Question on bi-amping - Page 28 - AVS Forum
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post #811 of 1044 Old 11-30-2013, 06:24 AM
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Originally Posted by stereoforsale View Post


At then end of the day, my understanding is that more power is never a bad thing - you can never have too much power, no?

Sure you can have too much power. Power is what fries speakers, and excessively powerful amps make it more likely that an otherwise survivable mishap will become a fatal event.
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You always read about amps being under powered and you need lots of microfarads (or whatever they are called) for dynamic movies, etc, etc.

If you run the numbers, you generally find that the common AVR with 125 wpc dynamic power or more can cleanly drive most speakers as used to reference levels.

The SPLs that people listen to is more commonly known and it generally turns out to be far less than reference levels. That right there is reliable evidence that AVR amplifier clipping is relatively uncommon.

Almost no audiophile who posts on AVS seems to know for sure whether his AVR is clipping or not.
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Hence people need (or are made to be believe they need) more and more power.

Exactly. That is a beautiful clear statement of the common audiophile power amplifer conundrum.
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Ultimately, my fear is that with all 9 channels driven, can the Marantz sr7008 produce enough clean power?

The use of the word fear seems to be highly relevant. I think it is very healthy to call this a fear or a phobia instead of misrepresenting it to be a true and genuine identified problem.

One cheap and easy way to develop reliable evidence about this situation is to know what kinds of peak SPLs you actually engage in. Do you have a SPL meter with a peak hold function? I don't mean a fast response mode, I mean one that detects peak levels and holds them indefinitely?
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I take arnyk's point that power demands in real use are not as steady and demanding as in bench testing, but as a consumer we have nothing else to refer to. Then when you throw in things like "THX Ultra 2 certification", and it makes you think "gee, my AVR is not THX certified so I'm already on thin ice to begin with!". All of this makes you want to squeeze out every bit of performance we can get, especially if it's as easy as simply using the biamping feature you already have access to (this is why the "waste of time & money" arguments against passive bi-amping meant nothing to me... it cost me nothing to do it, I just have to move from 9.1 to 7.1... and frankly, 9.1 has proven to be a much bigger "waste of time and money" in my opinion... I wasted considerable time and money setting up those last 2 useless speakers... but I digress).

I've been contemplating this problem since last year when I first encountered the ways that some people are using fear and rumor to justify the purchase of external power amps, some of which seem to be bad jokes. I'm referring to power amps that may produce less useful power than the AVRs they purportedly upgrade.

I have been chasing this problem on 3 fronts:

(1) I have obtained an AZ 8926 SPL meter which appears to have a fast-responding peak hold feature for acoustical measurements. I can listen as long as I want and have an reliable measure of peak SPLs in my listening room.

(2) I have obtained a UT61E DVM that appears to have fast-responding peak volt measure and hold facility that works in a similar fashion to the AZ 8926 SPL meter. I can have an reliable measure of peak amplifier output in my listening room.

(3) I am collecting parts for a precision attenuator that will allow me to operate my AVRs up to clipping and monitor their amplifier outputs accurately with a 24/96 professional computer audio interface. I can have an reliable indication of whether or not my AVR is clipping and when and how..
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post #812 of 1044 Old 11-30-2013, 06:37 AM
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Originally Posted by kiwi2 View Post


You mean you have decided that that's what the problem was because it fits your angle better.

could be + probably was ≠ decided

just sayin'.
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post #813 of 1044 Old 11-30-2013, 06:37 AM
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Originally Posted by kiwi2 View Post

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Originally Posted by arnyk View Post

The approach to this problem described above seems to lack a solid technical base.

There was no objective determination of the problem or its cause.

When I'm chilling out listening to music late in the evening - that's not the time I start playing around with SPL meters and such.

You seem to have other times, such as the ones in which you obtain new power amps. ;-)
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The statement

" I had to turn the volume up more yet it sounded like the whole system was getting quieter."

The above could be describing the ear's well known property called "Temporary Threshold Shift". Probably was.

You mean you have decided that that's what the problem was because it fits your angle better.

The expected attack on my character.

How defensive!

Read the words I wrote, not the words you want to see! I wrote: "The above could be describing the ear's well known property called "Temporary Threshold Shift".

What's unclear about "Could be"?
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All I can describe it as, as it would start to sound very strangled and harsh and required more and more volume but still didn't sound full bodied from adding any extra volume.

All I can say is that could be a well known psychoacoustic effect. If you want to stifle all discussion of real possibilities, you may be in the wrong place! ;-) Don't think that you are the first person around here who has experienced such things.
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Then we have the idea of addressing a perceived lack of power output of an AVR that might have been capable of 160 wpc by adding an 80 watt amplifer.

I already have some big old 150w ss poweramps lying around but I don't like their size and the space they take up and their inefficient power use (as they would be used all day long) and the audible transformer hum I could hear from the listening position. I had been using them in the past but went back to the AVR's amps for those reasons but then run into the problem mentioned above from doing so. Some nice small quiet efficient class-D amps appealed to me. I haven't experienced that strangled harshness since going back to outboard amps. The new amp would just gracefully shut itself off for a few seconds instead when I just had the one by itself.

Yes, but that was not exactly an unbiased evaluation either. Again, if you want to stifle all discussion of listener bias, this may also be the wrong place to do it. ;-)

If you haven't noticed I'm all about nailing down reliable facts. Some of the reactions I get for that are not exactly pleasant, but the truth is worth something to me.
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post #814 of 1044 Old 11-30-2013, 06:40 AM
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Originally Posted by arnyk View Post

It was a serious question.
And the serious answer is that clipping is a Boolean state; it's either happening or it isn't.

Amplifier clipping is the friend of many electric guitar players, but when it comes to audio reproduction the amount of wanted clipping should always be zero. Why waste any time at all in measuring the amount of evil that is in a signal? Isn't it enough that evil has corrupted it?

