One tweeter has failed on my B&W DM7 MK2 speakers. B&W no longer seem to make an exact replacement. However it looks like I can get a similar one from a newer Matrix 801 S2 speaker. Wondering what I would need to do to the series resistance in the crossover to keep the output sensitivity the same?
Original DM7 MK2 - TS26 fabric dome tweeter
Overall sensitivity of system - 86 dB
Series resistance - 3 ohms
Matrix 801 S2 - metal dome tweeter
Overall sensitivity of system - 87 dB
Series resistance - 0.47 ohms
So if I want to keep sensitivity at 86 dB but with the Matrix tweeter installed, what value of resistor do I need?
Original DM7 MK2 - TS26 fabric dome tweeter
Overall sensitivity of system - 86 dB
Series resistance - 3 ohms
Matrix 801 S2 - metal dome tweeter
Overall sensitivity of system - 87 dB
Series resistance - 0.47 ohms
So if I want to keep sensitivity at 86 dB but with the Matrix tweeter installed, what value of resistor do I need?
I'm thinking it should not be all that complicated. If you just consider 15K Hz for example that should be well past the crossover frequency influence of the inductors and capacitors, and only the resistor should be influencing sensitivity. And, to put things in perspective my sensitivity right now at 15k Hz is 0 dB. I'm thinking of putting a 1 ohm in parallel with the existing 3 ohm, to give me an equivalent resistance of 0.75 ohms, or just a touch more than the Matrix resistance of 0.47 ohms.
If you want to dig a little you can look at the crossover circuit drawing of each speaker. I don't know how to link direct to the file, and the PDF is too large to upload to this site. But, if you go to the link below, you can find the "service manual" for each of these two speakers in the appropriate section; DM for the DM7 Mk2, and Matrix for the Matrix 801 S2. The sections are arranged in alphabetical order. And for the matrix the circuit drawing is on page 16, with the component values on page 15.
B&W Service Manuals
However, this said, I think the only factor influencing the basic sensitivity of the tweeter is the resistor. On some models such as the DM6 B&W gives you a 3 position selector switch to change resistance on the tweeter from 0 or 1, or 3 ohms.
If you want to dig a little you can look at the crossover circuit drawing of each speaker. I don't know how to link direct to the file, and the PDF is too large to upload to this site. But, if you go to the link below, you can find the "service manual" for each of these two speakers in the appropriate section; DM for the DM7 Mk2, and Matrix for the Matrix 801 S2. The sections are arranged in alphabetical order. And for the matrix the circuit drawing is on page 16, with the component values on page 15.
B&W Service Manuals
However, this said, I think the only factor influencing the basic sensitivity of the tweeter is the resistor. On some models such as the DM6 B&W gives you a 3 position selector switch to change resistance on the tweeter from 0 or 1, or 3 ohms.
You can also test the "variable L-pad project" very common in this forum. That is, using one (or a stereo pair) to adjust for the right volume before substituting with fixed value resistors.
L-PADS
Solen Electronique Inc.
A tweeter can also be repaired, if you look for.
L-PADS
Solen Electronique Inc.
A tweeter can also be repaired, if you look for.
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You are thinking wrong.
What let you think that the 801S2 tweeter is similar to your DM7/II one? Appearance? Frequency response? Impedance vs frequency? If they both have the same FR and impedance plot they can be swapped otherwise they are just two different tweeter. Without measuring you are essentially shooting in the dark.
If you insist in using the 801S2 tweeter and padding it down, keep in mind that the amount of series resistance needed is dependent on that of the tweeter, which we don't know. And moreover series resistor before the crossover is not an L-pad, and varying the value will change the behavior of the x/o.
Ralf
What the other forum members are telling you, Ron, is that it is much more promising to replace the tweeters as a pair. If the new one is more sensitive but has a similar power handling and frequency response and Fs (fundamental resonance), you have room to manouvre with Zobels and L-Pads.
On a cursory glance, both speakers employ 4th order Linkwitz riley highpass filters, with an input resistor as you say of 3R on your speaker and 0R47 on the Matrix, at roughly similar frequencies, and they are not too different except the Matrix employs a Zobel (2.2UF and 15R) on the tweeter too.
Since a protection circuit is built in too, there are other considerations too. This is not a totally simple problem. I've seen enough to suggest this is doable, but if it was my speaker, I'd do the work on the two manuals first. Particularly check sensitivity and crossover frequency and tweeter impedance if you can. But yes, it looks promising.
