Isobaric (Series vs Parallel) - 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 4th May 2012, 05:18 PM   #1
schmeet is offline schmeet  United Kingdom
diyAudio Member
 
schmeet's Avatar
 
Join Date: Mar 2008
Default Isobaric (Series vs Parallel)

Ok, so with an isobaric sub you are essentially 'creating' a new driver with slightly different T/S Parameters.

The Mechanical Resistance, Stiffness and Mass all double. Which is logical.

Cms is 1 / Stiffness so that halves.

The magnetic field strength effectively stays the same but the voice coil wire length doubles so the Bl doubles.

Vas is a function of Cms and so the Vas halves which is why we can use enclosures of half the size. This all makes sense.

What I'm struggling with is the fact that if you wire them in series then the Re doubles but if you wire them in Parallel then the Re halves. So there is a 4 times difference between series and parallel.

Click the image to open in full size.

Looking at the above equation. If we double Mms and Re and top of the division and double Bl^2 then the driver Q stays the same and so the response will stay the same.

However if re is not doubled but halved then the Qes will be reduced by a factor of 4 which will in turn reduce Qts by a significant amount. Therefore the entire response of the system will be altered quite dramatically. This doesn't seem logical to me but i can't see what I'm missing??

So if we wire isobaric drivers in Series then the response will be unchanged but if we wire them in parallel it completely changes. Is this correct or have I missed something fundamental here?

Last edited by schmeet; 4th May 2012 at 09:32 PM.
  Reply With Quote
Old 5th May 2012, 04:44 AM   #2
diyAudio Member
 
Join Date: Jan 2008
Quote:
Originally Posted by schmeet View Post
So if we wire isobaric drivers in Series then the response will be unchanged but if we wire them in parallel it completely changes. Is this correct or have I missed something fundamental here?
The sensitivity will change, but frequency response of the isobaric pair will be unchanged regardless of whether the pair are wired parallel or series, or in the case of double voice coils, series parallel, parallel or series.

If you have a pair of speakers,an amp, a dB meter and test tones you can easily verify this fact for yourself.
  Reply With Quote
Old 5th May 2012, 06:29 AM   #3
diyAudio Member
 
▀art West-VL.'s Avatar
 
Join Date: Jun 2005
Location: West Vlaanderen
I think schmeet wants to understand the math behind it, not just verify it.

So do I
__________________
Break in your loudspeakers at 35% RMS power Right-click'save as...'
Brown noise mono 192kbps(hit "repeat")
  Reply With Quote
Old 5th May 2012, 06:57 AM   #4
diyAudio Member
 
Join Date: May 2009
Location: New Zealand
One related point on isobaric configuration: The drivers are better wired in parallel, because they aren't truly "isobaric". The compliance of the air between them means that they are loaded differently, will not move exactly in unison, so will reflect different impedances. The difference can be quite large if used in a resonant enclosure such as a ported enclosure or tapped horn.
  Reply With Quote
Old 5th May 2012, 07:17 AM   #5
diyAudio Member
 
Join Date: Jun 2007
Quote:
Originally Posted by schmeet View Post
The magnetic field strength effectively stays the same but the voice coil wire length doubles so the Bl doubles.
Hi schmeet,

It is only for two drivers connected in series that Bl is doubled - Bl stays the same for two drivers connected in parallel.

If it is assumed that Fs does not change (not strictly correct), then the value of Qes will remain constant.

Single driver:

Qes = Re / (2 * Pi * Fs * Cms * Bl ^ 2)

Two series isobaric drivers:

Qes = [2 * Re] / (2 * Pi * Fs * [Cms / 2] * [2 * Bl] ^ 2) = Re / (2 * Pi * Fs * Cms * Bl ^ 2)

Two parallel isobaric drivers:

Qes = [Re / 2] / (2 * Pi * Fs * [Cms / 2] * [Bl] ^ 2) = Re / (2 * Pi * Fs * Cms * Bl ^ 2)

Kind regards,

David
__________________
www.hornresp.net
  Reply With Quote
Old 5th May 2012, 07:54 AM   #6
schmeet is offline schmeet  United Kingdom
diyAudio Member
 
schmeet's Avatar
 
Join Date: Mar 2008
Thanks David,

I know its not a perfect situation, but for the sake of modelling:

Cms is Halved
Mms is doubled
Rms is doubled

Bl is doubled in series
Bl is the same in parallel

Re is doubled in series
Re is halved in parallel

Lvc is doubled in series
Lvc is halved in parallel

I can then work out the other parameters from this and just model as a single driver..
  Reply With Quote
Old 5th May 2012, 08:02 AM   #7
schmeet is offline schmeet  United Kingdom
diyAudio Member
 
schmeet's Avatar
 
Join Date: Mar 2008
Also, could you briefly explain why Bl stays the same when wired in parallel. I'd like to understand that...
  Reply With Quote
Old 5th May 2012, 08:55 AM   #8
Did it Himself
diyAudio Member
 
richie00boy's Avatar
 
Join Date: Nov 2003
Location: Gloucestershire, England, UK
Because the same current is flowing through the coil as would be for a single driver.
__________________
www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more.
  Reply With Quote
Old 5th May 2012, 09:24 AM   #9
schmeet is offline schmeet  United Kingdom
diyAudio Member
 
schmeet's Avatar
 
Join Date: Mar 2008
Hey richie00boy.

But Bl is B (Magnet strength in Teslas) multiplied by L (length of the voice coil wire). Current is not involved.

Bl * Current gives you the force applied by the magnet.

The magnet field strength of the magnet doesn't change and so I can only assume that the length of the wire is considered to be doubled in series and the same in parallel. Not completely sure why that would be though.
  Reply With Quote
Old 5th May 2012, 11:43 AM   #10
diyAudio Member
 
Join Date: Mar 2008
Maybe i am allowed to use this picture for illustration:

B stays the same regardless whether wiring the two
voice coils in series or parallel.

Series wiring means doubling the length of the wire in the field
but maintaining the same cross sectional area of the wire as in
the single driver case.

(Bl) doubles, because wire length (l) doubles.
Rg doubles, because wire length (l) doubles.


Parallel wiring instead means (effectively) doubling the
cross sectional area of the wire in the field instead while
maintaining the same length of the wire as in the single driver
case.

(Bl) stays the same, because B and l stay the same.
Rg halves, because the cross sectional area of the wire doubles.

__________________

However this illustration does not account for the wire to be wound
as 2 separate coils and only holds for low frequencies.

It does e.g. not explain why resulting voice coil inductance Lvc halves
in the parallel case, which is because in fact we have 2 coils in parallel.
__________________
Oliver, RFZ believer (?)
www.dipol-audio.de

Last edited by LineArray; 5th May 2012 at 11:56 AM.
  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
Three 10" 4Ohm subs, wired in series or series-parallel? Nagamitsu Car Audio 38 19th February 2014 11:16 PM
Series or Parallel / Bridge or Parallel? Tenson Chip Amps 2 3rd October 2011 12:53 AM
winISD calcs: parallel vs series-parallel sadams Multi-Way 1 20th February 2011 07:45 PM
Series-Parallel Or Parallel-Series shaan Full Range 43 13th December 2009 04:10 AM
What would you do? series/parallel MtnBob Multi-Way 13 14th April 2005 10:17 PM


New To Site? Need Help?

All times are GMT. The time now is 08:33 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ę1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2