Maybe they are being overdriven with LF drive, and the cone excursion is "Bottoming Out" ?

If this is the case, the sound should go away at modest sound levels....

Just my guess.

Have you played the speakers at very high SPL's? How about heavy bass content? If so, you probably damaged the voice coil and it is catching on the edge of the pole piece as it travels back and forth in the gap.

The low frequency limit of your speakers doesn't mean the speakers won't respond to low frequency information beneath that "cutoff" point. The response is simply down so much in level as to be considered unusable. The woofer will respond to very low frequency information as anyone who has had cone flutter from a turntable/tonearm will tell you. (An 8Hz pulse is interesting to watch at first until your realize what's actually happening.)

Place your fingers around the dust cap and push in very gently while listening for any noises. Push evenly and symetrically or you will hear scraping which isn't related to this problem. Even if this doesn't reveal any obvious problems, if you've played the system at high levels or with excessive bass content, you have probably done a dirty deed to the voice coil.

How's your "spider"......loose, glue come apart, woofers shouldn't make any noise when moving, unless the spider broke free, adhesive didn't hold.

If you find 10db of bass boost necessary you need a subwoofer. With 10db of boost you could be overdriving your amplifier. What kind of music has 18hz tones? Just how much bass are you trying to get? Is it possible you are trying to get that punchy "bass" you hear in clubs and discos? If so please be advised that is not bass. It is really lower midrange. Tweeter damgage usually comes from driving an amp into clipping. This occurs when you have insufficient power. Having too much power usually damages woofers.

10dB boost? every 3dB needs 10X the watts...you ain't increasing nutin 10dB, certainly no 18Hz... rethink your idea here. 65W now X 10 you be at 650W already and you only went up 3...dB, now we go another 3dB...hmmmm, now anyone understand why I have 4800W RMS out of 4 AVA OmegaStar EX/Hafler amps...ain't sounding so crazy now is it, ain't got no distortion either

DUP

Actually, an increase of 3db only requires 2 X the power not 10 X. But for our ears to percieve that the sound has gotten twice as loud you do need 10 X the power. But yes you do run out of power quickly either way.

Most speakers are damaged by too little power as opposed to too much power. When you have too little power, people tend to push the amp into clipping and the distortion is what blows the speaker. Also, the physical placement of the volume control at half way or any other point on the dial is not entirely indicative of how much power you are sending to your speakers. It is possible that half way on the dial is producing too much distortion.

In any event, before I did anything else I would ensure that my interconnects and cables were firmly attached and hope for the best.

3dB is twice as loud I thinks...I thinks 10X is correct. It be log not linear, I thinks, but I may be wrong or I might be right. You are correct the dial pos on a vol pot means nutin'. The taper of the pot influcnes what it does to the ckt. There is no substitute for WATTS. Good Clean HEALTHY WATTS, remeber mo' WATTS is BETTER, always, always always. And that is not just for increasing volume, but just opens up the sound, using teh same speakers, they will always sound better with more WATTS.

What kind of amp or receiver are you using?

Mrlowry be right, I reckon.

A 3 dB increase requires twice the wattage.

So, his 10 dB correction would require slightly more than threee doublings, or just over 8 times the wattage of his baseline volume.

So...

He mentions that his amp supplies less than the 65 watts his tweeters are rated for.

The speaker is rated at 89 dB sensitivity. I know this can vary somewhat, but let's use AE's data.

At 89 dB for the rest of the frequency range, Ali will be using 8 watts for his bass correction.

For 92 dB, he needs 16 watts for that range.

For 95 dB, 32 watts.

For 98 dB, 64 watts - above what he implies his amp will do.

I bet, for this guy, 98 dB peaks are below his expectations, and he's overdriving the amp and getting some nasties from that behavior rather than his woofer being "overdriven" with clean power.

So, I would guess that the problem here is...

A) Expecting too much bass from that speaker, even with "correction."

B) Underpowering his current requirements for that amount of equalization.

A two faceted problem...a speaker that can't physically deliver what he wants, and too little power even if it could.

True! I still want to know what music has 18Hz tones.

I believe that the some giant pipe organs have notes that have their fundamentals at 16hz. But other than that not much.

Ali doesn't sound like an organ aficionado. Thats why I asked.