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post #241 of 309 Old 09-03-2014, 09:07 PM
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I know what I am hearing, but I don't understand it. Can someone please explain?
+++
Referencing Mr. M Code, Post #5 in this Amp FAQ thread
+++

AVR: Onkyo TX NR-717 125wpc 2 channels driven. I am driving 5.0 speakers, so 125/5 = 25 wpc, approximately.

Speakers: The 5.0 system is mismatched with speakers, but has a pair of huge Klipsch CF-4 (two 12" woofs, one 12" horn) for L/R. Center is a Dayton Audio MTM with 7" Usher mid/bass drivers and an Usher 1" dome tweeter. The surrounds are Bose 301 II's, with 8" woofs. Don't laugh, it really sounds pretty good.

The Onk Audyssey matches them up pretty well, and relative to reference, Audyssey sets the Klipsch at -5, the center at +4, and the Bose 301 at +3. At reference which is 82 on the 717, with 5.0 driven it plays as loud as I can stand it. My math says that 25wpc is driving each speaker pair, and seems to do the job quite well; it can rattle the pictures right off the wall, with chest thumping mid-bass. The sound quality is great, at all SPL levels.

What I don't understand is if I put the Onk into "All Speakers Stereo" it gets REALLY loud, maybe "punchy" is a better word. When I set the Onk to "Stereo Only" where it drives only the CF-4, it does not seem to be as loud, and usually doesn't sound as good as "All Speakers Stereo." My logic says that putting the full 125wpc into the CF-4 ought to be magnificent and sound better than everything else, but it isn't, it just sounds really good.

Granted, that I don't push anything to its full upper SPL limits, and 86 on the dial is as far as I push the Onk. Feel free to point out flaws in my logic, perceptions, or math.

Explanations?

Last edited by wvu80; 09-03-2014 at 09:29 PM.
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post #242 of 309 Old 09-03-2014, 09:19 PM - Thread Starter
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I have used 5 or 7 channel stereo. There's variables using that to consider. For example, I have a speaker almost right next to my left ear due to my setup. Sure, all the channels have been balanced, but it takes very little power for that one speaker to play loud. Then you 5 speakers adding their output to the overall volume. Thinking about it, it may take less power for a given overall SPL with the 5 channel "stereo" than with the usual layout.

Also, with sound coming from every direction and room reinforcement of the sound you have complex acoustics. Apparently it sounds better to you that way.

That's my thinking, nothing mysterious there I think. I do recall having a 600 series Yamaha 10+ years ago that had better sounding 5 channel stereo than it's replacement. NO clue how that could be. Too many variables

"But this one goes up to 11"
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post #243 of 309 Old 09-18-2014, 03:25 PM
 
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Post typo

Interesting writeup. If I can help proof though, I was confused by the writer's mixing of the word "its" and "it's". This issue was on and off, but made some sentences sound funny and others completely incomprehensible. For example, "There's two ways to damage a speaker - exceeding it is mechanical limits, or exceeding it is thermal limits." should have read, "There's two ways to damage a speaker - exceeding its mechanical limits or exceeding its thermal limits.". "That is it is supply voltage" should have been written, "That is its supply voltage". "As such it is relation to reality is limited." would have made more sense if it were printed, "As such, its relation to reality is limited.". And so on and so fourth...
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post #244 of 309 Old 09-18-2014, 04:13 PM
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It's a tech forum, not an English forum. You could probably spend the rest of your life nitpicking the English in AVS if you'd like.
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post #245 of 309 Old 09-18-2014, 07:26 PM - Thread Starter
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I admit I make that mistake. I have tried to fix the mistakes when I see them

"But this one goes up to 11"
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post #246 of 309 Old 09-18-2014, 07:28 PM - Thread Starter
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Quote:
Originally Posted by Channel 2012 View Post
Interesting writeup. If I can help proof though, I was confused by the writer's mixing of the word "its" and "it's". This issue was on and off, but made some sentences sound funny and others completely incomprehensible. For example, "There's two ways to damage a speaker - exceeding it is mechanical limits, or exceeding it is thermal limits." should have read, "There's two ways to damage a speaker - exceeding its mechanical limits or exceeding its thermal limits.". "That is it is supply voltage" should have been written, "That is its supply voltage". "As such it is relation to reality is limited." would have made more sense if it were printed, "As such, its relation to reality is limited.". And so on and so fourth...
Isn't it usually 'And so forth' ? I see a number of mistakes in your post actually

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post #247 of 309 Old 12-21-2014, 05:03 AM
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This is a great thread.
I posted URL for a bunch of new (and old?) amp buyers to review FAQ.

Mike

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post #248 of 309 Old 01-04-2015, 04:27 PM
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Quote:
Originally Posted by MichaelJHuman View Post
Amplifier FAQ

* How much power do I need?

A typical speaker might produce 85 to 90 dB SPL at one meter from the speaker with one watt of power ( as supplied by an amplifier.) As 85 to 90 dB is loud, I hope it's obvious it takes very little power to get subjectively loud sound.

As you increase volume, power needs will rapdily increase. You may have heard that you need to double power for each 3 dB increase in SPL. How much louder is 3 dB more? Some sources say "just" noticable. I think that's a fair explantion. You will notice a 3 dB increase, but it won't be dramatic.
To DOUBLE perceived loudness you will need a 10 dB increase in SPL. An increase in 10 dB SPL requires 10 times the power. In other words you need TEN TIMES the power for TWICE the perceived loudness.

Summarizing, you need very little power to get a loud music or movie, but as you increase volume you very quickly run out of power.

Speaker sensitivity, as mentioned above can be quite helpful in being able to play your system more loudly. The higher the sensitvity, the less power you will need to play at the same loudness. To some extent, sensitive speakers greater than 90 dB will cost more money than lower sensitivity speakers, so there is a financial trade off between amplifier power and speaker sensitivity. This is only a general observation.

In open space, for each doubling of distance away from a speaker, SPL will drop by 6 dB DPL. At 2 meters, SPL will be down 6 dB (from what it was at one meter). At 4 meters, 12 dB. In a room, the situation changes, as sound is reflected. With an SPL meter, you can get some idea of what the drop would be in your own room.

There are handy online calculators which can be help give you an idea (e.g. http://www.crownaudio.com/apps_htm/d...ct-pwr-req.htm
Your SPL will be higher with seven channels playing at the same time, than it would would say, two channels. I compared one channel playing to seven channels once, and got an increase of 3 dB SPL. I can't say if this is typical though.

You may ask why you need 100 or more Watts if you can play loudly with one Watt of power. I would say it's because sound is very dynamic, especially movies. If a movie's sound adheres to the THX standard, it's average level would be 20 dB below peak level. This means you need 100 times the power at peak level than average level. You may not need this much peak power for every channel at the same time. For movies, it's clear that the loud scenes in the movie are the scenes you need a lot of power for.

Using one or more more powered subwoofers will reduce the power your amplifier needs to power the other channels. Which is why it's typical to use the bass management available in most audio video receivers.

It might be helpful to have more power if you do a lot of music listening and are critical about sound quality. Distortion due to running out of power may be more obvious for music. This is because a lot of music has a lower dynamic range than movies, so the average level is higher and if distortion is happening, it might be more obvious.

Different individuals will have different sensitivity or interest in ensuring inaudible distortion. Therefore their interest in spending more money to ensure they are not hearing distortion due to running out of power will vary.

A number people like to throw around is THX reference level. This means your system can play EACH (excepting the subwoofer) channel at 105 dB. The subwoofer would have to play at 115 dB, and that's just for LFE - it does not include any bass signals crossed over from other speakers via bass management. I personally don't think this is an important goal unless you actually want to listen to movies this loud. If you can live with less SPL, you can likely save money.

I think that about covers the basics. In summary -
* Your power needs will vary a lot depending on listening tastes, your speakers, and how your speakers are positioned in your room
* You don't need a lot of power to play loudly
* You may need a lot of power if THX reference level is a goal

* How can I assure the best sound for my budget?

There are two answers to this.

One answer is to buy as much power as you think you will need, budget permitting. Compromising between power and budget is a good idea, as you can accept a 3 dB drop in SPL, which is not much of a drop in loudness and reduce power needs by half.

The other answer is that amplifiers can sound different, and you will have to take this into account. Quite a large number of blind listening tests have shown that amplifiers sound very similar. To take one extreme case, the most budget of Pioneer receivers was once involved in a listening test with much more expensive amplifiers. No one could do better than chance in identifying the Pioneer (statistically speaking). If someone tells you they heard a dramatic or a night and day difference by switching amplifiers, you may want to consider the possibility they are overstating the situation.

ALL amplifiers distort. None is perfect.

Distortion could be grouped into three general categories - noise, harmonic distortion, and non linear frequency response (these are my own broad definitions rather than a strictly academic set of defintions.)

Noise is an inescapable fact of the physics of electronics. Even the best amps can't eliminate noise. The good news is that noise can be very low when compared to the signal. A specification called Signal to Noise Ratio (SNR) is often given for amps. Say an amp has a SNR of 80 dB. That means the signal is 80 dB higher than the noise (100,000,000 times higher.) This is pretty good if you consider that an average room might have an ambient sound level somewhere in the range of 10 dB to 20 dB SPL. 80 dB above 10 dB (ambient) is 90 dB, which I would call loud. And 80 dB is not a particularly good SNR for an amp. With highly sensitive speakers, you may want an amp with better than average SNR.

