Reciever + Amplifier(s) - Frequency Response, THD, Stability, etc

[PENG]

My thoughts on the 6 ohm rating are that it may be a misprint? I tried to find it on the web site but didn't list it. Such a drastic difference between 8 Ohms, full spectrum FR listing and so low, and 6 Ohms, one frequency listing and sky high compared to the other, from a top tier receiver is unusual. I'd like to see a real bench test report on it.

It is on page 92 of the downloadable manual. I don't think it is a misprint and I don't think it is that unusual for mid end class AB amps to behave that way.

 

[mtrycrafts]

It is on page 92 of the downloadable manual. I don't think it is a misprint and I don't think it is that unusual for mid end class AB amps to behave that way.

Thanks on the ref. I didn't download that manual, just the other sheets on it.
The Yam 659 can deliver an impressive amount into 4 ohms, no less at the same THD as into 8 ohms.
http://www.audioholics.com/reviews/receivers/yamaha-rx-v659/rx-v659-measurements-analysis

Is that Denon, almost $5x so much inferior to the Yam that its 6 ohm rating has such a high THD and at only 1 frequency?

 

[zumbo]

All name brand quality receivers have enough power supply to drive 4 ohm loads. That's why I didn't see a problem. I'm not aware of any amp made today that buckles against a 4 ohm load.

Not true. My separate amp is capable of producing 175W@4ohm. It buckles every time I crank it. I would say very few models in each brand name receiver can handle a 4ohm load.

I would also like to add another fact. People keep responding about human hearing not being able to hear distortion, or certain frequencies. The fact is, the speaker can. And, when an amp acts in this way, it does effect the overall SQ.

 

[tbewick]

When amplifiers are overdriven, they will clip the waveforms and distort. That is an extremely severe situation you won't encounter in any kind of normal use in a normal home. Amplifier distortion is not something to be concerned about with modern equipment. Not even a little. Let it go.

I think this contradicts something I've read previously. A while ago I looked at a RaneNote which discussed amplifier clipping. I thought that it would be helpful to quote the relevant sections directly from it:

'Studies show the typical spectral energy for different types of music have high frequency energy considerably lower in level than low frequency energy [2]...

Loudspeaker manufacturers use this knowledge about the energy distribution of music when they design their products...For a speaker system rated to handle a given number of watts, the tweeter by itself can probably handle less than one-tenth that amount.

...While doing research into the reliability and protection of power amplifiers, I had to study how the typical consumer used amplifiers and speakers. I found that clipping is a common occurrence and is not as audible as most people think. I also found that the operation of many clipping indicators is very slow and does not always show actual clipping. (Many manufacturers slow them down, using their own rule of thumb for how much clipping can occur until it lights the indicator.)

...analysis shows if a small tweeter that only handles 5 or 10 watts is used in a 100 watt speaker system it would not blow out, even under square wave conditions. Yet it does. It takes a lot more than this to cause major failure. So what’s happening? Compression is what’s happening [3].

Today’s newer higher quality amplifiers have greater dynamic range and sound better when clipped with musical transients than older amplifier designs. So it is more likely for a user to overdrive and clip newer amplifiers on low frequency dynamic peaks because of lower audible distortion. This results in compression of the dynamics of the music. The high frequencies get louder but the low frequencies can’t. This may be heard as an increase in brightness of the sound. Some may simply interpret it as louder with no change in tonal balance.

For example, in a 100 watt amplifier, as you turn up the level, the low frequency components will limit (clip) at 100 watts. Meanwhile the high frequency components continue to increase until they (the high frequencies) approach the 100 watt clipping point.

...If you overdrive the amplifier by 10dB, the high frequency amplitude goes up by 10dB. This goes on dB for dB as you turn up the volume, until the high frequency reaches the 100 watt level. Meanwhile the peak level of the low frequency portion can not increase above 100 watts (See Fig. 4). This now represents nearly 100% compression (no difference between HF amplitude and LF amplitude).

Now it is easy to see how the high frequency portion exceeds the 5 or 10 watts tweeter rating. Sure, clipping is producing extra harmonics but they never approach the levels of the amplified high frequency source signals.

It may be argued that the signal’s distortion would be intolerable. Don’t fool yourself. It really surprises people how much clipping they tolerate before they cannot listen anymore. Just disconnect the clipping indicator on a power amplifier and see how loud someone drives it. Watch the amplifier output with an oscilloscope. There will be a surprising level of clipping. 10 dB clipped off the top of low frequency transients is not an uncommon occurrence when the purpose is to impress your neighbors.'

