Isobaric (Series vs Parallel)

[forr]

I propose the following reasoning.

Let's start with the well known formula

F = (Bl) * I <==> (Bl) = F / I

Then (Bl) can be considered as the ratio of the driving force, F, to the current in the voice coil, I.

If between different configurations, the current through the circuit is maintained at a constant value I :


Single driver

Fsingle = (Bl)single * I

(Bl)single = Fsingle / I


Series Isobarik

Current I goes through each voice coil, each motor gives the same force as in the single driver case, and both forces add :

Fser = Fsingle * 2

(Bl)ser = Fser / I = (Fsingle * 2) / I = (Fsingle / I) * 2 = (Bl)single * 2


Parallel Isobarik

Current I is equally split to I/2 into each coil, the force of each motor is halved compared to the single driver case, and both forces add :

Fpar = (Fsingle / 2) * 2 = Fsingle

(Bl)par = Fsingle / I

In this configuration, for the same current, the force is the same as for the single driver case.
Hence the wire can be considered as having the same length l with its resistance halved compared to the single driver case.


Edit : similar thinking to Line Array but I did not read his post before sending this one.

[LineArray]

So for LF enclosure design the only thing relevant
happening - besides voltage sensitivity changing -
is Vas halves for the compound driver, regardless
if wiring series or parallel.

Qes and Qms remain unchanged.

One could even short circuit one of the two driver's
voice coils and connect only one of them to the amp.

Having one coil disconnected and open would rise Qes.

[Zoodle]

Will two Isobariced drivers have a different QTS compared with a single driver? Also can one use lowish QTS drivers in Isobaric configuration (Eg .3)?

[Don Hills]

No. Yes.
(Qts remains the same, because Qes and Qms stay the same - see post #12.)

[Patrick Bateman]

This paper on BL seems to imply that low-BL drivers have worse impulse response than high BL drivers.

This is rather interesting, as I've long noted that high BL prosound drivers tend to sound 'tight', but I'd assumed this was purely a function of their response shape. Someone with a better grasp of the relation between impulse response and frequency response could likely provide a better commentary than I can.

http://www.extra.research.philips.co...s/aar05pu3.pdf

"Because Bl influences the transient response of normal
drivers and low-Bl drivers in particular, a transient response analysis is presented next. In [24] the response to a sinusoid which is switched on at t 0 was calculated. Those results showed that the medium- and high-Bl driver systems rapidly converge to their steady-state response, while this is not generally the case for low-Bl drivers. This can also be seen by calculating the impulse response."

Either way, it's a good lunch time read.

[Shadydave]

Could it be the case that a series isobaric configuration, with each driver having the full current flow, they would experience higher I^2*R losses and thus go into thermal compression sooner?
It would seem to me that the parallel setup may have advantages in power handling.
This of course is only an issue in some circumstances, but I have always believed that THD is markedly reduced and SQ improved by running LF speaker systems at less than half their power capability and also much less than Xmax.

Dave

Footnote: In working with dual linear alternator systems, the series vs. parallel question seems to always end up with no clear winner, so this is one reason I pose this question.

[ßart West-VL.]

A Watt is a Watt...
Be it in series or parallel, result is the same.
The only difference is, for series the Voltage needs to be higher, parallel lower.
Series the current will be lower. parallel→higher current.
Result: the same power. So it will generate the same heat. (do the maths)

[Don Hills]

Parallel connection is preferred over series connection for isobaric drivers, especially in cases where there is significant pressure on the "inner" driver such as smaller than optimum enclosures or ported enclosures - basically, any situation where one driver experiences different forces than the other.

Shadydave, it alo applies to linear actuators driving uncoupled loads which may differ in weight / resistance, such as amp racks that are heavier on one side then the other...

[Shadydave]

Originally Posted by ßart West-VL.

A Watt is a Watt...
Be it in series or parallel, result is the same.
The only difference is, for series the Voltage needs to be higher, parallel lower.
Series the current will be lower. parallel→higher current.
Result: the same power. So it will generate the same heat. (do the maths)

I knew there was a good explanation why it didn't really matter.
Thank You

Dave

PS

it alo(sic) applies to linear actuators driving uncoupled loads which may differ in weight / resistance, such as amp racks that are heavier on one side then the other...

OK, just wondering why one may have linear actuators on an amp rack

[Don Hills]

Originally Posted by Shadydave

... PS OK, just wondering why one may have linear actuators on an amp rack

To make it tilt up, of course. (I'm talking about competition car audio installations.)