Headunit RMS power discussion
08-15-2004, 10:49 AM
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Headunit RMS power discussion
You guys got me thinking about my understanding of power in a stereo system. I think there is a mistake about either mine or other peoples understanding. You really got me thinking about it.
So if a headunit has 18 watts per channel vs. 32 watts per channel. Which is better?
If I understand correctly you look at a make-believe speaker that is rated at putting out 90db at 1 watt. So to get an additional 3 db you have to double the power. Thus it is good to have a more efficient speaker.
To get 93 db your unit has to put out 2 watts.
96db = 4 watts
99db = 8 watts
102db = 16 watts (18 watt per channel unit peters out just above this)
105db = 32 watts (32 watt per channel unit peters out here)
108db = 64 watts
111db = 128 watts
(You can see how the power requirements soar for db competition vehicles)
To go any louder with clarity and without peaking/clipping the amplifer you would have to resort to a more powerful unit or amplifier.
So in all fairness the 32 watt per channel unit is marginal in benefit over the 18 watt per channel unit.
Interesting. Am I right? Wrong? Crazy...nevermind on crazy I know that answer.
So if a headunit has 18 watts per channel vs. 32 watts per channel. Which is better?
If I understand correctly you look at a make-believe speaker that is rated at putting out 90db at 1 watt. So to get an additional 3 db you have to double the power. Thus it is good to have a more efficient speaker.
To get 93 db your unit has to put out 2 watts.
96db = 4 watts
99db = 8 watts
102db = 16 watts (18 watt per channel unit peters out just above this)
105db = 32 watts (32 watt per channel unit peters out here)
108db = 64 watts
111db = 128 watts
(You can see how the power requirements soar for db competition vehicles)
To go any louder with clarity and without peaking/clipping the amplifer you would have to resort to a more powerful unit or amplifier.
So in all fairness the 32 watt per channel unit is marginal in benefit over the 18 watt per channel unit.
Interesting. Am I right? Wrong? Crazy...nevermind on crazy I know that answer.
Last edited by DavidA; 08-15-2004 at 10:51 AM.
08-15-2004, 04:06 PM
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That sounds about right. Keep in mind that the issue of sound pressure level or spl gets much more complex. A good sound quality driver may be only 86db 1 watt 1 meter effecient at best. Many are only 83 to 86. You also have to take into consideration the frequency range its being used in as well as the finished "Q" or damping of the driver in its enclosure. A very effecient driver may be a very peaky sounding speaker.
An 18 watt HU vs a 32 watt HU presents differences in sound, but they are small in the grand scheme of things. It is most noticable at the edges of clipping. Most mfg. however will use better quality components and better features in the higher power units. You have to decide if the volume produced by 18 watts is right at what you would want. If you would never listen at that volume, then go for it. If you feel that you would like to listen at that volume, go for the higher power unit for the extra headroom, or a seperate amp.
A 32 watt per channel amp will in my opinion outperform a 32 watt per channel HU simply because the amp can be larger, more beefy, use better quality components and because it is built for that one purpose.
An 18 watt HU vs a 32 watt HU presents differences in sound, but they are small in the grand scheme of things. It is most noticable at the edges of clipping. Most mfg. however will use better quality components and better features in the higher power units. You have to decide if the volume produced by 18 watts is right at what you would want. If you would never listen at that volume, then go for it. If you feel that you would like to listen at that volume, go for the higher power unit for the extra headroom, or a seperate amp.
A 32 watt per channel amp will in my opinion outperform a 32 watt per channel HU simply because the amp can be larger, more beefy, use better quality components and because it is built for that one purpose.
08-15-2004, 06:30 PM
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Before ppl get too excited about 18 vs 30 watts.... You cant go by the simple manufacture provided rating itself. ALso theres more to amplification than "watts"
It always helps to be able to read the WHOLE STORY, (regarding comprehension of the rest of the measurements) to base line that wattage rating. Measured at what voltage, Channel seperation, S/N ratio, +- db variance across the freq, the freq spectrum used, THD, also damping factor can be significantly different from the powered HU vs a seperate amp that will make huge (subjective as some ppl have no clue what a "good" system sounds like) sonic differences.
Watts are like Horsepower, you gotta watch how its measured and then advertised.
Example.... (very simple and usable for this point) 300watt booster EQ.... 150 blazing watts per channel, according to package. Yet it comes with 10 amp fuse. hmmmmm ?
Real World 10A x 12v =120 watts... 50% heat loss = 60 watts music.... ==> 30watts per channel. NOT 150 as manufacture claims. False advertising, well not if you look at the specs on how they measured it and came up with 150watts. 10% THD, 1W/M at 1KHz, peak power (eccch !).
It always helps to be able to read the WHOLE STORY, (regarding comprehension of the rest of the measurements) to base line that wattage rating. Measured at what voltage, Channel seperation, S/N ratio, +- db variance across the freq, the freq spectrum used, THD, also damping factor can be significantly different from the powered HU vs a seperate amp that will make huge (subjective as some ppl have no clue what a "good" system sounds like) sonic differences.
Watts are like Horsepower, you gotta watch how its measured and then advertised.
Example.... (very simple and usable for this point) 300watt booster EQ.... 150 blazing watts per channel, according to package. Yet it comes with 10 amp fuse. hmmmmm ?
Real World 10A x 12v =120 watts... 50% heat loss = 60 watts music.... ==> 30watts per channel. NOT 150 as manufacture claims. False advertising, well not if you look at the specs on how they measured it and came up with 150watts. 10% THD, 1W/M at 1KHz, peak power (eccch !).
Last edited by COYOTA $x$; 08-15-2004 at 06:31 PM.
08-25-2004, 10:42 PM
#4
David A
that whole DB scale thing from the 70's only applies to frequencies at or around 1kHz, it has nothing to do with any of the frequencies which tax the amplifier due to dynamic impedance shifts or power density. Then there is the problem of dynamic power compression inside the vehicle and absorbtion coefficients of the fabric.... my advice, dont use a deck to power speakers-- at about 80Hz, the deck loses almost all of its ability to drive a reactive load and you are left with about .1 watts of clean power.
T
that whole DB scale thing from the 70's only applies to frequencies at or around 1kHz, it has nothing to do with any of the frequencies which tax the amplifier due to dynamic impedance shifts or power density. Then there is the problem of dynamic power compression inside the vehicle and absorbtion coefficients of the fabric.... my advice, dont use a deck to power speakers-- at about 80Hz, the deck loses almost all of its ability to drive a reactive load and you are left with about .1 watts of clean power.
T
08-26-2004, 07:47 AM
#5
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Originally Posted by Duffdog
David A
that whole DB scale thing from the 70's only applies to frequencies at or around 1kHz, it has nothing to do with any of the frequencies which tax the amplifier due to dynamic impedance shifts or power density. Then there is the problem of dynamic power compression inside the vehicle and absorbtion coefficients of the fabric.... my advice, dont use a deck to power speakers-- at about 80Hz, the deck loses almost all of its ability to drive a reactive load and you are left with about .1 watts of clean power.
T
that whole DB scale thing from the 70's only applies to frequencies at or around 1kHz, it has nothing to do with any of the frequencies which tax the amplifier due to dynamic impedance shifts or power density. Then there is the problem of dynamic power compression inside the vehicle and absorbtion coefficients of the fabric.... my advice, dont use a deck to power speakers-- at about 80Hz, the deck loses almost all of its ability to drive a reactive load and you are left with about .1 watts of clean power.
T
HU's that have an internal amp are trash imho....
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