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post #815 of 1044 Old 11-30-2013, 06:54 AM
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Originally Posted by stereoforsale View Post

Can they handle what kind of power? The power of my AVR, which is rated at 125wpc with 2 ch driven? Or do you mean the 200w Emotiva, or the 400w bridged Lexicon?

At then end of the day, my understanding is that more power is never a bad thing - you can never have too much power, no? You always read about amps being under powered and you need lots of microfarads (or whatever they are called) for dynamic movies, etc, etc. Hence people need (or are made to be believe they need) more and more power. Ultimately, my fear is that with all 9 channels driven, can the Marantz sr7008 produce enough clean power?

I take arnyk's point that power demands in real use are not as steady and demanding as in bench testing, but as a consumer we have nothing else to refer to. Then when you throw in things like "THX Ultra 2 certification", and it makes you think "gee, my AVR is not THX certified so I'm already on thin ice to begin with!". All of this makes you want to squeeze out every bit of performance we can get, especially if it's as easy as simply using the biamping feature you already have access to (this is why the "waste of time & money" arguments against passive bi-amping meant nothing to me... it cost me nothing to do it, I just have to move from 9.1 to 7.1... and frankly, 9.1 has proven to be a much bigger "waste of time and money" in my opinion... I wasted considerable time and money setting up those last 2 useless speakers... but I digress).

If it is about making yourself feel better science and real needs do not enter into the equation. If one channel is three dB below another the lower channel needs half the power. Afaik zero movies ever have all channels at the same maxes out level so I think it's a worry about a nonexistent problem. But again if you can afford and simply want to, go nuts. You do not need the permission of a dozen strangers on the internet
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post #816 of 1044 Old 11-30-2013, 06:57 AM
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Originally Posted by Speed Daemon View Post

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Originally Posted by arnyk View Post

It was a serious question.
And the serious answer is that clipping is a Boolean state; it's either happening or it isn't.

+1
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Amplifier clipping is the friend of many electric guitar players, but when it comes to audio reproduction the amount of wanted clipping should always be zero

+1
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Why waste any time at all in measuring the amount of evil that is in a signal? Isn't it enough that evil has corrupted it?

The point of the measurements is to determine the relevant Boolean state. My thesis is that it is largely unknown and that it varies.

For example, if one obtains a $20 SPL meter (AZ 8926) and find that they never come near, or routinely exceed reference level (105 dB SPL) they have a reliable, relevant data point.

Maybe not the final solution, but at least they know which way to Honolulu. ;-)
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post #817 of 1044 Old 11-30-2013, 07:11 AM
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If it is about making yourself feel better science and real needs do not enter into the equation.

I'm not sure that you are against this in your mind, but I strongly feel that better science and real need have helped me feel a lot better about all sorts of things, audio included.
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If one channel is three dB below another the lower channel needs half the power.

That seems a relevant rebuttal to the AVR testers who entertain themselves by doing "All Channels Driven" tests.
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Afaik zero movies ever have all channels at the same maxes out level so I think it's a worry about a nonexistent problem.

I have to admit that I swallowed the full power all channels driven doctrine for many decades and tested dozens if not hundreds of amplifiers that way. I smirked at the hapless owners of power amps that did not cut that particular band of mustard.
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But again if you can afford and simply want to, go nuts. You do not need the permission of a dozen strangers on the internet

That applies to going either way on this issue. If you want to rate your audio system based on tonnage, its a hobby and go wild! If you want to be happy with a lightweight AVR you may not be sacrificing that much sound quality, if any at all.
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post #818 of 1044 Old 11-30-2013, 08:04 AM
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Originally Posted by JHAz View Post

Afaik zero movies ever have all channels at the same maxes out level so I think it's a worry about a nonexistent problem.
The fact that not all channels could be active doesn't mean only one is smile.gif. In movies, the center channel is dominant. It puts out massive amount of soundtrack energy. Then the left and right are added to that in dynamic scenes. So it is very common to have three front channels pushed hard. Ideally one would have 2X more power for the center channel. Unless you put together your own discreet channels, you can't do that. AVRs as such, need not apply smile.gif.
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But again if you can afford and simply want to, go nuts. You do not need the permission of a dozen strangers on the internet
He needs to do that silently. If he as much as opens his mouth, there will be a bunch of theories that he will not need that. smile.gif

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post #819 of 1044 Old 11-30-2013, 08:24 AM
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Originally Posted by arnyk View Post

(earlier) Almost no audiophile who posts on AVS seems to know for sure whether his AVR is clipping or not.
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The point of the measurements is to determine the relevant Boolean state. My thesis is that it is largely unknown and that it varies.
The fact that the average AVR fails to give that necessary information is a reason to eschew that class of products altogether. It reminds me of a car without a gas gauge. While not a necessity strictly speaking, a gauge (or at the very least an "idiot light" that comes on when you're low) can often be the thing that keeps you from being a pedestrian. And while such an omission might be acceptable for cheap, entry level automobiles, eventually a driver will want to drive something that gives the vital information. Likewise, I'd think that the ambitious AVR owner will hope to graduate to a better class of product when finances permit.

Before the AVR came to be, the typical music lover might start with a receiver in his salad years, then move to a component system as finances permitted. Bridge products like tuner-preamps and integrated amps helped smooth the transition. I don't see any clear path like that in the AVR marketplace. Instead, things like blue lights and extra "features" seem to separate the high end of the market from the low. Seeing that, I can't help but wonder if the AVR market is simply the most efficient way to separate fools from their money.

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For example, if one obtains a $20 SPL meter (AZ 8926) and find that they never come near, or routinely exceed reference level (105 dB SPL) they have a reliable, relevant data point.

Maybe not the final solution, but at least they know which way to Honolulu. ;-)
Ah, so you're using the loudness meter as a substitute for the missing level indicators? Clever! Not quite as fun as watching the bargraph LED display on a H/K Citation 16 power amp, but should have the same utility if properly calibrated.

