Brian Roth
Well-known member
Does the summing have to be totally passive? Should be easier if you add an active summer.
Bri
Balanced Attenuator for Stereo Monitors + Subwoofer
- Thread starter Freddy G
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Bri
sure!
Brian Roth
Well-known member
Ok....here's an idea. Do you have a "spare" output from the Antelope? You could sum the monitor L/R signal into a mono sum. Downside....that would require six poles/decks on the attenuator switch...
balanced L, R and sub.
Bri
balanced L, R and sub.
Bri
The
This means you will end up with response problems - LF summing between 32Hz and 200Hz as well as phase errors/cancellations in that frequency range depending on sub position.
The summing to mono can easily be done with resistors after your attenuator switch so the attenuator sets overall level and incorporating a simple trim control after the merge to mono to set the mono sub level relative to the main speakers plus a passive LPF to set the cutoff frequency of the sub and two passive HPF’s for the main speakers. The sub’s performance range for +3 dB is 29 - 110Hz so the set-point for each crossover nominally should be at around 80Hz.
If your interface on the other hand has multiple outs you could set up a 2.1 output scenario in your DAW software as a preset with HP/LP filtering applied internally and route out through 3 outputs to a 3 way (6 bank) attenuator.
looking at the specs there is definitely a need for a crossover - the sub is rolled off internally at 200Hz by its internal LPF, the HD-1 response + 3dB is from 32Hz - 22KHz, + 1dB 40Hz - 20KHz, mono pass through loop is not filtered - it is hardwired - P6 of the manual.
This means you will end up with response problems - LF summing between 32Hz and 200Hz as well as phase errors/cancellations in that frequency range depending on sub position.
The summing to mono can easily be done with resistors after your attenuator switch so the attenuator sets overall level and incorporating a simple trim control after the merge to mono to set the mono sub level relative to the main speakers plus a passive LPF to set the cutoff frequency of the sub and two passive HPF’s for the main speakers. The sub’s performance range for +3 dB is 29 - 110Hz so the set-point for each crossover nominally should be at around 80Hz.
If your interface on the other hand has multiple outs you could set up a 2.1 output scenario in your DAW software as a preset with HP/LP filtering applied internally and route out through 3 outputs to a 3 way (6 bank) attenuator.
Brian Roth
Well-known member
Ignoring the probable need for some sort of crossover....
Two things "concern" me about passive summing after the stepped attenuator.
1. There will be at least a 6dB loss through the summer feeding the sub. That might be too low of a signal level for the sub to balance out with the mains. Unknown mystery.
2. The loading of the summer (plus the input impedance of the sub) must be calculated and accounted for when choosing the resistors of the attenuator....less of an issue.
Bri
Two things "concern" me about passive summing after the stepped attenuator.
1. There will be at least a 6dB loss through the summer feeding the sub. That might be too low of a signal level for the sub to balance out with the mains. Unknown mystery.
2. The loading of the summer (plus the input impedance of the sub) must be calculated and accounted for when choosing the resistors of the attenuator....less of an issue.
Bri
Easy enough to set the attenuation of the L/R to match the sub by using a fixed attenuator for each of the L/R feeds, after the variable attenuator. A simple trimpot would allow this or a stereo miniature pot, to allow calibration. Once set, forget.
Brian Roth
Well-known member
Point taken....and padding the L/R feeds MAY not even be needed IF the sub's level control would have to be reduced in a "lossless" summing situation to balance the system. "Unknown mystery"! <g>
Too bad the mains don't have a usable level pot on each.
Bri
Brian Roth
Well-known member
A CLASSIC case of gain structuring....<g>
Bri
Bri
Need to decide on the crossover types and setting frequency first to establish the level ratios between mains and sub post filter.
Found this for passive filters:
http://ethanwiner.com/gadgets.html
Active crossovers/filters do have the advantage of adjustable frequency and level so using them would solve the problem - there are plenty of DIY active LP & HP one (dual) chip filter schematics available but the problem there is they’re usually unbalanced - there are commercially available balanced sub controller/ crossover filters but they get expensive.
Found this for passive filters:
http://ethanwiner.com/gadgets.html
Active crossovers/filters do have the advantage of adjustable frequency and level so using them would solve the problem - there are plenty of DIY active LP & HP one (dual) chip filter schematics available but the problem there is they’re usually unbalanced - there are commercially available balanced sub controller/ crossover filters but they get expensive.
As this simple-seeming problem gets more complicated I have a suggestion that won’t add any extra gear after the interface. It is not what the OP specifically asked for, but would solve the problem in an elegant away at a similar cost (especially in time invested).
Ginger Audio makes software monitor controls that could do exactly what you want. I thing Sphere is the one with provisions for the sun, but Room might also offer solutions.
Your Daw feeds the software controller and the app feeds your interface. The app can bass manage and send the sub signal out a separate output on your interface, so out 1 = L, out 2=R, out 3 = mono sub. You can choose to apply crossovers or not and you can add more subs, too.
Plus the app provides level control, mono, L/R swap and polarity reverse, etc… it is a fully featured monitor control, but software.
