So, a few of you will be aware that I've been building some speakers based on B&W drivers which I picked up cheap-ish.
As with a lot of things, I'd have done a massive amount differently if I knew from the start what I do now, but I have 'what I have' to work with.
So, I have one (pair of) tweeter mid and bass units from the XT4 speaker, but the mid unit is a mid/woofer used in a full range 2-way (the XT2)
After lots of technical attempts at making a crossover from calculations, the eventual design was finalised through trial and error, and checked with final measurements.
So, my design is a 2.5 way whist the original was a 3 way with two bass woofers per cab instead of one. Since finishing my crossover I've managed to find the original design used in the B&W 3 way version (pictures of mine and theirs attached)
I've copied the B&W design into one cabinet, just for the high freq. xo.
It sounds great, but a bit dull and life-less compared to my 'personal' xo design (though hard to direct compare due to the difference in output levels)
What i don't understand is how I'm getting away with such low/high inductor/cap values in comparison, and what on earth is going on with the two inductor values on the mid xo of the official design...
help!
As with a lot of things, I'd have done a massive amount differently if I knew from the start what I do now, but I have 'what I have' to work with.
So, I have one (pair of) tweeter mid and bass units from the XT4 speaker, but the mid unit is a mid/woofer used in a full range 2-way (the XT2)
After lots of technical attempts at making a crossover from calculations, the eventual design was finalised through trial and error, and checked with final measurements.
So, my design is a 2.5 way whist the original was a 3 way with two bass woofers per cab instead of one. Since finishing my crossover I've managed to find the original design used in the B&W 3 way version (pictures of mine and theirs attached)
I've copied the B&W design into one cabinet, just for the high freq. xo.
It sounds great, but a bit dull and life-less compared to my 'personal' xo design (though hard to direct compare due to the difference in output levels)
What i don't understand is how I'm getting away with such low/high inductor/cap values in comparison, and what on earth is going on with the two inductor values on the mid xo of the official design...
help!
Attachments
Sorry, the right schematic is the 'positive' input of my crossover, each wired directly into the positive terminal of the tweeter/mid/woofer respectively, all are then connected to ground/negative
does that help?
does that help?
It helps understand that your crossover is not remotely similar to the "official" B&W design, which probably was designed to achieve a specific acoustical response for each bandpass, and a flat combined response using specific drivers.
What are your goals with your crossover?
What are your goals with your crossover?
It's hard to describe my goals without being cliche!
Obviously i want to sepperate the frequency distribution enough to protect the drivers and prevent them from being used in frequencies where they perform badly or break up.
Sound wise I'm looking for the best imaging possible (no.1 priority) followed by detail and accuracy (i.e. fast sounding).I'm tempted to say 'I want them to sound high fidelity' but that would be way too obvious surely?
In regards to the actual sound and differences between the crossovers, my understanding is that with the higher cap values and lower inductors I'm certainly running the mid higher and the tweeter lower, but they are still behaving at all but unbearably loud volumes, when mid breakup distortion becomes perceptible.
The set up I have at the moment is one speaker as shown in the right, 1st order 2.5 way configuration, and one with the same big inductor on the bass woofer, but a 2.4Ohm resistor on the tweeter, with a 3.6uF capacitor, and a single 1.17mH inductor on the mid woofer. (this is an attempt to match the B&W spec of 3.3uF, 1.1mH, obviously the 2.4 ohm resistor is way below the 4.7 used by B&W)
The Sound:
'My' crossover design sounds very open and airy, details are clear, symbols and vocals both sound incredibly fast and detailed. However when set as a pair imaging was very good but nowhere near the standard of PMC or 800 series B&W speakers I've compared to, and improving the imaging was a concern to achieve if possible. The only 'down side' of this xo was that it can sound a bit bright, and when turned very loud the attach of low trebble seems to 'snap' from the mid, sounding somewhat uncomfortable (this i presume is the cone break up being reached). On axis FR is pretty much flat, and in listening position is flat from 80Hz to 1k then gently rolls off.
The 'B&W' design sounds very controlled and presentable, but also boring. there's nothing exciting about the sound, it isn't analytical, and I can only describe it as 'fine, very good but boring'. It's interesting to note that the same mid woofer and tweeter were used in the XT2 (standmount) XTC (centre, MTM) and the XT4. So I'm working on what's almost an XT3 - the non existant 2.5 way that would fit between the XT2 and XT4. I am tempted to rebuild into larger cabinets, order the additional bass driver and build to the original xo specification, but the great open fast mid range that the mid is capable of is clearly restrained (in testing, with .32, .56 and even .64mh inductors on the mid it sounds way more open and images better than with the next step up available to me, a .96mh inductor, which should still be more open than the 1.1mH specified by b&w)
The XT2 used a 3.3ohm resistor, 3.3uF cap and 1.4mH inductor. Interesting to note that this was reviewed as a little dull sounding, whilst the XT4 was much more exciting to listen to. the XT3 uses a 0.56ohm resistor on the tweeter with the same 3.3uF cap again, and goes back to the 1.1mH inductor used in the XT4.