Harmonic distortion means that if you feed the amp a sine wave signal, for example at 1 khz, unwanted waveforms at other frequencies will appear on the output. Harmonic distortion is measured as THD (Total Harmonic Distortion.) This measures what percentage of the amplified signal is made up of harmonic distortion. Most amps will have a very low THD spec. THD is not absolute, it varies depending on power output. An amp with what looks like a high THD (> .1% THD) will almost certainly have a lower THD at lower power output. THD levels on good amps are well below the point of audibility, which is 1% THD according to some studies. 1% is not an absolute though. Humans are more sensitive if the harmonic distortion is odd order and/or higher order. Higher order just means higher multiples of the base frequency. We notice distortion more if the harmonics are higher multiples of the base frequency. As an example, a 7 khz harmonic distortion component from a 1 khz test signal would be odd order and would probably considered to be high order.

The last type of distortion mentioned is frequency response non linearity. In other words, the amplifier does not respond identically to all frequencies. Ideally, if we want a perfect amplifier all frequencies would be treated equally. This is not the case in reality, but most amplifiers have excellent response linearity over the audio frequency range of 20 hz to 20 khz.

If you run out of power, the amplifier will distort the signal. If it's severe enough, it will be audible.

Now that I have mentioned these various types of distortion, I think it's safe to say a well designed amplifier will reduce these effects to the point of inaudibility. Because of this, and because of the conclusions from blind listening tests, it's not clear why some people hear differences in how amplifiers sound.

In spite of some common beliefs, I think it's safe to say the job of an amplifier is to amplify the input signal while adding as little as possible distortion. This is not always true in reality, but it should be the goal. The preamplifier, pre processor or other device hooked into the amplifier should apply tone controls, room correction and such and the amplifier should just do what it sounds like it does - amplify.

Some people will spend a lot of time and money finding that perfect amp. I can't think of any guidance here. Make sure you can return the amplifier if you don't like it, with small or no restocking fees, and try to minimize the cost of shipping where possible. Reviews may be helpful, but some of them seem of questionable value given that humans have been shown to have bias and that bias effects their judgement.

* Does too little power damage speakers?

You may see statements like this in various sources. "It's not too much power that damages speakers. Too little power damages speakers."

I feel this sort of statement deserves clarification.

In one sense, it's 100% wrong. Too much power damages speakers. This is not debatable.

There's two ways to damage a speaker - exceeding it's mechanical limits, or exceeding it's thermal limits. Both situations require "too much power." If you are pushing so much power to a speaker that it's woofer is experiencing overcursion, that's too much power ( it's not a pretty sound.) If you push sufficient power to a speaker for long enough, you can damage it's drivers. Voice coils in a speaker's drivers will heat up, and if they heat up too much, they will fail (this seems more common with tweeters than woofers.)

* Why do people say that too little power damages speakers?

If you play your system too loud, the amplifier will clip. Clipping means that the amplifier is trying to amplify the signal, but hits a limit. That limit is it's supply voltage. This supply voltage could be reduced by load on the power supply or the amplifier's limiter circuits kicking in to try to save the amplifer from the abuse you are trying to inflict on it.

When an amplifier clips the result is that average power increases more quickly than it would if the amplifier is not clipping. This topic is non trivial, and Rodd Eliott explains it better than I ever could so if you want the gory details, read this (http://sound.westhost.com/clipping.htm)

This increase in average power is the most likely reason for speaker damage.

Modern music is highly compressed which makes the situation worse. Average signal level is so high in compressed music, that the speaker drivers don't have as much time to cool down.

If you have sufficent amplifier power to avoid clipping, your chance of doing damage to your speakers will be lower.

Can you buy an amp with too much power? This seems possible. While many sources of online info say you can't have too much power, that's clearly an oversimplification. If you had a 1000 watt amp, and you connected one of those cheap portable 8 ohm speakers to it, which is designed for less than a watt of power, I am 100% sure you could damage it, and with no clipping present. This does seems like an unlikely scenario with normal speakers and with normal music/movie sources though.

* What specs are important?

Not many, except for power. And power is measured in different ways, so direct comparisons should be taken lightly.

Hopefully, power will be measured from 20hz to 20khz into 8 ohms (ideally also into 4 ohms,) at some low THD figure, such as .01 % THD. And hopefully this is a continuous power measurement as dictated by the FTC rules (in the US.) A multi-channel (more than two) amplifier may include an all channels driven measurement. If not, it will almost certainly put out less power into all channels. Some people have criticized the all channels driven measurement. The main reason is that when playing movies, the most common use for mult-channel amplifiers, it's said that max power will never be demanded from all channels at the same time. Personally, I think it's nice to know the ACD spec, but realize that in some cases, it might not be continuous (it may have been measured with a short duration "sweep".)

THD is considered important, but consider that any good amp designed for high fidelity will have very low THD. THD is not an absolute for a given amplifier. It will vary with power, and manufacturers may squeeze out a bit more power by measuring at a higher THD than another manufacturer. A commonly stated theory is that THD of below 1 % THD is inaudible. This is also not an absolute as human sensitivity to harmonic distortion varies depending on the type of disortion. For example, if you consider a musical chord, and consider the 2nd and 3rd notes as disortion, they are actually pleasing to listen to. But if you try to play an off note, it will be perceived of as discordant. On paper, it looks like the harmonic distortion for most amps should be inaudible.

The SNR (noise) spec could be important in some cases. It's measured as Signal to Noise ratio. It will usually be very high, at least in amps I have seen. If you consider that noise in a quite room may be no lower than 20 dB, and breathing is 10 dB, a SNR of more than 80 dB seems pretty good. If you have very high efficiency speakers, you might want to pay some attention to the SNR.

There are various other measurements, none of which are of real use. Slew rate does not tell you much, unless it was abnormally low (in which case, they are not going to list it Damping factor has been critcized as being pointless in a number of articles by knowledgeable people. Occasionally you will see some max current output measurement. Not sure what that tells us with no other info. For all I know, they shorted the all the amp's output terminals and measured the peak output amperage before it shut down or blew up.

* Do I need to match an amplifier's impedance (such as 8 ohms or 4 ohms) to my speakers?

A solid state amplifier does not have an impedance as such (tube amps are a bit different in this respect.)

Almost any audio amplifier will work with 8 ohm speakers (with some exceptions such as fixed voltage amps.) As you lower the impedance of speakers you connect to a amp, you place more demand on it. Lower impedance means more current will flow through it's output devices (usually transistors). More current means more heat.

4 ohm loads present a more difficult load for amplifiers. The lower impedance means electricity will flow more easily. That means the current flow will be higher. Higher current means more heat will develop in the amplifier, especially in the output devices. Amps typically have themal protection circuits. If you your amp is shutting down due to thermal overload, you are driving it too hard, not giving it enough ventilation, or the amp is not working properly.

Amplifiers sold for pro audio applications, and for home audio would usually be able to handle 4 ohm loads with no issues. Receivers may shut down under heavy load. Or perhaps their longevity could be reduced, because they were not really designed for 4 ohm loads. Lower impedance is not suggested, such as connecting two 4 ohm speakers in parallel.

* How do I connect an amplifier?

For connecting an amplifier to a source such as a pre processor, there are four standard connectons -

* Unbalanced RCA jacks
* Unbalanced 1/4" jack (aka phono jack)
* Balanced 1/4" (aka TRS)
* Balanced XLR

An unbalanced connection has two wires. One is a ground, the other carries the audio signal.

A balanced connection needs three wires. One carries the audio signal, another an inverted "copy" of the audio signal, and the third is a ground.

The cheapest method is probably RCA. This should work fine when the cable length will be short, and the device being connected lacks balanced outputs.

If an amplifier lacks RCA inputs, and your device has only RCA output, such as an Audio/Video Receiver, use a cable with RCA jacks on one side, and 1/4" cables on the other side. This will be an unbalanced connection.

If the device being connected to the amp has balanced outputs, it makes sense to use them. For home audio, this is often an XLR connector requiring use of an XLR cable. You may also have the option for a 1/4" connection. For balanced 1/4" connections, you must use a cable with TRS jacks on both sides. These will have two insulators on the jack, giving it 3 contact points. Hence the acronym TRS for Tip, Ring, Sleeve. This is also known as a stereo 1/4" jack (as opposed to a mono 1/4" jack with only two contacts.)

* What do input sensitivity and gain mean?

They measure the same thing.

Input sensitvity is simple to understand. If the input sensitivity is 1 volt, the amp will be able to hit full power with an input of 1 volt. A higher input sensitivty means you need more voltage to drive the amp to full power. Many receivers have a pre amp rated for 1 volt RMS, which means they may not be able to drive all amps to full power.

Gain is measuring the same thing as input sensitvity in a different way. I will give a handy formula -

Gain (as a multiple) = 10 ^ (gain / 20)
Divide gain (dB) by 20, and use inverse logarithm (base 10) on your calculator

For 32 dB, we would get a gain of 40 times.

To convert this to input sensitivity, we would use this formula -
Input sensitvity = sqrt(max_amp_power * 8) / gain_multiple

Assuming a 200 watt / channel amp into 8 ohms with a 32 dB sensitivity -

sqrt (200 watts * 8 ohms ) / 40 = 1 volt

So a 32 dB gain would mean a 1 volt input sensitvity. Higher gain means an amp will match better with processors, preamps and receivers with lower pre amp output.

