Benefits:
- Reduction of significant peaks and nulls in the modal region
- Better integration with the mains
- Less expensive method of reaching the best bass performance in a given room
- You can avoid expensive processing
- Distributing the bass serves to reduce the duty on each sub, generally resulting in lower distortion due to more linear operation.
- The reduction in duty can lessen the requirements for superior performance. The need for exotic motor systems is reduced.
Drawbacks:
- Subjective preferences may go against their use.
- For best results, you'd need to have measuring equipment to pull off the best results. A mic, an FFT analyzer and a few hours to spend would be the minimum requirements.
- In conjunction with the above, traditional placement methods may not result in the best performance.
At the risk of going slightly off topic...
I'll give some more thought to the drawbacks, at first glance, I was tempted to say there weren't any. But, I realize that not everybody has the time, patience, equipment or desire to learn how to properly implement an optimum bass solution. There are subjective preferences based on listening experiences that can significantly bias people against subwoofers as a whole, or various methods of implementing them. There are distinct biases for and against every type of cabinet, cone material, voice coil winding material, magnet material, etc. Misconceptions rule the roost.
Distributed bass systems are very well recognized to work well in most rooms.
My personal experience involves 4 rooms using distributed bass.
1.) My own system experimentations.
2.) Geddes' system
3.) Two systems of friends of mine I've convinced to try it.
In addition, I have convinced 7 other audio friends to attempt it but haven't heard their systems first hand. 3 live on continents I've never visited, the 4 others live in distant states.
Also, there are a number of threads on the internet where people have properly implemented distributed bass systems based on JBL/Harmans, Welti's, or Geddes' system and I have yet to find anyone who has attempted it that didn't prefer the results with at least 3 subwoofers.
For me, hearing the differences was an eye opening experience and a bit of a Eureka moment. I have always been a fan of subwoofers, but had a love hate relationship with them because of the room integration issues that are involved with them. I built my first home subwoofer using an Avatar Audio Shiva in a critically damped sealed box. At my listening position, I was able to dial it in nearly perfectly. There were no apparent weaknesses in the integration between satellites and subwoofers, nothing ever drew my attention away from the mains towards the subs. However, even a slight move from my listening position and all hell broke loose with the sound. The integration i struggled to achieve in one location was all but destroyed over the matter of inches. Having someone come over and sit anywhere but the sweetspot left people with the impression I didn't have a clue on how to integrate the sub.
I then moved up to stereo subs using another Shiva in the same critically damped alignment. I was a believer, stereo bass was the way to go. I was able to get signicantly better bass with a pair of stereo subs in addition to the mains than I was with just the mains.
When I started reading Geddes' recommendations for adding a third sub, I also found the other documents and started playing around with options. Having as many as 5 subwoofers installed in my system at times with the two mains and sometimes in 5.1 mode. It was then that I discovered that the reason stereo bass performed so well is because of the second sub, not because of the fact that they were "stereo".
Each additional sub added, up to the 4th, there was a noticeable improvement. The improvement wasn't a matter of output, it was an improvement in perceived imaging. Soundstage solidified, perceived dynamics increased, measured distortion dropped, musicality of the subwoofers increased significantly. Instead of hearing the limitations imposed by no subs, one sub, or stereo subs (which at one point, I didn't feel existed until I learned more and listened more).
The ultimate implementation of distributed bass I've heard was obviously Geddes' system. Within a few seconds of listening to his system, it's obvious that his system works and works absolute wonders. With surprisingly small investment, he has created a system that likely rivals the best in the world. there is no apparent weakness. Tonality, imaging, soundstage, etc remain constant while moving around the room. Bass depth and musicality is unparalled in any systems I've heard. The number of systems I've heard is vast, back prior to getting married, I regularly traveled around the Midwest to various audio get-togethers, shows, etc and got to hear some excellent systems. Since I've been married, that has obviously slowed, but over the course of the last 10 years, I've had the privilege of hearing some of the best systems I've heard. Over the course of 20 years in the hobby, I have had just about everyone of my misconceptions shattered with experience. The distributed bass methodology is probably the latest one in a long list.