dual 12" floor monitor tweeter questions

[brainbanana]

Hello all of you brilliant gents. and the not-so-brilliant chaps as well, haha.
Sorry to bother anyone, but I am trying to build a looooow budget floor monitor for our vocals in my band.
We are a Classic Rock Trio, and play small clubs at high volumes. I have a 2X12 guitar cabinet that I want to convert into a half way decent floor monitor. We only put vocals through the monitors, and I will be running it with three other 8 ohm 1x12 wedges. I want this cabinet to pull 8 ohms as well, if possible. That way, I can run two wedges at 4 ohms on one 400w side of power amp, and run one wedge with this 2x12 monitor at 4 ohms for the other 400w side of power amp. I was considering putting two small round piezo tweeters in the 2x12 cab, and just using resistors instead of a full blown crossover. I believe the speakers are Eminence 12" 8 ohm speakers? Don't know the rated wattage. I am thinking budget tweeters here, not more than $30 for both? I am not looking for pristine sound, but more for an affordable "boost" to our monitor system.

Can ANYONE please help me out with a wiring diagram and suggestions? I am not very good at all this figuring out resistance and crossover points etc... so I would rather just wire up a couple of resistors and piezos and run with it.

Thank you for reading this, and I apologize for another noob wasting more time here, hahaha.
seriously, though, Thank You. Great place here.

[wg_ski]

Re: dual 12" floor monitor tweeter questions

If that guitar cab has two 8 ohms in it, you'll get 4 or 16. There is no way to get 8. What I'd be inclined to do is use them separately - a 2x vocal monitor is probably a bad idea, but two separate wedges a good one.

A guitar speaker (especially w/o a crossover) probably isn't the best choice for a wedge because of the breakup peak. Peaks in the response tend to be magnets for feedback. But if they're paid for the worst you could be out is a couple bucks for the piezos and crossover. You need a crossover - if you run piezos without them they WILL blow up on a 400W amp... eventually. For a quick and dirty crossover, use a 3 to 4 uF polypropylene cap in series followed by 0.6 to 0.8 mH coil in shunt. Use the lowest cost coil you can get. Do not use an electrolytic cap unless you want it to explode and blow little pieces of paper all around inside the box. Parallel the piezo(s) with a 10 ohm 25 watt resistor and provide ventilation for it (do not bury it in insulation or acoustic foam). Do not omit the resistor or the response will REALLY be peaky. Run the 12 direct, with the caveat of having peaks/holes in the response as a result. If that does not result in "acceptable" performance you'll need a real proper crosssover. It will likely be as good as a cheap $100 wedge, because that's about what's in it and about the extent of the engineering.

[brainbanana]

Re: dual 12" floor monitor tweeter questions

great information! Thank you. I apologize for the ohmage slip up. I knew that much about it, I just spaced it when I typed that question. The two speakers that I put in the cabinet are actually the old old speakers that have been in my pair of 1x12 wedge monitors for about 15 years. I just replaced them, and thought I might get some extra use from them, as they still sound decent, just really old. I tried to find info on them, but didn't find much. They have no name on them, but I believe they are eminence going by what info I could find. Small magnets, and I believe they were specified for full range or guitar use? Anyhow, they're not too bad of speakers. I know that I may not be doing what should be done in this situation, but I would still like to use this cabinet with our band. So, I have to get a crossover for this? What's my least expensive route for piezos and crossover? Keeping in mind I am not a professional at soldering, and have never created a crossover before in my life. I would probably wire it up to get 16 ohms, since I will be pairing it with another 8 ohm cab, and I do not want the total for both cabs to go below 4 ohms.

[wg_ski]

Re: dual 12" floor monitor tweeter questions

The simplest crossover (that works and won't fry anything) is the one I described earlier. Filters below about 2800 Hz, three parts.

[drmcclainphd]

Re: dual 12" floor monitor tweeter questions

If you use piezos (such as Goldwood GT-1005) you don't need a crossover. Piezos appear to a driver network as an open circuit until they start to work, then they only pull what they need (very little) and don't contribute anything noticeable to impedance. They don't require a resistor either unless they're too "hot". From experience, use only one in your 2x12, and you can wire it in parallel to the signal line (across the + and - of the incoming line) if you want. If it's still too hot, you can add a 20 watt resistor (10 ohm; 20 ohm if 10 isn't enough) on the hot leg of the piezo. But if they're for monitors, you might just want to let them be hot, it'll help cut through the ambient noise. As for your configuration, wire the 2x12 in series, 16 ohms, and run it in parallel to the wedge on that side (like you do on the two-wedge side) and you'll be fine. The impedance of the 2x12 and the wedge in parallel are 5.33 ohms, safer than the 4 ohms on the other channel, and probably louder because of the 12" Emi's. Definitely louder is you add the piezo.

