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| Thread ID: 30846 | 2003-03-04 18:18:00 | OT - measuring the power coming out of a car stereo... | tango (2697) | Press F1 |
| Post ID | Timestamp | Content | User | ||
| 125583 | 2003-03-05 02:47:00 | :D If you measure the amount of heat generated in a resistor fed by an amplifier you are measuring the power output of the amplifier regardless of music waveform without any high technology. In fact you will get true RMS. I suppose a thermocouple ammeter might work too, but their weak point was always their overload protection: none. I suspect that many so-called high power amplifiers wouldn't cause any risk of blowing out the jug elements. (Like the 120W computer speakers with 12V, 300 mA power bricks). My preferred power measurement method for car systems would be: (1) start the system (2) get out and close the door (3) can you hear it (4) reach in and turn it down. (5) open a window (6) repeat 2-4 |
Graham L (2) | ||
| 125584 | 2003-03-05 07:17:00 | I agree completely with Clueless regarding damage to speakers with a underpowereds amp. The biggest damage you can do to speakers is run them into clipping, where the distortion will damage the speakers. A amp with a high current rating will gladly power smallish bookshelfs, but a big set of floorstanding speakers will go to mush if they are powered by a tinny amp. As a point of interest, a lot of esoteric American valve amps are rated at around 20watts per chanell, yet can drive extremely large beefy audiophile speakers. It will also go louder than the average 150watt Jap amp. Why? its not the watts per chanel, but the current loading Sorry this has got away from the car audio topic. But it is audio |
Baldy (26) | ||
| 125585 | 2003-03-05 07:23:00 | Forgot to add, I think its hilarious when people tell you their little Aiwa mini system stereo is 650watts per channel, or the favourite question is "how many watts per channel are those speakers?" | Baldy (26) | ||
| 125586 | 2003-03-05 08:09:00 | We need a law as in some parts of Europe, where it is an offence if your car stereo can be heard at a distance of 7 metres from the car. | godfather (25) | ||
| 125587 | 2003-03-05 08:13:00 | I dont suppose anyone remembers the Mullard 510 valve amplifier, which had 5 valves, 10 watts output, and when combined with the Mullard 3 valve pre-amp and a 9 cubic foot corner bass reflex cabinet with 10" Stentorian speaker, gave all the output anyone would normally want in a normal room. Speaker and cabinet design has changed radically over the years, with so much emphasis on exaggerated bass response and so much damping applied to the speakers that power output doesnt mean the same as it did. Also I dont suppose many people remember what real unamplified dance/jazz band music sounded like with real non-electronic instruments being played, like brass, string and reed, by superbly technical musicians, it was a different world entirely :) |
Terry Porritt (14) | ||
| 125588 | 2003-03-05 08:14:00 | I wonder if that law applies to driving on the open road? There's nothing like a long drive with an el grunto sound system! Ahh one day it shall be! .Clueless |
Clueless (181) | ||
| 125589 | 2003-03-05 08:34:00 | Accoustic music??? Yes i remember.. i seem to remember it from a party a few months ago, friends of mine who are rather talented were jamming with various percussion instruments, accoustic guitar, a couple of wind instruments, and vocals. Very unexpected, and very powerful! .Clueless |
Clueless (181) | ||
| 125590 | 2003-03-05 22:07:00 | Said with the greatest of respect Baldy, Bollocks :p Power is current into impedance and is an incontravertable law of physics . The subjective loudness of an amplifier, valve or otherwise is a function of: (a) the instantaneous (undistorted) peak power output, (b) the efficiency of the speakers, (c) the characteristics of the signal input, (d) the listening environment, and (e) the preconceived expectations of the listener . Measured power output is quite another matter . Take away (d) & (e), use a professional-grade sound pressure meter (yes, I have one), and compare watts with watts from different amps on the same signal source and speakers, and you will find that there is no difference in sound pressure levels . Substitute inefficient speakers on the solid state amp, put high efficiency speakers on the valve amp, and the sound pressure figures will be quite different . Speakers designed for valve amplifier use are commonly of much higher efficiency because the available input power is strictly limited . Solid state amps have an abundance of raw power, consequently speaker systems have been designed to handle that power and they are often significantly less sensitive . Note that I do not hold these propositions up to be absolutes . There are efficient speakers designed for solid state amps and inefficient speakers designed for valve amps . Neither do I comment on the subjective quality of the sound from the two different amplifier types, that is for audiophiles to debate, ad nauseum . Speaker damage is a function of power input, and a 100W RMS rated speaker system can be run all day and all night on a 25 or 50 watt amp at full amplifier overload, clipping and mush notwithstanding, without sustaining any damage at all, unless the neighbours come over with an axe . :D Speakers are damaged by excessive heat build-up in their voice coil or by excessive excursions of the voice coil/cone combination . Crappy signal input quality is of no consequence . For heavens sakes, they can handle anything from orchestral transients, 1812 Overture cannon blasts, synthetic (electronically generated) music, gross overload-type distortion as introduced by special effects equipment for guitarists and various bleeding-edge musos . At various times during development they may be subjected to or tested with squarewaves and other nasties to check their transient response and cone-break up characteristics at their rated power levels . Don't tell me that they can't handle amplifier clipping at RMS power inputs substantially below their normal continuous RMS power rating . Don't tell me either that you can damage a speaker operating in a properly designed enclosure with any musical input from an amplifier running at full output (distortion and all) within the continuous RMS (not music power) operating ratings of the speaker system . Speakers don't care about input quality, they don't have ears . Only a faulty speaker will fail, and it is even less likely with an underpowered amp . Of course car audio systems are another matter, automotive speaker systems are rarely baffled and loaded correctly because proper enclosures are difficult to incorporate into most motor vehicles . They cop sun, heat, dust, dirt and all manner of abuses . Not surprisingly, they fail often . Here endeth the rant :8} Cheers Billy 8-{) :| |
Billy T (70) | ||
| 125591 | 2003-03-06 01:58:00 | Terry, I built a Mullard 3-3 amplifier once (that was EF86, EL84, and a 6X4). Then I got modern and built the transistor one from the Mullard book: OC71 and 2 OC84s ... marvellous state of the art technology ... built on .156" Veroboard, and 250 mW out. :D I'm still using Veroboard, but I more often wirewarp digital stuff on it. |
Graham L (2) | ||
| 125592 | 2003-03-06 02:12:00 | Hi Graham, yes that was a good amplifier for just 2 valves. I still have the Parmeko output transformers for the 510 and 3-3, they were too good to throw away, kept them just in case they would be useful one day :) | Terry Porritt (14) | ||
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