Bi-amping B&W CM10 - Page 4 - AVS Forum
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post #91 of 651 Old 12-28-2013, 06:42 AM
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Originally Posted by arnyk View Post


I hope this dispels the audiophile myth that only large amps can control speakers or that they have some kind of inherent advantage. Yet another idea that seems intuitively clear but doesn't hang together in the real world. Negative or inverse feedback is usually introduced in junior/300 level engineering courses but it is a complex area and I did PhD level work in that area. One of the more interesting problems in feedback-based automatic control systems is controlling a very large rocket. Think of it as a flexible water hose that you are trying to balance in the palm of your hand. Just for fun all of your position sensors are vibrating like the dickens due to the blast of the rocket engine and there is a stiff side wind. Audio power amps aren't rocket science!

And then there is the Audioholics article on damping factor that futher dispels common belief that high DF numbers are essential/big deal.

http://www.audioholics.com/audio-amplifier/damping-factor-effects-on-system-response

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post #92 of 651 Old 12-28-2013, 08:14 AM
 
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So a high damping factor means a low output impedance???

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post #93 of 651 Old 12-28-2013, 08:34 AM
 
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I think some of you are just discounting the need for power amps in consumer systems. Those CM10s are big speakers, and you need ample power to get them to sound their best.


Thinking you can use a garden variety AVR to extract the full potential from these speakers is a very unwise move.

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post #94 of 651 Old 12-28-2013, 08:40 AM
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Originally Posted by Shaun B View Post

I think some of you are just discounting the need for power amps in consumer systems. Those CM10s are big speakers, and you need ample power to get them to sound their best.


Thinking you can use a garden variety AVR to extract the full potential from these speakers is a very unwise move.
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Recommended amplifier power 30W - 300W into 8Ω

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so how much power do they need? i'm confused! seems like many many avr's are capable of delivering power within the manufactures published specs. confused.gif

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post #95 of 651 Old 12-28-2013, 08:43 AM
 
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It's not just about wattage. It's about current. Power amps can supply more current to the speakers. AVRs have very puny power supplies. You can't compare an AVR whose power supply is shared by all channels to a dedicated power amp.


Not about wattage. It is about current.

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post #96 of 651 Old 12-28-2013, 08:46 AM
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Originally Posted by Shaun B View Post

It's not just about wattage. It's about current. Power amps can supply more current to the speakers. AVRs have very puny power supplies. You can't compare an AVR whose power supply is shared by all channels to a dedicated power amp.


Not about wattage. It is about current.

so 1 watt of power from a low current power supply is somehow different from 1 watt from a high current power supply?

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post #97 of 651 Old 12-28-2013, 10:09 AM
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Originally Posted by Shaun B View Post

It's not just about wattage. It's about current. Power amps can supply more current to the speakers. AVRs have very puny power supplies. You can't compare an AVR whose power supply is shared by all channels to a dedicated power amp.


Not about wattage. It is about current.

And power (wattage as you put it) is the product of voltage and what?
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post #98 of 651 Old 12-28-2013, 10:37 AM
 
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And power (wattage as you put it) is the product of voltage and what?

 

Current. But you can have an amp which has low current and high voltage to equal the same power. One amp at 100 watt can have a high current design. A garden variety AVR can have 100 watt, like a run of the mill Sony, and it won't be high current. Lots of watts, but very little current.

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post #99 of 651 Old 12-28-2013, 11:25 AM
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Originally Posted by Shaun B View Post

Current. But you can have an amp which has low current and high voltage to equal the same power.

Amps amplify voltages - specifically the AC voiltages provided by the preamplifier. The voltage at the speaker terminals is whatever the output of the amplifier is. It isn't higher voltage or lower voltage. It is simply the voltage that is the end result of the amplification. It is determined by where you sent the volume control on the preamplifier. It is fixed in that sense. Power is dissipated when you connect a load to the terminals and current flows. That doesn't change the voltage. It affects the power dissipation.

It is possible for the load to draw more current than the amplifier can deliver without overheating. That is a function mostly of the current capacity of the power supply and the type and cooling capability of the final amplifier output stage. Yes it is possible to to build an amp that can deliver more current without overheating and it is done every day. But that has no benefit whatsoever if the load isn't drawing more current than the amp can handle. In other words having 500 watts instead 50 watts available doesn't matter as long as the load is dissipating less than 50 watts. Unused power doesn't contribute anything. The 50 watts from the 500 watt amp isn't any better than the 50 watts from the 50 watt amp.
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One amp at 100 watt can have a high current design. A garden variety AVR can have 100 watt, like a run of the mill Sony, and it won't be high current. Lots of watts, but very little current.

