Biamp question

[Rupp]

When people choose to bi-amp their systems it seems they often use a cheap class D amplifier for the woofers. Why is it considered okay to use a cheap amp for woofers while using a high-grade amplifier for the higher frequency drivers?

 

[Solypsa]

Not sure that 'cheap class D' sub amps are considered the best way to do it, however:

Bottom few octaves require a lot of power OR very large and complex cabinets. Most people at home choose the former.

 

[Gregadd]

I would not call class d cheap.
The emphasis in bass is clean power.
The flavor is determined by the mids and highs.
You can get away with some things when you only have to deal with bass.

 

[ddk]

When people choose to bi-amp their systems it seems they often use a cheap class D amplifier for the woofers. Why is it considered okay to use a cheap amp for woofers while using a high-grade amplifier for the higher frequency drivers?

It's not ok at all to mix amplification in this manner, for best result ideally one should use the same amplification or at least very similar amplifiers. There are many half ass speakers that sell you half a speaker mated to an active half with dsp and plate amps and the only way to get a coherent sound from them is to use a similarly low quality amplifier on top but you'll end up with a shitty sound. Of course the overall resolution of the system is important, I've come across many systems clad with heavily colored audiophile power cords and wiring that would homogenize any combination of amps.

david

 

[Addicted to hifi]

Class d amplifiers have come a long way and can sound excellent.

 

[Addicted to hifi]

My two 15 inch subwoofers have class d amplifiers Build in.

 

[Addicted to hifi]

Class d amplifiers are more efficient and space saving.

 

[gian60]

To biamp for
My experience need 2 same amp
Of different loose homegenous sound
I Tried also with CH M1 on bass and mid and A1 on tweeter bit sound was better with M1 alone
Tried to biamp woth Kondo,Mactone,Audiotekne,Shindo,ANJ,
Jadis with ARC,ML and YBA,Burmester and Gryphon
For me or so with same amp
Or better dont do

 

[DonH50]

When people choose to bi-amp their systems it seems they often use a cheap class D amplifier for the woofers. Why is it considered okay to use a cheap amp for woofers while using a high-grade amplifier for the higher frequency drivers?

I think this is a rather complex subject... The following is in my opinion based upon my experience using multiple (two to six per side) amplifiers and crossovers in a number of systems over the years. I am also generalizing quite a bit so realize there will always be specific exceptions to any rule of thumb. And finally I am going beyond the original question, just because I have a little extra time while my laundry finishes this morning and before I go back to work.

There are also a lot of very good class D amplifiers, and some poor class A or AB amplifiers, but by and large these days most of them have similar performance that is very good to excellent. There are always differences to argue over, and a bunch of very cheap ones that may or may not sound good, but I think there are few really "bad" amplifiers these days. On to bi-amping...

First, many if not most HT systems, and many music systems bi-amp by adding a subwoofer, usually a powered one. The crossover frequency is usually very low, ideally below that at which we really "hear" the sound and it is more of a "feel". Also below where the subs are localizable -- the frequency at which you can't tell where the sound is coming from. Subwoofer frequencies typically require 10x to 1000x the power of midrange frequencies just to be heard at the same level due to the way our hearing rolls off. Look at equal-loudness curves, eg. https://en.wikipedia.org/wiki/Equal-loudness_contour and this figure:



In power, 10 dB is 10x the power, 20 dB is 100x, 30 dB is 100x, and so forth. At 80 dB SPL, about ten times the power (10 dB) is needed for a 100 Hz tone to sound as loud as 1 kHz. It rises to ~100x at 50 Hz, and almost 40 dB (10,000x) at 20 Hz. In practice you probably do not really want the deep bass as loud as the midrange, but generally it takes much more power to produce pleasing deep bass loud enough for us to appreciate.

Class D amplifiers can provide much more power than most other amplifier classes, and do it for far less cost in materials, and these days with lower distortion than most other designs. That makes them an easy choice for subwoofers.

Where I think it gets (much) more complex is when you talk about bi-amplifying (or more-way amplifying) above the very deep bass frequencies. There, amp integration with the speakers can be more challenging, and the common perception of significantly lower power needed for treble can be invalid (wrong). With a crossover in the lower midrange, and a sub to take over the deepest bass, the bass may need to provide say 10x more power than the treble amp, but then again the modern curves show a similar rise in the upper midrange. And of course the impedance of your speakers also matters, as well as your taste in sound.

Now the power needed and how the amplifiers interact with the speaker becomes much more critical. Some speakers, like my old Magnepans, used not only a fairly low crossover to the bass panel, but also a very low slope, so there was a lot of interaction between bass and treble panels (and amplifiers). Getting matching amplifiers was key for me, and a major PITA since I wanted a big powerful bass amp but wanted to keep my lush-sounding ARC D-79 for the treble. I ruled out the majority of SS amps, not because they did not sound great, but because they did not blend seamlessly with the tube amp in the midrange. I ultimately picked a hybrid bass amp (Counterpoint SA220) and was able to achieve great integration after a lot of measuring, tweaking, and listening. Other speakers, with more complex (higher-order, steeper-sloping) crossovers and at different frequencies, were more tolerant of amps that were not so closely matched. At times, particularly for sound reinforcement, a low-power tweeter amp would be mated with a higher-powered midrange and much higher-powered bass amps and nobody noticed. Those were often from the same manufacturer and amp line, however.

