# How much power is enough... which amp would you buy?



## Sonnie (Apr 11, 2006)

Nope... not in the market for an amp, but another thread got me thinking about how we determine how much power we need in an amp. 

When and why should we pay more for extra watts?

If it depends on your speakers, then exactly what is it that influences our decision? Is is sensitivity, if so... at what point do we determine we need more power?



Let us suppose that we have three amps - all specs being equivalent other than transformers and watts per channel and number of channels. 

I have 5 speakers to power as normal. 
90db sensitivity.
4 ohms.
Medium size room with listening position at 12 feet from speakers.

Here are my choices:

Amp A - 125 WPC 8ohms x 7 with 2 toroidal transformers. $400

Amp B - 125 WPC 8ohms x 7 with 7 toroidal transformers. $600

Amp C - 200 WPC 8ohms x 5 with 5 toroidal transformers. $800

Which would be the better choice and why? 

If A is sufficient, why pay more?


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## avaserfi (Jul 5, 2007)

I think this is in sort a loaded question. There are quite a few factors which should go into place with amp choice.


 Speaker sensitivity - the less sensitive the speakers the more power needed
 Listening distance - the general rule of thumb is every meter drops sound level about 3dB
 Speaker impedance - speakers with highly variable impedance (especially downward) require better amps that are more stable at various loads
 Room size - the larger the room the more power needed to fill it
 Active/Passive crossover - my current build is going to be completely active and will require as little as 50 watts for some channels, but overall the speaker will have nearly 1000w. The specific application is extremely important

The list could go on as you can see. For general listening purposes most people will be clip free with 150WPC, but some people like having more. 

It is also important to remember with a high power amp one _needs_ a 20amp circuit to get the full benefits.


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## Sonnie (Apr 11, 2006)

Okay... I've added a few more specs for the speakers.


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## avaserfi (Jul 5, 2007)

With the added information I would probably go with option A*. The speakers are extremely sensitive and assuming the amps are stable at 4 ohms and built of the same quality there is no reason you shouldn't be able to make yourself go deaf with 125WPC.

*The choice of option A also relies on the ability for the amp to supply 125w all channels driven if it can't option B would be picked.*

Lets do some math. 1 Watt makes 90dB with these speakers - you are about 4 meters out so you can subtract 12dB so it is 78dB, but you have two speakers so you can add about 6 dB so you have 84dB with just *1 watt* at the listening position. If you get a 3dB increase for each doubling of power and assuming a normal listening level of 75dB one would be able to achieve quite large peaks more than sufficient for most listening.

Some people who listen to extremely well recorded classical music might run into clipping with this amplification set up, but that would be rare as most recording doesn't have 25-30dB increases.


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## yourgrandma (Oct 29, 2007)

I dont want to lead this discussion astray because it is a very interesting topic, but how does one determine what differences to expect when increasing power? For example, I have a Denon AVR-3803 (110wpc) and may be getting an Onkyo 805 (130wpc). 

I've heard that sound level goes up by the inverse power of the increase in wattage. Rather that the more power you have, the less of a difference adding more makes. 

Evidence of this is the fact that a lot of speakers put out [email protected]/1m. But they put out a maximum of 120dB at 200w. I know this has a lot to do with the way sound is measured, but 120dB is certainly not 200 times louder than 100dB, right?

Anyway, just thought I'd make a complex question more difficult to nail down...


Wow, it took me so long to post that that the question was answered while I typed!


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## avaserfi (Jul 5, 2007)

I guess I should also let people know that there are quite a few methods of measuring power output from receivers and amplifiers. Often times receivers do not really live up to their power ratings with _all channels driven_. This misleading representation is why I generally tell people to ignore power ratings on quality receivers. This is also where THX certification plays a role as the methods of power rating THX labs requires are more strenuous than most manufacturers use themselves.


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## brent_s (Feb 26, 2007)

Since the speakers are 4 ohm, you need to specify the amp's ratings into 4 ohms. Not all power supplies are designed/built equally so the 4 ohm power wouldn't necessarily be the same proportional difference as the 8 ohm rating.

That said, you've pretty much nailed my setup with option A. I use a 5 channel Adcom GFA-7000, rated at 125 or 130 wpc into 8, 200 wpc into 4. Speakers are 89dB, but 8 ohms. I've used it in rooms as large as 26x20x9, my ears give up before the amp does. On two channel music, I've hit 110dB averages (unadjusted Radio Shack analog) at probably 13-14' and the distortion warning indicators were only occasionally flickering...protection shutdown is somewhere above where those lights stay on constantly...never found it.

My subwoofer amp is a NAD 2400THX. Rated at 100/150 8/4. Of course, that's kind of conservative. NAD actually rates dynamic power at almost 6dB per some officially defined standard, unlike the unqualified "peak power" you see with some amps. Sterophile actually bench tested it to confirm that it'll deliver the short term 400ish wpc that NAD claims. Amp weights about 20 pounds. Just like the Adcom, I've gotten it to briefly flash it's warning indicator (when my goal was trying to drive the amp to shutdown), but it's never stumbled in any way.

