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Passive Biamping: How much improvement?


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#61 of 66 OFFLINE   kobo

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Posted February 07 2010 - 12:28 PM

I just want to share my experience very quick. The benefit of the biwire, passive biamp and active biamp are direct proportional with the reactance of your speakers. If your speakers have near constant impedance across the frequency then you won't hear a big improvement. If your speaker cables are or very high quality wire, with very low resitance and depending on case impedance, capacitance the effect won't be so big. BUT if you have some very reactive speakers, wich fluctuating impedance then you will hear a very big impreovement in this order: biwire, passive biamp, active biamp. This is generaly valable for speakers with electrostatic panels, ribbon tweeters etc. For example I was building a small second setup with some Elac BS 203.2 with ribbon tweeters and I was planing to use a Muse 160 poweramp (160W@8ohm) and even for these small speakers rated at 60W if I remember right, I ended biamping with a B&K AV-5125 poweramp which has a simetric design and I was using two chanels per speaker. Biamping with B&K resulted in a sound far more dynamic, detalied and cleaner, the Muse was starting to roll off the high frequencies and it was loosing control on the woofer. Now trying again these configurations on a pair of Rogers LS7t the difference was not so big. I found this article interesting: Link removed by moderator.

#62 of 66 OFFLINE   Mario0511

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Posted January 01 2011 - 08:10 AM

A little technical explanation.   I've been electronics technician for over 22 years, involved in custom speaker, x-over designs.   The purpose of x-over is to either allow or reject certain frequency (s) to the drivers.   When allowed, (passed thru), the amplifier sees low impedance and therefore creates necessary wattage (AC sine wave).  The lower the impedance it sees, the higher output will be delivered, unless too low, causing catastrophic short. Any frequency (s) rejected by x-over, has essentialy in perfect world, infinite impedance and physical resistance, and therefore your amp will not output those frequencies, even thou it's running in full range.  Obviously if you quickly connect full range speaker to the circuit, it will show it's getting full range, and that's only because suddenly amp no longer sees any x-over's for that particular external driver.   This is very easly tested with resistor.   Hook up, say 4 ohm (10 watt) resistor to your speaker output and crank up the amp, resistor will heat up because amp sees somewhat of a 4 ohm load.   Now take a 1 Mega (million) ohm (10 watt) resistor and perform same test.  Resistor will be cold, and that's because amp sees such a huge load, amp thinks it's an open circuit (no driver), and therefore there is NO output from the amp.   Unless it's a tube amp, but that's another animal, and I don't want to confuse anyone. And this is what x-overs do to the output of the amp.   This is why bi-amping doesn't really give you more power, or loudness.  But what it does give you is more headroom from your amp/receiver, thus delivering cleaner power. X-over inside a speaker box or active x-over inside amp unit is essentialy the same.  The only difference is the slope 6-dB, -12dB and so on.  The more aggresive slope, the lower rate of frequencies overlap, and thus less of impedance drop.  Sometimes this might create un-natural if slope is too aggresive.   So removing tabs in the back of your speakers does 2 things. 1. Gets rid of imperfections in x-over frequencies thus limiting impedance drop (frequency overlap) between tweeters/mids and woofer(s). 2. Limits, yes limits the ouput frequencies from the amp/receiver.   X-overs will dictate to the output of the amp which frequencies are to be reproduced, and only those will be present at the output of the amp, NOT FULL RANGE.   And because of that, your headroom will somewhat increase, thus during peak demands, amp can essentially deliver slightly higher output(s).   So when bi-amping, does the receiver/amp send bass to the woofers and not high frequencies, and vise versa, high frequencies to mids/tweeter but not bass even thou has no internal x-over on it's own? Y E S, and thats's because internal speaker x-overs make sure of that.   It all comes down to impedance.   And if you still won't believe me,  hook up say, piezzo tweeters to your amp.  If anyone knows how these guys work, basicaly, as the frequency increases, piezzo's impedance decreases thus allowing the frequency to go thru.  The only reason you would use x-over on these little guys, is to control the intensity/loudness of these tweeters, not to prevent from burning out.   If you were to measure physical resistance of piezzo, it would read infinate(open), and it almost behaves like a capacitor.   Below operating frequency of piezzo, amp sees infinite impedance and therefore will not produce any output, unless there is another driver present in the circuit which will demand that part of spectrum.   Unless individual has understanding of OHM's law and have understanding how resonant circuits work and behave in AC applications which that what your speakers see when operating, there is no further need for discussion.   There is tons of physics behind sound reproduction.   Food for thought:  When drivers operate, they create negative voltage which is send back to the output of the amp/receiver.   Impedance can drop to 0.5 ohms and shoot to over hundreds of ohms of resistance.   This is why different speakers, sound different, besides having different cone material, voice coils, etc, their electrical impedance allows or rejects certain frequencies more or less than other speaker, thus having different sound. And since the negative voltage is send back to amp, amp/receiver has to have good enough Damping Factor to deal with that unwanted voltage.   Like the name says DAMping Factor, it's a meassure how well the amp can control the movement of the cone and stop the unwanted voltages from introducing false frequencies thus distortion. Modern amp's use negative feedback from output to deal with that, but sometimes if too high, could create unwanted noise in the circuitry.