Now we are at the point of dealing with speaker impedance. We know that the lower the impedance of the speaker, the more current it will draw to reach the same SPL from the speaker. What happens is that, since the voltage is the same regardless of the load and the current increases, the power dissipation increases. That is why amplifiers normally have a higher power rating into lower impedances. What that means is that the high current amp design to which you refer can deal with lower impedances at a given SPL than one with a lower current delivery capacity. There are limits to every amplifier's performance and the "high current" amplifier has a higher limit.

But here is the catch. The ability of the amplifier to deliver current is rated at full power. Since we hardly ever, if ever reach full power from something like a 100 amplifier, the impedance rating becomes less important. The amplifier will always handle a lower impedance at a lower level of power dissipation. The full power impedance rating is a worst case rating. So, when the speaker is dissipating, say, 20 watts, it may not matter how much current is flowing because we aren't near full rated output power. You know as well as I do, that the speaker manufacturers put nominal impedance ratings on speakers that are usually "optimistic." Yet the receivers to which they are connected are not burning up. Why? Because they are overpowered for the job at hand. This is for the protection of the manufacturer who doesn't want people burning up their product or hearing distortion. They don't have to handle the extremes at which things like current delivery become important. Amplifier power is probably the biggest red herring in all of home audio. It just isn't a problem except in extreme situations.

I'm not against powerful amplifiers. I just think people buy them for the wrong reasons. I'm not even against their buying them for the wrong reasons. I just think it is better that they understand the situation so that their decision, whatever it is, is an informed decision.
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post #100 of 651 Old 12-28-2013, 11:28 AM
 
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The 50 watts from the 500 watt amp isn't any better than the 500 watts from the 50 watt amp.

 

Uh, 500 watts from a 50 watt amp? In what universe is that possible?

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post #101 of 651 Old 12-28-2013, 12:05 PM
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Originally Posted by Shaun B View Post

I think some of you are just discounting the need for power amps in consumer systems. Those CM10s are big speakers, and you need ample power to get them to sound their best.


Thinking you can use a garden variety AVR to extract the full potential from these speakers is a very unwise move.

They need more power because they're big? Does the size of a speaker correlate with how much power it needs?

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post #102 of 651 Old 12-28-2013, 12:26 PM
 
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They need more power because they're big? Does the size of a speaker correlate with how much power it needs?

 

The quality of power is what is important. Throwing 100 watts from run-of-the-mill AVR is not the same as a Pass Labs amp. I've heard B&W 800's and 802s, with proper amplification using high current designs. The bass sections on those speakers sounded far more taut and clean with proper current behind them. Not just throwing watts around from an AVR. In fact I've tried a few AVRS before and the bass was reedy and sounded anemic at a realistic volume level.

 

Current, amperage is what is needed, not just throwing watts around. Some people seem to think all watts are created equal!

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post #103 of 651 Old 12-28-2013, 12:35 PM
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as far as i can tell, to those that make money off of selling hi-fi amps, nothing is ever good enough.
So what is your alternative? Believing some sensitivity spec created in best case situation for a speaker as to sell better? And plugged into a formula that can be way off for home listening environments? What do you think happens in your room when you add carpet? Does it not absorb sound energy? Isn't that energy produced by the amp? Where would you plug that into that formula? How about seating, furniture, curtains, absorbers on the wall, etc.? Where did your formula account for their acoustic response? Yes, I said "response" because the absorption is frequency specific. I know there is a desire to simply everything into a simple formula but science doesn't owe you a simple answer. Acoustics of a room can be quite complex when you are dealing with thousands of reflections there. The formulas were created for open space and large performance spaces. You can't blindly apply them to your very different listening room. You kneed to know concepts such as Critical Distance (Dc) which determine the drop off with distance. And even that is an approximation. Now imagine an open floor plan and all bets are off as any open wall means near 100% absorption.

So no, we don't get to define "good enough" with precision. The math could be way off. As I showed, just a 2 db error means you have to go from a 50 watt amp to 80 watts. Know what is behind the numbers before you use them. Ditto for the formulas. If you want to ignore the science, that's fine. But don't pound the table saying the rest of us have to do the same.