This combination can easily soldier through the opening battle scene of M&C or any other bombastic spectacle at Reference in my current 24x16x9 theater room, which I would probably call large, not medium, sized since it's larger than the living/great room in any house I've lived in or considered buying except this one. At almost 3500 ft^3, it's slightly larger than the 3000 ft^3 acoustic space used for THX Ultra/Ultra2 certification standards. Select only requires 2000 ft^3.

My opinion is people buy more amp power than they need for the same reason many folks buy Porsches/Ferrarris/Corvettes/etc. for US roads. Especially when the nationwide speed limit was still 55 mph, even on the Interstates. It's about ego, image, the Jones', what have you. If some is good, more is better, right? 

-Brent


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## Sonnie (Apr 11, 2006)

lol... even the Jones' don't have a home theater in our neck of the woods.

One thing that does irritate me is we have no standard for power ratings. I remember seeing a test report on an older Denon receiver that was rated at 110 or 120 wpc x 7 channels, but when measured the real power was only 65-75 wpc.

NAD was the first real system I ever owned back in 1984. I've always been impressed with their ratings, knowing you could pretty much take them to the bank... and have loads of dynamic power in reserve.


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## avaserfi (Jul 5, 2007)

Sonnie said:


> One thing that does irritate me is we have no standard for power ratings. I remember seeing a test report on an older Denon receiver that was rated at 110 or 120 wpc x 7 channels, but when measured the real power was only 65-75 wpc.


That is the all channels driven fallacy I mentioned earlier. Normally receivers power ratings are done under a two channel load in the most flattering of lights. There is a reason I normally look for credible third part measurements before looking at what the manufacturer puts out .

The same idea is behind those ****** cheap HTiBs that claim to be 2000W of pure power to those little cubes that are plastic and have transducers the size of quarters. Its all in the angle the manufacturer look at it and how many really want to look at it straight on :explode:.


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## brent_s (Feb 26, 2007)

Sonnie said:


> lol... even the Jones' don't have a home theater in our neck of the woods.
> 
> One thing that does irritate me is we have no standard for power ratings. I remember seeing a test report on an older Denon receiver that was rated at 110 or 120 wpc x 7 channels, but when measured the real power was only 65-75 wpc.
> 
> NAD was the first real system I ever owned back in 1984. I've always been impressed with their ratings, knowing you could pretty much take them to the bank... and have loads of dynamic power in reserve.


The FTC does have power rating standards for *stereo* amplifiers/receivers. Probably applies to monoblocks as well, since they were more common when the standard was written. However, the standard apparently has a loophole that doesn't apply to multichannel (>2 channels?) amps/receivers.

It's been documented (implicitly...not wise to offend the paying advertisers) pretty extensively by magazines that do full bench testing, such as Sound&Vision and HomeTheater Mag, that very few receivers will deliver their rated power x all channels, even into a pure resistor load. The good news, that's a condition that no one's actually found a need for, yet. Those receivers will (should) still meet the rated power per FTC two channel standards. Sound&Vision recently tested the Yamaha 1800 rated at 130x7...it managed 55x7 simultaneously. It had no trouble doing 150/237 into 8/4 with 2 channels driven. The output devices on most/all receivers are there for any channel to deliver the rated power, but it's usually the power supply (transformer?) that's the weak link and can't service all channels simultaneously. Again, it bears repeating, this isn't something that's been found to be needed in the wild...yet. 

On the other hand, all of the separate power amp makers that I've looked at seem to have taken a conservative intepretation of the FTC standard and not used the multichannel loophole. So, if your house power doesn't sag and your circuit breaker doesn't pop, your 5/7 channel Mr. Fusion will deliver full power all channels driven 20-20kHz, if you can find source material that needs it. Anyone noticing a trend here? 

Last year, Dennis Murphy was asking for opinions on this topic on the PE board. For those of you that don't know, in addition to being a talented crossover designer and musician, he pays the bills by being an economist (proper title?) with the FTC. Sounds like the FTC is aware, at least, of this "problem". Unclear if/when it will be addressed, or if it really needs to be.

To bring an end to volume 2 of my contribution to this thread. I've got a little Pioneer 516, rated at 100x7 in my living room. Now, how seriously do you take that with an MSRP of $200 and my purchase price of $100. The living room itself is 20x22x9 with an 6'x15'x18' foyer and open staircase where one wall should be plus plenty more connected space. Anyway, definitely qualifies as large. I've measured 105dB peaks (C-weighted, unadjusted) with 2 pairs of Polk R150s (xover 100hz to sub) at 17' to the mains on DD demos. More than loud enough for me. It may not have been the cleanest at that SPL, but that could also be the nature of the speakers at that level. Needless to say, it's more than one has a right to ask from such an inexpensive receiver and speaker ($50/pair) combo. The top plate got fairly hot, but still no behavioral problems were observed.

