Subwoofer Placement & Integration

[Satanica]

Hello, I've been looking to optimse my Legend Big Red speaker and SVS stereo sub-woofer setup.

From the 3-way DEQX the bass units have a crossover of 150Hz at 72 db.

I then run the SVS sub-woofer DSP Low and High Pass crossover at 80Hz-12db.

Using DEQX I measured that the Legend bass units are 3ms ahead of the SVS subs, so I added 3ms to the High Pass Delay of the SVS subs.

Below are the DEQX measurements; I'm a bit unhappy with the bass frequency suck-outs and thus the point of this thread.

 

I can change the SVS sub-woofer DSP Low and High Pass crossover points individually from 80Hz to higher or lower, the slope from 12db to 24db, or remove either one completely.

Below is a picture of what I have and what is where.

I can't move the main speakers as a projection screen drops in between them.

I can move the SVS sub-woofers a bit; I'm thinking of corner positioning them.

Any ideas are welcome.

 

 

Edited August 17, 2017 by Satanica

[Pieface]

I'm assuming the combined measurement of the sub/s and the L or R main shows the big bass suckouts still present?

 

My take on it would be to run the subs mono and optimise the subs first. Get the subs behaving as well as possible as a "unit" then integrate that "unit" with the mains. If you are crossing them at 80Hz I don't see a lot of merit in running them in stereo rather than mono.

 

That both subs taking a beating at ~40Hz and 80Hz means you are going to have to move one of them at least I reckon, to get one sub filling in the troughs of the other. Have you tried corner loading them in the front corners? You have the DEQX to tame any peaks easily. I'm guessing you have tried the simple things like flipping the phase on one of the subs?

 

 

[Satanica]

20 minutes ago, Pieface said:

I'm assuming the combined measurement of the sub/s and the L or R main shows the big bass suckouts still present?

 

My take on it would be to run the subs mono and optimise the subs first. Get the subs behaving as well as possible as a "unit" then integrate that "unit" with the mains. If you are crossing them at 80Hz I don't see a lot of merit in running them in stereo rather than mono.

 

That both subs taking a beating at ~40Hz and 80Hz means you are going to have to move one of them at least I reckon, to get one sub filling in the troughs of the other. Have you tried corner loading them in the front corners? You have the DEQX to tame any peaks easily. I'm guessing you have tried the simple things like flipping the phase on one of the subs?

 

 

 

Yes, at the moment they are running in stereo Left and Right channel not dual mono.

I understand that running mono could quite likely have some merit and be an improvement.

I think it's a good idea to continue to use the High Pass Delay function of the SVS DSP to time align the SVS subs to the Legend bass units.

I think I'd have to run the left and right bass outputs of the DEQX to one of the subs; then the left and right outputs of that sub into the left and right in of the other sub; then run the left and right outputs of the second sub singularly to the left and right inputs of the Legend bass units. I'm torn, it could quite likely improve LF suck-outs but create a whole lot of cable mess.

[Happy]

knowing you're prolly in the objectivist camp i wonder what prompted you to go stereo subs in the first place?

[Satanica]

1 minute ago, Happy said:

knowing you're prolly in the objectivist camp i wonder what prompted you to go stereo subs in the first place?

 

You mean over using them dual mono?

[Happy]

Just now, Satanica said:

 

You mean over using them dual mono?

 

yup. in my rudimentary imagination stereo subs make no sense since bass is non-directional but i wouldnt be surprised if i was wrong.

[Satanica]

1 minute ago, Happy said:

 

yup. in my rudimentary imagination stereo subs make no sense since bass is non-directional but i wouldnt be surprised if i was wrong.

 

Probably because I was too lazy to do anything other than daisy chain left and right and didn't and still don't (if I can help it) create a whole lot more cable mess.

[Happy]

fair enough

[Pieface]

14 minutes ago, Satanica said:

 

Yes, at the moment they are running in stereo Left and Right channel not dual mono.

I understand that running mono could quite likely have some merit and be an improvement.

I think it's a good idea to continue to use the High Pass Delay function of the SVS DSP to time align the SVS subs to the Legend bass units.

I think I'd have to run the left and right bass outputs of the DEQX to one of the subs; then the left and right outputs of that sub into the left and right in of the other sub; then run the left and right outputs of the second sub singularly to the left and right inputs of the Legend bass units. I'm torn, it could quite likely improve LF suck-outs but create a whole lot of cable mess.

 

If the DEQX lets you get the relative phase right i agree it is worthwhile to align the subs and the Big Reds.

