Model 19 network mod for K145

[89-300ce]

I'm thinking of ordering components to build my networks.

K145, 511b, BMS 4552nd.

I'm looking at using a model 19 (N1201-8a) network

From WinISD

416-8b , Re=6.9, Z= 8
K145 , Re=8.8, Z= 16

WinISD uses Z for calculating crossover components, and using Z I would have to double the inductance and halve the capacitance.

Since L1 in the crossover also affects the HF circuit I would modify only L2.

Stock L1 (.3mh) and L2 (2.7mh) = 3.0 mh
I need

L1 (.3mh) and L2 (5.7mh) = 6.0 mh

Is my thinking correct on this? I know real world will differ but I'm looking for a reasonable start point to begin experimenting.

Thanks

Jorg

[rs237]

yes , your thoughts are correct , only change C3 from 21µF to 10µF.
Or buy Altec 416-8b and give me your K145

regards
juergen

[Earl K]

Hi Jorg,

Is my thinking correct on this?

- The problem with your thinking is that it appears that you assume that a woofer has an AC impedance curve that resembles a flat line.
- They don't / they all resemble big happy smiles .

- You should run an AC impedance curve for your K145s and then plot them out before doing too much else .

- K145 , Re=8.8, Z= 16

- WinISD uses Z for calculating crossover components, and using Z I would have to double the inductance and halve the capacitance.

- A DCR of 8.8 ohms implies a nominal AC impedance of @ 11-12 ohms ( somewhere on the curve ) / though it's a certainty that a Z of 16 ohms will be reached at some point on the curve.

- FWIW, JBL referred to this woofer as an 8 ohm driver / while a similar or identical voice-coil as found in the le15a was referenced as 16 ohm .
- As mentioned , I'd go with 12 ohms as my starting reference "Z" (for transposing values of an exisitng crossover ) . This means multiplying existing coil values ( on the LF section ) by 1.5 and multiplying capacitor values by .6667 ( the reciprocal of 1.5 ) .

Since L1 in the crossover also affects the HF circuit I would modify only L2.

Stock L1 (.3mh) and L2 (2.7mh) = 3.0 mh
I need

L1 (.3mh) and L2 (5.7mh) = 6.0 mh

I know real world will differ but I'm looking for a reasonable start point to begin experimenting.

- Off the top of my head ( when being experimental ) / I'd add a Zobel ( RC conjugate placed across the woofer terminals ) that forces ( averages down ) all impedances above say 300 hz into a 12 ohm value ( maybe even 8 ohms ).
- This approach will have an advantage of allowing the use of smaller ( less expensive ) coils . A disadvantage ( if it can be called as such ) is that the lower impedance Zobels will burn off a couple of db in efficiency . OTOH, this wider spread in apparent efficiencies could be used to eke out a bit of extra UHF ( with a redesigned HF circuit / offer Zilch money to help ) .

- BTW, the Altec N1209-8a topolgy uses a Zobel on the LF section . This was undoubtably included into the design so that this network could be effectively matched to a bunch of different Altec woofers . ie; It was meant for more general purpose duty .

- Something to remember when playing ( experimenting ) with crossover designs / you can always create a larger value coil by wiring two smaller valued coils in series to each other ( the mH values will add directly if the coils are kept apart from each other ). One needs to separate them so they don't mutually couple ( ie; don't stack them ) . If you couple or stack them / you'll need to measure their new inductance with an inductance meter .

- Capacitors can be paralled to each other to create larger values.

- If you don't already have it / get something like TruaAudios' TrueRTA so you can measure the acoustic results of your experiments ( the Cdn $$$, being at an all-time high to the US $$$, means now is an opportune time to purchase ).


<> Earl K

[89-300ce]

yes , your thoughts are correct , only change C3 from 21µF to 10µF.
Or buy Altec 416-8b and give me your K145

regards
juergen

If you knew what I had to go through to get these drivers you'd understand why I'm not going to give them up. That, plus I got needs. Needs that only 40 lbs of AlNiCo seem to satisfy.

Jorg

[89-300ce]

Hello Earl,

- The problem with your thinking is that it appears that you assume that a woofer has an AC impedance curve that resembles a flat line.
- They don't / they all resemble big happy smiles .

- You should run an AC impedance curve for your K145s and then plot them out before doing too much else .

Wouldn't I need to do the 416-8b's as well for it to be meaningfull in this case?

- A DCR of 8.8 ohms implies a nominal AC impedance of @ 11-12 ohms ( somewhere on the curve ) / though it's a certainty that a Z of 16 ohms will be reached at some point on the curve.

- FWIW, JBL referred to this woofer as an 8 ohm driver / while a similar or identical voice-coil as found in the le15a was referenced as 16 ohm .
- As mentioned , I'd go with 12 ohms as my starting reference "Z" (for transposing values of an exisitng crossover ) . This means multiplying existing coil values ( on the LF section ) by 1.5 and multiplying capacitor values by .6667 ( the reciprocal of 1.5 ) .

