[julian67]

Im sure thats all true, but my point is that the KSC75 has a rated sensitivity of 101 dB/mW. Thats louder than anyone should listen for more than a handful of minutes at a time. So even if we worse case the Clip at 3 or 4 mW its still way more than is needed to drive the KSC75.

That is simply incorrect. The Clip+ is not producing hundreds of dB at the ear with a 60 ohm earphone!

In a previous post I've already described how at maximum volume the Clip+ with the KSC75 is only moderately loud with a recording of good dynamic range, definitely nowhere near producing any discomfort or damage.

How about with a louder, modern recording which is close to maximum volume throughout?



It's now loud but not super loud. There is no discomfort. You could probably listen to this for 24 hours straight and not suffer damage or discomfort. The level is still much much lower than is possible with typical IEMs at much lower points in the Clip+'s volume range..

To produce 110 dB SPL the Clip+ would need to output about 10 mW per channel into 60 ohms. It definitely can't get anywhere close to this. As it has been measured as being able to only output 15mW into 16 ohms then it hardly seems possible that can even produce 10 mW output into 32 ohms.*

There is a very good blog with a concise explanation of the relationship between sensitivity, impedance and power output but it's authored by a banned ex head-fier and can't be linked to. If you google the exact phrase (with quotes) "THE EASY WAY (ROUGH ESTIMATE): If the sensitivity of your headphones is listed in dB/mW you can get a rough idea how much amplifier power is needed" you will find it.

*edit: the Clip+ outputs only 7.5 mW per channel into 32 ohms! There is absolutely no way it can ever get really loud with a 60 ohm headphone with sensitivity of 101 dB SPL/1mW. These specs are not meaningless, they do actually match the real world experience of siting here with my Clip+ and KSC75 and playing back files at maximum volume.

 

[Hutnicks]

Quote:

That is simply incorrect. The Clip+ is not producing hundreds of dB at the ear with a 60 ohm earphone!

In a previous post I've already described how at maximum volume the Clip+ with the KSC75 is only moderately loud with a recording of good dynamic range, definitely nowhere near producing any discomfort or damage.

How about with a louder, modern recording which is close to maximum volume throughout?



It's now loud but not super loud. There is no discomfort. You could probably listen to this for 24 hours straight and not suffer damage or discomfort. The level is still much much lower than is possible with typical IEMs at much lower points in the Clip+'s volume range..

To produce 110 dB SPL the Clip+ would need to output about 10 mW per channel into 60 ohms. It definitely can't get anywhere close to this. As it has been measured as being able to only output 15mW into 16 ohms then it hardly seems possible that can even produce 10 mW output into 32 ohms.

There is a very good blog with a concise explanation of the relationship between sensitivity, impedance and power output but it's authored by a banned ex head-fier and can't be linked to. If you google the exact phrase (with quotes) "THE EASY WAY (ROUGH ESTIMATE): If the sensitivity of your headphones is listed in dB/mW you can get a rough idea how much amplifier power is needed" you will find it.

I'd heard that the outright ban on naming him was not true.

 

[julian67]

I'd heard that the outright ban on naming him was not true.

I mentioned linking, not naming. It's nwavguy, but as my suggested search terms return precisely one result and the important thing is the data not the person it didn't seem to matter much except to explain why I wasn't making a direct link.

 

[palmfish]

Thank you for the link Julian67, I have a better understanding of the relationship between sensitivity and resistance now.

There is a question Im still not sure I understand though. I always thought that low impedance loads where more difficult to drive than high impedance loads because they require more current. Therefore, based on Ohm's law, higher impedance loads require more voltage. On a small DAP like the Clip, I would think that current is limited but voltage should be either 2V (standard line out) or 5V (USB power). How does all this (assuming its correct) factor in with the sensitivity of the load and the power output of the amplifier?

 

[julian67]

A quick addition to note Clip+ power output at 60 ohms and to calculate a value for SPL.

According to nwavguy the Clip+'s real measured max power (Vmax) is 489 mV.

P = (Vmax * Vmax) / Headphone Impedance

(0.489*0.489)/60=.003985

So the Clip+'s output into 60 ohms is below 4 mW.

To calculate the dB SPL:

dBSPL = Sensitivity in dB/mW + 10 * LOG ( Pmax in mW)

10 * LOG ( Pmax in mW) is 6.00, so SPL of the KSC75 with the Clip+ is about 107 dB.

A peak level of 107 dB is modest.

By comparison the same calculations suggest that the Sennheiser CX95 with the Clip+ can achieve over 131 dB SPL. Ouch! The Sennheiser's specs (117 dB SPL/mW and Impedance 16 Ω) are pretty much typical for the type of 'phones the Clip+ is designed for.

