Questions about subwoofer in 2 channel system

[andyr]

2 hours ago, davewantsmoore said:

 

It's a really tough one between what you've said and AndyR.....  as if the artist really did make stereo bass, then I'd like to respect that (sometimes).

 

 

I suggest it's HT folk who do mono bass (with 2 subs) ... music folk like stereo bass.  

 

2 hours ago, davewantsmoore said:

 

Ultimately I almost always do what you do.... as in theory, doing what AndyR suggested is very likely to lead to worse results (if anything).

 

In what way does it deliver worse results by keeping stereo subs, Dave?

 

Andy

 

[DT999]

Thanks to everyone who has contributed to this thread, I have been learning a lot.

 

One thing that seems to be consistent is the view that 2 subs is better than 1. I got the SB 1000 at home and it is actually smaller than I was imagining and fits in well, but better still I think if I move things a little I have room for a second sub. Better still my wife didn't seem to object when I suggested it. 

 

So, I have now ordered a second sub. I still don't have the RCA cables yet as I ordered these from Bill through this Forum and they have not been made yet.

 

So a follow up question on how to connect the second sub. I initially ordered a pair of RCA cables to connect from my pre amp out to sub. Do I get a second pair to connect from RCA out of 1st sub to the second, or do I change my order to get different cables and connect L to one sub in and R to second. 

 

The subs will be 3m and 5m approx. from the amp, would it be detrimental to have rca's different lenghts if I connect one cable to each.

 

There has also been some discussion about using DSP, but mine is an analouge system and I don't have or know anything about DSP and will be using the Sub x-over to integrate these.

 

Thanks again

Derek

On 18/04/2021 at 6:44 PM, lemarquis said:

I'm sure you'll love it. Do you have any spare speaker cables?

No I don’t  have speaker cables, and I need 3m RCA cables to reach from my amp to where sub will be located.  I'll just have to wait a bit, hopefully not too long though before I can try it out. Have been listening today and can't help wonder what the sub will add. 

[almikel]

57 minutes ago, DT999 said:

The subs will be 3m and 5m approx. from the amp, would it be detrimental to have rca's different lenghts if I connect one cable to each.

no - that will be fine

 

59 minutes ago, DT999 said:

So a follow up question on how to connect the second sub. I initially ordered a pair of RCA cables to connect from my pre amp out to sub. Do I get a second pair to connect from RCA out of 1st sub to the second, or do I change my order to get different cables and connect L to one sub in and R to second. 

Either/or - IMO it won't make much difference.

 

If you connect 2 x RCAs from pre-amp to 1st sub - the sub will combine the signals internally to produce mono bass on that sub - which is fine IMO.

It sounds like your 1st sub has RCA line outs? Very handy - you could connect both of those to your 2nd sub.

This will have both subs playing mono bass, as the 2nd sub will also combine the signals to mono.

 

You could also connect each sub as @andyr suggests and have stereo subs...I would only recommend this approach if you have the subs symmetrical and aligned left and right with your main speakers.

 

If your subs are playing a mono signal, you can place them anywhere in the room to get the smoothest "in room" bass, without the restriction of needing to place them near your speakers, or oriented "left" and "right".

 

cheers,

Mike

 

[almikel]

18 hours ago, andyr said:

In what way does it deliver worse results by keeping stereo subs, Dave?

 

Hi Andy,

 

@davewantsmoore may have a different perspective, but my view is:

• 1 or more subs should be placed in the room for the smoothest "in room" bass response at the listening position - which is not necessarily close to your main speakers
• dual subs provide an opportunity for achieving smoother bass at the listening position than a single sub, and especially across a listening couch (it's nice to share great bass across the couch - and of course the HT guys want great bass across multiple rows of seats...which is very hard to achieve) 
• as above, the best positions for dual subs in the room for the smoothest "in room bass" may not be left and right subs in proximity with your main speakers - the best position could be centre front wall and centre rear wall, or lots of other sub positions that don't reconcile with "stereo" subs
• having gone around the mulberry bush many times with time alignment of subs/mains, and the flaws in using measurements such as the impulse response to achieve "time alignment" between subs and mains - I've come to the conclusion that tools such as Multi Sub Optimizer (MSO) is the best approach - which assumes a mono sub signal and operates in the frequency domain and applies EQ and delay to each sub to achieve the smoothest bass across multiple listening positions
• Toole uses the term "bass management" using mono bass for multiple subs to achieve the smoothest bass across multiple listening positions for HT, commenting that smooth bass across a wide area is impossible in our small rooms, and compromises are required to ensure great bass at the primary listening position, and OK bass in secondary listening positions
• Stereo subs removes the flexibility of placing your subs in the best positions, with appropriate EQ/delay to achieve the smoothest bass in your room 

I am coming from a theoretical perspective - I only run a single (mono) sub - but I've tuned EQ/delay across mains and sub to get the smoothest bass response across my listening couch.

