Summing quad outputs for subwoofers.

[audiomaster]

I need to sum the 4 discrete line outputs of my Bose 4401 preamp to feed the 2 sub inputs on the discrete line inputs on my Marantz receiver. How do I do this without losing separation between them? I get the low freq but also some mids which I don't want. The Marantz doesn't seem to be able to fix this for the discrete LF analog inputs
Is there a simple passive circuit that can do this and if so, how much gain would I lose?
Or is there some simple active box that can do this at low cost. I know I could use a 4ch mixer and mix down the 4ch to a L and R and then use an electronic crossover but that seems complicated and expensive. I'd like to feed everything below about 50 Hz to the sub inputs for my 18" Gauss 12 cu ft sub cabinets.

Also how important is it to sum all four outputs, or should I just be using the front two outputs?

 

[par4ken]

You can find inline low pass filters here.
Parts Express, crossover rca
You could try it out via some RCA splitter cables.
The mixer idea sounds good, it would better isolate the four outputs. It might also work OK without the mixer.

Many quad mixes carry a lot of bass in the rear so it would be good to sum all of the outputs. You might get away with the front only if you listen more to newer 5.1 mixes which are usually bass shy in the rear.

 

[audiomaster]

I got two of the 50hz low pass and inserted them in the front followed by a Y cord to the sub input which helped a good bit. They don't seem to reduce separation by much if any. I don't know why Marantz has stereo outputs for subs but not stereo inputs?
They do reduce the level. I can raise that on my Crown sub amp, but then it's too loud for operation from other sourced. My Marantz doesn't have separate level controls for each of it's 7.1 analog inputs. I guess I could insert 10dB pads in the 4 main channels. May try that but would reduce signal to noise.

 

[par4ken]

As an avid DIY'er I would build an op-amp based mixer to combine the signals and then run through one of the low pass filters. The similar/same idea that you mentioned originally to use a mixer to combine the four signals and then low pass filter. You could filter first but then you need more filters (four). Alternately the filter itself could be designed into the mixer circuit itself.

 

[audiomaster]

Is there a schematic for such a thing somewhere? And for a power supply for it?

 

[jimfisheye]

The pure analog solution is a mixing board and crossover eq's. Or building those circuits DIY. There isn't just some simple Y-cable solution.

If you serve the audio from a computer you can dial up any speaker management you need and it can all be perfect spec no compromise. That requires digital sources and an audio interface setup. Or your own original analog rips with said system.

Not many in-between solutions. There are powered subwoofers sold where the preamp input stage includes crossover eq and a post eq output for the high passed mains output. Not a solution if you have your own passive speakers and amps already. It's either analog preamps and crossovers and chasing ground loops and hum through that or going digital. Extreme audiophile quality is easier to hit with a digital system IMHO.

 

[par4ken]

Is there a schematic for such a thing somewhere? And for a power supply for it?

Circuits abound! Here is a link to to Elliott Sound Products. You can simply follow the design yourself building up on perfboard or purchase the PC board. A lot of good information on DIY projects provided on this site.

Note on the mixer circuit it shows only L & R inputs connected via 33K resistors, you can add more resistors connected to that same summing point to add Lb and Rb as well.

Active Sub-Woofer and Controller

 

[audiomaster]

The pure analog solution is a mixing board and crossover eq's. Or building those circuits DIY. There isn't just some simple Y-cable solution.

If you serve the audio from a computer you can dial up any speaker management you need and it can all be perfect spec no compromise. That requires digital sources and an audio interface setup. Or your own original analog rips with said system.

Not many in-between solutions. There are powered subwoofers sold where the preamp input stage includes crossover eq and a post eq output for the high passed mains output. Not a solution if you have your own passive speakers and amps already. It's either analog preamps and crossovers and chasing ground loops and hum through that or going digital. Extreme audiophile quality is easier to hit with a digital system IMHO.

Thanks for the info. I'm not going digital. My PC is at the opposite end of the house from my theater, about 50 ft.
And digitizing my record collection is not,at age 77, something I want to comprehend. I did buy a Zoom L12 mixer/recorder which, I think, is going to let me record some things on to SD cards for my car or PC, maybe even in quad, as soon as I figure out how to use it. It can record 12 channels and output up to 5 separate mixes in analog feeds.
At my age, I have lost my hearing above 7-8Khz so not sure "audiophile" matters so much.

 

[audiomaster]

Circuits abound! Here is a link to to Elliott Sound Products. You can simply follow the design yourself building up on perfboard or purchase the PC board. A lot of good information on DIY projects provided on this site.

Note on the mixer circuit it shows only L & R inputs connected via 33K resistors, you can add more resistors connected to that same summing point to add Lb and Rb as well.

Active Sub-Woofer and Controller

Looks interesting, might be a DYI project as I probably have most of the parts in my parts collection. Thanks.

 

[surroundophile]

Another possible solution would be to see if you can find on eBay an Outlaw ICBM 1 Bass Management unit. It was made for DVD & SACD players when they first came out as they had no internal bass management like they do now.

 

[MidiMagic]

There are some caveats when dealing with matrix recordings:

- Those made for phonograph records have to have the deep bass in mono (horizontal groove modulation) so a single mono sub takeoff before the decoder works.
- If you have a subwoofer with a stereo input, feed it with the signal taken before the decoder (what I have).
- The bass may be at different phases in different channels after matrix decoding. Summing the matrix outputs may cause cancellation.

 

[kfbkfb]

https://www.amazon.com/BESTISAN-Subwoofer-Integration-Receivers-SW65C/dp/B09H26JSFH
It occurred to me that using (for quad) 4 bookshelf speakers + 4 of the above small subwoofers would be a low cost way to deal with the bass phase differences in the 4 channels (no electrical cancellation due to a single subwoofer).

Has anyone tried using 4 bookshelf speakers + 4 small subwoofers?


Kirk Bayne

 

[par4ken]

There are some caveats when dealing with matrix recordings:

- Those made for phonograph records have to have the deep bass in mono (horizontal groove modulation) so a single mono sub takeoff before the decoder works.
- If you have a subwoofer with a stereo input, feed it with the signal taken before the decoder (what I have).
- The bass may be at different phases in different channels after matrix decoding. Summing the matrix outputs may cause cancellation.

Yes, taking that into consideration the best way for matrix might be to take the bass from the L and R decoder input signals. That still leaves the special case of discrete recordings with bass in the rear.

Provision would have to be made to change the subwoofer input depending on source material.

https://www.amazon.com/BESTISAN-Subwoofer-Integration-Receivers-SW65C/dp/B09H26JSFH
It occurred to me that using (for quad) 4 bookshelf speakers + 4 of the above small subwoofers would be a low cost way to deal with the bass phase differences in the 4 channels (no electrical cancellation due to a single subwoofer).

Has anyone tried using 4 bookshelf speakers + 4 small subwoofers?


Kirk Bayne

What you are suggesting is really just bi-amping. That is basically what I do but with large speakers all around. Removing the bass from the main audio signal is a great way to reduce distortion. Widely used in automotive sound systems but not so much at home.

From experience it's best to keep the woofers close to the mid/high speakers. Placing them too far away just does not sound right. Less of a problem I suppose the lower your crossover frequency is.

 

[MidiMagic]

Yes, taking that into consideration the best way for matrix might be to take the bass from the L and R decoder input signals. That still leaves the special case of discrete recordings with bass in the rear.

In the CD-4 recording, the undemodulated L and R channels should have all of the bass.

Sum the lf and lb to get the L bass. Sum the rf and rb to get the R bass.