B&W speaker - mid-range driver crackle

JohnVFR

Standard Member
I have some old B&W P5 speakers that I bought used quite a long time ago. They look great but they never really performed well. Both speakers seem equally as bad and they are really unuseable in the current state.

The main problem seems to be crackle and hiss on the mid-range driver (part no. ZZ11029). The other components seem OK as far as I can tell. I've taken the speakers apart and can't see any obvious fault with the drivers. They look in great condition but when I tested in alone with some test tones they clearly make a crackling/static noise accross a range of frequencies.

I've tested the amp/cables combo with another speaker pair and it works fine.

Does anyone know why both mid-range drivers would fail like this? A manufacturing fault?

I thought about replacing these drivers but they don't appear to be available from B&W ZZ11029 Bowers &Wilkins Midrange

My question is really whether I should cut my losses and bin the speakers? It seems a real shame. The bass drivers and tweeters could be sold on Ebay I suppose.

Any suggestions? Thanks in advance for your help and comments.
 

Orobas

Well-known Member
I have some old B&W P5 speakers that I bought used quite a long time ago. They look great but they never really performed well. Both speakers seem equally as bad and they are really unuseable in the current state.

The main problem seems to be crackle and hiss on the mid-range driver (part no. ZZ11029). The other components seem OK as far as I can tell. I've taken the speakers apart and can't see any obvious fault with the drivers. They look in great condition but when I tested in alone with some test tones they clearly make a crackling/static noise accross a range of frequencies.

I've tested the amp/cables combo with another speaker pair and it works fine.

Does anyone know why both mid-range drivers would fail like this? A manufacturing fault?

I thought about replacing these drivers but they don't appear to be available from B&W ZZ11029 Bowers &Wilkins Midrange

My question is really whether I should cut my losses and bin the speakers? It seems a real shame. The bass drivers and tweeters could be sold on Ebay I suppose.

Any suggestions? Thanks in advance for your help and comments.
Could be a crossover component failure given the age of the speakers.. dry cap or something.. Hard to test though without the right tools. The good news though is that crossovers can be rebuilt from quite a few companies.. "if" that is the case in that the crossover's are on their way out
 

JohnVFR

Standard Member
Thank you Orobas. You make a very good suggestion. I actually have a little bit of test equipment (including an ESR meter) so it is something I can investigate. I can also replace caps if needed.

I actually removed the mid-range driver and tested directly with the output from the amp (by clamping the speaker cable to the individual driver inputs). The problem persisted.

If I understand correctly, this should have removed the crossover circuity from the equation (as it is located somewhere in the cabinet of the speaker). I will go and have look now.
 

Orobas

Well-known Member
Thank you Orobas. You make a very good suggestion. I actually have a little bit of test equipment (including an ESR meter) so it is something I can investigate. I can also replace caps if needed.

I actually removed the mid-range driver and tested directly with the output from the amp (by clamping the speaker cable to the individual driver inputs). The problem persisted.

If I understand correctly, this should have removed the crossover circuity from the equation (as it is located somewhere in the cabinet of the speaker). I will go and have look now.
If you completely disconnected the driver from the crossover ... and the problem was there.. then its worn or burnt out voice coil wires most likely.. which will mean a new or rebuilt mid-range (these can still be rebuilt / reconed)

If the crossover was still connected.. then you may still have crossover issues as opposed to the driver
 

dogfonos

Well-known Member
Agree with Orobas - could be the crossover, however, when you tested the midrange units,was the crossover in circuit?. If it wasn't yet the crackling noise was heard then I guess it's a drive unit problem and not a crossover fault.

IME, it's rare for a dedicated midrange drive unit, with rubber surround, to fail following a period of successful service (caveat: assuming no external physical damage). Most drive unit failures with 3-way speakers concern the bass driver or the tweeter but I'm a little suspicious of this design. The specs I've seen for these speakers state they are 3-way but I'm unsure. From images I've seen, the "midrange" driver looks like it was designed to handle bass. Also, the "midrange" driver has a reasonably large ported chamber all to itself - why do that if it's not handling bass?

