Best inductor type for B139

metako · 01:44 PM

I'm rebuilding my crossovers and I'd like to buy a new 8.2mH bass inductor for the Kef B139s with lower resistance than the existing 2.4ohm inductor in order to maximise amplifier damping effect and bass volume.

How low do I need to go in resistance in order for the inductor to have no effect on the damping of the B139? 0.30ohm (Jantzen P-core) or 0.23ohm (Erse Super Q) or 0.095ohm (Jantzen C-coils)? I've seen a figure of 0.7ohm mentioned on here but is this low enough? Is the figure amplifier dependent?

ERSE THD distortion test drive - YouTube

Jantzen 8.2mH 14 AWG C-Coil Toroidal Inductor

Jantzen 8.2mH 15 AWG P-Core Inductor

ERSE - Super Q

moray james · 7th September 2011, 06:16 PM

Take a look at the Northcreek 8 gage inductors. Best regards Moray James.

metako · 8th September 2011, 08:13 AM

Thanks Moray but no listing for a 8mH 8AWG inductor and $214.37 each for the 10AWG version!!! Holy cow!!!

http://www.northcreekmusic.com/NorthCreekCoilPrices.PDF

Also that does not really answer my question: what resistance has no longer any negative effect on the driver.

googlyone · 8th September 2011, 08:24 AM

I would have thought that anything "well under" 1 ohm would do. I would not pay a premoum for 0.23 ohms over 0.3.

Any less than this is getting silly. More than an ohm starts becoming significant at a range of levels.

For what it is worth:

I would go to a motor rewinder and but a big bunch of heavy guage (work out guage on one of the many online inductor calcs) wire, make a spool and wind my own given the stratospheric 200dollar quote above!

I bought a 15 kilo spool of 1.5mm wire for 90dollars a few years back. You will need heavier guage than this, but that should not be hard to find.

Good luck!

metako · 8th September 2011, 09:13 AM

Thanks Googlyone. I may look into winding my own. So you think the P-core inductors do introduce audible distortion?

moray james · 8th September 2011, 01:59 PM

Quote:

Originally Posted by metako

Thanks Moray but no listing for a 8mH 8AWG inductor and $214.37 each for the 10AWG version!!! Holy cow!!!

http://www.northcreekmusic.com/NorthCreekCoilPrices.PDF

Also that does not really answer my question: what resistance has no longer any negative effect on the driver.

anything not listed is special order and yes the price would be very high. There is a fair amount of information on the site. You can go to audio karma dot org and check out SET12`s thread on a Forte crossover upgrade in the Klipsch section to talk with those who have hands on. The answer in a nu shell is yes lower is better. Hope this helps best regards Moray James.

rabbitz · 9th September 2011, 06:57 AM

metako

Look for an inductor with a DCR <10% of the driver's Re. For example a driver with an Re of 6R would use an inductor with a DCR < 0R6. Look at Loudspeaker Design Cookbook (6th ed) section 7.80.

No need to go stupidly low and 5% of the driver's Re would be as low as ever needed.

The Jantzen P-Core are very good and I replaced a very expensive Mundorf 2mm wire with a 15AWG (1.4mm wire approx) P-Core with no ill effects.
Mundorf 2mm inductor

What you also have to consider is that the original crossover design should have taken the inductor DCR into account and lowering this value can have an effect on the filter operation but for a woofer, should not be significant.

googlyone · 9th September 2011, 09:57 AM

Metako,
An answer in three parts...

The academic answer: Using a core in any inductor introduces the potential for non linearities. I think this is simplistic, as... Academia aside, a well designed inductor with appropriate material, run well below saturation, is just fine.

Practical answer: The B139 (I have owned a few of these in my time) is a good woofer, but not a kilowatt consuming PA monster. The relevance here is that you are extremely unlikely to drive these hard, so a decent cored inductor will likely be fine. I did not look up tech details on the P core units - but expect they are decent from other comments people have made.

The DIYers answer: I just did the calcs for an air cored 8.2mH inductor using 14AWG wire (have a huge reel of this in the shed). This is only 1.6mm so it is heavy guage but not silly.

On a 1 inch diameter former, with the windings 2 inches deep - is a coil length of 2 inches, you need 490 turns (16 layers) and will have an inductor with 0.65 Ohms DCR. OK, this is a damn big inductor. But imagine, a huge chunky coil of solid copper that you wound yourself (and possibly got tennis elbow doing!) siting in that crossover...

Oh, and an air core coil has NO saturation issues to worry about.

Choice is yours really.

metako · 9th September 2011, 12:56 PM

Sounds like the P-core with a resistance of .30 ohm and rated at 400watts might be the go. My power amps are a Rotel RB980-BX with 120WPC and a pair of HK775 monoblocks with 130WPC so not feeding huge power levels.

The 0.3 ohm is also 5% of the drivers Re of around 6 so this also conforms to Rabbitz's formula.

alspe · 9th September 2011, 01:17 PM

Ummm, doesn't changing R in lowpass filter change sound balance of speaker? If big resistance is designed to be used with B139.

