Balanced Attenuator for Stereo Monitors + Subwoofer

[Freddy G]

Hi!

I would like to build a stepped attenuator to control my monitors. I have lots of Elma A4 switch parts and I can figure out how to wire them for balanced stereo operation. But here's the thing....I have a subwoofer (balanced input as well) and I would like to if possible control it's level at the same time with the same switch. I don't know how to do that. I know I need 4 decks for balanced stereo. Do I need only one more deck for the sub? and how would I sum the L + R signal to mono just for the sub.

Thanks in advance!

Freddy

 

[Brian Roth]

Not enough info. Where in the signal chain is the crossover? With some (many?) subs the crossover is in the actual subwoofer electronics.

Bri

 

[Freddy G]

Not enough info. Where in the signal chain is the crossover? With some (many?) subs the crossover is in the actual subwoofer electronics.

Bri

Brian,
The monitors are Meyer Sound Hd1s and the sub is a Meyer UMS 1P. Just got them....i think the sub has a low pass filter

 

[Brian Roth]

I didn't spend much time searching the 'net for manuals of each model but what I found for the UMS 1P made no mention of a crossover. The limited info I found for the HD1s didn't seem to indicate inclusion of a crossover.

Perhaps you can post links for the manuals so we can sort through this. There is a chance you may require an external crossover.

Bri

 

[Freddy G]

Thanks Brian. I don't have manuals....i will call Meyer tomorrow and ask them.

 

[pvision]

"Integrating a built-in low-pass crossover while accepting a full-range signal, the UMS-1P’s input allows for simple daisy-chain signal distribution and eliminates the need for external crossovers."

Looks like the sub has a loop-through output without a crossover so you'd just feed a stereo signal to the sub and loop out to the speakers

 

[Brian Roth]

"Integrating a built-in low-pass crossover while accepting a full-range signal, the UMS-1P’s input allows for simple daisy-chain signal distribution and eliminates the need for external crossovers."

Looks like the sub has a loop-through output without a crossover so you'd just feed a stereo signal to the sub and loop out to the speakers

Interesting. I had found this manual last night:

https://cdn-docs.av-iq.com/instructions/Meyer Sound UMS-1P Operating Instructions.pdf

I'm probably blind, but saw no mention of the crossover. I'll "leave the ball in Meyer's court'. <g>

Bri

 

[Freddy G]

"Integrating a built-in low-pass crossover while accepting a full-range signal, the UMS-1P’s input allows for simple daisy-chain signal distribution and eliminates the need for external crossovers."

Looks like the sub has a loop-through output without a crossover so you'd just feed a stereo signal to the sub and loop out to the speakers

Thanks for digging that up pvision! i hadn't seen that datasheet... UMS-1P datasheet

Interesting. I had found this manual last night:

https://cdn-docs.av-iq.com/instructions/Meyer Sound UMS-1P Operating Instructions.pdf

I'm probably blind, but saw no mention of the crossover. I'll "leave the ball in Meyer's court'. <g>

Bri

Brian, that's the manual I found too last night. I called Meyer this morning, but I didn't get to speak to a tech. They took my number and said someone will call back.... still waiting for that call.....
But according to the datasheet then, I don't need a crossover....yeah!

pvision suggests I can send a stereo signal to the sub and loop out to the speakers. But it's just a mono loop through. In any case....looks like this clears some things up eh?

 

[Brian Roth]

@Freddy G I am still confused. The typical powered subwoofers I've seen have stereo line inputs as well as stereo line outs. An internal crossover takes the full range signal, feeds the bass info to the internal amps and sends the high passed signal to the output jacks. Hence, four audio connectors on the sub.

Perhaps the manual we both found is a counterfeit...lol.....but there aren't that many jacks on the sub according to the manual.

Bri

 

[Freddy G]

@Freddy G I am still confused. The typical powered subwoofers I've seen have stereo line inputs as well as stereo line outs. An internal crossover takes the full range signal, feeds the bass info to the internal amps and sends the high passed signal to the output jacks. Hence, four audio connectors on the sub.

