Ugh, I could rewire my SBL PAXOs but pulling teeth would seem easier than all that faff with NACA 5. So what is the theory behind this? Is it a universal thing? Getting cross over away from speakers reducing vibrations? SBL PAXOs are already outside the box, on rubber mounts ... anybody tried this on SBLs?
Amp-Crossover-Speaker connection quiz...
- Thread starter Mr Tibbs
- Start date
mega lord
Centre tapped
There must be advantages due to less vibration but i also suspect there are electrical things going on.
Les W uses this aproach and says it is absolutely safe with Avondale NCC200 power amps. A NAPA board would be a different story though unless an inductor was put on the output.
Stu
Les W uses this aproach and says it is absolutely safe with Avondale NCC200 power amps. A NAPA board would be a different story though unless an inductor was put on the output.
Stu
Chris
pfm Member
In the case of those very few manufacturers of both speakers and amps I would have thought a Xover module could be offered to mount on the back of or even inside their amps to suit their own speakers with 2 or 3 terminals, post Xover, for connection to the speakers. A sort of "smart" bi-wiring, midway between normal passive crossovers inside speaker boxes and fully fledged xovers for bi-amping. Would help promote customer loyalty to a marque and sell more cables at least !
Chris
pfm Member
Surely less vibration cannot be the explanation because my crossovers were on the floor in wooden boxes with squidgy feet, under a sideboard which separates my two speakers and well clear of any vibrations caused by my sealed boxes. It´s too big a transformation to be caused by vibration. I would bet it is an electrical thing or maybe the little people. I swear I never touched a drop yesterday !
I don't understand, all that is happening here is moving the cross over from closer to the speaker to closer to the amp, a few metres of cable moved from one side of the cross over to the other, surely the load difference is minimal?
mega lord
Centre tapped
I don't understand either but the results speak for themselves.
The list of people endorsing this approach is growing. Mr Tibbs is a hugely respected diy enthusiast and Les W is god as far as i am concerned. Eguth (PFM member) has talked of this approach and even gave details of articles written in Hifi news magazine in the eighties i think. The articles are not on the net however, you have to purchase the back issues.
Stu, still marvelling in the new sound.
The list of people endorsing this approach is growing. Mr Tibbs is a hugely respected diy enthusiast and Les W is god as far as i am concerned. Eguth (PFM member) has talked of this approach and even gave details of articles written in Hifi news magazine in the eighties i think. The articles are not on the net however, you have to purchase the back issues.
Stu, still marvelling in the new sound.
In essence this is what I have, one very short cable from nCore to E-IIIr crossover then individual longer cables to each driver.
The amps and crossovers sit right behind each speaker.
I can't comment on SQ improvements as it's the configuration I have always run.
IMO it's the best practice and the effect is to reduce woofer currents modulating mid and tweeter signals, essentially what we pinkos call star earthiness
The thicker and shorter the primary cable from the amp the better within sensible selections.
The amps and crossovers sit right behind each speaker.
I can't comment on SQ improvements as it's the configuration I have always run.
IMO it's the best practice and the effect is to reduce woofer currents modulating mid and tweeter signals, essentially what we pinkos call star earthiness
The thicker and shorter the primary cable from the amp the better within sensible selections.
James
Lord of the Erg\o/s
If it is avoidance of inter-driver modulation and maximisation of star-earthiness, then the results will depend on the existing 0V arrangements. For my E-IIIR, each driver's 0V is connected to a common 0V point on the XO board, which is then taken connected to the amp's negative terminal. For this to be improved upon, I need to run the 0V returns of each driver directly to the amp. Hence, my suggestion in post #35. So a very short run of very low DCR cable between the amp and XO could be a valid proxy for direct grounding.
That would mean three separate runs of cables from the XO enclosure to the loudspeakers in my case, whereas I had conceived using a single run of four-core cable (or six-core, doubling up conductors for 0V and + for LF), but I can't see how that improves my current set-up, which has a 7m run of 4-core #15AWG Mogami W2972. I've doubled up the conductors, so they are closer to #12AWG with DCR of 0.0044Ω/m. Over a 7m run, that's a barely measureable 0.03Ω.
It would be useful to know the LCR characteristics of cables used by those who reported a difference.
