Subwoofer connections, why single RCA/Jack input and output feed?

[canidoit]

Hi All,

I am considering getting a subwoofer to compliment my NS10s and noticed that some subwoofers only have a single RCA or TS socket for the input feed.

Are manufacturer expecting that the user will feed it a summed mono signal of left and right?

Not all music or films have the bass in the center, so I am considering using a left and right RCA to mono RCA adaptor so that it covers all bass being played on both left and right channels.

Will this produce unwanted artefacts when using the adaptor, such as phasing?

There are also subwoofers that have a single output socket to daisy chain another subwoofer. Does anyone know if the consensus for sub outs are summed mono or left or right channel only?

Does it matter if its left or right only?

Thank you.

 

[abbey road d enfer]

Hi All,

I am considering getting a subwoofer to compliment my NS10s and noticed that some subwoofers only have a single RCA or TS socket for the input feed.

Are manufacturer expecting that the user will feed it a summed mono signal of left and right?

No. They just expect their customers to feed the subwoofer with the desired signal.
Subwoofers with two (or more) inputs generally include a summing circuit that combines bass from both channels.

Not all music or films have the bass in the center, so I am considering using a left and right RCA to mono RCA adaptor so that it covers all bass being played on both left and right channels.

You would need something that combines the L and R signals into a mono sum without compromizing L-R separation.

Will this produce unwanted artefacts when using the adaptor, such as phasing?

A Y cable would just put everything in mono.

There are also subwoofers that have a single output socket to daisy chain another subwoofer. Does anyone know if the consensus for sub outs are summed mono or left or right channel only?

There's no consensus, in fact there are many possible choices. A 2.1 system sums L & R to feed the single sub, but a 7.2 system has L sub and R sub signals.

Does it matter if its left or right only?

It depends. For years, the concept was that bass being non directional, it didn't matter; since most programs had bass put in the center, it didn't make any difference. Today, it is recognized that there is a directional effect on bass when two or more subs are used. In that case, yes, distinction between L and R matters.

 

[canidoit]

Thanks Abbey Road Denfer!

 

[canidoit]

Hi Abbey,

Test 1
I tried using a Left and Right rca(into DA out) to stereo plug(trs) cable (into left channel(trs socket) on Mackie MRS10 sub) and the sub sounds muffled and comes in and out like its breathing and phasing. Not sure why this did not work?

Test 2
If I used Left and Right rca(into DA out) to single rca cable > ts 1/4 TS jack adaptor (into left channel(trs socket) on Mackie MRS10 sub) the sub works fine.

If I was to build my own XLR to left and right RCA cable, how would I wire it so that it sums mono properly so I can feed the sub with the XLR? Judging by the result of the first test, not sure how the wiring would be?

Would it be correct to wire the positives of the rca(inside connection) to the hot of the XLR(pin 2) and both the outside connection of the RCA(ground shield) to the ground of the XLR?

No. They just expect their customers to feed the subwoofer with the desired signal.
Subwoofers with two (or more) inputs generally include a summing circuit that combines bass from both channels.

You would need something that combines the L and R signals into a mono sum without compromizing L-R separation.

A Y cable would just put everything in mono.

There's no consensus, in fact there are many possible choices. A 2.1 system sums L & R to feed the single sub, but a 7.2 system has L sub and R sub signals.

It depends. For years, the concept was that bass being non directional, it didn't matter; since most programs had bass put in the center, it didn't make any difference. Today, it is recognized that there is a directional effect on bass when two or more subs are used. In that case, yes, distinction between L and R matters.

 

[abbey road d enfer]

Test 1
I tried using a Left and Right rca(into DA out) to stereo plug(trs) cable (into left channel(trs socket) on Mackie MRS10 sub) and the sub sounds muffled and comes in and out like its breathing and phasing. Not sure why this did not work?

Because it's atupid connection.

Test 2
If I used Left and Right rca(into DA out) to single rca cable > ts 1/4 TS jack adaptor (into left channel(trs socket) on Mackie MRS10 sub) the sub works fine.

Another stupid connection.

If I was to build my own XLR to left and right RCA cable, how would I wire it so that it sums mono properly so I can feed the sub with the XLR? Judging by the result of the first test, not sure how the wiring would be?

You can't sum in mono just by connecting two signals together.

Would it be correct to wire the positives of the rca(inside connection) to the hot of the XLR(pin 2) and both the outside connection of the RCA(ground shield) to the ground of the XLR?

No.
Aren't subwoofers supposed to come with some guide as to connecting them?
The diagram on page 6 of the owner's manual is clear enough.

 

[canidoit]

Because it's atupid connection.

