Short Subwoofer Tips

I guess that primarily due to Home Theatre, there has been increased interest in adding subwoofers to an existing system. I've owned a REL Strata II before and have an SVS now and I thought I'd share some of my experiences.

First thing. If you have a small listening room, say 12' x 13' and are only using the system for music and not HT, I don't believe that getting a subwoofer is the right move, because a decent hi-fi speaker should give you all the bass you need in such a small room. In my old 12' x 13' listening room, after changing my speakers to the Proac 1.5, I felt no need to keep the Strata anymore so I sold it. This necessarily implies that I should have moved from my Zephyrs straight to the Proacs without the intervening Strata purchased (fortunately, I bought my Strata II just before the price increase and it had a good resale value. Incidentally, the eventual new owner of my Strata II posted a very, very long review of it on audioreview.com - according to it, I think I sold my Strata at too low a price ;) ).

With the Proacs installed, the Strata added minimally to the sound and was taking up valuable floorspace in my tiny room. So my recommendation for small rooms is: save your money and upgrade the main speakers.

For larger rooms, certainly, a subwoofer to give increased bass extension and quantity is a viable option (considering the price of full-range speakers as well as the demands they make on amplification. Eg: Joseph Audio RM50si really need to be biamped in order to sing, 1 250wpc amp not enough...)

I'm not familiar with the performance of that many brands of subwoofer, but from my experience, REL ST series (not a big fan of their Q series though) and SVS should be ok. MJ Acoustics is a direct REL competitor so I guess they should sound similar (but one dealer in Adelphi refused to demo them for me, unlike Kingsley which is very happy to hook up whatever REL sub you want to hear... if they have a demo set available). Hsu is also reputedly good (its apparently finally back in stock at Reference so may I'll finally have a chance to hear one...) But heres a buying guide:

 

Subwoofer performance aside, there is also the issue of setting up:

Positioning: I'm a believer in corner placement. Anyway, most of us are limited by where we can place subs so they'll end up in the corner. If you have alternative placements available, then by all means try the sub in these locations to see whether you like the sound.

Phase: At any given sub location, set the phase to ensure that maximum bass output is obtained. I don't quite understand why REL only has two settings whereas almost all other manufacturers are willing to give you fully variable phase controls to fine tune. Based on my own setting of phase for my sub, the loudest bass was not exactly at 0, 180 or even 90 degrees for that matter (digital signal processing may cause phase changes).

Doing it by 'ear' or with measurement devices: Personally, I still believe that any with good enough ears (you're into hi-fi, right? :) ) can do it by ear. But, having a SPL meter (like the good old radioshack meter - I bought mine from a Radioshack at Palos Verdes, LA, 5 years ago where the sales assistant didn't have a clue what I was referring too - fortunately the manager did) helps a lot. Basically, using an SPL meter will help a lot determine exactly where maximum bass volume is as you slowly turn the phase dial. It will also determine at which location the bass sounds loudest (though loudest is not necessarily the best - could just be that you hit a room mode). If you want to be more advanced, you can download sinewaves off the internet and play them and measure the volume through the SPL meter (caution: don't play them too loud, can damage equipment. Under 80dB C weighted should be ok, but usual disclaimer applies).

Sinewaves (plus an article on equalising an subwoofer) can be found here:

 

Setting the Correct Volume: The advice is the manual is usually to turn up the volume until the bass becomes obstrusive and turn it down until it becomes unobstrusive. Yeah, but you spent so much money on the subwoofer, you want to hear it right? Ok, tell you what, for the first few weeks, turn it up louder a bit just to make sure it works and also to speed up the running in processes (subwoofers really need a good running in and actually, movies like Twister etc are far better for running in subwoofers than some wimpy symphonic piece ;) ). Thereafter, set it to the correct level and enjoy the bass. If you get into equalisation, you can do it even more precisely.

Crossover Frequency: As a starting point (repeat starting point), set it based on the -3dB point of your main speaker. i.e., your speaker specs say 40Hz at -3dB, then you set your crossover to 40Hz. This is rarely the correct setting but is a starting point. Thereafter you go down or up from there until to get a crossover point that sounds good.

Cabling/Connectivity: REL/MJA feature high-level inputs which allow you to connect a speaker cable to the speaker terminals (in parallel with the main speaker cables) which ends up as a Neutrik Speakon connector on the subwoofer (too complicated to explain, just read the manual). The most common connection is RCA inputs. Currently, I favour RCA connections because this allows you to put an equaliser in between to equalise the sub. However, in order to use RCA connections you ideally need an additional set of pre-outs from your pre-amp/integrated amp.

And guess what, interconnects between your pre-amp and subwoofer do in fact sound different. Fortunately, good sounding subwoofer cables can be had for cheap. Personally, for subwoofer cables, I favour those that do not give an overblown or bloated bass. Good old Belden 89259 (from LHS at Sim Lim Tower) is an excellent sounding subwoofer cable - lean and tight sound. Currently I'm using a Canare made by someone over at xtremeplace which is about the same standard but a little bit fuller sounding (my 89259 is for HT). I bought a QED subwoofer on impulse but sold it off.

 

Conclusion (or an article cut short)

As I'm not really a bass/subwoofer expert (those really in the HT are the subwoofer experts), the purpose of this short note is to give some food for thought for those wanting to get a subwoofer for stereo use. The way I'm currently connecting my subwoofer to my hi-fi system is a bit more complicated as it involved a digital equaliser - this will be the topic of another article.