General Forum

Re: Replacing woofers and tweeter on Beolabs

Jon — Mon, 16 Nov 2009 19:07:40 GMT

Well, I went to Beocentral to read up on the BL8000's, and this paragraph caught my attention:

"Despite the drivers being permanently connected to an amplifier of known characteristics, the designers chose them poorly, during the life of the loudspeaker both had to be modified for satisfactory, reliable operation. Some of the woofers used had a plastic cone which would melt and become detached from the voice coil, whilst the tweeter was insufficiently robust and would fall into permanent silence if the full power of the amplifier was used. The tweeter problem was made worse because there was no blocking capacitor to protect the delicate windings of the tweeter voice coil from the output of the treble amplifier, an elaborate (but largely ineffective) “tweeter protection circuit” was included instead. Text copyright © Beocentral. Unauthorised reproduction prohibited."

Regarding the BL6000's, it had this to say:

"Unfortunately, the same problems with drive unit reliability that had affected the Beolab 8000 re-appeared with the 6000, which used the same tweeter. The woofers were not of the plastic coned type, but did suffer with torn rubber roll edges, because the material used was too thin and became hardened with use. Text copyright © Beocentral. Unauthorised reproduction prohibited."

So, assuming the person who wrote the reviews on Beocentral is right (which they aren't always...), I'd make the changes to the circuits for better protection if it were me. It sounds like B&O really dropped the ball on some things when they designed the first couple of versions of these speakers, so it seems the revisions would be worth the peace of mind. I like playing at loud volumes though.

Also, Graham is saying that these new tweeters have been revised. If B&O has seen fit to revise them, then it's possible there might be major enough differences between the new and the old to warrant a change in the circuitry, and recalibration of the drivers. Maybe the old tweeters didn't use ferrofluid, and B&O had their supplier switch to a ferrofluid design, which would damp the resonant peak of the tweeter quite a bit and necessitate a crossover redesign. You know? It could be something to that effect.

Lastly, if you DON'T make the changes to the circuitry, will B&O honor your warranty if these new drivers fail within the warranty period? That's something to think about as well.

You know, if you could find some old versions of these tweeters somewhere in good shape, you could just swap them out and be done with it. You might try that too. Could be cheaper to boot.

Jon

Re: Replacing woofers and tweeter on Beolabs

B&Ola — Sun, 15 Nov 2009 18:02:00 GMT

Jon:

Well, if you're going to change out some of the components in the amplifier/crossover/protection/whatever circuits, then I would follow B&O's directions to the tee. So, yes, if B&O calls for hooking a tone generator up and recalibrating the tweeter levels, then by all means, do that.

I was under the impression that you'd just get a new OEM B&O tweeter, stick it in, and be good to go. But when you start altering things like the crossover slopes or frequencies (or any of the signal circuits), it WILL change the frequency response. In that case, you'd need to recalibrate for sure. I didn't realize you'd be doing that. So apparently, don't listen to me, hahaha!

Glad to be of help, if I helped at all. :)

Jon

You all helps me out here! =)

I really wants the easiest way possible without paying a fortune. The easiest way for me is to just change the tweeters and woofers and be happy with that. But I want to know why B&O says that those components needs to be replaced. If it's only for "higher safety" for the tweeters or woofers then I can live with it and leave the components unreplaced. But if the sound quality is affected in a way that I will notice I will have to send them to better equipped technician as Graham recommended.

What do you think Graham and Jon, what are your recommendations?

/Ola

Re: Replacing woofers and tweeter on Beolabs

joeyboygolf — Sun, 15 Nov 2009 05:27:38 GMT

The instructions and components are provided for good reason, not least because the new tweeter is different to the old one.

You need to be experienced at working with micro components. I would suggest that it is best left to an experienced technician.

Re: Replacing woofers and tweeter on Beolabs

Jon — Sat, 14 Nov 2009 23:39:43 GMT

Well, if you're going to change out some of the components in the amplifier/crossover/protection/whatever circuits, then I would follow B&O's directions to the tee. So, yes, if B&O calls for hooking a tone generator up and recalibrating the tweeter levels, then by all means, do that.

I was under the impression that you'd just get a new OEM B&O tweeter, stick it in, and be good to go. But when you start altering things like the crossover slopes or frequencies (or any of the signal circuits), it WILL change the frequency response. In that case, you'd need to recalibrate for sure. I didn't realize you'd be doing that. So apparently, don't listen to me, hahaha!

