hi all
i want to purchase power amps for bi-amping application. my doubt is can i use different amplifiers for woofers and tweeters? i mean is it ok to use 100w/ch stereo amplifier for woofers and 50w/ch stereo amplifier for tweeters? will there be any issue due to tonal differences in the amplifiers.
also i have come across following affordable power amp kits on ebay. pls let me know if anybody have used any of them. what are your opinions about quality.
TDA7293 stereo amplifier board Assembled AMP 85W+85W | eBay
QUAD405 Stereo Audio Power Amplifier Board Assembled | eBay
Assembled H-140 Power Amplifier with Power supply Board | eBay
LM4702+2SA1943+2SC5200 Audio power Amplifier AMP Board | eBay
Audio Power Amplifier X2+ Pre-Amplifier + Power Supply | eBay
thanks
pranam
i want to purchase power amps for bi-amping application. my doubt is can i use different amplifiers for woofers and tweeters? i mean is it ok to use 100w/ch stereo amplifier for woofers and 50w/ch stereo amplifier for tweeters? will there be any issue due to tonal differences in the amplifiers.
also i have come across following affordable power amp kits on ebay. pls let me know if anybody have used any of them. what are your opinions about quality.
TDA7293 stereo amplifier board Assembled AMP 85W+85W | eBay
QUAD405 Stereo Audio Power Amplifier Board Assembled | eBay
Assembled H-140 Power Amplifier with Power supply Board | eBay
LM4702+2SA1943+2SC5200 Audio power Amplifier AMP Board | eBay
Audio Power Amplifier X2+ Pre-Amplifier + Power Supply | eBay
thanks
pranam
is there a formula/procedure to determine how much power would be required for high frequencies for given power for low frequencies?
Frequencies under 4kHz or 5kHz need roughly the same power. From 5kHz you can reduce the power by 10dB. So if you have crossover around 6kHz, you'll be able to manage with just a10th of power over 6kHz.
However if cross-over is around 2kHz, you'll need same power above and below 2kHz.
For a cross-over around 4kHz, you should be able to manage with half power for tweeters.
Check Peak frequency response for common audio for more information.
However if cross-over is around 2kHz, you'll need same power above and below 2kHz.
For a cross-over around 4kHz, you should be able to manage with half power for tweeters.
Check Peak frequency response for common audio for more information.
So the best answer is "it depends". As always, Wikipedia is the keeper of all knowledge...
http://en.wikipedia.org/wiki/A-weighting
Notice in the graph how much more energy is needed to reproduce the bottom octaves over something in the "middle" (say above 200-300 Hz). Also what is the content of the music you like listening to? Is it bass-heavy?
Are you going to be running the stock crossovers (sounds like it)? Then you don't have to worry about difference in driver sensitivity.
A lot of people bi-amp (IMHO) specifically because they do want the "sound" of he amps to be different. Have a big-bruiser of a transistor amp running the lower frequencies and something with lower power but having a better/preferred high frequency response (eg. tubes, FETs, et. al.) for the upper octaves.
Depending on where the crossover point is (usually 2-3kHz or thereabouts) you could probably have about a 10:1 difference in the power ratings of the two amps, especially if you are listening to material with significant low frequency (<50Hz) content.
-bill
http://en.wikipedia.org/wiki/A-weighting
Notice in the graph how much more energy is needed to reproduce the bottom octaves over something in the "middle" (say above 200-300 Hz). Also what is the content of the music you like listening to? Is it bass-heavy?
Are you going to be running the stock crossovers (sounds like it)? Then you don't have to worry about difference in driver sensitivity.
A lot of people bi-amp (IMHO) specifically because they do want the "sound" of he amps to be different. Have a big-bruiser of a transistor amp running the lower frequencies and something with lower power but having a better/preferred high frequency response (eg. tubes, FETs, et. al.) for the upper octaves.
