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Old 19th September 2012, 10:23 PM   #1
88bruce is offline 88bruce  United States
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Default Subwoofer Inductance Reduction

I have two Soundsplinter Rl-p18's in an isobaric configuration in a sealed box
wired series/series. Each speaker has dual 4 ohm voice coils which when in
series gives Z = 8 ohms and Le = 4.34 mH, so for the complete sub, Z = 16
ohms and Le = 8.68 mH. I'm using a bridged Crest Cpx-1500 to power this,
which has a minimum bridged load of 8 ohms. The Crest is fed a low pass
80Hz LR signal.

I am considering getting an amp with a lower bridged impedance capability.
Here are the sub impedance/inductance options:

1) series/parallel: Z = 4 ohms, Le = 2.17mH.

2) parallel/parallel: Z = 1 ohm, Le = 0.5425mH.

I've read the transient response would be improved from an inductance reduction of 8.68mH to 2.17mH. But besides not having
many choices of an amp to deliver a 1 ohm bridged load into 500W
(maybe Hypex?), would it be worth the effort to reduce it to 0.5425mH?

Last edited by 88bruce; 19th September 2012 at 11:02 PM.
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Old 20th September 2012, 03:57 AM   #2
DUG is offline DUG  Canada
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Consider: Each speaker still has its own Z / Le ratio

Would putting them in parallel change that?
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Old 20th September 2012, 09:41 AM   #3
88bruce is offline 88bruce  United States
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So what you're implying is that reducing the Z/Le ratio would involve
replacing the existing speakers, i.e.; it is fixed. What I really want to
know is considering the Soundsplinter Rl-p18's high inductance, would an
alternative with a lower inductance have a more accurate sound? Currently,
there is a peak in the 80Hz area which I have almost EQ'd out. I am
assuming this is caused by the high inductance of the speakers. The sub
crosses over to Altec A7's, and when run with no sub, there is no peak.
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Old 20th September 2012, 11:28 AM   #4
DrDyna is offline DrDyna  United States
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It should be easy enough to see what the effect would be. Un-bridge the amplifier and run one channel to each driver that's wired in series for 8 ohms.

That's probably how I'd have them driven anyway.

Edit: As far as lower inductance drivers, remember that the inductance comes from the driver's coil. It works just like a coil that one might use in a crossover. The larger and beefier the coil is, the more inductance it's going to have. Going to a lower inductance speaker, means you'd probably end up with one that had a smaller coil.

The beefier the woofer's motor structure, the more inductance it usually has.
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Last edited by DrDyna; 20th September 2012 at 11:32 AM.
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Old 20th September 2012, 11:30 AM   #5
DUG is offline DUG  Canada
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Is the peak at ~80Hz in the SPL or in the impedance plot?

The speaker will have a resonance and the enclosure design is there to minimize the effects of it as best it can. This is a mechanical resonance, not electrical.

To get an electrical resonance at 80 Hz with 4.34mH you would need 912uF.
I don't think there is that much C in the voice coil.
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Old 20th September 2012, 11:48 AM   #6
DrDyna is offline DrDyna  United States
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Just for fun, these are the recommended cabinet sizes according to Soundsplinter.

7.0 cu ft net volume sealed
12.8 cu ft net volume vented, Fb = 18 Hz
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Old 20th September 2012, 02:23 PM   #7
epa is offline epa  Netherlands
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consider that le is not fixed,it risez to lower freq.
Click the image to open in full size.
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Old 20th September 2012, 03:14 PM   #8
88bruce is offline 88bruce  United States
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The 80Hz is a SPL peak. The sealed part of the box is approximately 4.0 cu.
ft. This is in an isobaric "clamshell" configuration. The box itself is two 4.0
cu. ft. chambers, one sealed and the other with a 14"X22" "port". The
drivers mount on the center line between the two chambers. I figured
the huge port was like having no containment on the outer driver. Could
this be tuning the box? The calculated F3 of the box is in the low thirties,
and low frequency extension is very good.

So consensus here is that high inductance is not necessarily a bad thing,
and is a byproduct of building a driver with low frequency capability.
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Old 20th September 2012, 08:31 PM   #9
bjorno is offline bjorno  Sweden
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Quote:
Originally Posted by 88bruce View Post
The 80Hz is a SPL peak. The sealed part of the box is approximately 4.0 cu.
ft. This is in an isobaric "clamshell" configuration. The box itself is two 4.0
cu. ft. chambers, one sealed and the other with a 14"X22" "port". The
drivers mount on the center line between the two chambers. I figured
the huge port was like having no containment on the outer driver. Could
this be tuning the box? The calculated F3 of the box is in the low thirties,
and low frequency extension is very good.

So consensus here is that high inductance is not necessarily a bad thing,
and is a byproduct of building a driver with low frequency capability.
Hi Bruse,

Am I right that the 'clamshell' drivers is in a 8 cu.ft box where 4 cu.ft is closed and the front-box is also 4 cu.ft equipped with a port system= 14" diameter,22" long...if so I couldn't design this using HR showing an acceptable FR.

I may be wrong but I guess you have used the driver parameters in a way the returned odd box dimensions.

Here is another example using one of your drivers in a box that IMO would be hard to beat SQ performance wise and is IMO capable to wreck your walls if placed in an ordinary living room It's an OD_T-TQWT of-course, a kind of pointsource quarter-wave BP box that should be folded at least two times.


b

PS: Why not put your design dimensions into HR and post here for (eventual help and ) examination?
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File Type: jpg Soundsplinter_RL-p18_OD-T-TQWT.JPG (920.8 KB, 95 views)
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Old 20th September 2012, 08:32 PM   #10
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Quote:
Originally Posted by epa View Post
consider that le is not fixed,it risez to lower freq.
Click the image to open in full size.
I don't understand this. I always thought that the inductance value is fixed (Henry) and that the apparent resistance changed in function of frequency.
In the graphic the Henry value changes with frequency
If this is true, how can a coil be labeled having a fixed value of xx mH?
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