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Author Topic: Speaker distortion vs drive level question  (Read 1069 times)

Wayne Smith2

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Speaker distortion vs drive level question
« on: March 01, 2019, 05:04:09 am »

I've been seeking to better understand or answer a question, that being; That the amount -or portions of a given driver's distortions, remain mostly a constant, and (within it's safe usable limits), being rather independent of the input drive levels?
« Last Edit: March 01, 2019, 05:07:03 am by Wayne Smith2 »
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David Morison

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Re: Speaker distortion vs drive level question
« Reply #1 on: March 01, 2019, 05:57:23 am »

I've been seeking to better understand or answer a question, that being; That the amount -or portions of a given driver's distortions, remain mostly a constant, and (within it's safe usable limits), being rather independent of the input drive levels?

Depends on the driver (and box/tuning/processing of course) but distortion will always rise with drive level - well designed systems will keep it as low as possible as loud as possible of course but there will be a rise.

Josh Ricci's site Data Bass has a lot of real world measurements, eg: https://www.data-bass.com/data?page=system&id=142&mset=165 (click the orange "measurements" button then "Multi Series Charts" tab to see the distortion curves).
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Wayne Smith2

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Re: Speaker distortion vs drive level question
« Reply #2 on: March 01, 2019, 06:36:58 pm »

Depends on the driver (and box/tuning/processing of course) but distortion will always rise with drive level - well designed systems will keep it as low as possible as loud as possible of course but there will be a rise.

Josh Ricci's site Data Bass has a lot of real world measurements, eg: https://www.data-bass.com/data?page=system&id=142&mset=165 (click the orange "measurements" button then "Multi Series Charts" tab to see the distortion curves).
Thanks for that! My first interest wasn't low freq drivers per say, but did get at least a good starter/reference example. A single JBL rig.
https://www.data-bass.com/data?page=system&id=68&mset=73
On the multi-series, picking in the 60Hz range, filtered for clarity to the 105 and 125 dB plots..
The differences hover in the 4--8% range.

The question delves further, in that distortion remains relatively the same into even much lower drive levels.
Here is a good part of what got me reconsidering some of my previous assumptions. The subject here is Ian White dispelling notions of their being 'desirable speaker distortion sweet spots' via drive level' For guitar speakers, however..

https://www.soundonsound.com/techniques/understanding-recording-guitar-speakers

He basically says; drivers distort' as they will, but depending on the makeup of their construction ..not drive level!
Guitar speakers, yes ok. But in doing so he also branches into the connection of 'higher power/high efficiency = lower distortion' camp, and their following the same 'rule -Construction/design determines how clean' (or not). Not so much 'drive level.

Go ahead hit me :>) I could probably use a good smack about now ;)
« Last Edit: March 01, 2019, 06:49:17 pm by Wayne Smith2 »
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Kevin Conlon

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Re: Speaker distortion vs drive level question
« Reply #3 on: March 01, 2019, 08:11:25 pm »

Thanks for that! My first interest wasn't low freq drivers per say, but did get at least a good starter/reference example. A single JBL rig.
https://www.data-bass.com/data?page=system&id=68&mset=73
On the multi-series, picking in the 60Hz range, filtered for clarity to the 105 and 125 dB plots..
The differences hover in the 4--8% range.

The question delves further, in that distortion remains relatively the same into even much lower drive levels.
Here is a good part of what got me reconsidering some of my previous assumptions. The subject here is Ian White dispelling notions of their being 'desirable speaker distortion sweet spots' via drive level' For guitar speakers, however..

https://www.soundonsound.com/techniques/understanding-recording-guitar-speakers

He basically says; drivers distort' as they will, but depending on the makeup of their construction ..not drive level!
Guitar speakers, yes ok. But in doing so he also branches into the connection of 'higher power/high efficiency = lower distortion' camp, and their following the same 'rule -Construction/design determines how clean' (or not). Not so much 'drive level.

Go ahead hit me :>) I could probably use a good smack about now ;)
BAM. As someone here says "stop confusing the facts with logic". (i am kidding)
« Last Edit: March 01, 2019, 08:23:38 pm by Kevin Conlon »
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Wayne Smith2

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Re: Speaker distortion vs drive level question
« Reply #4 on: March 04, 2019, 02:01:49 pm »

Giving this a bump here, hoping for some more input and better understanding. Thanks
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John Roberts {JR}

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Re: Speaker distortion vs drive level question
« Reply #5 on: March 04, 2019, 03:06:34 pm »

I will warn in advance that I am not the speaker expert around here, but of course level matters. When discussing this with operators we tend to focus on things under our (their) control like drive level.

Speakers have a few different ways to distort from bottoming out (with loud snap like sound) and power compression where they gradually lose output as they overheat before releasing their magic smoke.

Everything (almost everything) in life becomes progressively more distorted before breaking (except perhaps personal relationships that can snap suddenly).

The distortions that are not effected by drive level are not really worth losing much sleep over because we cannot affect that. Control what you can optimize.