#63 of 66 OFFLINE   Mario0511

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Posted January 01 2011 - 08:34 AM

No such thing as constant impedance accross frequencies.   If that  is the case, your driver burned out and you're listening to the spirit of that speaker, lol.   Any movement of the cone, no matter how small, changes electrical impedance, in any speaker, unless manufactured by aliens in outer space, or some imaginary drivers, lol.   SPEAKER  IS  AN  EXTENSION  OF  THE  OUTPUT  OF  ANY  AMPLIFIER  AND  BECOMES  PHYSICAL  PART  OF  THE  CIRCUIT.   Speakers create voltage when voice coil moves thru magnetic field.  Test it for yourself.   Measure electrical resistance accross (+ and - ) terminals of the speakers, and at the same time move physicaly the cone.  You will see the resistance changes.   Speakers directly affect the output of any amplifier, speakers' frequency and power output.    All comes down to OHM's law of electrical circuits.

#64 of 66 OFFLINE   Mario0511

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Posted January 01 2011 - 08:43 AM

A little technical explanation.   I've been electronics technician for over 22 years, involved in custom speaker, x-over designs.   The purpose of x-over is to either allow or reject certain frequency (s) to the drivers.   When allowed, (passed thru), the amplifier sees low impedance and therefore creates necessary wattage (AC sine wave).  The lower the impedance it sees, the higher output will be delivered, unless too low, causing catastrophic short.


Any frequency (s) rejected by x-over, has essentialy in perfect world, infinite impedance and physical resistance, and therefore your amp will not output those frequencies, even thou it's running in full range.  Obviously if you quickly connect full range speaker to the circuit, it will show it's getting full range, and that's only because suddenly amp no longer sees any x-over's for that particular external driver.


 


This is very easly tested with resistor.  


Hook up, say 4 ohm (10 watt) resistor to your speaker output and crank up the amp, resistor will heat up because amp sees somewhat of a 4 ohm load.  


Now take a 1 Mega (million) ohm (10 watt) resistor and perform same test.  Resistor will be cold, and that's because amp sees such a huge load, amp thinks it's an open circuit (no driver), and therefore there is NO output from the amp.   Unless it's a tube amp, but that's another animal, and I don't want to confuse anyone.


And this is what x-overs do to the output of the amp.


 


This is why bi-amping doesn't really give you more power, or loudness.  But what it does give you is more headroom from your amp/receiver, thus delivering cleaner power.


X-over inside a speaker box or active x-over inside amp unit is essentialy the same.  The only difference is the slope 6-dB, -12dB and so on.  The more aggresive slope, the lower rate of frequencies overlap, and thus less of impedance drop.  Sometimes this might create un-natural if slope is too aggresive.