On a cursory glance, both speakers employ 4th order Linkwitz riley highpass filters, with an input resistor as you say of 3R on your speaker and 0R47 on the Matrix, at roughly similar frequencies, and they are not too different except the Matrix employs a Zobel (2.2UF and 15R) on the tweeter too.
Since a protection circuit is built in too, there are other considerations too. This is not a totally simple problem. I've seen enough to suggest this is doable, but if it was my speaker, I'd do the work on the two manuals first. Particularly check sensitivity and crossover frequency and tweeter impedance if you can. But yes, it looks promising.
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System 7, first I much appreciate your taking the time to review the circuit drawings.
As an update, I ordered two ZZ09709 tweeters (original Matrix 801 S2 component) from the B&W Group. I decided that I'm going to keep these speakers for some time, and I don't know how much longer parts are going to be available. The plan is to install both and keep the one good original DM7 tweeter as a spare.
On the simplicity side, I just discovered yesterday that I had missed that parallel resistor/capacitor on the 801 S2 crossover circuit. I assume this is what you mean by the Zobel. Yes, that does complicate things, and gave me some reason for panic when I discovered it. The other piece of this B&W evolution of tweeters is that they updated the ZZ09709 to the ZZ04372, which was used in the 801 S3. The main difference seems to be the addition of ferrofluid to the 4372. B&W now sell the later tweeter as equivalent to the older 9709 design, and recommend it for the 801 S2 as well.
If (big if) one assumes the performance characteristics of the two tweeters are the same, and they are interchangeable, then it makes sense to consider the crossover circuit used in the 801 S3 as well. It is very simple with no Zobel compensation. The overall S3 speaker claims 87 dB sensitivity and uses one single 2.2 resistor in series.
So now I'm thinking if a single 2.2 gives 87 dB and I want 86 dB with a single series resistor, then I must be real close with my current 3 ohm, and my first cut attempt at this would be to just put in the new ZZ09709 with the crossover untouched.
I will play around with the L Pad calculators a bit to see if I can get a similar level of comfort working back from the S2 circuit with the Zobel compensation. Thanks PeteMcK and Inductor for those.
But, I still would appreciate opinions on whether or not the existing 3 ohm is in the ballpark.
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Those replacement tweeters aren't cheap, eh? 
B&W Parts Retail Price List
I think you'll be able to slot them in with no change. 1dB is nothing really.
You can figure out the crossover circuits to compare from this:
2-Way Crossover Designer / Calculator
Generally, increasing the input series resistance to a filter raises the Q of the filter and produces a peak in output. A resistor in series with a tweeter will slope top end response up. A Zobel rolls off high frequency response while flattening impedance. Ferrofluid flattens impedance and increases power handling. Confusing, isn't it. I think you'll be alright.
B&W Parts Retail Price List
I think you'll be able to slot them in with no change. 1dB is nothing really.
You can figure out the crossover circuits to compare from this:
2-Way Crossover Designer / Calculator
Generally, increasing the input series resistance to a filter raises the Q of the filter and produces a peak in output. A resistor in series with a tweeter will slope top end response up. A Zobel rolls off high frequency response while flattening impedance. Ferrofluid flattens impedance and increases power handling. Confusing, isn't it. I think you'll be alright.
Those replacement tweeters aren't cheap, eh?
B&W Parts Retail Price List
A resistor in series with a tweeter will slope top end response up. A Zobel rolls off high frequency response while flattening impedance.
Yes, they are not so cheap, but these were quite expensive speakers in their day. In one of the technical manuals I think they gave their cost for the original fabric dome tweeter in the 801 as $79 around 1980. I couldn't justify the $360 they want now for the ferrofluid version, plus they only had one in stock. I gather the main reason for the ferrofluid was to allow them to drop the self powered protection circuit. I will be leaving the circuit in place.
Yes, I wondered also about the high end frequency response effect of the Zobel. One review I found on the 802 S2 showed a marked roll off effect, 5 dB at 20 kHz. See image below. Makes you wonder if they were not trying to control the peak beyond 20 kHz. At my age, I'm not thinking I will hear anything up there unless it creates sub harmonics in the audible range. With CD's it would seem there is a pretty hard cutoff above 20 kHz in any case, and I doubt my MC cartridge is producing much at that frequency, although it may be more probable than the CD source.
Thanks again for the input. Now thinking I will just put in one tweeter and see how it sounds compared to the undamaged original speaker. Assuming it is OK, then I will replace the good tweeter too.
yes, adding a Zobel in parallel to the driver decreases the impedance seen by the amplifier and/or the crossovcer components before the Zobel.
That reduced impedance has the effect of introducing a low pass filter to that part of the passband. It also increases the demands on the amplifier and reduces the sensitivity of the speaker.
