Just curious..
How much input wattage is actually carried over and added to the output watts of an amp?
For example if my stereo is pushing 20 watts per channel and I install an amp that pushes 50 watts per channel, am I running 70 or is there some loss before amplification? Just looking for an average or 'in most cases' answer as I know it probably depends on the amp itself.
Replies (3)
Swez on 11/10/2003 08:04:37
Yes, it does depend entirely on the amp you add to the system.
Example: Say you have a 20 watt/ch., HU/receiver. You can connect it to the input side of an outboard amp via high signal inputs or LOC/RCA's to the amp input. The HU power will be reduced to a voltage level the amp can handle, then processsed through the preamp and output transistors that feed your speakers.
As for how much amp power you actually get to your speakers, depends on the amp used and the speaker impedence load. Depending on the amp design, there is a heat loss factor.. (efficiency rating) to consider too. Class D amps (subs only) are very efficient and generate ~90% output watts VS the watts the amp consumes. If A Class A/B Mosfet PWM power supply amp (full range or subs) is used, you get ~60% efficiency here as the amp grabs 40% in heat losses etc.
Finally, there is only a +3.3 dB increase in audio output from the speakers in a 20 watt amp VS a 50 watt amp. Enough to notice a difference. But not enough power difference to really kick up the over all audio output. If you go up to an 80 watt amp, now you get +6dB of added output. That will make a difference in what you hear in output.
NOTE: For every doubling of amp power you use to power your speakers, you'll get a +3dB increase in audio output. A +9dB increase will effectively double the audio SPL your ears will detect.
Here's a rough chart of how it all works out:
Assume a speaker efficiency rating of: 90 dB SPL @ 1w/1m, all are RMS watts. (not peak)
1 watt input = 90 dB SPL
2 watts = 93 dB
4 watts = 96 dB
8 watts = 99 dB
16 watts = 102 dB
32 watts = 105 dB
64 watts = 108 dB
132 watts = 111 dB
264 watts = 114 dB
528 watts = 117 dB
Now, in a car environment, there is a "cabin gain factor" that can add 15-25 dB to your numbers, depending on the vehicle and location of the speakers. If this is a HT application... the "room gain factor" is much less. More like 10-15 dB of added acoustical coupling. Depends on the location of the speakers.
Comments?
Swez
cplkittle on 11/11/2003 08:26:51
very thorough, and much appreciated. I did think about it after I posted the question that once I attempted to 'fix' a blown amp and noticed that all of the imputs had resistors. I assumed that this was to drop the imput to a level the amplifier could handle as you mentioned. As far as the cabin gain factor is Dynamat really worth the money?
ttocs on 11/11/2003 12:08:42
I will put it in my car, and I would recommend putting something in your car. There are alot of very good and cheaper alternatives to dynamat. Check out brown bread(In my truck now) or rammat...
How much input wattage is actually carried over and added to the output watts of an amp?
For example if my stereo is pushing 20 watts per channel and I install an amp that pushes 50 watts per channel, am I running 70 or is there some loss before amplification? Just looking for an average or 'in most cases' answer as I know it probably depends on the amp itself.
Replies (3)
Swez on 11/10/2003 08:04:37
Yes, it does depend entirely on the amp you add to the system.
Example: Say you have a 20 watt/ch., HU/receiver. You can connect it to the input side of an outboard amp via high signal inputs or LOC/RCA's to the amp input. The HU power will be reduced to a voltage level the amp can handle, then processsed through the preamp and output transistors that feed your speakers.
As for how much amp power you actually get to your speakers, depends on the amp used and the speaker impedence load. Depending on the amp design, there is a heat loss factor.. (efficiency rating) to consider too. Class D amps (subs only) are very efficient and generate ~90% output watts VS the watts the amp consumes. If A Class A/B Mosfet PWM power supply amp (full range or subs) is used, you get ~60% efficiency here as the amp grabs 40% in heat losses etc.
Finally, there is only a +3.3 dB increase in audio output from the speakers in a 20 watt amp VS a 50 watt amp. Enough to notice a difference. But not enough power difference to really kick up the over all audio output. If you go up to an 80 watt amp, now you get +6dB of added output. That will make a difference in what you hear in output.
NOTE: For every doubling of amp power you use to power your speakers, you'll get a +3dB increase in audio output. A +9dB increase will effectively double the audio SPL your ears will detect.
Here's a rough chart of how it all works out:
Assume a speaker efficiency rating of: 90 dB SPL @ 1w/1m, all are RMS watts. (not peak)
1 watt input = 90 dB SPL
2 watts = 93 dB
4 watts = 96 dB
8 watts = 99 dB
16 watts = 102 dB
32 watts = 105 dB
64 watts = 108 dB
132 watts = 111 dB
264 watts = 114 dB
528 watts = 117 dB
Now, in a car environment, there is a "cabin gain factor" that can add 15-25 dB to your numbers, depending on the vehicle and location of the speakers. If this is a HT application... the "room gain factor" is much less. More like 10-15 dB of added acoustical coupling. Depends on the location of the speakers.
Comments?
Swez
cplkittle on 11/11/2003 08:26:51
very thorough, and much appreciated. I did think about it after I posted the question that once I attempted to 'fix' a blown amp and noticed that all of the imputs had resistors. I assumed that this was to drop the imput to a level the amplifier could handle as you mentioned. As far as the cabin gain factor is Dynamat really worth the money?
ttocs on 11/11/2003 12:08:42
I will put it in my car, and I would recommend putting something in your car. There are alot of very good and cheaper alternatives to dynamat. Check out brown bread(In my truck now) or rammat...
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