subs and small room

Duke offers a lot of "sound" advice. 2 subs are almost minimum, but you can sometimes get away with one sub depending on where it's crossed over and the use of a good parametric EQ. Quite often in small rooms the crossover point may be as low as 35 Hz, which may be lower than the first 1/2 wavelength of any axial mode (roughly 17 feet). Thus you really aren't exciting any of the modes in that application.

We used a Talon Thunderbird and Rives sub-PARC at RMAF and won an Audio Oasis award. This was nearly the case in that we did not really need the parametrics in the sub-PARC because we crossed over so low.

Rives, thanks for the kind words - you could so easily have accused me of double-talk!

Seriously, my apologies for the double-post. I thought I was editing (instead of double-posting), and then my connection failed and I couldn't get back online.

Duke

Tobias,
Its not frequency doubling that occur with room modes but amplitude doubling or cancellation i.e peaks and dips.

Duke,
Multiple subs would only work in a large room. In a small room this would only create nodes (peaks/dips) at mid-bass and higher frequencies. So the result without any other form of control e.g EQ as suggested would be mid-bass prominence.

Samuellaudio,
Can I suggest you plot your room (Rives CD2 plus RS SPL meter) to know where you stand currently and then do it again with a sub i.e a loaner. You will then know for sure how much the sub affects the room.

Athipaul, I don't see how multiple subs in a small room "would only create nodes (peaks/dips) at mid-bass and higher frequencies".

The subs are not contributing at mid-bass and higher frequencies, so they do not "create nodes". They do smooth the in-room response in the region where they are contributing, as I will explain.

The problem in a small room is not too many room-induced peaks and dips; the problem is too few! In a large room you will have more room-induced peaks and dips bunched up closer together, and the ear tends to average them out across 1/3 octave intervals (called "critical bands) so the individual peaks and dips don't stand out - just the broader trends. In a small room, the room-induced peaks and dips are too far apart for the ear to average them out so they tend to stick out like a sore thumb. But by using multiple subs spread around in a small room (each contributing its own unique peak-and-dip pattern at any given listening position), we approximate the more dense peak-and-dip pattern that exists in a large room, and the ear's smoothing mechanism can work in our favor. I have done some simplifying in this one-paragraph explanation; you might want to take a look at Welti's paper.

Equalization is not necessarily the panacea it seems to be at first glance. Equalization can smooth the response in one listening position, but actually make it worse elsewhere in the room because the peaks and dips move around as the listening position changes, so from a different listening position the equalization may well be boosting a peak and/or cutting a dip. Multiple subs gives a more uniform response throughout the room, so that any equalization still called for will probably be beneficial throughout the room rather than in one location only.

Duke

Lot's of good advice above (I am now inspired to add a second sub!). To relay a little personal experience, for the past couple of years I had ported monitor speakers in my 11'x 22' room. I have my setup on a short wall, which effectively requires that I use a near-field approach. I wrestled with excessive bass "boom" for some time, but after some experimentation I noticed that I could plug the ports on the monitors and control the bass very effectively. Based upon this experience, I have recently decided to go with a sealed monitor (Merlin TSM) and added a Martin Logan Dynamo (10") sealed sub. Like Timrhu, I found the corner didn't work well and I have my sub positioned just as he does in his system pics (sorry my pics are not up to date). I get great bass response with no boom - except occasionally on poorly recorded material. So, the moral of my story, you can get good bass in a small room, but I would highly recommend sealed enclosures both for the speakers and sub. Also, experiment a lot with your crossover and volume levels (get an spl meter) and fight the temptation to turn the volume levels up. The goal, I believe, is not to hear the sub per se, but rather to miss it when you turn it off.