* How do I bridge an amplifier

Some amplifiers can be bridged. Don't try to bridge an amplifier not designed to be bridged. See the manual for detailed instructions.

Bridging is pretty simple. Two of the amp's outputs are used for one speaker. This will double voltage, and quadruple the power. This requires that one signal uis inverted.

In a typical bridgeable amplifier you need to set a switch for bridge mode. You will then carefully note the wiring diagram in the manual and/or on the back of the amp, and connect your speaker to the indicated outputs on the amp.

* How important is an all channels driven power measurement

This is discussed better than I can manage by other sources, such as Audioholics.com. I do have some thoughts on it though.
There's some factors to think about when considering how useful an all channels driven power rating is.

* Test signal correlation vs real audio correlation
* Test signal crest factor vs real audio crest factor
* Real world average power usage
* Law of diminishing returns

It's helpful to understand how an all channels driven test is conducted. It's done using test signals. The test signals are also likely correlated. By that I mean that they all peak at the exact same time. Music signals may tend to peak in the same spot, but are certainly not test tones. We don't expect all the channels in a movie soundtrack to peak at the same time ( based on various expert sources.)

Because test signals are likely correlated, by that I mean they peak at the same time this means the AVR/amplifier is being asked to provide peak power to all channels at the same time. Real audio is likely not like that especially movies (peaks in stereo music may happen at the same point in time.)

Crest factor is a measure of peak vs average level. A rough crest factor for movies might be 20 dB. That works out to require 100 times peak vs average power. All channels driven testing is very different than movie audio unless it's some sort of burst testing. As such it's relation to reality is limited.

Average power level may be quite low for a typical listening situation ( typical being very poorly defined, but it's the best I can do.) A typical speaker has a sensitivity close to 90 dB. That means it will put out 90 dB SPL with one watt of input. That's loud. There is some loss for distance. There's no great rule of thumb here, I use 6 dB. To output 90 dB factoring in the 6 dB loss for distance we need four times the power or 4 watts. A typical listener may listen a bit lower than that. For argument's sake let's say a typical listener listens 84 dB (which makes math simple too.) We are back to one watt. If peaks take 100 times the power that's 100 watts.

Using the above logic, we expect even budget receivers to manage this or manage it with minimal sonic impact. Consider that people usually use subwoofers taking a load off the receiver's power needs. Consider that every channel is NOT peaking at the same point in time according to various sources. Consider that even if the receiver runs out of power it's only for some brief moments. I once test Yamaha's cheapest receiver and did not find it wanting for movie use and moderate volume music use.

The final point is about the law of diminishing returns. Say we have an AVR which manages 100 watts peak per channel under real world listening. Well, say you don't believe that due to looking at all channels driven numbers. Let's call it 50 watts for argument's sake. So you buy an amp that can do 200 watts. Four times the power. Each doubling of power is a gain of 6 dB SPL ( sound pressure level.) That's louder but note that it takes 10 dB to double the perceived loudness. So it's not unreasonable to think we can't do much better than 6 dB more SPL even after spending a lot more money. My point is a person could save some money accepting whatever SPL their AVR could safely deliver without compromising a lot.


* What's the difference between solid state and tube amps

Perhaps the number one reason people state for buying a tube amp is that they say tubes have a warmer sound.

Tubes are less efficient, and potentially more fragile than solid state amps. To get a tube amp with the same power as a solid state amp, you would usually pay more more. High power tube amps are uncommon. Very few people would choose tube amps in a set up designed mainly for surround sound use, as the expense would be high, and they would take up more room.

Tube amplifiers may not measure as well as solid state amplifiers, Randy Slone mentions this in his book on high power amplifiers. There's a class of tube amps known as SET (single ended triode) amplfiiers. In bench tests I have seen for this sort of amplifier, they have measured very badly when compared to solid state amplifiers.

From an audio fidelity perspective, I could find no evidence that tube amplifiers are more accurate than solid state amplifiers. A number of sources said that tube amps can be more linear and thus would need less negative feedback. This would be an advantage if negative feedback was a bad thing. A number of audio designers have specifically addressed criticisms of negative feedback, and have rejected the criticisms. There are audio designers who seem to dislike negative feedback however.

Is there a reason the sound of tube amps is preferred to solid state amplifiers by some people?

One often stated reason is that tube amplifiers sound better due to second order hamonic distortion. Rather than being discordant, second order harmonic distortion is said to sound pleasant. So even though it's distortion, it's pleasant sounding distortion.

Vaccum tube amps are said to sound better then they are overdriven than solid state amplifiers. This would help explain their popularity as guitar amplifiers.

For more information, I suggest doing a search online for 'tube sound.' You should be able to read about studies that have been done which better explain the technical details on how solid state amplifiers and tube amplifiers can sound different.

* What are amplifier classes?

This is covered in numerous places online in better detail. And in general, it's not that important. If an amplifier is lighter than other amplifiers of the same power output, it is helpful to know what design it uses. If the lighter amp is more efficient, such as class D, the difference in weight can be understood.

Class A - Theoretically the amp with the least distortion. The downside is that it will be more expensive, heavier, run hotter, and be less efficient than a class AB amp. Two writers of two books on amplifier design, Self and Slone downplay the real world advantage of this design. Put simply, the design is inefficient, because the transistors are "fed" a bias current such that they are always on when the amp is turned on. This means that with no signal, the transistors still consume a lot of power, which is wasted power, and dissipated as heat.

Class B or AB - Used in receivers, and most other power amps. The downside of class B or AB amps is crossover distortion. There are two sets of output devices (e.g. transistors.) If the audio signal is positive, one set is used for amplification, and if negative the other set is used. Both sets of output devices are not always on, making this design more efficient than class A. When the audio signal passes through 0 volts from positive to negative, or vice-versa a "glitch" occurs in the point of crossover. There are ways of dealing with this issue, which is good news as this is the most common design in amplifiers. The only difference between pure class B and class AB is that the class AB biases the output devices such that they conduct for more of the cycle. Some people extol the virtues of class AB, but not everyone agrees ( See Audio Power Amplifier Design Handbook by Douglas Self for the details.)

Class D - An more efficient when compared to other all other designs. The design is interesting. The incoming signal is converted to a square wave, where the duration of the pulses in the signal carry the audio signal. This signal is then used to switch on and off the power transistors in the output stage leading to a very high efficiency. This is called switch mode, and class D amplifiers are sometimes called switch mode. Another name for class D is PWM because the audio signal is converted to a Pulse Width Modulated signal. Along with the efficiency comes a decrease in weight. These amps are very common in powered subwoofers and the pro sound amp market. They seem to be slowly becoming more common. There's one line of Pioneer receivers now using them. Time will tell if they overcome the popularity of class AB. Note that class D does not mean digital. The term digital is often applied when the class D amplifier's input is a PCM signal rather than an analog signal (the amp can directly convert the PCM signal to the PWM signal used to drive the output devices.)

Class G/H - Amplifiers which improve efficiency by using more than one supply voltage. They otherwise work like class B amplifiers. If an amplifier's power supply voltage was exactly what was needed at any instant in time, it's more efficient. Class G and H differ in how this is done, neither achieves the goal of suppling the exact voltage needed. A class H amplifier has an infinitely variable power supply voltage. A class G amplifier has two or more supply voltages.

Switching power supply amps - This is not an amplifier class. But an efficiency can be gained by using switching rather than linear power supplies. Transistors in circuits are said to operated in linear mode or switch mode. In switch mode, they are turned on or off, there's no intermediate state. In linear mode, they are fed varying amounts of current. Switching power supplies are used in computers. Switch mode power supplies are seeing more use in pro audio amplifiers. They are uncommon in home audio at this point in time. Your typical home audio amplifier uses an unregulated power supply (see the section on "How do amplifiers work")

* How do amplifiers work?

A brief explanation of how amplifiers work might be helpful.

This section will explain the most common amplifier design - a three stage class B amplifier using an unregulated power supply.

The amplifier's "heart" is the power supply. The power supply transformer puts a limit on how much power the amplifier can produce. Bigger is better in this case, and very high power amplifiers of the type we are discussing here can weigh over 100 pounds.

A typical unregulated power supply is really simple. The incoming AC voltage (120 Volts in the US,) would typically be lowered to a smaller voltage. Higher amps would need a higher voltage. A bridge rectifier then converts this smaller voltage into a postive and negative DC voltage. An audio signal will alternate between positive to negative (it's alternating current.) Class B (or AB) amps need two voltage "rails" as they have two "sides" one of which amplifies the positive part of the signal, and the other the negative part.

The typical three stage amplifier has the following stages -

* Input stage; converts the alternating voltage input to an alternating current signal
* Voltage amplifier stage; the signal will be increased to a much higher voltage
* Output stage; This could be considered to be a current amplifying stage - or to put it another way perhaps, it buffers the voltage amplifier stage from the speakers, and allows the amplifier to provide the potentially large current needed by the speakers

The goal of the input stage is to convert the input signal where a changing voltage is converted to a changing current while introducing little additional noise and distortion. It also needs to cope with ripple from the power supply, which is not providing a perfectly constant DC signal. The input stage also takes feedback from the output to lineraize (reduce distortion.) There are quite a few sources of distortion in an amplifier, and feedback is used to reduce them.

The voltage amplifier stage (VAS) is doing the real amplifying of the input signal. The input signal might be one or two volts at maximum, and the output from the VAS will be tens of Volts. For example in my receiver, it's max voltage is going to be close to 70 Volts.

