fEARful Configuration Dilemma

[mrjim123]

I've decided to build two fEARful 12subs, and a headcase for the 6" mid and crossover. Weight reduction is the only reason I'm building new cabs, and I'm committed to 12subs, not 12/6s or any other enclosure. I want a rig I can lug around when I'm 70 (only 9 years away!). I'm not here to ask for weight reduction suggestions - that has been covered in another thread.

I'd like to have the flexibility of using the headcase with one 12sub for quieter gigs, and the same headcase with two 12subs for louder gigs. I play flatwound strings, I don't slap, and so I don't know need a lot of top end, but I do want some added mid presence. I have a mono amp, 500W @ 4 ohms.

One possibility is put an Alpha6A and a 12/6 crossover in the headcase, which would be ideal for gigs where I only use one sub. For louder gigs I would plug one sub directly in to the amp and the second sub into the headcase, which would then be plugged into the amp. Am I going to run into any nasty phasing issues as a result of some mids coming from both the Alpha6A and the 12sub that is plugged directly into the amp? Also, will the Alpha6A give me enough output when I use two 12subs? I'm really interested in how this setup will sound, more so than how it looks on paper. How many guys are using or have used a 12sub with a 12/6, and what is/was their experience?

Another possibility is to put a 6ND410 and two crossovers (a 12/6 and a 1212/6) in the headcase, with a switch (four pole, double throw?) to connect one crossover or the other to the 6ND410 and headcase jack plate. This would be more expensive and heavier, which I'm hoping to avoid. Also, would I have to add an L-pad to attenuate the 6ND410 output for gigs when I'm only using a single 12sub?

Would a Zobel circuit solve my impedance matching problems? Is there another possibility I haven't considered?

[domestique]

I would post this over at the fEARful forums, or pm greenboy. You would probably get a more specific answer there.

[wcriley]

I'm sure greenboy and the guys over on his forum fEARful can answer better than I can, but I'll take a shot at it. (Why let ignorance get in the way now. I never have before.)

I doubt very much that a single Alpha6 could keep up with with 2 woofers. I have an Alpha6 in each of my 12/6 cabs and it seems about right.

If you really want to do two 12subs and a headcase, I'd say use the 18Sound mid in the head case.

For the crossovers, I think the simplest solution would be put a full 12/6 Xover in the headcase, with a switch to pad it for either one or two bottom cabs.Then put an additional low pass portion of the Xover in the spare sub.

EDIT: I'm 60 and have bad knees. I can easily load/carry a 12/6 with one hand. You might want to reconsider the headcase idea. The 18Sound mid and Xover won't add much weight.

[will33]

You can run like that without phasing issues if you plug the sub that has it's own lowpass filter built in straight into the amp. The sub you chain to the topbox would be a 12 driver only, no filter as it's filter would be built into the topbox and connected to the "low out" jack.

The Alpha6 is a pretty even spl match for one of those 12's. Adding the second 12 would then put your mid 3db lower than the woofers. I run a rig like that all the time (non-fearful). Works fine for me but it's geared sort of toward playing outdoor gigs where you need the extra lowend output to get back to even as there are no boundry enhancements. It keeps from having to boost lows at the amp and lose headroom, or deal with a thin sound to save power. Turning the bass down a notch or 2 when playing indoors is all it takes to correct it. With a P and flats, I'd think that type of voicing would work fine.

Of course, the 6nd410 would guaranty you'd never be short on mids. You may want a switch for 2 different padding schemes in the crossover, one for a single sub, one for both. Or you could just fix it all with eq if you have enough in the right spots on whatever amp you're using.

[DukeLeJeune]

Originally Posted by will33

Adding the second 12 would then put your mid 3db lower than the woofers.

Your concept is correct, but the difference is actually 6 dB, for level-matching purposes (relative to the single midrange). You get +3 dB in efficiency by adding the second woofer, and another effective +3 dB in voltage sensitivity because you've gone from an 8 ohm load to a 4 ohm load.

[will33]

Originally Posted by DukeLeJeune

Your concept is correct, but the difference is actually 6 dB, for level-matching purposes (relative to the single midrange). You get +3 dB in efficiency by adding the second woofer, and another effective +3 dB in voltage sensitivity because you've gone from an 8 ohm load to a 4 ohm load.

Good catch..I left that part out.

I guess I'd call it 4-5db as I don't of too many amps where power all the way doubles as impedance is halved but, yes, I left out that aspect.

[DukeLeJeune]

Originally Posted by will33

Good catch..I left that part out.

I guess I'd call it 4-5db as I don't of too many amps where power all the way doubles as impedance is halved but, yes, I left out that aspect.

