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Author Topic: Distortion in Front Loaded Subs  (Read 2091 times)

Art Welter

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Re: Distortion in Front Loaded Subs
« Reply #20 on: December 10, 2019, 02:44:16 pm »

It would be interesting to see the distortion measurements at the same SPL.

After all, that is what it is about in the end.  Not the drive voltage.

Does speaker A have less or more distortion at X Hz than speaker B while producing some specified SPL?

After all, 5dB is almost 4 times the power.

I don't know the answer, because I haven't done it.  But curious.
Ivan,

Distortion and output SPL are two different metrics, but this post is called “distortion in front loaded subs”, the OP stated “In a recent thread Ivan indicated that front loaded subs have more distortion compared to tapped horn subs.”
Without voltage, no enclosure will make SPL or distortion, but fortunately we can measure both metrics individually.

In reply #2, you wrote:
“With any loudspeaker, the more it moves, the more distortion it has.”

In reply 10,  I posted examples showing that distortion was not specifically excursion (movement) related, the TH example exhibiting more distortion than the BR for a given drive level, even though driver excursion was reduced.

In post #14  Josh Ricci’s measurements also confirm that distortion for a similar drive level was higher in the TH than the BR.
Josh’s measurements also show that to achieve the same SPL levels, the TH distortion levels are generally less than the BR.
You can look at his tests in detail on his site to answer your question:
“Does speaker A have less or more distortion at X Hz than speaker B while producing some specified SPL?”

The fact that double the drivers, amplification, power distribution, and more truck space may be needed using BR compared to TH to achieve the same SPL does not negate the increased distortion the TH exhibits at the same drive levels.

Knowing the above, I’d still choose the cost effectiveness of the TH over the slight reduction in distortion twice the BR cabinets could afford.

Art
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Keith Broughton

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Re: Distortion in Front Loaded Subs
« Reply #21 on: December 10, 2019, 08:57:27 pm »

Quote
Josh’s measurements also show that to achieve the same SPL levels, the TH distortion levels are generally less than the BR.
For me, that is the deciding factor.
If I can get the same output with less distortion, that's a win.
Conversely, if I get the same distortion with less equipment, that could also be considered a win.
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Mark Wilkinson

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Re: Distortion in Front Loaded Subs
« Reply #22 on: December 11, 2019, 11:28:07 am »

Not enough to talk about. With reflex subs the highest excursion occurs at midband frequencies.. up around 60hz give or take, and excursion is minimized down at the tuning frequency.. that is what the box porting does, so any reasonable highpass you might use won't have much effect on excursion based distortion.
The distortion these boxes produce is a bit of a love/hate thing, there is a group of users that prefer the sound of reflex subs over horns because "reflex boxes sound louder" or "horns are too clean". That same group are also likely to insist on powering their subs to the max and are not happy until they are "growling" which is a nice way of describing large quantities of distortion, yes you can make a reflex sub produce so much distortion that it actually adds to the SPL output. It's not true that a driver needs some minimum power level to be safe but in some circles you may hear people say that a particular driver or sub "needs xxxx watts before it comes alive", what they are really saying is they actually like a certain level of distortion but they would probably call it warmth of fullness instead.

Paul, I think you stated a little recognized fact about excursion being highest at mid-band frequencies.

We are all so concerned with over excursion below port tuning, and having a proper high-pass-filter in place, we seldom look the other way to see what excursion is higher up.

I bet your call is spot on about mid-band over excursion being the source of folks' audible like or dislike.


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Tim McCulloch

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Re: Distortion in Front Loaded Subs
« Reply #23 on: December 11, 2019, 11:41:35 am »

Paul, I think you stated a little recognized fact about excursion being highest at mid-band frequencies.

We are all so concerned with over excursion below port tuning, and having a proper high-pass-filter in place, we seldom look the other way to see what excursion is higher up.

I bet your call is spot on about mid-band over excursion being the source of folks' audible like or dislike.

Mid-band distortion for a sub means harmonic distortion that is *above* the sub's LPF corner frequency.  We were using a "pSeudo-4" loudspeaker designed in the spirit of the early Clair S-4 by a company Clair bought ~15 years ago (we still have 8 of them).  Note that I'm NOT talking about the actual Clair box... The distortion from the LF section (18") in the 150-300Hz range was astounding, to the point where one could severely under-lap the electrical crossover.  Pink noise would show a reasonably flat magnitude through crossover but when auditioned with program audio the failure was audibly obvious.

There is a whole lot going on in loudspeaker operation, more than most folks realize (present company excepted).  The more speaker systems I measured - while learning to make good measurements - made me realize just how many compromises a designer has to accommodate to deliver a packaged product.  The fewer compromises, the higher the price.
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John Roberts {JR}

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Re: Distortion in Front Loaded Subs
« Reply #24 on: December 11, 2019, 02:04:36 pm »

Loudspeakers are the poster boy for engineering (and I use that term loosely) design tradeoffs. As the old saw goes, if you want to optimize some parameter(s) decide what can get worse to pay for it.