The output stage does the heavy lifting. The output devices, commonly bipolar junction transistors (MOSFETs are also used,) are connected directly to your speakers. The current flowing through the transistors can be very high. Consider a 100 Watt amp connected to a 4 ohm speaker. Voltage would peak around 24 Volts. Current would be be pushing 6 Amperes peak. If you don't think 100 Watts is a lot of power, consider how you almost certainly have no desire to touch a hot 100 Watt light bulb. Don't do it, you will get a painful burn.

An amplifier is not that complex a device in some ways, and there has been little change in it's basic design for a long time (I believe the basic 3 stage amp design has been around since an RCA engineer developed it in the 1950s)
Great description! Now to go play with my mic and spl meter.
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Although it is easy to provide almost any speaker with the power needed to provide 90 dB at 1 meter, very short, very loud peaks require quite an increase in power. Modern motion picture standards (Audyssey, THX, etc.) demand peaks through the main speakers of up to105 dB, and through the subwoofer (which almost always has its own amp) of up to 115 dB, both from the listening position, which, in the home, could be anywhere from about 5 to 20 feet. Paul W. Klipsch said that to reproduce the "blood stirring" peak levels of a large symphony orchestra, you need "115 dB at your ears." I believe he arrived at that figure by repeatedly measuring the SPL of the Arkansas Symphony Orchestra as he recorded them (his hobby).

Since the peaks being referred to are quite brief in most music, they are very unlikely to damage hearing. Music that has a more or less constant very loud level (some Rock, Metal, etc.) should be kept at a lower level.
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Originally Posted by garygarrison View Post
Although it is easy to provide almost any speaker with the power needed to provide 90 dB at 1 meter, very short, very loud peaks require quite an increase in power. Modern motion picture standards (Audyssey, THX, etc.) demand peaks through the main speakers of up to105 dB, and through the subwoofer (which almost always has its own amp) of up to 115 dB, both from the listening position, which, in the home, could be anywhere from about 5 to 20 feet. Paul W. Klipsch said that to reproduce the "blood stirring" peak levels of a large symphony orchestra, you need "115 dB at your ears." I believe he arrived at that figure by repeatedly measuring the SPL of the Arkansas Symphony Orchestra as he recorded them (his hobby).

Since the peaks being referred to are quite brief in most music, they are very unlikely to damage hearing. Music that has a more or less constant very loud level (some Rock, Metal, etc.) should be kept at a lower level.
I think 115 dB peaks may make sense in an orchestra hall, but in an untreated home listening space may not work. Also your speakers have to be up to the task without compressing.

I find -10 dB levels are good for movies. But others will desire more.

"But this one goes up to 11"
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Amplifier FAQ

* How much power do I need?... you need very little power to get a loud music or movie, but as you increase volume you very quickly run out of power.
Is this a reference to "Headroom"? Using a good SPL meter I can see that, to my ears, 85 dB is pretty loud. My AVR (95 wpc / 2ch driven) when set at 0 dB is pretty loud, but not "very" loud, IMO. If I increased my volume, I feel as though I may get into the area of distortion in the AVR (I've never taken it past 0 so I really do not know what might happen). This should mean that I do not have enough headroom, right? Would going to a more powerful amp not only give me more headroom, but also, somehow give me better (perceived) sound through my speakers at the same SPL given that I'd be that much further away from the area of distortion?

Oh, and great FAQ thread, BTW. Very informative.
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Is this a reference to "Headroom"? Using a good SPL meter I can see that, to my ears, 85 dB is pretty loud. My AVR (95 wpc / 2ch driven) when set at 0 dB is pretty loud, but not "very" loud, IMO. If I increased my volume, I feel as though I may get into the area of distortion in the AVR (I've never taken it past 0 so I really do not know what might happen). This should mean that I do not have enough headroom, right? Would going to a more powerful amp not only give me more headroom, but also, somehow give me better (perceived) sound through my speakers at the same SPL given that I'd be that much further away from the area of distortion? ...
  • What is the rated sensitivity of your speakers?
  • 95 wpc 2/ch driven is a bit odd for a manufacturer's spec (many would fudge, and round up to 100 wts). Was this figure obtained from a bench test you or your service person did?
  • Do you run movies? If so, what is the RMS power per channel with all used channels operating (e.g. 5 for 5.1)?
  • To respond to your last question, at the same average SPL (say, 85 dB) with low dynamic range music it may sound the same, and with high dynamic range music a bigger amp might make it sound better on brief transients, such as cymbal crashes, rim shots, etc., or with especially loud passages that are longer (not composed exclusively of transients).
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Originally Posted by garygarrison View Post
  • What is the rated sensitivity of your speakers?
  • 95 wpc 2/ch driven is a bit odd for a manufacturer's spec (many would fudge, and round up to 100 wts). Was this figure obtained from a bench test you or your service person did?
  • Do you run movies? If so, what is the RMS power per channel with all used channels operating (e.g. 5 for 5.1)?
  • To respond to your last question, at the same average SPL (say, 85 dB) with low dynamic range music it may sound the same, and with high dynamic range music a bigger amp might make it sound better on brief transients, such as cymbal crashes, rim shots, etc., or with especially loud passages that are longer (not composed exclusively of transients).
92 dB mains, 91 dB center, 89 dB surrounds.
Denon AVR-X2000 - 95 wpc is the stated rating in the manual with 2 channels driven. Agreed - a little strange.
Mostly movies, so running 5.1 - actual would be likely somewhere around 45 - 50 wpc with all 5 channels driven.

I'm thinking a dedicated amp and pre/pro would open things up, but I was unsure on the concept of headroom and wanted to be sure I was interpreting it correctly.
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I think 115 dB peaks may make sense in an orchestra hall, but in an untreated home listening space may not work. Also your speakers have to be up to the task without compressing.

I find -10 dB levels are good for movies. But others will desire more.
I agree, but most people have at least a rug (or several). I used to run JBLs in a room with a Persian rug, two couches, and the rest bricks, glass, and hardwood, and hit 115 dB once in a while (Fanfare for the Common Man; The Great Gate of Kiev), and it sounded great. In our current room, (c. 4,500 cu. ft.) we have carpet, absorbers, and diffusers, and hit (by calculation) 100 dB on movies (running at about 5 dB below Audyssey determined reference level), and somewhat more on occasional musical selections, like the ones listed above. I am one of the others who will desire more.

I've heard that all loudspeakers compress at least a little. Mine have a rated efficiency of 105 dB @ 1W @ 1M, and 120 dB max output, although I'd never push them quite that far. I have little doubt that they are compressing a little, but there is no blatantly obviously distortion at higher SPLs than at lower levels. I get along fine with 150 wpc, all channels driven. Most of our music is classical, romanticist, modern orchestral, or jazz, plus movies, so there is a great deal of dynamic range. On the rare occasions we play rock/pop/metal, we play it softer, for our ears' sake.
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good info

mods, can we get a sticky on this?
Hi
I joined today and have been reading for hours. Your process and approach of the subject made sense. It improved my understanding. You managed to steer me through what was becoming an obstacle course of misleading information. Thanks for the Uturn.
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How many watts is enough, without reaching overkill status?

Hi all - Great FAQ! I am building a dedicated, full acoustically treated room and would love to get your thoughts on the best way to power it. The speaker set up will be a 9.1.6 Atmos setup. Initially I realize I will only be able to use it as a 9.1.2 or 7.1.4 (without buying a Trinov!), but eventually I suppose we'll have more channels available to use at the consumer level pricing. So I'm building in these capabilities now for a full 9.1.6 as to avoid doing reconstruction on the room down the road.

My speakers are all 4 ohm. The L/C/R (KEF Ci5160) are rated for max output of 250 watts. The other 6 listening-level speakers (KEF Ci3160) are rated for a max 180 watts. And my 6 in-ceiling Atmos speakers (KEF Ci200RR) are rated for max 190 watts. All of the speakers are listed as having 90 dB sensitivity 2.83V/1M.

Question 1: I'm trying to determine what level of power would be considered "plenty!" without it being overkill and would love your thoughts on it please. My goal is to reach THX reference level. The main seats are 13 feet away. The excellent online SPL calculators expect the dB sensitivity to be entered at 1V/1M. However in my case I only have the 90 dB rating in volts/meter. Since its a 4 ohm load, I'm not sure what value to put into the calculator for the calculator? Does the 90 dB need to be converted to a new number that changes it from the 2.83V/1M to the equivalent of 1V/1M?

Question 2: What are some good amp configurations in terms of number of channels and watts per channel to consider? One option is to consider an amp like the ATI 3007 that puts out 450 watts x 7. I would need two of them to power all channels except one. So that still leaves me one channel short. So perhaps two 7 channel amps isn't the way to go. Maybe three 5 channel amps like a ATI 3005 - that's 15 channels at 450. This however would be very costly, likely something like $12k. Or maybe three Parasound A51? Well I think that's even more expensive.

Question 3: Another option is to do a mix I suppose. Like 450 watts to the front L/C/R (most demanding for home theater plus I plan to do a quite a bit of 2.1 channel music listening), and then less watts to the other speakers. For example, the side surround speakers are only about 8 feet from me, so they require a lot less power than the front L/C/R (not to mention their wattage requirement is lower at 180 vs 250 max as mentioned earlier). Likewise the in-ceiling Atmos speakers are also relatively closer to me, plus how demanding are these speakers going to be for power if Atmos mainly is using them for diffuse sound and ambiance/effects. So the gist of this question is whether it is ok to mix and match wattages like this, as opposed to having the same watts going to all speakers?