JR
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Chris Grimshaw

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Re: Speaker distortion vs drive level question
« Reply #6 on: March 05, 2019, 04:41:18 am »


He basically says; drivers distort' as they will, but depending on the makeup of their construction ..not drive level!
Guitar speakers, yes ok. But in doing so he also branches into the connection of 'higher power/high efficiency = lower distortion' camp, and their following the same 'rule -Construction/design determines how clean' (or not). Not so much 'drive level.

Go ahead hit me :>) I could probably use a good smack about now ;)


For a given SPL, higher efficiency = less power. Less power = less distortion. He's actually contradicting himself a little.

As you increase the power levels, one effect that comes up is this: flux modulation.

The textbook equations are a useful starting point, but don't cover the full story. When the voice coil makes a magnetic field (due to current flowing through the coil), that field will start to bend the field that's being maintained by the permanent magnet.
More coil current means more distortion of the permanent field. Distortion of the magnetic field means the "B" in F=BIL now has some dependency on "I", and the whole thing gets more complex, and will result in distortion products forming.

Now, if we add some demodulating rings (or better yet, a copper sleeve over the polepiece), eddy currents can flow there, which reduce the distortion of the permanent magnetic field. That directly lowers distortion.


Other effects do come up. At low frequencies, you'll find that the magnetic field strength isn't constant as you move the cone. The suspension often isn't particularly linear, either. The good drivers keep those things as linear as possible within the driver's operating range, and then taper off so that it's very difficult to make the driver hit the mechanical stops (which usually results in instant permanent damage).


Another distortion effect will be from the cone. Let's consider a simple aluminium cone for a start. They tend to have one break-up mode, and it's a big one - the primary bell-mode resonance.
Let's say the cone has geometry such that the bell-mode resonance is at 3kHz. You'll often find that there's a spike in 3rd harmonic distortion at 1kHz. The cone happens to want to ring at 3kHz, so any excitation of that resonance (lets say the motor produces a little 3rd harmonic - see above) will be amplified hugely.
It should be clear that increasing the drive level at 1kHz will produce more distortion in the motor, which in turn gets amplified by the cone resonance. The distortion profile will have a peak in the 3rd harmonic at 1kHz, and that peak will increase with drive level.

Moving back to paper cones (we see those often in PA systems, for various reasons, abuse tolerance being one of them), the bell-mode resonance still exists. However, a lot of other resonances also come up. Standing waves from dustcap to cone edge, voice coil joint to cone edge, etc etc etc. Stiff metal cones suppress a lot of those, but usually have a big mess concentrated in one place in exchange. Everything's a trade-off, after all.
Paper cones, however, are often reasonably well-damped so while resonances may occur, they might be sufficiently low-Q that it just looks like a trend in the frequency response, with minimal ringing in the time domain. The distortion profile would follow suit - wide but shallow increases in the various harmonics as drive level increases.

I actually have a 10" paper coned driver here that's very well behaved - a couple of response peaks (2.5kHz and 4kHz). The distance from cone edge to dustcap is about 6.5cm, and the speed of sound in paper is pretty close to that in air, so you can guess that the 2.5kHz peak is a half-wave standing wave between the dustcap and the cone edge.
Usefully, the driver is well-behaved in the time domain - those peaks don't ring much at all, so you can actually use them as part of the crossover. At the moment, the 2.5kHz peak helps to form the knee.

Back on-topic.

It's worth taking a look at the work done by John at Zaph Audio. It's almost entirely HiFi gear under review/test, but there's a huge amount of information there, including options to compare metal vs paper coned drivers with similar motors if you dig around.

Chris
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Wayne Smith2

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Re: Speaker distortion vs drive level question
« Reply #7 on: March 06, 2019, 10:09:06 pm »

Thank you Chris for all of that! I'll look into your lead to Zaph Audio as well.
Wayne
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Ivan Beaver

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Re: Speaker distortion vs drive level question
« Reply #8 on: March 07, 2019, 08:19:56 am »

I've been seeking to better understand or answer a question, that being; That the amount -or portions of a given driver's distortions, remain mostly a constant, and (within it's safe usable limits), being rather independent of the input drive levels?
Lets start with "what is distortion"?

To me, distortion is ANYTHING that changes the input signal.  To others they are simply talking about harmonic distortion.

But there are other types as well.

So EVERY loudspeaker changes the input signal, so therefore is creating distortion.

With every loudspeaker, the harder you drive it, the more harmonic distortion there is.

This is easily seen by any number of easy to do different measurements.

But the other question is, "How much is acceptable?"  That is a lot harder to answer and different people will have different opinions.

So, once again, it depends.
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Dave Garoutte

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Re: Speaker distortion vs drive level question
« Reply #9 on: March 07, 2019, 12:01:12 pm »

Lets start with "what is distortion"?

But the other question is, "How much is acceptable?"  That is a lot harder to answer and different people will have different opinions.

So, once again, it depends.

Plus what sounds good / bad.
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Re: Speaker distortion vs drive level question
« Reply #9 on: March 07, 2019, 12:01:12 pm »


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