DVC subwoofer BL and SPL data - diyAudio
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Old 22nd September 2009, 04:07 PM   #1
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Default DVC subwoofer BL and SPL data

Hi guys,

I was doing some surfing and came across a DVC subwoofer with different published BL number, depending on if the VCs are wired in series, or in parallel. On the website, the BL is effectively doubled for series VC, but is the same for single coil or parallel coil wiring. I was referring to the Maelstrom-X, incidentally.

http://www.diycable.com/main/product...roducts_id=681

Got me thinking, this rockford sub i have (datasheet attached), i'm currently using wired in series. Is the BL effectively doubled based on the published specs?

Also, any idea if the sensitivity of 87.9dB is with 1W power, or 2.83V input?

Appreciate your knowledge on this. Thanks!!

Gavin
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Old 22nd September 2009, 05:55 PM   #2
bjorno is offline bjorno  Sweden
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Quote:
Originally Posted by rhapsodee View Post
Hi Gavin,as I can see the diycable.com DVC T/S data needs to be corrected.

b
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Old 23rd September 2009, 01:27 AM   #3
Ron E is offline Ron E  United States
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Quote:
Originally Posted by rhapsodee View Post
Hi guys,
I was doing some surfing and came across a DVC subwoofer with different published BL number, depending on if the VCs are wired in series, or in parallel.

Got me thinking, this rockford sub i have (datasheet attached), i'm currently using wired in series. Is the BL effectively doubled based on the published specs?

Also, any idea if the sensitivity of 87.9dB is with 1W power, or 2.83V input?
Not sure how to interpret Bjorno's reply...

Bl Doubles when wired in series and is the same for single or parallel coil

The 87.8 figure is for 1W, from 2.83V you get ~91dB
IF you wire in parallel (one ohm load) you get 97dB for 2.83V
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Old 23rd September 2009, 01:33 PM   #4
bjorno is offline bjorno  Sweden
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Quote:
Originally Posted by Ron E View Post
...Not sure how to interpret Bjorno's reply...
Hi Ron,
What I've found is probably a minor point as few users will use a single coil in a real driver application but published T/S data should IMO always be correct.

b
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Old 23rd September 2009, 02:01 PM   #5
forr is offline forr  France
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Strictly speaking, Bl (in Tesla.meter) does not change in series or parallel configuration, as neither magnetic flux, B, nor length of wire in it, l, change. So the reference efficiency does not change in either configuration. But the sensitivity of the driver expressed for a given voltage usually normalised et 2.83 V, changes of course, because, with voice coils in parallel, there is four times more current in the motor than when in series, then four times hte movinf force.

Considered as the force factor, the misnommed Bl (in Newton/Ampere) changes with the configuration. With one ampere injected into the motor, there is 0.5 A in each coil when in parallel, and 1 A in each coil in series.
This is the way how force factors are measured. To avoid confusion, it has been suggested to use the unequivocal terms "effective Bl" (where the length of wire is ignored) or "force factor "FF".

Knowing the real meaning of "Bl" makes everything coherent.
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Old 23rd September 2009, 03:25 PM   #6
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Forr,

I think i understand what you mean, bits of physics class coming back to me.

However, Force on the coil is proportional to the B field strength (constant for a given motor), length of wire in the coil, as well as current flowing in the wire. As you said, series of parallel connection of the voice coils will cause a 4 x difference in current, but this implies there is a 4 x difference in power input. Obviously the force on the coil will be higher with higher power.

I'm thinking, with the same 1W power:
1) Series coil will draw 1/4 of the current I, but have 2x length of coil L in the B field.
F series = k*B*2L*1/4I = 0.5kBLI
2) Parallel coil each draws current 1/2I, but each have 1x length of coil L in the B field.
F parallel = 2*k*B*L*1/2I = kBLI

This seems to suggest it is better to use a DVC sub in parallel, provided of course the amp can drive the 1Ohm load...

This is also contrary to the misleading impression that doubling BL with a series config is better, since high BL is good... Perhaps this is what Forr is trying to allude to.

Did i confuse myself?

Last edited by rhapsodee; 23rd September 2009 at 03:30 PM.
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Old 23rd September 2009, 03:31 PM   #7
AndrewT is offline AndrewT  Scotland
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what's wrong with at least considering using the two 2ohm voice coils in series?
They will be a far easier load for the amplifier to drive, 4ohm cf 1ohm.
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Old 23rd September 2009, 09:34 PM   #8
bjorno is offline bjorno  Sweden
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Quote:
Originally Posted by forr View Post
Strictly speaking..
..Knowing the real meaning of "Bl" makes everything coherent...
Hi forr,

Agree,It's not my day today I'm Should stay in bed instead, I've got the flu)
To prove you're right Ive dug up a measurement I made for over a year ago on two Peerless 830846 DVC drivers where one was tested with a single coil and the other using both in series.

b
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