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Audiophile Related - Understanding power, peak, contious and dBs

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DW1961:
My original post was all messed up. I've corrected that below--sheesh! Sorry.


Lets say you a have a speaker that is 45 watts continuous/100 peak at 93dB sensitivity @ 8 ohms.

(We'll fill in the other aspects as we go.)

Now lets say you have two amps:

Amp 1 = has 19 watts per channel continuous @ 8 ohms and 19V.

Amp 2 = 30 watts  per channel continuous @ 8 ohms and 24V.

So you get roughly 32.5% more power on amp 1.
-------------------------------------------------------------

"Increasing an amplifier from 25 watts to 50 watts (double the power) increases the acoustic power by 3dB."
https://geoffthegreygeek.com/amplifier-power/

So you hear any difference in volume between amp 1 and amp 2.

So why not go with a lower wattage amp and save money? In other words, what's the benefit having amp 2 instead of amp 1?

TimFox:
Wrong analysis.
1.  If you have two amplifiers, both rated to drive 8 ohms, with different maximum power ratings, and you connect them one at a time to an 8 ohm speaker, you can get more output from the speaker when driven at higher power.
2.  If you adjust the gain (volume control) to get the same power (within the maximum limit of both amplifiers), you will get the same output from the speaker.
3.  You do not "double the volume" with twice the power.  Sound level is perceived logarithmically, and doubling the volume is not a defined concept.  See the many discussions of the Weber-Fechner Law, e.g., https://ocw.upc.edu/webs/42254/Acustica_EN/Bloc2/Fitxes/T07_02_Llei_Weber_Fechner.htm
4.  If amplifier 1 is not loud enough to annoy the neighbors, then amplifier 2 will give you more sound output.  (Not the result you stated.)
5.  The speaker rating of 45 watts continuous/100 watts peak is a maximum rating:  you may damage the unit if you apply more power.  The amplifier ratings are the maximum output with a specified level of distortion. 
6.  The voltages you mention for the amplifiers are not correct:  19 V rms into 8 ohms is 45 W mean power (NOT rms power, a common misnomer) and 24 V rms into 8 ohms is 72 W mean power.
7.  The speaker sensitivity rating is a specification of how much acoustical output you get for a given electrical input.  It is defined as the indicated sound level (in dB SPL) obtained 1 meter from the speaker with 1 W electrical input.  The definition of "dB SPL" is the ratio of the acoustic power divided by a very low reference level, usually 20 x 10-6 pascal sound pressure, which is roughly the threshold of hearing, and defined in the ANSI S1.1-2013 spec for sound level meters.

DW1961:

--- Quote from: TimFox on August 01, 2020, 09:04:12 pm ---Wrong analysis.
1.  If you have two amplifiers, both rated to drive 8 ohms, with different maximum power ratings, and you connect them one at a time to an 8 ohm speaker, you can get more output from the speaker when driven at higher power.
2.  If you adjust the gain (volume control) to get the same power (within the maximum limit of both amplifiers), you will get the same output from the speaker.
3.  You do not "double the volume" with twice the power.  Sound level is perceived logarithmically, and doubling the volume is not a defined concept.  See the many discussions of the Weber-Fechner Law, e.g., https://ocw.upc.edu/webs/42254/Acustica_EN/Bloc2/Fitxes/T07_02_Llei_Weber_Fechner.htm
4.  If amplifier 1 is not loud enough to annoy the neighbors, then amplifier 2 will give you more sound output.  (Not the result you stated.)
5.  The speaker rating of 45 watts continuous/100 watts peak is a maximum rating:  you may damage the unit if you apply more power.  The amplifier ratings are the maximum output with a specified level of distortion. 
6.  The voltages you mention for the amplifiers are not correct:  19 V rms into 8 ohms is 45 W mean power (NOT rms power, a common misnomer) and 24 V rms into 8 ohms is 72 W mean power.
7.  The speaker sensitivity rating is a specification of how much acoustical output you get for a given electrical input.  It is defined as the indicated sound level (in dB SPL) obtained 1 meter from the speaker with 1 W electrical input.  The definition of "dB SPL" is the ratio of the acoustic power divided by a very low reference level, usually 20 x 10-6 pascal sound pressure, which is roughly the threshold of hearing, and defined in the ANSI S1.1-2013 spec for sound level meters.

--- End quote ---

Of GEZUZ! I misaddressed that up. No kidding you don't double power volume by doubling power!  I've now changed my question. Please comment again!  Sorry!

TimFox:
The higher power amplifier can make more acoustic power out of the speaker than can the lower power amplifier out of the same speaker.  I really don’t understand your question.
If you are comparing two different amplifiers, there's a lot of "all other things being equal".  An excellent 19 W amplifier putting out 15 W may have lower distortion than a crappy 30 W amplifier putting out the same power (15 W).  Were all other things equal, however, if you only need 15 W to achieve the desired sound level for your application, one would expect the 30 W amplifier to have lower distortion at 15 W than does the 19 W amplifier at 15 W output.  That is one reason to use the higher power amplifier.  93 dB sensitivity means that 1 W will achieve 93 dB SPL out of the speaker (1 meter from the speaker), which is enough for many applications.  500 W would drive the speaker (if it could handle it) to 120 dB SPL, which is nearly painful and may cause hearing damage.  If you put the maximum peak level of 100 W into the speaker (which is 20 dB above 1 W), you will get a respectable 113 dB SPL, louder than a jackhammer and comparable to a chainsaw.  The 30 W amplifier (15 dB above 1 W) will give 108 dB SPL at 1 m.  Long term exposure to 85 dB SPL is considered to be harmful to hearing, and is regulated by OSHA.  The sound level will fall off as you move back from the speaker;  in a normal room, the fall-off is complicated by reflections from the walls, but in free space the power falls off with the square of the distance.

Bassman59:

--- Quote from: DW1961 on August 01, 2020, 08:42:54 pm ---
Now lets say you have two amps:

Amp 1 = has 19 watts per channel continuous @ 8 ohms and 19V.

Amp 2 = 30 watts  per channel continuous @ 8 ohms and 24V.

So you get roughly 32.5% more power on amp 1.
-------------------------------------------------------------

So why not go with a lower wattage amp and save money? In other words, what's the benefit having amp 2 instead of amp 1?

--- End quote ---

Amp 2 will be louder than Amp 1, all other things being equal. Significantly louder? No. Cleaner louder? Yes, assuming distortion specs are the same at the rated output.

Driven into distortion, Amp 1 could be as loud as Amp 2.

The spec that ultimately matters is desired SPL at a particular distortion level. If the SPL you get with Amp 1 and your speakers suffices, then you use Amp 1.

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