Question: Isobaric vs. DVC - Page 2 - 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 18th October 2011, 05:50 PM   #11
ODougbo is offline ODougbo  United States
diyAudio Member
 
Join Date: Aug 2011
Location: Maryland USA
I have two of these 8” isobaric subs (total 4 drivers) in the back of my HT ~ they sound great. Total cost (no amps) $200.
The second speaker is mounted inside with small 5” tunnel.
Attached Images
File Type: jpg halfoverhalf.JPG (636.6 KB, 99 views)
  Reply With Quote
Old 18th October 2011, 06:06 PM   #12
diyAudio Member
 
Join Date: Jan 2008
Quote:
Originally Posted by Brian Oshman View Post
The advantage of isobaric configuration is that you can build a box half the size of that required for one woofer. You will not get the 3db gain from the second woofer but you will get the space saving from it.

Example: You have a 1 cu ft box and a woofer. You add a second woofer and another 1 cu ft box. You have increased the space by 2 and increased the output by 3db.

If you isobarically mount the woofers you will not get the 3db gain but you will only need a box of .5 cu ft. which is half the space of one box or 25% the space of the two boxes. This is best used in car stereo where space is at a premium.

If you run them face to face then you reverse the polarity of one so they still move in the same direction.
All true.

And the .5 cu ft. isobaric pair now requires double the power (+3dB) to equal the single driver in 1 cu ft box.
Given the same power, two drivers each in 1 cu ft box would have 6 dB more output than the isobaric pair in the .5 cubic foot box.

At very low frequencies, 6 dB more output sounds twice as loud.
  Reply With Quote
Old 18th October 2011, 06:53 PM   #13
diyAudio Member
 
vacuphile's Avatar
 
Join Date: Apr 2011
Location: Seaside
Quote:
Originally Posted by Tytte71 View Post
Vac,
I was also thinking the way you describe here, but Don's post did me rethink through the problem. Maybe I was a little quick in accepting his statement of half the pressure, but there is something to it.
Isobaric configuration is equal to doubling the mass of a driver and it must therefore be an interacting force between the two driver diaphragms. The only force (I see) that can interact between the two drivers would be though the air in the isobaric cavity.
The drivers "helps each other" in compressing/decompressing the sealed cabinet air volume. The cavity pressure should therefore be something like constant (not atmospheric) with exeption of the equalization of nonlinear driver behavoiur caused by asymetric BL(x) and k(x) when mounted push/pull. Also, due to the inertia of the air, the isobaric cavity volume should be kept as small (stiff) as possible.
Have I completely lost it?
Tytte, upon rethinking my train of thoughts that led me to this conclusion, I think I was wrong, so you have't lost it and I have to eat my hat. Which I am doing, right now.

vac
  Reply With Quote
Old 18th October 2011, 07:11 PM   #14
sreten is online now sreten  United Kingdom
diyAudio Member
 
Join Date: Nov 2003
Location: Brighton UK
Hi,

Increasing cone mass is not the same as isobaric, as isobaric has two motors.
Having said that, increasing cone mass could suit particular drivers, but the
changes are not so straightforward as the isobaric arrangement *.

However its always possible to make a single driver with the same parameters
as an isobaric driver pair, if you have that design flexibility. If you don't then
isobaric is a good way of effectively changing the driver Vas parameter**,
and very useful for some cheap higher Q drivers to reduce the volume needed.

Low Q drivers simply don't benefit from isobaric typically.

rgds, sreten.

* play with changing cone mass in WinISDpro's driver definition window.

** Halving Vas, and leaving Fs and Qts the same.
__________________
There is nothing so practical as a really good theory - Ludwig Boltzmann
When your only tool is a hammer, every problem looks like a nail - Abraham Maslow
  Reply With Quote
Old 18th October 2011, 07:36 PM   #15
Tytte71 is offline Tytte71  Norway
diyAudio Member
 
Join Date: Oct 2010
Quote:
Originally Posted by vacuphile View Post
Tytte, upon rethinking my train of thoughts that led me to this conclusion, I think I was wrong, so you have't lost it and I have to eat my hat. Which I am doing, right now.

vac
Please, you don't have to. I ate mine after Don's post and it tastes shi..
  Reply With Quote
Old 18th October 2011, 07:56 PM   #16
diyAudio Member
 
vacuphile's Avatar
 
Join Date: Apr 2011
Location: Seaside
shiitake-like, that's what I found too.
  Reply With Quote
Old 18th October 2011, 08:10 PM   #17
diyAudio Member
 
Join Date: Oct 2011
Haha

So drivers with a high Q have the advantage that they need a lower enclosure volume?
If so then mounting two drivers in isobaric configuration does the same? Besides the higher cone mass, I understand that connecting both woofers with the airspace makes that both drivers have only half the airload to deal with?

So if you have a DVC, the two coils wit a certain Q, driving them both will add both Q's together for the whole driver?