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post #820 of 1044 Old 11-30-2013, 08:49 AM
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So many post. hard to reply to all, but for what it's worth:

- Amirm raises an excellent point, if I want to upgrade (as a matter of pure choice for the fun of the hobby) then perhaps the right solution is a mono block for the CENTRE channel.... cheaper, less bulky, more likely to have any real benefit (if at all, of course), etc. But I wonder, do I need to be concerned with sonic matching with the L & R, or is that audiophile-b.s. too?... do all amps sound the same?... sorry, I don't mean to take this discussion off topic.

- I do have a SP meter, but just the simple radio shack version... doesn't hold peak levels.

In any event, I'm still enjoying the passive biamping debate and I can't wait to hear more from Amirm's experiments.
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post #821 of 1044 Old 11-30-2013, 10:02 AM
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You seem to have other times, such as the ones in which you obtain new power amps.

Forgive me your Holiness.

In the future I shall seek your approval first before any audio purchase.
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post #822 of 1044 Old 11-30-2013, 10:25 AM
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@stereoforsale: The center carries most of the dialogue in movies and most everything else is at least present in the center mix. However, the L/R speakers carry the rest of the "front" load and handle lower bass (above the sub, below the center). The center speaker is rarely large enough to handle bass so the L/R often have as much or more power going to them even though the center sounds loudest most of the time. At least based on very minimal spot-checking I have done in my system. I am sure it varies with the movie etc. And of course if your L/R speakers don't go any lower than the center then it doesn't matter. I would amplify the front three main speakers (L/C/R) if you are going to amplify. There are a lot of three-channel amps around for HT. For pro amps, you can get a stereo and a mono amp, two stereo amps and either not use one channel or bridge the center amp, etc.

@Speed Daemon: AVRs typically offer more features such as more/different/"better" decoders and more advanced room correction as you go up the line. Also, higher-end units offer more channels (5-7-9-11 channels). Power increases, natch, but IMO that is mostly marketing. Last time I bought an AVR I had a sales guy trying to extol the benefits of upgrading from 115 W/ch to 125 W/ch; he did not like my attempt to explain to him why that was a foolish reason to upgrade. smile.gif I am not sure clipping indicators are all that beneficial in the consumer world. What happens to the guy who saves all his money and buys a new AVR, and first thing sees the clipping lights flicker? Most people are probably better off not knowing, even if they are clipping briefly now and then.

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post #823 of 1044 Old 11-30-2013, 11:18 AM
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Originally Posted by DonH50 View Post

However, the L/R speakers carry the rest of the "front" load and handle lower bass (above the sub, below the center). The center speaker is rarely large enough to handle bass so the L/R often have as much or more power going to them even though the center sounds loudest most of the time.
+1
Easy way to check this is to disconnect center speaker cable and watch the movie, then reconnect and disconnect the L&R speaker cables for the same passage of the movie. I've noticed that generally L&R channel take on considerably more program than center.
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post #824 of 1044 Old 11-30-2013, 02:07 PM
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Originally Posted by arnyk View Post

Wrong again Amir. What your superficial analysis has failed to take into account is the fact that QSC's clipping indicator is inside the amp's feedback loop and only sees large voltages when the output stage is saturated.
Arny that thing could have warp drive and photon torpedoes and still wouldn't make that circuit less crusty! biggrin.gif What is the standard engineering product design rule? Cheap, fast, good, take two. They clearly went for cheap and fast. A bridge rectifier, resistor and LED and call it done. While the rest of the engineering world sweats the details and builds more sophisticated circuits that don't try to harm what they are monitoring. And work with much better precision.

As to it being in "amp's' feedback loop and only sees large voltages" that is technomarketing Arny. If you are going to say something about the circuit, you need to say more than the service manual says: "But because this point is within the overall feedback loop, when clipping occurs, the op amp approcahes [sic] full open-loop gain and puts out a much higher signal voltage to try to make the output signal track the input."

Let me explain what they didn't. There is no latching mechanism on that LED. An audio peak may only last 1 or 2 milliseconds. Assuming that the clipping circuit does saturate, it will only do so for that length of time. Maybe you have super human vision but I am pretty sure the rest of us can't see an LED flicker for 1/1000 of a second. And that's if you give it enough time to reach 4-5 volts on the output of the Op Amp or it would either be barely lit or not at all. Given all of this, the only time you would see the LED is if the amp had heavily clipped and you had a bunch of audio segments all maxed out. That would keep the LED lit for enough time to have mere mortals see it. I want to see the onset of clipping and not when it has gotten out of hand. I guess from marketing point of view it is better to light up the LED as late as you can as to not have people return the gear due to it appearing to not have enough power with the LED coming on.

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It is true that there is no capacitor to act as a pulse stretcher or filter, and that is because the indicator is highly effective without it.
No, they didn't put the cap there either because they were too cheap or likely, it interfered with the response of that op amp. The cap would charge up and not let go post clipping, In other words, it would cause severe slew rate limiting (in the reverse direction) once clipping occurs. This is probably another reason they don't have this trigger until the amp is way, way under water.
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It's pretty amazing to see this light flickering on when the THD is well under 0.05%, but that's what happens.
THD? This circuit does not measure THD. Further the distortion spec for RMX 1450 amp says: " A full complementary output circuit using the highest-grade linear output devices delivers ultra-low distortion (<0.05% THD) " If it could achieve "well under 0.05%" don't you think that is what they would advertise? Here is what they say further in the specs: "Distortion (Typical) 20 Hz - 20 kHz: 10 dB below rated power: Less than 0.03% THD, 4 and 8 ohms." So at 10 db below rated power which presumably is below clipping, the distortion only drops to 0.03%. And you say you saw the LED blinking at well under those distortion levels? And thought the amp was clipping even though they say it is -10 db below rated power?

