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Mid-box question (fEarful headcase?)

christw

christw

Get low!
May 11, 2008
6,417
518
Dayton OH
Disclosures
THE MADDEST SCIENTIST
#1
Before I delve into the engineering, I was considering building a mid-box to run along side one of more of my cabinets. I don't ordinarily like what HF horns add and often find myself wanting more high end extension than my cabs have (horns off) but want it to be between that HF sizzle and the muffled sounding higher end of the drivers in the cabs. My goal is to quickly add versatility to any cab I own, especially my PF115 stack which are my main rig.

I was looking at a design like greenboy's fEarful Headcase. At minimum I want an adjustable mid driver that'll keep up with one of two of these PF cabs. I think the Headcase can do that, I just don't know if it'll work for me with these cabs. At most, I want an adjustable mid and high loaded box that'll do anything from one PF115 to an 810. The latter would be amazing but isn't nearly necessary. Can the Headcase or a variant of it's design do either of those?

I don't want to worry about this any more if you guys tell me that the PF115 aren't good candidates. I know a lot of the you on here will intimidate me with your intimate knowledge of areas of engineering that I barely knew existed two years ago but I love reading what you have to say every time! I learn a lot, even when people have bad ideas, including myself. On that note, shoot away! ;)
 
#3
It could work, but what it hinges on is the crossover. In order to design a good passive one, you'll need to know quite a bit about your other drivers. Bi-amp with an electronic crossover would enable trial and error experimentation. The fearful cbg crossover is probably not useful here, unless the xover frequency is appropriate, but you'd have little idea about phase relationships between the drivers without knowing some key info about your existing drivers.
 
#4
JdoubleH said:
It could work, but what it hinges on is the crossover. In order to design a good passive one, you'll need to know quite a bit about your other drivers. Bi-amp with an electronic crossover would enable trial and error experimentation. The fearful cbg crossover is probably not useful here, unless the xover frequency is appropriate, but you'd have little idea about phase relationships between the drivers without knowing some key info about your existing drivers.
Click to expand...

Good points. It can work with more of an "off the shelf" crossover. Not ideally designed for the specific woofer(s) on the low side but would be ok for driver protection, splitting frequencies, etc. Many advise against using an adjustable L-pad on mid drivers. I think there's too much power potential there and could fry all but the sturdiest of them. A better idea may be to get a hot mid and put in a switchable hardwired pad in the crossover like say -6db and full on or something to give it a bit of matching ability with various bottom cabs.

Somebody with more experience than I would have to work out all that.
 
#6
I had figured that I'd do something to that degree with a full on to -12db in 3 db increments or something if it was switchable. Maybe that's overkill. I just want to be able to use it with nearly any cab I've got from the '72 810 to the new PF. Maybe that's unreasonable. That's why I'm asking.
 
#7
For ideal results and predictable response in any room , you'd need a crossover specific to each cab. A well designed crossover does more then simply filter frequencies from whichever driver at a given frequency and slope, it also affects the phase response and impedance at the crossover frequency (keep in mind that a 4 or 8 ohm driver isn't 4 or 8 ohms at every frequency, that figure is the nominal load presented by that driver). So the crossover effects the relative loudness of frequencies produced by the drivers near the crossover frequency. Thus a poorly designed or unsuitable crossover can cause undesirable dips or peaks. Phase issues can cause similar issues and worse depending on where you are in relation to the cab (on /off axis). Forget everything you've been sold through marketing concerning mixing cabs. What you are creating a two way speaker cabinet. Making this work well with multiple cabs is a pipe dream in my opinion - especially the 8x10. The (2x) 1x15 is a better candidate.

An electronic crossover / biamp setup would simplify much of this, but you'll want to get a good understanding of the similarities and differences between passive and active filtering, and how they affect the outcome. I am no crossover expert by any stretch. But understanding the basic topologies, slopes, and what to expect from the drivers will enable you to understand what you are hearing and better answer the question "better or worse"? Again knowing what your woofer is doing on its upper end will help you decide where to cross it over. Unless the driver in question is off the shelf with published specs and response, this gets much more complicated.
 