I have also heard "stories" of shorting one of the DVC coils giving a better bass response?

I'm just trying to understand the physics behind the "lowering of the enclosure volume", thanks for your efforts!
  Reply With Quote
Old 18th October 2011, 10:46 PM   #18
diyAudio Member
 
Join Date: May 2009
Location: Wellington
Quote:
Originally Posted by vacuphile View Post
shiitake-like, that's what I found too.
Mmmm, mushrooms...

I found it easier to visualise as a rigidly coupled system. Imagine placing two drivers face to face and gluing a cardboard tube between the centres of their cones, so that they must move together. This is a true "isobaric" driver. In fact, the term "isobaric" is misleading - like the term "tapped horn". In a true isobaric setup, the rear driver would move independently to keep the air pressure between the drivers constant - as if the enclosure size was infinite. In real life "isobaric" configurations the pressure between the drivers does vary, so it is not truly isobaric.

To show that the pressure between the drivers is half that in the enclosure, imagine connecting the rear driver to a battery so that it pushes into the enclosure with a force of (say) 1 newton, raising the enclosure air pressure by (say) 1 kPa. Now connect the "front" driver to the battery so that it also moves into the enclosure.

If the drivers are rigidly coupled, the front driver will apply 1 newton of force to the rear driver. This will add to the 1 newton of force being generated by the rear driver, making a total of 2 newtons, raising the enclosure air pressure by 2 kPa.

Next, replace the rigid coupling with a spring. It can be a real coil spring or an air spring. The front driver will apply 1 newton to the spring, compressing it - the front cone will move closer to the rear cone. If it is an air spring, the pressure between the cones will rise by 1 kPa.

Things get messy when the air volume between the drivers becomes significant compared with the enclosure volume. The drivers will not move in unison. For homework, try and work out what the cone movement behaviour will be if the volume between the drivers equals the volume of the enclosure...

Last edited by Don Hills; 18th October 2011 at 10:49 PM.
  Reply With Quote
Old 19th October 2011, 06:57 AM   #19
diyAudio Member
 
Join Date: Oct 2011
Interesting, so actually each driver in a isobaric configuration uses half the power of one single driver in normal configuration to build up the same pressure in the enclosure...

Witch actually means that the increased powerhandling (double the drivers) of an isobaric configuration will make up for the 3dB loss of efficiency?

The air load on the rear and the front of the driver pair is actually just divided over both "pistons", so two "pistons" in series... would this also count for more then 2 drivers in "series"?
  Reply With Quote
Old 20th October 2011, 12:10 AM   #20
diyAudio Member
 
Join Date: May 2009
Location: Wellington
Quote:
Originally Posted by manuelbauwens View Post
Interesting, so actually each driver in a isobaric configuration uses half the power of one single driver in normal configuration to build up the same pressure in the enclosure...

Witch actually means that the increased powerhandling (double the drivers) of an isobaric configuration will make up for the 3dB loss of efficiency?
It makes up for it exactly. There is no increase in output.

The driver cone has to move a certain distance (say 1 cm) to generate a certain SPL (say 90 dB SPL) at a given frequency (say 40 Hz).
Doubling the drivers in isobaric configuration does not change the cone travel required to reach the same SPL. But you also halve the enclosure volume, which means that the enclosure pressure change will double for a given SPL. The same 1 cm movement will generate twice the pressure in the enclosure. This will require twice the total force from the drivers, which will require twice the power from the amplifier.

1 driver, 1 watt, 10 litre enclosure, 1 mm travel, 1 kPa pressure change = xx dB SPL.

Halve the enclosure size. 1 mm of travel will now generate 2 kPa pressure in the enclosure, which will require twice the force from the driver (twice the power). Now add a second driver in series (isobaric) and share the power between them. So for a given SPL in isobaric configuration you require twice the total power to compensate for the "half sized" box. There is thus no increase in overall power handling, because each driver still requires 1 watt.




Quote:
Originally Posted by manuelbauwens View Post
... would this also count for more then 2 drivers in "series"?
In theory, yes. You reach a point of diminishing returns because the total of the volumes between the drivers starts to become significant compared with the enclosure volume.
  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
Two Infiniti Perfect 12 DVC --> Isobaric Box ProjectRob Subwoofers 8 8th August 2011 11:43 AM
Isobaric loading question IG81 Multi-Way 5 26th April 2009 09:46 PM
crazy DVC question, has this been done?? Jonny Hotnuts Car Audio 3 3rd December 2008 10:43 PM
DVC Wiring Question 69stingray Multi-Way 3 6th April 2007 12:42 PM
Peerless XXLS 12" DVC (830837)- replacement for PE Dayton 12" DVC 295-185? tktran Subwoofers 2 14th August 2005 02:04 PM


New To Site? Need Help?

All times are GMT. The time now is 09:27 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