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B&W DM640 - is there anything wrong?

Hello all,
I just purchased a pair of B&W DM640s at a really great price to replace my DM602s. One tweeter was physically damaged, and I replaced it with a new one (thanks, B&W)

But for some reason, something does not sound right. I can't really tell what it is, obviously there's a difference going from bookshelf to floor standing. I'm still messing around with the speaker placement and room acoustics (I have panels), and I'm also contemplating building an MDF stand to raise them a foot or two.

Is there any real way to test the speakers to make sure everything is right? With 4 drivers on each (tweeter, mid, 2 woofers) I don't want to guess on this. The drivers look fine to the naked eye. I'm thinking removing each driver one by one and checking things out that way.

Thoughts?

Thanks,
alex333

Showing 2 responses by alex333

alex333 OP
38 posts
 
I could describe the original problem as sounding muffled, dirty, and some echo.

At this point, I've found nothing wrong with the speakers themselves. No visual damage, the mid / woofer cones move smoothly without any friction or rubbing, polarity checks out good.

I have improved significantly the sound by:

Removing the plinth / spikes, placing the speaker directly on the floor (ceramic tile)
Speaker placement, by separating from sides and rear wall based on the standard formulas, and some tweaking
Tightening the screws on all of the drivers, some were loose
Plugging the vent port with a rolled up towel (don't have the cap or short tube)
Adding more acoustic panels behind the main speakers (dead end)
Moved the Velodyne subwoofer to the rear wall, placed in the center.

Also, I found that my 55" Mitsubishi projection TV (big ol' box) is rattling quite a bit, and being between the main speakers I know it's affecting the acoustics significantly. Not much I can do until I replace the TV later this year with an LCD flat panel.

Thanks,
alex333 OP
38 posts
 
These speakers do sound great now.

I did make a couple of additional changes since my post above.

I cut the long port tube to make it the short size to get more bass.

Also, I noticed that the midrange is out of phase with the woofers (same on both speakers), can't really tell if the tweeter is out of phase. So I'm bi-wiring to the amp, and fixing the phase issue at the speaker posts. Eventually I want to open the speaker and find the cause of this, probably a wire is connected backwards. This made the biggest improvement of all for obvious reasons.

About raising them off the floor, I may try the plinth / spikes again, now that the polarity is fixed. A friend of mine has 802s and he also likes them right on the floor, without the plinth / spikes. Maybe it has to do with the concrete / tile floors here in S FL.
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