GTM said:
Sub manufacturers quoting their figures in anechoic chambers is all well and good. But unfortunately such figures tell you next to nothing about how it will respond "in-room". Despite what many people will have you believe, (including Velodyne no doubt), having a flat response to 20hz in an anechoic chamber is NOT desirable. Unless you're looking for subs for outdoor concert use that is. Even the largest living room will have considerable bass augmentation and such a sub will be seriously overblown in any real listening environment. Impressive maybe, accurate it won't be no matter how low the THD figures are.
But at least an anechoic measurement is a level playing field – with in-room figures who knows what sized room they used? It's useless as a comparison – the only way it could work would be if a standard room could be agreed upon and I can't see that happening somehow, especially with the differences between the average UK and US room.
I'm also struggling to see how making a sub that will play flat to 20Hz with no room loading is a bad thing – why should a sub that does this be any worse than one that will only play flat to 28Hz? Okay, so maybe if there is a big room peak at 20Hz then the latter sub will create less of a problem but who says the peak will be at 20Hz? Surely the peaks will vary depending upon the room in question (and various other factors) so it would be impossible to a sub manufacturer to anticipate this and therefore going for a flat response has to be the best bet?
I guess the ultimate integrated solution is the inbuilt EQ system in the DD12 sub that Merlin's trying out – I think that one plays flat to something like 18Hz anechoic but , unless I'm mistaken, it also analyses its in room response and then adjusts its output (and phase) at various different frequencies in order to produce a flat in-room response – bloody clever stuff.
GTM said:
On the point of THD figures. It's more of a sales pitch than anything else as the human ear is very insensitive to distortion at low frequencies. I'd be willing to bet that the vast majority of people would be unable to hear the difference between 1% and 5% distortion at below 40hz in a blind test, (at 20hz you probably couldn't hear less than 10% THD). That is of course assuming that the harmonics aren't all odd and at 3khz or something. If all the harmonics are in the bass region, ie mostly 2nd and 3rd harmonic distortion then they will have to be a lot higher than most people think before they are audiable.
GTM
Agree with this – I don't think a lot of people could hear a difference between 1% and 10% distortion at the lower frequencies. However, my understanding is that it's not unusual for certain popular subs to produce 30% or more distortion when attempting to produce the low frequencies at a reasonably high volume level.
Play a movie with some really low bass through one of these lesser subs and then swap to a low distortion model and the difference is more than noticeable. I tried this on 'The Haunting' DTS – my old REL Q200 had convinced me the film had ridiculously bloated, over the top LFE content – when I got my Velodyne HGS15 I gave it another try and it sounded as clean as you like – very deep but no distortion.
One other point on THD figures – it's interesting to note that THX (who I think it's fair to say know a bit about reproducing movie bass) now stipulate some pretty tough requirements for subwoofers. To obtain THX Ultra II certification I understand subs have to be able to reproduce 20Hz @ 105dB with no more than 4% distortion. I don't think you'll find many subs that can do this – no doubt many manufacturers whose subs aren't up to this will simply claim that they are not willing to spend the money on THX certification.
Finally – and this ties in the THX bit with what Dunkyboy was saying – I guess even if all manufacturers used either anechoic or 'same sized room' –3dB measurements (and provided distortion figures) then this wouldn't could for a lot unless they quoted output levels in dB too i.e. I presume it's a fair assumption that getting a sub to play flat in room to 20Hz with little distortion is a lot easier at 80dB than it is at 95dB.
Matt.
