Hey, all. Wondering if anybody has some input on a problem I have with my sub. I use the AX500a, which is the top Axiom sub from the previous product line. Rather than a cube, it's a tower (just a few inches shorter than the M40), with a backwards-firing woofer and 2 down-firing ports.

We've moved into a new place with a much bigger rec room, and a couple of problems have popped up. The first is that bass impact during movies has decreased significantly, and I wonder if it's because of the ports firing down into carpet as well as the larger room.

Secondly, I'd been noticing some buzzing from all speakers as I turned up the volume on the reciever. Initially thinking it was the receiver clipping, I discussed it with the AV shop and made adjustments as per their suggestions. To make a long story short, I cranked the receiver today, this time with the sub off, and movie soundtracks were crystal clear.

My first question is, assuming the buzzing is mechanical vibration due to the sub, is such vibrating potentially damaging to the other speakers?

Secondly, would changing to a different sub with front or back ports decrease this effect? Are the down-firing ports a cause?

Finally, any other suggestions as to how to adjust things, since replacing the sub isn't an option yet (unless I have a shockingly busy week at the office)? Position hasn't seemed to make much of a difference, and I'm pretty sure nothing is physically wrong with the sub, since everything is fine when it's on at low volumes for music.

Fhw, if you're absolutely certain that this is a mechanical vibration coming from the speakers rather than some object in the room vibrating, I don't have a clue. If the bass level has been reduced(most likely due to the larger room, unless the carpet pile is so high that it actually blocks the ports),you would think that this would be less likely to cause vibrations.

Hey, JohnK.

Checking things out again, the source of the vibration is probably the rather thin walls leading to speaker vibration, but then again they vibrate because of the sub. The carpet pile is actually thin, and you can easily feel the spikes striking concrete when the speakers are placed.

I'm wondering if the effect is a result of so-called "sub-wall interactions", and might decrease with a forward-firing sub with non-floor firing ports.

In addition, does room vibration cause damage to loudspeakers?

fhw,
Are you trying to say that your sub is rumbling enough, constantly enough that the walls are vibrating and hence causing your speakers to vibrate which is causing a buzz?

Do you have an all wood basement (perhaps subfloor) or is it cement block/cement below the carpet/behind the drywall?

I would find it odd that moving to a larger room would actually cause an increase in vibrations over a smaller room unless the rooms were made with different materials.

Have you tried moving your sub somewhere out into the middle or further back in the room, away from any walls to see if vibrations decreased?

You certainly have an odd problem there.

Chess,

The house is a only few years old, one of those hastily-assembled suburbia specials. The basement has cement under the carpet. The walls are relatively thin drywall, presumably with wood for the loads. Our old place was an apartment building, although the construction was quite solid there.

It's very bizarre...I actually can't move the sub much farther out into the room, because the driver fires backwards to reflect bass off the walls, and moving it out decreases bass output markedly without much help on the vibration. To describe the AX500, imagine an M40 backwards, with the driver and control panel on the broad baffle facing the wall.

Essentially, in the bigger room I'm getting less clean bass, and far more mechanical vibration of the walls and other speakers. My electronics are on a sturdy rack.

If I remember, you use an EP350. Do you get much shaking of the walls? I am considering a trial purchase to see if a front-firing sub corrects the problem, barring any suggestions that work.

I imagine your house is not much different from my own. A hastily built suburbia special as you say.
Our basement is concrete floor with berber carpeting (quite thin) and a small underpad. The walls are standard 1/4" drywall with 2x4 studs at 22" distances (apparently a way of cutting down on costs vs 16" distance studs that still meets construction codes).
Other than a vapor barrier, i don't expect there is much in the way of insulation in our walls but don't quote me on that. I haven't checked that throughly.
Of course you can find some pics on my basement as wel to refresh your memory:
my setup pics site

I do have the ep350 and yes, it does rattle my drop ceiling but not the walls. I can certainly feel the ep350 upstairs (that is to say 2 floors up) but that is not unexpected.
Other than 'loose' items in my basement, the walls do not rumble enough to cause sound artifacts like you are describing.
However, if you wish, i can turn my ep350 around this evening and tinker with some bass notes and see if that does cause my walls to rattle at all.

I guess more importantly than "can the EP350 shake the walls?" (which I have no doubt it can), I'm wondering if it provides punchy and controlled bass with visceral impact.

As it is now, the back-firing AX500 is not liking my room at all. I'm getting visceral impact, but at a price of a whole lot of wall vibration and poorly-defined output.

To give an example of what I'm getting at, I went auditioning subs at a local HT shop. I listened to two sealed models, a $1000 B&W and a $1250 M&K. Playing the lightsaber duel scene from Attack of the Clones, the B&W shook my seat but not the walls (and it was backed up against a wall next to a rack of equipment). The M&K took the performance to a new level, as it was able to delineate new notes and sound effects that simply were not there with the B&W. It was much more realistic, without losing the visceral impact...a performance difference that almost certainly indicates the B&W is overpriced. Then again, the M&K is an eyesore, but now I'm off topic.

In the end I naturally have to decide whether or not to buy a new sub, I'm just concerned in the meantime that all the vibration might be damaging the other speakers. The search for a cause to the problem is a definite curiosity, but I can live with the uncertainty if it doesn't make sense.

Thanks again.

I can't really envision how your other speakers would be shaking them to the point of damage. I'm sure you are ok on that front.
As for the vibration issue, buying a front firing sub would be no different than turning your present sub around so its woofer faces the front (a bit simplistic mind you but you understand the point).
If you have tried to turn your sub around so it does fire forward, does that remove the problem that you have?
If not then you have one piece of evidence towards thinking that a front firing sub may not make a difference.

Second type of test would be to bring home a sub for auditioning from a quality audio store (brand is a little less relevant as long as its a front firing sub of decent quality) and give it a test with your system.
See what happens.
Does it still rattle the basement in the same way or not?

Should give you the fastest answer to your question about whether to replace your sub and if so, to replace it with a front firing one or not.

Try taking the spikes off.

I never though to turn the sub around to diagnose the problem. Duh! Anyway, I turned the sub around so it faced forward, and moved it in front of the L/C/R speakers and equipment rack. HUGE improvement. The walls only shook twice with the scenes I was testing (during the loudest bass instances from FOTR, and the initial flyby in Attack of the Clones), and there was far more impact throughout the room. Overall output still wasn't perfect, but the sound was much cleaner, and the buzzing became almost a non-issue. I suspect a front-firing sub placed well in front of the mains and equipment rack will solve the problem perfectly.

Now comes the real fun...auditioning!

Big thanks again.

That's great fhw.
Maybe you will also consider a down firing design assuming that you don't have an underlying wood subfloor.