 


So removing tabs in the back of your speakers does 2 things.


1. Gets rid of imperfections in x-over frequencies thus limiting impedance drop (frequency overlap) between tweeters/mids and woofer(s).


2. Limits, yes limits the ouput frequencies from the amp/receiver.   X-overs will dictate to the output of the amp which frequencies are to be reproduced, and only those will be present at the output of the amp, NOT FULL RANGE.   And because of that, your headroom will somewhat increase, thus during peak demands, amp can essentially deliver slightly higher output(s).


 


So when bi-amping, does the receiver/amp send bass to the woofers and not high frequencies, and vise versa, high frequencies to mids/tweeter but not bass even thou has no internal x-over on it's own?


Y E S, and thats's because internal speaker x-overs make sure of that.   It all comes down to impedance.


 


And if you still won't believe me,  hook up say, piezzo tweeters to your amp.  If anyone knows how these guys work, basicaly, as the frequency increases, piezzo's impedance decreases thus allowing the frequency to go thru.  The only reason you would use x-over on these little guys, is to control the intensity/loudness of these tweeters, not to prevent from burning out.   If you were to measure physical resistance of piezzo, it would read infinate(open), and it almost behaves like a capacitor.   Below operating frequency of piezzo, amp sees infinite impedance and therefore will not produce any output, unless there is another driver present in the circuit which will demand that part of spectrum.


 


Unless individual has understanding of OHM's law and have understanding how resonant circuits work and behave in AC applications which that what your speakers see when operating, there is no further need for discussion.   There is tons of physics behind sound reproduction.


 


Food for thought:  When drivers operate, they create negative voltage which is send back to the output of the amp/receiver.   Impedance can drop to 0.5 ohms and shoot to over hundreds of ohms of resistance.   This is why different speakers, sound different, besides having different cone material, voice coils, etc, their electrical impedance allows or rejects certain frequencies more or less than other speaker, thus having different sound.


And since the negative voltage is send back to amp, amp/receiver has to have good enough Damping Factor to deal with that unwanted voltage.   Like the name says DAMping Factor, it's a meassure how well the amp can control the movement of the cone and stop the unwanted voltages from introducing false frequencies thus distortion.


Modern amp's use negative feedback from output to deal with that, but sometimes if too high, could create unwanted noise in the circuitry. 

#65 of 66 OFFLINE   walshbouchard

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Posted November 19 2012 - 11:46 AM

This is completely wrong, when bi wiring you are simply enlarging the cross sectional area of the "one" cable delivering a full range signal to the now separated crossover ( shorting plates removed) the full range signal is still being delivered by one and the same amp. When you remove the shorting plates and connect two different amps with two different power supplies ( not a stereo integrated or a multi channel receiver ) but a proper set of power amps you are effectively delivering a full range range signal to two different XO one high pass one low pass with two separate amps doubling the power overall to each speaker . these modern binding posts with there shorting straps /plates completely separate the hi and lo sections of the cross over so there is nothing to stop you using ,say a valve amp for the highs and a more powerful solid state for the lows , which may not be true bi amping as in active bi amping but is certainly not the same as bio wiring which achieves absolutely nothing at all unless you were using bell wire before you bi wired why not just remove the passive crossovers from the speakers and use a couple of attenuatiors and bang them between the pre amp and power amps and hey passive active bi amping lol

#66 of 66 OFFLINE   walshbouchard

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Posted November 19 2012 - 12:40 PM

this forum made me look as though i was replay to Mario above i was NOT i was replying to to a suggestion the be wiring was the same as passive bi amping . So SORRY Mario [ I have read your article and I do know ohms law very well as i am an electrical engineer but not so hot on resonant circuits which i am about to read up on as I am not an electronic engineer or even a want to be one like some people on here Thank you for the reality check among all the pseudo scientists ( which I have referenced elsewhere and proved correct) , I found your explanation of this constant and irritating argument conclusive , so as far as I am concerned there is nothing further to discuss!




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