Thanks guys! Any recommendations on watts to use, number of amps/channels to go with, brands of amps and approaches to take in general are greatly appreciated!!
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The excellent online SPL calculators expect the dB sensitivity to be entered at 1V/1M. However in my case I only have the 90 dB rating in volts/meter. Since its a 4 ohm load, I'm not sure what value to put into the calculator for the calculator? Does the 90 dB need to be converted to a new number that changes it from the 2.83V/1M to the equivalent of 1V/1M?
It is very weird for an online calculator to ask for the dB @ 1V @ 1M. The usual standard is dB @ [email protected], which is equivalent to dB @ 1 W @ 1M @ 8 ohms. Can you look again at the calculator?

Unfortunately, the calculators themselves vary. One of them (the Crown???) indicates that people need much greater power for a given Sound Pressure Level than the others.

When you find the calculator you want to use, go for the professional cinema standard of full scale (fs) of 105 dB peak through each regular speaker, and evaluate your powered subwoofer knowing that it would be expected to produce fs of 115 dB peak, on occasion. In a home sized room (3,000 cu ft) of average liveness, many people would set the main volume at 5 dB lower than reference, for most movies. This puts dialog at a realistic average SPL (in the mid '70s, with a range of maybe 50 for whispering to 80 something for raised voices), and everything else -- music, sound effects -- falls into place a la the film director's preference. You will need something to automatically or manually set up your equipment so that reference level is at a known setting of the Main Volume Control. Audyssey does a pretty good job of this. If you get or have an AVR or AV preamp/processor with Audyssey, IMO, the very best resource for setting it up is on the AVS forum, @ The Audyssey FAQ

My guess is that you should use amps equal to the maximum power handling of each speaker. For your fronts, 250 watts seems reasonable. But do use a calculator. A popular one is http://myhometheater.homestead.com/splcalculator.html
It is O.K., IMO, but his "How Loud is That?" chart is rather misleading, IMO. "Very loud" is more like 100/105 dB. In most kinds of music, only the transients reach that level (and very occasionally go to 115 dB, just for a moment, "fast" "C" weighted). Rock/Metal can sometimes be steadily at that level, and can damage hearing -- which is why the musicians wear earplugs, or tight fitting headphones being fed with a live mix with the volume turned down a bit. Notice that classical orchestra members only rarely wear earplugs. For a few movies, with the SPL pushed up against the top (Pacific Rim, etc.), I turn it down.

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Originally Posted by garygarrison View Post
It is very weird for an online calculator to ask for the dB @ 1V @ 1M. The usual standard is dB @ [email protected], which is equivalent to dB @ 1 W @ 1M @ 8 ohms. Can you look again at the calculator?
Yes all of the online calculators I have come across, including http://myhometheater.homestead.com/splcalculator.html which is the one you linked too and the one most people on AVS reference, all show that the dB sensitivity input should be in dB @ 1V @ 1M, not 2.83v/1M. So given 90 dB at 2.83V/1M, for a 4 ohm speaker how do you convert that 90 dB @ 2.83V/1M into a dB number that is equivalent to a 1W/1M number to be used in these calculators?

Quote:
When you find the calculator you want to use, go for the professional cinema standard of full scale (fs) of 105 dB peak through each regular speaker, and evaluate your powered subwoofer knowing that it would be expected to produce fs of 115 dB peak, on occasion. In a home sized room (3,000 cu ft) of average liveness, many people would set the main volume at 5 dB lower than reference, for most movies.
Yup, I'm aware of that and the goal of the calculator. Just don't know what dB I should use given that it want is in 1W/1M and I only have it in 2.83V/M. I meant to list it in my original post - my room is approximately 3900 cubic feet (30Lx17Wx7.5H). I should also mention that I will be using a prepro like the Marantz 8802 and separate amps (not interest or intention to try using an AVR for this). Also I do not intent to list at reference levels too often. I want the flexibility to do so from time to time, but more so than that, I want the extra headroom of the wide dynamic range that movies often require.

Quote:
My guess is that you should use amps equal to the maximum power handling of each speaker. For your fronts, 250 watts seems reasonable. But do use a calculator...
From what I've read, I don't think using an amp that rates at the maximum power handling for each speaker is anywhere near enough because of the headroom I mentioned. I've heard people on AVS say to use something like 1.5x - 2.0x times the maximum rated wattage of the speaker. I'm all for that if this is recommended - just want to make sure I don't have too much power that I am wasting money for excess headroom that will never even be close to being used or too much power that could wind up damaging the speaker.
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Yes all of the online calculators I have come across, including http://myhometheater.homestead.com/splcalculator.html which is the one you linked too and the one most people on AVS reference, all show that the dB sensitivity input should be in dB @ 1V @ 1M, not 2.83v/1M. So given 90 dB at 2.83V/1M, for a 4 ohm speaker how do you convert that 90 dB @ 2.83V/1M into a dB number that is equivalent to a 1W/1M number to be used in these calculators?
I looked at http://myhometheater.homestead.com/splcalculator.html again, and I don't see 1V anywhere. I see 1 W @ 1M, which the author says is the same as 2.83V @1M across 8 Ohns. Since KEF rates the sensitivity of your front speakers (at least) as 90 dB @ 2.83V, you can probably just go with that. Having a "nominal" impedance of only 4 Ohms is not a problem in and of itself (providing they don't drop very much below 4 Ohms somewhere in the frequency spectrum). Most speaker makers spec at 8 Ohms, since almost all Solid State amplifiers have an 8 Ohm tap only, unlike with tubes). Since you are concerned about headroom, you could arbitrarily add 3 dB to your Front channel estimated power needs (twice the amplifier power in watts). With the 3 dB increase, 500 watts should produce almost 110 dB @ 13 feet in a big room like yours, which is 5 dB greater than standard fs at reference level on your MVC. 250 watts should produce almost 107 dB, which is still over fs demands. I assume you are using a powered subwoofer. If you crossover at 80 Hz (standard) for bass management, while setting the LPF for LFE at 120 dB (standard), and set your main speakers for "small" (recommended), a fair amount of burden for music & dialog, and a great amount of burden for special effects will be taken off of your main speakers. But you should wait until someone else answers.

Good for you for not planning to use an AVR. Most AVRs are advertised at a given power per channel "with 2 channels operating," rather than with all channels operating. According to bench tests in many magazines, with all channels operating, they only put out about 80% of their rated power into each channel. High quality separate power amps, even with many channels, tend to put out their rated power into all of their channels, with all channels operating. Their "rated power," while less misleading than AVR ratings, still might not be as conservative as the RMS power per channel at which amps used to be rated. My separate power amps, for instance, were rated at 150 w.p.c, but when the dealer put a sine wave into all channels, turned the volume up until he could barely see flattening -- clipping -- and then backed it off to get rid of the clipping, he got 171 watts per channel, all channels operating. To estimate the old standard of RMS, you multiply by 0.707, which produced 120.89, so I have power amps rated at 150 w.p.c, less misleadingly than with most AVRs, but with the approximate equivalent of 121 w.p.s., RMS, all channels operating. That's O.K. for me, because my speakers are about 105 dB @ 1W @ 1M.

I'm biased in favor of a Preamp/Processor with at least Audyssey XT, preferably Audyssey XT32. I think the Marantz Pre/Pro you are considering has Audyssey XT32. See The Audyssey FAQ.

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Originally Posted by lovingdvd View Post
Hi all - Great FAQ! I am building a dedicated, full acoustically treated room and would love to get your thoughts on the best way to power it. The speaker set up will be a 9.1.6 Atmos setup. Initially I realize I will only be able to use it as a 9.1.2 or 7.1.4 (without buying a Trinov!), but eventually I suppose we'll have more channels available to use at the consumer level pricing. So I'm building in these capabilities now for a full 9.1.6 as to avoid doing reconstruction on the room down the road.

My speakers are all 4 ohm. The L/C/R (KEF Ci5160) are rated for max output of 250 watts. The other 6 listening-level speakers (KEF Ci3160) are rated for a max 180 watts. And my 6 in-ceiling Atmos speakers (KEF Ci200RR) are rated for max 190 watts. All of the speakers are listed as having 90 dB sensitivity 2.83V/1M.

Question 1: I'm trying to determine what level of power would be considered "plenty!" without it being overkill and would love your thoughts on it please. My goal is to reach THX reference level. The main seats are 13 feet away. The excellent online SPL calculators expect the dB sensitivity to be entered at 1V/1M. However in my case I only have the 90 dB rating in volts/meter. Since its a 4 ohm load, I'm not sure what value to put into the calculator for the calculator? Does the 90 dB need to be converted to a new number that changes it from the 2.83V/1M to the equivalent of 1V/1M?

Question 2: What are some good amp configurations in terms of number of channels and watts per channel to consider? One option is to consider an amp like the ATI 3007 that puts out 450 watts x 7. I would need two of them to power all channels except one. So that still leaves me one channel short. So perhaps two 7 channel amps isn't the way to go. Maybe three 5 channel amps like a ATI 3005 - that's 15 channels at 450. This however would be very costly, likely something like $12k. Or maybe three Parasound A51? Well I think that's even more expensive.