Really Arny, please don't try to wear the market hat for companies and help hide circuit/performance deficiencies. Let their own marketing departments do that. Everything can't be good enough. Some things are not. And this is one of them. Unless one has no standards of quality or fidelity.

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post #825 of 1044 Old 11-30-2013, 02:17 PM
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Originally Posted by DonH50 View Post

@stereoforsale: The center carries most of the dialogue in movies and most everything else is at least present in the center mix. However, the L/R speakers carry the rest of the "front" load and handle lower bass (above the sub, below the center). The center speaker is rarely large enough to handle bass so the L/R often have as much or more power going to them even though the center sounds loudest most of the time[/U]. At least based on very minimal spot-checking I have done in my system. I am sure it varies with the movie etc. And of course if your L/R speakers don't go any lower than the center then it doesn't matter. I would amplify the front three main speakers (L/C/R) if you are going to amplify. There are a lot of three-channel amps around for HT. For pro amps, you can get a stereo and a mono amp, two stereo amps and either not use one channel or bridge the center amp, etc.

Ok, great point, but that leads me back to something I said earlier: why do tower L&R speakers need more power than other smaller speakers, to which everyone said "they don't". I understand that smaller speakers are less sensitive, but they also produce much less bass, so I thought they needed less power than full range tower speakers. Clearly I'm missing something. I'm not trying to be difficult, but from a layman's point of view it's hard to make sense of all this. smile.gif

EDIT:
I didn't bother mentioning this before, but I suspected the people who told me I was wrong, were themselves incorrect. My guess is these people misunderstand what speaker sensitivity means. If you remove a woofer, of course it won't be as loud as the equivalent speaker with a woofer, assuming both speakers' tweeters/midranges are producing the same db. In other words, it's not the need for more power that makes smaller speakers less sensitive, it's the absence of bass.... so if you want to match the volume of the larger speaker, the tweeter/midrange of the smaller speaker needs to play much louder than the tweeter/midrange of the larger speaker... so you're not really comparing apples to apples, so it's incorrect to say larger speakers need less power. As Don noted, larger speakers DO need more power. If I'm wrong, I apologize. If I'm right, then score another point for the layman! smile.gif
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post #826 of 1044 Old 11-30-2013, 03:44 PM
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Originally Posted by amirm View Post

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Originally Posted by JHAz View Post

Afaik zero movies ever have all channels at the same maxes out level so I think it's a worry about a nonexistent problem.

The fact that not all channels could be active doesn't mean only one is smile.gif.

Weave and deflect again, eh Amir? There is a long distance between *anything* that has been said so far and your assertion that everybody but you is claiming that only one channel is active at a time.
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In movies, the center channel is dominant. It puts out massive amount of soundtrack energy. Then the left and right are added to that in dynamic scenes. So it is very common to have three front channels pushed hard. Ideally one would have 2X more power for the center channel. Unless you put together your own discreet channels, you can't do that. AVRs as such, need not apply smile.gif.

Of course you can do the above with an AVR.. If the center channel has as you say 2X the power of either the L&R, then that means that the L&R channel are each 3 dB down. That means that all three front channels sum together to have the same power as 2 channels running full power. We must not forget that the crest factor of music and drama is an absolute minimum of 3 dB more than that of pure sine waves. That means that any AVR that can power 2 channels for sine waves can power 4 channels for music or drama.
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post #827 of 1044 Old 11-30-2013, 04:03 PM
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Originally Posted by stereoforsale View Post


Ok, great point, but that leads me back to something I said earlier: why do tower L&R speakers need more power than other smaller speakers, to which everyone said "they don't".

First off there is no such rule as "All tower speakers are the same". So any global rule anybody makes for towers has to at least allow for exceptions. There is nothing special about making a speaker in the shape of a tower. It is possible for a robust bookshelf speaker to outperform a wimpy tower.

That all said there is a tendency for speakers made in the shape of a tower to have larger internal volume and have more and/or larger woofers. The larger internal volume means more bass extension, all other things being equal. The more and/or larger woofers means that the tower will have more bass dynamic range. The larger internal volume means that the speaker can be more efficient, all other things being equal. All of those things fall out of the laws of physics, particularly one that applies to speakers called "Hoffman's Iron Law".

http://en.wikipedia.org/wiki/Loudspeaker

'It is typically not possible to combine high efficiency (especially at low frequencies) with compact enclosure size and adequate low frequency response. One can, for the most part, choose only two of the three parameters when designing a speaker system. So, for example, if extended low-frequency performance and small box size are important, one must accept low efficiency.[35] This rule of thumb is sometimes called Hofmann's Iron Law (after J.A. Hofmann, the "H" in KLH)"

If a speaker is more efficient then it takes less power to make the same amount of sound. Therefore the idea that "...tower L&R speakers need more power..." violates the laws of physics because all other things being equal they require less power to generate the same amount of sound since they are generally larger.

Quote:
I understand that smaller speakers are less sensitive, but they also produce much less bass, so I thought they needed less power than full range tower speakers.

Less sensitive means that they take more power to produce the same amount of sound. You have to figure out what you want to believe, audiophile myths or the laws of physics. Myself, I have a preference for the laws of physics. ;-)
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Clearly I'm missing something. I'm not trying to be difficult, but from a layman's point of view it's hard to make sense of all this. smile.gif

What you are missing is an appreciation for the laws of physics. This is cross to bear for every well-informed person who deals with you. You seem to have a strong preference for myth over science.

Quote:
I didn't bother mentioning this before, but I suspected the people who told me I was wrong, were themselves incorrect. My guess is these people misunderstand what speaker sensitivity means. If you remove a woofer, of course it won't be as loud as the equivalent speaker with a woofer, assuming both speakers' tweeters/midranges are producing the same db. In other words, it's not the need for more power that makes smaller speakers less sensitive, it's the absence of bass.... so if you want to match the volume of the larger speaker, the tweeter/midrange of the smaller speaker needs to play much louder than the tweeter/midrange of the larger speaker... so you're not really comparing apples to apples, so it's incorrect to say larger speakers need less power. As Don noted, larger speakers DO need more power. If I'm wrong, I apologize.

