T-bass for dual alpha's
I am re-reading Graham's initial post, and got to get some things figured out before ordering some parts.....
The series coil (2mh or 5mh) is affected by driver spec's.
I am using two alpha's in parallel now. Is there a way to calculate a good value here for this setup? It looks I may want to go lower for parallel operation. Resistors are cheap but the inductors are not. I would like to get close with the coil here, and tweak with a cap and resistor if needed.
The zobel also changed a bit here as well from the first post to what Graham has posted on his web site.
Thanks for any assistance!
Mike
I am re-reading Graham's initial post, and got to get some things figured out before ordering some parts.....
The series coil (2mh or 5mh) is affected by driver spec's.
I am using two alpha's in parallel now. Is there a way to calculate a good value here for this setup? It looks I may want to go lower for parallel operation. Resistors are cheap but the inductors are not. I would like to get close with the coil here, and tweak with a cap and resistor if needed.
The zobel also changed a bit here as well from the first post to what Graham has posted on his web site.
Thanks for any assistance!
Mike
Hi Mike,
Whether the second choke is necessary, and whatever value might prove optimum is down to the LF driver chosen, its baffle mounting (whether rear or forward facing) and also is dependent upon the frequency of a desired crossover to mid or fullrange driver.
There are new and old type Alphas having different mid frequency characteristics and personally I have not run either.
The basis of the T-bass circuit is to overcome resonant driver energy storage within original music time frame (so that fundamental driver resonance does not predominate in non-music driver time) plus provide a degree of correction to assist with inefficient LF radiation from an OB. Anything beyond that, as with the second choke, is back to conventional crossover circuitry with all of the music time phase delay that this imposes.
Cheers ...... Graham.
Whether the second choke is necessary, and whatever value might prove optimum is down to the LF driver chosen, its baffle mounting (whether rear or forward facing) and also is dependent upon the frequency of a desired crossover to mid or fullrange driver.
There are new and old type Alphas having different mid frequency characteristics and personally I have not run either.
The basis of the T-bass circuit is to overcome resonant driver energy storage within original music time frame (so that fundamental driver resonance does not predominate in non-music driver time) plus provide a degree of correction to assist with inefficient LF radiation from an OB. Anything beyond that, as with the second choke, is back to conventional crossover circuitry with all of the music time phase delay that this imposes.
Cheers ...... Graham.
T-bass for dual alpha's
Thanks Graham. These are new production Alphas, two of them forward facing.
I am currently Bi-Amping - using an external crossover, so if I understand this a little, I might not need the second choke or even the zobel? Your suggesting I think that there is more at play.
And if I go to a single power amp setup (something that might make things simpler for my setup) then I calculate this similiar to a 6db low-pass filter. I missed that, and I hopefully have this correct. The parallel cap makes it look like more of a notch filter to me, but my understanding of crossovers is limited.
Mike
Thanks Graham. These are new production Alphas, two of them forward facing.
I am currently Bi-Amping - using an external crossover, so if I understand this a little, I might not need the second choke or even the zobel? Your suggesting I think that there is more at play.
And if I go to a single power amp setup (something that might make things simpler for my setup) then I calculate this similiar to a 6db low-pass filter. I missed that, and I hopefully have this correct. The parallel cap makes it look like more of a notch filter to me, but my understanding of crossovers is limited.
Mike
Hi Mike,
Biamping will make the system. easier to adjust, and yes, with line level crossover you should not need the second choke, though do keep the Zobel.
You can have rear facing LF drivers for greater cut around what otherwise would be the mid range peak.
Yes that small capacitor is to act as a notch with drivers having a pronounced mid peak.
All components between an amplifier and driver modify reproduction, though the T-bass induced modification is there to act equal but opposite to driver resonance characteristics and thus provide improvement.
T-bass must go direct to the amp, preferably right at the LF channel output terminals.
Cheers ....... Graham.
Biamping will make the system. easier to adjust, and yes, with line level crossover you should not need the second choke, though do keep the Zobel.