I'm sure your setup sounds amazing.

 

cheers

Mike

 

[DT999]

3 hours ago, almikel said:

no - that will be fine

 

Either/or - IMO it won't make much difference.

 

If you connect 2 x RCAs from pre-amp to 1st sub - the sub will combine the signals internally to produce mono bass on that sub - which is fine IMO.

It sounds like your 1st sub has RCA line outs? Very handy - you could connect both of those to your 2nd sub.

This will have both subs playing mono bass, as the 2nd sub will also combine the signals to mono.

 

You could also connect each sub as @andyr suggests and have stereo subs...I would only recommend this approach if you have the subs symmetrical and aligned left and right with your main speakers.

 

If your subs are playing a mono signal, you can place them anywhere in the room to get the smoothest "in room" bass, without the restriction of needing to place them near your speakers, or oriented "left" and "right".

 

cheers,

Mike

 

This is the back of the subs, it has both line level in and out, so I am assuming I can run L&R RCA  to line in on sub 1 and RCA s out from sub 1 to sub 2? Or would it be better to run L to one and R to the other?

 

The position of the subs will be symmetrical and close to L&R mains as per attached picture. I will put the second sub where the guitar amp currently is near the R main.

 

[almikel]

1 hour ago, DT999 said:

This is the back of the subs, it has both line level in and out, so I am assuming I can run L&R RCA  to line in on sub 1 and RCA s out from sub 1 to sub 2? Or would it be better to run L to one and R to the other?

 

The position of the subs will be symmetrical and close to L&R mains as per attached picture. I will put the second sub where the guitar amp currently is near the R main.

 

 

IMO I would run both subs with 2 RCAs - left and right, and each sub will combine the signals to mono.

With that setup you could run left RCA to left sub and right RCA to right sub...but those sub positions aren't necessarily the best spots for your subs to achieve the smoothest "in room bass".

 

Mike

 

 

[davewantsmoore]

6 hours ago, almikel said:

You could also connect each sub as @andyr suggests and have stereo subs...I would only recommend this approach if you have the subs symmetrical and aligned left and right with your main speakers.

 

It really depends on where you have the lowpass filter set (and how steep it is).    The higher up it is, the more "aligned with the mains" the "stereo" subs need to be.

 

80Hz is very different from 160 or 320.

 

[davewantsmoore]

On 24/04/2021 at 7:12 PM, andyr said:

In what way does it deliver worse results by keeping stereo subs, Dave?

 

It depends ..... let's limit the discussion to well into subwoofer territory (<<80Hz) .....  if we talk about >> 100Hz, then things are less cut and dry.

 

Let's say we have stereo bass.....  Signal which is in one channel but not the other.

 

You cannot localise this.   There is no way for you to tell that it is coming from one speaker and not the other.

 

You are missing out on efficiency.   Two subwoofers could be reproducing the signal, vs. one.

 

The summing of two (different) bass sources in a room, will never be what the artist might expect .... as no two rooms are the same.   The point is that even if an artist was to construct a "stereo bass effect" in their recording, eg. by putting differing phased waves in either channel and intending the listener to experience the sum .... it wouldn't work.

 

There's really no benefit.... and only potential drawback.

 

This is why the recommendation is for << 80Hz to always be mixed to mono..... and this is why there is rarely any stereo bass to begin with (as the recommendation is mostly followed).

 

 

It would be much better to mix the channels to mono.... and send the same SW signal to both subwoofers.   That is on the proviso that it only contains <<80Hz (or <<100Hz) content....  ie. a relatively steep rolloff (lets say 12dB is not steep enough.... but 24dB/octave would be fine.... somewhere around 80 to 100).

 

 

 

In short, or said another way......  It unlikely you actually have stereo bass content.... and if you do, you probably don't want it.

[davewantsmoore]

2 hours ago, DT999 said:

This is the back of the subs, it has both line level in and out, so I am assuming I can run L&R RCA  to line in on sub 1 and RCA s out from sub 1 to sub 2?