[brainbanana]

Re: dual 12" floor monitor tweeter questions

thanks for your help guys! Much appreciated!!!!

[wg_ski]

Re: dual 12" floor monitor tweeter questions

Piezos appear to a driver network as an open circuit until they start to work, then they only pull what they need (very little) and don't contribute anything noticeable to impedance.

True, but if you feed it a full range signal you're still hitting it with full voltage, and it has to deal with the mechanical stresses of low frequency input that it can't respond well to. Above 35 volts (regardless of frequency) and it dies. High level low frequency will stress the joint between the piezo element and the diaphragm - and when it does that it loses output... permanently. I've ruined my share of KSN1005's back in the 80's. You can play a lot louder and cleaner if you do use a crossover.

[brainbanana]

Re: dual 12" floor monitor tweeter questions

that makes sense wg_ski. I will probably waste $10 on a goldwood and resistor for experimentation sake, and just see how it sounds and how long it lasts. If I want to move forward, then I'll have to figure out that crossover diagram, because I have no clue exactly what it is saying. I can't even tell which is positive and negative on the diagram. and I don't know where the speakers wire in to that setup. I apologize, but I am a severe wiring newb, and can't read that :o

[billfitzmaurice]

Re: dual 12" floor monitor tweeter questions

True, but if you feed it a full range signal you're still hitting it with full voltage, and it has to deal with the mechanical stresses of low frequency input that it can't respond well to. Above 35 volts (regardless of frequency) and it dies. High level low frequency will stress the joint between the piezo element and the diaphragm - and when it does that it loses output... permanently. I've ruined my share of KSN1005's back in the 80's. You can play a lot louder and cleaner if you do use a crossover.

+1. The notion that piezos don't benefit from being high passed is false. They can be run without one, but that doesn't mean that they should. They usually aren't, because they're usually used in cheap, poorly designed speakers because they're inexpensive, and someone making a cheap, poorly designed speaker for a price point isn't going to invest in the additional five bucks for a proper high pass filter. Adding a good filter at least quadruples power handing, while reducing THD levels by some 90%. But even with a filter the voltage limit remains, so to get around that piezos should always be used in pairs, series wired (or parallel banks, series wired) to double the voltage limit.

Piezos appear to a driver network as an open circuit until they start to work, then they only pull what they need (very little) and don't contribute anything noticeable to impedance.

Piezos are a capacitive load, and they very much contribute to impedance, as like all capacitors their impedance goes down as frequency goes up. They essentially appear as a dead short above 50kHz or so, which can lead to destructive oscillation in the output stage of an amp that's not protected against that possibility. Since that generally applies to the cheap amps often used with speakers loaded with piezos it's a bad combination. Using a series resistor to present a minimum load to the amp is a cheap, easy fix, but one not used by most manufacturers of piezo loaded speakers.

If it's still too hot, you can add a 20 watt resistor (10 ohm; 20 ohm if 10 isn't enough) on the hot leg of the piezo.

The piezo being a capacitive load a series resistor will have very little, if any, attenuating effect.
The correct implementation methods for piezos can be found here:

http://www.parts-express.com/pdf/piezo.pdf

[brainbanana]

Re: dual 12" floor monitor tweeter questions

So, since this is definitely a poorly designed speaker at a low price point, and since I have absolutely no clue how to make a crossover, I will probably be using two of the goldwood 1005 piezos and two 20 watt resistors. Just for learning and experimentation, of course. So, would I run the two piezos in series.
Here is my stab at wiring this abomination, haha.

8 ohm 12" speakers in series:
From the input jack + to first 12" speaker +
from first 12" speaker - to second 12" speaker +
from second 12" speaker + to input jack -

Piezos in series:
from the input jack + to first 20w resistor
from first 20w resistor to first piezo +
from first piezo - to second 20w resistor
from second 20w resistor to second piezo +
from second piezo - to input jack -

sooooo, I truly appreciate and respect all the knowledge being passed around here, Thank You! If I am doing something that will just plain not work at all, please let me know? Thanks guys

[billfitzmaurice]

Re: dual 12" floor monitor tweeter questions

If I am doing something that will just plain not work at all, please let me know?

