Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Multiple Small Subs - Geddes Approach
Multiple Small Subs - Geddes Approach
Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 15th February 2020, 07:54 PM   #2251
DAMIC is offline DAMIC  Serbia
diyAudio Member
 
Join Date: Jan 2006
Location: Beograd
Quote:
Originally Posted by gedlee View Post
Seems to me that you should have a big hole between 60 Hz and 100 Hz.

Again, I do not recommend crossovers to subs.

Without measurements I can't comment further, but if it all works then that's what counts.
"but if it all works then that's what counts" this is actually the answer to my post.

Thank's for reply very much.
  Reply With Quote
Old 15th February 2020, 09:42 PM   #2252
beige is offline beige  Europe
diyAudio Member
 
beige's Avatar
 
Join Date: Nov 2014
Quote:
Originally Posted by gedlee View Post
Since it has been in every one of your measurements, I doubt that it is a coincidence. It's real, but probably very obscure as to its origin. And since it is meaningless just ignore it.
That's exactly what I'm asking. Since it's on every measurement I thought this might be caused by room modes?
I know I probably can't eliminate this no matter what is causing this. And I'm not concerned. Just curious how it did get there.
  Reply With Quote
Old 15th February 2020, 11:37 PM   #2253
gedlee is offline gedlee  United States
diyAudio Member
 
gedlee's Avatar
 
Join Date: Dec 2004
Location: Novi, Michigan
Good enough, it's not a problem so it's not worth worry about. Just remember that it can happen. It's a classic theoretical problem in room acoustics, how two spaces couple each other. A larger room coupled to a smaller (maybe much smaller room) will couple like you see. If this were more pronounced you might hear it as an echo.
__________________
Earl Geddes Gedlee Website
  Reply With Quote
Old 16th February 2020, 10:48 AM   #2254
beige is offline beige  Europe
diyAudio Member
 
beige's Avatar
 
Join Date: Nov 2014
And this can be seen as an edge (or a staircase) on a graph?
In other words, how can one see if this is a coupling issue or a classic ringing?
  Reply With Quote
Old 16th February 2020, 01:24 PM   #2255
Manpole is offline Manpole
diyAudio Member
 
Join Date: May 2019
Quote:
Originally Posted by gedlee View Post
Yea, I would say that's likely. It would act just like a free field - outdoors. I have not heard one, but the concept is solid and probably will do what they say - no modes. The question is: Is that what you want to do? Modes are not bad things if they are not high Q. Broaden them with more overlap and the Schroeder frequency falls. The modes then still carry some energy and add to a longer held signal for a better bass perception. Smooth it all out and I'd say that's the best that you can do. In my room there is only a single mode that is evident at about 30 Hz. - the room length mode. It may even be pumping the doors which is why it's a higher Q.
I just want to include a few measurements of a large room (about 50 m2) with a double bass array to demonstrate that the DBA configuration will not be particularly more effective against longer bass decay times than any other method of flattening the frequency response. It looks like you will get about 20-25 db drop before 200 ms, which is about the same as I do with a simple PEQ at a mode.

The benefit is that you will get the same response everywhere and at every frequency where the array is effective. In this particular case it's 120 hz. I will not include pictures of the system because this system is not mine, but it's a rectangular room with 16 10" wooferes on both sides of the array.

Included are waterfalls of the DBA at 200 ms and 300 ms and then an example from my rectangular concrete livingroom before and after simple PEQs. I believe this is all evidence we need to support the notion that even a DBA is just another multi-sub configuration, just a predictable one in a rectangular room.
Attached Images
File Type: jpg DBA waterfall 200 ms.jpg (239.5 KB, 118 views)
File Type: jpg DBA waterfall 300 ms.jpg (255.3 KB, 111 views)
File Type: jpg Uten PEQ - vannfall.jpg (189.0 KB, 115 views)
File Type: jpg Med PEQ - vannfall.jpg (203.1 KB, 119 views)
  Reply With Quote
Old 16th February 2020, 06:33 PM   #2256
gedlee is offline gedlee  United States
diyAudio Member
 
gedlee's Avatar
 
Join Date: Dec 2004
Location: Novi, Michigan
Manpole - thanks for this data. I agree with you completely.