You can have rear facing LF drivers for greater cut around what otherwise would be the mid range peak.
Yes that small capacitor is to act as a notch with drivers having a pronounced mid peak.
All components between an amplifier and driver modify reproduction, though the T-bass induced modification is there to act equal but opposite to driver resonance characteristics and thus provide improvement.
T-bass must go direct to the amp, preferably right at the LF channel output terminals.
Cheers ....... Graham.
T-bass for use on free-air car loading woofers
Hi Graham, all.
Time to revive this useful thread. I've been working on my car's audio setup recently.
Starting from the top we have a Mondeo with uprated battery and some sound deadening on key panels, early 2000s Pioneer head unit and CD changer. This feeds an ok 4 channel amp and 4 upgraded door speakers.
I recently added 2 x 12" woofers to the parcel shelf as a test and ran off a separate amp (active bi-amping with suitable low and high pass filters). The result was encouraging. I since built a false shelf from 18mm WBP plywood and put the 2 x 12" woofers on there. These are my cheapo Skytronic 902-222 as I'll be using on my new open baffles. It's now getting very good, probably the best in-car sounds I've personally heard (I've not heard much).
There's just a touch too much upper bass and I'd like more low bass... so it's time to try t-bass in the car.
Given this sort of setup do you have any warnings or suggestions for how best to do this Graham? The "box" is a leaky ~400L boot and the filter is active. The drivers are 2 x 8ohm in parallel.
Simon
Hi Graham, all.
Time to revive this useful thread. I've been working on my car's audio setup recently.
Starting from the top we have a Mondeo with uprated battery and some sound deadening on key panels, early 2000s Pioneer head unit and CD changer. This feeds an ok 4 channel amp and 4 upgraded door speakers.
I recently added 2 x 12" woofers to the parcel shelf as a test and ran off a separate amp (active bi-amping with suitable low and high pass filters). The result was encouraging. I since built a false shelf from 18mm WBP plywood and put the 2 x 12" woofers on there. These are my cheapo Skytronic 902-222 as I'll be using on my new open baffles. It's now getting very good, probably the best in-car sounds I've personally heard (I've not heard much).
There's just a touch too much upper bass and I'd like more low bass... so it's time to try t-bass in the car.
Given this sort of setup do you have any warnings or suggestions for how best to do this Graham? The "box" is a leaky ~400L boot and the filter is active. The drivers are 2 x 8ohm in parallel.
Simon
Hi Graham,
I'm not sure I want the weight or the cost of a 500VA in my car to be honest. I'll try the 2x100VA as I have them already, and decide if it's enough.
I've not done this yet as I've been busy renewing my drop link rods and anti-roll bar bushes and improving my signal wiring in there.... very busy with that car!
Simon
I'm not sure I want the weight or the cost of a 500VA in my car to be honest. I'll try the 2x100VA as I have them already, and decide if it's enough.
I've not done this yet as I've been busy renewing my drop link rods and anti-roll bar bushes and improving my signal wiring in there.... very busy with that car!
Simon
Hi Graham,
I'd like to let you know that I introduced your T-bass circuit to the public in my personal blog (in Chinese) last year. One of the reader got interested and made one for himself. I received an email just now, he said the circuit is just amazing for his fullranger on OB.
Best Regards,
CLS
I'd like to let you know that I introduced your T-bass circuit to the public in my personal blog (in Chinese) last year. One of the reader got interested and made one for himself. I received an email just now, he said the circuit is just amazing for his fullranger on OB.
Best Regards,
CLS
Thanks for the feedback CLS.
Of course the performance must relate to any individual driver's X-max capabilities and linearity through that working range.
This circuit is intended to counter the amplifier-driver interface storing and re-releasing of resonant energy during *driver time* wrt amplified *music time* output.
Via L-C-R component choice, it does this in a manner that line and amplifier circuits cannot, because active voltage or current related (EQ etc.) circuits cannot compensate for dynamic V^2 and I^2 energy related waveform induced amplifier-driver reactions arising during *music* time (whether dipole, enclosure or other) !!!!!
