[purk]

Mystyler,
Nice math!! I love math!!! We need to constant the variable, such as voltage...etc.

 

[AssafL]

Headphones (or speakers) conver electrical energy to acoustical energy. The is why the headphone packages have a sensitivity figure (E.g. 102dB/mW).
As you can see, only the power input affects the volume and impedance has nothing to do with the percieved volume of the headphone

So, just what is the Impedance number and why is it shown?
When a manufacturer states 3mW at 16 Ohms it means the following:

The voltage present at the output (at maximum power output):
V*I=P
I=V/R
=> P=V^2/R (Where ^ means power, ie: V squared)

A similar equation for current:
or V=I*R
=> P=I^2*R

i.e. the voltage is V=Square root of (P*R) = SQR(P*R)

Case A: 3mW at 16 Ohms: V= SQR (3mW*16Ohms) = SQR (0.003*16) = 0.219V
Case B: 3mW at 32 Ohms: V= SQR (3mW*32Ohms) = 0.309V

The current at the output (I = SQR (P/R)):
Case A: 3mW at 16 Ohms: I= SQR (3mW/16Ohms) = SQR (0.003/16) = 0.013A=13mA
Case B: 3mW at 32 Ohms: I= SQR (3mW/32Ohms) = 0.0096A=~10mA 0.013A=13mA

I.e. for Case A, the voltage is lower but the current is higher, while for case B the voltage is higher but the current is lower.

What does all this mean? the internal circutry can handle 3mW output without overheating. The actual performance, however, will depend on the amplifier rail voltage (when reached, clipping occurs, or the chopping of any signal part higher than the rail voltage), and the absolute maximum current capability of the output device.

E.g. some portable electronic equipment have both line out and headphone outputs. Plugging a low impedance headphone into the line out usually results in a higher volume but with a really high distortion.
What happens is as follows: The voltage capability is there (as evidenced by the line out when connected to a high impedance input), however, the current is limited so the resultant waveform is clipped when connected to a low impedance headphone.

Tips: If a manufacturer specified 16 or 32 Ohms, try to stick with low impedance headphones (16 or 32 Ohm should not differ at all). HD 600 will not work (the voltage rails are too low to "move" the phones), and 100Ohm phones may or may not work satisfactorily (test before you buy). Also the sensitivity will change the volume, so a 100Ohm 106dB/mW (some sony models) may be much louder than a 32Ohm 100dB/mW.

I hope this makes sense to someone...

 

[Mystyler]

I think the Panasonic is the SL900...
I love maths when I don't understand what I'm doing, Purk!

BTW AssafL, that makes sense to me!

Thanks

 

[acidtripwow]

I love math, I used to be a math major in college.

I asked Audio Cubes and they said they will be selling this PCDP when they can get it. No pricing was mentioned.

 

[Mystyler]

Did you get any specs, acidtripwow?

I don't think I could hack studying maths full-time. I like it when I try to invent new maths equations though. Most of the time its rubbish, but still fun.

 

[purk]

Quote:

I love math, I used to be a math major in college.

As a grad student in Structural engineering.....I'm tired of advance calculus.

Anyway, I hope that this pana pcdp sounds great. I'm tired of the headphone out from the crappy sony's.

 

[leon]

Okay, there's now a catalog page for the J900:

http://prodb.matsu****a.co.jp/produc...L/SL-J900.html

Frequency response 20-20000Hz (+0dB ~ -8dB)
Output: 6mW+6mW (@ 16 ohm)
speaker 1.2+1.2W
Full recharge: 2-3 hours

Battery life:
CD-DA playback
alkaline battery: 26-hour
supplied Ni-Cd (yep!) rechargeable: 8-hour
Ni-MH rechargeable (sold separately): 16-hour
Ni-Cd and alkaline combined: 34-hour
Ni-MH and alkaline combined: 42-hour

MP3 playback
alkaline battery: 40-hour
supplied Ni-Cd (yep!) rechargeable: 12-hour
Ni-MH rechargeable (sold separately): 24-hour
Ni-Cd and alkaline combined: 52-hour
Ni-MH and alkaline combined: 64-hour

Minimum dimensions: 127x14.5x126.5mm
Maximum dimensions: 280x153.7x66mm (apparently includes speakers)
Weight 224g with rechargeables, 178g without

Whatever shortcoming it's got, I don't mind - just got my iPod today

 

[purk]

Leon,
So this Pana is CD/CDMP3? Hey, would you share your thought on the IPod? Please, make the comparison on b/w the IPOD and SHarp MT-831. Sound quality...and such. What's the version you have for the IPod?

Thanks,
Purk