Only add a Zobel when you know that is what is actually needed.
That reduced impedance has the effect of introducing a low pass filter to that part of the passband. It also increases the demands on the amplifier and reduces the sensitivity of the speaker.
Only add a Zobel when you know that is what is actually needed.
I have now received and installed the new ZZ09709 tweeter and have done an initial quick test with the original crossover untouched (3.0 ohm resistor in series). The new tweeter has a DC resistance of 5.8 ohms. The purpose of the test was to compare the speaker with the new tweeter to the other untouched speaker with the functioning original TS26 tweeter. My tools are quite crude (Bink test tones, iPod touch dB Volume app). The environment is far from a test chamber but the readings (except for one frequency) were quite steady and seem repeatable. My purpose was not to determine absolute magnitude of output but to compare one speaker to the other to determine relative difference. Amp volume was unchanged, and used the same channel, and speaker positions were identical relative to the iPod Touch mic (3' straight in front of the tweeter). The crossover is at 3000 hz Here are the results:
Freq - dB New - dB Old - Diff
800 - 85 - 85 - 0
1250 - 85 - 85 - 0
1600 - 84 - 84 - 0
2000 - 79 - 72?? - 7?? Reading not steady
2500 - 85 - 85 - 0
3150 - 85 - 85 - 0
4000 - 83 - 84 - -1
5000 - 83 - 85 - -2
6300 - 80 - 84 - -4
8000 - 76 - 81 - -5
10000 - 83 - 85 - -2
12500 - 77 - 80 - -3
16000 - 76 - 76 - 0
20000 - 65 - 67 - -2 (low but the rolloff may be the iPod Touch mic)
So my first conclusion is that the new tweeter is down about 2-3 dB compared to the old. Your thoughts?
I'm now thinking of shorting out the 3.0 ohm series resistor and repeating the test to see what I get. Again your thoughts? It would seem I will have two data points on performance and should be able to fair closely determine how much resistance I need if 0 ohms is a little hot.
Freq - dB New - dB Old - Diff
800 - 85 - 85 - 0
1250 - 85 - 85 - 0
1600 - 84 - 84 - 0
2000 - 79 - 72?? - 7?? Reading not steady
2500 - 85 - 85 - 0
3150 - 85 - 85 - 0
4000 - 83 - 84 - -1
5000 - 83 - 85 - -2
6300 - 80 - 84 - -4
8000 - 76 - 81 - -5
10000 - 83 - 85 - -2
12500 - 77 - 80 - -3
16000 - 76 - 76 - 0
20000 - 65 - 67 - -2 (low but the rolloff may be the iPod Touch mic)
So my first conclusion is that the new tweeter is down about 2-3 dB compared to the old. Your thoughts?
I'm now thinking of shorting out the 3.0 ohm series resistor and repeating the test to see what I get. Again your thoughts? It would seem I will have two data points on performance and should be able to fair closely determine how much resistance I need if 0 ohms is a little hot.
Ron, this is your interesting problem, not mine, so you're going to have to figure it out yourself. Start by getting the issues clear in your mind.
Your old tweeter was a fabric dome with 3R input resistance to the DM7 MkII filter, your new one is a (shudders...LOL) metal dome with 0.7R input resistance on a slightly different filter. B&W see fit to add a 15R + 2.2uF Zobel to the metal dome in the Matrix 801 S2, perhaps to tame it at the top end.
The filter in the DM7 MkII looks like Linkwitz-Riley 4th order ca. 4000 Hz. You should find out how the Matrix 801 S2 filter works too. Write the values down!
2-Way Crossover Designer / Calculator
I would then model it with a similar metal dome tweeter and mid/bass woofer from the visaton range, but that's just me:
Visaton - Lautsprecher und Zubehör, Loudspeakers and Accessories
Broadly speaking, reducing that 3 ohm input resistance raises the level of the tweeter. Adding a Zobel rolls it off at the top end. You might be able to add a small resistance to the output of the filter which will slope its response upwards too. This depends a bit on the resistance Re of the two tweeters too, which you should measure and ideally match. Try modelling the effects in that Boxsim program so you get the hang of it. Beware that the woofer input will affect things, particularly near crossover.
IMO, you're probably going to have to adjust this to taste. I would think the Zobel is worth fitting, and then hopefully you can just adjust that input resistor to get the level about right overall. You'll then just have to put up with the tonal change due to the different tweeter.
Your old tweeter was a fabric dome with 3R input resistance to the DM7 MkII filter, your new one is a (shudders...LOL) metal dome with 0.7R input resistance on a slightly different filter. B&W see fit to add a 15R + 2.2uF Zobel to the metal dome in the Matrix 801 S2, perhaps to tame it at the top end.
