Final Equalizer Settings and Conclusions

I’ve settled the equalizer settings and finalized the system as below.

1. Analysis of Source Signal Level
Below figures are showing original signal levels (PEAK VALUE) in three frequency bands (-50Hz, 50-100Hz, 100-1kHz) measured from several single tracks. music sources(from left);
- "Beethoven Cello sonata No3 I (Classical)"
- "Beethoven Symphony No.8 I (Classical)"
- "Paul Chambers Yesterdays (Jazz)"
- "Chick Corea Return to Forever (Jazz Elec.)"
- "Beethoven Symphony No.5 IV (Classical)"
- "Jaco Pastrius Crisis (Jazz Elec.)"
- "Miles Davis So What (Jazz)"
- "Weather Report Volcano for Hire (Jazz Elec.)"
- "Stravinsky The Rite of Spring（Classical）"

Low end signal levels below 50Hz are generally quite low except in "Rite of Spring".

Below figure is another result measured from totally 45 CDs (including all tracks) (-50Hz only). music sources(from left);
- "Pink Floyd The dark side of the moon (Rock)"
- "Beethoven Symphony No.1-9 (Classical)"
- "Miles Davis 21CDs (Jazz, incl. Elec.)"
- "Weather Report 12 CDs (Jazz, Elec.)"
- "Stravinsky The Rite of Spring (Classical)"
- "Madonna Erotica 1 CD (Pops)"

These are only Maximum Peak values measured in a number of tracks. Generally, it is exceedingly rare and quite short moment to reach –10 dB in this frequency band (below 50Hz).

2. Final Equalizer Setting

Based on the results above I finally made two equalizer settings, i.e. Full Boost Version (30Hz flat) for most of music sources, and Limited Boost Version for e.g. “Rite of Spring”.

Base level of each setting is determined so as to suppress signal overflows (–13.5 dB for Full, -12 dB for Limited). This is necessary to avoid sudden volume down due to AVC (Automatic Volume Control) implemented in the software Frieve Audio, which automatically reduces the total gain (i.e. expands the dynamic range) at the moment of digital overflow.

Generally, signal overflow is inevitable in this kind of extreme digital boosting. Thus higher bit number (more than 24bit) and excellent S/N (120dB in my case) is required for DAC (digital-analog converter) to avoid significant deterioration of the sound quality.

Here is the compensated response curves;

Blue: Limited Boost Version
Red: Full Boost Version

Black: FOSTEX G2000, 4way, 20cm woofer x2
(catalog data, as reference)

You might be anxious about phase delay in low-end frequency range.
Below is the measured delay in nearly maximum excursion driving.

The result indicates clear delaying tendency in lower frequency (absolute vertical scale is not disclosed in the software), which is inevitable in any laud speakers. The DSP also compensates this delay.

3. Conclusions

Now, I’m going to finish this audio trial on my desktop. It is quite comfortable to listen the real full range sound (30Hz to 30kHz) generated from just a single cone with a quite small diameter (approx. 5cm) in a simple sealed box without any reverse ports. This was a kind of dream.

If you can accept this kind of new technologies (i.e. computer audio system with digital equalizing), limited sound volume (near-field listening style) and trivial sacrifices in the sound qualities (i.e. deterioration in S/N due to expanded dynamic range and distortions due to larger diaphragm excursion, honestly I don't feel any significant problems) , then you can realize the dream quite easily.

I selected Alpair5 originally because of the subwoofer integration. If you would not be so adhering to the super detail of Alpair5 in mid-high range, I would recommend Alpair6(fs=74Hz) or CHR-70(fs=70Hz) for desktop applications to reduce the boosting factors. I expect 6dB reduction with those drivers in my calculation.

If your listening distance exceeds 1 m substantially, then Alpair10 full range or Alpair10 woofer + Alpair5 could be suitable. In this case, I expect 10dB or more reduction in the boosting factors.

Let's try !