RaneNote 128, 'Power Amplifier Clipping and its Effects on Loudspeaker Reliability'. Monty Ross. Rane Corporation, 1991.
http://www.audiovisualdevices.com.au/downloads/rane/note128.pdf

 

[fmw]

Not true. My separate amp is capable of producing 175W@4ohm. It buckles every time I crank it. I would say very few models in each brand name receiver can handle a 4ohm load.

.

Yes you can operate the equipment beyond its design capabilities. Perhaps a better term would be "overcrank it." You could accomplish the same thing with an 8 ohm load if you "crank" it enough.

 

[fmw]

I think this contradicts something I've read previously. A while ago I looked at a RaneNote which discussed amplifier clipping. I thought that it would be helpful to quote the relevant sections directly from it:

'Studies show the typical spectral energy for different types of music have high frequency energy considerably lower in level than low frequency energy [2]...

Loudspeaker manufacturers use this knowledge about the energy distribution of music when they design their products...For a speaker system rated to handle a given number of watts, the tweeter by itself can probably handle less than one-tenth that amount.

...While doing research into the reliability and protection of power amplifiers, I had to study how the typical consumer used amplifiers and speakers. I found that clipping is a common occurrence and is not as audible as most people think. I also found that the operation of many clipping indicators is very slow and does not always show actual clipping. (Many manufacturers slow them down, using their own rule of thumb for how much clipping can occur until it lights the indicator.)

...analysis shows if a small tweeter that only handles 5 or 10 watts is used in a 100 watt speaker system it would not blow out, even under square wave conditions. Yet it does. It takes a lot more than this to cause major failure. So what’s happening? Compression is what’s happening [3].

Today’s newer higher quality amplifiers have greater dynamic range and sound better when clipped with musical transients than older amplifier designs. So it is more likely for a user to overdrive and clip newer amplifiers on low frequency dynamic peaks because of lower audible distortion. This results in compression of the dynamics of the music. The high frequencies get louder but the low frequencies can’t. This may be heard as an increase in brightness of the sound. Some may simply interpret it as louder with no change in tonal balance.

For example, in a 100 watt amplifier, as you turn up the level, the low frequency components will limit (clip) at 100 watts. Meanwhile the high frequency components continue to increase until they (the high frequencies) approach the 100 watt clipping point.

...If you overdrive the amplifier by 10dB, the high frequency amplitude goes up by 10dB. This goes on dB for dB as you turn up the volume, until the high frequency reaches the 100 watt level. Meanwhile the peak level of the low frequency portion can not increase above 100 watts (See Fig. 4). This now represents nearly 100% compression (no difference between HF amplitude and LF amplitude).

Now it is easy to see how the high frequency portion exceeds the 5 or 10 watts tweeter rating. Sure, clipping is producing extra harmonics but they never approach the levels of the amplified high frequency source signals.

It may be argued that the signal’s distortion would be intolerable. Don’t fool yourself. It really surprises people how much clipping they tolerate before they cannot listen anymore. Just disconnect the clipping indicator on a power amplifier and see how loud someone drives it. Watch the amplifier output with an oscilloscope. There will be a surprising level of clipping. 10 dB clipped off the top of low frequency transients is not an uncommon occurrence when the purpose is to impress your neighbors.'

RaneNote 128, 'Power Amplifier Clipping and its Effects on Loudspeaker Reliability'. Monty Ross. Rane Corporation, 1991.
http://www.audiovisualdevices.com.au/downloads/rane/note128.pdf

Whew! you people are into loud. No wonder you buy 500 watt amps.

 

[jostenmeat]

I read a lot theory on this forum that doesn't relate to actual practice in a real environment for home entertainment. I think it is because the magazine writers like to expound on theory without ever putting it into context.

Your "thinking" might be "assuming". I for one have never bought an audio magazine, and my opinions are pretty much based on first-hand experiences, albeit limited ones.

Whew! you people are into loud. No wonder you buy 500 watt amps.

You mean per channel, right? (My former Onkyo HTIB stated 1000 watts total or something, HAH!). I wonder if anyone here has a 500w/ch amp, let alone 400w, or 300w, or maybe even 250w.

I chose my 140w/ch NAD not because its 140w, but because it increases power with load, replete with a 2 ohm rating, and especially because I could afford to put into budget at the time for $1k.
(My speakers drop to 0.7 ohms)

I do not think there is a right or wrong. As has been stated waaaaaay too many times, these kinds of arguments are highly dependent on numerous parameters, many of which are never stated by OP's around the world who might start a thread on such a topic.