I wonder if the P5 is a 2.5-way speaker where the "midrange" driver works as a bass and midrange driver. Of course, this is speculation and I may be wrong but if I'm right, then the "midrange" driver will handle all bass as well as midrange and that could be the reason for the driver failure. Over time, playing heavy music at high volumes can cause bass and bass/midrange drivers to suffer the problem you describe (maybe the previous owner enjoyed Drum&Bass at ear-bleeding volumes?). I've personally damaged four bass/mid drivers in this way over the decades - each driver surviving around 4 - 5 years of heavy use before gradual failure. The noise I heard with mine was the voice coil (or voice coil former) rubbing either on the pole piece or the surrounding magnet structure.

One way to check this out is to, gently, push the driver inwards with your fingers spread around the centre of the cone (avoid pressing on the dustcap) so that applied force is as even as possible. Listen/feel for rubbing/grating. Don't force the cone back further than it wants to go.

There seem to be several cases of tweeter failure with this speaker where the ferrofluid has leaked or dried out over the years. You could go to the trouble of fixing/replacing the "midrange" drivers only for the tweeters to fail soon after.

May be worth talking to speaker repair experts for advice/suggestions before making a decision:

There is another option. Make use of the cabinet and fit a speaker kit into it. Done this myself to good effect. Obviously, some DIY will be required.

EDIT: Ooops. Bit slow in posting. Orobas beat me to it!
 

Orobas

Well-known Member
Agree with Orobas - could be the crossover, however, when you tested the midrange units,was the crossover in circuit?. If it wasn't yet the crackling noise was heard then I guess it's a drive unit problem and not a crossover fault.

IME, it's rare for a dedicated midrange drive unit, with rubber surround, to fail following a period of successful service (caveat: assuming no external physical damage). Most drive unit failures with 3-way speakers concern the bass driver or the tweeter but I'm a little suspicious of this design. The specs I've seen for these speakers state they are 3-way but I'm unsure. From images I've seen, the "midrange" driver looks like it was designed to handle bass. Also, the "midrange" driver has a reasonably large ported chamber all to itself - why do that if it's not handling bass?

I wonder if the P5 is a 2.5-way speaker where the "midrange" driver works as a bass and midrange driver. Of course, this is speculation and I may be wrong but if I'm right, then the "midrange" driver will handle all bass as well as midrange and that could be the reason for the driver failure. Over time, playing heavy music at high volumes can cause bass and bass/midrange drivers to suffer the problem you describe (maybe the previous owner enjoyed Drum&Bass at ear-bleeding volumes?). I've personally damaged four bass/mid drivers in this way over the decades - each driver surviving around 4 - 5 years of heavy use before gradual failure. The noise I heard with mine was the voice coil (or voice coil former) rubbing either on the pole piece or the surrounding magnet structure.

One way to check this out is to, gently, push the driver inwards with your fingers spread around the centre of the cone (avoid pressing on the dustcap) so that applied force is as even as possible. Listen/feel for rubbing/grating. Don't force the cone back further than it wants to go.

There seem to be several cases of tweeter failure with this speaker where the ferrofluid has leaked or dried out over the years. You could go to the trouble of fixing/replacing the "midrange" drivers only for the tweeters to fail soon after.

May be worth talking to speaker repair experts for advice/suggestions before making a decision:

There is another option. Make use of the cabinet and fit a speaker kit into it. Done this myself to good effect. Obviously, some DIY will be required.

EDIT: Ooops. Bit slow in posting. Orobas beat me to it!
B&W P5 Specifications
Systems: 3-way, twin 4th order vented box system
Drive Units:
High Frequency : 1 x 25 mm metal dome
Bass/Midrange Frequency : 1 x 165 mm woven kevlar cone
Bass : 1 x 165 mm Cobex cone bass
Frequency Response: 32 Hz - 20 kHz ±2 dB on reference axis
Frequency Range (-6 dB Frequencies): 28 Hz - 22 kHz
Dispersion (20 Hz - 10 kHz):
Horizontal : ±2 dB over 60° arc
Vertical : ±2 dB 10° arc
Sensitivity: 90 dB spl (2,83 V at 1m)
Crossover Frequency: 150 Hz, 3 kHz
Nominal Impedance: 8 Ω (minimum 3,7 Ω)
Power Handling: 50 W - 200 W into 8 Ω on undistored programme
Dimensions (H x W x D): 905 x 200 x 301 mm
Weight: 14,5 kg net
 

JohnVFR

Standard Member
Thank you dogfonos and Orobas once again.

