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Meaningful stereo-equipment specs

Rate amplifiers and speakers by their useful ability
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I would like to see amplifiers and speakers each provided with a pair of power ratings. For amplifiers, the numbers would be:

1. What is the maximum power this amplifier can output while meeting published distortion/frequency response specifications.

2. What is the maximum power this amplifier might output, perhaps "accidentally", regardless of quality.

For speakers, the numbers would be:

1. What is the maximum power this speaker can handle while meeting published distortion/frequency-response specifications.

2. What is the maximum power that this speaker can safely handle, at worst-case frequency, for 10 seconds without damage.

The first spec from each pair would allow someone to determine which equipment would meet their power-handling needs, while the latter spec would help people avoid trashing their speakers.

BTW, a related feature I'd like to see on stereo systems would be a dial one could set which would limit the maximum power the system would output. This could be useful in case someone has an amplifier whose maximum output power would otherwise damage their speakers.

supercat, Jun 23 2001


       And something I'd like to see is a maximum volume that can be set by someone else. Is it -really- necessary to play music so loud that it gives people more than 100 yards away on the second floor of an office building with no outside windows headaches? <This happened where I am now. Some idiot had a boom-car outside.>
StarChaser, Jun 24 2001

       Manufacturers won't go for it. Manufacturers of cheap equipment want to be able to obfuscate the actual power of their equipment, and manufactures of high quality equipment want to discourage comparison of simple power numbers, because they (rightly) argue that they're less important than the overall quality of the component.   

       Besides, any decent manufacturer or vendor should be able to provide you with the numbers you're looking for, if they're not on the box.
TickleMeElmo, Jun 24 2001

       >>...because they (rightly) argue that they're less important than the overall quality of the component.   

       Actually, the key would be how manufacturers decide to rate their power vs distortion specs. An amp may be able to achieve 0.05%THD at 10 watts, but 1%THD at 25 watts; while nowadays makers would have no problem labeling such an amp as probably about 35 watts, under my proposal the maker would have to choose a THD/power combination that was actually obtainable (or list more than one).   

       One of the problems with today's "peak power" ratings is that in many cases one doesn't want a "peak power" level which is too much higher than the actual usable power level, since the only thing a higher peak rating will do is increase the likelihood of one destroying one's speakers.
supercat, Jun 25 2001

       I have to admit that these are the same issues I ask about in shops when I go to buy a new gramophone.
Aristotle, Jun 25 2001

       To be truly helpful to an audiophile (or a sound reinforcement professional catering to audiophiles), the spec would need not just a pair of numbers, but a full range plot of THD vs. total power with a well-defined, *industry-standard* input signal. For example, the standard input might be a pure sine wave at 1 KHz, or a sum of pure sine waves at certain different frequencies and equal powers. The plot would need at least a few tens of data points (evenly spaced), so that the degradation at the high end would be clearly shown.   

       Even without all that, just to get the manufacturer to publish (yes, on the outside of the box) the THD at 80% Max Rated Power with a Known Signal would give the buyer enough information to make an informed decision. That is exactly why consumer electronics manufacturers DO NOT publish that information. They benefit from consumer ignorance and gullibility, and generally go out of the way to obfuscate the actual performance of the products they sell.   

       By the way, [supercat], your #2 rating requirement is an excellent idea. While speakers generally come with a peak input power specifaction already, never have I seen any amplifier with a Worst-Case Guaranteed Maximum Power rating. Croissants just for that, if nothing else.
BigBrother, Aug 14 2001

       The trouble with any simplified specs for hi-fi is that they must over-simplify. I agree with [BB] that the no. 2 rating is a good idea, but you would need to specify the frequency of the input signal. I have a 18" speaker rated at 200W for bass guitar, but it would probably die if I put 100W of 16kHz through it. You also need to be aware of the characteristics of your particular amplifier. I have an old Mullard valve (tube) amp rated at 20W which is significantly louder than my 35W JVC solid-state amp because of the way valve amps work.
angel, Aug 14 2001

       Supercat...you're on to something again. In terms of real "truth" of recording....NO specs are useful. THD or other distortion figures don't tell a thing about the "quality" of the music. Music realism is actually the ability produce the real dynamics of the original signal. You are correct that one of the important points is to spec the ability to produce real POWER. I would suggest that it would be easy to spec a speaker's ability to provide a certain dB into a "standard" living area of X square feet and dimensions. Sensitivity and other speaker parameters do not relate to this ability to "project" a "music power level".   

       Meanwhile...my only concern is over the illusive "slew rate" parameter which defines the systems ability to produce the realistic "wide band" transients that people discern as the real difference between live and recorded music. The phono cartridge and speakers are capable of following signals to microsecond transient response. CD at 44.1KHz cannot follow such transients. New DVD audio and SACD are making strides...but why can't we have a true measure of this "realistic" ability to reproduce the real signature? Come up with that....and you really have something. Another thing to note is that there is no measure of all the "digital distortion" and especially "phase smearing" which occurs due to imperfect digital filters. Much to much to write on this. But you're absolutely correct. Start putting some attention to the specs....and you'll see an industry responsiveness to this issue.
BobWade, May 07 2002

       [BobWade] I disagree with a bit of what you are writing here. I believe that, to those who are experienced listeners of audio equipment and who understand standard ratings, the THD directly represents the amount of listener fatigue one might expect to confront when listening to a given amplifier. I do not disagree, at all, that some better, more meaningful, spec should be created as a metric for "sustained listen-ability" (transparency?) at a given power level. Since such a thing is so subjective, I can't imagine that this standard metric can be easily arrived at.   

