I've searched around the forums, but so far haven't come across what I'm looking for. I'm getting ready to build an MTM speaker where the mids are 6 ohms nominal. If I put them in series, I don't get the increased sensitivity I want, but if I put them in parallel I get a load that looks like 2.5-3 ohms through the midrange.
SO, has anyone put together an amplifier PCB or kit that will deal with a 2-ohm load? I'd be looking for something that could generate 300WPC into 2 ohms, roughly.
Thanks in advance for any advice you might have.
Paul Pickard
SO, has anyone put together an amplifier PCB or kit that will deal with a 2-ohm load? I'd be looking for something that could generate 300WPC into 2 ohms, roughly.
Thanks in advance for any advice you might have.
Paul Pickard
why not "tri-amp"?
separate amps for each driver; the M amps could share power supply, the output devices/heatsinking will cost nearly the same with 2 amp approach, the only "extra" cost over a lo-Z amp is small signal/dirver stage stuf and a superior performing low power T amp and the active crossover
separate amps for each driver; the M amps could share power supply, the output devices/heatsinking will cost nearly the same with 2 amp approach, the only "extra" cost over a lo-Z amp is small signal/dirver stage stuf and a superior performing low power T amp and the active crossover
The advice about series resistance is completely incorrect.
Its as lot easier in terms of output devices to build a 300W/8ohm
amplifier than a 300W/2 ohm amplifier, personally I can't see the
point of your concern with voltage sensitivity, efficiency of the
series or parallel connected drivers is identical.
(Any difference in speaker voltage sensistivity in a multi channel
set up can be addressed by adjusting the amplifier gains.)
sreten.
Its as lot easier in terms of output devices to build a 300W/8ohm
amplifier than a 300W/2 ohm amplifier, personally I can't see the
point of your concern with voltage sensitivity, efficiency of the
series or parallel connected drivers is identical.
(Any difference in speaker voltage sensistivity in a multi channel
set up can be addressed by adjusting the amplifier gains.)
sreten.
I'm hoping my famously bad memory doesn't get me into trouble yet again
I think ribbon speakers are low impedance (right?) so this Borbely Audio amp may be worth investigating
On the other hand, "ribbon" is probably just a name for the amp model.
mlloyd1
I think ribbon speakers are low impedance (right?) so this Borbely Audio amp may be worth investigating
On the other hand, "ribbon" is probably just a name for the amp model.
mlloyd1
sensitivity not a concern?
OK, I'm a gearhead so I will admit that this stuff isn't easy for me, but let me explain my thinking. When using two midranges, folks typically assume a 6db increase in sensitivity (at 2.83 V/1m), which as I understand it is because you've doubled the radiating area and doubled the current from the amp. So, if you wire these two drivers in series you double the radiating area but halve the current through the drivers, which then gives the same sensitivity as a single driver. Is this correct? If not, please explain where my I'm goofing this up.
In my MTM I have 2 mids that are 92db/2.83V/1m, and a tweeter that is 96db/2.83V/1m. Ignoring baffle step (for the moment), if I want a 96db/2.83V/1m MTM, I need to put these 6 ohm mids in parallel. Before anybody says it, I'm already planning an active system (which is why I can ignore the baffle step for the MTM): the MTM from 300hz to 20kHz, Lambda TD-12S from 300Hz to about 60 Hz, and a dedicated subwoofer from 60 Hz down. My wife is tolerant of this hobby, but I don't know how tolerant she would be of having to turn on the CD player, preamp, crossover, and 4 amplifiers to listen to music. I'm already getting comments about how difficult it is to work my bi-amped setup today.
sreten said:The advice about series resistance is completely incorrect.
Its as lot easier in terms of output devices to build a 300W/8ohm
amplifier than a 300W/2 ohm amplifier, personally I can't see the
point of your concern with voltage sensitivity, efficiency of the
series or parallel connected drivers is identical.
(Any difference in speaker voltage sensistivity in a multi channel
set up can be addressed by adjusting the amplifier gains.)
OK, I'm a gearhead so I will admit that this stuff isn't easy for me, but let me explain my thinking. When using two midranges, folks typically assume a 6db increase in sensitivity (at 2.83 V/1m), which as I understand it is because you've doubled the radiating area and doubled the current from the amp. So, if you wire these two drivers in series you double the radiating area but halve the current through the drivers, which then gives the same sensitivity as a single driver. Is this correct? If not, please explain where my I'm goofing this up.
In my MTM I have 2 mids that are 92db/2.83V/1m, and a tweeter that is 96db/2.83V/1m. Ignoring baffle step (for the moment), if I want a 96db/2.83V/1m MTM, I need to put these 6 ohm mids in parallel. Before anybody says it, I'm already planning an active system (which is why I can ignore the baffle step for the MTM): the MTM from 300hz to 20kHz, Lambda TD-12S from 300Hz to about 60 Hz, and a dedicated subwoofer from 60 Hz down. My wife is tolerant of this hobby, but I don't know how tolerant she would be of having to turn on the CD player, preamp, crossover, and 4 amplifiers to listen to music. I'm already getting comments about how difficult it is to work my bi-amped setup today.
