PA Speakers 2 Way how to separate the volume

LazerBeakShiek

LazerBeakShiek

Rad Racing Team
How do I control volume to each speaker in a 2 way 8 ohm 15"/ 4" horns PA cabinet. I want more wattage going to the 15" woofer than the 4" Driver horns. If I use a crossover with more than 4Khz -12 db per octave , that will not be the same. I want the horn frequencies, just not as loud. If there was only a volume knob for the horn speakers to separate the volume.

My ADA Bass amp has hi and low on a bi amplifier. A Vol nob for the 10" cab and a knob for the 15". They can be balanced out as needed.

That is kinda what I want for my PA. Is there a way to place a volume potentiometer before the speaker contacts on the horn? Could I turn them down some like that. Like a guitar vol knob.

How about a dummy load resistor placed in series just before the 4k crossover?

Like a 200 watt 8 ohm resistor on the horn wires. Would that drop the horn speakers 200 watts of PA volume compared to the woofer in the same cabinet? What am I looking for?
 
You won't need anywhere near a 200W resistor - My JBL VRX can be fed with 1600W and only a maximum of 160W goes to the horn driver. The crossover uses 4 x 30W resistors. In these particular speakers, there are 3 HF drivers and the units get switched by linking out two of the resistors to decrease power to two of the drivers. If the HF unit is 8 Ohms, then an 8 Ohm dropper will cut the power to the unit by half as you surmise. The HF doesn't have a continuous power anywhere near the spec max - so a 30W resistor in the feed to the speaker is best. Don't put it before the crossover as it can change the circuit impedance and the cutoff frequency could change - they're usually very simple circuits with coils - so impedance in that part of the circuit is important - less so, after the crossover has done it's work.
 
30 watts.. Only? and it drops 1440 watts? Is this before or after the crossover?

linking two resistors..so is that 60 watts?

The answer looks to be a resistor. Could it be a rheostat? That way I could dial it up or down in volume as needed.
 
You could use a variable one, although the ratings tend not to be speaker figures. In the JBLs, the crossover feeds the vast majority to the LF driver - the HF units get very little. Have a look at the rating on the HF unit - you'll see it's way less than the big one. We have some bi-amped speakers too and they have an internal crossover with a switch - the two 15" drivers are run from an amp that is about 1500W per channel - straight into the low frequency units, the HF unit is driven by a 2 x 400W amp, and the knob on the front rarely gets past half way to get a good balance with the bigger amp running with the control nearly at max. The ratings on the HF units in quite big PA's are usually around the 80W RMS rating - a few a bit higher.
 
There's a device called an L-Pad that's effectively a high power pot that's used for very much this same purpose.
The input always sees the same load (typically 8 ohms) and the output is whatever you want.
 
An L pad is ...

Like on car stereos , so when you max the volume at the head unit, and the speakers don't distort at all. That way 0-100% volume is usable.

I could be wrong.
 
The L pad is exactly what I was looking for. Thank you.

I can only find them up to 100 watts. That should make enough of a difference to trim the peaks off the tweeters. So I can bring the main fader up to 5-6 instead of 2-3.
 
Most of the power is going to the low-pass of the crossover. Low frequencies take a lot more power because you're moving a lot more air. Although I can't be absolutely certain, I suspect a 100W L-pad will work for tweeter control.

Technically speaking, doing that moves the crossover frequency (i.e. equal amplitude frequency) higher, so if the high- and low-pass sections are well designed and in phase at the crossover frequency, they will no longer be so when you attenuate the tweeter.

You could just use an eq patched in before the power amp.
 
bouldersoundguy said:
Technically speaking, doing that moves the crossover frequency (i.e. equal amplitude frequency) higher, so if the high- and low-pass sections are well designed and in phase at the crossover frequency, they will no longer be so when you attenuate the tweeter.
Click to expand...
Higher is ok. Higher is safe.

At worst it will sound a little scooped.
 
LazerBeakShiek said:
Higher is ok. Higher is safe.

At worst it will sound a little scooped.
Click to expand...
You're not understanding what I'm saying. The high-pass frequency, as defined by the -3dB point, doesn't change What changes is the frequency where the high- and low-pass bands are at equal amplitude. Since the phase responses of the two filters are sloped in opposite directions, that will lead to a different phase relationship at the new equal amplitude (crossover) frequency. If the crossover is well designed so that the two bands are in phase at the crossover frequency, they won't be in phase when that frequency changes. You could go from having a slightly wavy response either side of the crossover frequency to having a fairly deep hole in the response.
 
Your idea is fine, it will simply drop the Hf level. My combo has a switch to drop the tweeters out on my guitar you hear it. On my bass you don’t. I could wire a restsistor across the terminal to drop it in level rather than out quite simply. 30w resistors should do the trick. If you overdrive them they’ll get hot and fail, and the only downside is the volume to the Hf cuts out, so quite safe. If your typical use means they start to get hot, then wire two in parallel and they share the load, so of course you need to choose the values to compensate so if you want 8 Ohms, you wire two 16s in parallel. If you use 30w resistors this can dissipate 60w. A good project to fiddle with and as it fails safe, give it a go. you can buy a selection of resistors for less than a happy meal.
 
Trouble their typical values mean everything's squeezed down one end. I always think about Peavey with their over level protection - a lightbulb! They worked pretty well to tame excess HF taking out the tweeter coils in their cheap PAs.
 
Awe man..For 12 years I been trying to figure out what was going on.
20210405_124029.jpg
The speaker was replaced +10 years ago..The balance was always off. Now I know.

The 025H is only rated to 75 RMS/150 peak , half of the other.

Who makes /sells 025N27 Foster compression horns that are 150 RMS?
 
rob aylestone said:
. I always think about Peavey with their over level protection - a lightbulb! They worked pretty well to tame excess HF taking out the tweeter coils in their cheap PAs.
Click to expand...
Yeah. everyone had those terrible Peavey cabinets with the PEIZO dual horn section. The peizo dual horn array did not even have an impedance.. It was not needed. They couldn't handle much. The cabinets armed with them were garbage.

Screenshot 2021-04-05 125429.jpg
 
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