B&W speaker diagnosis

[Wolverine72]

After a 7 year hiatus and 5000 mile journey, I finally got my B&W "P6" speakers hooked up. Unfortunately, to my dismay, the sound which came out was nothing like I remember of the crisp mids and tight bass. Instead I got each speaker sounding and acting differently.

On one speaker, the mid and highs sound great but the bass driver is not functioning at all. On the other, all drivers work but the overall sound is extremely muffled and distant. My first thought is a crossover problem but I have no real way of diagnosing this? Any suggestions?? Has anyone experienced this with ANY speaker? Like I said, these babies have been in storage for years, in their original boxes but they have been moved around a bit. Thanks for any help!

 

[chadnliz]

Where were they stored, indoors...outdoors?

 

[Wolverine72]

They were in a friend's basement "sound room" for 4 of those 7 years - being used occasionally. The other 3 they have been in a basement, in original foam/c-board boxes. Temps ranging between 50 & 65.

 

[TLS Guy]

After a 7 year hiatus and 5000 mile journey, I finally got my B&W "P6" speakers hooked up. Unfortunately, to my dismay, the sound which came out was nothing like I remember of the crisp mids and tight bass. Instead I got each speaker sounding and acting differently.

On one speaker, the mid and highs sound great but the bass driver is not functioning at all. On the other, all drivers work but the overall sound is extremely muffled and distant. My first thought is a crossover problem but I have no real way of diagnosing this? Any suggestions?? Has anyone experienced this with ANY speaker? Like I said, these babies have been in storage for years, in their original boxes but they have been moved around a bit. Thanks for any help!

I would start by checking the connections. Then make a schematic of the crossover. Then we might be able to help.

 

[Wolverine72]

I would start by checking the connections. Then make a schematic of the crossover. Then we might be able to help.

Thanks for the advice. I checked some connections already - switching between HF & LF on the bi-amp posts and switching output from the amp. No change. Going to try different cables just as a test too. Using Kimber 4TC which were in storage with the speakers. I hoped I wouldn't have to open them up just yet to look at the crossover but may be inevitable.

 

[TLS Guy]

Thanks for the advice. I checked some connections already - switching between HF & LF on the bi-amp posts and switching output from the amp. No change. Going to try different cables just as a test too. Using Kimber 4TC which were in storage with the speakers. I hoped I wouldn't have to open them up just yet to look at the crossover but may be inevitable.

You will have to open up the speakers. The most likely thing is that wires have come off speakers and or crossover boards in all the shipping around.

You will need a meter. Disconnect all speakers, labeling and remembering where all the wires go. Check the resistance of each voice coil. If all is well reconnect them, and if there is still a problem, make a copy of the crossover and we will come up with a plan to trouble shoot them. Crossover failures are rare unless there are non polarizing electrolytic caps involved. These all fail over time especially with non use. Hopefully your speakers are of a quality that they don't have those. If they do, then you should replace them all with polypropylene types.

 

[Wolverine72]

You will have to open up the speakers. The most likely thing is that wires have come off speakers and or crossover boards in all the shipping around.

You will need a meter. Disconnect all speakers, labeling and remembering where all the wires go. Check the resistance of each voice coil. If all is well reconnect them, and if there is still a problem, make a copy of the crossover and we will come up with a plan to trouble shoot them. Crossover failures are rare unless there are non polarizing electrolytic caps involved. These all fail over time especially with non use. Hopefully your speakers are of a quality that they don't have those. If they do, then you should replace them all with polypropylene types.

Thanks very much! I'll open 'em up this weekend and get back to this post. I'll see if B&W can tell me what type of crossover they used also - maybe they even have a schematic. These speakers were just below their Matrix line so I assume they used quality parts!

 

[Jamesnails]

What is wrong with my B&W woofer????

Hi there,

my system is:

-B&W 801 Series 2 Bi-wire
-Bryston 4B power amp
-Ps5.0 Pre Amp ( high current pre amp with separate power supply)

I just bought the Ps5.0 Pre Amp on Ebay. Then owner warned us that the switches of the equipment makes noise and will require cleaning. After it has been cleaned, we installed it into the system.

At first when we tested it with a cd at straight wire mode it seemed that the left channel did have noise. At that point, I turned off the right channel to test only the left. After turning the selector knob from cd to tuner the following happened:
1)A slight noise occured
2)The overloading signal on the poweramp's lefside flashed once
3)After that, the left woofer was no longer working
4)However, the mid range + metal dome tweeter is still working

Does anyone know what happened? and how come the protective circuit did nothing to prevent this from happening?
Did the damage only reach the speaker board or did it even get to the cone bass?

Thank you

 

[TLS Guy]

Hi there,

my system is:

-B&W 801 Series 2 Bi-wire
-Bryston 4B power amp
-Ps5.0 Pre Amp ( high current pre amp with separate power supply)

I just bought the Ps5.0 Pre Amp on Ebay. Then owner warned us that the switches of the equipment makes noise and will require cleaning. After it has been cleaned, we installed it into the system.

At first when we tested it with a cd at straight wire mode it seemed that the left channel did have noise. At that point, I turned off the right channel to test only the left. After turning the selector knob from cd to tuner the following happened:
1)A slight noise occured
2)The overloading signal on the poweramp's lefside flashed once
3)After that, the left woofer was no longer working
4)However, the mid range + metal dome tweeter is still working

Does anyone know what happened? and how come the protective circuit did nothing to prevent this from happening?
Did the damage only reach the speaker board or did it even get to the cone bass?

Thank you

Unfortunately the news for you is likely bad. The Bryston 4B has no speaker protection against DC offset, which all direct coupled amps should have.

Your circuit is on page 8.

http://www.bryston.ca/BrystonSite05/pdfs/LegacyPowerAmplifiers/3B-8Bst_Schematics.pdf

Now a direct coupled amp like the Bryston 4B will amplify DC and present it to the speaker.

Since you have just bought the Ps5.0 on eBay my guess is that it has much bigger issues than noisy switches.

This is likely what happened.

Your new preamp has a fault which presents DC at the left channel output. Your Bryston amplified it and passed it to the speaker and fried your woofer voice coil.

Unfortunately this may have also taken down the output devices of your Bryston, and your Bryston may have DC off set now. Do not connect it to any other speaker.

It is possible that the Bryston failed and it is coincidence this happened when you connected your new unit, but obviously that is unlikely.

It is always the woofer that blows in these situations, the voice coil is much more fragile than inductors in the low pass crossover. There are always crossover caps in series with mid and HF drivers. Caps do not pass DC, so it is always the woofer that blows.

Now remove the woofer that does not work. Measure the DC resistance of the woofer with it disconnected. You will likely find that either it is open circuit,(infinite resistance), because the voice coil has a burnt gap in the wiring, or that the resistance is very low, due to the insulation of the voice coil wire having melted, and now the turns of wire are shorting.

It would be a good idea to compare your readings to the one from the working woofer.

Push the woofer cone in and out, and see if you feel any grittiness.

Lastly connect a 1.5 volt battery to the woofer terminals and make and break the circuit and see if the cone pops in and out.

Lastly, we have had these sorts of issues before with vintage amps. I strongly advise against the use of any power amp that does not protect the speakers from DC off set. Unfortunately there are quite a few vintage amps that don't, and your is one of them. You are always one power output device failure away from a loudspeaker destruction. Your B4 has output power transistors in multiples in parallel, as that was the only way to get high current output back then. The problem is that it greatly increases the odds of failure as the chance is the same for each output device.