YOU ARE WRONG about larger speakers needing more power. All other things being equal, smaller speakers take more power. It is possible to make tiny speakers with good bass extension, only they will take a lot more power to do the same thing.
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If I'm right, then score another point for the layman! smile.gif

There are such things as well informed laymen who believe in science and even know how it applies to audio. You represent yourself, not them!
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post #828 of 1044 Old 11-30-2013, 04:16 PM
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@stereoforsale: The center carries most of the dialogue in movies and most everything else is at least present in the center mix. However, the L/R speakers carry the rest of the "front" load and handle lower bass (above the sub, below the center). The center speaker is rarely large enough to handle bass so the L/R often have as much or more power going to them even though the center sounds loudest most of the time[/U]. At least based on very minimal spot-checking I have done in my system. I am sure it varies with the movie etc. And of course if your L/R speakers don't go any lower than the center then it doesn't matter. I would amplify the front three main speakers (L/C/R) if you are going to amplify. There are a lot of three-channel amps around for HT. For pro amps, you can get a stereo and a mono amp, two stereo amps and either not use one channel or bridge the center amp, etc.

Ok, great point, but that leads me back to something I said earlier: why do tower L&R speakers need more power than other smaller speakers, to which everyone said "they don't". I understand that smaller speakers are less sensitive, but they also produce much less bass, so I thought they needed less power than full range tower speakers. Clearly I'm missing something. I'm not trying to be difficult, but from a layman's point of view it's hard to make sense of all this. smile.gif

EDIT:
I didn't bother mentioning this before, but I suspected the people who told me I was wrong, were themselves incorrect. My guess is these people misunderstand what speaker sensitivity means. If you remove a woofer, of course it won't be as loud as the equivalent speaker with a woofer, assuming both speakers' tweeters/midranges are producing the same db. In other words, it's not the need for more power that makes smaller speakers less sensitive, it's the absence of bass.... so if you want to match the volume of the larger speaker, the tweeter/midrange of the smaller speaker needs to play much louder than the tweeter/midrange of the larger speaker... so you're not really comparing apples to apples, so it's incorrect to say larger speakers need less power. As Don noted, larger speakers DO need more power. If I'm wrong, I apologize. If I'm right, then score another point for the layman! smile.gif

Small speakers are generally less sensitive than larger speakers for a variety of reasons. One common one is that the midrange is suppressed to provide more bass extension, reducing overall sensitivity to provide a little more bass.The smaller cabinet may contribute, and a host of other design parameters; I am not a speaker designer so would not presume to guess them all. Whether towers or smaller speakers require more power is more complex than just that, however. It depends on the relative sensitivity of the two systems, the crossover point, distance, etc. There is not a cut and dry answer, too many variables. Most larger speakers are more sensitive than most bookshelf speakers IME, but it is pretty easy to find counter examples either way. E.g., a small pair of horn speakers with high low-frequency cutoff compared to cheaper towers struggling to get an extra bit of bass extension. I imagine the comments were because a small speaker crossed over at 80 Hz to a sub is likely to require more power than a larger speaker crossed over at 80 Hz, given that 80 Hz is a pretty common crossover point in an AVR. I would not expect much change if the crossover was moved up to 100 Hz. The subwoofer in most systems requires the most power, and tends to take the mains out of the picture, or at least further down in priority as far as power needed is concerned.

Most centers I have seen cross over much higher than the L/R speakers so it's not really an apple-to-apples comparison. My comment was directed to that point, the higher crossover, not that larger speakers are less sensitive. Usually it's the other way around. As to which requires more power, well, "it's complicated".

Look up Fletcher-Munson equal-loudness curves to get an idea how we hear and what relative SPLs are needed over frequency. Remember 3 dB is twice the power, and 10 dB is 10x the power. It will also be clear why handing off the lows to a dedicated sub is a good idea rather than running the L/R speakers full-range (wastes too much power/headroom).

EDIT: I see Arny already covered pretty much the same points whilst I was composing.

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post #829 of 1044 Old 11-30-2013, 04:19 PM
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Originally Posted by amirm View Post

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Originally Posted by arnyk View Post

Wrong again Amir. What your superficial analysis has failed to take into account is the fact that QSC's clipping indicator is inside the amp's feedback loop and only sees large voltages when the output stage is saturated.

As to it being in "amp's' feedback loop and only sees large voltages" that is technomarketing Arny.

Well indict yourself if you will Amir, but the above statement is the product of your weird ideas about quoting people which includes chopping sensible statements into nonsense.

What I said was:

":QSC's clipping indicator is inside the amp's feedback loop and only sees large voltages when the output stage is saturated."

Not the same thing as your bastardized version:

"amp's' feedback loop and only sees large voltages"

Here's what happens. In the QSC power amp circuit (and just about any SS amp), the whole amp is inside an inverse feedback loop. Typically power amps have from 20 to 40 dB or more inverse feedback which means that the open loop gain of the power amp circuit is 20 to 40 dB more than whatever gain the amp has with the inverse feedback loop closed. However, when the output stage saturates, it looses most if not all of its gain, and the excess gain in the driver circuits causes the signal voltage provided to the output stage to increase by from 20 to 40 dB or more. The QSC clipping circuit monitors the signal voltage at the input to the output stage and when it increases by 20 to 40 dB or more when the amp clips it activates the LED.

Amir if you can, get one of the big tech boys in your shop who actually takes the covers off of power amps and knows how to probe around inside them without hurting themselves or the amp show you how this works. ;-)

Or, add $100 to my Paypal account (arnyk@wowway,com) and I'll rip open one my QSC amps and post some information here about how the signal voltages inside the amp changes dramatically when it clips. ;-)

Again some variation in this happens in just about every SS amp. It is particularly pronounced in power amps with output stages that have gain, which is not always the rule. If the output stage has unity gain, you may have to back up a stage so that there is gain between the point you are probing and the amps output terminals.
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post #830 of 1044 Old 11-30-2013, 04:30 PM
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I'm not going to bother responding to arnyk anymore. Maybe it's a US vs. Canadian thing, but we find his manner uncivilized [insert Mayor Rob Ford joke].