Depending on where the crossover point is (usually 2-3kHz or thereabouts) you could probably have about a 10:1 difference in the power ratings of the two amps, especially if you are listening to material with significant low frequency (<50Hz) content.
-bill
Rubbish.
You are suggesting that irrespective of driver impedance and sensitivity that one can and should use 1/10th the power for a driver operating at >6kHz, one will obtain similar performance over a range of music types and over a range of preferred volume (SPL).
Take an example:
10W main amplifier, 1W treble amplifier.
90dB/W @ 1m 8 ohm bass mid driver, 88dB/W @ 1m treble driver.
Maximum SPL @ 2.5m listening distance from the two drivers will be:
bass/mid 92dB, treble 80dB.
Provided the volume of the treble content never goes above 80dB the drivers stay in unison. The gain of the two amplifiers will be adjusted such that the frequency response of the combined driver set is near flat. That automatically limits a flat frequency sample to the limit set by the treble of 80dB.
If one asks the "system" to play louder than 80dB with a flat frequency sample then the treble channel will overload and the reproduction quality will be ruined.
I contend that the peak SPL from all the drivers should be roughly the same, to allow all types of music to be reproduced in the domestic environment.
Very interesting article - but I am more than a little confused (and skeptical) about their methods. They keep referring to their measurements as "SPL" which implies that they measured the sounds acoustically. But in the article it does not seem like this is the case:
and
So it looks like they collected their data from some unknown "frequency spectrum analyser" connected to the analog signal output of a line source. This is most definitely NOT SPL. In addition their frequency data intervals are all over the place - one data point for the top octave, five data samples for the next octave down and back to a single data sample for the entire 1k-2k octave. I can't held but question both their knowledge of signals and acoustics as well as what type of "spectrum analyzer" would return these results (is it measuring peak signal or actual power within those intervals, which would be very different things).
It would be easier (and more accurate) to run multiple FFT's against the raw music data and combine the results. I would definitely be interested in seeing that sort of data. If anyone has a reference to those kind of results (AES probably) I'm would love to see them.
Thanks, and take care.
-bill
Power is a difficult question in bi-amping. I run all speakers in fully active mode with no passive crossovers. I agree with AndrewT that you should be primarily concerned with achieving a roughly equivalent SPL from each driver.
Using the sensitivity of the driver, you can establish what the required gain difference should for the amplifiers. For instance, if we use a 90 dB/W @ 1m midrange and a 96 dB/W @ 1m tweeter, we will need an additional 6 dB of gain in the amplifier for the midrange (twice as much voltage applied across the driver). Note that higher frequency drivers typically have higher sensitivities, and therefore require less gain.
Now that we have figured out our gain requirements, we can examine our power requirements. The impedance of the driver becomes important at this point due to Ohm's law. The actual power provided to the driver by a voltage source (read ideal amplifier) is determined by (voltage^2)/z, where z is the complex impedance of the driver. Often, drivers are chosen to operate in a range where 'z' is fairly constant, and is assumed to be constant at the nominal value (typically 4-8 ohms). For our rough back of the envelope calculations, this nominal value will be sufficient, and will be referred to as 'z'.
I would make an estimate of the power level that you want, multiply it by 'z' of the driver in question, and square root that number to determine what voltage supply will be necessary for you to achieve your power goals.
Most amplifiers spec power in watts, which will not provide sufficient information to determine if they are suitable for use in your system. More important is the maximum voltage they can supply, and the max current. Power= volts*current. Keep in mind that as the impedance of the driver goes down, the current must go up to maintain the proper voltage drop. This is where most amps fall short. The output stage will have some current limit that it cannot surpass without overheating, this will limit the range of voltages and impedances that are compatible with it.
As a word of caution, beware of ebay sales. Be aware that you may end up with an amp more suited to an ipod than a hifi sound system. There are several sources of amp kits that have proven reliable, for starting, chipamps produce decent sound for an incredibly cheap price.
