Distortion measurements are at equiv. of 1 meter/3.3 feet. In reality they are performed at 1/3 of a meter but then compensated to represent 1 meter.
Messy post, made some mistakes in my testing & re-edited my post, crossed out stuff that is wrong so you don't have to read it!
Ah, so if you listen at a further distance (like I do) of about 2m, then distortion could become more of a practical problem as you have to turn up the signal. I thought I'd try to work out just now how many dB's my JBL 308p Mkii's would put out during my loudest listening, so I left the volume knob on the back of the speakers at 4.5 and put my E30 DAC to 0dB with -2dB in windows volume for intersample overs, and ran a REW frequency sweep configured at 0dB in REW software, and measured at my 2m listening position and
this is what I got: Ignore this first graph, made a config error in REW.
On average I guess that's 73dB at a 2m listening position with maximums of 80dB (this is including a little bit of RoomEQ too, as well as Anechoic EQ). I'm not sure how valid the distortion measurement is, but I think I remember hearing somewhere that is was important that distortion was below the Noise Floor.....I highlighted Noise Floor in the pic there and it looks like distortion is below that curve for the most part.
How valid is this and what kind of 1m equivalent dB would my speakers be outputting given this measurement was done at 2m? I'm just trying to get a perspective on where my maximum listening level is in relation to the listening level you used in your distortion test - thereby I can judge if I'm getting more or less distortion during my listening than what was presented in your review?
EDIT: just realised something, you were measuring 1 speaker and I'm measuring 2 speakers in my graph there. So would I subtract 6dB from my graph to normalise the influence of me having 2 speakers vs your 1 speaker? If that's the case then each of my speakers is operating at an average of 67dB and a peak of 74dB. In terms of translating your 1m dB measurement to my 2m listening position I found this online calculator (http://www.sengpielaudio.com/calculator-distance.htm), and if I put in your 86dB at 1m distance I get 80dB at my 2m listening position. Given all of the above that I have written in this "EDIT" then my max listening volume per speaker is 19dB on average lower than your 86dB distortion test and at the maximum peaks in the frequency response it is 12dB lower than your 86dB distortion test. I'm not sure if I've made the correct premises here though. I guess this means that distortion is likely a lot lower at my listening levels than your test, even at my 2m listening position. If peoples know if my assumptions are valid or not then would be good to hear, I'm not 100% sure.
EDIT #2: just realised my previous graph was wrong somehow as the SPL was too low so I re-ran it and got a higher SPL, not sure what I did wrong in the REW setup before, I think I must have
not set dBFS for the sweep to 0 dBFS properly. Will attach the proper graph following:
So there are a few times where the 2nd Harmonic is above the noise floor, at 40Hz and at 200Hz, but again I don't know how valid this kind of test is in determining true distortion. Will redo my calculations from my first edit now......following is the thought calculation process:
- At 2m listening position average SPL of 81dB, max peaks of 90dB.
- This equates to 75dB average SPL and 84dB for max peaks per speaker if you subtract 6dB for the fact I'm measuring 2 speakers rather than Amir measuring one.
- We can add back 6dB though to normalise it to Amir's 1m distance distortion measurement because I'm at 2m listening position, so back at 81dB average SPL and max peaks of 90dB per speaker at hypothetical 1m measuring distance. Conclusion: The 86dB Amir distortion measurement is really quite applicable/equatable to my max listening volume. In reality most of the time I'm running around -6dB on my E30 DAC Preamp though, but I do turn it up to 0dB sometimes which is applicable to Amir's 86dB distortion measurment.
Not sure how valid this all is, but it's my best interpretation, ha!