-Brent


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## thxgoon (Feb 23, 2007)

Sonnie, check your PM, it is not the latest version of this article but would like your input. I'm in the process of getting other EE opinions and the such before I post it on the forum...


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## atledreier (Mar 2, 2007)

I'd say get as much as you can afford. then go back the next month and buy more. It's not really about absolute spl, but headroom and linearity. I'd much rather have a 400W amp idling at 50w than a straining 80W. They both deliver the same amount of power, but... It's like doing 55 in a Hyunday vs a Lamborghini. Both can do it, but only one with style..


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## jackfish (Dec 27, 2006)

http://forum.ecoustics.com/bbs/messages/34579/109459.html

More good, clean power is always better. JMHO


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## Sonnie (Apr 11, 2006)

How about this scenario...

Sensitivity: 90 dB/2.83 volts/meter
Impedance: Nominal: 4 ohms / Minimum: 1.2 ohms @ 20 kHz

What would be the minimum power you'd use?


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## thxgoon (Feb 23, 2007)

Sonnie said:


> How about this scenario...
> 
> Sensitivity: 90 dB/2.83 volts/meter
> Impedance: Nominal: 4 ohms / Minimum: 1.2 ohms @ 20 kHz
> ...


Well the good thing is that your speakers won't requir much power at 20khz as there's not much there in normal programming anyway so your amp won't need to strain much. Do you have a graph of the impedence response by chance? 

At 90db sensitivity you'll need 32 watts to reach reference output (105db at 1m) or about 7.2 amps of current into a 1.2 ohm load. From that we can infer that an amp capable of at least 106 watts at 4 ohms could drive your speakers to reference at 1.2 ohms as long as there is no protection circuitry involved to shut it down. Beyond that the quality of the amp build will determine the quality of the sound. Which amps are you looking at?


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## brent_s (Feb 26, 2007)

The headroom/dynamic range argument is a bit of a red herring. It's just physics. If the amp/speaker combination will produce the desired SPL a 0dbFS signal, any available wattage above that is excess. That's kind of the purpose of THX Reference level calibration. We use -30/20dbFS test tones to produce 75/85dB so that 0dbFS will produce 105dB. That's 30/20dB of headroom relative to the calibration tone. It's worh remembering that the OSHA exposure for 105dB is only 1 hour per day to avoid hearing damage. I would think this level should plenty loud for most folks. 

The -6dB for doubling of distance is the theoretical ideal for anechoic measurements. Room acoustics makes it virtually impossible to even have a rule of thumb. I've got REQW measurements of my sub measured at 3', 7', and 10' using the same sweep level. Depending on frequency, the SPL readings are intertwined...the closest measurement actually had the lowest SPL below a certain frequency.

To address another point made. The scenario with two equally competent amps capable of 80 watts or 400 watts max clean output. The amps would be audibly indistinguisable delivering a 50 watt output. Take a look at the distortion graphs for the solid state amps (tubes don't count). Notice that most have virtually flat distortion curves up until right before clipping, where the distortion/power slope goes almost vertical. If 50 watts is the power you need to reach your SPL requirement, there's no extra strain on the 80 watt amp relative to the 400 watt amp. And if you want to add the Green factor, amplifiers are generally more efficient the closer they run to max power.

In the end, this devolves to a religious argument. If the subjectivists is convinced they hear a difference with excess wattage available, no amount of science and measurement by the objective camp is going to change their mind. Somebody want to set up a blind taste test? :surrender:

-Brent


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## thxgoon (Feb 23, 2007)

brent_s said:


> The headroom/dynamic range argument is a bit of a red herring. It's just physics. If the amp/speaker combination will produce the desired SPL a 0dbFS signal, any available wattage above that is excess. That's kind of the purpose of THX Reference level calibration. We use -30/20dbFS test tones to produce 75/85dB so that 0dbFS will produce 105dB. That's 30/20dB of headroom relative to the calibration tone. It's worh remembering that the OSHA exposure for 105dB is only 1 hour per day to avoid hearing damage. I would think this level should plenty loud for most folks.
> 
> The -6dB for doubling of distance is the theoretical ideal for anechoic measurements. Room acoustics makes it virtually impossible to even have a rule of thumb. I've got REQW measurements of my sub measured at 3', 7', and 10' using the same sweep level. Depending on frequency, the SPL readings are intertwined...the closest measurement actually had the lowest SPL below a certain frequency.
> 
> ...


:T:hail:

I'd love to hear a the results of a blind test. While amplifiers might measure the same distortion while driving an 'ideal' test load, things change quite a bit when you start to drive reactive speaker loads. This is where matching amplifiers with speakers becomes important and sound quality will change. I'd be interested to hear if people ended up liking the more powerfull ones over the less powerfull ones though because IMO power has little to do with sound quality.


