Multiple Cabinet Combined Response - 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 14th January 2012, 03:40 AM   #1
diyAudio Member
 
Join Date: Jan 2008
Default Multiple Cabinet Combined Response

After noting differences between measured results of single cabinets of various types (TH, FLH, and BR) compared to multiple cabinet simulations using Hornresp, I conducted an extensive series of outdoor tests using one through eight bass reflex (BR) cabinets in various arrays.

Coherent summation of multiple cabinets should yield a 6 dB addition per doubling, +3 dB for doubling radiation area, and +3 dB for doubling power.
The closest to coherent summation was achieved with the speakers placed in an arc with all cabinets ten meters from the measurement mic, resulting in a net even response between one and 8 cabinets from F3 to around 250 Hz.

Incoherent summation results in only an average +3 dB addition per doubling of power and cabinets.

The graphs have been “normalized” with a 6 dB reduction for 2 cabinets, 12 dB reduction for 4, 18 dB reduction for 8 cabinets so that differences from coherent summation can be seen. Series cabinets have no normalization, as the net result of less power per cabinet and increased radiation net a 0 dB change.

The results of the tests show how different arrays result in quite different upper response from single units. Although David McBean is considering some changes to Hornresp, they still will not be able to reflect each type of array response, a complicated combination of many factors beyond the present model.

Similar upper frequency response reduction and general smoothing as is seen and heard in FLH and TH response occurs in the BR cabinets also.

The frontal area of the stack makes a significant difference in response shape, adding “wings”, flat pieces of plywood (AKA “barn doors”) to the stacks add 2 to 3 dB to the LF response when the frontal area is tripled.

Art Welter
Attached Images
File Type: jpg ArrayMult.jpg (139.5 KB, 499 views)
File Type: png Test ID.png (44.5 KB, 473 views)
File Type: jpg FLH 1&2.jpg (56.8 KB, 472 views)
File Type: png WingsVmult.png (186.2 KB, 463 views)
File Type: jpg Stacks.jpg (102.9 KB, 473 views)
File Type: jpg Series Mult.jpg (126.7 KB, 279 views)
  Reply With Quote
Old 14th January 2012, 05:37 AM   #2
18Hurts is offline 18Hurts  United States
diyAudio Member
 
Join Date: Nov 2010
I like the "barn doors"

So when I build my tapped horn--would adding barn doors to it give me about 2 to 3 extra dB also? If the horn is tuned for 18Hz, would it be advisable to use heavy bracing--say pieces of 2x2 lumber to frame the doors?

I'm always interested in "free dBs" and the barn doors would help when dragging the speakers outside for BBQs and such.
  Reply With Quote
Old 14th January 2012, 05:47 AM   #3
diyAudio Member
 
Join Date: Jun 2007
Quote:
Originally Posted by weltersys View Post
The results of the tests show how different arrays result in quite different upper response from single units. Although David McBean is considering some changes to Hornresp, they still will not be able to reflect each type of array response, a complicated combination of many factors beyond the present model.
Hi Art,

Many thanks for taking the time and effort to conduct these very comprehensive tests.

Your measurements now make it quite clear to me that unfortunately, I am probably wasting my time trying to develop a new multiple speakers model that will ultimately be any better overall, than the current one. There are just too many variables to take into account.

In the circumstances, perhaps a more sensible approach may be to simply keep the current model, but to document known limitations in the Hornresp Help file so that users are aware of the shortcomings.

A couple of comments on speaker testing in general, in relation to Hornresp:

Hornresp assumes that the outputs from multiple speakers are in effect combined into one "concentrated" sound source. This means that to most accurately reflect the simulation assumption, four speakers should ideally be configured in a 2 x 2 square array - rather than a 1 x 4 linear array, for example. Eight speakers should be configured in a 3 x 3 array, but with only two speakers in the top row, centrally positioned. Not sure how much of a difference, if any, this would actually make to measured results though :-).

Tests should ideally be done under anechoic conditions, meaning that to replicate 2 x Pi half space conditions outdoors, it would be necessary to place the speakers on solid ground, pointing vertically towards the sky with the microphone suspended an appropriate distance above the geometric centre of the array, suitably shielded from the wind. Not a very practical proposition in your case :-).

Thanks again for all your assistance - it is greatly appreciated!

Kind regards,

David
__________________
www.hornresp.net
  Reply With Quote
Old 14th January 2012, 06:32 AM   #4
sebDIY is offline sebDIY  Belgium
diyAudio Member
 
Join Date: Oct 2011
An other intested PDF from LinearX about arrays sum in LEAP : http://www.linearx.com/files/pdf/EncShopApp_02.pdf
  Reply With Quote
Old 14th January 2012, 07:52 AM   #5
diyAudio Member
 
Join Date: Mar 2010
Location: Salzburg
Default Thanks for reminding me to build

some barndoors of my own!