Glad to be of help, if I helped at all. :)

Jon

Re: Replacing woofers and tweeter on Beolabs

B&Ola — Sat, 14 Nov 2009 17:47:18 GMT

Thanks Graham!

So, I don't have to do this component upgrade to get the correct sound, this is only for protection? Is it hard to replace those components?

I thought a tone generator was at least 250 €! If it's only 20£ I will get one.

/Ola

Re: Replacing woofers and tweeter on Beolabs

joeyboygolf — Sat, 14 Nov 2009 10:01:18 GMT

The kit of components together with instructions is included with each tweeter and is designed to modify the protection circuit so it won't be as easy to blow the new tweeter.

An audio tone generator can be bought for around £20. I use a Tenma 72-502 combined with my DMM and seem to get satisfactory results.

Re: Replacing woofers and tweeter on Beolabs

B&Ola — Sat, 14 Nov 2009 06:44:08 GMT

Thank you Jon!

Yes, my idea was to replace the tweeters on a pair of 6000 and a pair of 8000. They are all broken (I have checked them with a multimeter).

On one of the 6000 speakers the surroundings are broken but the coil is OK so I replace them to.

I will use OEM B&O woofers and tweeters. Nothing else.

I got a manual from Peter with instructions of how to replace woofers and tweeters. In that manual it says that you also need to replace a number of components:

------------------------------------------------------------------------------------

Section B: serial number between 10145230 and 14282364

Replace the following components:

Change PCB12/02 R146 co-ordinate 2C to 6.8Kohm 5% - 5011186

Change PCB12/02 R147 co-ordinate 2C to 10Kohm 5% - 5011557

Change PCB12/02 R148 co-ordinate 2C to 221Kohm 5% - 5012553

Change PCB12/02 R149 co-ordinate 2C to 150Kohm 5% - 5011259

Change PCB12/02 R150 co-ordinate 2C to 162Kohm 5% - 5013071

Change PCB12/02 R151 co-ordinate 1B to 150Kohm 5% - 5011259

Change PCB12/02 C87 co-ordinate 1B to 10μF 50 V - 4201173

After replacing the components, adjust the new unit as

described under “Signal levels”, using the dB values mentioned

under “BeoLab 8000”.

------------------------------------------------------------------------------------

What do you think of that? Do I need to do that?

Regars Ola

Re: Replacing woofers and tweeter on Beolabs

Jon — Wed, 11 Nov 2009 17:43:27 GMT

Also, you asked if it was possible to damage the drivers with a tone generator. Yes! If you are able to get access to one be careful of how much voltage (or power, however the tone generator's output is rated) you put into the speaker. Mostly, within excursion limits (how much it moves back and forth), the woofer will be fine. However, the tweeter is the delicate one, and frequencies fed into it around it's natural resonant frequency will be *especially* potentially destructive to it! It will get pushed past it's excursion limits really quick around that frequency and potentially damage the tweeter. I have no idea the Fs (resonant frequency) of the BL6000 tweeters. It's a 3/4" dome...maybe 2KHz or so???

Anyway, if you try and do a frequency sweep with a tweeter, at least do it with a resonance trap circuit hooked up and a properly sized capacitor in line with it. And good luck figuring out what values you'll need to use without the Theile Small parameters of the driver....

Jon

Re: Replacing woofers and tweeter on Beolabs

Jon — Wed, 11 Nov 2009 17:20:29 GMT

Okay, first, it's NOT necessary to test the new tweeters with a tone generator. I'm not sure where this idea came from. Just plug the new ones in and play. As long as the membrane hasn't separated from the former, or the voice coil is off-center, or something like that, they'll be fine. You'll know if that's the case because you'll hear the tweeters buzz with musical content below their passband. I guess if you wanted to check that, you could do a sweep with a tone generator, but it seems kinda pointless. Especially if you replaced the tweeters with brand new ones, which I'm assuming you did. The chances of getting a bad tweet are extremely small. But just to stick a tweeter in there and get some sound doesn't require a tone generator.

