Balanced Attenuator for Stereo Monitors + Subwoofer

[Freddy G]

Burning brain cells...lol
Hey I'm grateful you are willing to help. I haven't been on this forum in quite some time, but I do remember you as one of the very smart guys!
I just learned about that module.....so I'll have to look into availability.

I have an Earthworks M30 Mic....i could do some test sweeps. Not something I know much about. Is there special software I would need?

 

[kags]

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

Which Antelope? Mine has a sub with a selectable low-pass filter. My Antelope has an integrated monitor volume control - which will keep the mains and sub(s) balanced.

 

[Freddy G]

Which Antelope? Mine has a sub with a selectable low-pass filter. My Antelope has an integrated monitor volume control - which will keep the mains and sub(s) balanced.

Orion

 

[kags]

Orion

Won’t that do monitor control? I think the Gen2 have that feature

 

[Freddy G]

Won’t that do monitor control? I think the Gen2 have that feature

Mine is the first version

 

[kags]

Gotcha. No monitor control, then?

I think Meyer put the loop through to allow dual subs, rather than bass management for the tops, but I could be wrong. I haven’t seen those in 20 years. Great monitors, though. Roger Nichols, RIP, was involved in their design, I believe.

 

[Freddy G]

No monitor control. Dual subs.....that makes some sense! Yeah....i really like the HD1s

 

[Brian Roth]

Burning brain cells...lol
Hey I'm grateful you are willing to help. I haven't been on this forum in quite some time, but I do remember you as one of the very smart guys!
I just learned about that module.....so I'll have to look into availability.

I have an Earthworks M30 Mic....i could do some test sweeps. Not something I know much about. Is there special software I would need?

re. "....smart guy..." got you fooled...lol. More of a smart ass here....<g>

Well, as an easy basic test, using your ears and a sine wave generator. Try running a sweep from, say, 500 Hz down to Thunder Hertz. Not scientific, but it can give some clues, like "Dammit....that door in my wall rattles at 92 Hz". There are a LOT of "moving parts" when setting up a new monitoring system and room. That's why I'm fretting about level balancing with the sub.

REW (Room EQ Wizard) seems to be a free software app that many folks use, and not only for checking room acoustics but as a general purpose test system. Never used it myself, but it has a lot of fans. Price is right, too!

Bri

 

[kags]

The basic test would be a slow sweep from like 30 Hz up to around 250 hz while listening from the mix position. See if the transition from the sub ti main speaker is smooth. In an untreated room there will be a roller coaster, but the xover region shouldn’t have any large dips or build-ups.

The Sam sweep with only the sub will show its freq response.

REW generates sweeps, among other things. So does www.onlinetonegenerator.com

 

[Brian Roth]

I would think there will be an "acoustic sum" happening if there isn't a crossover in the system as the bass adds between the sub and mains as they overlap.

But, I'm not an acoustics expert.....but it might sound FUN when you crank it up with some rock albums! lol

Bri

 

[Freddy G]

OK got it...I'll try it today. Thanks fellas!

 

[Freddy G]

Did the sine sweeps. Earthworks M30 mic where my head would be at mix position. I used my cleanest mic pre....Apogee Trak 2.
Yep...I see the roller coaster ! wow....

 

[Freddy G]

Just got this reply from Meyer....

"I generally don't use an electronic crossover between these devices and let them overlap normally, but some of this depends on the space and what I see on the FFT analyzer. (Any time you are adding and electronic crossover you are introducing a phase tradeoff somewhere else in the frequency band, so I don' use it unless really needed). I will say you will most likely need to polarity reverse the HD1's to play nicely with UMS and time them correctly at the acoustic crossover point."

 

[dmp]

Check out the monitor controller from KA electronics (member here) which uses receivers and unbalanced attenuators, then you can also see a nice example of how to build a mono out, using a THAT1240.
You could add filtering to the sub (LPF) and mains (HPF) within this design because of the buffering and line drivers on the output.