7th September 2011, 01:25 PM	#1
metako diyAudio Member Join Date: Jun 2005 Location: Melbourne	Best inductor type for B139 I'm rebuilding my crossovers and I'd like to buy a new 8.2mH bass inductor for the Kef B139s with lower resistance than the existing 2.4ohm inductor in order to maximise amplifier damping effect and bass volume. How low do I need to go in resistance in order for the inductor to have no effect on the damping of the B139? 0.30ohm (Jantzen P-core) or 0.23ohm (Erse Super Q) or 0.095ohm (Jantzen C-coils)? I've seen a figure of 0.7ohm mentioned on here but is this low enough? Is the figure amplifier dependent? ERSE THD distortion test drive - YouTube Jantzen 8.2mH 14 AWG C-Coil Toroidal Inductor Jantzen 8.2mH 15 AWG P-Core Inductor ERSE - Super Q Last edited by metako; 7th September 2011 at 01:44 PM.

7th September 2011, 06:16 PM	#2
moray james diyAudio Member Join Date: Aug 2003 Location: Calgary on the Bow	Take a look at the Northcreek 8 gage inductors. Best regards Moray James. __________________ moray james

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8th September 2011, 08:13 AM	#3
metako diyAudio Member Join Date: Jun 2005 Location: Melbourne	Thanks Moray but no listing for a 8mH 8AWG inductor and $214.37 each for the 10AWG version!!! Holy cow!!! http://www.northcreekmusic.com/NorthCreekCoilPrices.PDF Also that does not really answer my question: what resistance has no longer any negative effect on the driver.

8th September 2011, 08:24 AM	#4
googlyone diyAudio Member Join Date: Nov 2006 Location: Adelaide, South Australia Blog Entries: 5	I would have thought that anything "well under" 1 ohm would do. I would not pay a premoum for 0.23 ohms over 0.3. Any less than this is getting silly. More than an ohm starts becoming significant at a range of levels. For what it is worth: I would go to a motor rewinder and but a big bunch of heavy guage (work out guage on one of the many online inductor calcs) wire, make a spool and wind my own given the stratospheric 200dollar quote above! I bought a 15 kilo spool of 1.5mm wire for 90dollars a few years back. You will need heavier guage than this, but that should not be hard to find. Good luck!

8th September 2011, 09:13 AM	#5
metako diyAudio Member Join Date: Jun 2005 Location: Melbourne	Thanks Googlyone. I may look into winding my own. So you think the P-core inductors do introduce audible distortion?

9th September 2011, 06:57 AM	#7
rabbitz diyAudio Member Join Date: Jul 2003 Location: Newcastle, Australia	metako Look for an inductor with a DCR <10% of the driver's Re. For example a driver with an Re of 6R would use an inductor with a DCR < 0R6. Look at Loudspeaker Design Cookbook (6th ed) section 7.80. No need to go stupidly low and 5% of the driver's Re would be as low as ever needed. The Jantzen P-Core are very good and I replaced a very expensive Mundorf 2mm wire with a 15AWG (1.4mm wire approx) P-Core with no ill effects. Mundorf 2mm inductor What you also have to consider is that the original crossover design should have taken the inductor DCR into account and lowering this value can have an effect on the filter operation but for a woofer, should not be significant.

9th September 2011, 09:57 AM	#8
googlyone diyAudio Member Join Date: Nov 2006 Location: Adelaide, South Australia Blog Entries: 5	Metako, An answer in three parts... The academic answer: Using a core in any inductor introduces the potential for non linearities. I think this is simplistic, as... Academia aside, a well designed inductor with appropriate material, run well below saturation, is just fine. Practical answer: The B139 (I have owned a few of these in my time) is a good woofer, but not a kilowatt consuming PA monster. The relevance here is that you are extremely unlikely to drive these hard, so a decent cored inductor will likely be fine. I did not look up tech details on the P core units - but expect they are decent from other comments people have made. The DIYers answer: I just did the calcs for an air cored 8.2mH inductor using 14AWG wire (have a huge reel of this in the shed). This is only 1.6mm so it is heavy guage but not silly. On a 1 inch diameter former, with the windings 2 inches deep - is a coil length of 2 inches, you need 490 turns (16 layers) and will have an inductor with 0.65 Ohms DCR. OK, this is a damn big inductor. But imagine, a huge chunky coil of solid copper that you wound yourself (and possibly got tennis elbow doing!) siting in that crossover... Oh, and an air core coil has NO saturation issues to worry about. Choice is yours really.

9th September 2011, 12:56 PM	#9
metako diyAudio Member Join Date: Jun 2005 Location: Melbourne	Sounds like the P-core with a resistance of .30 ohm and rated at 400watts might be the go. My power amps are a Rotel RB980-BX with 120WPC and a pair of HK775 monoblocks with 130WPC so not feeding huge power levels. The 0.3 ohm is also 5% of the drivers Re of around 6 so this also conforms to Rabbitz's formula.

9th September 2011, 01:17 PM	#10
alspe diyAudio Member Join Date: Jan 2007 Location: Finland/Tampere	Ummm, doesn't changing R in lowpass filter change sound balance of speaker? If big resistance is designed to be used with B139.

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