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.


You need to define in someway what's not sounding right to your ears, find a couple of adjectives and that's a good place to start.
I would make sure the "polarity" is correct on the tweeter you just replaced. (Either call B&W or look to see how the other tweeter is wired up....Brown (+) blue (-) ???? (Hopefully the original tweeter is correctly hooked-up.) You may want to check all the drivers. I personally wouldn't raise the spks. any higher. One other thing, those spks. came w/ a long/short tube and a cap for the rear port to adjust the bass output. Very fine spks. I hope things work out. Bill.
I have a chromatic scale mp3 I can email you if you like. Basically a frequency sweep from 20hz to 20khz starting with the left speaker and then moving to the right.

This may be helpful.
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.

The 640 is a great speaker. Have had mine for 14 yrs and they still sound great. looking to replace them with the 683 just because of age. I figure 14 yrs is a long time and the 683's sound every bit as good and maybe even better in the mids and highs. Any way, they really need to be about 2.5 feet from the rear wall and that is the minimum reccomended from B&W. I know sometimes that is tough but when they are too close and being rear ported they start to get a little muddy. Not having the ports doesnt help either as they can really be fine tuned with them. I also wouldnt put them right on the floor. The base's with the spikes are there for a reason. There is definately a big difference when not using them. Well hope you find your problem because they are great speakers.
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.
Hi, I know this is an old post, hope you're still on the forum!  I've got a pair of these speakers, but didn't get the different bass port tubes or block.  I do have the 150mm port tubes, but I can't find anywhere online or in the manuals if these are the long or shorter tubes that were originally included.

I'm thinking about cutting mine down also, what length did you shorten yours to?