#8
Well, I know it's an Eminence driver. It's just got a black Ampeg Portaflex / Eminence sticker with PF15 and 8 ohms on it. Probably not an off the shelf speaker.

Maybe I'll just slave some little tube amp as a permanent bright box on top if this doesn't work out. :ninja:
 
#9
One other thing- getting this right is more crucial than say adding a subwoofer. Our ears and brains are more keen to the mid and upper mid frequencies, and this its also where the character and quality of electric bass lives.
 
#11
So for those in the know-I follow that I should I scrap this idea as a one-size fits all solution to begin with but should I scrap the whole mid box idea since my cabs haven't got published data?
 
#12
It's pretty good as a fits all solution when using a great active crossover, but kind of lame with many boxes when using a passive crossover. As others have said here, a passive crossover design has a lot more gotchas that need to be dealt with on a case by case basis, because of reactance, and spacing between drivers, how far back or forward of the woofer the mid driver is placed, etc etc.

Active crossovers really give a lot more latitude in these types of scenarios.
 
#13
In order to get the flexibility you're after, active really is the way to go. The upshot is you don't need a lot of power to drive the mids and highs. Could use a 20-50 watt tube guitar head for crunch or something like a 1U-150 watt poweramp like you drive studio monitors with, or a Crate Powerblock. I use an 80 or so watt amp I yanked out of an old TKO combo to biamp the high out from my T-max. It works fine, it's the low half that needs all the power.
 
#14
Is there any particular model of active crossover that you would recommend to me for this application? If not, no worries! I'm unfamiliar with makes and models within this particular market segment and still trying to gather information. To me it's starting to sound like I should just get over it and buy a used/new fEarful 15/6 or 15/6/1 later this year instead of dumping a lot of effort (and possibly money?) into occasionally trying to coax my Ampegs into being something they're not while adding a significant amount of extra gear to schlep. Cost and size [storage/transportation] are my most significant stumbling blocks right now.
 
#15
Most any decent PA level crossover would do what you need to do. FWIW, I have a Carvin XC3000? in my PA rack. It has 4th order slopes and enough options to run the PA system and sounds nice. I got it used for like $60-$80. Some of the newer ones have programmable slopes, filters, etc. but that really isn't needed in a bass rig. The ability to reverse polarity on one side is good to have, especially if you'll be using it with a bunch of different speakers.

If you're looking at new, $300 units, yeah, that's a healthy step towards a fEARful. If you do go this route, you could do a full fearful headcase but if you don't need the HF component, you could just use that mid driver in it's own little sealed box. It's loud enough on it's own to hang with most any bass cab you put on the low side.
 
#16
As far as cost, if you use the 18sound mid, you can re-use it in a later fEARful build so that's more of an investment. So is the HF driver and the portion of the passive crossover that splits the two should you go that route. If you by the crossover used, you could likely sell it later for close to the same cost should you scrap the idea.

As far as size/transport, etc. the crossover is a 1 rackspace, light unit. The headcase would be a headcase obviously, a midbox by itself would be like an 8" cube or something....small stuff.
 
#17
I wasn't even thinking of reusing the drivers or reselling the crossover if I built a headcase. D'oh!

Thanks for all the advice so far guys. I think that I'll just spring for a 15/6/1 late this year. It makes more sense to me to just grab a different cabinet than drag along the extra crossover, amp, and cab.

As far as this thread's direction, Bongo, it's all yours if you'd like to find out more about your intentions.
 
#18
@ bongomania--

If you did a cab that went Woofer(s)--->Passive crossover--->guitar driver, you'd get the natural cone breakup of the guitar driver + whatever additional drive you get from a pushed SVT or various pedals or whatever and still play the system like a regular 1 amp + cab setup.

If you went the active crossover--->2 amp route, you'd be able to use a real guitar amp on the high side with the added benefit of more manipulation of tone and volume, letting you get the "pushed tube rig" sound at virtually any volume provided you used the right guitar amp, not too powerful, maybe 1/2 power option or something and an OD channel you like. The drawback of course is more expense and more stuff to carry.
 

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