Setting up subwoofers purely by ear is not easy. Just as designing a loudspeaker crossover by ear only is likely to result in a seriously sub-standard sound. I am all for setting up systems to sound the way you want them to sound, a neutral setup can sound way too anemic. What I'm advocating here is that there needs to be a measured baseline understanding of how the bass in your system measures, you can then decide to tweak to taste from a known good starting point.
I had been looking for an affordable sound analyzer for some time, an accurate analyzer is not going to be bargain basement priced but at 220€ the XTZ Room Analyzer is definitely affordable. It is also vital to optimizing a system that includes subwoofers. If you spend say $4,000 or whatever on your system but then fail to set it properly you are missing out big-time.
XTZ are based in Sweden, they make a range of amplifiers and loudspeakers. Amongst their loudspeakers are subwoofers with digital equalization. This is where the analogue signal is converted to digital; DSP is then applied to correct for frequency aberrations caused by the room. The signal is then converted back to analogue. The XTZ Room Analyzer can be used in conjunction with the XTZ 99 W12 DSP subwoofer where the room is measured and then you upload the corrections required for the subwoofer to produce a flat frequency response compensating for room interactions. This is the ultimate way to tailor your subwoofers to your room.
In this article I am using the Room Analyzer to help setup my subwoofers, no DSP is involved, here I am purely adjusting the level, crossover frequency and phase as well as subwoofer positioning to suit the room and main loudspeakers. First of all let's cover why I'm doing this. There are two main reasons – all rooms have resonances or “room modes” defined by their dimensions, these are troublesome as they over-emphasise certain frequencies and cause long decay times, this results in notes that coincide with these frequencies sounding boomy. Some recordings may be quite unpleasant to listen to. The second reason is that when setting the controls on subwoofers it is all too easy to leave a gap in the frequencies where the subwoofer and main loudspeakers should integrate. If you do this you can then turn up the bass on the subwoofers to sound very impressive without too badly impacting the music from the main loudspeakers. In my experience most subwoofers set up ear are setup this way leaving a hole in the frequency range. When you get to the point where the subwoofers are well integrated with the main loudspeakers you will find that very fine adjustments make a surprisingly large difference to the sound. Get it right and you will gain tight, deep and detailed bass. Timing should be good and there will likely be mid to upper bass detail that you have missed previously. The mid-range and treble will improve too as these are not being masked by poor bass.
So, what do you get with the Room Analyzer? Hardware and software - there is a calibrated microphone that plugs into a base. The base contains a soundcard and two RCA sockets, one is the microphone input; the other is the soundcard output to your subwoofer or amplifier. There is also a USB connection to your PC.
You are given access to download software to run the Room Analyzer. The version of the software I used is suitable for Windows 98se/ME/2000 and XP. Use of Vista should be discussed with XTZ. The software is downloadable from their website. The software plays a frequency sweep up to 250Hz; measurements can be made using the microphone in three positions or a single position. XTZ recommend the use of three positions, as room modes not discernable from the listening position can still be problematic. Three-position measurement reveals all room modes and provides an extensive set of data to work with. The single position method only takes into account the room character as an instantaneous reading from the listening position. This may work in some rooms, but it is guaranteed to fail in rooms where room modes affect the reproduction, this is where the decay frequency response differs significantly from the instant frequency response. The Behringer DEQ2496 for example is DSP-based room correction product that as part of its immense armory uses single position measurements, I note that the manufacturer recommends ignoring the Real-Time Analyzer readings below 100Hz, I suspect this is due to use of just a single microphone position.
As well as measuring bass, the XTZ Room Analyzer includes a 32-band Real-Time Analyzer 16Hz to 20kHz.
Did The Room Analyzer Do For Me?
Looking at graphs for bass response of someone else's loudspeakers in a room you don't know is not the most interesting pastime I can think of so I've only included a few graphs showing extremes to illustrate the usefulness of the Room Analyzer.
Here is a an extreme setup example, actually it's probably quite typical: the first thing that Room Analyzer did was to confirm for me that I had excited some pretty awful room modes with the setup and there was a big hole in the sound between 100Hz and 250Hz. At 33Hz I had a boost of 15db with a consequential lousy decay time.
Bass Frequency Response
By twiddling with the subwoofer settings I ended up with two smaller peaks at 36Hz and 58Hz. This does not sound ideal but it is reality quite a good in-room response, at least it is in my room.
The next screenshot shows one of the worst decay readings I took. I did not do anything specifically to improve decay, in my situation decay improves as I reduce the room modes. For very live rooms with poor decay it, may be necessary to use soft furnishings, carpets or curtains to bring decay under control. As you can imagine long decay times kill any notion of a fast sound or good timing by masking and smearing notes.
You can see from the following screenshot that the remaining room modes still cause poor decay but the effect is now very limited by being narrow-band.
I found that once I had zoomed into reasonable settings for my room using averaged measurements using the full three microphone positions I could then go with single position readings, the microphone being placed in the listening position. This allowed me to achieve a finely tuned setup rapidly, I was also able to fine to the location of the listening position. – only use a single mic position once you are doing the final fine-tuning. Once you reach your nirvana I suggest you do a three-position check just to be sure all is as you expect. What is really useful is the ability to click “store” once you have a good curve to work from, your latest measurement is then super-imposed on the same graph allowing you to determine at a glance whether you have improved the setup.
The stored curve facility was invaluable once I was in the zone for a good setup, the slightest control tweak made a very visible and audible change. With a poor setup and subwoofers exciting room modes and when integration with the main loudspeakers isn't working then quite large control changes have surprisingly little effect, just more or less boom. In the above screenshot the “stored” curve shows a big gap between the subwoofers and open baffles (the blue trace), until this gap is closed up the “zone of sensitivity” is not achieved. Reach the upper (green) curve where integration is good and you hit that zone where small tweaks result in big changes.
The Room Analyzer works on the bass region in detail but there is also a 32-Bnad Real-Time Analyzer which provides a picture of what's happening right across the frequency range. This may help you understand if you have a very uneven frequency response, if you do you may want to consider using DSP across the whole audio spectrum or you may be very happy with the sound and character you have.
We Have Seen What The Graphs Show... What About The Sound?
The impact of optimizing subwoofer settings is, not surprisingly, very dramatic. First off I found the sound a lot drier with less reverb (decay), walking around the room bass was way more consistent than it had been. On certain albums where notes previously coincided with a suckout I found whole bass lines that had only been hinted at in the past. Bass strings and percussion achieved the greatest improvements. Timing was enhanced along with scale, tonal balance was more even and the incidence of unnatural sibilance was much reduced, as there was more upper bass to balance vocals. Integration between subwoofers and open baffles definitely took a big step forward. Some albums did not sound as good, these were ones that gained from the room modes because they were mixed to be bass-light or for some reason the music could that an artificial boost. A few albums that were uncomfortable to listen to due to over-blown bass now became much better balanced. Returning the subwoofers to their original settings still gave a tremendous sound but the new, much more balanced settings give a way more consistent sound that contains much more musical information with much improved timing. Getting to this point without a way to measure and analyze your setup requires skill that I don't possess and luck that I don't have. The XTZ Room Analyzer is very good value for money, the improvement it can bring to a subwoofer-based system is huge and it is hard to imagine how your can find another way of achieving this by spending just $320.
Check their website for many more examples and explanations about subwoofer setup. Finally I should mention that if you run the Room Analyzer software with a suitable XTZ subwoofer you will find extra Room Analyzer functionality in addition to my descriptions.