Lastly, for every zumbo there is also a fmw. AVS thread: Amp vs Receiver experiment:
http://www.avsforum.com/avs-vb/showthread.php?t=911338

 

[zumbo]

Yes you can operate the equipment beyond its design capabilities.

That is the point, isn't it? The equipment states it's capabilities, which clearly states it can't do what you say it can, and many can't even do what they state.

Perhaps a better term would be "overcrank it."

No. That is not what I am saying. My amp has indicators that let you know it has reached it's limit. My speakers could take more. Much more.

You could accomplish the same thing with an 8 ohm load if you "crank" it enough.

Sure. But with a 4ohm load on the same said equipment, that accomplishment would be made much sooner.

 

[mtrycrafts]

Whew! you people are into loud. No wonder you buy 500 watt amps.

Probably because 1000watt amps are much more, demand different outlets, and may need a handcart to move around Even if it only plays at .1 watts much of the time

 

[Seth=L]

Probably because 1000watt amps are much more, demand different outlets, and may need a handcart to move around Even if it only plays at .1 watts much of the time

You can pound it into everyone's head for days and it isn't going to get through. I mean, look at me, how long did it take to break me?

 

[mtrycrafts]

You can pound it into everyone's head for days and it isn't going to get through. I mean, look at me, how long did it take to break me?

You are broken in? I must have missed that line someplace

I guess it is similar to cars cannot have too much horsepower, even if the speed limit is 65, right?

 

[Seth=L]

I guess it is similar to cars cannot have too much horsepower, even if the speed limit is 65, right?

That might be what it is, maybe someone is trying to compensate for something?

 

[jcPanny]

AH Receiver Reviews

Check out some of the detailed AH reciever reviews including the Denon 4306.
http://www.audioholics.com/reviews/receivers/denon-avr-4306/avr-4306-measurements-and-analysis

The detailed measurements include the pre-amp stage and output into 4 ohm loads. The modern Denon and Yamaha pre-amps measure very well and the 4308 shouldn't have a problem with a pair of 4 ohm speakers.

Emotiva builds some great amps, but the BPA-1 (in bridged mode) is designed for an 8 ohm load and would not be appropriate for the 4 ohm axiom speakers.

 

[Ampdog]

Electrocutor,

You have received a lot of good advice here over many posts; I come in late and will therefore not deal with your well-formulated quiery point-by-point. But unless I missed something a few matters need further exploring.

I must respectfully disagree about figures given for audible distortion; it was already determined some 50 years ago that critical human hearing can discern as low as 0,1% distortion under certain conditions. (Particularly Scandanavian universities have done valuable research on this.) But this matter is by no means simple, as I will try to explain briefly (and therefore incompletely!):

It absolutely depends on what the distortion comprises; the ear is not equally sensitive to everything. On the contrary: Some 0,02% combinations of high order products (7th - 13th) can be so strident that with time they cause what is termed listener fatigue. I.e. one does not hear the distortion as it is caused at each music tone; but with time one tends to "reject" the response as compared to that of a "clean" amplifier. Thus the term listener fatigue.

It now happens especially with certain semiconductor topologies that although the total distortion figure is admirably low, it contains high order products and thus listener fatigue is experienced to a greater extent that e.g. with an amplifier with a far higher thd, but where the latter consists of say only 2nd and 3rd order products and little else. This is a discussion on its own; I will stop at saying that thd is a rather useless indication of the "cleanness" of an amplifier. (Folks are becoming increasingly aware of this fact; the above is why.)

It is unfortunately also true (as previously said) that distortion is not linearly related to output power; at low power semiconductor devices can present a nasty type of distortion called cross-over distortion. When some members said that one could neglect amplifier distortion nowadays, this should be true - these design problems have been solved long ago. But sadly it is not always true with certain commercial products, and the correct specs (e.g. spectrum analysis) are not given so that one can judge. Listening of course will show the above effects up with time, but requires the right type of music. One may be stuck with an amplifier for some time before something comes along that will manifest listener fatigue.

Where does that leave you? Only to agree with others that specs, at least as far as amplifiers go, are unfortunately not a reliable norm. Do not be over-impressed by the 0,00x% fraternity. To also agree with others, loudspeakers give significantly higher distortion and should be the determining factor, but amplifiers could contribute when the above matters are not in order.

Hope this helps somewhat.

 

[zumbo]

I must respectfully disagree about figures given for audible distortion; it was already determined some 50 years ago that critical human hearing can discern as low as 0,1% distortion under certain conditions. (Particularly Scandanavian universities have done valuable research on this.)
Listening of course will show the above effects up with time, but requires the right type of music.

Might as well use the type of music they must have used in that university.
http://www.youtube.com/watch?v=G5l74teXC5w