Of course the performance must relate to any individual driver's X-max capabilities and linearity through that working range.
This circuit is intended to counter the amplifier-driver interface storing and re-releasing of resonant energy during *driver time* wrt amplified *music time* output.
Via L-C-R component choice, it does this in a manner that line and amplifier circuits cannot, because active voltage or current related (EQ etc.) circuits cannot compensate for dynamic V^2 and I^2 energy related waveform induced amplifier-driver reactions arising during *music* time (whether dipole, enclosure or other) !!!!!
Hi Graham,
I know you also designed amplifiers, so you must know something about the negative feedback and related stuff...
I've been on and off thinking of the current feedback, mixed feedback, current amplifier, high output impedance.... sort of things.
Variable Amplifier Impedance
An amp with very high output impedance would also drive the woofer with more power around the resonant peak (related to the ordinary low Zo ones). What are the differences between this and T-bass circuit?
Other than the feature of LC cut in the midbass region to counteract the dipole peak or reflections, I think the 'contour' of boost by T-bass is different from the high Zo amp. The (relative) boost by the latter would be closely related to the impedance curve of the speaker, which might not be optimal for 'shaping' the real frequency response.
What else? What's your opinion on these?
I know you also designed amplifiers, so you must know something about the negative feedback and related stuff...
I've been on and off thinking of the current feedback, mixed feedback, current amplifier, high output impedance.... sort of things.
Variable Amplifier Impedance
An amp with very high output impedance would also drive the woofer with more power around the resonant peak (related to the ordinary low Zo ones). What are the differences between this and T-bass circuit?
Other than the feature of LC cut in the midbass region to counteract the dipole peak or reflections, I think the 'contour' of boost by T-bass is different from the high Zo amp. The (relative) boost by the latter would be closely related to the impedance curve of the speaker, which might not be optimal for 'shaping' the real frequency response.
What else? What's your opinion on these?
Hi CLS,
A high impedance amplifier CANNOT control (= damp) driver system resonance, and the result is deleteriously audible.
Agreed, 'T'-bass boost might not be optimal for 'shaping' the real frequency response - different mounting and different drivers could be beyond what the 'T'-bass can cope with.
The 'T'-bass is there to control the dynamic response of the driver wrt a low Z power amplifier. Once this has been done then other methods of frequency control may be utilised.
Direct amplifier connection cannot produce the same dynamic correction no matter how much frequency related amplitude control is inserted. Indeed, trying to control LF reproduction via passive line circuitry can actually make LF sound awful, in spite of the measured sine frequency amplitude response being 'improved'.
Variable impedance (with frequency) amplifiers also tend to have risk for increased LF phase change due to the feedback network.
I had wrestled with this problem on and off for 40 years before the simple 'T'-bass solution suddenly came to me.
A high impedance amplifier CANNOT control (= damp) driver system resonance, and the result is deleteriously audible.
Agreed, 'T'-bass boost might not be optimal for 'shaping' the real frequency response - different mounting and different drivers could be beyond what the 'T'-bass can cope with.
The 'T'-bass is there to control the dynamic response of the driver wrt a low Z power amplifier. Once this has been done then other methods of frequency control may be utilised.
Direct amplifier connection cannot produce the same dynamic correction no matter how much frequency related amplitude control is inserted. Indeed, trying to control LF reproduction via passive line circuitry can actually make LF sound awful, in spite of the measured sine frequency amplitude response being 'improved'.
Variable impedance (with frequency) amplifiers also tend to have risk for increased LF phase change due to the feedback network.
I had wrestled with this problem on and off for 40 years before the simple 'T'-bass solution suddenly came to me.
Hi Graham,
Thanks for reply.
I think, the woofers on OB do not need very much help from the amp to control the resonance. Many people use high Q woofers on OB and no (or, at least, less) EQ with satisfied results. And high Zo amp + low Q woofer behave like low Zo amp + high Q woofer because in both cases, the series impedance can be 'merged' into the Qes. No?