If the crossover is well up in the midrange, then you do not want the transition between amps to be noticeable. In their normal operating range, with moderate speaker and amplifier output impedances, this is not too difficult. The problem is many loudspeakers vary greatly in impedance over frequency, as do different amplifier designs, so blending and matching becomes more important. A SS amp with low output impedance will sound different than a tube amp with high output impedance after a speaker with large impedance changes. The SS amp may be more accurate, but you may prefer the frequency response of the tube amp, as it emphasizes or de-emphasizes certainly frequencies due to the loading of the speaker.

So you have power, output impedance and how it interacts with the speakers, and the more subjective "tone" of an amplifier (which is often a function of the first two points), and the optimum choice also depends upon the crossover point. For some, identical amps are best for their combination of speakers and amps. For others, choosing different amps allows them to control the sound to suit their speakers and taste. There is not really a right or wrong choice IMO.

There is one exception to having freedom to choose based upon power: "passive" bi-amping implemented by so many AVRs used for HT and music reproduction. Those components send the same voltage signal to the bass and treble amps, depending upon the speaker's crossover to split the frequencies to the drivers. Since both amps must output the same voltage, whether the same power (product of voltage and current) is needed or not, then both amps must have the same power rating if you want them to clip (reach their limit) at the same loudness.

HTH - Don

 

[Rupp]

I would not call class d cheap.
The emphasis in bass is clean power.
The flavor is determined by the mids and highs.
You can get away with some things when you only have to deal with bass.

I did not mean to call class d amplification "cheap" rather that people buy the cheaper version of class d (sometimes) to power sub woofers.

 

[Rupp]

I think this is a rather complex subject... The following is in my opinion based upon my experience using multiple (two to six per side) amplifiers and crossovers in a number of systems over the years. I am also generalizing quite a bit so realize there will always be specific exceptions to any rule of thumb. And finally I am going beyond the original question, just because I have a little extra time while my laundry finishes this morning and before I go back to work.

There are also a lot of very good class D amplifiers, and some poor class A or AB amplifiers, but by and large these days most of them have similar performance that is very good to excellent. There are always differences to argue over, and a bunch of very cheap ones that may or may not sound good, but I think there are few really "bad" amplifiers these days. On to bi-amping...

First, many if not most HT systems, and many music systems bi-amp by adding a subwoofer, usually a powered one. The crossover frequency is usually very low, ideally below that at which we really "hear" the sound and it is more of a "feel". Also below where the subs are localizable -- the frequency at which you can't tell where the sound is coming from. Subwoofer frequencies typically require 10x to 1000x the power of midrange frequencies just to be heard at the same level due to the way our hearing rolls off. Look at equal-loudness curves, eg. https://en.wikipedia.org/wiki/Equal-loudness_contour and this figure:

View attachment 80657

In power, 10 dB is 10x the power, 20 dB is 100x, 30 dB is 100x, and so forth. At 80 dB SPL, about ten times the power (10 dB) is needed for a 100 Hz tone to sound as loud as 1 kHz. It rises to ~100x at 50 Hz, and almost 40 dB (10,000x) at 20 Hz. In practice you probably do not really want the deep bass as loud as the midrange, but generally it takes much more power to produce pleasing deep bass loud enough for us to appreciate.

Class D amplifiers can provide much more power than most other amplifier classes, and do it for far less cost in materials, and these days with lower distortion than most other designs. That makes them an easy choice for subwoofers.

Where I think it gets (much) more complex is when you talk about bi-amplifying (or more-way amplifying) above the very deep bass frequencies. There, amp integration with the speakers can be more challenging, and the common perception of significantly lower power needed for treble can be invalid (wrong). With a crossover in the lower midrange, and a sub to take over the deepest bass, the bass may need to provide say 10x more power than the treble amp, but then again the modern curves show a similar rise in the upper midrange. And of course the impedance of your speakers also matters, as well as your taste in sound.

Now the power needed and how the amplifiers interact with the speaker becomes much more critical. Some speakers, like my old Magnepans, used not only a fairly low crossover to the bass panel, but also a very low slope, so there was a lot of interaction between bass and treble panels (and amplifiers). Getting matching amplifiers was key for me, and a major PITA since I wanted a big powerful bass amp but wanted to keep my lush-sounding ARC D-79 for the treble. I ruled out the majority of SS amps, not because they did not sound great, but because they did not blend seamlessly with the tube amp in the midrange. I ultimately picked a hybrid bass amp (Counterpoint SA220) and was able to achieve great integration after a lot of measuring, tweaking, and listening. Other speakers, with more complex (higher-order, steeper-sloping) crossovers and at different frequencies, were more tolerant of amps that were not so closely matched. At times, particularly for sound reinforcement, a low-power tweeter amp would be mated with a higher-powered midrange and much higher-powered bass amps and nobody noticed. Those were often from the same manufacturer and amp line, however.

