sub distortion?

I read some subs have a lot of distortion. Is this important? Because amps might have .0001 distortion, but if subs have 1%, is that bad?
How much does one have to spend to get high quality sub for music
My understanding is that all woofers distort not just subwoofers. The distortion increases rapidly as the level increases and the frequency decreases. We're talking about easily > 10%. Adding a subwoofer and high-passing the main speakers will typically lower the total distortion produced by your speaker system.

The solution is to ensure that your use of the sub does not push it into distortion -- just like with an amplifier.

Both Hsu Research and SVS make good subwoofers that perform well that are under $1000.

Here's a couple of subwoofer testing web sites: AV Talk, Home Theater Shack
In a cone driver distortion increases rapidly as the excursion of the cone (travel in and out) increases. Drivers made for subwoofer use generally have a large range of excursion, but it's obvious by looking at a busy subwoofer that the full range is easily used up. The more cone area you have the less excursion is necessary, and therefore the lower the distortion. Large drivers, 12" 15" 18" (and even 30") are most suitable. Multiple drivers also help, and a pair of 10" (roughly equal to one 12") is sometimes used.

The custom design subwoofer systems of my three front channels include three 15" and three 12" cone drivers. Even so, they have less area than my Maggies.
Distortion is very important because it is often harmonic and you hearing is WAY more sensitive at 80 Hz then at 20 Hz! A mere once percent harmonic distortion at 80 Hz from a reference signal at 20 Hz is LOUDER to your ears then the primary signal!

So guess what.....unfortunately most of what you hear from impressive subs is the harmonic distortion (usually around 10% at 20 Hz on good subs and perhaps 50% or more on not such good subs). There is very little out there with less than 1 % THD. Those who shun subs altogether have a good argument for doing so...
Why I perfer bass horns limited excursions allow detail to bass that sub designs lose to excursion and distortions. Also bass horns are always at ease never pushed hard. This again allows more bass detail than subwoofers which need 100 watts or more just to move the cone with such a stiff surround. Toss in the one large null instead of the many peaks nulls that happen with subwoofer systems. This 1 null is located near bass horns so is not a issue at all volume is slightly reduced as you move close to bass horn this is slight and basicaly means bass pressures very even through out room something one subwoofer can not do. And why multiple subs are used in the best HT and music systems. Subwoofers are all about comprimised design small cab thus you need massive power and driver with much excursion that needs boundery reinforcment to generate bass. Trying to get deep bass out of such a comprimised design is mostly sub optimal:)
Johnk, can you expand on this:
Toss in the one large null instead of the many peaks nulls that happen with subwoofer systems. This 1 null is located near bass horns so is not a issue at all volume is slightly reduced as you move close to bass horn this is slight and basicaly means bass pressures very even through out room something one subwoofer can not do.

Hi Bob trying to think what I can add and my mind goes blank wish I where a technical writer but saddly am not just a loudspeaker designer;)But I will try. Bass horns do have some problems size, cost and if not done right you can pick up much sound from cabinet vibrations. But when design is right bass doesnt get any better. The pressures amazing. I was working on one new bass horn design was running test tones. I had a new front door installed in my studio. I was running test tones arround 20hz I noticed day light arround my new doors magnetic seal. I though darn just bought it so was checking out this space with my fingers the tone switched to next one, the door was bowed out due too bass pressures and once tone was off, door sprang back smashing 3 of my finger nails;) This even pressure and detail to bass notes is the bass horns advantage. You can stand by room bounderys and bass SPL doesnt increase, in corners, near wall bass SPL is even. A sub will cause a peak or null to form. One can set up a sub to give decent bass to a few seating areas but if your close to a wall or corner bass level will increase if in a null it will be reduced using more than 1 sub can help even this loading out. With a bass horn pretty much anywhere you set it in room it will produce null near horn but even pressure through room. Bass horns also have very low distortion due to limited excursion driver doesnt need to travil as far so can reproduce notes lost to violent movements of most subwoofer designs.
Thanks John. But, I'm confused (nothing new about that!). I thought room modes (and their associated peaks and troughs) are a function of frequency and dimensions of the room. I've never read where the type of the source (horn, cone, panel) of the frequency made any difference. I thought that was fundamental acoustics. So I don't understand how a bass horn is getting around this problem. Specifically, that was the clarification I was requesting. I'll try researching bass horns. Thanks again.
agree Shadorne. So I am confused when some say add sub for music!
Samuell, the thing that Shadorne didn't mention is that the distortion being produced by the woofers in your main speakers have the exact same problems. The reason a sub is suggested for music systems is to remove the bass load from the main speakers (80Hz and below) and let a specially designed speaker handle it. Is it perfect? No, but it will be better than letting the main speakers handle it.

The other advantage of a subwoofer is that it can be located separately from the main speakers.
Thanks Bob-reynolds. My bookshelfs go to 55Hz or 65Hz. I was using a sub for music fixed from 80hz and below , is that too high? It didn't sound that good.
Samuell, are you doing bass augmentation (running the main speakers full range) or bass replacement (high-passing the main speakers)? I didn't have good results the one time I tried bass augmentation with stand mount speakers. I now high-pass the main speakers at 80Hz so that the bass is completely handled by the sub. If that's what you're doing then I would look at level matching between the main speakers and the sub. I think test tones and an SPL meter is necessary to do this well.
I think bass replacement. Sub was plugged between the poweramp and preamp. maybe room placement was a problem.

I noticed asc sells a subwoofer stand. Is this a good idea? they say it
prevents vertical nodes
If you haven't already given it a look, you might find Dr. Toole's paper Getting the Bass Right interesting (click on the Papers link).
What sub are you using? And how are you matching the level between the sub and the main speakers? By ear or SPL meter with test tones?
who's in charge of audiogon?