Mixer headphone volume question (with some research)

[tothemax]

In recent posts I've mentioned having volume discrepancies between DAW mixing volume and exported song volume (apparently from the way the driver handles USB output between the OS and DAW). It appears that output volume continues to an ongoing learning curve with hardware. Last year I picked up a Zoom L-8 mixer to use for smaller acoustic gigs. With this cold spurt the studio has been on the chilly side, so the L-8 was an easy option to move inside to be able to practice with headphones and not drive my wife crazy. While the mixer worked fine to blend YouTube music, with a mic, and a DI for my bass, the headphone volume at max was barely acceptable (OK, but not loud enough to present clarity to my aging hearing, which is pretty good for my age). This was using AKG K240 headphones. In the studio with the Tascam Model 16, you can blow your ears out with these headphones, so I was a little confused.

This morning I did a little research and looked up the specs on the two mixers and there lies the issue. Phones output on the Tascam is 80mW x 80mW @ 32 ohms where the L-8 max output is 10mW x 10mW @ 60 ohms. The K240 impedance is rated @ 55 ohms, this where the math loses me...

My gut says that to get more volume out of the L-8, there are two options. Either add a headphone amp post mixer, or use headphones with lower impedance (btw: this was correct). To resolve this I did some digging and found a source of info, not sure if it really cleared it up.

Please feel free add a simple formula or explanation to understand how the headphone specs work with mixer output specs. I guess my main takeaway was that all gear is not created equal or compatible.

Cheers

Headphones Impedance Explained​

Output Specs from these two mixers

Zoom LiveTrak L-8



Tascam Model 16

 

[tothemax]

Following up,
Tried a pair of inexpensive folding headphones probably low impedance, purple no name brand. Actually wasn't much louder, and less quality than the AKG's. So added an inexpensive Behringer headphone amp (HA400) and that resolved the issue, plenty of volume (on either pair of headphones).
One other thing that I did not mention, the L-8 USB driver automatically sets the PC output volume to 100%, the Tascam driver leaves it variable.

 

[Wasnex]

his morning I did a little research and looked up the specs on the two mixers and there lies the issue. Phones output on the Tascam is 80mW x 80mW @ 32 ohms where the L-8 max output is 10mW x 10mW @ 60 ohms. The K240 impedance is rated @ 55 ohms, this where the math loses me...

Hopefully I do this correctly .

Here's our Ohm's Law/Watt's Law formula wheel:

Generally solid solid-state amps try to deliver the same voltage regardless of impedance. We will do an estimate based on this assumption.

Let's calculate the voltage:

80mW at 32 ohms

• Voltage = sq rt(0.08 * 32) = 1.6V

10mW at 60 ohms

• Voltage = sq rt(0.01 * 60) = 0.775V

Power at 55 ohms.

• with 1.6V = (1.6^2)/55 = 47mW
• with 0.775V = (0.775^2)/55 = 11mW

The decibel difference is ~6.3dB

• Based on power difference 10Log(47/11) = ~6.3dB
• Based on voltage difference 20Log(1.6/0.775) = ~6.3dB

 

[tothemax]

That is significant... thank you. And this is why I love this forum

 

[Wasnex]

AKG K240

• Sensitivity (dB SPL/V @ 1 kHz) 104
• Max Input Power 200mW
• Voltage for 200mW at 55 ohms = sq rt(0.2 * 55) = 3.32V
• Calculated SPL at 3.32V = 20Log(3.32) + 104 = 114dB...this is with full rated power

Calculated SPL of K240 with proposed headphone amps

• with 1.6V = 20log(1.6) + 104 = ~108dB
• with 0.775V = 20log(0.775) + 104 = ~101.8
• 

For comparison--AKG K361

• Impedance 32 ohms
• Sensitivity (dB SPL/V @ 1 kHz) 114

Calculated SPL with proposed headphone amps

• with 1.6V = 20log(1.6) + 114 = ~118dB
• with 0.775V = 20log(0.775) + 114 = ~111.8
•