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Author Topic: Distortion in Front Loaded Subs  (Read 1563 times)

Robert Lunceford

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Distortion in Front Loaded Subs
« on: December 04, 2019, 07:39:28 pm »

In a recent thread Ivan indicated that front loaded subs have more distortion compared to tapped horn subs. Is the distortion a function of the low frequencies produced by the sub or is distortion inherent to all front loaded speakers?
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Tim McCulloch

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Re: Distortion in Front Loaded Subs
« Reply #1 on: December 04, 2019, 08:15:34 pm »

It's been a few years so we'll see if my memory is good...

It's inherent in the design and distortion rises exponentially with excursion, whereas in horns distortion is linear with excursion until Xmax is reached.

I think...
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Ivan Beaver

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Re: Distortion in Front Loaded Subs
« Reply #2 on: December 04, 2019, 09:01:18 pm »

In a recent thread Ivan indicated that front loaded subs have more distortion compared to tapped horn subs. Is the distortion a function of the low frequencies produced by the sub or is distortion inherent to all front loaded speakers?
It was not in regards to tapped horns, but rather horns in general.

Horns act as an "acoustic transformer" between the stiff suspension of the driver and the "loose air".

They basically "control the motion" so the drivers are not moving as far, to produce the same SPL.

With any loudspeaker, the more it moves, the more distortion it has.  So if the motion is less, the distortion.

A good analogy is a baseball pitcher.  Give him a whiffle ball and ask him to throw it 90MPH.  Can't be done, because the mass of the ball is not matched to the medium of the air, no matter how strong his arm is.

Not every driver on a horn works well, the driver parameters must be matched for the horn design in order to get the most gain over the widest bandwidth.

But if done correctly, you can get 15dB or so of gain.  That would be like taking a driver rated at 100 watts and then getting the same SPL with around 3 watts.  Or put another way, you would have to "apply" 3,000 watts to it to get the same SPL.

But not all horn/driver combinations can get you that much.  But some can.  6dB or more is pretty easy.
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Ivan Beaver
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Robert Lunceford

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Re: Distortion in Front Loaded Subs
« Reply #3 on: December 04, 2019, 11:42:12 pm »

It was not in regards to tapped horns, but rather horns in general.

Horns act as an "acoustic transformer" between the stiff suspension of the driver and the "loose air".

They basically "control the motion" so the drivers are not moving as far, to produce the same SPL.

With any loudspeaker, the more it moves, the more distortion it has.  So if the motion is less, the distortion.

A good analogy is a baseball pitcher.  Give him a whiffle ball and ask him to throw it 90MPH.  Can't be done, because the mass of the ball is not matched to the medium of the air, no matter how strong his arm is.

Not every driver on a horn works well, the driver parameters must be matched for the horn design in order to get the most gain over the widest bandwidth.

But if done correctly, you can get 15dB or so of gain.  That would be like taking a driver rated at 100 watts and then getting the same SPL with around 3 watts.  Or put another way, you would have to "apply" 3,000 watts to it to get the same SPL.

But not all horn/driver combinations can get you that much.  But some can.  6dB or more is pretty easy.

My subs are 18" front loaded and the manufacturer claims 35Hz at -3db. I am using the Waves MaxxBCL and setting the low cut filter at 48Hz. Since the subwoofer is low cut at 48Hz, will it produce less distortion than if it were allowed to produce frequencies down to 35Hz ?
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Paul G. OBrien

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Re: Distortion in Front Loaded Subs
« Reply #4 on: December 05, 2019, 12:41:28 am »

Since the subwoofer is low cut at 48Hz, will it produce less distortion than if it were allowed to produce frequencies down to 35Hz ? o
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.
« Last Edit: December 05, 2019, 12:47:18 am by Paul G. OBrien »
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Keith Broughton

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Re: Distortion in Front Loaded Subs
« Reply #5 on: December 05, 2019, 07:31:59 am »

Something else to consider when talking distortion is the harmonics above the range the bass driver is working in.
Higher harmonics are created that fall into the low mid and mid band having a negative effect on more than the bass range.
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Ivan Beaver

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Re: Distortion in Front Loaded Subs-A simple test
« Reply #6 on: December 05, 2019, 08:20:26 am »

Something else to consider when talking distortion is the harmonics above the range the bass driver is working in.
Higher harmonics are created that fall into the low mid and mid band having a negative effect on more than the bass range.
Yeah.  MANY people do not understand what harmonic distortion actually is.

