Amps and Recievers- Tonal qualities???

[mtrycrafts]

Isn't there the problem that the frequency response tests are usually done with an 8 ohm resistor, which only approximates a real loudspeaker load?

If the amps output impedance is very low, SS amps, it will not follow the speakers FR pattern. If a speaker has terrible phase problems, the rail voltages sag on some amps, not the Behringer A500 .
If one has a speaker with impedance that an amp is not designed for, then why pair it up?


Isn't there still the problem that the continuous power output spec into 8 ohms does not realistically model a typical loudspeaker's impedance? I think Stanley Lipshitz contributed to a paper in the 80's which showed how a typical speaker's impedance can dip considerably (~2 ohms) on non-sinusoidal programme material.

Speaker impedance is a frequency related impedance, not how much nonsinusodial it is, no? Music is mostly this signal, no sine waves at all. I don't remember that paper.
Speaker impedance is measured with sine waves. If that didn't hold water, then a new impedance method is needed, no?

Besides, his claim is testable and would show up in testing, on the bench, or comparing two components under DBT. But, urban legends about preconceived sound of brands of components is just that.

 

[tbewick]

Isn't there still the problem that the continuous power output spec into 8 ohms does not realistically model a typical loudspeaker's impedance? I think Stanley Lipshitz contributed to a paper in the 80's which showed how a typical speaker's impedance can dip considerably (~2 ohms) on non-sinusoidal programme material.

Speaker impedance is a frequency related impedance, not how much nonsinusodial it is, no? Music is mostly this signal, no sine waves at all. I don't remember that paper.
Speaker impedance is measured with sine waves. If that didn't hold water, then a new impedance method is needed, no?

I think the point is that the transients in a musical signal require a greater current than that required to produce sine waves in continuous power output tests. This means that an amplifier with a continuous power output of 100 watts into 8 ohms may clip at lower than 100 watts with a real loudspeaker, because it can't supply enough current. So there can be differences in performance between two 100 watt amps, i.e. the maximum volume you can put them at before clipping, which is down to the amplifier's ability to deal with low impedances presented by the loudspeaker. I've also heard that real signal peaks may last for a longer duration than the continuous power output test.

The Rane website does suggest a test which better matches a real loudspeaker load.

In terms of audibility, obviously I'd say it's a case of how much clipping is going on. Clipping is more likely with recordings having a large and realistic dynamic range. For example, a recording with 20 dB of dynamic range listened to at an average volume of 85 dB would most likely clip on an average system. I'd say having the extra amplifier power is useful as a more powerful amplifier it is less likely to send a damaging clipped signal to the speakers.

Edit: It would probably be fairer to say that a typical 100 watt amplifier would be working almost flat out on such material.

 

[mtrycrafts]

I think the point is that the transients in a musical signal require a greater current than that required to produce sine waves in continuous power output tests. This means that an amplifier with a continuous power output of 100 watts into 8 ohms may clip at lower than 100 watts with a real loudspeaker, because it can't supply enough current. So there can be differences in performance between two 100 watt amps, i.e. the maximum volume you can put them at before clipping, which is down to the amplifier's ability to deal with low impedances presented by the loudspeaker. I've also heard that real signal peaks may last for a longer duration than the continuous power output test.

The Rane website does suggest a test which better matches a real loudspeaker load.

In terms of audibility, obviously I'd say it's a case of how much clipping is going on. Clipping is more likely with recordings having a large and realistic dynamic range. For example, a recording with 20 dB of dynamic range listened to at an average volume of 85 dB would most likely clip on an average system. I'd say having the extra amplifier power is useful as a more powerful amplifier it is less likely to send a damaging clipped signal to the speakers.

Edit: It would probably be fairer to say that a typical 100 watt amplifier would be working almost flat out on such material.

I am not aware that a music signal transient of equal magnitude as a sine wave needs more power than a sine wave would, just because it is nonsimmetrical. Such a transient's RMS need is actually less, by a lot. I need to find that link. Looked but not yet found

Speaker phase issue is a separate issue from being musical transients.
Here is how the inventor does on this issue:
http://www.audiograph.se/subpages/technical/powercubemeasuringsystem.htm


Actually, one only has to use an amp with power meters and see what level of power is output. Being flat out is is lots of urban legend. I have access to such an amp at friends. I rarely see the center channel going beyond 2 watts, and never have seen it peak beyond 10-20 watts, even with good bit of lows. On the other hand, I have seen the sub amp up around 150watts on some passages in a good movie, or the cannon shots in Telarc 1812.