Louis
Using the sensitivity of the driver, you can establish what the required gain difference should for the amplifiers. For instance, if we use a 90 dB/W @ 1m midrange and a 96 dB/W @ 1m tweeter, we will need an additional 6 dB of gain in the amplifier for the midrange (twice as much voltage applied across the driver). Note that higher frequency drivers typically have higher sensitivities, and therefore require less gain.
Now that we have figured out our gain requirements, we can examine our power requirements. The impedance of the driver becomes important at this point due to Ohm's law. The actual power provided to the driver by a voltage source (read ideal amplifier) is determined by (voltage^2)/z, where z is the complex impedance of the driver. Often, drivers are chosen to operate in a range where 'z' is fairly constant, and is assumed to be constant at the nominal value (typically 4-8 ohms). For our rough back of the envelope calculations, this nominal value will be sufficient, and will be referred to as 'z'.
I would make an estimate of the power level that you want, multiply it by 'z' of the driver in question, and square root that number to determine what voltage supply will be necessary for you to achieve your power goals.
Most amplifiers spec power in watts, which will not provide sufficient information to determine if they are suitable for use in your system. More important is the maximum voltage they can supply, and the max current. Power= volts*current. Keep in mind that as the impedance of the driver goes down, the current must go up to maintain the proper voltage drop. This is where most amps fall short. The output stage will have some current limit that it cannot surpass without overheating, this will limit the range of voltages and impedances that are compatible with it.
As a word of caution, beware of ebay sales. Be aware that you may end up with an amp more suited to an ipod than a hifi sound system. There are several sources of amp kits that have proven reliable, for starting, chipamps produce decent sound for an incredibly cheap price.
Louis
You won't need 100W amps for bi-amping unless you want to use it as a PA for a small hall. Passive speakers need more power because they waste energy in the crossover.
I use LM3886 (50W max for 88dB drivers) chip amps for all three drivers in an active three way (but bridged for for the woofer).
Might I also suggest proper grammar, capitalisation (no "z", I'm Australian and use "proper" English
) and punctuation out of respect for your fellow forum members?
Frank
I use LM3886 (50W max for 88dB drivers) chip amps for all three drivers in an active three way (but bridged for for the woofer).
Might I also suggest proper grammar, capitalisation (no "z", I'm Australian and use "proper" English
) and punctuation out of respect for your fellow forum members?Frank
Here are a couple links to a bi-amp project I have been working on.
http://www.diyaudio.com/forums/group-buys/137430-bpa300-round-2-a-115.html#post2710763
http://www.diyaudio.com/forums/group-buys/137430-bpa300-round-2-a-116.html#post2716187
http://www.diyaudio.com/forums/group-buys/137430-bpa300-round-2-a-119.html#post2723568
The BPA-150s will be driving PExpress 8” 4ohm speakers in a tuned bass reflex cabinet. The MyRefs push the tweeters. My approach is more from the listener’s side than that of an amp designer. The active crossover I’m using has both low/mid and mid/high adjustments as well as a low-sum mode for a subwoofer. Both of these amps have a proven ability to produce excellent sound and it’s my contention/hope the adjustments provided by the crossover will provide the correct SPL from the multiple drivers.
I’m suspecting I might have to switch to something like the Behringer DCX2496 to obtain the signal shaping for the correct balances. In addition to all the calculations for the amps as mentioned above, each driver has its own peculiarities to deal with
.
The setup I have now is working well in test mode with el-cheapo drivers. I fried a couple tweeter voice coils that I believe was the result of oscillation triggered by a grounding issue, but that appears to be corrected. There is still a bit of hum (completely masked by the music) in the BPA section that has to be tracked down.