The crossover was not in circuit when I tested the driver directly with the output from the amp (as you can tell I don't know much about audio, so I hope this didn't make the problem sound worse by not having the crossover circuitry in place).

I have also had a look at the crossover circuitry. The components are much bigger than I imagined. It appears to be two large copper coils, two surprisingly large capacitors and a resistor. There may be other parts I couldn't see on the other side of the board. I'll investigate further tomorrow.

The noise I heard with mine was the voice coil (or voice coil former) rubbing either on the pole piece or the surrounding magnet structure.

This is really useful to know and something I can look at. I was really having difficulty understanding what exactly causes them to fail.

I will test the drivers as you suggest. Thank you for the links - they look very useful.

I wondered whether there was some way I could crow bar a third-party driver in. It seems such a waste of the world's resources to chuck things like this away (even though it's probably cheaper to buy a lightly used one from somewhere) .
 
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Orobas

Well-known Member
Thank you dogfonos and Orobas once again.

The crossover was not in circuit when I tested the driver directly with the output from the amp (as you can tell I don't know much about audio, so I hope this didn't make the problem sound worse by not having the crossover circuitry in place).

I have also had a look at the crossover circuitry. The components are much bigger than I imagined. It appears to be two large copper coils, two surprisingly large capacitors and a resistor. There may be other parts I couldn't see on the other side of the board. I'll investigate further tomorrow.

I will test the drivers as you suggest. Thank you for the links - they look very useful.

I wondered whether there was some way I could crow bar a third-party driver in. It seems such a waste of the worlds resources to chuck things like this away.
You "could" ... but you would have to do both speakers, and match the drivers to the crossover splits. This will also very audibly change the sound from a B&W's trademark signature to something else

I would probably enquire with the likes of Wilmslow Audio etc on the cost of getting the P5's reconed if you like their sound.. and decide when you get the quote back if that is the right option

Obviously this is dependant on your final tests of the drivers on their own.. multimeter for resistance.. then test the sound.. if faulty.. like i say most likely voice coil or worn surround which either way would be a rebuild/cone :)

The "coils" are the inductors they allow the bass / different frequencies through but block the high
The Capacitors allow high frequencies through but block low
Resistors are limiters for the treble power to stop too much power getting to them

This is just a rough guide.. to a crossover
 
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JohnVFR

Standard Member
I thought I'd follow this up in case it is useful to someone in the future.

After a bit more investigation it did appear that the voice coil had gone - when I pushed down gently on the cone in some (but not all) areas I could hear a slight noise with both drivers. However, the coils looked perfect from what I could see (it was impossible to take off the rear magnet for a better look).

It turned out that the problem was due to the plastic centre pieces being deformed (by heat I would say). See photo attached. It's very obvious on the left on but not the right. The deformation must move the voice coil out of centre enough to cause it to catch and crackle.

Removing these plastic centre pieces allows the drivers to work perfectly.

Problem solved! Well, not quite...
 

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JohnVFR

Standard Member
The next problem was a non-working tweeter. In fact, there are two problems - and I could only solve the first. There didn't appear to be a signal coming out of the tweeter connection. I suspected a bad solder joint on the crossover pcb and sure enough - see photo attached.

I solved this on my second attempt. I ended up adding a jumper wire between this wire and the adjacent capacitor terminus (see slightly behind and to the left) to make sure of a solid connection.

So, all good? Well not quite - as one of the tweeters itself appear to be kaput. It doesn't look repairable, so I may have to see if I can find one..
 

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JohnVFR

Standard Member
After a spot of Araldite and some rather delicate soldering, I managed to get the tweeter working too. So now I have two fully working P5's and they sound fantastic.

Thanks once again for your help :)
 

dogfonos

Well-known Member
It turned out that the problem was due to the plastic centre pieces being deformed (by heat I would say). See photo attached. It's very obvious on the left on but not the right. The deformation must move the voice coil out of centre enough to cause it to catch and crackle.

Removing these plastic centre pieces allows the drivers to work perfectly.

Very interesting. Never heard of that particular cause of voice coil rubbing/grating before.