 

[Nick250]

You maybe on to something here Mtrycrafts. If we all had some inexpensive meters to integrate into our systems, that tells us how many watts are being drawn at any give time, would that not be really useful in amp/receiver discussions? I'm not an electronics guy, so the question I have is, would such meters be something that could be added to our existing systems without huge expenditures?

Twenty years ago my Dads Mac had little led bars that went up and down depending on the load.

Nick

 

[Buckeyefan 1]

You maybe on to something here Mtrycrafts. If we all had some inexpensive meters to integrate into our systems, that tells us how many watts are being drawn at any give time, would that not be really useful in amp/receiver discussions? I'm not an electronics guy, so the question I have is, would such meters be something that could be added to our existing systems without huge expenditures?

Twenty years ago my Dads Mac had little led bars that went up and down depending on the load.

Nick

I've got an older Pioneer receiver with the VU meters. I could hit 100+ dB's in the room, and the meters would barely hit 30 watts on peaks.

Wattage meters don't tell you the dB output in a room, since the speaker sensitivity and room size have a lot to do with output. You may need 10 watts with one speaker and 100 watts with another speaker to equal similar output in a given room.

I've seen McIntosh 500 watt monoblocs running "sponge" McIntosh towers hitting well over 300 watts at peaks, but those speakers are known to suck the life out of amplifiers.

 

[mtrycrafts]

You maybe on to something here Mtrycrafts. If we all had some inexpensive meters to integrate into our systems, that tells us how many watts are being drawn at any give time, would that not be really useful in amp/receiver discussions? I'm not an electronics guy, so the question I have is, would such meters be something that could be added to our existing systems without huge expenditures?

Twenty years ago my Dads Mac had little led bars that went up and down depending on the load.

Nick

Sorry, those are not add on meters my friend has but part of the amp, similar to Buckeye's meters but a whole slew of bars, with peak hold feature so it is easy to see the peak power instead of just a needle swing someplace around 50 watts .
His speakers are about 90dB sensitive. I suppose some would like to listen to music much louder; my ears start to ring with loud music, not used to rock concerts.
There might be such a meter on the market one could place across the amp output terminal. Google is a great tool

Yes, Buckeye, different speakers need different power, as we have hopefully been discussing here over time, impedance and sensitivity.

 

[tbewick]

I am not aware that a music signal transient of equal magnitude as a sine wave needs more power than a sine wave would, just because it is nonsimmetrical. Such a transient's RMS need is actually less, by a lot. I need to find that link. Looked but not yet found

Speaker phase issue is a separate issue from being musical transients.
Here is how the inventor does on this issue:
http://www.audiograph.se/subpages/technical/powercubemeasuringsystem.htm

Thanks for the link. I can't say I fully understand the 3D surface, but I'll have a further look around the site. Martin Colloms referred to the Lipshitz paper in a chapter he wrote in The Loudspeaker and Headphone Handbook. I had a quick check on Google and I think that this is the paper:

Computing Peak Currents into Loudspeakers, by J. Vanderkooy and S. P. Lipshitz.

- http://www.aes.org/e-lib/browse.cfm?elib=5019

The site you referred to says pretty much the same thing, and maybe this is what the above paper goes on about -

"We took a commercial ’off-the shelf’ loudspeaker and did a standard impedance plot for it. We swept the frequency from 20 Hz to 20 kHz, measured the input voltage and current, and calculated the impedance.

However, instead of using a sine wave input signal, we used a square wave. The reason for this is that square waves consist of a large amount of sine waves, as does music. The square wave is of course not an equivalent of music, but for this test it was an easy way of showing that a complex signal (not just a simple sine wave signal) may make the load, from the amplifier point of view, very low.

If you study the graph [see linked-to website] resulting from the test, you will probably agree that not only is it necessary to check the amplifier’s behavior for resistive, capacitive and inductive loads – the amplifier should also be checked for loads with lower impedance than the nominal impedance of the loudspeaker.

This proves to be very important, since a loudspeaker with a nominal impedance of 4 ohms will sometimes have an actual impedance of 1 ohm or less. The PowerCube helps you perform testing of an amplifier, taking all these load attributes into consideration."

- http://www.audiograph.se/subpages/technical/whatmakesagoodamplifier.htm

and this is in agreement with the advice given by B&W. The problem is the the only amplifiers that I've seen that behave in this way are 200 watts + (into 8 ohms). How valid then are the distortion measurements for amplifiers that don't manage to double their output with halving of impedance?