JR 
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Ivan Beaver

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Re: Distortion in Front Loaded Subs
« Reply #25 on: December 11, 2019, 04:19:11 pm »

Loudspeakers are the poster boy for engineering (and I use that term loosely) design tradeoffs. As the old saw goes, if you want to optimize some parameter(s) decide what can get worse to pay for it.

JR
It is all a matter of tradeoffs.  As many things are.

Understanding what the tradeoffs are help people to make informed decisions, one way or the other
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Peter Morris

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Re: Distortion in Front Loaded Subs
« Reply #26 on: December 12, 2019, 08:33:55 am »


The only time I've done any distortion comparisons among box types was in this thread    https://forums.prosoundweb.com/index.php/topic,167351.0.html
But it was a double 18 bass-reflex and a Labhorn…..not sure if any distortion conclusions can be drawn from it at all.

The best comparison of the same driver with different box types I've seen is Ricci's article on sealed, vs ported, vs tapped, that uses a 12".
https://data-bass.com/#/articles/5cb774640ca6e70004e10828?_k=7muugk

FWIW I did a quick SIM in Hornresp of something like a Danley TH118 Vs a typical BR double 18" using the same driver (B&C 18SW115). 

The boxes would have been a similar sizes, the Xmax was similar and the output was almost identical for the same input voltage.  Both had similar LF extension but the BR had a much greater band width, its response was much flatter and it had a much better impulse response.

.... so its really about the cost of the second driver and the amplifier to drive it Vs the flat response, greater bandwidth, and better impulse response .... I suspect using a quality new driver like the B&C 18SW115 the distortion in both cases will be OK.

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Chris Grimshaw

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Re: Distortion in Front Loaded Subs
« Reply #27 on: December 12, 2019, 11:44:11 am »

How did it look with an LR24 lowpass applied at 100Hz?

If your distortion levels are acceptable, you're not pushing the rig hard enough!  8)

Chris
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Mark Wilkinson

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Re: Distortion in Front Loaded Subs
« Reply #28 on: December 12, 2019, 02:47:46 pm »

Mid-band distortion for a sub means harmonic distortion that is *above* the sub's LPF corner frequency.  We were using a "pSeudo-4" loudspeaker designed in the spirit of the early Clair S-4 by a company Clair bought ~15 years ago (we still have 8 of them).  Note that I'm NOT talking about the actual Clair box... The distortion from the LF section (18") in the 150-300Hz range was astounding, to the point where one could severely under-lap the electrical crossover.  Pink noise would show a reasonably flat magnitude through crossover but when auditioned with program audio the failure was audibly obvious.

There is a whole lot going on in loudspeaker operation, more than most folks realize (present company excepted).  The more speaker systems I measured - while learning to make good measurements - made me realize just how many compromises a designer has to accommodate to deliver a packaged product.  The fewer compromises, the higher the price.

Yep to all said. 
On your pSeudo-s4's, was the distortion in the 150-300Hz range at all levels, or only when cranked up? 
I'm wondering if you decided the drivers were crap from the gitgo, or if they just couldn't take any power without distorting.
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Mark Wilkinson

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Re: Distortion in Front Loaded Subs
« Reply #29 on: December 12, 2019, 03:37:59 pm »

FWIW I did a quick SIM in Hornresp of something like a Danley TH118 Vs a typical BR double 18" using the same driver (B&C 18SW115). 

The boxes would have been a similar sizes, the Xmax was similar and the output was almost identical for the same input voltage.  Both had similar LF extension but the BR had a much greater band width, its response was much flatter and it had a much better impulse response.

.... so its really about the cost of the second driver and the amplifier to drive it Vs the flat response, greater bandwidth, and better impulse response .... I suspect using a quality new driver like the B&C 18SW115 the distortion in both cases will be OK.

I've come to about the same conclusions.
Distortion-wise, I also think a good double 18" bass-reflex and a single 18" tapped are both equivalently clean at the same SPL levels...when operated sanely.
And like you say,  from a logistics point of view, a tapped horn wins with less drivers and amps needed....but box sizes will be close to a wash.

IMO, one thing I think a bass-reflex does easier than a tapped horn, is low end extension.
It's not that hard get an unboosted f-3 @30hz with a BR, and the box doesn't have to climb as fast in size to get there, like a tapped horn box does.


I see your sims have the BR measuring flatter...my experience copies that.
One thing I'd like to ask you about is your impulse assessments. 
I've nearly come to the conclusion impulse responses don't really have value when measuring subs, because impulse responses are so dominated by higher frequency data.
So in the case of a BR reaching higher in bandwidth than a tapped horn, I'd almost expect its impulse to look better,  no matter how the subs actually compared in normal operation (say below 100Hz for example).
But this is just looking at  linear impulses.
Do you have a better way of judging impulse down low with equivalent low passes?... Bandwidth Filtered, or maybe log view? thx



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Re: Distortion in Front Loaded Subs
« Reply #29 on: December 12, 2019, 03:37:59 pm »


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