And what is good enough anyway? That is a subjective call. Take Arny for example. His "multi channel" solution comprises of just 3 mains speakers. He doesn't have the surrounds. That is good enough for him. It sure as heck is not good enough for me or countless enthusiasts watching movies. He is missing the ambiance, flyovers and any rear sound. But again, his solution fits his budget and modest goals for fidelity. To the extent that he doesn't go around telling people 3 channels is good enough, we don't get to do the same for power, fidelity level, expense.
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post #104 of 651 Old 12-28-2013, 12:40 PM
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Originally Posted by Shaun B View Post

The quality of power is what is important. Throwing 100 watts from run-of-the-mill AVR is not the same as a Pass Labs amp. I've heard B&W 800's and 802s, with proper amplification using high current designs. The bass sections on those speakers sounded far more taut and clean with proper current behind them. Not just throwing watts around from an AVR. In fact I've tried a few AVRS before and the bass was reedy and sounded anemic at a realistic volume level.

Current, amperage is what is needed, not just throwing watts around. Some people seem to think all watts are created equal!

Did you forget to read the previous several posts? Seems you're "throwing words around" without understanding their meaning.

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post #105 of 651 Old 12-28-2013, 12:57 PM
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Originally Posted by Shaun B View Post

Uh, 500 watts from a 50 watt amp? In what universe is that possible?

None but I want to thank you for pointing out the typographical error. The second 500 should be 50. I assume you understood that.
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post #106 of 651 Old 12-28-2013, 01:00 PM
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that would be absolutely amazing if true . wink.gif

www.allegrosound.com/Power_AllegroSound.html

As a little test, put in the numbers of your system in this calculator then tell me how much amp power it recommends for you.
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post #107 of 651 Old 12-28-2013, 01:04 PM
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Originally Posted by whoaru99 View Post

And then there is the Audioholics article on damping factor that futher dispels common belief that high DF numbers are essential/big deal.

http://www.audioholics.com/audio-amplifier/damping-factor-effects-on-system-response

The first table in that article calculats for a driver in a sealed enclosure. A more common ported speaker or even an open baffle speaker would be quite a different scenario. In a sealed speaker the air pressure resistance is obviously going to be the biggest factor.
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post #108 of 651 Old 12-28-2013, 01:11 PM
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Originally Posted by Shaun B View Post

The quality of power is what is important. Throwing 100 watts from run-of-the-mill AVR is not the same as a Pass Labs amp. I've heard B&W 800's and 802s, with proper amplification using high current designs. The bass sections on those speakers sounded far more taut and clean with proper current behind them. Not just throwing watts around from an AVR. In fact I've tried a few AVRS before and the bass was reedy and sounded anemic at a realistic volume level.

Current, amperage is what is needed, not just throwing watts around. Some people seem to think all watts are created equal!

Apparently my explanation didn't help. 100 watts is 100 watts. If that is the power dissipation of the system and nothing is clipping or distorting beyond spec, the source of the power is immaterial. The Pass amplifier is a great one and very strong. There is no question that it has higher limits for current delivery than an AVR. But below the limits, it doesn't matter. That's the crux of what I tried to explain to you. The Pass amp can handle more load than the AVR. But below the limits of the AVR, it doesn't do any better than the AVR. It's value arises when the limits of the AVR are exceeded. There are situations in which the limits of an AVR are exceeded. It is just that those situations are not common in home theaters. Is that explanation any better?

As to what you heard, that was the result of hearing bias. If it was a blind, level matched comparison, you wouldn't have heard any difference assuming nothing was operating beyond their limits. I say that with confidence because I've done a bunch of those bias controlled tests.
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post #109 of 651 Old 12-28-2013, 01:11 PM
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Originally Posted by FMW View Post

But here is the catch. The ability of the amplifier to deliver current is rated at full power. Since we hardly ever, if ever reach full power from something like a 100 amplifier, the impedance rating becomes less important.

And that assumption that nobody will hardly ever use the full power from a 100w amp is made by someone who listens at much lower volumes than average, uses ear plugs when he goes to a movie theatre because he finds them too loud, and incorrectly calculats for a 3dB drop off in volume for every doubling of distance from a speaker when in reality could be as much as a 6dB drop off for every doubling of distance.