OK, ignoring BSD.
You are correct about the voltage sensitivities of the two arrangements.
Neverless they have identical power efficiency, as the +6dB
case draws 6dB more current than the 0dB case.
IMO its a lot simpler, and a little safer to pad the tweeter
back to 92dB than running the two mids at 98dB / 2 ohms.
The tweeter ends up with the same current : A 300W/2R
amplifier will only manage 75W into 8R, i.e. the tweeter.
If the tweeter has its own amplifier then sensistitivities are
equalised by adjusting the gain of the seperate amplifiers.
And all that matters is real efficiency dB/Watt, not dB/V.
sreten.
P.S. there is no need for the 4 amplifiers to have equal power
rating and 300W per amplifier for midrange is seriously too much.
You need something like 100W+100W+50W+25W.
But is does depend on the power efficiency of each driver.
Note that 4 100w amplifiers used in an active 4-way have a
total voltage swing capability equivalent to a 1.6KW amplifier
driving a passive 4-way.
At 300w each this equals 4.8kW !
sreten.
You are correct about the voltage sensitivities of the two arrangements.
Neverless they have identical power efficiency, as the +6dB
case draws 6dB more current than the 0dB case.
IMO its a lot simpler, and a little safer to pad the tweeter
back to 92dB than running the two mids at 98dB / 2 ohms.
The tweeter ends up with the same current : A 300W/2R
amplifier will only manage 75W into 8R, i.e. the tweeter.
If the tweeter has its own amplifier then sensistitivities are
equalised by adjusting the gain of the seperate amplifiers.
And all that matters is real efficiency dB/Watt, not dB/V.
sreten.P.S. there is no need for the 4 amplifiers to have equal power
rating and 300W per amplifier for midrange is seriously too much.
You need something like 100W+100W+50W+25W.
But is does depend on the power efficiency of each driver.
Note that 4 100w amplifiers used in an active 4-way have a
total voltage swing capability equivalent to a 1.6KW amplifier
driving a passive 4-way.
At 300w each this equals 4.8kW !
sreten.
If you are wiring your speakers to get a nominal 2 ohm load, isn't there a good chance that at some frequency, it will be lower?
Many protection circuits built into the output section of amplifiers will be active at this low a load. Even if you don't hear anything unpleasent, the protection will limit the power the amp delivers wich may negate any benefits you intended by trying to wire the speakers to increase sensetivity.
On top of that, due to a characteristic called "beta droop", driving a 2 ohm load will roughly quadruple the distortion figure for the amp as comparred to an 8 ohm load. That may be ok if the distortion figure is very low to begin with, depending on the amp it is quite concievable you would notice it at high frequency peaks.
I think your plan of action may be creating many more problems for you than it solves and may result in an overall listening experience that will diappoint you.
Many protection circuits built into the output section of amplifiers will be active at this low a load. Even if you don't hear anything unpleasent, the protection will limit the power the amp delivers wich may negate any benefits you intended by trying to wire the speakers to increase sensetivity.
On top of that, due to a characteristic called "beta droop", driving a 2 ohm load will roughly quadruple the distortion figure for the amp as comparred to an 8 ohm load. That may be ok if the distortion figure is very low to begin with, depending on the amp it is quite concievable you would notice it at high frequency peaks.
I think your plan of action may be creating many more problems for you than it solves and may result in an overall listening experience that will diappoint you.
OK, I give!
You all have convinced me. Sam, the nominal load would be closer to 3 ohms but yes, it would dip to 2.5 at it's lowest. I will wire up an amp for the tweeter, and an amplifier each for the two mids, plus an amp for the woofer and and amp for the subwoofer. An active 4-way with 5 amplifiers... this project could get a little over the top.
So now I just need to go about generating 4 2-channel amplifiers with 50-100WPC into 8 ohms in a single enclosure. (I already have a Carver TFM-42 I can use for the subs.) Looks like it's time to start considering P3A and gainclone PCBs....
You all have convinced me. Sam, the nominal load would be closer to 3 ohms but yes, it would dip to 2.5 at it's lowest. I will wire up an amp for the tweeter, and an amplifier each for the two mids, plus an amp for the woofer and and amp for the subwoofer. An active 4-way with 5 amplifiers... this project could get a little over the top.
So now I just need to go about generating 4 2-channel amplifiers with 50-100WPC into 8 ohms in a single enclosure. (I already have a Carver TFM-42 I can use for the subs.) Looks like it's time to start considering P3A and gainclone PCBs....
Here is a proposed solution to this problem that I started looking at today at lunch:
http://www.diyaudio.com/forums/showthread.php?s=&postid=352209#post352209
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Brian
http://www.diyaudio.com/forums/showthread.php?s=&postid=352209#post352209
--
Brian
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