Second, different drivers have different sensitivies (and other parameters too) - put simply, the sound pressure level produced with a certain voltage input. Some are more sensitive than others. Usually, drivers are replaced in pairs. But, as long as you replaced one tweeter with another of the exact same type, any small variance in the response of the drivers are going to be unnoticable, I promise. Now if you went and put two completely different types of tweeters (or woofers, or any driver for that matter) in there, then yes, you're going to have differences and possible problems. But, I'm assuming you mean replacing the OEM B&O drivers with OEM B&O drivers, right?

You can stick any ol' tweeters in there and get sound, but it won't match unless you use the same drivers left and right. Even then, the OEM B&O drivers are specifically designed for those amps and crossover networks in the BL6000, and those would be the ideal drivers to use. Other drivers may distort or cause severe response anomolies, just because you'd need measurement equipment to test, and make changes to the circuits to optimize them for the BL6000. B&O has already done that.

As far as a frequency sweep with a tone generator, don't bother. Especially if you're going with new, OEM B&O drivers.

Third, I have to ask, what makes you think your drivers are bad? What is the speaker doing? Are you getting sound from all the drivers when you put your ear up to them? Is the sound distorted? Before you go to all the trouble of testing the drivers, let's make sure it's not something more simple first.

Jon

Re: Replacing woofers and tweeter on Beolabs

B&Ola — Wed, 11 Nov 2009 16:31:44 GMT

B&Ola:

koning:

B&Ola:

koning:

B&Ola:

Hi all

Is it necessary to a tone generator test after replacing woofers and tweeters on a pair of Beolab 6000 and 8000?

Is there a simple way to check if a woofer or tweeter i broken or not?

Thanks for help!

Best regards Ola

tweeters yes

Bass no

Are you answering my first or second question?

The first Question.

If you just switch the tweeters; Will it clearly noticeable that it's not calibrated?

Thanks all for helping me out!

One more thing: Why is it necessary to do the tone generator adjustments?
Will the sound difference be noticeable and can I damage the speaker in any way?
If I can't find a tone generator, is there another way to fix this? (other than leaving it for the service man)

/Ola

Re: Replacing woofers and tweeter on Beolabs

Jon — Tue, 10 Nov 2009 23:20:38 GMT

B&Ola:

Jon:

Take a multimeter and see if it reads a DC resistance when you touch the leads to the driver terminals. If it does, your drivers are likely good. Well, the voice coils are good. If the cone has separated from the former or something like that, you'll hear it.

Hope that helps.

Jon

Can I do this both with a woofer and a tweeter?

/Ola

Yes.

Re: Replacing woofers and tweeter on Beolabs

B&Ola — Tue, 10 Nov 2009 18:13:51 GMT

koning:

B&Ola:

koning:

B&Ola:

Hi all

Is it necessary to a tone generator test after replacing woofers and tweeters on a pair of Beolab 6000 and 8000?

Is there a simple way to check if a woofer or tweeter i broken or not?

Thanks for help!

Best regards Ola

tweeters yes

Bass no

Are you answering my first or second question?

The first Question.

If you just switch the tweeters; Will it clearly noticeable that it's not calibrated?

Re: Replacing woofers and tweeter on Beolabs

ipaul — Tue, 10 Nov 2009 17:17:13 GMT

easiest way without having to take out the speaker units: just put a FM radio NOT tuned to any station on the speakers: you'll just hear the static (hissss).

Now if you move your ear close to the speaker-units you can hear if it makes noise.

If still doubts: just put your hand in between the speaker and your ear and move it in and out (so: in between your ear and the speaker and out), if that doesn't make any difference you can be pretty sure the unti is dead and do an ohm measurement to be sure :).

Re: Replacing woofers and tweeter on Beolabs

koning — Tue, 10 Nov 2009 16:59:57 GMT

B&Ola:

koning:

B&Ola:

Hi all

Is it necessary to a tone generator test after replacing woofers and tweeters on a pair of Beolab 6000 and 8000?

Is there a simple way to check if a woofer or tweeter i broken or not?

Thanks for help!

Best regards Ola

tweeters yes

Bass no

Are you answering my first or second question?

The first Question.

Re: Replacing woofers and tweeter on Beolabs

B&Ola — Tue, 10 Nov 2009 16:06:22 GMT

Jon:

Take a multimeter and see if it reads a DC resistance when you touch the leads to the driver terminals. If it does, your drivers are likely good. Well, the voice coils are good. If the cone has separated from the former or something like that, you'll hear it.

Hope that helps.

Jon

Can I do this both with a woofer and a tweeter?

/Ola