Goodman's Magnum K series MEGA collection... Mod advice

[lysergic-skies]

Here is the K2 crossover with all values:

Goodmans Magnum K2 Crossover.png (15.05 KiB) Viewed 3772 times

I don't pretend to know too much about the relationship of crossover components and how the drivers affect each other, but I am wondering if I should just try this and see what it sounds like:

K2 alterations.png (11.34 KiB) Viewed 3772 times

The K2 bass is already doped. And a lower cap on the tweet might be worth a shot, apart from that it's the same on the mid. If things sound like they are reasonable, I can look at doping the mid. Will use the shipreck K2s and fish tank Alnicos for experimentation to preserve the perfect units, so don't worry Riat!

Does anyone have a crossover diagram for the final doc mod? I can't remember which thread it was in, but he advised a couple of coats of Plastidip to the mid, and resistors on the tweet to taste. If anyone has an example final circuit that would be very helpful.

[lysergic-skies]

Remember doping is an alternative to a crossover , not in my opinion a compliment

I've just re-read this and I think I misunderstood it. Having not tried driver doping before, I have no knowledge to fall back on. Are you saying that the eventual aim is that none of the drivers have any crossover components at all? Or were you just referring to individual drivers?

[CycleCoach]

The NVA Cube speaker has two crossover components: A capacitor and a resistor, these protect the tweeter. The woofer runs wide open and in parallel with the doping mechanically rolling the treble off.
That's the simplest crossover possible and the lack of electronic complexity puts less in the way of the music.
Things are a little more complicated with three drivers.
Here there are a couple of options. You can either run the midrange and bass in series relying on the doping to sort out the frequency response, or you can run them in parallel with an inductor to block some treble from the woofer (you might need a resistor on either the mid or bass to get the levels right.
The sole arbiter at each step should be your own ears and trial and error will get you there.
There is a lot of really good and detailed information on here on the "Doc Mods" threads. They really are worth a read. Goodmans and Wharfedales are particularly suited to these kind of mods.

[lysergic-skies]

Thanks @CycleCoach. Great info there.

I wasn’t even aware that you could run the bass and mid in series. I’ll have a little read of the doc mod threads and come up with something.

[Daniel Quinn]

The tweeter can be protected just by a capacitor if it's the same ohms as the other drivers . Its largely personnel depending on how you want the treble .

The bass and midrange you dope and run full range and run in series .

[CycleCoach]

The resistor value for the tweeter sets the relative levels (I'd start in the 8-12ohm range (a selection of ceramic wire-wound resistors won't break the bank.) And the capacitor value sets the crossover point. Around 3.5uF is a good starting point. (as long as you don't buy boutique caps, a selection around that value - say one either side - again isn't too dear.) You can always buy flasher bits when you're happy with the sound.

[lysergic-skies]

The tweeter can be protected just by a capacitor if it's the same ohms as the other drivers . Its largely personnel depending on how you want the treble .

The bass and midrange you dope and run full range and run in series .

Driver impedance is the same AFAIK - will double check before proceeding. I tend to favour slightly forward treble but I think a suck it and see approach is the only way here.

The resistor value for the tweeter sets the relative levels (I'd start in the 8-12ohm range (a selection of ceramic wire-wound resistors won't break the bank.) And the capacitor value sets the crossover point. Around 3.5uF is a good starting point. (as long as you don't buy boutique caps, a selection around that value - say one either side - again isn't too dear.) You can always buy flasher bits when you're happy with the sound.

I happen to have a box of 5w/10w/20w ceramic resistors I'm a super scrimper and I tend to do things on a budget so I get the well known red AliExpress caps. I'm not sure if these fall into the category of boutique caps but I've used them for a while now and I've had good results from them - they are always within spec and sound great. I recapped some Laser 100s with them and they sound phenomenal now.

[CycleCoach]

Sounds like you're ready to go. Have fun!

[Daniel Quinn]

Just use the capacitor to protect the tweeter and start from there.

Remember you can alter the balance by altering the capacitor don't immediately rush for a resistor .

I use cheap capacitors till I find the value the buy a decent cap with its settled .

[lysergic-skies]

Well I must say that this alnico mid from the Ks is really quite impressive. It's hard to appreciate individual drivers when in the cab with the others, but on the bench alone you can hear what it's capable of. It could almost be a full range driver.

I've temporarily added a 22uF cap to it because I don't have plastidip yet and was experiencing some low frequency distortion but it's handling most of it really well including the highs. Only when there's something really quite piercing do I get distortion on the top end. The alnico magnet is showing itself here - this driver is LOUD. It swamps the others so it might need attenuating.

Did I say I was impressed with it? Just for comparison, I grabbed a K2 mid and a modern generic mid I ripped out of something going to the tip and they don't come anywhere close. I am wondering if this mid was used in any of Goodman's two way designs because it really is spectacular. Obviously it doesn't completely negate the tweeter but it comes bloody close!

I experimented with several cap values for the tweeter and 4.7uF seems to be the best. Anything below that and it just takes too much away.

So this is what we have until the plastidip comes along:

K2 alterations 2.jpg (21.13 KiB) Viewed 3453 times

Edit: Ha, thought so: https://www.radiomuseum.org/r/goodmans_mezzo_ii.html it's the same driver in the 2 way Mezzo II. Good show Goodmans!

Edit2: I have just disconnected the mid, and left the K2 bass and tweeter connected, and they also sound pretty good as a 2 way. I really don't think that K2 mid brings much to the table at all!