It will work, just not very well. There's no need to use more than one resistor. With all the available plans out there that are well designed and will work well I don't see the point in this myself. I'd sell the guitar cab to finance building real monitors.
One thing not touched on yet is that unless separately EQd having different monitors will be a nightmare where controlling feedback is concerned. Also, since you already have three 1x12 wedges, one per player, why do you need more? If that's not enough to hear yourselves you should go to in-ears, not only to hear the monitor feed, but also to keep from going deaf.

[brainbanana]

Re: dual 12" floor monitor tweeter questions

Well, we do have one wedge each right now, yes. It is actually okay for myself and the drummer. I am the lead singer, and I don't normally have a problem hearing myself sing, as I have a very loud voice in general, and am able to project into the mic well. I am actually trying to do this for my bass player, who lead sings on just a few songs, because he INEVITABLY, during EVERY SINGLE gig, will look at me and shout "I can't hear a damn thing through the monitors!". To which I will reply "I'm givin' her all I've got Cap'n!", and then try to increase his volume slightly (feedback), and tweak the EQ for more mid presence (feedback). We have a small system, and I run it from the stage. We have separate monitor mixes, but he still says he can't hear anything. When I walk over and check his mic, it's quite loud. I think he's losing his hearing (as we all are in this band). I just thought I would try and give him an extra cab to have his vocals through so maybe he would quit bitching at me :applause: I used to think it was my guitar that was so loud that nobody could hear, but even when I'm completely off on his side, he still complains. I know that the bass stage volume is loud, and the live drums are very loud. I like building stuff, so I thought I'd take this old cab and do some construction work. It keeps me busy.

So, you're saying skip the extra resistor between the piezos, and it should work. I understand and accept that this is not the optimum way to create a full range cab, and I really do thank you very much for this knowledge and advice. If it doesn't work well at all, I will probably be posting again asking for help in making a crossover. Or else I will just end up throwing the 2X12 cab through the air directly at my bass player, and maybe then he will be able to hear it!

by the way, I love my bass player like a brother, just so ya know

[billfitzmaurice]

Re: dual 12" floor monitor tweeter questions

I am actually trying to do this for my bass player, who lead sings on just a few songs, because he INEVITABLY, during EVERY SINGLE gig, will look at me and shout "I can't hear a damn thing through the monitors!". To which I will reply "I'm givin' her all I've got Cap'n!", and then try to increase his volume slightly (feedback), and tweak the EQ for more mid presence (feedback). We have a small system, and I run it from the stage. We have separate monitor mixes, but he still says he can't hear anything. When I walk over and check his mic, it's quite loud. I think he's losing his hearing (as we all are in this band).

Adding more SPLs will only make him deaf all the faster. You seem to be in the same mindset of most newbies, and to me that's someone who's been a professional musician for less than 10 years, of having the stage volume enough to carry the room. The stage volume should be enough to carry the stage, carrying the room is the PA's job. BTW, when you see all those massive stacks on stage at concerts, that's all for show. This is what the roadies see from backstage:

[brainbanana]

Re: dual 12" floor monitor tweeter questions

haha, I love that pic. I believe you sent me that once before to illustrate that same point! Yes, I do believe our bass player is going deaf and stubborn as a mule. But, while I am a newbie to building crossovers, I am not a newbie to the stage, as I have been gigging consistently for over 25 years now without a break. Yes, I play covers on the weekends, but hey a gig is a gig. Point taken, stage volume is directly related to the ability to hear vocal monitors, for sure. I kind of thought maybe the 2X12 monitor would possibly create a "placebo" effect for him. If he sees that big pair of 12's looking at him along with his other wedge, then maybe, just maybe, he'll talk himself into actually hearing his vocals a little better. A little Spanish Fly, if you will. Anyhows, it is always great conversing with you folks. My sincere thanks for your time and help.

[wg_ski]

Re: dual 12" floor monitor tweeter questions

The placebo effect had better work, because I doubt you could give him any more volume with the 2x12 *without feedback*. Probably less, actually. The peaks and nulls in the pattern will make it even less intelligible than a single driver solution. You'd need a real crossover, at a low enough frequency (1200 Hz) to prevent that. Not happening here. And any time there is a peak in the response there's that much less gain you can give it before it starts squealing.