Another stupid connection.

You can't sum in mono just by connecting two signals together.

No.
Aren't subwoofers supposed to come with some guide as to connecting them?
The diagram on page 6 of the owner's manual is clear enough.

You lost me here, you said the Y cable would work and it would turn it into mono, now you're telling me its a stupid connection?

The guide only applies to a stereo feed, not single signal feed to the sub which I am trying to do.

 

[abbey road d enfer]

You lost me here, you said the Y cable would work and it would turn it into mono, now you're telling me its a stupid connection?

Read again: "A Y cable would just put everything in mono."

The guide only applies to a stereo feed, not single signal feed to the sub which I am trying to do.

You are trying to do it without a proper mono source.
Why don't you use the recommended set-up?

 

[JohnRoberts]

Low bass signals are not very directional so stereo subs are not that useful.

Most add on subs purchased by consumers are used in home theater systems that had dedicated mono sub outputs.

For use in a proper hifi stereo system you would need active crossovers to separate the low bass from the rest of the audio band to avoid interactions between speakers. The two low bass signals could be summed to mono.

Passive mono sums require build out resistors so you don't overload output circuits driving the left with right and vice versa.

What is your application? You mention NS10 which were popular studio monitors.

JR

 

[abbey road d enfer]

Low bass signals are not very directional so stereo subs are not that useful.

Not for spatialization, but very useful for optimization of the listening area; properly arranged multiple subwoofers limit excitation of room modes.

 

[JohnRoberts]

I am speculating that the poster is interested in studio monitoring.

He probably wants two but should filter the full range material out of the feed to the sub, then sum L & R to use only one sub.

JR

 

[abbey road d enfer]

Well, the subwoofer he uses has filtered outputs for the main speakers. The mono sum + low pass is done inside it.

 

[JohnRoberts]

sounds like its all sorted then.... sorry to waste even more of your time

JR

 

[canidoit]

To clarify the purpose, I am using it with studio monitors as a subwoofer. The issue is, with my setup, I am only able to provide one feed(single XLR or single TRS) from my patchbay. This is why I am only feeding the subwoofer with one signal. The Mackie MRS10 sub does not state it accepts a mono signal like other subs, it just states balanced Left and Right to feed the sub.

I have built a Y cable using Left and Right RCA to one 6.5mm TS jack(both hot of RCA tied together to Tip of jack and both shield of RCA tied together to sleeve of jack) which I will feed to one side of a balanced(TRS/XLR) volume attenuator, which will then output it as an XLR that will feed the Left XLR input of my sub.

DA > RCA left and Right out > Left and Right RCA [Y cable] TS Jack > left TRS [Volume Attenuator] left XLR > XLR Patchbay > Left XLR Mackie MRS10 Sub

Hoping in this setup, that it has successfully converted my stereo signal from my DA converter to mono signal into my sub.

It seems to sound fine, I am hoping it is correct as I do not want to lose one sided bass frequencies because it did not sum it properly.

Any feedback would be appreciated.

Thank you all for your help!

 

[radardoug]

As has been pointed out to you, this sub includes the necessary passthrough signals to drive your monitors. Why dont you just RTFM?? And do it the way Mackie tells you to do it, with diagrams and everything? By the way, just using the bass from one channel is not a good idea.

 

[scott2000]

Hi Abbey,

Test 1
I tried using a Left and Right rca(into DA out) to stereo plug(trs) cable (into left channel(trs socket) on Mackie MRS10 sub) and the sub sounds muffled and comes in and out like its breathing and phasing. Not sure why this did not work?

Test 2
If I used Left and Right rca(into DA out) to single rca cable > ts 1/4 TS jack adaptor (into left channel(trs socket) on Mackie MRS10 sub) the sub works fine.

If I was to build my own XLR to left and right RCA cable, how would I wire it so that it sums mono properly so I can feed the sub with the XLR? Judging by the result of the first test, not sure how the wiring would be?

Would it be correct to wire the positives of the rca(inside connection) to the hot of the XLR(pin 2) and both the outside connection of the RCA(ground shield) to the ground of the XLR?

The terms are confusing a bit. Left and right rca into DA out? Do you mean you have a DAC that has Left and Right rca outputs?
Then it's mentioned there is only one output from patchbay? Confusing.
Are you saying you're trying to sum the left and right unbalanced outputs from the DAC to a balanced input on the patchbay, and then from the patchbay to a side of a stereo balanced attenuator? For a second it sounded like you could just use 2 unbalanced to balanced cables to feed your stereo attenuator then go to the sub in stereo but I got lost in the construction techniques and couldn't picture what the setup is.

