mijostyn:"Tim, I’m all for the subs but since when is Class D the harbinger of good bass? Or good anything for that matter?"
Hello mijostyn,
I mentioned this on one of my earlier posts. Here’s a copy of what I stated on that post:
" Yes, the old loudness controls boosted both the bass and treble to compensate for the Fletcher-Munson curve reality of human hearing.
Strange, but this is also one of the 1st qualities I noticed with all the high quality class D amps I’ve owned. The bass, midrange and treble balance seemed to be properly balanced to me no matter the volume. YMMV? Not sure."
This quality I clearly noticed very early on in listening to the first class D amp I ever used in my system, a Class D Audio SDS-440-CS stereo amp. At that time about 4-5 years ago, my system consisted of a VTL 2.5L preamp swapped out with a set of 4 NOS Mullard tubes, an Oppo 105 as a source for playback of CD/SACD discs with an attached Synology hard drive storage unit for hi-rez FLAC music file playback using the Oppo as a DAC and Magnepan 2.7QR speakers.
I replaced my Aragon class AB stereo amp with the new class D stereo amp in my system and just let it warm up enough to become acclimated to the heated indoor temp on a winter day in Indiana before giving it a thorough tryout. I didn’t know what to expect at this point, playing the first few CD tracks, but was very curious and all ears.
The second sound quality difference I clearly noticed was the lack of virtually all background noise to the point of being a bit startled when the first track began playing because the room was so quiet, as if I’d forgotten to press the Play button on the Oppo.
The music seemed to just emerge from an inky black, dead-silent background that was quite impressive and that I believe was responsible for the third sound quality difference I clearly noticed, a very vivid presentation that had obviously increased detail levels but that sounded consistently smooth in the treble range with no hint of brightness or harshness.
I believe the fourth sound quality difference that was clearly evident was the improved bass response which was more solid, powerful, detailed and dynamic than I had ever heard and felt my Magnepan 2.7Qrs perform up to that point. I didn’t know until then that these speakers were even capable of this level of bass performance.
The complete story of my knowledge gained from my fairly consistent efforts to improve bass performance in my system and room do not end there with class D, however. I subsequently added an Audio Kinesis Debra 4-sub distributed bass array (DBA) system powered by a separate 1K watt class AB sub amp a few months later and realized by comparison that the deep bass sounded, of course, more powerful and dynamic because there were now 4 subs sharing the deep bass duties as opposed to only my pair of 2.7QRs previously.
But what I wasn’t expecting was that the bass also sounded significantly more natural and real than with this system than the class D amp alone driving my 2.7QR speakers. I stiil ran the 2.7QRs full range down to their rated bass extension of 35 Hz but used a 40 Hz cutoff on the AK 4-sub DBA system so that they supplemented all bass reproduced between 20 and 40 Hz with an overlap between 35 and 40 Hz.
I believe this was due to the class D amp having a much higher Damping Factor than the DBA class AB amp/control unit driving all 4 subs. By comparison,it seemed to me that the class D amp with 2.7QRs was truncating the deep bass notes’ natural decays. The AK Debra subs, all powered by a class AB amp with a much lower Damping Factor, seemed to reproduce the deep bass notes’ natural decays much more, ahem, naturally and completely without any noticeable truncation. The strange part is that I perceived the class D bass as sounding very good in power, dynamics and detail up until I heard the improved bass performance of the AK 4-sub DBA system.
My point being that I believe many would be satisfied with the class D amps improved bass performance, even with the somewhat truncated deep bass notes’ decays, if they can’t afford the $3K for an AK Swarm or Debra 4-sub DBA system at the moment.
As to the old loudness controls boosting both the bass and treble to compensate for the Fletcher-Munson curve reality of human hearing, this is also one of the initial qualities I noticed with all the high quality class D amps I’ve owned. The bass, midrange and treble balance seemed to be properly balanced to me no matter the volume.
I remember noticing this when I decided to test out how loudly my first class D amp sounded when played at high volume, I would estimate I increased the volume slowly from zero up to a much higher volume than I would ever soberly listen to my music, which I’m estimating to be at least 120 dBs. I was amazed to discover that I perceived the relative balance between bass, midrange and treble remained remarkably consistent as I progressed from a volume level of zero all the way to about 120 dBs, which was excruciatingly loud but still lacked any sonic signs of clipping.
I’ve clearly noticed the above qualities on all 3 class D amps I now own: the Class D Audio stereo SDS-440-CS amp I currently use to power my pair of rear surround speakers, the Emerald Physics stereo EP-101.2SE amp that I currently use in bridged mono mode to power my center channel speaker and the pair of D-Sonic monoblock M3-600-M amps I currently use to power my Magnepan 3.7i main speakers.
I’ve personally experienced this ’built-in automatic loudness control’ quality not only on the class D amps I own but on numerous good quality class D amps I’ve listened to on other systems. I realize this seemingly universal quality of class D amps is rarely discussed but I perceive it so distinctly that I seriously doubt I’m the only individual that’s able to perceive it and assuming this circuitry even actually exists.
As I understand it, class D power modules contain circuitry that constantly compares the inputted signal to the outputted signal and makes any necessary adjustments to the outputted signal before releasing the analog signal to the speakers. I believe this circuitry is called a comparator circuit and this would be the obvious circuitry choice to incorporate an automatic loudness control function into that would function according to a pre-coded algorithm.
However, I think it’s important to note the above is only my theory based on my numerous class D amp listening experiences on a relatively small sample of the total currently available class D amps. I’m very interested to learn what leading class D amp designers would have to say about this quality and subject if asked. So as always, YMMV.
Tim
