what happens with more drivers inside isobaric? - 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 8th February 2007, 04:38 AM   #1
diyAudio Member
 
neutron7's Avatar
 
Join Date: Dec 2003
Location: Toronto Canada
Default what happens with more drivers inside isobaric?

I cant really figure out if a line of 4 woofers would have "4x the virtual surface area" or the ones between the outside world ones would actually do nothing much because the outside drivers would be doing most of the work.

on the one hand there is "the 2 outside woofers" doing all the work and the inside ones not doing anything, on the other hand the air has to be moved and the inside ones might help the outside ones.

i got 4 half decent TB woofers i bought on a whim here but they are only 25 w RMS. i just got them to try experiments with

i want to put them all in a line with a fairly small enclosure.
  Reply With Quote
Old 8th February 2007, 04:42 PM   #2
pjpoes is offline pjpoes  United States
diyAudio Member
 
Join Date: Jan 2005
Location: New York
Send a message via AIM to pjpoes
I by no means am an expert, and maybe someone with better knowledge can give you a more techincal explanation of this, but let me at least take a stab at it. When you put woofers in an isobaric configuration it has a few affects, one is that you can get a similar response in about half the volume, at least based on models I have run in programs like WinISD. However, its at the expense of efficiency, which lowers drasticly in my experience. I believe you lose about 6 decibles of efficiency.

Just as an exercise, I took and modeled a single Brahma Subwoofer in a 3 cubic foot sealed box, and a pair mounted isobaricly. The response was about the same, however the cone excursion was considerably less at any given power level, but so was output. As I said, about 6 decibles compared to the single woofer.

Now my guess based on what I'm seeing in WinISD, and based one what I think I have read about Isobaric mounting is that they share the load pretty evenly, and actually the benefit is that you get a large reduction in distortion, and a large increase in power handeling. However you end up needing it given the reduction in effeciency. In the case of the Brahma, you go from the 1600watt power handeling of the single driver to 3200 watts, effecticly doubling its power handeling.

Doing a quick web search I found that Isobarics couples the woofers as one causing them to act the same as a single driver in twice the volume of the box. It reduces the VAS, and allows the same output in half the box volume, but at the expense of a 3db loss in efficiency. I modeled 6, but who knows. It goes on the mention that you could potentially get an increase in output by using 4 woofers and 4 times the power and get about 6 decibles more ouput in the same size box as a single woofer. It sounds like a great space saving method, but somewhat cost prohibitive for most.

I speculate still about the reduced distortion, I would imagine that any nonlinear movement of one cone might be canceled, at least to a point, but the other. However, I'm guessing, I havne't read that. As I said, maybe someone more knowing will be able to chime in.
  Reply With Quote
Old 10th February 2007, 01:11 AM   #3
Svante is offline Svante  Sweden
diyAudio Member
 
Svante's Avatar
 
Join Date: Feb 2004
Location: Stockholm
I posted a very similar post to this yesterday on a swedish forum:

Compared to one driver:

Using isobaric halves Vas and the box can be made to have half the volume. The efficiency drops to half (-3 dB) but the thermal power limit is doubled as a whole. The maximum output level in the half-as-big box will therefore be identical* to the single driver in the original volume.

If the drivers are mounted side-by-side, Vas is doubled and the box needs to be twice as big. The power limit will double and the efficiency is increased by 3 dB. As a result, the maximum output level increases by 6 dB.

Example:

Thick line= frequency response, thin line= maximum output level, dashed line= electrical impedance. All designs have the same length for the vent, ie the diameter varies. This results in a too small tube for this isobaric design, which in turn results in a lower maximum output level around the vent tuning.

Click the image to open in full size.

*Apart from potential problems with overloading the vent.
__________________
Simulate loudspeakers: Basta!
Simulate the baffle step: The Edge
  Reply With Quote
Old 10th February 2007, 03:49 AM   #4
diyAudio Member
 
neutron7's Avatar
 
Join Date: Dec 2003
Location: Toronto Canada
From that i gather one thing might be to design box size for 1 driver and then put 2 sets of isobaric pairs. then the required box size would stay the same but it could handle the extra power.
  Reply With Quote
Old 10th February 2007, 10:56 AM   #5
Svante is offline Svante  Sweden
diyAudio Member
 
Svante's Avatar
 
Join Date: Feb 2004
Location: Stockholm
Quote:
Originally posted by neutron7
From that i gather one thing might be to design box size for 1 driver and then put 2 sets of isobaric pairs. then the required box size would stay the same but it could handle the extra power.
Yes, true, apart from the overloading effects of the vent if the box is bass-reflex. Sensitivity*, efficiency, frequency response remains the same, max power quadruples and max output level increases by 6 dB**.

* Given series-parallel connection

** Again apart from around vent resonance.
__________________
Simulate loudspeakers: Basta!
Simulate the baffle step: The Edge
  Reply With Quote
Old 10th February 2007, 11:04 AM   #6
Svante is offline Svante  Sweden
diyAudio Member
 
Svante's Avatar
 
Join Date: Feb 2004
Location: Stockholm
...and yes, distortion is reduced, in principle even order harmonics are canceled. However, small boxes can provoke distortion from the air itself, so the distortion gain from the push-pull style of isobaric may be eaten up by the use of a smaller box for the same output level.
__________________
Simulate loudspeakers: Basta!
Simulate the baffle step: The Edge
  Reply With Quote
Old 10th February 2007, 08:31 PM   #7
diyAudio Member
 
neutron7's Avatar
 
Join Date: Dec 2003
Location: Toronto Canada
do you mean push - pull as in having the speakers facing or pointing away from each other reduces distortion but having them facing the same way does not?

does it mean that asymmetric non linearity Is being canceled out?
  Reply With Quote
Old 10th February 2007, 09:52 PM   #8
Svante is offline Svante  Sweden
diyAudio Member
 
Svante's Avatar
 
Join Date: Feb 2004
Location: Stockholm
Quote:
Originally posted by neutron7
do you mean push - pull as in having the speakers facing or pointing away from each other reduces distortion but having them facing the same way does not?

does it mean that asymmetric non linearity Is being canceled out?
Yes and yes.
__________________
Simulate loudspeakers: Basta!
Simulate the baffle step: The Edge
  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
tapped horn isobaric drivers bubblersound Subwoofers 4 18th June 2009 03:42 AM
Isobaric with dissimilar drivers. Circlotron Multi-Way 10 6th February 2007 10:09 AM
sd system inside of AudioTechnology drivers tf1216 Multi-Way 3 29th June 2006 06:54 PM
Isobaric with odd number of drivers? needtubes Subwoofers 9 11th June 2006 07:42 PM
Linkwitz Transform with multiple/isobaric drivers Matttcattt Multi-Way 2 8th July 2004 11:23 AM


New To Site? Need Help?

All times are GMT. The time now is 02:43 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