 

Yes, that is the best way  (because you have the crossover knob set to 80hz or less)

[andyr]

1 hour ago, davewantsmoore said:

 

You are missing out on efficiency.   Two subwoofers could be reproducing the signal, vs. one.

 

 

Each sub has an 800w (into the 4 ohm coil of the sub driver) ... so I would suggest "efficiency" is not important.

 

1 hour ago, davewantsmoore said:

The summing of two (different) bass sources in a room, will never be what the artist might expect .... as no two rooms are the same.   The point is that even if an artist was to construct a "stereo bass effect" in their recording, eg. by putting differing phased waves in either channel and intending the listener to experience the sum .... it wouldn't work.

 

Why would the artist (or the recording engineer) do this?

 

The mics set up by the recording engineer who is recording the music session (note: not dinosaur footfalls!) , hopefully to 10Hz (even though my playback system doesn't deliver this) will probably record a slightly different signal in each channel - due to the acoustics of the recording space.  (No artificially engineered 'phase effects' needed.)

 

Why shouldn't these differences be reproduced in my living room - just like the woofers' signals are?

 

1 hour ago, davewantsmoore said:

It would be much better to mix the channels to mono.... and send the same SW signal to both subwoofers.   That is on the proviso that it only contains <<80Hz (or <<100Hz) content....  ie. a relatively steep rolloff (lets say 12dB is not steep enough.... but 24dB/octave would be fine.... somewhere around 80 to 100).

 

Why on earth would you allow the signal delivered to subs (with a 24dB slope) to be above 100Hz?  (I personally would not use 48dB slopes because of their negative effect on Group Delay.)

 

Andy

 

[davewantsmoore]

11 hours ago, andyr said:

Each sub has an 800w (into the 4 ohm coil of the sub driver) ... so I would suggest "efficiency" is not important.

Big call.

 

11 hours ago, andyr said:

will probably record a slightly different signal in each channel

Will they?

 

If the recording space has even bass reproduction.... then no, not in any way which is even modestly significant.

 

If the recording space has lumpy bass reproduction .... then potentially it will be very significant difference.... which is a contrived example of the "intentional inter-channel differences" (ie. "artificial")....   So the recording artist has captured their uneven modal distribution in the recording (this is a bad idea for them to do that) ...... but you cannot play that back in your room, in a way which matches what they recorded - so there is no point to this rabbit hole.

 

 

11 hours ago, andyr said:

- due to the acoustics of the recording space.  (No artificially engineered 'phase effects' needed.)

 

Why shouldn't these differences be reproduced in my living room - just like the woofers' signals are?

Because you can't.

 

Your living room dominates the reprodution to such an extent, that even if there was some difference encoded in the recording ..... when you play it back it your room, it is completely different to what was captured.

 

 

That being said.... due to the same effects, what you play back is unlikely to be substantially different (to the mono sum), aside from some specific cases.

 

The more extreme the stereo in the recording.... the more likely you are to be playing back something substantially different (but this is correlated with how different your room size is [in wavelengths] from the reocrding space)

 

Loss of efficiency (usually very important)

 

Cannot EQ, and/or position subwoofers for optimal summed response (without giving up on optimising "stereo"... .ie. you have to optimise one or the other).

 

 

11 hours ago, andyr said:

Why on earth

 

 

11 hours ago, andyr said:

would you allow the signal delivered to subs (with a 24dB slope) to be above 100Hz? 

 

Sometimes... when people have positions their "subwoofer" symmetrically and near their main speakers "in stereo" ......  the run their subwoofers up higher than the typical 80 to 100Hz type of cut off.

 

In that case..... then a lot of what I'm saying doesn't apply in the same way.... and you would want to keep the stereo signal.

 

Ideally, through, you would/could keep the stereo content above ~100Hz, and mix to mono below.... all through the "symmetrically placed woofers"..... but that's starting to complicate the discussion.

 

11 hours ago, andyr said:

I personally would not use 48dB slopes because of their negative effect on Group Delay.

 

You could (should) use filters which have a resulting phase which is flat (ie. zero "group delay").

 

Yes... I don't see a huge point in filters that steep.  ~24dB seems like enough, usually..... although it depends and is hard to generalise.   I wouldn't typically use much less though, it's not enough (but again, there are exceptions).

[andyr]

 

8 hours ago, davewantsmoore said:

 

 

 

You could (should) use filters which have a resulting phase which is flat (ie. zero "group delay").

