz
Impedance: 8Ω
Sensitivity: 94dB
Sub Bass: 1 x 2245H 460mm cone
Enclosure: bass reflex
Dimensions: 631 x 974 x 616mm
Weight: 57kg

 

[Doodski]

JBL B-460

Specifications
Type: single driver subwoofer
Frequency Response: 24Hz to 70Hz
Recommended Amplifier: 800W (maximum)
Crossover Frequency: 63Hz
Impedance: 8Ω
Sensitivity: 94dB
Sub Bass: 1 x 2245H 460mm cone
Enclosure: bass reflex
Dimensions: 631 x 974 x 616mm
Weight: 57kg

Yeah! More big bore proper sound gear...

 

[Doodski]

Yeah! More big bore proper sound gear...

This would be good start before adding subs>
https://www.ebay.com/itm/Vintage-JB...558088?hash=item44253d6a88:g:AYsAAOSw1Ktbc7r0