Beige - Classic ringing - as I have said at least twice now - has a monotonic decay. When that doesn't happen its not "normal" and something else is involved. Look at the third plot above, at 250 Hz, something other than ringing is going on as this is not a normal decay. Same at 40 and 50 Hz in the fourth one. I can't tell what is going on, but I do know that it is not the ringing down of a mode. If the PEQ is high Q then this could be the ringing of the EQ, but not necessarily as it is very slow.
__________________
Earl Geddes Gedlee Website
  Reply With Quote
Old 16th February 2020, 09:00 PM   #2257
beige is offline beige  Europe
diyAudio Member
 
beige's Avatar
 
Join Date: Nov 2014
I see what you mean. I always saw these as room modes. If I put room's dimensions in a calculator I get modes at 23 and 45 Hz. But the more I think of your theory the more confused I get. If I make a measurement at the evening and then another one in the morning - the decay times sometimes change while FR remains the same. Everything in the room is intact, mic untouched, gear warmed up, furniture in place ... The only variable I see here is air humidity, pressure and temperature...
Makes me wonder if this is really caused by something outside the room.

However, I did more testing and this time I took more time and tried at least 50 songs I'm familiar with.
Turned out slight vibrations in my back seat were caused by EQ. It was mild (4-5 dB for taming a specific frequency on two subs and 3-4 for boosting on other two) but disabling it improved the sound but made of course an impact on the curve.
Some songs are really good, some have pretty hard bass and some may sound slightly boomy or with too loud low end.

Perhaps a crazy thought: all the songs with assumably high budget mastering sound excellent while some other low-budget songs does not. Listening on a low budget system masks everything so one can't hear so many details?

Here, the plots, no EQ.
Sub1, left corner, vol 24, 180+, HP20/12 LP40/18
Sub2, right corner, vol 25, 180+, HP15/24 LP85/18
Sub3, right sidewall, vol 18, 00+, HP 35/24 LP80/24
Sub4, left sidewall, vol 13, 00+, HP 15/06 LP75/06
Attached Images
File Type: jpg wf.jpg (511.2 KB, 90 views)
File Type: jpg spectrogram.jpg (287.8 KB, 21 views)
File Type: jpg fr.jpg (185.9 KB, 20 views)

Last edited by beige; 16th February 2020 at 09:05 PM.
  Reply With Quote
Old 17th February 2020, 12:05 AM   #2258
gedlee is offline gedlee  United States
diyAudio Member
 
gedlee's Avatar
 
Join Date: Dec 2004
Location: Novi, Michigan
Quote:
Perhaps a crazy thought: all the songs with assumably high budget mastering sound excellent while some other low-budget songs does not. Listening on a low budget system masks everything so one can't hear so many details?
That the recording industry for ya!

I would agree that:"Listening on a low budget system masks everything so one can't hear so many details"
__________________
Earl Geddes Gedlee Website
  Reply With Quote
Old 17th February 2020, 03:10 PM   #2259
Manpole is offline Manpole
diyAudio Member
 
Join Date: May 2019
Quote:
Originally Posted by gedlee View Post
Manpole - thanks for this data. I agree with you completely.
My privilege. I was dreaming about DBA until I realized that you are correct about how we perceive low frequencies.

Now I feel DBA is too costly, complicated and too limiting with regards to acoustical treatments like diffusors, furniture etc. If I can get the ~ same results with 3-4 subs, why go through the headache?

Quick question; what does it take for you to consider the bass issue a solved problem in a room? Aka the point where you feel there's nothing to gain by going further?
  Reply With Quote
Old 17th February 2020, 08:02 PM   #2260
digitalthor is offline digitalthor  Denmark
diyAudio Member
 
Join Date: Jan 2018
Quote:
Originally Posted by gedlee View Post
If the PEQ is high Q then this could be the ringing of the EQ, but not necessarily as it is very slow.
If I may dig deeper into the ringing thing Is it correct that exessive EQ might cause ringing, in the same manner, as it could remove/lower it? Or would it be less audible at low frequencies, compared to higher ones - at let's say 500 or 3khz?
  Reply With Quote

Reply


Multiple Small Subs - Geddes ApproachHide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


New To Site? Need Help?

All times are GMT. The time now is 01:21 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.79%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.
Copyright ©1999-2020 diyAudio
Wiki