 

[scott2000]

this sub includes the necessary passthrough signals to drive your monitors

It's not really a pass through? I think the frequency output is determined by the crossover point. Not sure that's always the goal in some cases?

 

[abbey road d enfer]

It's not really a pass through? I think the frequency output is determined by the crossover point. Not sure that's always the goal in some cases?

Actually it's a "high-passed pass-through", if it makes any sense.

 

[scott2000]

Actually it's a "high-passed pass-through", if it makes any sense.

Of course. Had a loss for words. Still not sure it's always going to be "preferred" in some cases .lol

 

[vintageampfixer]

Hi All,

I am considering getting a subwoofer to compliment my NS10s and noticed that some subwoofers only have a single RCA or TS socket for the input feed.

Are manufacturer expecting that the user will feed it a summed mono signal of left and right?

Not all music or films have the bass in the center, so I am considering using a left and right RCA to mono RCA adaptor so that it covers all bass being played on both left and right channels.

Will this produce unwanted artefacts when using the adaptor, such as phasing?

There are also subwoofers that have a single output socket to daisy chain another subwoofer. Does anyone know if the consensus for sub outs are summed mono or left or right channel only?

Does it matter if its left or right only?

Thank you.

Theoretically there's no stereo information below about 100Hz, thus none at sub-bass frequencies which are typically accepted as being below 60Hz, primarily because LF isn't terribly directional so with this in mind, it shouldn't matter whether the left or right channel or a sum of both is used. Most commercially available subs include a phase reversal switch and in most practical applications, I've round the "reverse" phase setting provides the clearest and deepest bass notes.

More than one sub is unusual in domestic setups - think 2.1, 5.1, 7.1 and so on - and (again, in my experience) even large scale venues tend to group bass bins together rather than attempting banks for left and right because distributed sub-bass can suffer noticeably from phase cancellation effects which of course vary by frequency according to the spacing.

While a sub that only works down to (say) 20Hz is unlikely to noticeably produce much below that frequency, LF reproduction is heavily dependent upon room acoustics, very significantly more so than higher "normal listening" frequencies so the room itself determines the lowest frequencies that are reproduced, not the frequency response of the sub. Positioning of the sub in the room is critical and as a general rule, placing it in the corner of the room, slightly away from the walls, will give best results although I'm sure others here may have different views based on empirical experiences and ultimately, it is about trying what works for you in your setup. I've read a few (BS) user manuals for subs, ranging from ultra-expensive, high-end units to bargain value ones ... the advice I like best reads something like this: "adjust the controls on your sub until you think it's the best sound"!

Finally, using a sub to extend the bass response in general listening is a quite different requirement to film sound effects. For Hi-Fi or studio monitoring, it's often best to use a signal derived from the main L & R loudspeaker outputs as a feed to the sub but to make the most of LFE, it's best to take a dedicated LFE output from your system and use that instead.

 

[abbey road d enfer]

Theoretically there's no stereo information below about 100Hz, thus none at sub-bass frequencies which are typically accepted as being below 60Hz, primarily because LF isn't terribly directional so with this in mind, it shouldn't matter whether the left or right channel or a sum of both is used. Most commercially available subs include a phase reversal switch and in most practical applications, I've round the "reverse" phase setting provides the clearest and deepest bass notes.

Have you actually measured the response with the sub out-of-phase?
Many prefer that position because it creates a dip at the cross-over frequency, so deep bass is not masked by low-mids/high bass.

More than one sub is unusual in domestic setups - think 2.1, 5.1, 7.1 and so on - and (again, in my experience) even large scale venues tend to group bass bins together rather than attempting banks for left and right because distributed sub-bass can suffer noticeably from phase cancellation effects which of course vary by frequency according to the spacing.

The .1 in x.1 means there's only one sub signal, but does not prevent using multiple subs fed from the same signal. The reason for using one sub only is cost. There are only benefits in using multiple subs, as long as they are sensibly installed, not for improving the soundscape, but for providing a better repartition of bass in the room.

the advice I like best reads something like this: "adjust the controls on your sub until you think it's the best sound"!

Ain't it often the case? How many times have I heard "if it sounds good, it's good"?
I like it when subjectivity (listening) meets objectivity (measurements), though.

Finally, using a sub to extend the bass response in general listening is a quite different requirement to film sound effects. For Hi-Fi or studio monitoring, it's often best to use a signal derived from the main L & R loudspeaker outputs as a feed to the sub

Agreed. The OP wants his sub to complement his monitors; the Mackie thing is perfectly adequate. Now I don't get why he wants to connect it to the patchbay...