Thanks. I use HiFiMAN Arya which (according to several reviews) has a pretty flat frequency response in range of 20Hz-1kHz. Not sure about impedance but let's assume it's flat for the sake of simplicity. It is rated at 90dB/1mW@1kHz. Would it mean the same efficiency for 20Hz, 100Hz and 1000Hz? I find it against what
@Aerith Gainsborough said regarding more air moved and power needed for low bass (in comparison to mids at the same SPL) reproduction. Same efficiency would not mean more power need for bass.
If this is not about excursion, am I right with following:
- let's say again efficiency is 90dB/1mW@1kHz
- bass frequency response is -10dB opposite 1kHz (and flat resistance)
- hearing curves say I need +5dB SPL to have same loudness perceived for bass (I think this solves issue with hearing in phon not SPL)
So do I need 15dB (10dB for headphone bass frequency response and 5dB for compensating hearing curves) more SPL to hear bass same as loud as mid tones in this case?
Sorry but I would really like to understand this.
For the Arya the voltage sensitivity = 104dB/V (90dB/mW)
This is the same for frequencies between 10Hz and 1kHz. From 2kHz to 6kHz the efficiency is about 98dB/V. Around 8kHz the efficiency is around 109dB/V
That is the efficiency part.
The efficiency part has absolutely nothing to do with how the human hearing works (equal loudness contours) nor with the recording and how this was made.
It also has nothing to do with boosting or lowering frequencies using EQ to suit our taste or compensate for efficiency differences.
Phon equal to SPL around 1kHz (and 6kHz) only.
Measurements are only done in SPL. These can have a dertain 'weighting'. The most common is A-weighting as it is somewhat similar to ur hearing at a certain sound level.
We hear in Phon... we measure efficiency in SPL.
At 100 Phon the hearing is 'flat' from 20Hz to 1kHz so at that level Phon = SPL
The amount of energy in recordings (for humans to perceive it as 'flat' is somewhat similar to pink noise. The 'bass boost' thus is NOT in the efficiency but in the recording. It is embedded in the electrical signal.
All the transducers have to do is reproduce each frequency in the same SPL (thus NOT Phon) as it is in the signal.
How loud we perceive the bass (relatively) depends on how loud the average level is.
Recordings are usually made between 75dB and 80dB SPL on average. When you play it back at the same (average, not peak) SPL it will sound balanced. When you play it louder the tonal balance does not change much. It only really becomes a 'thing' when levels drop below 80dB SPL
Again... this has nothing to do with efficiency nor with how much energy there is in low frequencies in the recording.
Now back to the original question as to how much power you need.
Uncomfortable loud levels, which you can listen to for about the duration of a few minutes top, is about 100dB SPL (Phon).
However, as music is dynamic there can be peaks about 5dB to 25dB louder than 100dB.
The 120dB+ peaks are really uncomfortable and will be hard to reach with speakers in a room but can easily be reached by quite a few headphones.
So this means (as dBSPL = Phon above 90dB SPL) your amplifier needs to supply enough voltage to reach 120dB (at 1kHz) when the frequency response is about flat. This has nothing to do with impedance peaks as headphones are voltage driven, not power driver.
In your case 120dB SPL is reached at 6.3V and when you want to build-in some extra headroom you need 12V.
6V in 35 Ohm = 1W
12V in 5 Ohm = 4W
These numbers is where the 'you need tons of power' story comes from. You need it with inefficient headphones when you want to reach more than impressive peak levels for short moments without any distortion of the electrical signal.
Now... do you really need this for listening to music at pleasant levels that one can sustain for a few hours ?
No of course not.
For this average levels are somewhere around 70dB average so peak levels of 90dB can be present.
For this you only need about 0.001 W (1mW) where even a phone can reach 1V = 30mW.
This explains why some folks say.. you don't really need a high amount of power... this or that headphone plays loud enough from a phone.
Calculations, however, say a different thing when you want to reach extreme levels.
This is where the discrepancy comes from.
Basically, for background listening to comfortable loud levels (100dB peaks) a 1V output (30mW) in case of the Arya is enough.
When you want to (shortly) reach impressive levels 1W is enough.
That is the fun of (close to) logarithmic hearing.
To put this in perspective... the Focal Spirit One for instance can reach 120dB at 1V already (30mW as well) so there can be huge differences in efficiency. For that reason you can use lists or the headphonesty calculators for each individual case.