Question 3: Another option is to do a mix I suppose. Like 450 watts to the front L/C/R (most demanding for home theater plus I plan to do a quite a bit of 2.1 channel music listening), and then less watts to the other speakers. For example, the side surround speakers are only about 8 feet from me, so they require a lot less power than the front L/C/R (not to mention their wattage requirement is lower at 180 vs 250 max as mentioned earlier). Likewise the in-ceiling Atmos speakers are also relatively closer to me, plus how demanding are these speakers going to be for power if Atmos mainly is using them for diffuse sound and ambiance/effects. So the gist of this question is whether it is ok to mix and match wattages like this, as opposed to having the same watts going to all speakers?

Thanks guys! Any recommendations on watts to use, number of amps/channels to go with, brands of amps and approaches to take in general are greatly appreciated!!

If you are going with ATI I suggest the AT1807. You'll get seven channels a pop if fully configured and AT1807's are a lot cheaper than AT3007's. The AT1807 rated output is about 2dB less, which would be hard to hear; if your speakers could take the extra power. The rated output of the AT1807 per channel at 4 ohms is 270 watts so they should provide sufficient power for your 4 ohm speakers. All this ATI gear has huge, heavy transformers with separate windings for each channel, and independent rectifiers and supply capacitors for each channel.

You need to remember that the AT3007 is a bridged amplifier. That means that the amplifier is made up of two amplifiers, one connected to the plus terminal of the speaker and one to the minus and driven 180 degrees out of phase with each other. A bridged amplifier is nominally able to deliver twice the voltage (+6dB) and four times the power (+6dB) as a regular amplifier. This makes for great advertising by amplifier manufacturers, however nominally is the key word. The two amplifiers can't deliver any more current than they could if connected individually unless their current capacity is increased, which costs money. Current delivery is what drives most of the cost of an amplifier, more current delivered means more output devices, a bigger transformer, more power supply capacitors, and bigger heat sinks. 1,000 watt conventional amplifiers need to be bridged to get enough voltage at that level of power, but most of their expense comes their ability to deliver current at those voltages.

If you are driving 4 ohm and below loads the amplifier will effectively run out of current (amps) first (although of course the current drain will have driven the voltage available down to a level where the amp clips, an amplifier is a voltage source after all...). Due to the way the bridged connection is done the impedance of the load the bridged amp sees is 1/2 the actual impedance of the speaker. it sees an 8 ohm speaker as 4 ohms and a 4 ohm speaker as 2 ohms, and heaven forbid, a 2 ohm speaker as 1 ohm. If you look at the amplifier measurements in Stereophile you'll see that even the most expensive bridged amplifiers have trouble with 2 ohm loads and often don't do real well with 4 ohm loads. That is because the amp 'sees" the 4 ohm load as a 2 ohm load. You'll also note that the AT3007 isn't rated to deliver close to four times the power (+6dB) of an AT1807. Bridging is far from something for nothing.

Many speakers hit an impedance of 4 ohms and less, often over a wide range of frequencies. If your speakers are rated at 4 ohms, they likely hit less than that at lower frequencies. Speakers are particularly likely to hit 4 ohms and below in the range of frequencies from 20 to 300 Hz. Music has a lot of energy at 40 Hz and above, and movies have energy at all these frequencies. Speakers require more energy (woofer cones are big and heavy) to play loudly in this frequency range, which means they need a lot of current (amps). A regular amplifier, say an AT1807 is likely to supply close to as much current, and therefore power, at these frequencies as an AT3007, and cost a lot less doing it.

Concerning Question 3, mixing amplifiers:

I'd suggest an Outlaw Audio Model 7125 seven channel amplifier. Likely there are other good choices available. I've been involved in the purchase and installation of these amplifiers for family members and they have worked very well. In those applications they drive tower speakers for the left and right channels from Revel and PSB plus the other channels. They could easily drive secondary channels. The Model 7125 is built by ATI in the U.S. and appears to have been designed by them as well. It appears to have the same architecture as the AT1807, it just has less output.

The Model 7125 costs $999 or less for B-stock. It's rated at 125 watts all channels driven into 8 ohms and 190 watts all channels in to 4 ohms. Not just rated to live connected to 4 ohms, but to drive 4 ohm loads. Each channel has six power transistors and its own windings on the transformer. Each channel has its own AC to DC conversion and storage capacitors; all the same as the AT1807. The heat sinks appear ample and the transformer is large, which accounts for much of the 51 lbs. weight.

The ATI products aren't as exciting, or have as big a name as some other products, but they are of high quality and provide large amounts of power at low impedance, with low distortion.
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I looked at http://myhometheater.homestead.com/splcalculator.html again, and I don't see 1V anywhere. I see 1 W @ 1M, which the author says is the same as 2.83V @1M across 8 Ohns. Since KEF rates the sensitivity of your front speakers (at least) as 90 dB @ 2.83V, you can probably just go with that.
Sorry for the typo. I meant that the calculator whats 1W/1M, and the KEF's are rated at 2.83V/1M. I am not sure, but I think that with an 8 ohm speaker, 1W/1M is identical to 2.83V/1M. However apparently this NOT the case for a 4 ohm speaker, which I believe is 2W/1M. What I understand from Mike Garret from earlier today, the sensitivity of a 4 ohm speaker rated at 2.83V/M needs to be reduced by 3 dB to have an equivalent rating based on 1W/1M. So IOW when I use a calculator like the one we've been discussing, I need to use 87 dB as the sensitivity at 1W/1M, not 90 dB.

That said, I am picking up somewhere between +3 dB and +6 dB since I will have these speakers in a baffle wall. That's a significant boost. Mike also said that these calculators do not account for power compression (from what I've gathered, dB loss due to the speakers getting hot) which he says can account for 3 to 9 dB loss depending on the speaker.

So, turning to the calculator, at 13 feet to my MLP at 250 watts with two speakers (L/R in this case) I'd have 102 dB of output. Add to that +3dB to +6dB from using a baffle wall, and subtract say 3dB to 6dB for power compression and it sounds like I should be right around reference. Maybe a little short. Which is OK considering that I rarely if ever will listen that loud (more likely around -5dB under reference as my "loud" listening level.


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Having a "nominal" impedance of only 4 Ohms is not a problem in and of itself (providing they don't drop very much below 4 Ohms somewhere in the frequency spectrum). Most speaker makers spec at 8 Ohms, since almost all Solid State amplifiers have an 8 Ohm tap only, unlike with tubes). Since you are concerned about headroom, you could arbitrarily add 3 dB to your Front channel estimated power needs (twice the amplifier power in watts). With the 3 dB increase, 500 watts should produce almost 110 dB @ 13 feet in a big room like yours, which is 5 dB greater than standard fs at reference level on your MVC. 250 watts should produce almost 107 dB, which is still over fs demands. I assume you are using a powered subwoofer. If you crossover at 80 Hz (standard) for bass management, while setting the LPF for LFE at 120 dB (standard), and set your main speakers for "small" (recommended), a fair amount of burden for music & dialog, and a great amount of burden for special effects will be taken off of your main speakers. But you should wait until someone else answers.
Yes, will be crossing my subs at 80 and using separate amps for the subs.

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Good for you for not planning to use an AVR. Most AVRs are advertised at a given power per channel "with 2 channels operating," rather than with all channels operating. According to bench tests in many magazines, with all channels operating, they only put out about 80% of their rated power into each channel. High quality separate power amps, even with many channels, tend to put out their rated power into all of their channels, with all channels operating. Their "rated power," while less misleading than AVR ratings, still might not be as conservative as the RMS power per channel at which amps used to be rated. My separate power amps, for instance, were rated at 150 w.p.c, but when the dealer put a sine wave into all channels, turned the volume up until he could barely see flattening -- clipping -- and then backed it off to get rid of the clipping, he got 171 watts per channel, all channels operating. To estimate the old standard of RMS, you multiply by 0.707, which produced 120.89, so I have power amps rated at 150 w.p.c, less misleadingly than with most AVRs, but with the approximate equivalent of 121 w.p.s., RMS, all channels operating. That's O.K. for me, because my speakers are about 100 dB @ 1W @ 1M.

I'm biased in favor of a Preamp/Processor with at least Audyssey XT, preferably Audyssey XT32. I think the Marantz Pre/Pro you are considering has Audyssey XT32. See The Audyssey FAQ.
Very interesting to hear how the dealer measured this. Its great to know there's a way to really know for sure how much power is being used/consumed in a complete system. I plan to use a MiniDSP 88A for Dirac Live calibration or possibly a QSC Core 250i with manual calibration by an audio engineer.
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If you are going with ATI I suggest the AT1807. You'll get seven channels a pop if fully configured and AT1807's are a lot cheaper than AT3007's. The AT1807 rated output is about 2dB less, which would be hard to hear; if your speakers could take the extra power. The rated output of the AT1807 per channel at 4 ohms is 270 watts so they should provide sufficient power for your 4 ohm speakers. All this ATI gear has huge, heavy transformers with separate windings for each channel, and independent rectifiers and supply capacitors for each channel.
Thanks! I like the idea of the ATI1807's a lot. This would only run me about a third of the cost of going with Parasound A51. My concern though is whether I'll have enough headroom with 270 watts, considering the max rating is 250 watts. I say this because people suggest that one should have amps that put out 1.5x the max rated output of the speakers (others have suggested as much as 2x) to ensure sufficient headroom at loud levels and account for the large dynamic range in music and movies. While others suggest that its only necessary to have around the max watts. Out of all 15 channels, all of the channels except for the front L/C/R have max watts at 180 or 190. In that case it seems 270 watts is very close to the 1.5x max watts, so I am comfortable with those having enough watts with some to spare for headroom

Now, regarding the L/C/R these speakers are identical to the ones that have requirements for 180 max watts, except instead of two 6.5" woofers and a tweeter they have four 6.5" woofers and a tweeter. Since I will be crossing these at 80 Hz, perhaps much of that additional max watts (250 vs 180) will not even be needed, if you are following my logic here.