That would mean three separate runs of cables from the XO enclosure to the loudspeakers in my case, whereas I had conceived using a single run of four-core cable (or six-core, doubling up conductors for 0V and + for LF), but I can't see how that improves my current set-up, which has a 7m run of 4-core #15AWG Mogami W2972. I've doubled up the conductors, so they are closer to #12AWG with DCR of 0.0044Ω/m. Over a 7m run, that's a barely measureable 0.03Ω.
It would be useful to know the LCR characteristics of cables used by those who reported a difference.
mega lord
Centre tapped
In my case it is Avondale blacklink between NCC200 and B&W P4 speakers (1996).
I have gone even further and starred the signal right back to the NCC200 output spades and the 0V lines to the ac side of the cap6 module.
Dont know the electrical characteristics of blacklink but it is VERY thin and Mr Tibbs says one core is a shield. About as far away from NACA5 as you can get.
Stu
I have gone even further and starred the signal right back to the NCC200 output spades and the 0V lines to the ac side of the cap6 module.
Dont know the electrical characteristics of blacklink but it is VERY thin and Mr Tibbs says one core is a shield. About as far away from NACA5 as you can get.
Stu
James, you could be in a better position to comment on what should be audible.
To me interdriver modulation is the only explanation I see.
Lets try for some number simulations.
Looking at your 0.03R, at a 20 amp bass transient thats a 0.6 volt modulation on your mid and tweeter.
So lets pick a amplifier rail voltage that does some easy sums, say 60 volt.
A 0.6v transient on a 60 volt rail is 40dB.
Now I'm not always so bright but I think I got the sum right and probably a ball park current.
For ref I used 20 x log(10) Vi / Vo for the voltage gain, obviously V=IR
To me interdriver modulation is the only explanation I see.
Lets try for some number simulations.
Looking at your 0.03R, at a 20 amp bass transient thats a 0.6 volt modulation on your mid and tweeter.
So lets pick a amplifier rail voltage that does some easy sums, say 60 volt.
A 0.6v transient on a 60 volt rail is 40dB.
Now I'm not always so bright but I think I got the sum right and probably a ball park current.
For ref I used 20 x log(10) Vi / Vo for the voltage gain, obviously V=IR
YNWOAN
100% Analogue
Avoidance of inter modulation distortion is often cited as the justification for bi-wiring and in much the way you describe. However, this mechanism is highly contentious and often disagreed with.
To be honest, I don't see how moving the crossovers can improve grounding in the way suggested unless, as James writes, the grounding is directly altered. There are already seperate runs of cable running from the crossover to the drivers whether that is inside the cabinet, just outside it, or near the amplifier. The only thing that has been altered is the proportion of cable before the crossover relative to that after it.
To be honest, I don't see how moving the crossovers can improve grounding in the way suggested unless, as James writes, the grounding is directly altered. There are already seperate runs of cable running from the crossover to the drivers whether that is inside the cabinet, just outside it, or near the amplifier. The only thing that has been altered is the proportion of cable before the crossover relative to that after it.
PigletsDad
My intelligence test came back negative.
None of this is intermodulation - which is a non-linear effect.
Everything described so far is linear.
Lets say we have a signal at say 70Hz, where maybe teh bass driver impedance is low, and for arguments sake, it is 20A. Fine, then we get 0.6V drop on the wires AT 70Hz. A tweeter signal at say 3 kHz can travel down the wires, and neither knowns no cares what happens at 70Hz.
Speaker wires don't have intermodulation processes - they are just passive impedances. At audio, that is dominantly resistive, but the inductance and capacitance can matter for amplifier stability.
Everything described so far is linear.
Lets say we have a signal at say 70Hz, where maybe teh bass driver impedance is low, and for arguments sake, it is 20A. Fine, then we get 0.6V drop on the wires AT 70Hz. A tweeter signal at say 3 kHz can travel down the wires, and neither knowns no cares what happens at 70Hz.
Speaker wires don't have intermodulation processes - they are just passive impedances. At audio, that is dominantly resistive, but the inductance and capacitance can matter for amplifier stability.
Thanks PD, just struggling with what is a new concept for me.
So if i have this right we can say at AC, voltage drops of a pair different frequencies do not sum in a common series R.
I think my head just exploded in a puff of reverse logic, cant help but think I'm missing something thats obvious to everyone else.
I can see how vdrops are not simple additive if they are phase shifted but can't see how just a frequency shift has the same effect.
So if i have this right we can say at AC, voltage drops of a pair different frequencies do not sum in a common series R.