- Something to remember when playing ( experimenting ) with crossover designs / you can always create a larger value coil by wiring two smaller valued coils in series to each other ( the mH values will add directly if the coils are kept apart from each other ). One needs to separate them so they don't mutually couple ( ie; don't stack them ) . If you couple or stack them / you'll need to measure their new inductance with an inductance meter .

- Capacitors can be paralled to each other to create larger values.

That's a good approach. I'll buy some quality coils and caps and combine them with some cheaper caps and coils for testing. Once I find a good setting I can upgrade these cheaper components as well.

- If you don't already have it / get something like TruaAudios' TrueRTA so you can measure the acoustic results of your experiments ( the Cdn $$$, being at an all-time high to the US $$$, means now is an opportune time to purchase ).

I'll look into this.

Thanks

Jorg

[Earl K]

Hi

- You should run an AC impedance curve for your K145s and then plot them out before doing too much else .

Wouldn't I need to do the 416-8b's as well for it to be meaningfull in this case?

- No, not really / not when you are going to "make it up as you go" to find the "best fit" for those K145 woofers .

- I don't really see what advantage or insight you would immediately gain ( in having the original impedance curves ) / apart from furthering your education on the "hows & whys" in some of these design matters.

- Having said that, do you have a 416-8b to measure ?

- Having a well appointed box of spare parts ( coils, caps & resistors ) , coupled with a capacity to immediately "see" the results of different part-substitutions ( as on a RTA ) will speedup your design process immensely .
- The coupling of basic electrical theory with some good empirical ( trial & error ) approaches will achieve decent results .

<>

[rs237]

If you knew what I had to go through to get these drivers you'd understand why I'm not going to give them up. That, plus I got needs. Needs that only 40 lbs of AlNiCo seem to satisfy.

Jorg

I can understand you well. Here in Germany it is certainly to be gotten still heavy K145. I possess unfortunately only one.

regards
juergen

[89-300ce]

Hi

- Having said that, do you have a 416-8b to measure ?

No, unfortunately. I'd love to someday have a collection of transducers, but just starting out in this DIY hobby means I have to satisfy myself by just listening to other peoples stuff. But, that's been a lot of fun too.

- Having a well appointed box of spare parts ( coils, caps & resistors ) , coupled with a capacity to immediately "see" the results of different part-substitutions ( as on a RTA ) will speedup your design process immensely .
- The coupling of basic electrical theory with some good empirical ( trial & error ) approaches will achieve decent results .

<>

These changes are too subtle to evaluate by ear?
I haven't had a chance to look at this RTA setup yet.

Jorg

[Earl K]

These changes are too subtle to evaluate by ear?

Yes.

[89-300ce]

When shopping for parts how close should my "part values" be to the design values.

eg. design calls for 4.2 mh

do I use 4 mh or 4 mh + .25 mh ?

I've found reference to < 2% on caps
< 7% on coils

Is this reasonable?

Thanks

Jorg

[Earl K]

- Try to keep LCR values to within 5% tolerance .

- You can always buy air-cored coils that are slightly larger in value than they need to be / & then unwind a few windings to get to the exact mH value .

- This means you'll need to own a LCR meter ( @ $100.00 at parts express )
- The meter is also handy for zeroing in on cap & resistor values .

[grumpy]

-
- The meter is also handy for zeroing in on cap & resistor values .

& also handy for matching, which I'll simply suggest might be of equal or more value
in the implementation process (L vs R tracking). -grumpy

[89-300ce]

Another question.

What wattage of resistors do I buy. PartsExpress sells them rated up to 20 watts. The BMS 4552 is rated to 60 watts. I've got 200 watts/channel in the amp.

If I need 3 ohm do I run 3 of the 20 watt 3 ohm resistors in parallel to achieve the 60 watt rating ?

Thanks

Jorg

[danwilliams]

I have a pair of L150's that I refoamed two years ago. Are there any upgrades members would suggest-new capacitors, different drivers, different internal bracing? Best amps tube or transistor for this unit?

Dan W.

[Baron030]

Hi Jorg

If you run three 20 watt 3 ohms resistors in parallel the power rating is going to be 60 watts. But, the impedance is only going to be 1 ohm.

I am assuming that you are talking about "R6" in the schematic, which has a value of 3 ohms.
And I am going to assume that the BMS 4552 driver has an impedance of 8 ohms and is rated 60 watts.
Since, the "R6" resistance value is lower then the driver's impedance, the resistor is not going to dissipate as much heat as the driver will.

Using the online L-Pad calculator listed below, I plugged in a 3 ohms series resistor value and a dummy shunt value 100,000,000 ohms and then I played around with the input power level until I came up with 60 watts going to the driver.
The calculated resistor wattage rating was only 22.5 ohms.

Since, it is very unlikely that you will be running your BMS 4552 driver at full power for sustained periods of time, even a single 3 ohm 10 watt resistor is not very likely to blow in this application. But, if you want to make absolutely sure that "R6" will never pop, then I would suggest using two 6 ohm 10 or 12 watt resistors wired in parallel or a single 20 watt 3 ohms resistor for the "R6" value.

L-PAD Calculator Link:
http://www.lautsprechershop.de/tools...ngkreis_en.htm

Baron030