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Re: Mono "flanking sub" [message #83001 is a reply to message #82998]

Thu, 14 July 2016 11:08

Wayne Parham
Messages: 18675
Registered: January 2001

Illuminati (33rd Degree)

Of course, the floor is the biggest reflector. But when I said "shading isn't an issue," what I meant was that subwoofer orientation won't cause much attenuation. Neither will acoustically small things like barstools and small furniture. Large padded chairs and sofas will attenuate the sound and walls definitely will, if they're between you and the subwoofer. So as long as the object in between you and the sub is acoustically small, it won't attenuate very much. While I personally would prefer having my flanking subs facing me, having them face a different direction isn't a deal-breaker.

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Re: Mono "flanking sub" [message #83004 is a reply to message #81624]

Thu, 14 July 2016 12:39

jonone
Messages: 67
Registered: October 2015

Viscount

Ok thanks Wayne, I might try and make them so there down firing for now but can be forward firing in the future when the children are bigger.

The speakers are close to the rear walls on brackets and the flanking subs will be directly below them, (the only space I have)so not in your recommended positions, so they should definitely help with the notch caused by the floor but maybe not much for the side or rear reflections? but having the mains so close to the rear should help with that reflection anyway?

Would you expect to see a improvement in the response by adding the second flanking sub over the single?

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Re: Mono "flanking sub" [message #83005 is a reply to message #83004]

Thu, 14 July 2016 12:46

Wayne Parham
Messages: 18675
Registered: January 2001

Illuminati (33rd Degree)

The best performance is when each main speaker has a flanking sub placed beside, below and behind two to three feet in each plane. The signal sent to each is a low-passed copy of what is sent to the mains, with a relatively mild (first or second order) slope, allowing content in the 100Hz-150Hz range to be presented to the subs. The knee frequency is usually around 100Hz, but with a gentle slope which provides significant energy blending with the mains through the octave above that.

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Re: Mono "flanking sub" [message #83007 is a reply to message #81624]

Thu, 14 July 2016 13:01

jonone
Messages: 67
Registered: October 2015

Viscount

But there should be somebenefit from my suggested setup?
At the moment I'm crossing over at 150hz with a Bessel filter.

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Re: Mono "flanking sub" [message #83008 is a reply to message #83007]

Thu, 14 July 2016 13:40

Wayne Parham
Messages: 18675
Registered: January 2001

Illuminati (33rd Degree)

I have realized over the last decade or so that it always helps to add bass sound sources, up to about four where we start to see diminishing returns. But even beyond that, there are improvements. I have also learned that placement matters most when there are fewer bass sound sources. In the midbass, we want helper woofers a.k.a flanking subs. For lower bass, we want distributed multisubs.

So there are many take-aways from this. For one thing, the idea of high-passing mains to crossover to a single sub is useful for reducing excursion on the mains, but it is counter-productive for bass smoothness. Where modal smoothing is concerned, it would be better to have the mains be more capable of good bass reproduction, and to blend the subwoofer with them. That provides several bass sound sources, from the mains and the sub(s).

That's where I see your approach. You have a single sub, but it's blended with the mains. That provides some modal smoothing. It also can probably help reduce self-interference notches from nearest boundaries, provided the summed signal matches the mains in the problem frequencies.

Self-interference and room modes are both boundary-related problems, by the way. So while they are different problems, they are related in both their general symptoms and by the suggested treatments. Not the same, but close.

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Re: Mono "flanking sub" [message #83009 is a reply to message #81624]

Thu, 14 July 2016 14:30

jonone
Messages: 67
Registered: October 2015

Viscount

Hi Wayne thanks for the detailed response again!
I have two subs now, the single "flanking sub" receiving a summed signal from the mains crossed over @150hz and a nearfield sub fed from the lfe out of my av amp with a 40hz crossover applied.
So eventually I will have three subs, one distributed ( nearfield ) fed from the lfe out put and stereo subs below the mains receiving a copied signal.

Can you explain by what you mean in saying "provided the summed signal matches the mains in the problem frequency's?"

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Re: Mono "flanking sub" [message #83010 is a reply to message #83009]

Thu, 14 July 2016 15:00

Wayne Parham
Messages: 18675
Registered: January 2001

Illuminati (33rd Degree)

Let's say your mains are 2.5 feet away from the wall behind them, creating a self-interference notch at 110Hz. If the flanking sub is somewhere closer to the back wall - say one foot away - and it is presented the exact same signal, then it will reduce the size of that notch considerably.

But let's say the two mains are phased in such a way that the summed signal is greatly reduced at 110Hz - like if they have some kind of flanger effect on a guitar or something that swaps phase - then the benefit of the summed flanking sub will be lost.

That's probably a rare scenario but it's what I was talking about when I said the summed signal must match the mains at the problem frequency.

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Re: Mono "flanking sub" [message #83011 is a reply to message #81624]

Thu, 14 July 2016 15:32

jonone
Messages: 67
Registered: October 2015

Viscount

Ok thanks again Wayne, I think I understand.

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Re: Mono "flanking sub" [message #83014 is a reply to message #81624]

Fri, 15 July 2016 03:27

jonone
Messages: 67
Registered: October 2015

Viscount

Wayne, am I right in thinking if a speaker is pushed very close to the rear wall the cancelation from the rear wall is reduced? ( but I take it people don't do this as it's not so good for imaging ?)

Also does the floor normally cause the biggest notch compared to the rear and side walls?

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Re: Mono "flanking sub" [message #83019 is a reply to message #83014]

Fri, 15 July 2016 08:36

Wayne Parham
Messages: 18675
Registered: January 2001

Illuminati (33rd Degree)

Each of the boundaries creates a self-interference notch. The wall behind the speakers makes a notch that is nearly fixed in frequency, because the path lengths between the direct sound and the reflection are nearly consistent even when the listener moves throughout the room. The floor bounce notch changes frequency as the listener moves because the path length difference changes much more.

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