Actually, one only has to use an amp with power meters and see what level of power is output. Being flat out is is lots of urban legend. I have access to such an amp at friends. I rarely see the center channel going beyond 2 watts, and never have seen it peak beyond 10-20 watts, even with good bit of lows. On the other hand, I have seen the sub amp up around 150watts on some passages in a good movie, or the cannon shots in Telarc 1812.

Do you know how accurate the meters are? Certainly what you've said is in agreement with what Martin Colloms wrote, that on good programme material, the demands on the amplifier will be fairly low most of the time. It's just a question of being able to produce the high currents necessary for reproducing the loud musical transients without clipping. If you're routing the bass to the subwoofer, then this must help to reduce the possibility of clipping, since it's usually the bass region that clips first. Of course using the subwoofer in this way is like bi-amping.

 

[JAD2]

OH , NO, what did I start now?????

 

[Nick250]

Sorry, those are not add on meters
There might be such a meter on the market one could place across the amp output terminal. Google is a great tool

I understand that your friends meters were not add on. Google is a good idea.

Nick

 

[Nick250]

Wattage meters don't tell you the dB output in a room, since the speaker sensitivity and room size have a lot to do with output. You may need 10 watts with one speaker and 100 watts with another speaker to equal similar output in a given room.

Agreed. I forget about that part in the heat of the moment. I would need to add a sound meter to the mix. I am wondering what else might I be forgetting about in this scenario or if I am oversimplifying this process.

Nick

 

[mtrycrafts]

Thanks for the link. I can't say I fully understand the 3D surface, but I'll have a further look around the site. Martin Colloms referred to the Lipshitz paper in a chapter he wrote in The Loudspeaker and Headphone Handbook. I had a quick check on Google and I think that this is the paper:

Computing Peak Currents into Loudspeakers, by J. Vanderkooy and S. P. Lipshitz.

- http://www.aes.org/e-lib/browse.cfm?elib=5019

Thanks for the info and the link. I have problems finding papers on the AES web site.
Too bad this is not a Journal paper as a local library has them to about 1992 when they cut back due to budget. I don't have that paper

The left and right direction of the block is phase angle with the center being 0 degrees or totally resistive. Hence, the block that is bad, the center of it is closer to the good amp.

The front to back direction is the rail voltage in relationship to 8 Ohms being at the back and 1 ohms the very front.

The block that represents the Behringer A500 is similar to the good amp block, no rail voltage sag due to phase shifts.


By the way, the power cube measurement for it was a little better than for a Bryston 875 at $5k.

Do you know how accurate the meters are?

Unfortunately no, but it seems pretty good from rough, brief tests at around 1 watts and spl readings.

Certainly what you've said is in agreement with what Martin Colloms wrote, that on good programme material, the demands on the amplifier will be fairly low most of the time.

Yes. So, if it was around 1 watt, let's assume as in his case it was well below that, a 20dB peak would be 100 watts and that is before the dynamic headroom power is used.

Now, in his case, much was around .1 watts, that is why it was rarely peaking anywhere near 20 watts on the center ch. That would give a 30 dB headroom in his case, to 100 watts. But, some speakers are very demanding, no question. Amps are not designed around the most demanding speakers though as they are in the minority.


It's just a question of being able to produce the high currents necessary for reproducing the loud musical transients without clipping. If you're routing the bass to the subwoofer, then this must help to reduce the possibility of clipping, since it's usually the bass region that clips first. Of course using the subwoofer in this way is like bi-amping.

Yes, the bass does use a lot of power, no question. One reason is the ears insensitivity to it and the perception of loudness, Fletcher-Munson curve comes to mind.

The main speaker is on large though as it has a 12" driver beside the sub. The LFE goes to the sub to 80Hz. Other in channel lows do go to the speakers, however. Even with that, the observed power was what is above.

No question that not all speakers created equal and some are very demanding on amps. That is why speakers need to be picked first, not after the amp is home and a speaker must be found for it.


One more try
THD is usually measured at RMS power ratings, 1 watts or full power. So, you can get an idea of the 4 Ohm THD when it is given, usually not much worse than the 8 Ohms. Same goes with the dynamic power although that rating may be at a bit higher THD level, not sure.

 

[mtrycrafts]

OH , NO, what did I start now?????

Not much, just a friendly discussion. We all learn form these, hopefully.
There is way more to this than what is usually discussed, or most can contribute or understand or know.

Now, if only David Rich could participate, of Doug Self, that would be an priceless education.