More to come……..
http://www.diyaudio.com/forums/group-buys/137430-bpa300-round-2-a-115.html#post2710763
http://www.diyaudio.com/forums/group-buys/137430-bpa300-round-2-a-116.html#post2716187
http://www.diyaudio.com/forums/group-buys/137430-bpa300-round-2-a-119.html#post2723568
The BPA-150s will be driving PExpress 8” 4ohm speakers in a tuned bass reflex cabinet. The MyRefs push the tweeters. My approach is more from the listener’s side than that of an amp designer. The active crossover I’m using has both low/mid and mid/high adjustments as well as a low-sum mode for a subwoofer. Both of these amps have a proven ability to produce excellent sound and it’s my contention/hope the adjustments provided by the crossover will provide the correct SPL from the multiple drivers.
I’m suspecting I might have to switch to something like the Behringer DCX2496 to obtain the signal shaping for the correct balances. In addition to all the calculations for the amps as mentioned above, each driver has its own peculiarities to deal with
.
The setup I have now is working well in test mode with el-cheapo drivers. I fried a couple tweeter voice coils that I believe was the result of oscillation triggered by a grounding issue, but that appears to be corrected. There is still a bit of hum (completely masked by the music) in the BPA section that has to be tracked down.
More to come……..
I can't agree with that generalised statement.
How would you achieve 110dB peak SPL at the listening position, using stereo, not surround sound in any of it's forms?
You are confirming that active speaker set up has higher efficiency.
Please explain how bi-amping can have better efficiency than a standard amp & passive crossover speaker when the twin amps are still driving the speakers via their crossovers.
hi all
i read (again and again) the bi-amping article in the following link
BiAmp (Bi-Amplification - Not Quite Magic, But Close) - Part 1
as per the explaination (as far as my understanding goes), if xover point for 2way is 3khz, then only 15% of power goes to tweeter. that means in case of biamping if i am using 100w for woofers/mids then only 15w is needed to driver tweeters.
i read (again and again) the bi-amping article in the following link
BiAmp (Bi-Amplification - Not Quite Magic, But Close) - Part 1
as per the explaination (as far as my understanding goes), if xover point for 2way is 3khz, then only 15% of power goes to tweeter. that means in case of biamping if i am using 100w for woofers/mids then only 15w is needed to driver tweeters.
soundnovice, here is a real world example:
I have a number of amps available to me and I have always used a LF amp that is between 2X and 4X that of the HF amp. The XO's range from 650Hz to about 2.5KHz, all active, never an imbalance or an overdrive. And yes, the tweeter has always been more efficient the the LF driver. That's pretty standard with PA gear and rather the norm with HiFi stuff.
I have a number of amps available to me and I have always used a LF amp that is between 2X and 4X that of the HF amp. The XO's range from 650Hz to about 2.5KHz, all active, never an imbalance or an overdrive. And yes, the tweeter has always been more efficient the the LF driver. That's pretty standard with PA gear and rather the norm with HiFi stuff.
I absolutely agree.
Can I use this "real world example" to illustrate the point.
take a 90dB bass driver and a 96dB treble driver and cross them over to provide a full range speaker.
Add a four times power capable amp to the bass driver and a single power capable amp to the treble driver.
Result: the same peak SPL from both drivers.
Corollary:
take two or more drivers with the same impedance and the same sensitivity and supply them from equal power capability amplifiers and you get the same peak SPL, provided that both drivers can convert that electrical energy into useful sound energy.
controlling SPL is not an issue if u see the active xover ckt given in Rod Elliot's project page Linkwitz-Riley Electronic Crossover
copyright question: if i plan to design my own PCBs for personal use do I have to take permission from Rod Elliott?
copyright question: if i plan to design my own PCBs for personal use do I have to take permission from Rod Elliott?
Music may have more average power at low frequencies, but my own measurements show that many over compressed CDs have digital full scale swing when high passed at 2kHz with 3rd order cutoff. To avoid clipping the HF amplifier needs as much headroom as the LF although the peak to average ratio will be fairly high
It can be argued that clipping the active speaker HF amplifier does not sound too bad and clearly does not have the side effect of increasing HF power that a clipped full range amplifier can
It can be argued that clipping the active speaker HF amplifier does not sound too bad and clearly does not have the side effect of increasing HF power that a clipped full range amplifier can
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