@ Don, Ok, I accept the point that "it's complicated" and not waste my time trying to reconcile the apparent (apparent!) contradictions.

As for comparing large and small speakers, I was assuming speakers within the same series, e.g.: my 803 vs. 805.

Anyway, let's move on.
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post #831 of 1044 Old 11-30-2013, 04:43 PM
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Of course you can do the above with an AVR.. If the center channel has as you say 2X the power of either the L&R, then that means that the L&R channel are each 3 dB down.
We are not playing all three channels full blast Arny. Indeed you can't predict the dynamics for each channel. The goal is to have appropriate amount of power for each channel so that we don't max out that amp and cause distortion. If the center channel is louder at that point, it is what the content owner intended.
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That means that all three front channels sum together to have the same power as 2 channels running full power.
There is nothing to sum. Each channel is independently authored to have what it needs to have. If the action is in the middle of the screen, then that is the channel that is going to play. Content creator is not putting the same in left and right channels to help the center.
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We must not forget that the crest factor of music and drama is an absolute minimum of 3 dB more than that of pure sine waves. That means that any AVR that can power 2 channels for sine waves can power 4 channels for music or drama.
We are not talking about music or drama Arny. This is movies with synthetic content that can have any dynamics it wants. You can't apply any rules to it. An explosion in the middle of the screen is going to do what it is going to do. It does not obey the rules of any musical instrument.

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post #832 of 1044 Old 11-30-2013, 04:58 PM
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Originally Posted by arnyk View Post

Here's what happens. In the QSC power amp circuit (and just about any SS amp), the whole amp is inside an inverse feedback loop. Typically power amps have from 20 to 40 dB or more inverse feedback which means that the open loop gain of the power amp circuit is 20 to 40 dB more than whatever gain the amp has with the inverse feedback loop closed. However, when the output stage saturates, it looses most if not all of its gain, and the excess gain in the driver circuits causes the signal voltage provided to the output stage to increase by from 20 to 40 dB or more. The QSC clipping circuit monitors the signal voltage at the input to the output stage and when it increases by 20 to 40 dB or more when the amp clips it activates the LED.

Amir if you can, get one of the big tech boys in your shop who actually takes the covers off of power amps and knows how to probe around inside them without hurting themselves or the amp show you how this works. ;-)

Or, add $100 to my Paypal account (arnyk@wowway,com) and I'll rip open one my QSC amps and post some information here about how the signal voltages inside the amp changes dramatically when it clips. ;-)

Again some variation in this happens in just about every SS amp. It is particularly pronounced in power amps with output stages that have gain, which is not always the rule. If the output stage has unity gain, you may have to back up a stage so that there is gain between the point you are probing and the amps output terminals.
Arny, do you have specific measurements of the QSC amp that shows the clipping light to come on for a 2 millisecond music transient at well under 0.05% THD? Can you demonstrate that you can see the LED blinking that fast? That is what we need to see. I provided measurements to back what I said and didn't ask you for $100. Let me remind you that you can't read the output of a digital scope correctly, didn't know what the power supply in an amplifier looked like, and didn't realize that power amplifiers use variable voltages so one channel can clip while the other does not.

These are some of the other statements that need specific backup made in the other threads references earlier:
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Originally Posted by arnyk View Post

In general the only way to make a modern amp distort audibly is to clip it.
So if I showed you other ways it can happen, where would that leave your knowledge of amplifiers? Did you see the waveforms I showed? How come they don't look like textbook clipping? What leads to the shape of the waveforms being what they are?
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Originally Posted by arnyk View Post

The fact is that a power amp driving a speaker load with music is not working a fraction as hard as it does on a test bench with a resistive or even speaker load, amplifying test signals to near full output. Music is easier to amplify than than full-output test tones because it varies its level so much and because it it not a pure tone. Speaker loads are easier on most parts of a modern power amp than resistive loads, no matter what yu may hear which is based on how amps were 40 years ago. This is clearly observable in real life.
You want to demonstrate with real measurements how no music can be harder to reproduce than test tones? You can't think of anything harder to reproduce than a sine wave? Be sure to not confuse peak and average power.

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post #833 of 1044 Old 11-30-2013, 05:00 PM
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Originally Posted by stereoforsale View Post

Ok, great point, but that leads me back to something I said earlier: why do tower L&R speakers need more power than other smaller speakers, to which everyone said "they don't". I understand that smaller speakers are less sensitive, but they also produce much less bass, so I thought they needed less power than full range tower speakers. Clearly I'm missing something. I'm not trying to be difficult, but from a layman's point of view it's hard to make sense of all this. smile.gif

sfs,
Don't sweat it. Its easy to get confused when trying to absorb a lot of new information outside of a structured classroom. The need to sort out the misinformation makes it that much harder. But its free advice! So hey, quite a bargain!

That said, you misinterpreted DonH50's comments. His explanation of power needs rests on the difference in content found in each of the surround sound mix channels (Dolby, DTS, what have you), not the sensitivity of the speakers. His point is that power needs are greater in the l/r channels when compared to the center, because the l/r signals include lower bass frequencies.

Personally, I find Amir's pronouncement that the center channel puts out a massive amount of soundtrack energy to be pretty bizarre; given its primary role outputting/anchoring movie dialog.
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Originally Posted by UndersAVS View Post

Quote:
Originally Posted by stereoforsale View Post

Ok, great point, but that leads me back to something I said earlier: why do tower L&R speakers need more power than other smaller speakers, to which everyone said "they don't". I understand that smaller speakers are less sensitive, but they also produce much less bass, so I thought they needed less power than full range tower speakers. Clearly I'm missing something. I'm not trying to be difficult, but from a layman's point of view it's hard to make sense of all this. smile.gif

sfs,
Don't sweat it. Its easy to get confused when trying to absorb a lot of new information outside of a structured classroom. The need to sort out the misinformation makes it that much harder. But its free advice! So hey, quite a bargain!