My understanding is that the high end of the mid woofer is exceptionally accurate, but very close to the break up frequency (more so with this 1st order xo topolology that's been discussed) whilst I've tried to encourage out what is for me, the best part of the mid driver, B&W have reigned it in a little in order to prevent uncomfortable listening at high volumes.
I also feel like i have perhaps opened up 'too much' - frequencies are gently nudged away from each driver, and there is a large overlap region. The driver FR prevents this bing too peaky due to natural roll-off, and I have a personal theory that the amplifier is providing a set level of power across the frequency range, so the driver response at xo point can only jump up 'so much' anyway (I hope that statement is uderstandable, may need clarification)
So i worry that the very low inductor value and high cap value may make listening from the mid uncomfortable at high volume and risk blowing the tweeter.
So at this stage I'm thinking most likely I'll nudge my design toward the B&W design - use a .7mH inductor and play with lowering the capacitor value, but also build a 'B&W' crossover as well, and have both within the cabinet, allowing both options to be used.
Alternatively, as I said I could re-build into a true 3-way design, but my feeling is that B&W will have so much more at there disposal to mach transient, phase response etc that I should probably just follow their design and not bother with trying to build a 3-way xo, though I wuold probably still lower the inductor value or have a switch on the back of the speaker allowing this to be done (anyone know XO level speaker swtiches??), add to this that I have learnt so much since building the original cabinets that I'd quite like to change them to be a little larger (bass enclosure is only 7.5L), and provide more space behind the driver for them to 'breathe' and their could well be a full re-model happening...
At any rate, my level of respect to the good speaker builders out there continues to grow!
Obviously i want to sepperate the frequency distribution enough to protect the drivers and prevent them from being used in frequencies where they perform badly or break up.
Sound wise I'm looking for the best imaging possible (no.1 priority) followed by detail and accuracy (i.e. fast sounding).I'm tempted to say 'I want them to sound high fidelity' but that would be way too obvious surely?
In regards to the actual sound and differences between the crossovers, my understanding is that with the higher cap values and lower inductors I'm certainly running the mid higher and the tweeter lower, but they are still behaving at all but unbearably loud volumes, when mid breakup distortion becomes perceptible.
The set up I have at the moment is one speaker as shown in the right, 1st order 2.5 way configuration, and one with the same big inductor on the bass woofer, but a 2.4Ohm resistor on the tweeter, with a 3.6uF capacitor, and a single 1.17mH inductor on the mid woofer. (this is an attempt to match the B&W spec of 3.3uF, 1.1mH, obviously the 2.4 ohm resistor is way below the 4.7 used by B&W)
The Sound:
'My' crossover design sounds very open and airy, details are clear, symbols and vocals both sound incredibly fast and detailed. However when set as a pair imaging was very good but nowhere near the standard of PMC or 800 series B&W speakers I've compared to, and improving the imaging was a concern to achieve if possible. The only 'down side' of this xo was that it can sound a bit bright, and when turned very loud the attach of low trebble seems to 'snap' from the mid, sounding somewhat uncomfortable (this i presume is the cone break up being reached). On axis FR is pretty much flat, and in listening position is flat from 80Hz to 1k then gently rolls off.
The 'B&W' design sounds very controlled and presentable, but also boring. there's nothing exciting about the sound, it isn't analytical, and I can only describe it as 'fine, very good but boring'. It's interesting to note that the same mid woofer and tweeter were used in the XT2 (standmount) XTC (centre, MTM) and the XT4. So I'm working on what's almost an XT3 - the non existant 2.5 way that would fit between the XT2 and XT4. I am tempted to rebuild into larger cabinets, order the additional bass driver and build to the original xo specification, but the great open fast mid range that the mid is capable of is clearly restrained (in testing, with .32, .56 and even .64mh inductors on the mid it sounds way more open and images better than with the next step up available to me, a .96mh inductor, which should still be more open than the 1.1mH specified by b&w)
The XT2 used a 3.3ohm resistor, 3.3uF cap and 1.4mH inductor. Interesting to note that this was reviewed as a little dull sounding, whilst the XT4 was much more exciting to listen to. the XT3 uses a 0.56ohm resistor on the tweeter with the same 3.3uF cap again, and goes back to the 1.1mH inductor used in the XT4.
My understanding is that the high end of the mid woofer is exceptionally accurate, but very close to the break up frequency (more so with this 1st order xo topolology that's been discussed) whilst I've tried to encourage out what is for me, the best part of the mid driver, B&W have reigned it in a little in order to prevent uncomfortable listening at high volumes.
I also feel like i have perhaps opened up 'too much' - frequencies are gently nudged away from each driver, and there is a large overlap region. The driver FR prevents this bing too peaky due to natural roll-off, and I have a personal theory that the amplifier is providing a set level of power across the frequency range, so the driver response at xo point can only jump up 'so much' anyway (I hope that statement is uderstandable, may need clarification)
So i worry that the very low inductor value and high cap value may make listening from the mid uncomfortable at high volume and risk blowing the tweeter.