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## Sonnie (Apr 11, 2006)

Rodny and I have been talking about doing some blind testing on couple of different things. We've just got to figure out when and where and what all we will include.

I've actually already have what I plan to use on the ML's. The NAD T785 receiver is in hand. I was just curious and figured I throw in the specs for the ML's just for the fun of it.


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## Josuah (Apr 26, 2006)

I still don't think you have enough information, although the all-channels-driven answer would help. You need the VA ratings on the transformers and the power ratio for going to 4 ohms. Everything else is equal.

As an aside, I have 4 ohm speakers at 90dB sitting ~10 feet away and 300W is the minimum for me to playback movies at reference levels.


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## thxgoon (Feb 23, 2007)

The Voltage or Amperage into a given load is independent of the amplifier. Cheapo brand A will have the exact same voltage and amperage as expensive brand B if driving the same speaker at the same level (assuming the level is within the design parameters of the amp). It's a function of the speaker characteristics that place the power demands on the amp.

Josuah, how do you figure 300 watts is the minimum you need? At 105 db and 90 db sensitivity you only need 32 watts per channel to reach this level. I have all 4 ohm speakers with 87db sensitivity using a 125watt amp and I've driven the system well beyond reference with no trouble.


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## tonyvdb (Sep 5, 2007)

Its my understanding that for a good multi channel amp to preform properly it must have not only a good power source (a 20amp circuit) but also the power transformer inside must be able to drive the amps. A toroidal power supply is said to be one of the cleanest ways to go but it can not drive all 7 channels at full power sustained. Even the best receivers with 7 channels can't maintain a constant level with all channels driven to the rated power output. 
So would it not be better to have a 7 channel amp with 7 independent toroidal power supplies?


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## thxgoon (Feb 23, 2007)

DS-21 said:


> > Actually, there are plenty of well-conducted blind tests available for you to read, beginning with David L. Clarks' JAES article of ca. 1983. And all of them prove your second sentence irrefutably, incontrovertibly wrong.
> 
> 
> That's interesting, do you have any links attesting to this? Which sentence of mine is wrong and why?


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## avaserfi (Jul 5, 2007)

For those interested in amplifier audibility there are two very good articles out there:

Signal-to-Noise Ratio Requirement for Digital Transmission Systems
Spikofski, Gerhard
AES Preprint: 2196

Just Detectable Distortion Levels
James Moire, F.I.E.E.
Wireless World, Feb. 1981, Pages 32-34 and 38


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## Guest (Jan 25, 2008)

Personally also think 300w into 4 or 8 ohm is an ideal amount of power to have for music, movies in my opinion demand slightly less as the subs seems to add alot of impact.

We all work up to these levels usually, although for myself when i was younger i used to run 3 x 300 w p.a. amps so am used to what this power can deliver and much prefer it to 125 w even if this still sounds very good, with an average 90db at 1 m. 

In an ideal world all amps would have separate power supplies for each channel but these amps are very expensive, so will have to make do with lesser brands although i dont feel im missing too much, with Nad, Parasound and Arcam and dedicated feeds for all amps. 

When im ready an upgrade for my main amps which produce 225w and 200w for the floorstanders and 120w per channel for surround to 300w all round bi and tri amped will be welcomed and looking forward to it.


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## avaserfi (Jul 5, 2007)

Reading through this thread it seems there are two types of answers:

- The scientifically derived in which logic is applied in calculating needed power.

- The more power is better mentality in which the more the merrier despite the power *never* being used.

Nothing new with this dichotomy - it will always exist as long as the placebo effect does.


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## Guest (Jan 25, 2008)

On paper the power could be perceived as probably not be fully used, but all the power helps with dynamics and image etc... which can't be fully achieved with lesser wattage amps unless with highly sensitive speakers, and fantastic sounding highly efficient amps, IMO. 

You are right in some respects the power is not being fully used, as it would drive my closest neighbours mad, but sometimes a lot is and when they are on holiday enjoy it to its full.

I used to live in a quiet - ish village where no-one really cared about loud music within reason. 
One day i'm planning to move back to the countryside  and really enjoy the systems full potential and there must be some lucky few who do this already.

Its all good fun though, what a crazy hobby to have !! ??


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## avaserfi (Jul 5, 2007)

stephenb1 said:


> On paper the power could be perceived as probably not be fully used, but all the power helps with dynamics and image etc... which can't be fully achieved with lesser wattage amps unless with highly sensitive speakers, and fantastic sounding highly efficient amps, IMO.


Please explain to me two things about this statement. The first is if the power is not being used how does it help with dynamics at all? Unused power is still unused.