The filter in the DM7 MkII looks like Linkwitz-Riley 4th order ca. 4000 Hz. You should find out how the Matrix 801 S2 filter works too. Write the values down!
2-Way Crossover Designer / Calculator
I would then model it with a similar metal dome tweeter and mid/bass woofer from the visaton range, but that's just me:
Visaton - Lautsprecher und Zubehör, Loudspeakers and Accessories
Broadly speaking, reducing that 3 ohm input resistance raises the level of the tweeter. Adding a Zobel rolls it off at the top end. You might be able to add a small resistance to the output of the filter which will slope its response upwards too. This depends a bit on the resistance Re of the two tweeters too, which you should measure and ideally match. Try modelling the effects in that Boxsim program so you get the hang of it. Beware that the woofer input will affect things, particularly near crossover.
IMO, you're probably going to have to adjust this to taste. I would think the Zobel is worth fitting, and then hopefully you can just adjust that input resistor to get the level about right overall. You'll then just have to put up with the tonal change due to the different tweeter.
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Considering the replacement tweeter is a similar type to the original, matching a single measurement of the new to one of the old tweeter should get you close. (The quality of the mic you use won't be too critical as you don't need to know how they actually measure, just whether they are the same).
Checked the crossover and found the existing series resistance was 3.3 ohms (not the 3.0 on the drawing). I did some trial and error input to one of the calculators for series resistance and found that if I wanted to gain 2.5 dB I needed to drop the resistance to 1 ohm. That was using the 5.8 ohm DC resistance for the tweeter. If I use something higher like 9 ohms impedance then I need to drop resistance to near zero.
So the easy resistance to try was zero using a jumper on the board. I compared the two speakers with zero resistance in the one with the new tweeter, with the following results:
Freq - dB New - dB Old - Diff
800 - 85 - 85 - 0
1250 - 85 - 85 - 0
1600 - 82 - 81 - -1
2000 - 85 - 85 - 0
2500 - 85 - 85 - 0
3150 - 84 - 83 - -1
4000 - 81 - 84 - +3
5000 - 85 - 85 - 0
6300 - 85 - 85 - 0
8000 - 84 - 84 - 0
10000 - 82 - 82 - 0
12500 - 77 - 77 - 0
16000 - 73 - 68 - -5
20000 - 63 - 62 - -1
Still some odd readings, probably caused by reflections in the room, but I'm thinking this is probably as good as it gets and I'm done! I can't hear the 16k or 20k tone in any case, as I am 62. I also suspect they are probably higher than they measure and the iPod Touch mic is just not that sensitive up at that frequency. I'm guessing the mic starts to roll off at 10k.
Agreed? Next step is to install the other new tweeter to replace the original and solder in jumpers on both boards.
So the easy resistance to try was zero using a jumper on the board. I compared the two speakers with zero resistance in the one with the new tweeter, with the following results:
Freq - dB New - dB Old - Diff
800 - 85 - 85 - 0
1250 - 85 - 85 - 0
1600 - 82 - 81 - -1
2000 - 85 - 85 - 0
2500 - 85 - 85 - 0
3150 - 84 - 83 - -1
4000 - 81 - 84 - +3
5000 - 85 - 85 - 0
6300 - 85 - 85 - 0
8000 - 84 - 84 - 0
10000 - 82 - 82 - 0
12500 - 77 - 77 - 0
16000 - 73 - 68 - -5
20000 - 63 - 62 - -1
Still some odd readings, probably caused by reflections in the room, but I'm thinking this is probably as good as it gets and I'm done! I can't hear the 16k or 20k tone in any case, as I am 62. I also suspect they are probably higher than they measure and the iPod Touch mic is just not that sensitive up at that frequency. I'm guessing the mic starts to roll off at 10k.
Agreed? Next step is to install the other new tweeter to replace the original and solder in jumpers on both boards.
Using 1/3 octave tones it will be hard to get around extraneous things. I would try taking the measurements at 1', and pull it out from the walls and lift it a few feet off the ground if possible.
But it does look like you're close already.
Thanks all for the suggestions. I soldered the jumper in both speaker crossovers, and now have the new tweeters in both speakers. Did one final check and with the usual measurement glitches they pretty much match with 0 dB difference at most frequencies, and most of the rest within 1 dB. Listened to a couple of CD's and it sounds good! Still a bit surprised there was that much of a sensitivity difference between the older fabric dome tweeters and the new metal dome. But all is good now.
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