Multiple Small Subs - Geddes Approach - Page 53 - diyAudio
Go Back   Home > Forums > Loudspeakers > Subwoofers

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 1st February 2009, 04:19 PM   #521
soongsc is offline soongsc  Taiwan
diyAudio Member
 
soongsc's Avatar
 
Join Date: Mar 2005
Location: Taiwan
Hi John,

I am also interested in this subject as well. As a matter of fact, I've been trying to persuade a local electronics company to participate in this effort since they do plate amps. But if something like this can be done in a small room, it opens lots of possibilities. Having worked in simulation for a few years, I know various sound queues and how important they are.
__________________
Hear the real thing!
  Reply With Quote
Old 1st February 2009, 05:14 PM   #522
Banned
 
Join Date: May 2008
Location: Switzerland
Looking at the modal problem from a musical perspective, I think it's less of a problem if we hear "nooooote" (modal ringing but flat frequency response) instead of "note". But perceiving "note" as "NOTE" (peak in frequency response) or "NOOOOOOOOTE" (peak in frequency response and modal ringing) alters the musical content in a way it becomes audible as a defect. The same is true for dips in the frequency response.

Thinking a little bit more about Earl's approach that uses the mains as additional low frequency sources, I'm not sure if this is something that should be recommended by default. The simple reason is that we can't be sure that we will find coherent low frequency signals on every channel in each and every recording. But this is a requirement for multisub to work properly.
With Earl's Nathan I don't see much of a problem here as the woofer falls of with 12dB/octave from around 150Hz. With other speakers this is something that every AVR would be capable of by applying a high pass filter (but only to the mains as we might need the subs to run higher). Another solution could be to cut all low frequency content from each channel, sum and refeed it to each speaker and the subs. The latter might be the best solution.

Best, Markus
  Reply With Quote
Old 1st February 2009, 05:15 PM   #523
diyAudio Member
 
Join Date: Jan 2009
Quote:
Originally posted by john k...
Hi Todd,
...


I've shown that by looking at the amplitude response at a given point in a room, equalizing to to match some woofer target response, then computing the impulse response and comparing it to the impulse of the target. The result is that even though the amplitude is good, the impulse is highly distorted, and generally rings well past the decay time for the target. Here is a sample result. The woofer is equalized to a 20 Hz Q= 0.5 HP and 120 Hz B4 LP. Green is what the impulse of such a response would look like in free space. Blue, in a room. I guess I just don't believe that booOOooooooom is going to sound better than Boom.

Hi John,
So, your plots indicate that the response of the sub+room is non minimum phase. I have done my own investigations and had concluded that the phase is mostly minimum phase below 80 Hz in a small room. I did this by looking at a number of room responses, removing sufficient delay to make the unwrapped phase response as flat as possible, then comparing it to it's minphased version. In most, but not all cases I saw quite small differences. It wasn't a comprehensive study by any means. Your measurement seems to indicate otherwise. I would in general caution against "eyeballing" the impuse response. I just means that how we hear it doesn't necessarily correlate to our visual impression. Toole and Olive have done probably as much subjective investigation of resonances as anyone and concluded that time domain is not the best way to judge resonances. Not to say that in your example you wouldn't hear a difference, just that it's hard to say how big it would be or whether or not it would be preferred.

Have you ever listening to a subwoofer in an anechoic chamber? It sounds kind of pitifull/odd. If you remove the room by equalizing prefectly flat and removing any excess phase, you will have to add significant energy to get the same perceived bass level, and I think it will still sound odd.
  Reply With Quote
Old 1st February 2009, 05:51 PM   #524
Banned
 
Join Date: May 2008
Location: Switzerland
Quote:
Originally posted by cap'n todd
I have done my own investigations and had concluded that the phase is mostly minimum phase below 80 Hz in a small room.
If this is true then frequency response and and modal ringing can be fixed (at least for one listening location) by applying an EQ to the signal. But in real rooms I have never seen this happen. How can this be explained?

Best, Markus
  Reply With Quote
Old 1st February 2009, 06:35 PM   #525
diyAudio Member
 
Join Date: Jan 2009
Quote:
Originally posted by markus76


If this is true then frequency response and and modal ringing can be fixed (at least for one listening location) by applying an EQ to the signal. But in real rooms I have never seen this happen. How can this be explained?