I don't know much about "dustcaps" such as the ones you have but maybe they also act as phase plugs. IME, drive unit dust caps are fixed/glued to the driver cone, not, what looks to be, screwed into the pole piece!?! So what connected the "dustcaps" to the cone, or where they not connected to the cone?

One thing to watch out for is that dust and dirt could now get into the voice coil gap - especially magnetic material. I admire your persistance in getting these speakers fit-for-purpose again. Great to hear they sound fantastic.
 

JohnVFR

Standard Member
Yes, it surprised me that deformation of this centre "bullet" was what caused the crackling. I imagine it must be a reasonably common problem if both of my speakers developed it.

I've attached a couple of photos of some of the damage plus one of the driver with the centre removed. It does look like a potential dust trap. I could design and 3d print a replacement part quite easily.



20211119_120618.png20211119_120558.png20211119_120716.png
 

JohnVFR

Standard Member
I don't know much about "dustcaps" such as the ones you have but maybe they also act as phase plugs. IME, drive unit dust caps are fixed/glued to the driver cone, not, what looks to be, screwed into the pole piece!?! So what connected the "dustcaps" to the cone, or where they not connected to the cone?
Sorry I had missed this. Yes, they do appear to be phase plugs.

Explication above for the uninitiated. I should make the effort to replace them.

I can either grind down the originals so they no longer cause the problem (might not be pretty but hopefully mostly hidden from view) or 3 print a set (but the finish is unlikely to be as good in PLA or PETG. Acetone-smoothed ABS is probably the best solution but a bit of a faff).

They just screw into the centre pole piece and are not directly attached to the cone.
 
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dogfonos

Well-known Member
They just screw into the centre pole piece and are not directly attached to the cone.

I wondered how bass/mid drivers with phase plugs actually fitted and your photos clearly show how. Whether other phase-plug-equiped drive units are constructed in the same way, I wouldn't know but the B&W implementation doesn't actually provide a seal against dust/dirt ingress - there will still be a narrow gap around the phase plug. I guess B&W consider that acceptable - and maybe it is.

Someone must have driven those speakers hard for the phase plug to distort through heat. As you suggest, I'd try sanding down the (distorted) plastic phase plug in the first instance. It could be possible to get a nice finish on plastic (never tried doing this myself though):


But as you say, most of the area that needs reducing won't be visible. Be interested to hear how you get on with that.
 

JohnVFR

Standard Member
Thanks for the tip re: polishing compound.

It appears to have worked pretty well. I used 180 wet and dry paper (wetted with water and drop of washing up liquid).

I wanted to keep it as symetrical as possible, so I used a bit of latex glove to protect the thread and clamped it in a drill. It was quite easy to trigger the drill with the right hand while holding the sandpaper with finger and thumb of my left hand on the phase plug. I didn't have to take much off at all and tried to keep the paper damp to reduce risk of overheating.


20211120_093406.png
20211120_093638.png


You can see the results in the second photo. The sanding is not visible on this one when screwed back into the driver. I went a bit too far out on the other plug (making the sanding visible) but it could be sanded/polished further.

I've tested it and it seems to have fixed it although I did notice a slight noise on one during a frequency test, so it may need a little more off.
 
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Old Nait

Novice Member
I have some old B&W P5 speakers that I bought used quite a long time ago. They look great but they never really performed well. Both speakers seem equally as bad and they are really unuseable in the current state.

The main problem seems to be crackle and hiss on the mid-range driver (part no. ZZ11029). The other components seem OK as far as I can tell. I've taken the speakers apart and can't see any obvious fault with the drivers. They look in great condition but when I tested in alone with some test tones they clearly make a crackling/static noise accross a range of frequencies.

I've tested the amp/cables combo with another speaker pair and it works fine.

Does anyone know why both mid-range drivers would fail like this? A manufacturing fault?

I thought about replacing these drivers but they don't appear to be available from B&W ZZ11029 Bowers &Wilkins Midrange

My question is really whether I should cut my losses and bin the speakers? It seems a real shame. The bass drivers and tweeters could be sold on Ebay I suppose.

Any suggestions? Thanks in advance for your help and comments.
I posted a reply about replacing tweeters here: B&W P5 speaker tweeter repair The same chap is a very accomplished engineer, designing and building his own cross-overs and amps, so I am quite sure he could help.
 

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