 

The Legend bass units are active too? I was wondering how on earth you were needing to delay the subs. Normally you would need to delay the main speakers due to the signal delay through the subwoofer DSP.

 

How are you currently splitting the signals to feed the subs and the Big Red bass units?

Edited August 17, 2017 by Pieface

[aechmea]

The DEQX measures each item individually, so the peaks and troughs are not due to L sub interacting with R sub.  

 

The traces for L sub and R sub are essentially identical, so both subs are suffering the same 'problem' for the same reason.  My strong suspicion is that 2 bass sources at one end of the room are creating one large reflection off the rear wall (behind the head) which when combined with the direct sound is causing the reinforcements and cancellations = SBIR

 

As Pie suggested earlier, I think that you are going to have to move one sub, and that would be to move it to the other end of the room such that the path differences from walls to 'chair' are quite different for each.  Effectively one sub fills in the gaps in the other's response.

 

That's what I had to do.  

 

[Satanica]

1 minute ago, Pieface said:

 

If the DEQX lets you get the relative phase right i agree it is worthwhile to align the subs and the Big Reds.

 

The Legend bass units are active too? I was wondering how on earth you were needing to delay the subs. Normally you would need to delay the main speakers due to the signal delay through the subwoofer DSP.

 

How are you currently splitting the signals to feed the subs and the Big Red bass units?

 

Yeah, it's a bit complicated, maybe I should draw a picture.

The Big Reds are 3 way and a single DEQX is only capable of 3 way maximum; yes they are active.

So I've recently starting using the DSP in the SVS subs as a Low and High Pass Filter and they have a cool High Pass Delay feature that facilitates time alignment.

I'm not splitting the signal into the SVS subs and Big Reds bass units.

Each left and right out of the DEQX goes to the left and right SVS sub which have an out put for "daisy chaining".

So left SVS sub to left Big Red bass unit and right SVS sub to right Big Red bass unit.

[Satanica]

23 minutes ago, aechmea said:

The DEQX measures each item individually, so the peaks and troughs are not due to L sub interacting with R sub.  

 

The traces for L sub and R sub are essentially identical, so both subs are suffering the same 'problem' for the same reason.  My strong suspicion is that 2 bass sources at one end of the room are creating one large reflection off the rear wall (behind the head) which when combined with the direct sound is causing the reinforcements and cancellations = SBIR

 

As Pie suggested earlier, I think that you are going to have to move one sub, and that would be to move it to the other end of the room such that the path differences from walls to 'chair' are quite different for each.  Effectively one sub fills in the gaps in the other's response.

 

That's what I had to do.  

 

 

Yeah, that's the kind of thing I was afraid of. I don't really have a living room capable of having stuff other than the front wall.

[Pieface]

You could insert an active X-over, like a miniDSP(HD), into the chain on the Bass output of your DEQX. This can sum the L&R channels to mono for you subs, give you your crossover, delays and still send L&R information to the Big Red Bass Units. Not ideal admittedly but I am battling to see how you are going to deal with those big nulls in a stereo configuration. Even if you had some flexibility in placement I think you will find the nulls just "move around" rather than disappear. 

 

With a mono signal moving one of the subs to the corner might have a big impact on the summed response.

 

[Satanica]

10 minutes ago, Pieface said:

You could insert an active X-over, like a miniDSP(HD), into the chain on the Bass output of your DEQX. This can sum the L&R channels to mono for you subs, give you your crossover, delays and still send L&R information to the Big Red Bass Units. Not ideal admittedly but I am battling to see how you are going to deal with those big nulls in a stereo configuration. Even if you had some flexibility in placement I think you will find the nulls just "move around" rather than disappear. 

 

With a mono signal moving one of the subs to the corner might have a big impact on the summed response.

 

 

Something like this had crossed my mind. Could I get away with just the miniDSP instead of the (HD) version?

[Satanica]

A minidsp(HD) has been ordered. I'll report back with how it goes. 

[Satanica]

Up until a couple of days ago I was simply running the system with the L and R bass output of the DEQX into each L and R SVS sub with no DSP on each of the SVS subs.
Then from the output of each L and R sub into each L and R Legend bass unit.

 

A couple of days ago I thought I'd do something about improving this setup with some sophistication.

Thus setting an 80Hz Low and 80Hz High Pass filter and High Pass Delay on each of the L and R SVS subs to time align them to the Legend bass units.
I think this improved things somewhat in that previously without the low pass filter the SVS subs were contributing too much in the 80Hz to 150Hz area.

But I think the number and severity of bass suck-outs from nulls increased.
Listening this morning things sounded a bit "thin" compared to my previous setup of just a few days ago.