Before I built a fully featured monitor controller, I used a 4 deck attenuators and just fed the stereo signal through the sub, and that simpler option worked at the time.

 

[RCAguy]

"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

IMS-1P does not appear to HPF signal pass-thru to mains speakers, which may likely play more distorted very LF along with the SW. Best to use separate bass management.

 

[kags]

Just got this reply from Meyer....

"I generally don't use an electronic crossover between these devices and let them overlap normally, but some of this depends on the space and what I see on the FFT analyzer. (Any time you are adding and electronic crossover you are introducing a phase tradeoff somewhere else in the frequency band, so I don' use it unless really needed). I will say you will most likely need to polarity reverse the HD1's to play nicely with UMS and time them correctly at the acoustic crossover point."

That's surely a purist approach. Most people won't get the results they want without a crossover, unless the system is perfectly matched, which might be the case for the Meyers. One good reason to use a sub is that the sub can take the hard work of producing low freq away from the main speakers, so the mains have more headroom and lower distortion. This won't be the case without a sub. Another benefit of a crossover is to tailor the crossover point and volume of the sub vs. mains for a particular room, which can help smooth out the low freq range of the system.

The roller coaster of response is mostly due to the modal response of the room, especially if the room is not acoustically treated. The addition of a sub may worsen or improve the response depending on how it is integrated and where it is physically placed in the room. Also, remember that frequencies below about 80 Hz can't be localized, so the position of the sub won't affect the stereo image. If the sub plays above 80 Hz, and especially into the mid 100s, you will notice that the kick drum is coming from the sub and not from the main speaker phantom center.

Modern crossovers, even modestly priced ones, have very good phase and frequency response, so they will not adversely affect the sound of you speakers.

 

[Freddy G]

Thanks for all the replies and insights into potential issues. But back full circle...I just want to make a 2.1 stepped attenuator.

 

[kags]

If you want to go with VCAs, here is a scalable solutions:
https://sound-au.com/project141.htm

If you want passive attenuation, you're gonna need an expensive switch and several hours (days?) to calculate and build this thing. Here are some resources:
https://www.blackdahlia.com/html/tip_67.html

https://www.blore-ed.com/rotary-switches

Stepped volume attenuators for our SSL (quad but unbalanced) were over $500 for the parts a few years ago. We changed over to a stereo attenuator instead, and it was still around $300 for the part. The multi-deck switch came pre-loaded with resistors. Unfortunately, I don't have any info on where it came from, as I inherited the problem and solution from a previous tech...

 

[richiyobs]

Hd1 are great speakers.... One soundman in my country has them and used full range, no sub....
Try to find the old Ld1 processor ... You can adjust level, polarity and crossover out... 85Hz if i rember well.... Ld1 was used to drive old PA systems like Msl4, Hp650 and Ds2....
You could build a Little box with Summed L&R with any resistors to get the proper level for sub and 2 separate out for Hd1... No xover and no delay... But you could switch polarity in that Summed out to match the system if needed

 

[Freddy G]

If you want to go with VCAs, here is a scalable solutions:
https://sound-au.com/project141.htm

If you want passive attenuation, you're gonna need an expensive switch and several hours (days?) to calculate and build this thing. Here are some resources:
https://www.blackdahlia.com/html/tip_67.html

https://www.blore-ed.com/rotary-switches

Stepped volume attenuators for our SSL (quad but unbalanced) were over $500 for the parts a few years ago. We changed over to a stereo attenuator instead, and it was still around $300 for the part. The multi-deck switch came pre-loaded with resistors. Unfortunately, I don't have any info on where it came from, as I inherited the problem and solution from a previous tech...

I have all the parts to build multideck attenuators. Nice Elma 04 switch parts. I know how to make balanced stepped attenuators. All I'm asking is how to incorporate a summed signal to a sub.