I think it's worth reiterating that the measurements and calculations accord very well with real world experience. For example take the same rock track that is loud but not uncomfortable at max volume with the Clip+ and KSC75. When I switch to the Senn CX95 I can't get anywhere near maximum volume because well below that it gets loud enough to actually be distressing and I have no desire to damage my hearing. It's loud but comfortable about 14dB below maximum level and I would be unwilling to go higher than -12 dB for more than a few seconds.

 

[julian67]

Thank you for the link Julian67, I have a better understanding of the relationship between sensitivity and resistance now.

There is a question Im still not sure I understand though. I always thought that low impedance loads where more difficult to drive than high impedance loads because they require more current. Therefore, based on Ohm's law, higher impedance loads require more voltage. On a small DAP like the Clip, I would think that current is limited but voltage should be either 2V (standard line out) or 5V (USB power). How does all this (assuming its correct) factor in with the sensitivity of the load and the power output of the amplifier?

I posted above before seeing your last post, so I hope that the above is helpful.

The USB power has nothing to do with audio output.

Remember that the Clip+ doesn't have a line out. It has a headphone socket whose max output is only 489 mV.

I am really no kind of expert and am mostly happy plugging stuff in and seeing what I think (and doing level matched comparisons and abx for some tests) so I'm pleased that a few bloggers spell it out such that I can produce the figures to set alongside my impressions. It's quite a relief when they coincide If you have technical questions that go beyond the most basic then you'd do better to ask someone else.

 

[FieldingMellish]

The only thing I can add is there's no place like ohm.

 

[peskypesky]

I have KSC75's, a Clip+, and a CMoy. Will have to check it out and see what all the fuss is about.  

 

[Xaborus]

A much simplier way to roughly estimate how loud a driver gets is that any doubling in power increases dB by 3.

So for example with 101dB/1mW:
1mW- 101dB
2mW- 104dB
4mW- 107dB
8mW- 110dB
16mW- 113dB
Ect.

I'd also like to point out for the purposes of safety that NOISH guidelines only allow 8 Hours of exposure to 85dBA, 2 Hours to 90 dBA, and 15 minutes to 100 dBA to protect hearing. Also a fun fact is that sounds in the 2k-4khz spectrum are the most damaging to human ears.

 

[julian67]

..... NOISH guidelines only allow 8 Hours of exposure to ......

The headphone SPL figures are for peak levels while the health and safety standards or recommended levels are for average levels over long periods.

For example in the UK see www.hse.gov.uk/pubns/indg362.pdf where this is explained.

When you see warnings about potential damage at 85dB this is absolutely not referring to the peak level and it is a very big mistake to confuse the average or "personal exposure" figure with the peak.

 

[palmfish]

When I listen to headphones, my average level is closer to 75 dB. I listen louder on tare occasions, but not often and not for long periods.

Also, it is true that the KSC75 sits on the ear very loosely and therefore volume needs to be turned up louder to reach the same SPL as a circumaural headphone.

 

[julian67]

When I listen to headphones, my average level is closer to 75 dB. I listen louder on tare occasions, but not often and not for long periods.

Measurement or guesswork?

Also, it is true that the KSC75 sits on the ear very loosely and therefore volume needs to be turned up louder to reach the same SPL as a circumaural headphone.

I don't see how this can be right. A typical circumaural headphone's driver is kept at a distance from the ear while the driver of an earpad type headphone such as the KSC75 is by definition directly on the ear. I have an old pair of Sennheiser HD500 here and the distance from the driver to the front of the pad is over 3 cm. Of course there is some pad compression in use but still the driver will be well away from the ear. With a more modern set like Sony MDR ZX700 the casket and pad are much shallower but still the driver is not pressed onto the ear like with an earpad 'phone.

As for being loose or otherwise I can easily adjust my KSC75 clips so that they press on my ear just like with a headband.

 

[palmfish]

Quote:

Measurement or guesswork?
I don't see how this can be right. A typical circumaural headphone's driver is kept at a distance from the ear while the driver of an earpad type headphone such as the KSC75 is by definition directly on the ear. I have an old pair of Sennheiser HD500 here and the distance from the driver to the front of the pad is over 3 cm. Of course there is some pad compression in use but still the driver will be well away from the ear. With a more modern set like Sony MDR ZX700 the casket and pad are much shallower but still the driver is not pressed onto the ear like with an earpad 'phone.

As for being loose or otherwise I can easily adjust my KSC75 clips so that they press on my ear just like with a headband.

 
Measured.
 
A circumaural headphone seals against the head. The KSC75 does not. If you replace your KSC75 foam pads with Sennheiser PX200 leather pads, you too will have to turn the volume down significantly to maintain the same perceived SPL. I did this yesterday.

 

[julian67]

A closed circumaural headphone might make a seal. By definition an open or semi-open circumaural headphone cannot.

 

[palmfish]

I'm not going to belabor the point. Suffice it to say that the pads make a significant difference. I will gladly send my pads to you if you'd like to try for yourself.