Sub setups using Dr Earl Geddes method

[sonicbliss]

Introduction

This is a discussion of Earl Geddes sub setup method which deals with minimizing the ill effects of the room modes that are experienced in a typcial room.


Problem

The bass (50hz-150 hz modal region) in typical rooms is dominated by the room which really swamps it resulting in peaks and nulls all around the room. While it may seem intuitive to flatten the response by EQ, the nature of the problem does not lend itself to simple EQ. After all, the room modes are position dependent. EQ may flatten the response in one position but creates more problems in other positions. The moment the listener moves by a few inches the simple EQ is a disaster.


Whats is Earl Geddes method

Dr Earl Geddes' method solves the problem in a unique way. He recommends multiple subs randomly placed in a room with overlapping mains. By having overlapping mains the mains too contribute bass. Therefore there are many bass sources and each has a different position. While he recommends multiple subs (3 subs) folks have tried with less number of subs and achieved very good results both in measurement and listening tests.


Examples, measurements and reviews

A better description of the problem and the solution in general is found here.
mehlau.net > audio > multisub

Here is a review of system that uses 3 of Earl's subs
http://www.avsforum.com/avs-vb/showthread.php?t=1340062

Here is a nice review (including Geddes mains: Nathan) Earl Geddes Nathan system

Here is a two sub system with measurements
Bandpass sonotube subs - Home Theater Forum and Systems - HomeTheaterShack.com

And finally here is something that would interest the most of single sub owners Bass Integration Guide Part 1 | Hifi Zine
Though the article does talk about measurements being available in part 3, yet part 3 is, unfortunately, not avialble at the time of this post.

Finally here is an experienced member talking about the fact that the actual type of sub (sealed, ported or bandpass) does not really matter. http://www.avsforum.com/avs-vb/showthread.php?p=15793728#post15793728


If anyone does try the setup, do provide your feedback here.

While I have not tried the setup, at the moment I am working on bandpass subs based on this philosophy of 'multiple sub with overlapping mains' as per Dr Earl Geddes.

Sonicbliss

 

[sdurani]

Geddes is not the first person to promote positive results from using multiple subwoofers nor will he be the last. The improvements gained from multiple subs can easily be demonstrated via measurements and listening. So it works.

One of the downsides of Geddes' personal solution is that it comes along with his personal preferences: doesn't really care about bass below 50Hz, willing to cross over as high as 150Hz, etc. Some people do care about reproducing the bottom octave of sound properly, not to mention infrasonics (bass below 20Hz). And crossing over to above 80-90Hz can lead to smearing of localization (especially with the bottom end of male vocals).

Still, it works. And you can always adjust the parameters to your tastes (e.g., move the crossover point lower, etc). If you are going to use the low frequency response of your floorstanding speakers to help smoothen out bass in the room, then keep in mind that the results will change below where your speakers roll off. I tried it a few years ago with a pair of subs and my Kef Q70 speakers, with mixed results (pretty good above 45-50Hz, not as good below).

BTW, another good approach to using multiple subs comes from Todd Welti at Harman:
Subwoofers: Optimum Number and Locations