It is simply "more notes" than the original signal has in it.

You can see this easily on an RTA with a simple test.

Just put a sine wave into a sub (say 60Hz).  Now look at your RTA (or transfer function) as you turn up the level.  It is best if you have the RTA with as fine a resolution as you can (1/12th or 124th octave).  Btu 1/3rd octave will still work.

Of course you will see the 60Hz, but as you turn it up more and more, you will see higher freq get louder and louder.  120Hz, 180Hz, 240Hz etc. Even if the sub is low passed at 80Hz, you will see these.

These are signals that ARE NOT part of the original 60Hz tone.  THAT is the distortion-something that was not in the original signal.

Some people like to have a sound system that will reproduce the ORIGINAL signal as good as possible.  Others like to have the "free notes".  But remember, you CANNOT talk about how "accurate" your system is, it if is giving you more notes than you put into it.
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A complex question is easily answered by a simple-easy to understand WRONG answer!

Ivan Beaver
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Luke Geis

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Re: Distortion in Front Loaded Subs
« Reply #7 on: December 05, 2019, 02:35:14 pm »

Adding on, port design does have some influence in the sound and you could say distortion of a sub. You may have heard the term port chuffing, port distortion, or port noise? It is the sound that the port makes as air moves back and forth through it. At higher levels, the port chuffing is quite audible and could/should be considered distortion. Different designs and sizes have different outcomes. The port is designed around the needs of the driver and the box and generally bigger is better ( less chance for chuffing ), but it is not a one size fits all. I am not 100% versed in speaker design but have come to understand that larger ports mean a few things. The speaker is very efficient at producing SPL without needing a smaller port, they tend to go lower in frequency response and they are less prone ( require more output ) to cause port chuffing. My understanding is that smaller ports are used to increase gain at higher frequencies ( generally in the mid-band of the cabinet ) at the cost of low-end frequency response. Smaller ports are of course easier to make them chuff as well.

I have not used too many ported subs in my 17 years as an engineer. The few I have used had a thing going on for them that I wasn't fond of. They were one-note wonders ( butt loads of one frequency ) and it seemed it took a little distance before that output was noticed. Ported subs tend to be more suited en-mass where the # of subs increases the bandwidth they collectively reproduce. Although some designs are getting better at wideband reproduction with single or fewer # of cabinets. As for the distance thing, I don't know enough to quantify it, it could have just been me? I would like to know more about that though as I am not the only one who has gotten that impression.

In either case, just more food for thought.
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Ivan Beaver

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Re: Distortion in Front Loaded Subs
« Reply #8 on: December 05, 2019, 03:29:55 pm »

At higher levels, the port chuffing is quite audible and could/should be considered distortion.
There are different types of "distortion" and they come from different situations.

ANYTHING that is other than the original signal is distortion.  Distortion by the very meaning is something that is not the original.  It can be in a photo, audio, video etc.

Some types of distortion are desirable (guitar amps, gels in par cans etc), but not in something that is "supposed" to be a REPRODUCER of something.  If there is distortion, it is NOT an accurate reproduction.

In most cases, a sound system should be a REPRODUCER of sound, NOT a CREATOR of sound (like a guitar amp)

Whether or not someone prefers that, is a personal opinion.
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A complex question is easily answered by a simple-easy to understand WRONG answer!

Ivan Beaver
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duane massey

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Re: Distortion in Front Loaded Subs
« Reply #9 on: December 05, 2019, 09:44:48 pm »

My goal has always been very simple: "What goes in, comes out".
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Duane Massey
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ProSoundWeb Community

Re: Distortion in Front Loaded Subs
« Reply #9 on: December 05, 2019, 09:44:48 pm »


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