I could do three of the ATI1805's and have all 15 channels covered. But doing that is about $2,500 over the cost of going with two ATI1807's - but two of those leave me one channel short. I could pick up an ATI1802 to fill that in (and wind up with one unused channel) and still be about $1200 ahead. Also the ATI1807 says its NOMINAL power is 270 Watts RMS per channel into 4 ohms, but that TYPICAL output is 320W RMS per channel at 4 ohms. What's the difference between the nominal and "typical" in this case. Does typical mean I more than likely would have closer to 320W instead of 270? Probably a trivial difference, but I'd feel a little bit better driving the 250 max watt L/C/R with 320W because of the extra headroom. I also see in another place where ATI states that they could have rated the 270 about 20% higher so perhaps that is where this 320 is coming from.

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Concerning Question 3, mixing amplifiers:

I'd suggest an Outlaw Audio Model 7125 seven channel amplifier. Likely there are other good choices available. I've been involved in the purchase and installation of these amplifiers for family members and they have worked very well. In those applications they drive tower speakers for the left and right channels from Revel and PSB plus the other channels. They could easily drive secondary channels. The Model 7125 is built by ATI in the U.S. and appears to have been designed by them as well. It appears to have the same architecture as the AT1807, it just has less output.

The Model 7125 costs $999 or less for B-stock. It's rated at 125 watts all channels driven into 8 ohms and 190 watts all channels in to 4 ohms. Not just rated to live connected to 4 ohms, but to drive 4 ohm loads. Each channel has six power transistors and its own windings on the transformer. Each channel has its own AC to DC conversion and storage capacitors; all the same as the AT1807. The heat sinks appear ample and the transformer is large, which accounts for much of the 51 lbs. weight.

The ATI products aren't as exciting, or have as big a name as some other products, but they are of high quality and provide large amounts of power at low impedance, with low distortion.
Interesting. So maybe a configuration like one ATI1807 and one ATI1802 (together delivering 9x270w for the 9 listening level speakers), and one Outlaw 7125 for the 6 in-ceiling Atmos speakers. That feels a little tight given the max watts on those Atmos speakers are 190w and that's the max watts this delivers. Going that route would save me only $1200 compared to just doing two ATI1807's and one ATI1802, so I think I prefer the two ATIs just to keep everything ATI and a bit more "uniform". Make sense?
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... So IOW when I use a calculator like the one we've been discussing, I need to use 87 dB as the sensitivity at 1W/1M, not 90 dB. ...

That said, I am picking up somewhere between +3 dB and +6 dB since I will have these speakers in a baffle wall. That's a significant boost. Mike also said that these calculators do not account for power compression (from what I've gathered, dB loss due to the speakers getting hot) which he says can account for 3 to 9 dB loss depending on the speaker.

So, turning to the calculator, at 13 feet to my MLP at 250 watts with two speakers (L/R in this case) I'd have 102 dB of output. Add to that +3dB to +6dB from using a baffle wall, and subtract say 3dB to 6dB for power compression and it sounds like I should be right around reference. Maybe a little short. Which is OK considering that I rarely if ever will listen that loud (more likely around -5dB under reference as my "loud" listening level.
...
Yes, will be crossing my subs at 80 and using separate amps for the subs.
If you play MOVIES back at 5 dB below reference, you should be fine, I would think, providing you have the pre/pro set to subwoofer "YES," never "No." As you probably know, the subwoofer output on your pre/pro delivers two signals when playing movies: the regular bass management signal below ~~ 80 Hz (lowest frequencies of music & dialog) and, mixed with that, the special Low Frequency Effects put there by the filmmakers. If the pre/pro is accidentally set to subwoofer "No," movie LFE can be mixed into the mains -- it can destroy main speakers at reference (depending on whether or not the pre/pro prudently attenuates it). It can carry sound 10 dB louder than that normally sent to the mains (up to 115 db, instead of 105 dB, both at reference) and as low as 20 Hz with typical movies, and as low as 5 Hz or 10 Hz, if we are to believe the braggadocio of some producers/mixers.

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... So maybe a configuration like one ATI1807 and one ATI1802 (together delivering 9x270w for the 9 listening level speakers), and one Outlaw 7125 for the 6 in-ceiling Atmos speakers. That feels a little tight given the max watts on those Atmos speakers are 190w and that's the max watts this delivers. Going that route would save me only $1200 compared to just doing two ATI1807's and one ATI1802, so I think I prefer the two ATIs just to keep everything ATI and a bit more "uniform". Make sense?
I fully agree with your thinking. If you have sufficient budget; the flexibility, now and in the future, provided by uniform amplifiers is great. Being assured of having enough, or more than enough power, is very nice as well.
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I fully agree with your thinking. If you have sufficient budget; the flexibility, now and in the future, provided by uniform amplifiers is great. Being assured of having enough, or more than enough power, is very nice as well.
Right. I think the challenge is determining what amount if "more than plenty for now and in the future" without needlessly overspending. In my case if I knew that the most the speakers would ever need is X, regardless of how much X is, I'd get the amp that could handle it. The challenge is, I don't know what X is and it sounds like the only way to do it is to guestimate at something like 1.5-2x max rates watts. And if that winds up being too much power that is never used then "oh well". Seems like that may be the only way to go for someone that wants to be sure they have "plenty" of watts... ?
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If you are going with ATI I suggest the AT1807. You'll get seven channels a pop if fully configured and AT1807's are a lot cheaper than AT3007's. The AT1807 rated output is about 2dB less, which would be hard to hear; if your speakers could take the extra power. The rated output of the AT1807 per channel at 4 ohms is 270 watts so they should provide sufficient power for your 4 ohm speakers. All this ATI gear has huge, heavy transformers with separate windings for each channel, and independent rectifiers and supply capacitors for each channel.
How about the ATI2000 series bigguyca? On paper I prefer it to the ATI1800 series because I like that the 2000 series has balanced inputs and a little more power. I realize this additional power isn't much in the grand scheme of things, however I'm a bit concerned about headroom and it makes me feel better even if it doesn't matter. . I am thinking about an ATI2006 to power the 6 in-ceiling Atmos speakers (rated for max 190 watts), an ATI2004 for the front wides, and side surrounds (rated to 180 watts), and an ATI3005 to power the L/C/R (rated for 250 watts) and the rear surrounds (rated for 180 watts). I'm thinking about the 3005 for these because these speakers are the further from the MLP (13 feet for the L/C/R and 16 feet for the rear surrounds). Or I could do an ATI2006 instead of the ATI2004 and put the rear surrounds on that (since they are rated to 180 watts perhaps I don't need the 3005 power for that) while putting the L/C/R on an ATI3003.

One thing in particular I like is the customization of choosing from 2-7 channels in the ATI amps - makes it easy to get the exact number of channels I need (15) in a configuration that's a good fit number of channel-wise and power-wise.

Quote:
You need to remember that the AT3007 is a bridged amplifier. That means that the amplifier is made up of two amplifiers, one connected to the plus terminal of the speaker and one to the minus and driven 180 degrees out of phase with each other. A bridged amplifier is nominally able to deliver twice the voltage (+6dB) and four times the power (+6dB) as a regular amplifier. This makes for great advertising by amplifier manufacturers, however nominally is the key word. The two amplifiers can't deliver any more current than they could if connected individually unless their current capacity is increased, which costs money. Current delivery is what drives most of the cost of an amplifier, more current delivered means more output devices, a bigger transformer, more power supply capacitors, and bigger heat sinks. 1,000 watt conventional amplifiers need to be bridged to get enough voltage at that level of power, but most of their expense comes their ability to deliver current at those voltages...
I believe the architecture of the 3000 series is the same as the 2000 series, yes? Therefore is what you are saying about the bridge amplifier apply to the 2000 series as well? Are you saying that a 3000 series puts out virtually the same real-world power as the 1800 series?
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If you are going with ATI I suggest the AT1807. You'll get seven channels a pop if fully configured and AT1807's are a lot cheaper than AT3007's. The AT1807 rated output is about 2dB less, which would be hard to hear; if your speakers could take the extra power. The rated output of the AT1807 per channel at 4 ohms is 270 watts so they should provide sufficient power for your 4 ohm speakers. All this ATI gear has huge, heavy transformers with separate windings for each channel, and independent rectifiers and supply capacitors for each channel.
How about the ATI2000 series bigguyca? On paper I prefer it to the ATI1800 series because I like that the 2000 series has balanced inputs and a little more power. I realize this additional power isn't much in the grand scheme of things, however I'm a bit concerned about headroom and it makes me feel better even if it doesn't matter. . I am thinking about an ATI2006 to power the 6 in-ceiling Atmos speakers (rated for max 190 watts), an ATI2004 for the front wides, and side surrounds (rated to 180 watts), and an ATI3005 to power the L/C/R (rated for 250 watts) and the rear surrounds (rated for 180 watts). I'm thinking about the 3005 for these because these speakers are the further from the MLP (13 feet for the L/C/R and 16 feet for the rear surrounds). Or I could do an ATI2006 instead of the ATI2004 and put the rear surrounds on that (since they are rated to 180 watts perhaps I don't need the 3005 power for that) while putting the L/C/R on an ATI3003.