 

 

 

AIUI, filters which deliver flat phase are FIR filters.  If that is correct ... I would need a different DSP setup to what I have - as a miniDSP nano DIGI 2x8 can only deal with IIR filters.

 

Andy

 

Edited April 26, 2021 by andyr

[Cloth Ears]

19 hours ago, davewantsmoore said:

 

It depends ..... let's limit the discussion to well into subwoofer territory (<<80Hz) .....  if we talk about >> 100Hz, then things are less cut and dry.

 

Let's say we have stereo bass.....  Signal which is in one channel but not the other.

 

You cannot localise this.   There is no way for you to tell that it is coming from one speaker and not the other.

 

You are missing out on efficiency.   Two subwoofers could be reproducing the signal, vs. one.

 

The summing of two (different) bass sources in a room, will never be what the artist might expect .... as no two rooms are the same.   The point is that even if an artist was to construct a "stereo bass effect" in their recording, eg. by putting differing phased waves in either channel and intending the listener to experience the sum .... it wouldn't work.

 

There's really no benefit.... and only potential drawback.

 

This is why the recommendation is for << 80Hz to always be mixed to mono..... and this is why there is rarely any stereo bass to begin with (as the recommendation is mostly followed).

 

 

It would be much better to mix the channels to mono.... and send the same SW signal to both subwoofers.   That is on the proviso that it only contains <<80Hz (or <<100Hz) content....  ie. a relatively steep rolloff (lets say 12dB is not steep enough.... but 24dB/octave would be fine.... somewhere around 80 to 100).

 

 

 

In short, or said another way......  It unlikely you actually have stereo bass content.... and if you do, you probably don't want it.

Actually, you can localise some low bass sounds. A kick-drum, for example, is quite easy to work out where it's coming from, as the pressure on your chest feels it even if your ears cannot. My sub boxes are crossed at 50Hz (12dB/octave, I think - I'll have to check the NXT manual). But the same was true when using a 24dB/octave one.

 

But for sounds that are not concussive, like organ, bass (not 'slap' bass) guitar or double bass, it's a lot harder. often it's only the associate noise (fingers on strings, or the scrape of the bow) that give away the location. But turning off the main speaker amps give you an indication of whether the sounds can be localised or not.

[davewantsmoore]

3 hours ago, Cloth Ears said:

Actually, you can localise some low bass sounds.

 

Nope.

 

If you (really) filter out everything which is not << 80hz... then it cannot be localised.

 

Importantly... this requires filtering out harmonic distortion.... which is often (usually!) quite high in subwoofers.

 

 

3 hours ago, Cloth Ears said:

often it's only the associate noise (fingers on strings, or the scrape of the bow) that give away the location.

 

Yes... because these contain higher frequencies ... which is what you're localising.

[Cloth Ears]

13 hours ago, davewantsmoore said:

 

Nope.

 

If you (really) filter out everything which is not << 80hz... then it cannot be localised.

 

Importantly... this requires filtering out harmonic distortion.... which is often (usually!) quite high in subwoofers.

 

 

 

Yes... because these contain higher frequencies ... which is what you're localising.

"But turning off the main speaker amps give you an indication of whether the sounds can be localised or not. "

 

And an easy way to confirm if your ears/body are telling you fibs or not is to hold a large (width by height, not thickness) hardcover book vertically in front of your face. That increases the distance between your ears and will allow you to work out if you can 'hear' the difference or whether you were just fooling yourself.

Edited April 26, 2021 by Cloth Ears

[davewantsmoore]

4 hours ago, Cloth Ears said:

"But turning off the main speaker amps give you an indication of whether the sounds can be localised or not. "

 

Yes... doing this will help you understand if you can "localise" your subwoofers or not.

 

If you can... it is becuase they are loud enough above ~100Hz.

[Cloth Ears]

39 minutes ago, davewantsmoore said:

 

Yes... doing this will help you understand if you can "localise" your subwoofers or not.

 

If you can... it is becuase they are loud enough above ~100Hz.

I see. So you have made a decision and will not be swayed by someone else who hears differently. Sounds familiar. I will not mention my experience again.

[andyr]

22 hours ago, Cloth Ears said:

 

But for sounds that are not concussive, like organ, bass (not 'slap' bass) guitar or double bass, it's a lot harder. often it's only the associate noise (fingers on strings, or the scrape of the bow) that give away the location.

 

That makes sense (percussive sounds - eg. kick drums - are able to be localised easier than non-concussive LF sounds).  

