Sweeten my vocal rig

[Pbassred]

Caviat >>>>> If I need a bigger rig I would hire in.

I'm currently running an old Peavy 8.5 (425W per side) to push a pair of 8ohm "full range" cabs which consist of a 15" and a piezo tweeter. Plenty of smooth bottom but nasty highs. I could either;
A/ Defeat the piezo, build/buy better tops, and use a crossover. 8ohm load.
B/ Add a second "full range" cab but more biased towards the mid to high range - say 12" or 10" The amp would then be driving a 4 ohm load.
c/something else.

Im not looking for a balanced system. Just one targeted at vocals. Any thoughts?

[sreten]

The classic solution for controlled vocal directivity
and throw is a large horn c/o just above 1Khz.

sreten.

[Pbassred]

"C/0"?
Would that be 8ohm ( making a total of 4)?

[sreten]

Usually a full 2 way crossover is used, 2nd order on the bass unit
and 3rd order on the horn. Also the horn usually needs L-padding
back to the bass unit for balance. Impedance remains 8 ohms.

You can buy full c/o boards, they usually include
some form of additional protection for the tweeter.

http://www.partsexpress.com/pe/showd...number=290-620

sreten.

[electroaudio]

Originally posted by Pbassred

A/ Defeat the piezo, build/buy better tops, and use a crossover. 8ohm load.
B/ Add a second "full range" cab but more biased towards the mid to high range - say 12" or 10" The amp would then be driving a 4 ohm load.
c/something else.

Do you like the mids of the 15incher?
In that case a simple solution would be to get rid of the piezodriver and replace it with something better.
You could also add a small, 6.5inch maybe, midrange unit between them too. (I would recommend it)

Otherwise, your idea with a second box would mean that you would use the 15incher as a bassunit with a second box that has a bigger mid and a more appropriate trebleunit like a 1inch horn.
That would mean a much bigger system...

[BillFitzmaurice]

The problem is not the piezos; they work quite well above 4kHz, better for the most part than dynamic drivers. Your difficulty lies with the 15 inch woofer, which just isn't going to sound good above 1kHz. Even though pro sound 15s have response up to perhaps 4kHz they are very uneven and the HF dispersion pattern is very tight. The easiest fix is to add a closed-back 8" midrange driver like an Eminence Alpha 8MR, cross it over at 800 Hz. The difference will be startling and quite inexpensive.

[Pbassred]

firstly, my Sunday morning dumbness filter (Maplins £34.99) was not engaged. C/O = Crossover.

I like the way that a question on a forum can yeald 3 different answers. All feasable to a point. Would you all stand by your answers if I defined my (twisted) thinking more fully?

I would like to use my power amp to the full. So Ideally a 4ohm load would be best. However I can see that using a passive C/O to drive 3 units is sonically correct. ( better to be nice than just loud.)

Downside: It would still result in an overall 8 ohm load (this is my understanding. Feel free to correct me).
*I would need to discard my existing 2 way C/O (or not?).
*I can't find a 6.5in that would handle 300 watts @8ohm! I CAN find an efficient 8in that does 125W though. Would that be ok as part of a passive C/O system if the amp pushes 300W?
*It wont fit my existing cabinets, although I DO have suitable boxes and could jack out of the main cab.

I have another Amp that I may use to drive a real sub one day - via an active C/O.

[electroaudio]

Originally posted by Pbassred
I would like to use my power amp to the full. So Ideally a 4ohm load would be best. However I can see that using a passive C/O to drive 3 units is sonically correct. ( better to be nice than just loud.)

Well, then you would have to buy new drivers or to get a second setup at 8ohm in paralell with the first 8ohm system.

*I would need to discard my existing 2 way C/O (or not?).

It would be best, yes.
But they arent that expensive so.

*I can't find a 6.5in that would handle 300 watts @8ohm! I CAN find an efficient 8in that does 125W though. Would that be ok as part of a passive C/O system if the amp pushes 300W?

when i said 6.5" i was thinking of a speaker that i have been using at the company i have worked for the last week.
(Maybe i should ask him what 6.5" he was using in his boxes?)
Otherwise, if it is 6.5" 8" or 10" isnt that important.
But when you use the system it is usually the bassdriver who got to do the biggest work, but a feedback may destroy it.

*It wont fit my existing cabinets, although I DO have suitable boxes and could jack out of the main cab.
I have another Amp that I may use to drive a real sub one day - via an active C/O. [/B]

Maybe you should go that route, with an active Xover and to reuse the passive Xover in the top boxes with a poweful 10incher?
A simple active Xover is both easy and very cheap to build so this way may be a cheap and much more powerful solution.
which also would allow you to put the kickdrum into the mix.(Usually a good idea)

But, after this you have to specify a bit more what stuff you have.

[BillFitzmaurice]

You don't have a passive crossover right now if it's a 15 with a piezo tweeter; piezos don't use crossovers. You'd have to add a crossover at 800 Hz for the eight, preferably with an 18dB slope. You also don't need 300 watts capacity, as the midrange driver does not get the same kind of power that the woofer does. In fact probably 75% of the power will still go to the woofer, so an Alpha 8MR with 125 watts capacity is sufficient. In any event you have your wattage numbers backwards; your power amp should be rated at twice the capacity of your speakers for adequate headroom.

You don't need or want a 4 ohm load; you'd only get that if you run the woofer and mid in parallel with no crossover, which would not direct the frequency bands to the appropriate drivers and would result in a blown mid.

A proper crossover wil direct the frequency bands where they belong and maintain an 8 ohm load per box. Assuming your PA has two speakers and is not stereo you're already providing the amp with a 4 ohm load.

[Pbassred]

eek Mr Electroaudio! In MY (tilted) world subs are 18" driveres that don't run much above 150Hz. So the 15in would be wasted as a sub. I am warming to the general idea though.

Mr Fitzmaurice and I differ on the wattage numbers. The large amp concept comes from the idea that it is better to overdrive a speaker from a large, amp than to drive a big speaker from an overdriven amp. I agree, but surely a better idea than either, is to drive a tough speaker from an amp that is not over driven? The reason for wanting a 4ohm load, is to use the amplifier to its fullest without clipping. At 8ohms each side is 270W. At 4ohm they are 425W. I could run cleanly like this at 2X 350W all day. However I don't want to fall out over this issue. The most important task from what you say, is the restore the missing 800HZ The Emenence is exactly the speaker that I was looking at.

There IS a crossover in the cab at the moment. Using a 3 way would mean that I could never use the big cabs without the smalll ones. If the peizo tweeter could live without a C/O I could make a 2 way set at 800Hz to 1kHz. Eminence sell the PXB2-800 for a little more than the cost on the drivers. I'd be lucky to find components heavy enough to build them myself (but I'm hopefull).