If the crossover is well up in the midrange, then you do not want the transition between amps to be noticeable. In their normal operating range, with moderate speaker and amplifier output impedances, this is not too difficult. The problem is many loudspeakers vary greatly in impedance over frequency, as do different amplifier designs, so blending and matching becomes more important. A SS amp with low output impedance will sound different than a tube amp with high output impedance after a speaker with large impedance changes. The SS amp may be more accurate, but you may prefer the frequency response of the tube amp, as it emphasizes or de-emphasizes certainly frequencies due to the loading of the speaker.

So you have power, output impedance and how it interacts with the speakers, and the more subjective "tone" of an amplifier (which is often a function of the first two points), and the optimum choice also depends upon the crossover point. For some, identical amps are best for their combination of speakers and amps. For others, choosing different amps allows them to control the sound to suit their speakers and taste. There is not really a right or wrong choice IMO.

There is one exception to having freedom to choose based upon power: "passive" bi-amping implemented by so many AVRs used for HT and music reproduction. Those components send the same voltage signal to the bass and treble amps, depending upon the speaker's crossover to split the frequencies to the drivers. Since both amps must output the same voltage, whether the same power (product of voltage and current) is needed or not, then both amps must have the same power rating if you want them to clip (reach their limit) at the same loudness.

HTH - Don

Thank you for your well informed answer!

 

[izeek]

Never thought about using cheap class d or even class d period.
I chose a pair of high-current stereo amps(class ab) so it would be easier and passively, vertically bi-amped. I had earlier horizontally bi-amped then went vertical and stayed.
Better bass response vertically. Seperation, maybe.

 

[analogsa]

I would not call class d cheap.

You are free to call it anything you please. As manufacturers are free to price it any way they like.

The facts though are simple. Class D, especially when coupled with an smps is much cheaper to manufacture than class AB. Many times cheaper as far as parts and shipping costs are concerned but perhaps more costly to market.

 

[DasguteOhr]

for the subbass below 100hz you only need an amplifier that amplifies the impulses cleanly and has sufficient power reserves. Class D amplifiers do this extreme energy efficiently.
Example all signals below 100hz are only recorded in mono on the lp. maybe that's why it works very well with just one subwoofer.

 

[Solypsa]

...
Example all signals below 100hz are only recorded in mono on the lp. ...

This is true sometimes but not always

 

[Solypsa]

As an aside from my experiences in the PA side of things:

*Some* subs are pretty demanding on amplification. There are so many 1Kw amps available it can seem like 'use whatever it's all the same' but behind the specs there needs to be all the things that make a good amp whatever class.

 

[Gregadd]

You are free to call it anything you please. As manufacturers are free to price it any way they like.

The facts though are simple. Class D, especially when coupled with an smps is much cheaper to manufacture than class AB. Many times cheaper as far as parts and shipping costs are concerned but perhaps more costly to market.

Excuse me. I will accept your invitation and call it inexpensive and efficient. Cheap often connotes lack of quality.
It is my experience that cheap is not related to genre. I have found all types of amplifiers to be as expensive or inexpensive as the designer desires.
YEMV.

 

[mtemur]

Example all signals below 100hz are only recorded in mono on the lp.

As @Solypsa mentioned earlier that’s not always true. Occasionally I’m digitally preparing/mastering records to be released on vinyl and sometimes I prepare master from an old record if master tape is lost. I’ve come across lots of records that bass was panned to one side rather than center.

 

[audiobomber]

When people choose to bi-amp their systems it seems they often use a cheap class D amplifier for the woofers. Why is it considered okay to use a cheap amp for woofers while using a high-grade amplifier for the higher frequency drivers?

IME, using a different amp on the tweeter (and midrange) versus the woofer can easily provide better bass and treble, but coherence is lost and musicality suffers to an unacceptable degree. This however does not apply to subwoofers, where the amp choice is non-critical.

 

[Lagonda]

for the subbass below 100hz you only need an amplifier that amplifies the impulses cleanly and has sufficient power reserves. Class D amplifiers do this extreme energy efficiently.
Example all signals below 100hz are only recorded in mono on the lp. maybe that's why it works very well with just one subwoofer.

I use a crossover point at 100HZ for my subwoofer towers, after years of experimentation with class A, class D and Class AB i have come to the conclusion that amplifier quality and using the same amps/amp topology is very important for seamless integration with this high a crossover point. At 50HZ or lower it is easier to get away with different amps but still not perfect.
I have even tried using amps from MBL Reference line lower model and Reference line top model ( both 440 W and identical gain) on both mains and sub-towers with unsatisfactory result. It only became seamless with the exact same amplifiers powering all speakers/subwoofers. The quality and adjustability of your crossover is also very important, having at least continues phase settings is a must, Q settings are nice too if there is large diversions between driver types. I used a high quality crossover with only 4 different phase settings for a while, and could not make it sound right. I listen predominantly to vinyl and there is big difference between using stereo settings and mono settings on a crossover, in a decent size room anyway !