Secondly, how does power relate to imaging in anyway shape or form? There are three factors that effect imaging (to be listed in order of decreasing effect on imaging): 

*Room interaction* - It has been shown through countless perceptual studies that off-axis response with similar magnitude to the axial response increases listening enjoyment in stereophonic situations. This was found to be in part due to increase realism caused by superior imaging. There are however some exemptions to these findings. Any speaker with designed to have off axis dispersion will have terrible imaging if placed within one foot of boundaries in a highly reverberant room.

*Symmetry of response* - this refers to the frequency and phase of the loudspeakers and effects the perception of being in the centered. Symmetry of speaker placement and listener position do play a part in this.

*Treble response* - Referring to a typical two channel system a slight boost in treble (3dB above 6kHz) will yield perceived "tighter" imaging with a smaller sweet spot while the same cut will yield wider, but more "loose" imaging.

You will notice power is not once noted in this highly studied area. This is because of a plain and simple truth: If a speaker is receiving enough power [from a properly designed amplifier for the application] for the dynamics required of it this power will be inaudible. Excess power is pointless plain and simple that is what excess is...

Much of the information if you could call it that that has people buying high powered amps is completely unsubstantiated by _any_ credible research and is perpetuated by the same people who bring you "danceable cables."


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## Guest (Jan 25, 2008)

Tripling the output in my amps has certainly improved imaging and dynamics, IMO and would like more power as mentioned before.
I use kef uni q speakers which are renowned for their great imaging so the results are easy to hear. 
The increased loudness is also very easy to hear, once where the speakers distaughted a little with explosions and impacts now there is none, everything is just much louder, all most limitless which is what most of us are partly looking for. 

I think we will have to agree to disagree on this one and let our ears be the judge.


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## avaserfi (Jul 5, 2007)

stephenb1 said:


> Tripling the output in my amps has certainly improved imaging and dynamics, IMO and would like more power as mentioned before.
> I use kef uni q speakers which are renowned for their great imaging so the results are easy to hear.
> The increased loudness is also very easy to hear, once where the speakers distaughted a little with explosions and impacts now there is none, everything is just much louder, all most limitless which is what most of us are partly looking for.
> 
> I think we will have to agree to disagree on this one and let our ears be the judge.


It seems extremely likely you are succumbing to what is called the Placebo Effect.

Without a properly controlled environment your claims are completely unsubstantiated especially when held to the light of the large amounts of _credible_ research that has been done. You not wanting to accept the facts is where we will have to agree to disagree. 

Another good post by a member on this subject: http://www.hometheatershack.com/forums/75498-post7.html


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## thxgoon (Feb 23, 2007)

Its also possible that the new amp has a slightly different gain, did you recalibrate after adding the new amps? 

I'm not a complete subscriber to the objective camp. As an engineering student I have learned how amplifier/speaker systems work and have studied how an amplifier reacts with different loads in an AC application. On the other hand I have many years working with different amplifiers in home theater and pro audio and have heard differences between amps running within their design constrains into a given system. In many cases I was not the only one hearing the difference. 

One particular case - I worked at a mid level home theater retail chain for quite a while and we had a certain Krell amp. It was very easy to tell for almost all of us when the Krell was active and we all agreed that we didn't like the sound over other amps available to us except for one particular system, where it sounded the best. This is why I harp so much on matching amps to speakers and I DO believe there is an audible difference. I would love to setup a blind test in this matter....

I've been in the process of writing a fairly long article addressing a lot of misconceptions that seem to float around the internet with regard to amplifier power... I just need to stop putting it off and finish it. When I do I'll post it here on the Shack for all to read and discuss.


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## avaserfi (Jul 5, 2007)

I am not saying all amps sound the same in all situations. The amp must be sufficiently able to power the speakers in question at all frequencies with inaudible levels of distortion in a linear manner at required SPLS. Not every amp is able to do this with every set of speakers due to varying impedance curves and such. So before determining if an amp is actually transparent one would have to see measurements of the amp and correlate them to the amps performance with a specific loudspeaker.

Before publishing your article I strongly recommend you read the articles I mentioned here: http://www.hometheatershack.com/forums/76050-post26.html


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## thxgoon (Feb 23, 2007)

For sure! I've read those both in the past but I'll take another look at them. Thanks for the input!

Edit: I read those in the past but now the articles seem to have disappeared from the internet. Any idea where I can find them? Checked the local library as well... Thanks


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## JCD (Apr 20, 2006)

My quick answer -- watts are over-rated, so I'd stick with the 125watt system.

Longer answer with other info: 

Watts are needed, but not as much as we might think. In normal operation, you're only using ~10watts at any given time. 
All things being equal, a higher wattage amp will have a higher noise floor.
Watts to dB's is a logarithmic equation -- increasing the wattage from 125watts to 400watts will only give you an additional 5dB's at max output.
It takes an additional 10dB to perceive sound to be twice as loud. So you'd need an amp that was 1250watts to sound twice as loud.
Doubling the drivers will boost your SPL by 3dB -- if they're close enough to be "coupled".
You loose 6dB for every doubling of distance
Room gain will get some of that back. I'm pretty sure you get 3dB, at least in the bass region.
It'd be very hard to do a proper a/b test -- the respective levels would have to be matched precisely and the switching would have to be REALLY quick.
Without a blind test, perception is going to rule the roost rather than whatever the "real" answer may be.

