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Discussion Starter · #1 ·
Optimally, should you get an amp whose power rating is higher than the maximal recommended power handling of your speakers? If so, then how much higher? Optimally, how powerful an amp should you get for a 4 ohm speaker whose minimum recommended power is 100 watts and maximum recommended power handling is 300 watts?
 

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For your hypothetical situation, get an amp that delivers at least 100 watts RMS into 4 ohms. To overdrive the speakers would require 300 watts continuous output power, which is A LOT. An underpowered amp is more dangerous to speakers than an overpowered one.


How much power you would need in a real-world situation depends on the sensitivity of your speakers, the size and composition of the room, and how loud you want it.
 

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Discussion Starter · #3 ·
how about speaker sensitivity of 90, 22x15x7.5 foot room with acoustical paneling, and reference level loud
 

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100 WPC should do fine in that situation, especially if you have a 5.1, 6.1, or 7.1 setup.


The formula for amplifier power is that you have to double the power to get a 3 dB increase in volume. 3 dB is noticeable but not a huge difference (roughly equal to the difference you hear between -10 and -7 on your volume dial). Because of this, most people tend to overestimate their wattage needs. During actual listening, your amps are putting out less than 10 wpc about 90% of the time. That output can jump 1000% during brief signal peaks like explosions and loud bass drum whacks.


To put it in perspective, I have a living room that is 28' x 22' x 12', a receiver that puts out 80 wpc into 8 ohms, and a 5.1 speaker setup with speakers rated at 88 dB/watt. I play the system routinely at reference levels with no sound of strain, and the amps don't even get hot after 3 hours of continuous play.
 

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Discussion Starter · #5 ·
I've been told get an amp that is more than your max speaker handling. Filmnut, it does not appear you subscribe to this philosophy. Would you change your recommendation if I wanted to play the speakers louder than reference level?
 

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Quote:
Originally posted by Phil P
Would you change your recommendation if I wanted to play the speakers louder than reference level?
Yes, in that case my recommendation would be to use ear plugs.
 

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Discussion Starter · #7 ·
What if I changed the hypothetical speakers to 8 ohm, 50 to 500 watt handling, with 91dB efficiency?
 

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I have to say that I'm amazed at what the power consumption profile of my system is. My speakers are not particularly efficient (88 dB @ 1w @ 1ft). Even so, playing at 100dB in my admittedly small room (14x14x7), I'm only pulling about 20W. Yes, I know about peaks, and I'm sure I'm using them. Still, that's less than I would have expected.


Compare that with ~140w for the projector, and about 95w worth of "overhead" in each amplifier! (Ie each of my amps pulls about 95w with no signal at all.)
 

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Quote:
Originally posted by blw
I have to say that I'm amazed at what the power consumption profile of my system is. My speakers are not particularly efficient (88 dB @ 1w @ 1ft). Even so, playing at 100dB in my admittedly small room (14x14x7), I'm only pulling about 20W. Yes, I know about peaks, and I'm sure I'm using them. Still, that's less than I would have expected.
Yes indeed. Most people, including the vast majority of folks in this forum, WAY overestimate their wattage needs.
 

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Never mind the wattage needs, consider the sound quality. There's a lot more to a pleasurable HT experience than loud distorted volume. Regardless of your room size. Just a thought...
 

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Dont make the mistake of thinking just watts. Think power supply! Case in point: I have extremely ineffcient 4 ohm speakers called Ohm's Walsh 5's. I have a Carver 380 watt amp that cannot , to my satisfaction, drive these speakers. Why? Because the Carver amp has a small power supply so when I really need the power, I suck every watt out of that of its supply. What I need is a amp with a MUCH GREATER Transformer, like a ATI 2500, Krell etc. or more effcient speakers. Also the stability of the amp is very important, esp with a lower impedence/more reactive load. Most speakers willnot pose this problem, but I just hope that others dont fall in the trap I did by purchase a amp that has good wattage specs without looking for what counts the most, POWER SUPPLY!
 

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To get a feel for how much power I use, I purchased a used power meter a few years back. It uses LED indicators, which are much faster than needles and provide an easy way to see when peaks hit certain levels. It was fun after hooking it up to see how loud my system was playing when the LEDs were hitting 8 watt peaks (occasionally causing the 8 watt LED to quickly flicker). It was relatively loud (using 89dB speakers). Much louder than my wife would ever listen to music. At 64 watt peaks, it was extremely loud, up in the 105-106dB range. My wife would have to be out of our house for me to listen at this level.