Perhaps the manual we both found is a counterfeit...lol.....but there aren't that many jacks on the sub according to the manual.

Bri

yes, it seems it's a bit of a struggle to get clear info from Meyer! I did read on the datasheet that they have different input modules available....one of which does two inputs summed to mono.
Here's a pic of mine....if we trust that little diagram it looks like there is no high pass processing going on to the looped out.

 

[Brian Roth]

yes, it seems it's a bit of a struggle to get clear info from Meyer! I did read on the datasheet that they have different input modules available....one of which does two inputs summed to mono.
Here's a pic of mine....if we trust that little diagram it looks like there is no high pass processing going on to the looped out.

View attachment 127134

Your picture matches up with the manual we downloaded. The only other module the book described is some sort of "administration" gizmo. Perhaps that module included a crossover????

Bri

 

[Brian Roth]

I looked again.....nope, that "RMS" module doesn't have the required L/R output jacks.

Bri

 

[Freddy G]

Your picture matches up with the manual we downloaded. The only other module the book described is some sort of "administration" gizmo. Perhaps that module included a crossover????

Bri

I just ran some full range audio into the sub. It's low passing for sure....

 

[Brian Roth]

I just ran some full range audio into the sub. It's low passing for sure....

Could be just the inherent response of the internal amp plus the speakers. Still doesn't create a high-passed signal for the main speaker pair.

Bri

 

[Freddy G]

Could be just the inherent response of the internal amp plus the speakers. Still doesn't create a high-passed signal for the main speaker pair.

Bri

Right. But for what it's worth, I ran the sub and HD1s feeding them all full range and I will say I liked it! So at this point I'm happy with not worrying about it and just figuring out how to implement an attenuator for all three with feeding a L+R sum to the sub.

 

[Brian Roth]

Right. But for what it's worth, I ran the sub and HD1s feeding them all full range and I will say I liked it! So at this point I'm happy with not worrying about it and just figuring out how to implement an attenuator for all three with feeding a L+R sum to the sub.

OK...I won't belabor the point that the crossover is intended to keep any heavy LF from rattling the main stereo pair.

I need to find a manual for the main speakers. Do they have a level control pot like the subwoofer?

Bri

 

[Brian Roth]

OK....found a manual. Damn, just a +4/-10 switch. Makes it tricky to balance levels between the sub and mains.

I'm sure you want to keep the whole attenuator setup passive, but I'm seeing some "design issues". Breaking it down into "bite sizes".....

A passive LR summer for the sub will cause at least a 6 dB drop. Hence my question about level control pots on the main speakers.

In addition, adding a passive summer after a passive attenuator control...I see a real possibility of crosstalk between channels.

What is the signal source driving this system?

This might very well require an additional 2 poles on the attenuator switch....ie, create a LR sum before the attenuator.

Bri

 

[Freddy G]

Yes...i had a feeling the summing might be the fly in the ointment. The source is an Antelope interface

 

[Freddy G]

Regarding the levels.....i could tailor the sub's attenuation resistors for the offset if needed

 

[Brian Roth]

Oh what a tangled web we weave! <g> For some reason I need a mental challenge this week....lol!

OK, I retract the idea of complicating your stepped attenuator. Sum for the sub needs to happen post attenuator. Can you purchase the (unknown to me) Meyer summing module somewhere?

In this entire system you will need a method(s) to balance levels between the sub and mains without causing problems like crosstalk from the summer.

The Antelope should have a relative Low output impedance....which is useful! Problem as I see it is cascading a bunch of passive circuitry "post Antelope".

You mentioned already doing a "test listen" with what is at hand. I am not an acoustics guru and I don't know your control room acoustics. At his early part of the project, can you do any sort of acoustical frequency response sweeps with this "test setup" to see how well balanced the sub is with the mains?

I am overthinking....you can probably smell burning brain cells wafting all the way to Canada! <g>.

Bri