JCD


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## Guest (Jan 26, 2008)

Hi i use Kef q55.2 's tri-amped with a parasound 1205 for lower bass and a Nad 216Thx for mids, plus an Arcam alpha 8p for the tweeters. 
A Yamaha Z9 for the rear outputs q60 's 8" bi-amped, and for 1 front centre and rear centre and then the parasound running 2 further front centres, plus some other kefs and mission di-pole speakers powered with arcam power amps, through arcam dvd and cd. (its a small 10.2 system).

Its around 3000w rms as all speakers are 4 ohm also i have 17 speakers in total including 3 subs 3 q95.2 's for the front and 1 rear, a dcx-2496, 2 cx3400 cross-overs, a bfd, a peq2200 and some more q55s off ebay on there way, plus to much more to mention.

I can assure it sounds anything but nasal even at very high volumes and the increased output after upgrading most of my amps has gone from loud to very loud and is not the "placebo effect" as im sure my closet neighbours would confirm. 
Its very loud and i have n't found the stress level yet at 11-12 o'clock not sure how far it will go ? but quite alot more I'm sure. 

It was worth every penny upgrading to more powerfull amps.


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## thxgoon (Feb 23, 2007)

DS-21 said:


> Indeed. Which is why I'm always puzzled why the people who most often bleat about finding actually nonexistent differences in commodity parts such as amps, digital sources, wires, etc.


I'd agree with digital sources being a bit of a mixed bag these days as they all have great noise floor and resolution. There might be other factors involved like quality bass management that would make one digital source preferable over another, and then there's always the ipod...

For amps and cables, it's a different subjective story and as mentioned earlier can get quite religious. A speaker system (amp, cables, speakers) act in concert as an rlc _system_. Changing an amp or cables may indeed have a difference on the overall sound of the system. These differences are small compared to better speakers or proper setup but they do exist for some systems. The problem IMO, is that these differences cannot be attributed to any particular spec given to us by manufacturers because there are too many variables and opinions are too subjective.

I think a blind test would be perfectly achievable and if differences were to be found I think the observations would be consistent. In my experience, when there is a difference between to amps on a system, the difference is noticeable enough to be memorable. 

Anyone up for an htshack convention somewhere to try this? Vegas anyone


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## thxgoon (Feb 23, 2007)

DS-21 said:


> Religious is exactly the right word, because there really is nothing to go on here except for blind faith. Personally, I'd rather have faith in something important than in something stupid like saying that ugly black boxes sound different from each other.


I have to completely disagree. How do you explain the difference Sonnie heard between his Denon receiver and his Anthem gear with his ML's? All plecebo??? 

In your line of logic, a receiver taken from a $60 htib, driving whatever speakers you want, will sound identical to the best electronics offered in the world (under normal operating conditions) in a blind test? If digital devices, amps and cables have no affect on sq, what in the signal chain other than speakers, does?


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## Josuah (Apr 26, 2006)

thxgoon said:


> The Voltage or Amperage into a given load is independent of the amplifier. Cheapo brand A will have the exact same voltage and amperage as expensive brand B if driving the same speaker at the same level (assuming the level is within the design parameters of the amp). It's a function of the speaker characteristics that place the power demands on the amp.


Well the original question said all things being equal except the transformer, watts per channel, and number of channels. Under those rules, the transformer of cheapo brand A may not be able to drive a 2 ohm load whereas expensive brand B may. The load demanded by the speaker will be the same, but the amp may not be able to satisfy it. Thinking about it, simple VA rating isn't enough there either.

(I don't think I'm saying things correctly here. But transformers are rated for both voltage and current, or at least they will be subject to those things once you've got them paired up with all the other circuit components involved in regulating the power.)

That's why I also said the 8 ohm rating isn't useful enough when pairing it with 4 ohm speakers. Maybe cheapo brand A shuts down (or blows up) if attached to 4 ohm speakers.



thxgoon said:


> Josuah, how do you figure 300 watts is the minimum you need? At 105 db and 90 db sensitivity you only need 32 watts per channel to reach this level. I have all 4 ohm speakers with 87db sensitivity using a 125watt amp and I've driven the system well beyond reference with no trouble.


90dB/1W/1m with 300W gives you approx. +25dB, so 115dB/300W/1m. I sit ~10 feet away so I lose about 10dB. Places me at ~105dB. It's only 32W if you're sitting 1m away.

Sitting 10 feet away from your speakers, if 125W is your amp's peak output, you can only hit about 98dB.


