@PRR It used to be a cookie-bite slope. Piano sounded awful, whatever I did.
However, with the years the extreme’s have been coming down and I can now use my Bolero SP’s to amplify the piano quite well. Sometimes I forget to re-tune after changing thin-tubes and I get a distortion a some notes, sometimes the piano needs to be re-tuned, but most of the time I can play the piano. Even up to such levels that people can complain about loudness!
@Sierra Thanks for the info with the curves for the different receivers. I now have your technical user info (TUI) with specs about OPN1-3 and receivers 60-105, and those for the miniRITE and BTE from the download centre.
Frequency Range
First thing that really stands out for the miniRITE is that the frequency range decreases when going from receiver 60 to 105. For the OPN1 is goes from an extreme 9200 to 7800 and for the OPN2-3 they go from 7500-6500. So it is worse to wear lower OPN models than to have heavier receivers! These values in the TUI are the 2cc values given in the technical data. The ear simulation values are 300-400 Hz higher.
Looking at the BTE with a 105 receiver you see no difference in range for all OPN models. However, the top of the range is capped at 7000Hz.
Comparing that with miniRITE, only the OPN2-3 with a 105 receiver is worse.
So clearly the BTE is behind the miniRITE for the OPN series.
Total Harmonic Distortion
2cc: For all miniRITE models with all receivers the Total Harmonic Distortion (THD) for 2cc is given as <2% for 500, 800 and 1600Hz. Looking at the OPN BTE 105 the 2cc is 3% at 500Hz. Clearly, 2cc is a rather less informative test than ear simulation, because those values show more difference between the models.
Ear Simulation: This is where the technical data gets odd. All values are for (500, 800, 1600)Hz. The 105 receiver for the miniRITE has (<2%, <2%, <3%), while the 100 receiver has (<7%, <4%, <2%). This breaks the expectation somewhat, since the 85 and 60 both have (<2%, <3%, <2%). So while the 60 and 85 have most trouble around 800Hz, the 100 has most trouble at the lowest frequencies and the 105 has somewhat more trouble with 1600Hz. Comparing this with the BTE with a 105 receiver (7%, 5%, <2%) it is clearly the worst of all at lower frequencies but is already better than the miniRITE 105 at 1600Hz.
So I speculate that the 105 miniRITE re - or later designed to behave at approximately the same quality level as the other receivers with only a decrease of 200Hz of the high end frequency range for 2cc compared to the 100. Checking with a local store I see Oticon receivers of 65(!), 85 and 100, so it seems that the 105 are less commonly used.
Curves
The curves are all with a different vertical scale. So looking at them will give you the wrong impression. Obviously, the receivers with a smaller number fall off less rapidly at higher frequencies.
It also seems that the THD values are taken at the part of the curves where they are most smooth. The 2cc curves are indeed smoother at these values than the ear simulation. Would have been more interesting to see the THD values in the speech area of course. So the given THD data are best taken as an indication of the maximum performance, instead of as representative.
For the OPN1, if you look at a 7000 Hz, the miniRITE 60, 85, 100, 105 and BTE 105 reach a full on gain for 2cc of resp. 12, 28, 41, 38 and 40 (or 30 with corda miniFit). For 8000Hz it’s 9, 31, 30, 38 and 20 (extrapolating the straight line beyond the curve).
Stunningly enough looking at the OSPL90 (Outside sound pressure level of 90dB, I guess) the values for 9000Hz are resp. 98, 108, 95, 100 and 116 (or 110 with the corda miniFit). For 9500Hz the values are resp. 93, 103, 95, 93 and 108(both normal and miniFit).
This supports @PRR 's argument that driven at the same sound level larger speakers don’t necessarily have lower quality of sound. You can’t get 132 dB SPL at this frequency so the range of the larger receivers is limited for those that have profound hearing loss. However, for a (moderate-)severe hearing loss the BTE 105 receivers can output the same as the miniRITE 85 receivers!
Comparing the smoothness of the curves, I do see more hard to model curves for the BTE 105: at lot of local minima and maxima, while the RITE curves are smoother and keep getting smoother if you go from to 85 and 60. If that can be taken as an indication of expected THD, you can expect increasing distortion going from miniRITE 60, 85, 100, 105 to BTE 105. Looking at the increase in local max/min above 5000Hz, I would guess that they are all still pretty high in THD.
However, the argument of maximum power output limiting the use of power aids for higher frequencies doesn’t seem to apply to this data. The BTE 105 outperforms the miniRITE 85. The optimum in terms of MPO in high frequencies is BTE 105 followed by miniRITE 85, 100 and 105 and lastly the 60. However, the BTE does suffer from a dip in power at 8000Hz. Only 110dB for the ear measurement, while the miniRITE 85 dips earliers at 6000Hz and goes to 113dB at 8000Hz.
Concluding based on the data I should choose the OPN1 miniRITE 85 over the BTE 105.
However, as I tested that OPN1 85 and it couldn’t handle the piano well enough, while my Phonak Bolero B90 SP’s do, I do have to wonder whether that extra oompf that the BTE brings isn’t needed for piano. Too bad I can’t test it, yet! Would it be odd to buy those HA’s just to be able to test them?