So at this stage I'm thinking most likely I'll nudge my design toward the B&W design - use a .7mH inductor and play with lowering the capacitor value, but also build a 'B&W' crossover as well, and have both within the cabinet, allowing both options to be used.
Alternatively, as I said I could re-build into a true 3-way design, but my feeling is that B&W will have so much more at there disposal to mach transient, phase response etc that I should probably just follow their design and not bother with trying to build a 3-way xo, though I wuold probably still lower the inductor value or have a switch on the back of the speaker allowing this to be done (anyone know XO level speaker swtiches??), add to this that I have learnt so much since building the original cabinets that I'd quite like to change them to be a little larger (bass enclosure is only 7.5L), and provide more space behind the driver for them to 'breathe' and their could well be a full re-model happening...
At any rate, my level of respect to the good speaker builders out there continues to grow!
Having done more looking up and simming than I really should have to, I find these B&W XT4 and XT2 speakers are a home theatre solution. Rough and ready is the order of the day and the crossovers are cheap and cheerful...🙄
http://www.bwgroupsupport.com/manuals/bw-service
The XT2 using your midwoofer is about as basic as it gets, but better than your effort. You really should never put a resistor in series with a woofer, because it destroys the damping on the bass. 😀
The XT2 circuit below will let through a lot of bass cone breakup, and give the tweeter a rough ride. This sort of circuit is OK with a plastic polycone bass, but it a bit iffy with kevlar I'd think. But I'd need to see the frequency response of a kevlar bass to do better.
To convert that to a 2.5 way, you put a biggish coil on the bass, a smaller one on the midrange and maybe brighten up the tweeter with a smaller resistor.
http://www.bwgroupsupport.com/manuals/bw-service
The XT2 using your midwoofer is about as basic as it gets, but better than your effort. You really should never put a resistor in series with a woofer, because it destroys the damping on the bass. 😀
The XT2 circuit below will let through a lot of bass cone breakup, and give the tweeter a rough ride. This sort of circuit is OK with a plastic polycone bass, but it a bit iffy with kevlar I'd think. But I'd need to see the frequency response of a kevlar bass to do better.
To convert that to a 2.5 way, you put a biggish coil on the bass, a smaller one on the midrange and maybe brighten up the tweeter with a smaller resistor.
Attachments
Your midrange has no highpass which is not going to be a good thing. I don't know the drivers, but many midrange drivers roll off fast at low frequencies which might be giving you an "acoustic" bandpass in the midrange - but the mid will be handling the full acoustic spectrum. This might mean that at moderate levels it sounds ok.
The lack of highpass on the mid will however cause issues with power handling and excursion on the midrange. Both of these are not good.
It might be worth you perusing done texts on crossover design.
The lack of highpass on the mid will however cause issues with power handling and excursion on the midrange. Both of these are not good.
It might be worth you perusing done texts on crossover design.
The XT2 midbass is a different model from the XT4 midrange, but both are 5" kevlar units. I'd guess the XT2 driver has a longer voicecoil and can handle some excursion. The two speakers also have different tweeters, but ferrofluid, you'd guess.
nannoo's simple circuit is almost there really. But it could certainly use something more sophisticated than simple coils on the bass and midrange. Huge modelling effort though, or just hope for the best with the XT4 crossover. 😀
nannoo's simple circuit is almost there really. But it could certainly use something more sophisticated than simple coils on the bass and midrange. Huge modelling effort though, or just hope for the best with the XT4 crossover. 😀
The 'mid range' is pretty definately a mid-woofer, even if it isn't used as such, the suspension system and maximum throw are almost exactly the same as the bass woofer, the frequency response is also pretty similar - starts to roll of around 100Hz, as I said I'm utilising this in a 2.5 way design, but I'm not entirely against switching to 3-way, after all that was the original intent (see below)
Is the original XT2 design better than mine just because of the resistor situation?
I switched to 2.5 way for a few reasons, the efficiency of the mid is much higher than the bass woofer, and the bass is 8ohm whilst the mid is 4 - given that both the mid and tweeter were pretty hot and lower impedance it just seemed to make sense to drop them with a series resistor, at which point everything started behaving much more like it should - FR was spot on and impedance better too.
You mentioned you shouldn't use a resistor in line with a woofer - can you explain a bit more of the technical reasons behind this, or point me to a suitable article? If I switched to 3-way would I negate these issues?
Bass break up - are you thinking this because you think it's a 'MID' unit?
You said about how the tweeters would be given a rough ride - did you mean with the 5.6uF or the 3.3uF Caps?
What would you think of switching it to 4th order? I should say that I've had a set up of 2nd order on the mid with 3rd order on the tweeter which was 'perfect' on paper (measurements were flattest on axis that I'd managed so far) but the sound was very boring and dull, though this was before I 'opened up' the mid with a much lower value inductor.
Also, whilst this dioscussion is happening I should ask if anyone has an opinion on how much I should spend on caps and what to get? bearing in mind uk suppliers 🙄
The drivers list at £66 each (woofers/mid) and £37 for the tweeter, don't know if that can be used as any reflection on actual quality, but meh, I'm british!!
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