His "but here is the catch" is just a bunch of misguided assumptions.
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post #110 of 651 Old 12-28-2013, 01:26 PM - Thread Starter
 
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www.allegrosound.com/Power_AllegroSound.html

As a little test, put in the numbers of your system in this calculator then tell me how much amp power it recommends for you.

 

Thanks for providing this calculator although I'm a little confused. The calculator Arnyk provided gives me very different results.

 

With the calculator you provided it says speaker sensitivity rating (1W/1M) + 5 dB. What does that mean, the +5dB? Does that mean if I put in 90 dB, it would be 95 dB?

 

According to the results, with 1 dB of headroom, I would need 71 watts, presumably into 8 ohms. So 142 watts into 4 ohms, assuming 4 ohm dips along the speaker impedance curve. That's much higher than the previous calculator where apparently I only needed 10 watts to hit the same SPL!

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post #111 of 651 Old 12-28-2013, 01:31 PM - Thread Starter
 
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As a little test, put in the numbers of your system in this calculator then tell me how much amp power it recommends for you.


Thanks for providing the link. For some reason I can't quote with links yet, not sure if that's because I'm a new member or not.

 

Anyways, the results of your calculator appear to give very different results compared to the one Arnyk provided earlier on in the thread. According to that calculator I would need 10 watts to hit 98 dB SPL, presumably into 8 ohms.

 

According to your calculator I would need 47 watts to hit the same SPL at the same distance (this is with zero headroom). Not sure why there is such a large difference. But like Amirm says, I don't know how much credence can be given to these calculators especially when no frequencies are specified! Could be 1kHz for all I know. As soon as I have 40 Hz signal, or 30 Hz, or 60 Hz, the power could double, or triple.

 

What do you think?

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post #112 of 651 Old 12-28-2013, 01:35 PM
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Originally Posted by Mekail View Post

Anyways, the results of your calculator appear to give very different results compared to the one Arnyk provided earlier on in the thread. According to that calculator I would need 10 watts to hit 98 dB SPL, presumably into 8 ohms.

According to your calculator I would need 47 watts to hit the same SPL at the same distance (this is with zero headroom). Not sure why there is such a large difference.

Did you add 5dB to the sensitivity of your speakers to account for room gain?
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post #113 of 651 Old 12-28-2013, 01:43 PM - Thread Starter
 
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Did you add 5dB to the sensitivity of your speakers to account for room gain?


I saw that, but I was a little confused as I did not know exactly why I had to add the 5 dB. I just put in 90 dB.

 

Anyways, I'll put in 95 dB and I'll report back :D Thanks!

 

Edit : So I need 18 watts to hit 98 dB SPL at 3 meters with 0dB headroom. Almost double what the other calculator suggested, unless this one includes other variables into the mix, or lacks them. Not sure.

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post #114 of 651 Old 12-28-2013, 01:52 PM - Thread Starter
 
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Originally Posted by Shaun B View Post
 

 

The quality of power is what is important. Throwing 100 watts from run-of-the-mill AVR is not the same as a Pass Labs amp. I've heard B&W 800's and 802s, with proper amplification using high current designs. The bass sections on those speakers sounded far more taut and clean with proper current behind them. Not just throwing watts around from an AVR. In fact I've tried a few AVRS before and the bass was reedy and sounded anemic at a realistic volume level.

 

Current, amperage is what is needed, not just throwing watts around. Some people seem to think all watts are created equal!

 

I also used to think the same thing. Intuition will tell you (well it told me) that a big amp with a quality power supply could supply quality power, from a low output level to a high output level especially compared to AVRs that feature a shared power supply.

 

Now I'm not so sure about this. If quality power is determined by lack of distortion, then below a certain point I would imagine AVRs to deliver power at very low distortion too. Not sure how low the distortion would be on the Pass Labs, but I suspect lower than most AVR's at the same power level. However what is probably more relevant is whether you can hear this low distortion in actual use.

 

However I'm not confident enough to answer that question for you.

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post #115 of 651 Old 12-28-2013, 02:06 PM
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Originally Posted by Mekail View Post

Edit : So I need 18 watts to hit 98 dB SPL at 3 meters with 0dB headroom.

And that is with 0dB headroom.

Now it comes down to how much headroom you want.

