Further Adventures in Quad sub management : Geddes

[My adventures in stereo]

So I run a quad sub system,3 SVS & PB 2000 Pro and a Velodyne CHT 12
With Revel M 126 Be book shelves crossed over at 60 hz as my mains
A NAD C298 power the mains and the preamp duty is done by a minidsp SHD

System is controlled using REW, sligned using the REW tool and eq'ed in REW, with a 6 db Harman curve
Found that Dirac was killing bass, not using it anymore

Came across the Geddes method, of multi sub optimisation
Decided to give it a try

Changed the sub position, to one in the corner, 3 asymmetrically placed across the room

Geddes suggests not using a high pass filter for the mains
As my mains are not capable of much below 60hz, crossed over at 60 hz
The Subs close to the mains, I switched to 100 hz and the ones further away to 80 hz

Re calibrated from scratch, using REW
no time alignment done, only phase alignment

My results,objectively measured and subjectively were worse than my previous setup

Hence, I decided to try and mix the old system with some of Geddes techniques
Re calibrated with time alignment, subs left in new position, needed a timing delay of 2ms, compared to the 6 ms I was previously using

eq'ed with a 6 db Harman curve, results were much better
Objectively and subjectively

A final tip, noticed that my corner sub produces the best measurements and output in the room, so leaving it a 3db higher than the other subs produces the best results in my room

 

[My adventures in stereo]

A few more thoughts
- I am finding 90% of my response coming from two subs placed at diagonals of my room
- If I was doing this room again, I probably would use only 2 subs
- The one in the rear corner has the best gain and usable response
- Identical subs are not really essential, miixing and matching should be fine, as the responses across the room, measured are very different
- I prefer working with ported subs because of the gain advantage, to get the same SPL, you need roughly double the power on a sealed sub
- Find the position, where your single sub gives you maximum gain and usable response, then add the other subs one by one and measure
- In most cases two well positioned subs will get the job done, you very rarely will need four subs

Hope this info is useful, cheers

 

[AdamG247]

Hi My adventures in stereo,

Interesting results. It would be even more interesting if you have the before room measurement(s) for comparison purposes. It would also drive more member engagement in your thread. Thanks for sharing your journey so far!

 

[My adventures in stereo]

Hi My adventures in stereo,

Interesting results. It would be even more interesting if you have the before room measurement(s) for comparison purposes. It would also drive more member engagement in your thread. Thanks for sharing your journey so far!

Hi Adam

Good suggestion, I will do that

 

[My adventures in stereo]

I had another try at the Geddes method, using 3 SVS PB 2000 Pro subs
Set the rear sub to 80 hz cross over and front left and right subs to 100 hz
The mains crossed over at 50 hz

Liking the resulting sound, the bass sounds flat & clean, better integrated with the mains
Will post measurements soon

 

[Speedskater]

The Earl Geddes web page:

GedLee LLC

Two Great Articles on Multiple Subwoofers by Dr. Earl Geddes

Two Great Articles on Multiple Subwoofers by Dr. Earl Geddes

I have written before on the absolute necessity of multiple subwoofers for high-fidelity reproduction of modal region frequencies in a hom...

seriousaudioblog.blogspot.com

Most of his other subwoofer links have disappeared.

​

 

[My adventures in stereo]

C4 is the previous config
No Cross over in minidsp SHD , flat eq to 200 hz
Subs crossed over in SVS at 100hz Lt & Rt Sub; Rear Sub at 80 Hz

Did another config today
No Cross over in minidsp SHD , flat eq to 200 hz
Subs crossed over in SVS at 100hz Lt & Rt Sub; Rear Sub at 80 Hz

 

[My adventures in stereo]

Adding on to earlier feedback

I did a few more tweaks, repositioned my front left & right subs, recalibrated
Had been noting that once I put in standard 80 hz high pass & low pass filters at - 12db
There was a significant dip from around 60 to 100 hz
so tweaked them low pass at 80 hz -6db & high pass at 50 hz - 6db, mitigated the response loss completely

will post the measurements soon

 

[Sancus]

There's a lot of issues with Geddes' advice but the most important part is to use software to optimize each sub's settings and EQ. He literally makes fun of audiophiles who would try to do it manually.

Since he never provided the world with his software we don't know much about it. The best you can do with public free software is Multi-Sub Optimizer. There are some helpful miniDSP tutorials, a video, and the manual for MSO is good as well (if long).

 

[Kervel]

Nice work! In your figure C4 final there is about 30db difference between the min and the max, suggesting there is significant room for improvement. Given your skills with REW, you should definitely check out multisub optimizer!

 

[ozzy9832001]

A few more thoughts
- I am finding 90% of my response coming from two subs placed at diagonals of my room
- If I was doing this room again, I probably would use only 2 subs
- The one in the rear corner has the best gain and usable response
- Identical subs are not really essential, miixing and matching should be fine, as the responses across the room, measured are very different
- I prefer working with ported subs because of the gain advantage, to get the same SPL, you need roughly double the power on a sealed sub
- Find the position, where your single sub gives you maximum gain and usable response, then add the other subs one by one and measure
- In most cases two well positioned subs will get the job done, you very rarely will need four subs

Hope this info is useful, cheers

I found that 2 of my corners give odd responses as well. I attribute it to door and window placement. Possibly closet causing a different response as well.

 

[My adventures in stereo]

I found that setting my front subs breadth wise & the rear length wise gives the best raw responses in my room
FIxed a dip, while adding no new issues