Best, Markus
Well, I said mostly minimum phase. Also, depending on how you do your crossovers, I wonder if you could be effectively adding an allpass filter (if you are only measuring the sub, this wouldn't apply). Or, perhaps I'm wrong (but I wouldn't be the only one).
  Reply With Quote
Old 1st February 2009, 07:06 PM   #526
Pan is offline Pan  Sweden
diyAudio Member
 
Join Date: Sep 2002
Quote:
Originally posted by markus76
Looking at the modal problem from a musical perspective, I think it's less of a problem if we hear "nooooote" (modal ringing but flat frequency response) instead of "note". But perceiving "note" as "NOTE" (peak in frequency response) or "NOOOOOOOOTE" (peak in frequency response and modal ringing) alters the musical content in a way it becomes audible as a defect. The same is true for dips in the frequency response.
But you can't have modal ringing and flat frequency response.

Quote:
If this is true then frequency response and and modal ringing can be fixed (at least for one listening location) by applying an EQ to the signal. But in real rooms I have never seen this happen. How can this be explained?
Wasn't this discuessed allready and someone in this thread showed a measurement that actually suported this? Someone used a headphone in a box?


/Peter
  Reply With Quote
Old 1st February 2009, 08:17 PM   #527
Banned
 
Join Date: May 2008
Location: Switzerland
Quote:
Originally posted by Pan
But you can't have modal ringing and flat frequency response.
Ever looked at a waterfall diagram of a real room? Then you see this happen. I'd love to see a CSD from a real listening room that clearly shows a mode decaying significantly faster after an EQ was applied.

Quote:
Originally posted by Pan Wasn't this discuessed allready and someone in this thread showed a measurement that actually suported this? Someone used a headphone in a box?
It was discussed with no clear result.
  Reply With Quote
Old 1st February 2009, 08:27 PM   #528
diyAudio Member
 
Join Date: Jan 2009
Quote:
Originally posted by markus76


Ever looked at a waterfall diagram of a real room? Then you see this happen. I'd love to see a CSD from a real listening room that clearly shows a mode decaying significantly faster after an EQ was applied.
Hi Markus,
..Are you kidding? This is not hard to find. When I get into work tomorrow, I'm sure I can find one for you. Or,...get Floyd's book

  Reply With Quote
Old 1st February 2009, 08:52 PM   #529
Pan is offline Pan  Sweden
diyAudio Member
 
Join Date: Sep 2002
I can't believe this is even being questioned.. and in this thread also.


/Peter
  Reply With Quote
Old 2nd February 2009, 01:16 AM   #530
diyAudio Member
 
Join Date: Mar 2007
Location: Cleveland, Ohio, USA
Quote:
Originally posted by john k...
. . . I can tell you right now that I will at some point set up a DBA 4x4 system and listen to it before I pass any judgment on it.
While we're discussing the application of DBA (all issues of dry vs. big-room bass, or practical matters aside), I've begun to reconsider imagining DBA in my room - which is not 6-side shoebox. To clarify, my room is 12.4' wide at the listening end; 22' deep; and (due to a 4' lateral jog situated behind the listening area) ~16' wide at the rear wall. Basically a very chubby "L" shape, me sitting forward in the 3-wall 'top' end of the L

Walk with me for a moment here . . . It ought to work (even if different numbers of drivers at each room end) - as long as each array is aligned to its given wall dimensions, and capable of sufficient displacement. A plane wave is a plane wave . . . It simply becomes a matter of having the amplitude, delay, and phase of the rear array adjusted correctly.

IF I'm able to maintain room symmetry within the front and sides of my listening zone (say, from my chair's 8 o'clock to 4 o'clock range), and assuming arrays properly setup at each "end", might it still be possible to pull-off the effect?

The room is a sealed volume. The sudden room width change at the jog shouldn't matter, given that the (properly setup) system = zero net pressure change in the room, right?

Just thinking out loud here . . . Help me through it, Docs!

--Mark
  Reply With Quote

Reply


Hide 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
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



New To Site? Need Help?

All times are GMT. The time now is 04:16 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2