So this morning I changed the High Pass filter from 80Hz to 31.5 Hz for the Legend bass units.
I think Paul from Redspade has suggested this sort of action (a lower High Pass Filter than the Low Pass Filter) might improve things overall.
It certainly sounded like it brought back a lot of bass that seemingly went missing.
And the Legend bass units are not far from the corners of the room so provide some level of "corner loading";  they are much closer to the corners than the SVS subs.
I plan to remeasure this weekend.

[Satanica]

Well I moved the SVS sub-woofers into the front corners and changed the High Pass Filter to the Legend bass units back to 80Hz. After time aligning the Legend bass units to the SVS subs and doing another room measurement it certainly has helped. The null at 75Hz has been mostly filled in with there now just being a slight trough of -5db in that region, see below. I think I can add some EQ boost there now with effect. There's still a bit of a suck-out at 36Hz but nailing one out of two nulls ain't bad at this stage and arguably the more important one.

 

Interestingly SVS says to start with corner positioning.

"SVS recommends starting with corner placement. Corner placement excites all possible room modes, resulting in a denser standing wave pattern in the room. This reduces (but doesn’t eliminate) the potential to encounter nulls, which are acoustic cancellation points or ‘dead spots’ in the room."

https://www.svsound.com/blogs/svs/75365187-the-art-of-subwoofer-placement

 

 

 

[Satanica]

So, when the MiniDSP 2x4 HD arrives I'm thinking of a Linkwitz-Riley crossover of 80Hz at 48db per octave in stead of the current 80Hz at 12db per octave.

The main reason is I hoping to reduce some of the output from 80 to 110Hz of which an overabundance of can be seen above.

Thoughts?

[Pieface]

Can the Deqx give you a sweep on the left or right channel so you can see the whole channel operating together? Trying to predict what crossovers and EQ to implement when you can't see the over all response of each channel seems like you will be throwing darts in the dark to me.

 

It looks like you have sweeps for each speaker group (sub + BR Active L&R and Mid + Tweeter L&R) but not a "combined" sweep for the channel. Even with the time alignment of the Deqx it is fraught with risk to assume the bass units you have created and the mid-tweeter unit will combine their output predictably.

 

 

 

[Satanica]

15 minutes ago, Pieface said:

Can the Deqx give you a sweep on the left or right channel so you can see the whole channel operating together? Trying to predict what crossovers and EQ to implement when you can't see the over all response of each channel seems like you will be throwing darts in the dark to me.

 

It looks like you have sweeps for each speaker group (sub + BR Active L&R and Mid + Tweeter L&R) but not a "combined" sweep for the channel. Even with the time alignment of the Deqx it is fraught with risk to assume the bass units you have created and the mid-tweeter unit will combine their output predictably.

 

 

 

 

Good question, I'm not actually sure but I don't think so.

 

But seeing as though the crossover from bass to mid is at 150Hz at 72db per octave I don't think it's relevant to the true sub-woofer territory of 80Hz and less.

I don't think it's actually relevant up to about 110Hz looking at the readings.

OK, this is a bit of a generalisation but I think you know what I mean.

Edited August 23, 2017 by Satanica

[almikel]

Have you considered using the mini dsp for the top end xover instead?


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[Satanica]

3 minutes ago, almikel said:

Have you considered using the mini dsp for the top end xover instead?

Not at all.

[brabs]

Satanica, what are the dimensions of your room? I'm guessing roughly 4.5m wide?

I should be able t help with your 38 and 75 nulls hopefully

 

Edited September 14, 2017 by brabs

[Satanica]

6 minutes ago, brabs said:

Satanica, what are the dimensions of your room? I'm guessing roughly 4.5m wide?

I should be able t help with your 38 and 75 nulls hopefully

 

Approximately 4 by 7. I've managed to get rid of the 75 one by monoing the sub-woofers with a crossover of 80Hz-48db. Also the 38 one was more of a dip than a null and it seems to have responded reasonably well with some EQ. But what did you have in mind?

[brabs]

4m wide? This may not work as those modes resonate for a 4.5m

room, But If you can, try your subs along the subs along the front wall with the centre of the driver 1/4 in from the side walks EXACTLY.

your 38 should be improved and your 75 hopefully eliminated. The 1/4 points of the room are wavelength points of the 2nd order mode widthwise

the 75 could also be a phase issue. Try adjusting phase dial or adjust distance of the subs in the avr/processor. Let me know how it goes

always mark your spot so you can go back.

 

Edited September 14, 2017 by brabs