One thing in particular I like is the customization of choosing from 2-7 channels in the ATI amps - makes it easy to get the exact number of channels I need (15) in a configuration that's a good fit number of channel-wise and power-wise.

Quote:
You need to remember that the AT3007 is a bridged amplifier. That means that the amplifier is made up of two amplifiers, one connected to the plus terminal of the speaker and one to the minus and driven 180 degrees out of phase with each other. A bridged amplifier is nominally able to deliver twice the voltage (+6dB) and four times the power (+6dB) as a regular amplifier. This makes for great advertising by amplifier manufacturers, however nominally is the key word. The two amplifiers can't deliver any more current than they could if connected individually unless their current capacity is increased, which costs money. Current delivery is what drives most of the cost of an amplifier, more current delivered means more output devices, a bigger transformer, more power supply capacitors, and bigger heat sinks. 1,000 watt conventional amplifiers need to be bridged to get enough voltage at that level of power, but most of their expense comes their ability to deliver current at those voltages...
I believe the architecture of the 3000 series is the same as the 2000 series, yes? Therefore is what you are saying about the bridge amplifier apply to the 2000 series as well? Are you saying that a 3000 series puts out virtually the same real-world power as the 1800 series?

Also - what is your thoughts on Class D vs Class A/B amps. In an eq'ed system (such as everything running through Dirac Live) can you really hear a difference? If not, perhaps I should consider some class D options?
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Right. I think the challenge is determining what amount if "more than plenty for now and in the future" without needlessly overspending. In my case if I knew that the most the speakers would ever need is X, regardless of how much X is, I'd get the amp that could handle it. The challenge is, I don't know what X is and it sounds like the only way to do it is to guestimate at something like 1.5-2x max rates watts. And if that winds up being too much power that is never used then "oh well". Seems like that may be the only way to go for someone that wants to be sure they have "plenty" of watts... ?
I guess another question is "the most the speakers would ever need for how long?" With high quality amps, it is commonly thought that 3 dB above RMS can be delivered for a brief peak. How brief? ... Back to the same question! With or without clipping? The briefest peaks may conceivably be deliverable at an even higher level. Who objectively measures this stuff? How much can your speakers take for a very brief midrange burst (like the gunfire in Looper)? Search me!

Another issue is whether the movie people adhere to their own standards regarding "reference" (there are no such agreed upon standards for the music industry, so the movie people are ahead in that respect). Some movies seem much louder, but this may be due to cramming the sound up against fs by using compression and limiting, just as the pop/rock/metal recording mixers are commanded to do all too often in the "loudness wars."

By the way, when I run 250 watts through the calculator @ 87 dB @ 1W @ 1M, @ 13 feet, with 2 speakers (as you did), "near a wall" (of course yours would be "nearer than near") I get exactly 105 dB, rather than 102. It can be argued that it's better to run it with just 1 speaker entered in the speaker box, since there is no guarantee that the sound is evenly distributed between front speakers in movies. I would think that would result in 102 dB.

I'd be interested in what KEF thinks about how hard it is to blow out your speakers. I've heard some manufacturers have a limiter on some of their speakers, especially their subs, but I don't know if that's true, and I don't know which ones.

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I guess another question is "the most the speakers would ever need for how long?" With high quality amps, it is commonly thought that 3 dB above RMS can be delivered for a brief peak. How brief? ... Back to the same question! With or without clipping? The briefest peaks may conceivably be deliverable at an even higher level. Who objectively measures this stuff? How much can your speakers take for a very brief midrange burst (like the gunfire in Looper)? Search me!

Another issue is whether the movie people adhere to their own standards regarding "reference" (there are no such agreed upon standards for the music industry, so the movie people are ahead in that respect). Some movies seem much louder, but this may be due to cramming the sound up against fs by using compression and limiting, just as the pop/rock/metal recording mixers are commanded to do all too often in the "loudness wars."
Good point.

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By the way, when I run 250 watts through the calculator @ 87 dB @ 1W @ 1M, @ 13 feet, with 2 speakers (as you did), "near a wall" (of course yours would be "nearer than near") I get exactly 105 dB, rather than 102. It can be argued that it's better to run it with just 1 speaker entered in the speaker box, since there is no guarantee that the sound is evenly distributed between front speakers in movies. I would think that would result in 102 dB.
Yes. I ran it with one speaker for the reason you cited. I get 99 dB with 250w that way, when not located near a wall. Basically they give you a +6 dB bonus for being in a baffle wall, which is what I heard previously (actually I heard +3 dB to +6 dB benefit from baffle wall).

So yes, at just 250 watts I can hit 105 dB reference. However my concern is that if I don't go with something higher, like at least 300 or 350w, then there may not be any (or enough) headroom as needed. For example, as pointed out here, speakers can change their impedance at different frequencies. So if the KEFs drop to a 2 Ohm or whatever load then all of the sudden the 250 watts is no longer enough. Maybe it delivers 125 watts for those times which then drops things by 3 dB. So its nice to have at least the piece of mind that there is extra watts available as needed.

That said, even if it drops to a 2 ohm load with 250 watts then becomes 125 watts and the loss is only 3 dB. So essentially - if I have this straight - if I am OK with knowing that I can always play movies just fine at 3 dB below reference, that's acceptable to me. Realistically I won't listen at reference anyway - to my aging ears its painful and makes them ring. I like the idea of knowing I can play perfectly fine at reference because it then means I can play perfectly fine at any level below reference. But if I can be 100% confident that with 250w of power I can play with no problems at -3 dB or -5 dB below reference, I think I'm good to go. I really can't imagine watching a full movie any louder than that anyway.

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I'd be interested in what KEF thinks about how hard it is to blow out your speakers. I've heard some manufacturers have a limiter on some of their speakers, especially their subs, but I don't know if that's true, and I don't know which ones.
It would be great to know what numbers they have for power compression as well, which Mike Garret says can account for 3 dB to as much as 9 dB of loss depending on the speaker.
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Originally Posted by lovingdvd View Post
How about the ATI2000 series bigguyca? On paper I prefer it to the ATI1800 series because I like that the 2000 series has balanced inputs and a little more power. I realize this additional power isn't much in the grand scheme of things, however I'm a bit concerned about headroom and it makes me feel better even if it doesn't matter. . I am thinking about an ATI2006 to power the 6 in-ceiling Atmos speakers (rated for max 190 watts), an ATI2004 for the front wides, and side surrounds (rated to 180 watts), and an ATI3005 to power the L/C/R (rated for 250 watts) and the rear surrounds (rated for 180 watts). I'm thinking about the 3005 for these because these speakers are the further from the MLP (13 feet for the L/C/R and 16 feet for the rear surrounds). Or I could do an ATI2006 instead of the ATI2004 and put the rear surrounds on that (since they are rated to 180 watts perhaps I don't need the 3005 power for that) while putting the L/C/R on an ATI3003.

One thing in particular I like is the customization of choosing from 2-7 channels in the ATI amps - makes it easy to get the exact number of channels I need (15) in a configuration that's a good fit number of channel-wise and power-wise.


I believe the architecture of the 3000 series is the same as the 2000 series, yes? Therefore is what you are saying about the bridge amplifier apply to the 2000 series as well? Are you saying that a 3000 series puts out virtually the same real-world power as the 1800 series?

Also - what is your thoughts on Class D vs Class A/B amps. In an eq'ed system (such as everything running through Dirac Live) can you really hear a difference? If not, perhaps I should consider some class D options?

When compared in dB's, and that seems the relevant comparison, the output of all these ATI amplifiers is similar. It's hard to get excited about a dB or two from an engineering standpoint. That said, my personal choice is for big amplifiers. I don't think I ever use their full capability, but I get satisfaction in owning them; who knows why. I don't own a Corvette, but I doubt most owners drive 150 mph very often, if ever, but they like owning the beasts.

To be clear: I have no experience with high-end Class D amplifiers. Likely my iPhone, and the audio system in my car use them, but that's my limit of experience. I've read about Class D amplifiers and have a basic idea of how they work.

That said, there are a number of the characteristics that I don't like conceptually. Class D amplifiers put out a lot of high frequency noise. Looked at one way, they switch MOSFETS or the like, to generate high frequency square waves that correlate with the desired output, which are then filtered to make the output usable. If you are going to test one with a piece of Audio Precision gear you'll need to get the AP noise filter or the out of band noise from a Class D amplifier will over load the input stage of the AP equipment. I don't like the idea of that, but I don't know for sure how it might affect the sound, or other equipment in the area that received some of the noise. It does't seem promising however.

Often, perhaps always, Class D amplifiers have output filters to remove some of the high frequency noise, although there is a lot remaining as noted above. These filters are passive circuits and typically raise the output impedance of the amplifier, and also of course interact with passive crossover networks in speakers. These interactions are difficult to predict since each amplifier and speaker crossover network are different. Most speakers however are designed to be driven by very low impedance voltage sources, not through add-on passive networks.

Many brands of Class D amplifiers seem to get their basic and most important modules from one or two companies. Are the modules that hard to design that only a few can master the techniques or perhaps they are viewed as a fad and outsourced to reduce risk?

The components in Class D amplifiers are very inexpensive, unlike big power transformers and capacitors, and heavy cases in conventional amplifiers. The out the door prices of most of the Class D amplifiers I've seen don't seem to reflect what must be very low costs of production.
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