 

22 hours ago, Cloth Ears said:

 

But turning off the main speaker amps give you an indication of whether the sounds can be localised or not.

 

 

I just tried this experiment.  My Maggie amps were switched off - only the 2 subs were on.  Sub roll-off is 24dB @ 80Hz ... source was ABC 'Classic'.

 

It wasn't particularly bass-heavy music but what I could hear ... appeared to be coming from the centre, between the subs.  What surprised me was that I could (just!) hear the male presenter (Joel Carnegie)'s voice coming from the subs!  He hasn't got a deep speaking voice so it shows that a 24dB @ 80Hz filter probably allows you to hear 150Hz!

 

19 hours ago, davewantsmoore said:

 

Importantly... this requires filtering out harmonic distortion.... which is often (usually!) quite high in subwoofers.

 

 

Why would subs display a 'quite high' level of HD?

 

Andy

 

[sir sanders zingmore]

3 hours ago, andyr said:

That makes sense (percussive sounds - eg. kick drums - are able to be localised easier than non-concussive LF sounds).  

 

 

Not sure how accurate this chart is but it implies that the "attack" part of a kick-drum sound is way above anything your subs should be handling 

 

http://www.guitarbuilding.org/wp-content/uploads/2014/06/Instrument-Sound-EQ-Chart.pdf

[Cloth Ears]

3 hours ago, andyr said:

 

That makes sense (percussive sounds - eg. kick drums - are able to be localised easier than non-concussive LF sounds).  

 

 

I just tried this experiment.  My Maggie amps were switched off - only the 2 subs were on.  Sub roll-off is 24dB @ 80Hz ... source was ABC 'Classic'.

 

It wasn't particularly bass-heavy music but what I could hear ... appeared to be coming from the centre, between the subs.  What surprised me was that I could (just!) hear the male presenter (Joel Carnegie)'s voice coming from the subs!  He hasn't got a deep speaking voice so it shows that a 24dB @ 80Hz filter probably allows you to hear 150Hz!

 

 

Why would subs display a 'quite high' level of HD?

 

Andy

 

One of the things I was omitting was, of course, that my subs were crossed at 50Hz @24dB/octave. Which means, of course, that there's still energy at 100Hz that could quite possibly be picked up by ear. Not so much the attack part of a drum, the finger-pluck on a 5-string bass guitar 'B' string or the hammer hitting the bottom 'A' on a piano - maybe there's some other harmonic at work there?

 

Now that I'm using a crossover that's better suited to my set-up (the subs are now crossed at 12dB/octave) this would not apply.

 

But, if you try using a simple sine wave at 50Hz, alternating in the left and right channel (or even LCR), it does not sound like it's coming from the same place at each note.

[davewantsmoore]

12 minutes ago, Cloth Ears said:

One of the things I was omitting was, of course, that my subs were crossed at 50Hz @24dB/octave. Which means, of course, that there's still energy at 100Hz that could quite possibly be picked up by ear.

 

I doubt that...  maybe?!

 

100Hz, is barely localisable ..... and at 100Hz, the subwoofer will be drowned out by the +24dB (nearly 1000x louder) main speaker(s).

 

... but harmonic distortion from your subwoofer could be much louder than -24dB below the signal..... and extend up higher in frequency.... and this would be very audible.

 

12 minutes ago, Cloth Ears said:

Now that I'm using a crossover that's better suited to my set-up (the subs are now crossed at 12dB/octave) this would not apply.

 

Even at this not steep filter... .I'd still say distortion is the more likely culprit until ruled out..... as your turn over frequency is quite low (50Hz).

 

12 minutes ago, Cloth Ears said:

But, if you try using a simple sine wave at 50Hz, alternating in the left and right channel (or even LCR), it does not sound like it's coming from the same place at each note.

 

Yes.... distortion, I'd say.

 

You're getting 100Hz, 150Hz, 200Hz, etc.... and these can often be only a matter to 10 or 20dB below the intended 50Hz tone.

 

I'd have to actually measure what was coming out to be sure of anything, of course..... but what I am sure of is that frequencies below around 100Hz or simply not localisable..... unless something like distortion, or rattles, or whatever gives it away.

[Batty]

DIY subbie, just changed the plate amp from a Wharfedale 50 watt to a 250 watt, the Wharfedale had crossover up to 200 Hz the new (to me) amp max is 100Hz.

 

Although the new amp has to be almost at zero gain to work with my 8 watt ACA, the SQ is so much better and probably crossing over around 60 Hz.

Speakers are LK1.