I think my head just exploded in a puff of reverse logic, cant help but think I'm missing something thats obvious to everyone else.
I can see how vdrops are not simple additive if they are phase shifted but can't see how just a frequency shift has the same effect.
James
Lord of the Erg\o/s
I was never good with the maths around electrical stuff. It explains why I struggle to digest beyond the first chapter of the Art of Electronics. But I have some intuitive sense.
If the pipes that carry the audio to the drivers have a thin return pipe that is shared, then the relatively higher pressure or volume of electrons could arguably go up the 'wrong' way on the return pipes of the smaller drivers or affect their 'flow' or pressure.
But if there is a big FAT return pipe that is bigger than the sum of all the pipes feeding the drivers from the filters, then logic would suggest they would drain freely and not go the 'wrong' way or affect the upstream pressure in any meaningful way. A simple way to test this hypothesis is to significantly decrease the DCR of the 0V cable that takes the ground from a common (star) point on the crossover PCB back to the amp to see if that yields the same improvement, as others have posted about in moving the crossover closer to the amp.
The other possible effect at play is modification of the transfer function with the added DCR downstream of the crossover, which affects the LCR seen by the respective filter sections.
If the pipes that carry the audio to the drivers have a thin return pipe that is shared, then the relatively higher pressure or volume of electrons could arguably go up the 'wrong' way on the return pipes of the smaller drivers or affect their 'flow' or pressure.
But if there is a big FAT return pipe that is bigger than the sum of all the pipes feeding the drivers from the filters, then logic would suggest they would drain freely and not go the 'wrong' way or affect the upstream pressure in any meaningful way. A simple way to test this hypothesis is to significantly decrease the DCR of the 0V cable that takes the ground from a common (star) point on the crossover PCB back to the amp to see if that yields the same improvement, as others have posted about in moving the crossover closer to the amp.
The other possible effect at play is modification of the transfer function with the added DCR downstream of the crossover, which affects the LCR seen by the respective filter sections.
PigletsDad
My intelligence test came back negative.
Let's start off by defining what linear means.
A function f is linear if f(a + b) = f(a) + f(b) for any choice of a and b.
The effect of the wire just that of an impedance, and in the audio band it is purely resistive to very good approximation, but let us allow for a general impedance Z. Then V = IZ. To show that this is linear, consider two currents, so that I = IA + IB. Individually, we can see that VA = IA Z and VB = IB Z. Then V = IZ = (IA + IB) Z = IA Z + IB Z = VA + VB.
So in the approximation that speaker cable can be represented by an impedance, it is purely a linear process.
A function f is linear if f(a + b) = f(a) + f(b) for any choice of a and b.
The effect of the wire just that of an impedance, and in the audio band it is purely resistive to very good approximation, but let us allow for a general impedance Z. Then V = IZ. To show that this is linear, consider two currents, so that I = IA + IB. Individually, we can see that VA = IA Z and VB = IB Z. Then V = IZ = (IA + IB) Z = IA Z + IB Z = VA + VB.
So in the approximation that speaker cable can be represented by an impedance, it is purely a linear process.
Great PD, thanks for taking the time.
So I assume I was correct in thinking the tweeter and woofer currents sum linearly in the common impedance of the return cable to the amplifier. (Amp to crossover cable)
If the currents sum then the voltage drops in the common impedance sum.
So back to my simple values, along comes a great big instantaneous bass transient and the woofer pulls 20 amp giving rise to a 3 volt drop in the common Z of 0.3R.
The tweeter also pulls its current through the same common Z, but you say it is un affected by the 3 volt drop caused by the woofer as tweeter and woofer are in different frequency domains.
This is the bit I can't get my head around.
In essence you imply star grounding serves no purpose in a crossover?
Tony
So I assume I was correct in thinking the tweeter and woofer currents sum linearly in the common impedance of the return cable to the amplifier. (Amp to crossover cable)
If the currents sum then the voltage drops in the common impedance sum.
So back to my simple values, along comes a great big instantaneous bass transient and the woofer pulls 20 amp giving rise to a 3 volt drop in the common Z of 0.3R.
The tweeter also pulls its current through the same common Z, but you say it is un affected by the 3 volt drop caused by the woofer as tweeter and woofer are in different frequency domains.
This is the bit I can't get my head around.
In essence you imply star grounding serves no purpose in a crossover?
Tony