Regards, Ben
  Reply With Quote
Old 14th January 2012, 04:39 PM   #6
diyAudio Member
 
Join Date: Jan 2008
Quote:
Originally Posted by 18Hurts View Post
So when I build my tapped horn--would adding barn doors to it give me about 2 to 3 extra dB also? If the horn is tuned for 18Hz, would it be advisable to use heavy bracing--say pieces of 2x2 lumber to frame the doors?
Getting an extra 2 to 3 dB down to 18Hz would probably require much larger "barn doors" than what I have used, the extenders used on my TH and FLH provide an increase in level down to about 35 Hz.

If the panels are vibrating much, some acoustical energy is being wasted.
That said, flopping panels will loose more energy in the upper bass range than lower.

My panels have a 1.5" x 2" brace on the mouth side, that seems adequate to keep them from flexing.
  Reply With Quote
Old 14th January 2012, 06:30 PM   #7
18Hurts is offline 18Hurts  United States
diyAudio Member
 
Join Date: Nov 2010
Thank you Art,

So if triple-wide is good to 35Hz--that is good enough for outside use for BBQs. Since I've done some DIY stuff, there is a dedicated pile of wood for bracing so I'll give it a shot.

Once I finish my line array mod, I'll have spare wood to make some doors to attempt to get the most bass I can out of 24 five inch woofers. Ironically, I'll have enough wood and 24 feet of 2x2's to make one and check it out. If it's ugly, it has to work!

Last edited by 18Hurts; 14th January 2012 at 06:48 PM.
  Reply With Quote
Old 14th January 2012, 07:08 PM   #8
diyAudio Member
 
Join Date: Jan 2008
Quote:
Originally Posted by David McBean View Post
Hi Art,
Your measurements now make it quite clear to me that unfortunately, I am probably wasting my time trying to develop a new multiple speakers model that will ultimately be any better overall, than the current one. There are just too many variables to take into account.

In the circumstances, perhaps a more sensible approach may be to simply keep the current model, but to document known limitations in the Hornresp Help file so that users are aware of the shortcomings.

A couple of comments on speaker testing in general, in relation to Hornresp:

Hornresp assumes that the outputs from multiple speakers are in effect combined into one "concentrated" sound source. This means that to most accurately reflect the simulation assumption, four speakers should ideally be configured in a 2 x 2 square array - rather than a 1 x 4 linear array, for example. Eight speakers should be configured in a 3 x 3 array, but with only two speakers in the top row, centrally positioned. Not sure how much of a difference, if any, this would actually make to measured results though :-).

Kind regards,

David
Documenting known limitations in the Hornresp Help file so that users are aware of the shortcomings would be a good solution.

It is worth noting that the ground plane reflection made the 2x4 and 4x2 stacks both fairly equal, and 1-2 dB louder in the LF than the vertical or horizontal line of eight cabinets.

The addition of the wings adds a bit more level down low than I would have expected on BR cabinets, almost as much as the 3 dB they did when added as a 90 degree "waveguide" to TH or FLH horns.

Art
  Reply With Quote
Old 15th January 2012, 02:39 AM   #9
mdocod is offline mdocod  United States
diyAudio Member
 
Join Date: Dec 2011
Location: Black Forest, CO
Send a message via AIM to mdocod
Quote:
Originally Posted by 18Hurts View Post
... If the horn is tuned for 18Hz, would it be advisable to use heavy bracing--say pieces of 2x2 lumber to frame the doors?...
I'd imagine you'd have to have an effective baffle width/height of ~60ft to eliminate 4PI transition at 18hz.... uh.... I think?
  Reply With Quote
Old 15th January 2012, 03:08 AM   #10
18Hurts is offline 18Hurts  United States
diyAudio Member
 
Join Date: Nov 2010
Quote:
Originally Posted by mdocod View Post
I'd imagine you'd have to have an effective baffle width/height of ~60ft to eliminate 4PI transition at 18hz.... uh.... I think?
I have about 20 feet of garage wall, figured I could use it to give a boost down to a usable level if I do it right. Inside the garage I have plywood walls with corner loading--outside I lose that advantage.

Since I have 4 x 8 sheets of plywood, I'll screw around with putting them on either side of the line arrays to hear if it would increase the bass level enough so a subwoofer is not necessary--much easier for BBQs that way.
  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


Similar Threads
Thread Thread Starter Forum Replies Last Post
multiple references for multiple opamps sheepydog Everything Else 0 23rd January 2011 08:29 PM
help w/ cabinet response jdrum Subwoofers 5 20th June 2010 01:12 AM
Multiple subwoofer/multiple amp question boogs Subwoofers 5 13th November 2007 04:36 AM
Undivided Sealed Enclosure Response With Multiple Drivers... HsOffRoad Subwoofers 5 7th October 2007 02:59 PM
response 3.8 cabinet drawing harbeath Multi-Way 0 8th August 2007 11:34 AM


New To Site? Need Help?

All times are GMT. The time now is 05:24 AM.


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