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Additional comments…

Posted by David Aiken (A) on January 23, 2008 at 15:07:04

In Reply to: RE: Here's my challenge to you. posted by KlausR. on January 23, 2008 at 04:21:27:

In relation to bass problems you said "Another solution could be to use narrow-band equalisation or four subwoofers placed on the walls midway between the corners" and I failed to comment on those suggestions.

Narrow band equalisation will work for peaks but not for nulls. You can't correct for a null by equalisation without running the risk of overloading both amplifier and speaker, and all high quality digital room EQ products work on the basis of correcting the peaks but leaving the nulls which often tend not to be noticed. Physical treatments such as bass traps actually smooth the response by absorbing energy that contributes to both the peaks and nulls. You need test equipment to get the best out of narrow band EQ but you don't for physical treatments though you do need test equipment for both if you want to verify the scale of the change they make rather than simply relying on your ears and subjective evaluation. Subjective evaluation isn't necessarily bad in this case because the changes from both approaches will be clearly audible if both are implemented well.

The multiple subwoofer option will certainly work and I suspect it will deliver better results than EQ because it is likely to smooth out some of the nulls as well as the peaks, but I wonder how preferable it is on a practical level to physical treatments. Subwoofers cost at the purchase stage and also to run whereas physical acoustic treatments have a purchase cost and no running cost. A decent bass trap costs about half the price of a decent sub here in Australia and even if you're using 2 traps per corner and treating 4 corners, the bass trap option is going to be comparable in price to 4 subs in many cases. It will be dearer if you're buying cheap subs and cheaper if you're buying top flight subs but price can reasonably be considered comparable at the purchase stage. From there on in bass traps are definitely cheaper to run. There is the additional problem with subs of actually getting decent integration with the speakers. It's not necessarily easy. I thought I had done a reasonable job integrating my REL Storm III into my audio system which uses an integrated amp and the REL input was taken from the speaker outputs of the amp. After considerable time and effort over a period of months, I felt reasonably happy that I had achieved a good balance both tonally and with respect to level. Out of curiosity I moved it to a separate 2 channel HT system that used a surround sound AV receiver with sub outputs and automated set-up and equalisation. I ran the auto set-up and sat back staggered at the results which surpassed anything I had achieved in months in the audio system. The big difference was the fact that the receiver matched signal arrival times for all speakers and the effect of that on transient response and overall clarity was simply surprising. I could not achieve that result in the audio system though I could now go closer towards achieving it with some of the information I learned by moving the sub to the HT system where it still remains. The audio system also sounds better in respect of transient response and clarity in the bass region without the sub though I've definitely lost low bass extension. On balance I've decided I can do without the extension in my system and that the gain in transient response and clarity is more beneficial since my mains produce useful response down to close to 30 Hz anyway.

Set-up problems will be magnified with multiple subs. Receivers are now starting to appear that will deal with 2 subs and handle their integration but I've yet to hear of a receiver that will do that for 4 subs. Without test instruments and a lot of work I doubt that anyone will achieve really good results integrating 4 subs into most systems because of the differences in listening distance to them amongst other factors. In general my recommendation on multiple subs would be that they may be a worthwhile option in a surround sound system where you're going to have at least 1 sub anyway but they aren't anywhere near as likely to be a worthwhile option in an audio system, especially if the speakers there already have sufficiently good extension for the listener's preferred musical choices. Even in a surround sound system I think that multiple subs only start to become a really worthwhile option for most people when the receiver or AV controller is capable of controlling them individually and that, at the moment, would seem to limit choices to a 2 sub set-up though that will almost certainly change over time.

So, on balance and for entirely practical reasons I tend to prefer physical acoustic treatments over equalisation or multiple subs for resolving low frequency room problems. I have no doubt that quite effective results can be achieved with all 3 of those approaches and one may certainly be better than the others in theory but I don't know which. In practice I think physical treatments are the simplest to implement, the cheapest to run, and comparable in purchase price to the other options at similar quality levels.

You may certainly have a different view to me on those comparisons and my preference for physical treatments but I do stress that the main basis of my preference is practical with the proviso that the physical room treatments are appropriate to the scale of the problems. My main reason for stressing appropriateness here is simply the fact that there seem to be an increasing number of room treatment products coming out that seem to be designed for aesthetics first and with questionable efficacy. I'm talking about standard absorption based commercial products with proven effectiveness and those DIY treatments with a sound theoretical basis that are known to be effective at low frequencies.



David Aiken

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