That said, you misinterpreted DonH50's comments. His explanation of power needs rests on the difference in content found in each of the surround sound mix channels (Dolby, DTS, what have you), not the sensitivity of the speakers. His point is that power needs are greater in the l/r channels when compared to the center, because the l/r signals include lower bass frequencies.

Personally, I find Amir's pronouncement that the center channel puts out a massive amount of soundtrack energy to be pretty bizarre; given its primary role outputting/anchoring movie dialog.

I take it that Amir isagain recounting accepted wisdom (IOW potentially audiophile myth) in high end audio circles. I have a number of classical and one popular multichannel FLAC files to evaluate. and they show no such build up in the center channel.

I'm close to having the means to capture my own multichannel files from pre-recorded media. I tend to agree with your thoughts, but they only relate to those situations where the L & R channels are large.

http://www.2l.no/hires/

My 3.2 system uses the identical same speakers for LCR and all 3 are set small (60 Hz crossover picked by Audyssey) so when I get it instrumented and can measure it accurately, I'll probably come up with different results.

I suspect that the idea that a lot of power is going to the center channel is reinforced by the fact that both the real center channel and any residual phantom center channel due to the L&R speakers ends up in the same place, perceptually.
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post #835 of 1044 Old 11-30-2013, 05:35 PM
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Quote:
Originally Posted by amirm View Post

Quote:
Originally Posted by arnyk View Post

Here's what happens. In the QSC power amp circuit (and just about any SS amp), the whole amp is inside an inverse feedback loop. Typically power amps have from 20 to 40 dB or more inverse feedback which means that the open loop gain of the power amp circuit is 20 to 40 dB more than whatever gain the amp has with the inverse feedback loop closed. However, when the output stage saturates, it looses most if not all of its gain, and the excess gain in the driver circuits causes the signal voltage provided to the output stage to increase by from 20 to 40 dB or more. The QSC clipping circuit monitors the signal voltage at the input to the output stage and when it increases by 20 to 40 dB or more when the amp clips it activates the LED.

Amir if you can, get one of the big tech boys in your shop who actually takes the covers off of power amps and knows how to probe around inside them without hurting themselves or the amp show you how this works. ;-)

Or, add $100 to my Paypal account (arnyk@wowway,com) and I'll rip open one my QSC amps and post some information here about how the signal voltages inside the amp changes dramatically when it clips. ;-)

Again some variation in this happens in just about every SS amp. It is particularly pronounced in power amps with output stages that have gain, which is not always the rule. If the output stage has unity gain, you may have to back up a stage so that there is gain between the point you are probing and the amps output terminals.

Arny, do you have specific measurements of the QSC amp that shows the clipping light to come on for a 2 millisecond music transient at well under 0.05% THD?

Depends on the rep rate of the 2 millisecond tone burst.

My claim related to a sine wave.
Quote:
Can you demonstrate that you can see the LED blinking that fast? That is what we need to see. I provided measurements to back what I said and didn't ask you for $100.

Amir, you've missed the point - you claim to be self-sufficient for measurements.
Quote:
Let me remind you that you can't read the output of a digital scope correctly,

Amir, let me remind you that you are being very ugly about this. I can read digital scopes and instrucments like them just fine when they are in my hands.
Quote:
didn't know what the power supply in an amplifier looked like, and didn't realize that power amplifiers use variable voltages so one channel can clip while the other does not.

That was all due to your poor documentation, Amir.

Any fool can make a mystery out of a normally clear situation. ;-)
Quote:
These are some of the other statements that need specific backup made in the other threads references earlier:
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Originally Posted by arnyk View Post

In general the only way to make a modern amp distort audibly is to clip it.

So if I showed you other ways it can happen, where would that leave your knowledge of amplifiers?

Amir, if you showed other ways to do it, you would be showing why I said "in general" and not "all the time". ;-)

I know other ways to do it and I believe identified them while you were still in high school, but I also know how common they are in the real world.
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Did you see the waveforms I showed? How come they don't look like textbook clipping? What leads to the shape of the waveforms being what they are?

Two words: Switchmode amp.
Quote:
Quote:
Originally Posted by arnyk View Post

The fact is that a power amp driving a speaker load with music is not working a fraction as hard as it does on a test bench with a resistive or even speaker load, amplifying test signals to near full output. Music is easier to amplify than than full-output test tones because it varies its level so much and because it it not a pure tone. Speaker loads are easier on most parts of a modern power amp than resistive loads, no matter what yu may hear which is based on how amps were 40 years ago. This is clearly observable in real life.

You want to demonstrate with real measurements how no music can be harder to reproduce than test tones?

Not at all, because I've already done so, and the theoretical reasons why are very clear. I've posted them on AVS many times.

Also, you've rephrased my clear claim into a trick question, and I love to frustrate people who post deceptively. ;-)

Just to review here are two strong theoretical reasons:

(1) Crest factor of the signal being reproduced, high crest factors usually lighten the load on the amp.

(2) Average impedance of the load - while speakers can dip low for certain bands, accross the entire audio band they average out higher.
Quote:
You can't think of anything harder to reproduce than a sine wave? Be sure to not confuse peak and average power.

I can easily think of something harder to reproduce than sine waves. It can be square waves or other low-crest factor waves that usually turn out to be similar to them.
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post #836 of 1044 Old 11-30-2013, 05:58 PM
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I take it that Amir isagain recounting accepted wisdom (IOW potentially audiophile myth) in high end audio circles. I have a number of classical and one popular multichannel FLAC files to evaluate. and they show no such build up in the center channel.

