Report of Alpair5 Aplication

Here is the total report of the Alpair5 application on my desktop system.
Please also check the system introduction to see the overview of my LEAN AUDIO concept.

1. Sealed box
I built a pair of sealed boxes for Alpair5 drivers, which have exactly the same dimensions with those for F80AMG drivers.

main dimensions: W=115, H=170, D=240 mm, t=15 mm (lauan plywood), Vin=2.5 L, sound absorbent material (fiber) =32g (adjusted based on hearing )

T/S parameters; F80AMG vs Alpair5 (gold);

Calculation result; F80AMG vs Alpair5 (gold); 2.5L sealed box Calculation results;
F80AMG: Fs=125Hz, F3=103Hz
Alpair5: Fs=152Hz, F3=129Hz

Measured responses at 20cm distance on the axial center;
black=F80AMG, red=Alpair5 (gray)

The software(Frieve Audio M-Class) plots the curves automatically adjusting the levels. The actual absolute level of Alpair5 is approx. 3dB higher at the same amplifier volume position.
Roll-off frequencies seems nearly identical despite considerable differences in the T/S parameters (fs=89 Hz vs 125Hz). It is remarkable that Alpair5 indicates nearly the same low-end response with F80AMG whose bass performance is highly reputed in Japan.

Results of the automatic response compensation (20cm, axial center, 30Hz…18kHz flat);
black=F80AMG, red=Alpair5 (gray)

Equalizing factors (20cm, axial center);
black=F80AMG, red=Alpair5 (gray)

This time, I tried extreme equalization up to nearly +30dB ! Surprisingly both drivers were capable of such tremendous low-boosting as shown above.

2. System Integration
This is the current system configuration;

Current system without subwoofer

I bought a new amplifier ONKYO A-905 FX (60W/ch at 4 ohm) to drive Alpair5 (4 ohm) with a plenty of power margin for extreme low-end boosting. The former KENWOOD KA-S10 is not so powerful (only 12W/ch, 8 ohm) and doesn’t support 4 ohm speakers.

Measured responses at the standard position (Alpair5, 80cm distance, 25deg inside offset);
black=LHS, red=RHS

The response becomes uneven due to the room effect, reflections from the desktop and axial offset.

Results of the automatic compensation (25Hz to 18kHz flat,);
black=LHS, red=RHS
NO subwoofer !

Equalizing factors;

F80AMG also worked in the same way as Alpair5.

Do you believe this kind of extreme boosting can be realistic?
I had never believed so. However, surprisingly it works quite well. I also tried a combination with the desktop subwoofer in the same way as described in previous articles in this Blog, and compared both configurations with the same response curve (flat to 25Hz). As the result I decided not to use the subwoofer because Alpair5 without subwoofer produces more natural, clearer and tighter bass. Alpair5 seems maintain its super detail character even in low-end area.

I can play most of music sources including classical symphonies with full boost setting (25Hz flat) without suffering noticeable distortions (i.e. excess driver excursions). I tried a very steep Low-pass filter with 50Hz cut-off on several music sources to know the actual signal level in low-end. Generally the signal level below 50 Hz is not so strong in most tunes that considerable boosting can be possible if you are listening the music in relatively low volume level (ex. near field listening).

As exceptional cases, some modern orchestra tunes, like as “Rite of Spring”(Stravinsky) and “The Planets”(Holst), include extremely strong signals (nearly full dynamic range) in very low-end, which come from bass drums(timpani).
Stravinsky: Le Sacre Du Printemps
Chailly / Cleveland Orchestra
Check its super bass !

For this kind of tunes, I have to reduce the boosting factor in order to avoid excess excursions (distortions). Subwoofer could be beneficial in this case.

Reduced boosting factor;

3. Summary
Alpair5s were implemented in my desktop audio system to playback lossless WAV files stored on an audio PC equipped with powerful digital signal processing software Frieve Audio M-class that offers automatic response compensation.

On the system, Alpair5 and F80AMG (highly reputed 8cm driver in Japan) were compared under the same conditions each other, i.e. under the equalized output response (25Hz to 20kHz flat) without a subwoofer, using the same 2.5L sealed boxes.

Both drivers were capable of extreme low-end digital boosting (equalizing) down to 25Hz without noticeable distortions under the limited conditions, i.e. low sound volume due to near-field listening, thus plenty of margin for maximum excursion of the drivers as well as for maximum output power of the amplifier. Further more 24bit DAC enables to maintain the lowest level signals (the least significant bit) of the original 16bit data even under such the extreme signal processing (Frieve Audio itself performs the internal process with 64bit resolution). For this kind of applications, sealed boxes should be suitable because of no phase reverse thus no steep roll-off.

Only for few music sources with exceptionally high magnitude signal below 50Hz (modern orchestra with very strong bass drums, e.g. “Rite of Spring / Stravinsky), the boosting factors below 50Hz had to be reduced in order to avoid excess excursions. Most of other music sources within my music library including classical symphonies, jazz (acoustic and electric), rock and pops do not indicate noticeable distortions even with the full boost setting.

4. Impressions of Alpair5
Comparing to F80AMG, Alpair5 delivers much higher clarity and details not only in mid-high range as already well known but also surprisingly in very low range below 100Hz with digital boosting. I’m quite sure that I can identify Alpair5 perfectly even under a blind test. The reputations of Alpair5 on its mid-high range is quite famous, so I don't like to repeat it here but would only say “that’s really true” and just add “also in low-end range if you boosted it digitally”. I don’t need F80AMG no longer for any music categories.

The boosted bass from Alpair5 is so tighter and faster that I can no longer be satisified with my own cheap subwoofer. The boosted bass from solely Alpair5 sounds much better in most cases except for above special music.
I didn't have such uncomfortable feelings with F80AMG + subwoofer combination may be because the sound qualities from both units (sub and F80) are not so much different each other.

see the next article for the conclusions;