Stage monitors

Dan2

Member
2005-09-17 1:24 pm
i built up 4 stage monitors with a 12" driver and matching horn tweeter for my church. they sound really good - except the tweeters are a bit loud and this also is a problem with feedback.

I know you can connect a resister to the tweeter to drop the volume a bit. i only had 2 5W resistors lying around- 10R and 330R. i tried the 10R but it didn't do enough so now i am not too sure what value i should use. the speakers are 8R

the problem is the system that is being used has the equilizer on the mixing desk - but no "main" eq for monitor and front of house. So when i set the monitors to sound good, front of house sounds horrible. i was thinking of building an eq for the monitors (just need a stereo eq) using op-amps (i think the circuit is on rod elliott's webpage). i just need a cheap option for now.

thanks for any advice :)

PS: sound quality is not too important - this is a church so its not like we are using top of the range instruments.
 
You can use a variable L-pad on the horns before you have a better implementation for your setup. With many factory brands around the world, that you can choose from, having always in mind the power you are using. This is for the CD's (horns) only, not for the woofers. :att'n:

"L" pad lets you adjust the relative volume of individual drivers in a speaker system while maintaining a constant 8 ohm impedance. Comes complete with level indicator and wiring instructions. Rated at 100 watts RMS.

At $11.00 each, is about the same price as two good attenuation power resistors.

http://www.partsexpress.com/pe/showdetl.cfm?Partnumber=260-265

Good luck and post reports.
 
Dan2 said:
L-pads are a bit pricey here in SA - they cost around R400 and the speaker set (horn and tweeter) i got for R600.

If you think they are also so expensive in other cities, and there are lots of people with no Visa cards to buy it from abroad at a reasonable price maybe then it's time to start a business... You shoud look for the factories (in SA) and tell them you use their equipment for the manufacture of speakers, so they can sell to you directly.

Dan2 said:

I see u are steering me away from the eq - is that not such a good idea??

Please, can you elaborate on that? (What is the next question?) Is it that, and I am guessing here, the attenuation on the tweeter is your main problem... if this is the case, then state the dB for the woofer and dB for the tweeter to set the attenuation properly with (power) resistors, because those of 5W, well, they maight burn. Also state R (from specs) or impedance of the voice coil, not the nominal impedance, for the tweeter with horn, at crossover frequency.

Now going back to your Resistors available;
a 10R gives you about -7.0dB attenuation or 20% of power, and
a 15R gives you about -9.2dB or 12% of power,
a 25R gives you about -12.3dB or 5.9% of power,
a 34R gives you about -14.4dB or 3.6% of power.

Instead, to use an Lpad with two resitors R1 and R2 you can look at tables to set it properly. Since you don't give any more details of your setup, like the brand and model of the speakers and type of crossover if you have one.

I use this software calculator (also in spanish) a lot, for it. It gives the nominal power of the resistors also:

http://www.mcmantom.com/EN/
http://www.mcmantom.com/SP/utility/

there, go to:
1. Utility
2. Crossovers Calculator
3. Attenuators
(you can "Print Results" in the bottom)

If this is not where you "go", and you need more feedback, please post your next question.
 

Dan2

Member
2005-09-17 1:24 pm
i didn't get any specs with the speakers - they didn't even come with a box so they are no-name brands. but they do sound pretty good and are perfect for their application - except of course that the tweeters are a bit hot.

in my first post i asked if it was a good idea to build an equalizer for the monitors (it would need a stereo eq). i saw an equalizer circuit which was just an opamp, a few caps and some variable resistors - which looks really easy to build. then i would use the eq on the mixing desk for front of house and then set up the other eq for the monitors.
At the moment i can not set the high frequency up higher than flat without feedback from the monitors.

the only crossover network is a cap built into the tweeter - nothing else.

As for a protection fuse - that actually sounds like a good idea. could i just hook up a normal fuse in-line with the drivers?? if so what type of fuse.
 

Lsharptec1

Member
2004-10-29 6:53 pm
Guys,

Here is a tip that I use ... purchase a set of L-pads. Adjust them to attenuate the tweeters to a level that matches the woofer.

Remove the L-pads, and measure the DC resistance of both the series and parallel legs.

Then wire a fixed resistor L-pad with the same resistances.

If the measured resistances do not exactly match fixed resistor values, just use the closest available values.

Good luck.

Larry
 

Dan2

Member
2005-09-17 1:24 pm
I went to the electronics shop yesterday - they have a separate sound and lighting section so i was sure i could find an L-pad there. I spoke to the guy there and he never heard of an L-pad before!!! he said the closest thing he has is a crossover network (close???) I can get an equalizer for R1700 (which would probably work out cheaper than 4 L-pads if i could find some)

Still gonna try the foam tho - it would serve a double purpose too 'cos i already dropped a screw in one of the horns and it took like half an hour to get the damn thing out!
 
If you can get your hands on some cheap 10 or 20W cast resistors, and if your tweeters are 8 ohms, try using a 4 ohm in series and then an 8 ohm in parallel. That will reduce the power to the tweeter to 1/4 of the original or 3dB attenuation. If that still is not enough try a 5 ohm in series and a then 5 ohm in parallel. Unless there is something really mismatched, you should be OK with one of those two. Remember you can't just add resistance to the circuit or you will change the crossover frequency.

Cheers.
 

Dan2

Member
2005-09-17 1:24 pm
I forgot to take the foam with me yesterday :cannotbe:

I will try to remember next time....

Cal: if the foam doesn't work i will try the resistors. just so you know what power we're talking, the 5W 10R resistor that i put in the 1 tweeter doesn't even get warm so im sure it will be ok for me to use them.
I am just a bit confused - do i put 1 resistor in series with the 1 in parallel, or put the series resistor in first, check how it sounds, then take the resistor out and put 1 in parallel with tweeter??
 
You mentioned that you don't have xovers. Do you have piezos?

1.
R1 = 4 (series)
R2 = 8 (parallel)

2.
R1 = 5 (series)
R2 = 5 (parallel)

Note: ...and please don't touch the mains switch.:att'n:
 

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Dan2 said:

the only crossover network is a cap built into the tweeter - nothing else.


Do they sell resistors there, or do you ask by mail? (or do you have to travel a long distance to get them? I am confused.)

Note: : Why don't you start selling your stuff to the guy of the electronics shop for his "separate sound and lighting section". After you are set show him your monitors.
 
Dan2 said:
I am just a bit confused

Yes you wire them like Inductor has shown but you do so after the cap and before the tweeter so you may have to de-solder the existing cap to fit them in.

Dan2 said:
As for tweeters - i have no clue if they are piezo's or not.

If they have a magnet, they are not piezos. Also, piezos do not usually come with a cap.
 
Though very basic, here is a link to a page that will help with crossover design, even if the crossover is no more that an Capacitor in series with the high frequency horn.

Also, scroll down to the bottom, and there is an application that will calculate your series/parallel fix L-Pad resistor combination. Unfortunately, it hinges on knowing how much you want to attenuate the sound in DB.

Still, it can give you some ideas, and perhaps help.


Crossover Filter Design-

http://www.apicsllc.com/apics/Misc/filter2.html

Hopefully, this will be helpful.

Steve/bluewizard