Assuming the amp approximates a constant-voltage source (true for virtually all solid state amps), even if the amp's maximum power at the onset of clipping doesn't quite double, it's wattage output into a halved impedance load does double below the clipping point. We're used to thinking that amps put out "watts", but they really put out "volts". Imagine the amp is putting out a steady sine wave, and the levels are set such that it happens to be putting out 2.83 volts. Well if the speaker's impedance is 8 ohms, then that's one watt, but if it's 4 ohms, it's two watts. So up until the clipping point we get that 6 dB increase in loudness from adding the second woofer in parallel because we really are getting twice the watts (in addition to the doubled cone area).

Now something else happens when we go from an 8-ohm load to a 4-ohm load: The current that the amplifier delivers doubles, because less ohms = less resistance to current flow. And because wattage = current x volts, the wattage also doubles. So that's where the doubling of power comes from.

Few amps can deliver fully twice the maximum current into a 4-ohm load as what they can deliver into an 8-ohm load, so few amps actually deliver double the wattage at the onset of clipping. Hence the word "approximates" in my first sentence.

At least, this is my understanding. I welcome correction from any amp gurus out there.

[will33]

Originally Posted by DukeLeJeune

Assuming the amp approximates a constant-voltage source (true for virtually all solid state amps), even if the amp's maximum power at the onset of clipping doesn't quite double, it's wattage output into a halved impedance load does double below the clipping point. We're used to thinking that amps put out "watts", but they really put out "volts". Imagine the amp is putting out a steady sine wave, and the levels are set such that it happens to be putting out 2.83 volts. Well if the speaker's impedance is 8 ohms, then that's one watt, but if it's 4 ohms, it's two watts. So up until the clipping point we get that 6 dB increase in loudness from adding the second woofer in parallel because we really are getting twice the watts (in addition to the doubled cone area).

Now something else happens when we go from an 8-ohm load to a 4-ohm load: The current that the amplifier delivers doubles, because less ohms = less resistance to current flow. And because wattage = current x volts, the wattage also doubles. So that's where the doubling of power comes from.

Few amps can deliver fully twice the maximum current into a 4-ohm load as what they can deliver into an 8-ohm load, so few amps actually deliver double the wattage at the onset of clipping. Hence the word "approximates" in my first sentence.

At least, this is my understanding. I welcome correction from any amp gurus out there.

And that's why you don't see "will33" amps anywhere.


I think you got it with the voltage swing, at least in theory.

In my above speaker balance example, that system may indeed be a little too bottom heavy doing it all with passive XO's, you certainly wouldn't want to pad a woofer. I don't know enough to even know if you reasonably could (huge expensive parts, etc.). I run an out of balance system like that with biamping so obviously I can power the two halves as I see fit for the desired sound.

Works for me but maybe not the OP. He may indeed want to go with a hotter mid with a padding option (or two) done passively if need be.

[4Mal]

OK so this kinda low tech but.. I often play a PJ with near dead Chrome flats. I run a GK mB2-500 with a Fearful 12.6. I used the Alphalite and CBG crossover PLUS a 6 db pad in the mids courtesy of . I have never felt head room shy nor shy of mids. I also have 2 fEarful 12 subs for my PA. I have run a 12.6 on top of a 12 sub with the little GK. I dialed up the hi mids a bit and was pretty happy with the results.
I'm after the Conrad Lozano, Jamerson, Duck, Chris Hillman kind thing tonally. Pretty trad country rock and blues round tone. So I would be thinking about 2 12 subs and 2 head cases 1 with an Alphalite and crossover for an 8 ohm woofer. The other with the same mid driver and 4 ohm, crossover.

Actually - just do a 12.6 using the Alphalite and be done with it...

[will33]

Originally Posted by 4Mal

OK so this kinda low tech but.. I often play a PJ with near dead Chrome flats. I run a GK mB2-500 with a Fearful 12.6. I used the Alphalite and CBG crossover PLUS a 6 db pad in the mids courtesy of . I have never felt head room shy nor shy of mids. I also have 2 fEarful 12 subs for my PA. I have run a 12.6 on top of a 12 sub with the little GK. I dialed up the hi mids a bit and was pretty happy with the results.
I'm after the Conrad Lozano, Jamerson, Duck, Chris Hillman kind thing tonally. Pretty trad country rock and blues round tone. So I would be thinking about 2 12 subs and 2 head cases 1 with an Alphalite and crossover for an 8 ohm woofer. The other with the same mid driver and 4 ohm, crossover.

Actually - just do a 12.6 using the Alphalite and be done with it...

Your last line there is probably a good idea. "My tone" is also a bit on the warm/round/old school side if you will. I don't miss any mids having a 6 that runs a little quieter, even when everything is adjusted as even as I percieve it to be. I am hooked on these 6's and don't really want to go without one. Being able to hear everything and be even across the room is worth too much. There is still plenty of room for personal preference though. You don't have to have a "modern" sound at all. My P is far from it, you can just hear your "old school" better, and in more places throughout the room, that's all.