I use the Sphere app in my studio with a Streamdeck to control it. I can monitor stereo (with a sub) or 7.1.4, or stereo headphones, plus talkback and cue outputs all via my existing interfaces. Works great.
The app install software routing busses, so your playback source feeds “Sphere bus 1-2” and the app receives that audio and then routes it to your usb interface.
Lots of other features, too. With checking out. Mac only at this point, but Win is in the works, I hear.
Don’t mean to waste time if an analog solution is the only way for you…
Ginger Audio makes software monitor controls that could do exactly what you want. I thing Sphere is the one with provisions for the sun, but Room might also offer solutions.
Your Daw feeds the software controller and the app feeds your interface. The app can bass manage and send the sub signal out a separate output on your interface, so out 1 = L, out 2=R, out 3 = mono sub. You can choose to apply crossovers or not and you can add more subs, too.
Plus the app provides level control, mono, L/R swap and polarity reverse, etc… it is a fully featured monitor control, but software.
I use the Sphere app in my studio with a Streamdeck to control it. I can monitor stereo (with a sub) or 7.1.4, or stereo headphones, plus talkback and cue outputs all via my existing interfaces. Works great.
The app install software routing busses, so your playback source feeds “Sphere bus 1-2” and the app receives that audio and then routes it to your usb interface.
Lots of other features, too. With checking out. Mac only at this point, but Win is in the works, I hear.
Don’t mean to waste time if an analog solution is the only way for you…
ART makes a respectable analog crossover - not Bryston, but 1/10 the cost. The CX311 has good features and does no harm.
Unfortunately this has a high and a low frequency output for each side crossover starting at 250 Hz going up to only 6KHz, along with the sub out (whose frequency control does roll bottom end off the main outs) - designed for 2 x 2 way + sub - wouldn’t work here. Also outputs are unbalanced, inputs balanced. Designed for high + low x 2 plus sub for FOH applications.
Edit: correction - the sub frequency control only rolls off top end from the sub channel, not LF from the L/R channels - they receive full program.
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Brian Roth
Well-known member
Thanks Bri,
My workflow is all analog front end (pres, comps, EQs etc.) then in the box for mixing. However I will go back out to analog hardware (EQs, comps, EMT plate) and then back in to digital land. But once that is done the mix is digital.
Seems strange they say that when in the UMS-1P manual they suggest using their VX-1 crossover (and two subs).
For the VX-1 I guess channel A for main and channel B for sub times two is their suggestion (it’s not really a true crossover but a stereo EQ with a master gain control). I would envisage one stereo unit for the main stereo pair and one that’s daisy chained to the original signal feeds then set to mono would work in your case - main pair and sub then have independent level control - but this means buying more gear.
Their module options for the sub from reading the datasheet do include a stereo to mono module - it’s not the RMS module but I can’t seem to find it listed anywhere - perhaps it’s worth asking Meyer if that is available. Resistive stereo to mono summing and passive level control is pretty easy without having to buy more stuff however.
If you want to try using the sub without any additional filter/crossover control you’ll first need to choose your placement and then do measurements to obtain a smooth response (this needs to be done anyway) altering the sub level until you get a level response.
The “crawl test” is one simple way of choosing the best location in a room - you place the sub at the listening position and literally crawl around the room at sub height and listen for the best sound location - no booming bass or dips in response to a low frequency sweep signal and music with plenty of LF content.
The issue I see here is that you need to have control over the sub level independently of and after your stepped attenuator which controls level to all 3 speakers - 2 mains and the sub - as you move the sub close to a wall the gain in LF SPL increases (up to 18dB of gain in a corner on the floor - page 7 of the manual) so your placement will alter the level requirement from the sub as you select a final location. Phase reversal is required if more than 5 feet from your main speakers (page 8 of the manual) but that comes down to testing.
Brian Roth
Well-known member
Sorry for the slow reply. Let me go back to an earlier question. Can you "afford" using a third analog output from the Antelope to create a sum (via your DAW) of the monitor L/R signal? That would add at least two more decks on the attenuator switch to handle the adjustment to the sub.
Speaking of which...what topology are you considering for the balanced stepped attenuator? The simplest would be a potentiometer (voltage divider) arrangement, but there are ladders, H, etc.
Bri
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Brian Roth
Well-known member
This may be a "Phantom Menace" <g>.....but I see another possible downside to passively create a sum post attenuator. It will add crosstalk between LR that MAY vary depending on the setting (and design) of the attenuator.
Bri
Bri
I recently had to sum L/R to mono in a studio for a powered mono sub and wanted no crosstalk - I used a 12KΩ resistor on each feed from hot and cold from each side with a 10KΩ load resistor across the junctions feeding the mono line input on the sub. This worked perfectly with no crosstalk at all.
Brian Roth
Well-known member
Like I mentioned, perhaps a Phantom Menace. What source impedance fed the summing resistors? I've been stewing about the possible implications of driving the summer from a VERY non-zero source impedance...ie, a passive attenuator as the source. Probably worrying about nothing...
Bri
Low impedance (I think 600Ω) main monitor outs from a Neve 51 series