Thanks for reply.
I think, the woofers on OB do not need very much help from the amp to control the resonance. Many people use high Q woofers on OB and no (or, at least, less) EQ with satisfied results. And high Zo amp + low Q woofer behave like low Zo amp + high Q woofer because in both cases, the series impedance can be 'merged' into the Qes. No?
Hi CLS,
Have you actually checked out the aspects you mention for yourself ?
I mean with MUSIC drive as opposed to steady sine or computer simulation.
A Hi-Zo amp with Lo-Q woofer lacks LF wavefront drive attack on drums and picked bass guitar.
For example try say a pentode amp versus SS.
A Lo-Zo amp can provide the attack, but a HiQ LF driver generates an undampable tonal presence.
A high Q LS set up to sound correct with classical music will boom tiringly on organ works.
'Merging' weaknesses might produce a desired AF plot, but not correct reproduction, because if it is used as a substitute for cone area at LF, then loudspeaker 'Q' becomes audible.
End of story.
Have you actually checked out the aspects you mention for yourself ?
I mean with MUSIC drive as opposed to steady sine or computer simulation.
A Hi-Zo amp with Lo-Q woofer lacks LF wavefront drive attack on drums and picked bass guitar.
For example try say a pentode amp versus SS.
A Lo-Zo amp can provide the attack, but a HiQ LF driver generates an undampable tonal presence.
A high Q LS set up to sound correct with classical music will boom tiringly on organ works.
'Merging' weaknesses might produce a desired AF plot, but not correct reproduction, because if it is used as a substitute for cone area at LF, then loudspeaker 'Q' becomes audible.
End of story.
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Hi Graham,
I've tried some series resistors on W-baffle 'subwoofer' with plate amp (SS of course), and high Zo amp (tube) with fullrange OB. Both cases were not so thoroughly tested and I have yet to come to an conclusion on those.
I've been thinking of building an amp for replacing my poor old Hafler, so some thoughts are mixed messily. As to those 'weaknesses', I'll give them a try...
I've tried some series resistors on W-baffle 'subwoofer' with plate amp (SS of course), and high Zo amp (tube) with fullrange OB. Both cases were not so thoroughly tested and I have yet to come to an conclusion on those.
I've been thinking of building an amp for replacing my poor old Hafler, so some thoughts are mixed messily. As to those 'weaknesses', I'll give them a try...
Hi Graham,
I am using the T-bass for my OB speakers for some time. It's an Eminence Beta 15 woofer, run via Sony TA-N 511 amp. Yesterday I was playing with some test tones,and noticed the following: 30 Hz is barely audible, 35 can be heard well, but..there is a strong peak at 40 Hz. As I move toward 50 Hz (in steps of 1 Hz) it becomes quieter,and then (strange!) a 60 Hz tone is very quiet (as compared to 40 Hz). Upper in freq.(70-100hz) it goes back to "normal"...
Sorry for only subjective description, and no measurements...
I know that this behaviour can be caused by Beta's resonance (or room modes).
But, what I'd like to ask is: How can I modify the T-bass circuit so that I get more even response in the 40-60 Hz range?
Thanks,
vix
I am using the T-bass for my OB speakers for some time. It's an Eminence Beta 15 woofer, run via Sony TA-N 511 amp. Yesterday I was playing with some test tones,and noticed the following: 30 Hz is barely audible, 35 can be heard well, but..there is a strong peak at 40 Hz. As I move toward 50 Hz (in steps of 1 Hz) it becomes quieter,and then (strange!) a 60 Hz tone is very quiet (as compared to 40 Hz). Upper in freq.(70-100hz) it goes back to "normal"...
Sorry for only subjective description, and no measurements...
I know that this behaviour can be caused by Beta's resonance (or room modes).
But, what I'd like to ask is: How can I modify the T-bass circuit so that I get more even response in the 40-60 Hz range?
Thanks,
vix