At normal listening levels, the 2 watt LED would occasionally fiicker.


People, and professional reviewers, are always surprised by how loud a speaker can play when they use low-power amps, such as 8 watt SE tube amps and 20-25 watt Class A solidstate amps. This is because few people have a good grasp oh how little power they actually use, especially if they use a powered sub to handle low frequencies.


Of course, there are the head-bangers and reference level movie buffs, who really do need either high-power or high-efficiency speakers. I've clipped a 180 watt amp in my large room - it was really LOUD (Sheffield drum track, Dire Straits, 1812 Overture, and a few others - with no powered sub).


Tom B.
 

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This has always been an intriging subject. We all know the formula os double the power only yields a 3 DB increase. With extremely inefficient speakers like mine, with a sen. rating of 80. That is 1 watt at 1 meter distance will produce only a 80db spl on axis, then 2 watts yilds only 83 and so on. To reach that 106 to 107db levels, my speaker requires 512 watts. And this rating is based on a 1,000 hertz signal, so you can imagine the delemma some systems present. Good listening!
 

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Just ran the SPL calculator for my set up. Interesting. 120 watts will give me 100.5 db. ... I also realize what fishman points out: All watts are not created equal. My new Pioneer Elite VSX-45's 100 watts/channel are not as powerful as my old HK AVR7000's 100 watts.


SO... what is the specification to look for to determine "power supply"? Is it amps? Is it memory (i.e., "uF")? A combination of these and/or something else? How much of a factor is just plain old weight? (My HK with 5 channels was about 10 pounds heavier than my new Pioneer Elite with 7 channels.)
 

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Well, all watts are created equal if they are measured accurately and according to conservative standards. Trouble is, some receivers don't even come close to claimed output, a lot of single-ended tube amps don't either.


The last two posters must have very inefficient speakers. I see the fishman has 80db speakers, which are pretty rare nowadays. A lot of today's speakers fall into the 88dB-92dB range. A lot of older speakers were in the 80dB range, but most were designed for smaller rooms and never intended to be played at very loud levels.


The converse of the fishman's situation would be if someone had 100dB Klipsch, 5 of them, all located near walls. This system only needs 8 watts to hit 111dB.


Now if someone had a typical 90dB speaker, a real 100 watt amp, five speakers, placed 2'-3' ft from walls, and they are sitting 10' from the speaker, the calculation yields 110dB. That's more than enough. A lot of speakers don't sound very good when pushed into that range.


Tom B.
 

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Tom,


The point is, all watts are not measured accurately. That being the case, what should a person look for? Amps? Memory? Something else?
 

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I think a person first tries to determine how much power they need, then they go about identifying who actually meets that need.


There are a lot of reliable measurements out there. Several publications conduct power output benchtests.


In general, manufacturers of separate power amps tend to spend their equipment accurately. I rarely see a benchtest of a solidstate power amp where it falls woefully short of claims. Tube amps are a different story.


However manufacturers' claims of A/V receivers are not so reliable. Some of them base their claim on how much power they can produce into any 1 channel. So some receivers claiming they can produce 100 wpc into 5 channels, with all channels driven, can really only produce around 35-45 watts when all channels are driven with the same input signal.


Since we do have a lot of benchtest measurements, there are patterns by manufacturer. For example take Sony - their ES line tends to meet specs, but their lower-end lines do not, sometimes coming in at only 1/3 of spec. OTOH, Harman-Kardon & NAD nearly always meet spec. Onkyo's lower end stuff usually falls short by up to 50%. Denon is consistently around 75% of spec (except their 4802 exceeds spec).


Many A/V receivers do not design & build their amp sections to provide full sustained power to all channels. Their rationale is that few people actually need that. So they build'em so that any channel can hit spec alone, so that any two channels can come close to hitting spec, and trust that the total demand will not often exhaust the power supply. And they are usually right as there doesn't seem to be a lot of complaints about this, most people, even on these forums, don't seem to notice it in their own systems, and even the mag reviewers have said that they have a hard time detecting this deficiency in listening tests.


This is related to earlier statements in this thread in that many people only need 10, 20, or 40 watts per channel. So if a receiver claims to produce 5x100, but really is only 5x60 & can hit 100 watt peaks, the reality may be that the listener will never suspect anything.


So I think a person should still look for watts, but look for confirmed wattage. And if they have 4 ohm speakers, they should verify that their amp/receiver can adequately drive that load, as a LOT of receivers cannot handle 5 or 7 4-ohm speakers.


Tom B.
 
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