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
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
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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.
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.
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!
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!
well
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.
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.
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.
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.
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.
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.
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.
The 0.3 ohm is also 5% of the drivers Re of around 6 so this also conforms to Rabbitz's formula.
Hi Alspe, the DIY crossover plans I used do not specify the resistance of the inductors (ETI Transmission line). The inductor I currently use which was wound for me has a resistance of 2.4ohm and I think the wire size is too small for a 8.2mH.
After living with the speaker for many years it is my personal preference to have slightly more bass and I assume if it is too much with the new inductor I could add a resistor in series with the coil. I am planning to learn how to use a crossover simulation program so I can plug in these different values and see how they effect the overall response.
After living with the speaker for many years it is my personal preference to have slightly more bass and I assume if it is too much with the new inductor I could add a resistor in series with the coil. I am planning to learn how to use a crossover simulation program so I can plug in these different values and see how they effect the overall response.
I'd say the 2R4 value would be higher than the designer would have intended. It would have the effect of reducing SPL and altering driver Q that would give a hump in the bottom end. Go into a box modelling program and add 2R4 in series and watch the lower end hump appear and SPL drop higher up. It's a handy trick for OB bass though.
Troels is using the P-Core on woofers in his more recent projects and has made these comments on the last two:
Using better coils; thick-wire cored for bass and wax foil-coil for mid (using air cored coils for the bass does not improve performance).
.... a 10 mH air-cored coil for the bass is a waste of money - if you can find one with suitable low resistance.
Excerpts are from these projects:
Yamaha-NS1000
Jenzen-SEAS-ER
Troels is using the P-Core on woofers in his more recent projects and has made these comments on the last two:
Using better coils; thick-wire cored for bass and wax foil-coil for mid (using air cored coils for the bass does not improve performance).
.... a 10 mH air-cored coil for the bass is a waste of money - if you can find one with suitable low resistance.
Excerpts are from these projects:
Yamaha-NS1000
Jenzen-SEAS-ER
yes I think seeing Troel's comments recently made me reconsider non-air-cored inductors. He also adds: "If you want to up-grade here, use a Jantzen C-Coil". I assume it's because of their lower resistance.
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No need to fly by the seat of your pants, metako. You can calculate how the B139's Qe changes with various resistances (making sure to add resistance contributed by amp output, connecting cables and all Xover elements in series with the B139), recalculate the resulting Qts and then Qtc and see how damping actually changes. You will find that once you go below certain values, changes will be negligible and this might save you money as well as mental and physical effort.
Amp output resistance is usually available in specs. Cable resistance may be also, but can be measured fairly easily. You will also need Thiele/Small parameters for the woofer and details about the box and tuning. You don't actually need software: the woofer/box part can be done by hand and the box/vent part, if applicable, is unaffected by the X-over anyway.
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