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## thxgoon (Feb 23, 2007)

Josuah said:


> Well the original question said all things being equal except the transformer, watts per channel, and number of channels. Under those rules, the transformer of cheapo brand A may not be able to drive a 2 ohm load whereas expensive brand B may. The load demanded by the speaker will be the same, but the amp may not be able to satisfy it. Thinking about it, simple VA rating isn't enough there either.


Right. Manufactureres of power supplies rate them in VA, which gives you an idea of the power capabilities of the transformer. Volts time Amps = Power. ie 1200VA transformer=1200 watt transformer for all practical purposes. In order for us to know what voltage and current capabilites it has independently, the manufacturer would have to give us those individual specs, which they normally don't. Also, the VA specs do not take into account efficiency in the amp design. A 1200 watt transformer does not necessarily mean the amp can deliver 1200 watts continuously.. so another difficult spec to interpret. 



Josuah said:


> 90dB/1W/1m with 300W gives you approx. +25dB, so 115dB/300W/1m. I sit ~10 feet away so I lose about 10dB. Places me at ~105dB. It's only 32W if you're sitting 1m away.
> 
> Sitting 10 feet away from your speakers, if 125W is your amp's peak output, you can only hit about 98dB.


Correct, using a single speaker in a perfect environment. In practical usage though this is a very grey area. Practially, I've never seen more than a db or two when measuring between 3 feet and 10 feet from my speakers with standard noise. Also, in my case, the system is calibrated for reference leves _at the seat _and I've never had clipping issues at reference levels and higher. This brings us to another discussion about dynamic power capabilities of an amp which for home theater is one of the more relavent specs.

Edit: I think your math might be a bit fuzzy.. 10ft=approx 3 meters which means you 'double' that 1m distance about 1.5 times, for about 4.5db, not 10.


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## Josuah (Apr 26, 2006)

I think line sources are -3dB per doubling of distance, but otherwise it's -6dB. ???

I also know that while my amp is rated at 300W/ch at 4 ohms, if I push it close to there then distortion kicks in. Arguably not audible distortion.

Regardless, I don't think anyone can provide Sonnie with an answer that's correct.


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## thxgoon (Feb 23, 2007)

DS-21 said:


> That's nice. I like the way you bring evidence to support your position. But when you're runnin' on faith, I guess evidence doesn't so much matter, now does it?


Common man, comments like this don't belong at the shack... Please read the forum rules/regs. We're all here to learn and discuss...

To address your concerns...
Throughout this thread I've posted my experiences and some mathmatical discussion pertaining to the question at hand. I've addressed my position relative to both subjective/objective camps. It isn't 'faith', I've heard it, I've experienced it. I've seen and heard others experience it. I have educational background that says differences could occur. Sonnie's ML's are indeed an extreme case, but many other speakers are also different from an ideal test load where most amp measurements are taken. 

As to the original post, you represent the strictly objective camp, where you would probably agree with me that anything over 150 watts or so with 90db speakers is overkill, but would disagree by saying he should find the cheapest one he can that can deliver 1.2 ohms without burning up. Others on this thread represent the subjective camp where more money and more power always = better sound.

I fall in the middle. Where I DO believe there are differences in sound, but I DON'T think they can be directly attributed to any specifications that a manufacturer hands out in a literature brochure. Simple math can tell you what power requirements you need. I'm going to agree to disagree with you until evidence is provided that contradicts anything I've said.



Josuah said:


> I think line sources are -3dB per doubling of distance, but otherwise it's -6dB. ???


That's a good point and I can't remember. Blast... heading downstairs to take measurements...:dumbcrazy:


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## thxgoon (Feb 23, 2007)

Ok, here's an REW graph of one speaker playing from 80hz to 5khz from 3.3 feet and 10 feet. I picked my right speaker as it is essentially in the middle of the wall that it is on, so it would have the least benefit from room boundaries. Each horizontal line represents 3 db, so on average it looks like about 6db loss from 1m to seat. You can also see the effects of the room on the red line (seat).


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## Funkmonkey (Jan 13, 2008)

Wow, great thread Sonnie. Very interesting topic. This is something that I will have to consider in the very near future. I just wanted to say thanks for the "education." I am going to have to read through this thread again to get a better handle on it, though. Who would have thought that a discussion about Watts and Ohms, would turn into such a heated argument...


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## avaserfi (Jul 5, 2007)

Funkmonkey said:


> Who would have thought that a discussion about Watts and Ohms, would turn into such a heated argument...


Its not an "Watts and Ohms" debate that is so heated it is the underlying situation of objectivity versus subjectivity. 

I think those on the subjective things don't realize one things _amps can sound different_ when unable to drive a loudspeaker properly or if designed in such a way that makes them audible.

Plain and simple if an amp isn't able to properly drive a loudspeaker it will impart coloration on the sound.


