"My Disc" - The Sheffield / A2TB Test Disc, is an interesting evaluation tool as far as:
- Critical evaluation of audio components
And your critical listening ability.
- 58 (warble from 100 to 20 Hz for quick subjective evaluation of subwoofer systems) and
59 (low distortion sine waves - individual frequencies from 10 to 99 Hz)
Three years ago, after moving to my present listening room, I had to do some testing and measuring, for proper setting-up of my Genesis 300 speakers within the new listening environment. For that purpose and for calibrating the correct settings for the low frequency spectrum produced by the subwoofers, track 59 was used, correlating dB's vs. Hz, with different settings of the Genesis servo-amplifier [high pass & low pass (in Hz), phase (degrees) and volume (dB's)] via the tele-commander provided.
See my system set-up at http://aca.gr/pop_skal.htm for my system and room details and ...
Click http://aca.gr/forum/files/genesis_sub.zip (23 Kbytes) to download the .xls files, unzip the folder and open the 2 contained files in order for you to understand, what I will be talking about.
My target was to get the broadest low frequency spectrum (Hz), coming down to the lowest registers and, at the same time, the flattest response possible (dB's). This low area is the most difficult as you know and the mostly affected by the listening room's dimensions & configuration!
Watch the graphs from the '...._skal.xls' file if you will.
- Using 0 degrees phase, it seems I get a flatter response over the 20 - 50 Hz spectrum, than using 45 degrees phase, which Genesis recommends though "to start with..." as they say.
Filtering out everything below 32 Hz, I get the SPL down over the area 15 - 35 Hz and this is audible!!! With no filter at all (min. 16 Hz) I get the SPL over the low octave spectrum at adequate level.
Using the lowest overlap frequency (at 70 Hz), it seems that the response over the entire low frequency spectrum is more flat than using the sub overlap frequency at 85 Hz or above (max. 120 Hz).
- High pass= 16 Hz (16 - 32)
Low pass = 75 Hz (70 - 120)
Phase = 0 degrees (0 - 180) and
Volume = depending on the recording, but more or less constant to 30 - 35 (0 - 100)
Yesterday, I was trying to sense again the 16 Hz sound (wave rather...). I know I can do that because my listening room permits it (max. dimension 11.7 m. - 40 ft.) and my speaker is capable of.
So I put the test CD again (track 59) and started producing these 'clean' frequencies'. I have noticed the following:
- 1. The 8" woofers start vibrating even with the 10 Hz signal, without being noticed acoustically.
2. At 16 Hz, the sound pulse became evident, with the sense of pressure - vibration with adequate level. (At that exact time of 16 Hz produced, my wife being in the same room but not knowing what I was doing, warned me fearing there was some kind of earthquake going on ...!)
3. Going up to 40 Hz (after that I stopped the test), SPL's were kept at almost the same level.
4. After the whole test it was one of the few times my 1.5 Kw servo-amp got really hot...
5. Repeating the same test but with filtering out below 32 Hz instead of 16 Hz, the above phenomenon were very much reduced and practically the lower octave acoustically diminished!
I have also noticed that, although using the Sheffield test CD, the above facts were noticed, with real music coming from a CD - even with the "Discovery and Music for Christmas", ORG/Welch, (ORGAN & CHOIR recordings in St. Mark's Episcopal Church, Wilson Audiophile WCD-806/8419), listening differences between 16 & 32 Hz are hardly evident.
On the contrary, using my analogue source, in recordings such as:
- "POMPS & PIPES" , (Ref. Rec. RR-58 LP), Side 4 Charles-Marie Widor's "Lord save the people".
"VENICE" ROHO/Solti, (RCA Victor LSC-2313 LP), Side 1 band 4 The Tales of Hoffmann: "BARCAROLLE".
GRIEG's "PEER GYNT" LSO/Fjeldstad, (Decca SXL 2012 LP), Side 1 band 5 "In the Hall of the Mountain King".
R. STRAUSS "Also sprach Zarathustra" CSO/Reiner, (RCA Victor LSC-1806 LP), Side 1 "Introduction"
- The feeling of the Big Tympani of the Orchestra having a better presence and transmitting for longer time ('tail' ...),
The feeling of a larger and more realistic image of the body of the Orchestra,
The feeling of a more flat and comfortable sound over the rest of the low frequency spectrum.
Watch now the second file ('...._haluk.xls') and the 2 graphs in it.
They are referring to the response of the Genesis 200 (the model just above mine), which ...
- Instead of 6 x 8" woofers/channel, all around the sub at the bottom of each speaker (Genesis 300), it has 8; 4 front firing and 4 back firing 8" woofers, on independent towers, one for each channel.
The servo-amplifier and the x/over is exactly the same in both models (4-ch, 4 x 375 W / 2 Ohms).
Due to several peculiarities of his listening room (small for these speakers, back wall covered with wood etc.), after repeated movements of the sub towers, he concluded to these 2 frequency responses shown, as the best possible (never being satisfied with though...)
Watching to these 2 curves, one can easily comment that moving the subs away from the back wall, although he looses some of the low registers, he gains a flatter response over the rest of the 20 - 100 Hz spectrum. SPL seem to go down also but that is no problem for speakers, which can increase their gain with the tele-commanter.
My opinion so is that, if the listening room permits and the gain of the sub emission is possible, to move the speakers away from the back wall. (Special design speakers may be excluded of course...)
Looking again to the overall 'room's performance' between mine's and Haluk's and comparing my best case No11 (not the detailed one because it has no 'acoustical' meaning) and Haluk's best case, which to my mind is case No2 (away from the back wall), leads to the conclusion that a better room overpasses a better speaker... (See a related article I have written at http://aca.gr/paper23.htm )
and in any case ...
What I would like to point out at the end is that more and more I realize the immense importance of the listening environment to the overall acoustical performance, especially along the 'difficult' low frequency spectrum.
And surely, a speaker capable to adjust (sort of...) itself to the peculiarities of the listening room gives an advantage to the final result.
Thanks for your patience! Enjoy the Music...
President of the
Audiophile Club of Athens
My system: http://aca.gr/pop_skal.htm