Validation

Honestly, I cannot be really sure whether I'm doing the right thing (I’m sure many of you share the same feeling).

To be sure, I did simple measurements as below;

Testing method

1) Generates WAV files containing sinusoidal signals (30/40/50/70/100Hz, with 0/-6 dB).
2) Playbacks the test files with my usual amplifier volume position (approx. 1/5 angular position, full power=60W(spec.data)).
3) Records the sounds via a microphone just in front of a speaker.
4) Compares the recoded signals with the original signals.

Result s
1) 100Hz

0dB, std. volume

2) 70Hz
0dB, std. volume

3) 50Hz
0dB, std. volume

-6dB, std. volume

4) 40Hz
0dB, std. volume

-6dB, std. volume

-10dB, std. volume

5) 30Hz
0dB, std. volume

-6dB, std. volume

0dB corresponds to the absolute maximum signal magnitude in 16bit Wav data, thus any boosted signals cannot exceed this level. As described in previous articles, peak signal levels blow 50Hz in most of music sources do not exceed –20 dB , and it is exceedingly rare and quite short moment to reach to –10 dB. These levels correspond respectively to –10dB and 0dB with my standard boost setting (base level = -13.5dB, approx. +10dB at low end ). So basically blow 50Hz signal can be less than –10dB in most cases with my typical boosted listening conditions. If the signal reaches to 0dB, then I can know that via the AVC activations, which happen quite infrequently.

I would say, those conditions can be acceptable for any music sources as far as the volume level is maintained below this standard position, with which I can even play Stravinsky “Rite of Spring” without feeling problems (the signal level actually reaches to 0dB). I have the problem with this tune because the entire signal level of this CD is relatively low in order to record the extraordinary strong tympani within the 16bit dynamic range. In such case I have to turn up the volume beyond the standard position to listen it comfortably, then suffer the tragedy.

You can see a big distortion in 40Hz/0dB with slightly turned up volume position. "Rite of Spring" becomes the disaster.

40Hz, 0dB, std. + 1/20 volume - no mechanical attacking noise

Even with this volume position, I don't feel any critical distortions with classical music including LvB symphonies because of originally low signal level in low end, while sometimes feel a certain distortions with contra-basses in jazz tunes.

In other words, “maximum low boosting” means “reduction of mid-high range from the maximum powered condition of the driver". Therefore basically I would recommend to use Alpair6 or CHR-70 for this kind of extreme boosting applications, with which you could enjoy much more boosting potential (see below table).

driver / X-max(1way) / max. Power
Alpair5 / 2.5mm / 12W
Aplair6 / 5.0mm / 30W
CHR-70 / 4.5mm / 40W

(data from Mark Audio home page)