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## thxgoon (Feb 23, 2007)

DS-21 said:


> And yet, whenever anyone or any audio club sits down to do a serious same/different subjective listening result, the answer _always_ seems to come back "no difference" unless conditions were deliberately contrived to make things otherwise. (E.g. saying a Denon receiver and a Levinson whatever "sound different" because the poor Denon couldn't drive a pair of Apogee Scintillas without crapping out.)
> 
> People have heard other people speaking in tongues. Others have experienced running through streets with razor blades on chains self-flaggelating themselves. Rabbi Kahane had an "educational background" that told him Arabs were like apes. Does that make those things any less "faith?"
> 
> No. I represent the rational, realistic, and pragmatic camps. Or, if you prefer, the scientifically literate camp. There's plenty of room for subjectivity. Just not about trivial things that _have already been proven in peer reviewed scientific literature_ to the point where further inquiries in that direction are, frankly, pointless.


Like I said before, I will agree to disagree.

As far as the Denon 'crapping out', is this when it shuts itself off? The Denon, or any amp, running without clipping, is well within its design constraints, even if it is running a 1 ohm or a .5 ohm load. If the amp is _running and not clipping_, it is not 'crapping out'. This is fundamental physics.

I would absolutely love (and I'm serious here) to read the results of one of these tests. And if the scientifically literate camp has some 'science' to back this up, I'd love to hear that as well.


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## thxgoon (Feb 23, 2007)

avaserfi said:


> Plain and simple if an amp isn't able to properly drive a loudspeaker it will impart coloration on the sound.


Exactly. But what is the definition of being able to _properly_ drive a loudspeaker? IMO there's more to it than clipping or not clipping


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## Sonnie (Apr 11, 2006)

I have often thought I was wasting my money buying serious amounts of power, such as the Earthquake Cinenova Grande... and the McIntosh MC7300, both priced on up there. Obviously I was.

I have posted on more than one occasion that I never could seem to determine much (if any) difference between my prepro + amp combos: Sony, Lexicon, Rotel, Earthquake, Adcom vs. the receivers I've owned: Denon 3805 and 3806. I do remember the Sunfire Cinema Grand and McIntosh amps seemed to be more laid back in the upper range than any of the others. I also felt the same about the Yamaha receiver... it definitely seemed to be more laid back. I don't think it was my imagination, but then again maybe it was. :huh: All these were with speakers such as Snell, PSB, VMPS, JBL, Boston Acoustics and SVS. Sometimes the speakers did sound different, but for the most part swapping processors and power didn't make any difference. 

I did post that the Denon 2807 receiver sounded okay at low volumes with the Martin Logan speakers. The ML's sounded much better than the Boston speakers with the Denon. But the Denon is not designed to run anything less than 6ohms and there is absolutely no doubt the Anthem setup was better. Anyone could A/B those and realize a difference. The NAD receiver sounds as good as the Anthem as best I can tell and it is rated at about 1/3 less power. I definitely don't feel like I lost anything from the NAD to the Anthem, other than a host of video features that I don't think I would ever use. With the NAD I gained Audyssey, which has proven itself worthy already. 

I am beginning to agree that once you get to a certain level of power, what will make the difference from one product to the next will be quality, features, reliability, warranty and price.


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## Funkmonkey (Jan 13, 2008)

avaserfi said:


> Its not an "Watts and Ohms" debate that is so heated it is the underlying situation of objectivity versus subjectivity.


I realize that, which is why I stated "...discussion about Watts and Ohms, would turn into such a heated argument..." perhaps I should have have phrased it differently. I was only observing that the discussion had evolved into an argument, period, change of subject noted. 



avaserfi said:


> Plain and simple if an amp isn't able to properly drive a loudspeaker it will impart coloration on the sound.


Is it not true that you can actually damage a speaker if it is under amped? IMHO that is some pretty heavy coloration.


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## thxgoon (Feb 23, 2007)

Funkmonkey said:


> Is it not true that you can actually damage a speaker if it is under amped? IMHO that is some pretty heavy coloration.


Yes that it true, but only when the amp is driven into clipping. When that happens DC is sent into the voice coil at full strength and the energy is dissipated as heat in the voice coil instead of mechanical energy and you burn up your speaker. Additionally, clipping introduces full signal harmonics that extend into the ultrasonic region where your tweeters go fast.

Driving your speakers with a 1 watt amplifier will not harm them until you reach the level which exceeds 1 watt, and the amp clips. (though 1 watt dc prolly wouldn't hurt your speakers....)


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## avaserfi (Jul 5, 2007)

thxgoon said:


> Exactly. But what is the definition of being able to _properly_ drive a loudspeaker? IMO there's more to it than clipping or not clipping


The answer to how to "properly" power a speaker is simple: in a completely transparent fashion.



Funkmonkey said:


> Is it not true that you can actually damage a speaker if it is under amped? IMHO that is some pretty heavy coloration.


As thxgood said only when you are causing the amp to clip in a certain method otherwise it doesn't matter. If you think about it too little power isn't bad after all you aren't powering your speakers fully at low volumes .


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