Hi!
I have these old (and probably rather cheap) speakers. I thought it might be a fun exercise to bi-amp them. Not that I expect to be able to make them sound great, but rather as a learning experience. If I mess them up it's not the end of the world.
I'm thinking a single board computer running Linux, CamillaDSP, maybe an ICEpower 200AS2 amp. (I'd love to tri-amp but synchronized output of more than 2 channels doesn't seem to come cheap: €500+ for a multichannel DAC seems unreasonable to me, when a 2-channel one costs €30 or so. Anyone know of, say, a 4-channel DAC module for the Beaglebone McASP interface?)
Here are the guinea pigs (one with four oscilloscope probe leads coming out of its tweeter hole):
The name plate says:
Pioneer S-X450
Impedance: 8 Ω
Music Power (DIN): 140 W (Whatever that means. Is/was there really a DIN standard for "music power"?)
The drivers' active diameters measure approximately 164 mm (6.5 in or 0.21 french royal feet
- probably marketed as 8 in?), 69 mm (2.7 in), and 25 mm (1 in), respectively.
Construction is rather thin particle board and old-school point-to-point crossover. Hmm, these actually seem even worse than I expected! Oh well. Maybe I should have expected this given the asymmetric, surface mounted drivers.
Anyway, here's the schematic of the crossover:
I don't have any experience of crossover design. Woofer section looks like a 2nd order filter, right? Are the midrange and tweeter third order? Or what's with those "extra" "3.3/63V-" capacitors?
(The midrange damping resistor is a bit funny, I think they've used what's actually a thermal fuse using a low temperature solder bead to spring the wire open at a certain temperature. I've heard about these but I've not seen one in real life before! Anyway, I guess it's only used as a resistor here.)
Now the fun part: I hooked the crossover up to a Siglent SDS1104X-E oscilloscope and used its Bode plot functionality to characterise it:
How this works is that the 'scope tells a signal generator to output a series of frequencies - here the signal generator is my PC, hooked up to the 'scope over Ethernet; the computer's audio output is then connected to an audio amplifier and then on to the speaker - and then compares the input (channel 1 here, hooked up at the input of the crossover inside the speaker) to the other channels (ch2 being the bass here, ch3 midrange, and ch4 tweeter) and records the amplitude and phase differences. It does this for a configurable number of frequencies per octave to generate the Bode plot. The scope's small screen gets pretty cluttered so I saved the data to a USB stick and plotted it with gnuplot instead:
I'm surprised at the high crossover frequencies (about 1.9 kHz and 6.1 kHz). I'm wondering if I've made some kind of mistake here or if this is reasonable.
I have these old (and probably rather cheap) speakers. I thought it might be a fun exercise to bi-amp them. Not that I expect to be able to make them sound great, but rather as a learning experience. If I mess them up it's not the end of the world.
I'm thinking a single board computer running Linux, CamillaDSP, maybe an ICEpower 200AS2 amp. (I'd love to tri-amp but synchronized output of more than 2 channels doesn't seem to come cheap: €500+ for a multichannel DAC seems unreasonable to me, when a 2-channel one costs €30 or so. Anyone know of, say, a 4-channel DAC module for the Beaglebone McASP interface?)
Here are the guinea pigs (one with four oscilloscope probe leads coming out of its tweeter hole):
The name plate says:
Pioneer S-X450
Impedance: 8 Ω
Music Power (DIN): 140 W (Whatever that means. Is/was there really a DIN standard for "music power"?)
The drivers' active diameters measure approximately 164 mm (6.5 in or 0.21 french royal feet
- probably marketed as 8 in?), 69 mm (2.7 in), and 25 mm (1 in), respectively.Construction is rather thin particle board and old-school point-to-point crossover. Hmm, these actually seem even worse than I expected! Oh well. Maybe I should have expected this given the asymmetric, surface mounted drivers.
Anyway, here's the schematic of the crossover:
I don't have any experience of crossover design. Woofer section looks like a 2nd order filter, right? Are the midrange and tweeter third order? Or what's with those "extra" "3.3/63V-" capacitors?
(The midrange damping resistor is a bit funny, I think they've used what's actually a thermal fuse using a low temperature solder bead to spring the wire open at a certain temperature. I've heard about these but I've not seen one in real life before! Anyway, I guess it's only used as a resistor here.)
Now the fun part: I hooked the crossover up to a Siglent SDS1104X-E oscilloscope and used its Bode plot functionality to characterise it:
How this works is that the 'scope tells a signal generator to output a series of frequencies - here the signal generator is my PC, hooked up to the 'scope over Ethernet; the computer's audio output is then connected to an audio amplifier and then on to the speaker - and then compares the input (channel 1 here, hooked up at the input of the crossover inside the speaker) to the other channels (ch2 being the bass here, ch3 midrange, and ch4 tweeter) and records the amplitude and phase differences. It does this for a configurable number of frequencies per octave to generate the Bode plot. The scope's small screen gets pretty cluttered so I saved the data to a USB stick and plotted it with gnuplot instead:
I'm surprised at the high crossover frequencies (about 1.9 kHz and 6.1 kHz). I'm wondering if I've made some kind of mistake here or if this is reasonable.
