B460 malady

[doyall]

After two weeks of rearranging and running new cables for practically all of my AV equipment to accommodate a recently acquired B460, I finally got to fire it all up. Signals run from a Nakamichi CA-5 preamp into a BX63A crossover then to a bridged JBL Urei 6360 amp. I had it cranked up to what I thought was a moderate level and everything was sounding wonderful until I heard a rather loud pop immediately after a powerful bass note. Girlfriend heard it too. I take it this was the voice coil bottoming out. Is the 2245H just not designed to be driven hard or could this be a result of spider fatigue/some other cause? If it can’t be driven any harder than I had it, then its use for home theater would appear to be severely limited.

[toddalin]

I've bottomed out 130As and 2235s when used as subs in our home theater and also wondered "is that all there is?" Luckily, I quickly turn down the volume and have done no apparent harm.

I've never bottomed out the W15GTI, probably because of its architecture (i.e., dual voice coils out of phase that limit cone travel at the extremes).

You may try blocking one of the ports to limit woofer excursion, although, it would seem that the design should consider this.

[Robh3606]

I would be curious as to what it was, ie sound effect explosion that did the deed. These woofers are in bass reflex cabinets and should be protected from high level bass below the box tuning frequency. Simply said they should be run with high pass filters in place. You have to remember that these designs are older and done long before HT and digital cannons at 10 ft, That type of special effect LFE bass was not a consideration back in the early 80's.

I think the BX-63 has one Did you see how much cone excursion you are getting?? You can get close to an 1 inch out of a 2245 so I would pop the grille cloth and see what is actually going on. You getting any pumping or offset of the woofer?? Is the woofer new or is it old?? You could have an offset spider depending on how the driver was stored.

Rob

[Thom]

Real non expert here but if that is what you heard it may have been from too strong of a signal (information or noise) at a frequency lower than it can handle. A subsonic filter may be all you need. Caution, long distance trouble shooting is always pretty iffy.

[doyall]

I would be curious as to what it was, ie sound effect explosion that did the deed. ... You have to remember that these designs are older and done long before HT and digital cannons at 10 ft, That type of special effect LFE bass was not a consideration back in the early 80's.
... Did you see how much cone excursion you are getting?? You can get close to an 1 inch out of a 2245 so I would pop the grille cloth and see what is actually going on. You getting any pumping or offset of the woofer?? Is the woofer new or is it old?? You could have an offset spider depending on how the driver was stored.

Rob

It was playing music when it happened, either Pink Floyd or Barry White, I can't remember. I'm kind of reluctant to try any LFE's at the moment.

As a matter of fact I was watching the cone when it happened. The cone excursion could readily be seen but I don't think it was anywhere close to an inch. (With that small roll on the surround seems like an inch would blow it out.) If I remember correctly it happened after a quick series of maybe three powerful bass notes. Could this have caused "pumping?" I'm not exactly sure what that is. I haven't had the 2245 out of the cabinet to see if there is any discernable offset but that will be forthcoming. According to the previous owner this is the original woofer (he said he bought it new) and it was refoamed a year or two ago. From the outside it looks like a quality refoam job. He said good things about the shop that did the work. I specifically ask him if he ever rotated the woofer and he said he did not. Should I try rotating it?

[doyall]

Double post. Sorry.

[Thom]

If it's offset, I don't know if I can recommend this but I had a 2240 with real bad offset. I'm not sure if it was hurting anything but it was bothering me. I set it out in the sun face down supported by the rim. Put a couple of small balloons between the frame and the cone to give it a slightly positive offset and let it bake and then cool down. When I took out the balloons and brought it in it had no offset. Way to recent to know how permanent it is.

[grumpy]

you have the manual?

http://manuals.harman.com/JBL/HOM/Ow...ual/BX63om.pdf

If it's set up properly and still bottoming out, it's probably not what you need
for your environment/setup. -grumpy

[doyall]

you have the manual?

http://manuals.harman.com/JBL/HOM/Ow...ual/BX63om.pdf

If it's set up properly and still bottoming out, it's probably not what you need
for your environment/setup. -grumpy

I've got the manual and followed it to the letter.

While it didn't really sound like it was out of phase with my L250's, if it was could that have caused the cone to be pushed back farther than it otherwise should go?

Please don't tell me that I've spent all this time and money for naught.

[Thom]

Have you tried playing different tones through it?

I'm not suggesting that this is you, but sometimes people have a little boost here and a little boost there and when every thing is added up they have 30db boost at 10 hz and you can't hear it so until something fails it goes unnoticed.

[doyall]

[quote=Thom;184057]Have you tried playing different tones through it?
quote]

Haven't tried it but I certainly will.

[grumpy]

Please don't tell me that I've spent all this time and money for naught.

I certainly hope not, and you can always try the phase inversion, but short of
a failure (seems unlikely), having the will to turn down the LF Gain on the BX63A,
or relocating the sub for better reinforcement (or less bad cancellation), you might get
what you're after via another path.

Verifying that the 2245+cabinet frequency of minimum cone motion is close to where
the BX63A peaks (roughly 25Hz?) might be worthwhile (it does have an infra-sonic
filter built in as well as DC blocking). -grumpy

good read:
http://audioheritage.csdco.com/vbull...x63A+schematic

[doyall]

... Verifying that the 2245+cabinet frequency of minimum cone motion is close to where the BX63A peaks (roughly 25Hz?) might be worthwhile ...

I suppose that if I have to ask how to do this I am not really equipped to handle it?

[grumpy]

If you can do "tones" via CD or computer, that would get you there.
Could be a red herring anyway.
I'm really trying to not sound too pessimistic.

In some rooms, that sub can do dance-club level sub-bass, but it is a subwoofer...
a lot of folks crank up the sub level to hear or feel -bass- as opposed to sub-bass
and end up overdriving the very low end (which the BX63 has already peaked up 10dB).
Are you sure your amp isn't clipping? (~300W? ... wouldn't be terribly surprising)
Since there really aren't lots of recordings with much sub-bass material, it's easy to do.
The beginning of Dark Side of the Moon is an interesting example... if that's not shaking
your vases without causing the voice coil to bottom out, there's something wrong

-grumpy

[Robh3606]

The BX-63 has a subsonic filter. Listening to music it should be fine. I went back to double check the x-max and its about 3/4 inch peak to peak. That's a lot of movement and that is not the X mechanical where you would hit. By pumping I meant the cone moving slowly backwards and forward from a DC offset. Or if when you hit those 3 notes if the cone doesn't go back to rest like it gets offset by a DC voltage. I just went through this with a pair of sub's. In this case the spiders were offset from in box storage. Fortunately they were easy to fix. That woofer should kick butt I am sure you can figure out what the issue is.

Rob