Run it again but with a desired 10dB headroom.
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post #116 of 651 Old 12-28-2013, 02:09 PM
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Originally Posted by Mekail View Post

I also used to think the same thing. Intuition will tell you (well it told me) that a big amp with a quality power supply could supply quality power, from a low output level to a high output level especially compared to AVRs that feature a shared power supply.

Now I'm not so sure about this. If quality power is determined by lack of distortion, then below a certain point I would imagine AVRs to deliver power at very low distortion too. Not sure how low the distortion would be on the Pass Labs, but I suspect lower than most AVR's at the same power level. However what is probably more relevant is whether you can hear this low distortion in actual use.

However I'm not confident enough to answer that question for you.

While there are many performance parameters for amplifiers, only three are audible. They are distortion, noise and frequency response. Modern solid state amps have inaudible distortion and noise and inaudible variations from a flat frequency response. In other words they represent a fairly perfected technology.

The high end of the industry exists for the same reasons in exists in other industries. An expensive Swiss watch won't keep time better than a cheap quartz watch. A Ferrari won't get you through rush hour traffic any better than a Chevrolet (or a Skoda, if you are in Europe.) An expensive amp won't deliver prettier music than an AVR either. But it has higher performance limits as I mentioned earlier. The question boils down to whether or not a particular installation requires those higher limits.
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post #117 of 651 Old 12-28-2013, 02:42 PM - Thread Starter
 
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And that is with 0dB headroom.

Now it comes down to how much headroom you want.

Run it again but with a desired 10dB headroom.

 

It tells me I would need 180 watts. Still I have no idea how this calculation was made nor at what frequencies. I know some people will say it's reasonable close to what you need, but how does anyone actually know?

 

If my room is open-plan and double the size of your room, I would imagine that would factor into how much power I would need, which is not factored into the calculator. If I have speakers that have 30 Hz bass extension and listen at reasonable volumes (let's say 95 dB peaks) with music that has bass down to 40 Hz, wouldn't that significantly change how much power I would need?

 

I would think so.

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post #118 of 651 Old 12-28-2013, 02:55 PM
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Originally Posted by Mekail View Post

If my room is open-plan and double the size of your room, I would imagine that would factor into how much power I would need, which is not factored into the calculator.

A big open-plan room - put in less room gain.

Of course these are only going to be rough ballpark figures. See Amir's post #103 above.
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post #119 of 651 Old 12-28-2013, 03:26 PM - Thread Starter
 
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Originally Posted by kiwi2 View Post


A big open-plan room - put in less room gain.

Of course these are only going to be rough ballpark figures. See Amir's post #103 above.


I read Amirs reply which I found useful because I have the same nagging questions concerning the calculator. Is there a more reliable method of determining how much power is drawn from the speaker? Or must I just be content with rough calculations that could be 3 dB or more out? :D

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post #120 of 651 Old 12-28-2013, 03:33 PM
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Originally Posted by FMW View Post

Apparently my explanation didn't help. 100 watts is 100 watts.
Only as far as resistive load with an idealized amplifier. Otherwise, *delivering* 100 watts is not the same for each amp. One may fail to get there while the other does.
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If that is the power dissipation of the system and nothing is clipping or distorting beyond spec, the source of the power is immaterial.
And what indication of distortion do you have in your amp? See the measurement i provided. Why are the tops and bottoms of the graph not flat lined like textbook clipping says it would? What causes them to have the shapes they have?
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The Pass amplifier is a great one and very strong. There is no question that it has higher limits for current delivery than an AVR. But below the limits, it doesn't matter. That's the crux of what I tried to explain to you. The Pass amp can handle more load than the AVR. But below the limits of the AVR, it doesn't do any better than the AVR. It's value arises when the limits of the AVR are exceeded. There are situations in which the limits of an AVR are exceeded. It is just that those situations are not common in home theaters. Is that explanation any better?
Do you have data that shows it is not common in home theaters? What are some examples of uncommon situations? What makes them uncommon?
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As to what you heard, that was the result of hearing bias. If it was a blind, level matched comparison, you wouldn't have heard any difference assuming nothing was operating beyond their limits. I say that with confidence because I've done a bunch of those bias controlled tests.
It could have been bias. At the same time, your ability to read minds and results of tests is just as fallacious. I have asked you repeatedly to document such tests that you have run and you have refused. So while your experience is convincing to you, it is neither here nor there without the protocol and results disclosed.

Amir
Founder, Madrona Digital
"Insist on Quality Engineering"

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