I'm close to having the means to capture my own multichannel files from pre-recorded media. I tend to agree with your thoughts, but they only relate to those situations where the L & R channels are large.

http://www.2l.no/hires/

My 3.2 system uses the identical same speakers for LCR and all 3 are set small (60 Hz crossover picked by Audyssey) so when I get it instrumented and can measure it accurately, I'll probably come up with different results.

I suspect that the idea that a lot of power is going to the center channel is reinforced by the fact that both the real center channel and any residual phantom center channel due to the L&R speakers ends up in the same place, perceptually.

Regarding the comment concerning more bass in l/r front channels, I have little opinion. Like you, my subwoofer takes care of the lower frequencies, so I"m not worried about it either way. However, its hard to imagine why the movie soundtrack engineer would load up the center channel with more demanding content than the other two front channels. I suspect, action and musical scores sequences are as likely, if not more so to make use of the other channels. If Amir's explanations carry as much weight as they have in the past, I don't suspect a monoblock center channel amp is going into my system anytime soon ;-)

Have fun with the music files and thanks for the link. I might download a couple for listening. Now that I'm thinking about, it would be really interesting to see a few movie surround tracks analyzed.
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post #837 of 1044 Old 11-30-2013, 06:03 PM
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I take it that Amir isagain recounting accepted wisdom (IOW potentially audiophile myth) in high end audio circles. I have a number of classical and one popular multichannel FLAC files to evaluate. and they show no such build up in the center channel.
Audiophiles? Flac multi-channel? How did you connect movie soundtrack to those terms? You are confusing multi-channel music with movies Arny.
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My 3.2 system uses the identical same speakers for LCR and all 3 are set small (60 Hz crossover picked by Audyssey) so when I get it instrumented and can measure it accurately, I'll probably come up with different results.
3.2??? So much opinion on the topic and you don't even have a proper 5.1 system?
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I suspect that the idea that a lot of power is going to the center channel is reinforced by the fact that both the real center channel and any residual phantom center channel due to the L&R speakers ends up in the same place, perceptually.
Nope. You have to understand more about how movies are authored...

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post #838 of 1044 Old 11-30-2013, 06:09 PM
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Two words: Switchmode amp.

The first one he posted wasn't.... http://www.avsforum.com/t/1492314/question-on-bi-amping/660#post_24002262

It was a Yamaha AB amp. He also pointed out the non predicted clipping shape on that one too.
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post #839 of 1044 Old 11-30-2013, 06:11 PM
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Personally, I find Amir's pronouncement that the center channel puts out a massive amount of soundtrack energy to be pretty bizarre; given its primary role outputting/anchoring movie dialog.
That is why the channel is often called (dialog) but content producers long ago discovered that its use goes far past that Specifically, anything that is supposed to be in the middle of the screen needs to come out of center channel predominantly. If a car blows up there, you want the center channel to play that explosion the loudest. Having it come out of left and right will give you a fantom channel that has screwed up frequency response (due to comb filtering between the two channels). And the whole point of discrete multichannel is to not have to rely on phantom center.

This is a very little known fact to be sure. But it is a fact smile.gif. Here is a quick quote from Chris Kyriakakis of the Audyssey fame on this topic: https://audyssey.zendesk.com/entries/231579-center-speaker

"I don't consider the center speaker as an optional improvement. If your goal is to listen to the content the way it was created then it is an absolute necessity. Stereo was invented at Bell Labs in the 1930s with three channels! Left, Center, Right. It was because there was no medium to deliver proper stereo to consumers that it was limited to two channels on LPs. There is nothing perceptually correct about two-channel stereo because there is really no correspondence between the two speakers and our two ears. In fact, there are frequency response problems that are caused by phantom images. Sound from the left speaker reaching the right ear interferes with sound from the right speaker reaching the right ear because they arrive at different times. The same happens on the other side. This interference causes response problems in the midrange that are solved by a real center speaker. For movies, the majority of the content is in the center channel. It requires the most dynamic range and proper directivity. It is unfortunate that the industry in the early days tried to diminish the importance of the center speaker. "

Maybe I should have kept that secret tip to myself smile.gif.

Amir
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post #840 of 1044 Old 11-30-2013, 06:35 PM
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Originally Posted by UndersAVS View Post

sfs,
Don't sweat it. Its easy to get confused when trying to absorb a lot of new information outside of a structured classroom. The need to sort out the misinformation makes it that much harder. But its free advice! So hey, quite a bargain!

That said, you misinterpreted DonH50's comments. His explanation of power needs rests on the difference in content found in each of the surround sound mix channels (Dolby, DTS, what have you), not the sensitivity of the speakers. His point is that power needs are greater in the l/r channels when compared to the center, because the l/r signals include lower bass frequencies.

Personally, I find Amir's pronouncement that the center channel puts out a massive amount of soundtrack energy to be pretty bizarre; given its primary role outputting/anchoring movie dialog.

Not to go off on a tangent, but when I asked "why do larger speakers need more power", I was assuming the AVR/pre-pro set the smaller speakers to "small" so all the bass was going to a subwoofer, which I think was akin to Don's comments about the C vs. L&R. So I don't think I misunderstood Don's comments. Perhaps I didn't ask the question properly.

So the question is: with respect to speakers within the same series, do smaller ones (which are set to "small") need more or less power than larger speakers (which are set to "large")? I thought the bigger ones would need more power, which is what I thought Don was also saying. Regarding the sensitivity issue (which I did not bring up, but others did to explain why I was wrong), I'm not sure it is relevant once you set the smaller speakers to "small" and are using a subwoofer.

BTW Audyessy sets my L & R to "large" and "full range"... yes, I tried increasing the crossover to take some pressure off the L&R but the sound was way too boomy. So my point/question was I assumed my L&R speaker needed more power than my other smaller speakers that are set to "small", notwithstanding the larger speakers have a higher sensitivity.
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