       I agree that an amplifiers rise time is maybe not as important when the medium that is being reproduced is incapable of delivering those short transients to begin with. I do think, though, that an amplifiers ability to control overshoot following a near square transition is important and contributes to distortion.   

       [supercat]: I believe that good speakers are much more tolerant of a transient peak well beyond their rating than they are capable of handling the output of a lesser amp that is clipping.  A low power amplifier is much more capable of damaging speakers than a quality amplifier of high-power. When a low power amplifier clips ("put-puts") either due to being overdriven or due to a transient, the resulting mess passed to speakers can be much more damaging. Even worse is a crappy direct-coupled amp passing DC directly to the speakers (yum, molten voice coils).
bristolz, May 08 2002

       What I was trying to do was read between the lines and jump to a bottom line. My take was that supercat really wants to listen to loud music, but with quality.....but doesn't want to necessarily "pay the price" to get there.   

       If you started with a meaningful speaker spec to deliver POWER in a VOLUME (at a rated power input)....then you've progressed beyond what exists now....which provides NO measure of a true speakers output to MOVE YOU.   

       Various testing articles include such measures...but they haven't been universally adopted.   

       Once a true measure of speaker "efficiency" to produce power over volume is provided...then you can easily buy an amp with sufficient headroom to give you what you want. The mystery is basically gone. There are plenty of great amps out there....there aren't alot of great speakers that produce quality volumes of sound.   

       I still live with a pair of ESS monitors....affectionately called the "rock speaker" over the years....and bi-amp them with 50 watts X 2 each (it's a 2 way). Part of their appeal was this "unspeced" ability to produce rock levels of music enjoyment.   

       And for those crazed to desire max output for car stereos....such speaker ratings would be important.   

       Otherwise....maybe a better idea for measuring truth is to start by recording a complex musical passage....with inputs and outputs "mapped" to see the differences.   

       If we get a handle on how phase and risetime inaccuracies translate into listenable problems...then we might be getting somewhere.
BobWade1, May 08 2002

       Personally I don't want my music especially loud, but I would like to know what I'm really getting when I buy something.   

       Bristolz is quite correct in noting that clipping can be very bad for speakers; depending upon the speaker design and exact signals involved it may be more or less damaging than transients. One difficulty is that many speakers are designed to handle a mix of frequencies; a speaker may be able to output 100 watts of pink noise all day and yet be trashed in short order by 25 watts of 1000Hz. Clipping tends to produce large concentrations of harmonics which may, if they fall in a bad spot, cause severe speaker damage.   

       One thing, btw, I've not really seen covered in electronics magazines (and I don't get any audiophile magazines so I don't know if it's covered there) is the variability of speaker impednace with frequency and how an amplifier reacts to it. My impression is that most amplifiers will try to behave as though they have zero-ohm source impedance. If a 100mv signal produces a 12-volt output into an 8-ohm load at some volume setting, it would also output 12 volts into a 7 ohm load, a 16 ohm load, or a 1K ohm load. Such a design will cause power output to be inversely proportional to output impedance.   

       If the amplifier were instead designed to mimic an 8 ohm source impedance, then it would output the maximum amount of power into an 8 ohm load (e.g. 12 volts, 1.5 amps, 18 watts); a four-ohm load would receive somewhat less power (8 volts, 2 amps, 16 watts) as would a 16-ohm load (v6 bolts, 1 amp, 16 watts). Even a two-ohm load would be reasonable (4.8 volts, 2.4 amps; 11.5 watts) as would a 32-ohm load (19.2 volts; 0.6 amps; 11.5 watts). Having the amplifier minic an 8-ohm source impedance would, I would think, cause frequency response to be much flatter than if the amplifier simply acts as a voltage source.
supercat, May 08 2002

       Aristotle: Gramophones can produce 90 dBA with a soft tone needle. Use a loud tone needle and it rises to 93 dBA. This is with a collection of common 78's. Cut a 78 at 70 lines (grooves) per inch and put in frequencies that are most easily heard and you will have the loudest sound from a gramophone. I wonder if there is a 78 out there that will stop a gramophone spring from unwinding or will blow the sound-box? Perhaps some records from India will do the trick.
Amishman35, May 09 2002

       I like BigBrother's overall assessment, but with one addition...the ability to produce "sound volume" over a "standard listening room"....and with a realistic music piece or pieces.   

       One of the biggest prices one pays for is "volume of music". We would all be listening to very expensive, but low powered amps and headphones if this wasn't true.   

       The most impressive stereos produce quality loud sound over large areas.   

       If you can get a quality speaker, it is efficient, AND it produces alot of sound in a volume at a particular power level....then you have something.   

       Many speaker manufactures simply "replicate" certain "low music output" designs in order to get to these higher volume levels. But does doubling the number of drivers equate to "twice the sound volume"?   

       Should you be paying for that size speaker and all its drivers when another speaker with half the drivers will do?   

       And how about the price of either?   

       That's the bottom line I was talking about. The problem of course is agreeing to a "univeral sound test" and listening room. Any particular rag could adopt their own of course.   

       The rating would show dB of sound, THD, and power level. as BigBrother describes....and would run up in power numbers so that you could get a feel for what was happening in terms of power vs. sound output.   

       Another point of this would be to define the ability of a speaker to produce "midrange punch"....an often distressing inadequacy in expensive speakers.   

       Low end rumble therefore is not the answer.   

       One could note the ability of the speaker to produce a volume of sound, at particular power levels, and in different frequency ranges.   

       With this in mind, a good complex real music source is the best standard to use. Anything else could lead to erroneous conclusions.
Bob Wade, May 09 2002

       "The Fat of the Land" by The Prodigy is a good test of any system I reckon.
blammo, Oct 05 2004


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