Calculating SPL from S.E.X.

[PassionForSound]

Can anyone tell me the approximate wattage produced from the S.E.X. wired on the 4 ohm taps and driving a 600ohm load?

 

[Paul Joppa]

See post below for corrected numbers!!

"Twinkle, twinkle, little star;
power equals I-squared R"

so 2 watts equals current squared times 4, hence current is 1 amp into 4 ohms.

Ohm's law says voltage equals current times resistance, so 4 volts across the output.

Ohms law, second variant, says current equals voltage divided by resistance, so 0.006666 amps into 600 ohms.

Consult the stars again, to get 0.02666 watts, or 26.7mW into the 600 ohm cans.

:^)

 

[PassionForSound]

Thanks Paul.

Missing links for me was knowing that the 2 ohms came out prior to the OTs and that the 4 ohm taps are named thus for their impedance rather than what they match up with speaker-wise.  :-[

Your answer is extremely helpful and informative, thank you!

 

[PassionForSound]

By the way, does this mean that the output impedance of the S.E.X. is equal to the OT tap ratings? (4 / 8 / 16 or 32?)

 

[Paul Joppa]

By the way, does this mean that the output impedance of the S.E.X. is equal to the OT tap ratings? (4 / 8 / 16 or 32?)

Nope.

The 4/8/16/32 ohm taps are designed to feed the maximum available power to loads of 4/8/16/32 ohms, respectively. The actual source impedance looking back intot he outputs is somewhere between 1/3 and 1/2 of the tap's nominal impedance.

 

[PassionForSound]

OK. Thanks Paul.

 

[jrebman]

Paul,
1 squared times 4 = 2? Not following that...

-- Jim

 

[Paul Joppa]

Paul,
1 squared times 4 = 2? Not following that...

-- Jim

Sorry, that was pretty terse, and incorrect to boot! Try again:

"Twinkle, twinkle, little star;
power equals I-squared R"

so 2 watts equals current squared times 4 ohms, hence current squared is 1/2 and current is 0.707 amps.

Ohm's law says voltage equals current times resistance, so 2.83 volts across the output.

Ohms law, second variant, says current equals voltage divided by resistance, so 0.0047 amps into 600 ohms.

Consult the stars again, to get 0.0133 watts, or 13.3mW into the 600 ohm cans.

 

[PassionForSound]

Equal parts thankful and embarrassed.

Thankful that the correct maths brought available power down (gives me more confidence that I am not accidentally shredding my ears) and embarrassed that I didn't look at the sums closely enough to realise the error. Blind trust anyone!?  :-[

 

[jrebman]

Always trust the blind guy

Do I get a free BeePre for finding a PJ math error .

-- Jim

 

[Paul Joppa]

With apologies to Jim, I make so many math errors that even the blind guy finds them. Seriously though, there's much more to looking than just seeing, if you take my meaning ...  :^)

 

[jrebman]

No apology needed! Hey, we all do it -- some more than others.

-- Jim

 

[Grainger49]

All of us gray haired Electrical guys seem to do that from time to time.