Home » Audio » Speaker » Mono "flanking sub"
Mono "flanking sub" [message #81624] Sat, 24 October 2015 05:50 Go to next message
jonone is currently offline  jonone
Messages: 67
Registered: October 2015
Viscount
Hi,
I'm using avi adm10 active monitors as mains, they are on wall brackets so very close to the wall, they have a summed mono subwoofer out which is a full range summed signal of the left and right channel, this is what I'm sending to my single "flanking sub" which is a down firing a acoustic elegance td15h+ Apollo in a 17.5" cube with its on plate amp, it's a very clean driver.

I have an Av amp which at the moment is set to "fronts large "and sending the mains the l/r signal, the flanking sub gets a summed version of this.

I'm waiting on ae to make my sub driver which will be a single Av15h with its own plate amp, I'm planing on running this nearfield with maybe a 60hz crossover, so in the end the av amp will send 60hz hp to the mains+ flanking sub and the 60hz lp to the nearfield sub for lfe etc.

I'm going to use a mini dsp for gain/ delay and eq, and also the crossover for "flanking sub " but at the moment I'm just using the 200hz roll off on the plate amp with good effect, the minidsp has bw / Lr and Bessel crossovers ,is bessel the one to use?

I'm using rew and and a umik mic to set this up with the mini dsp but it's all new/ a big learning curve, so your have to bare with me!

I know this is not a true flanking sub method! but a summed mono "midbass" driver covering -up to 200hz, seems to work from initial listening, I.e the stereo image inst obviously effected to my ears, and according to rew it's helped pull out some dips compared to the speakers on there own.
I can't really afford more drivers due to cost and space and divorce! Very Happy
What are people thoughts on what I'm doing?
Thanks,
Jon
Re: Mono "flanking sub" [message #81626 is a reply to message #81624] Sun, 25 October 2015 15:20 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 18787
Registered: January 2001
Illuminati (33rd Degree)

A flanking sub is useful for one main speaker. So you can have just one, but if you do, it can't help both speakers of stereo mains. It can only help one.

The main job of a flanking sub is to smooth the self-interference anomalies from nearest boundaries, e.g. the wall behind the speaker and the floor. It also helps smooth vertical modes and other room modes at the high end of the modal region.

But a setup that only contains a single sub will always suffer room mode problems. You can't make the room smooth with just one sub. I think the best you can hope for is to settle for a "sweet spot" by either placing the subwoofer physically close to the listening position or equalizing the response or both. This can make the one spot sound pretty good, but the rest of the room will suffer.

Re: Mono "flanking sub" [message #81627 is a reply to message #81626] Mon, 26 October 2015 08:14 Go to previous messageGo to next message
jonone is currently offline  jonone
Messages: 67
Registered: October 2015
Viscount
Thanks for replying Wayne!
So will a summed single flanking sub not help the floor and rear wall notch if it was placed between the stereo pair?

I don't know if it wasn't clear? But I'm planing on having one "flanking sub " by the stereo pair and one true sub 60hz and down nearfield.

If I run the mains large then the flanking sub won't be high passed, so would act as a second sub 60hz and down, but the mains will not have the benefit of being high passed. Do you think that would be more beneficial?
Re: Mono "flanking sub" [message #81628 is a reply to message #81627] Mon, 26 October 2015 08:44 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 18787
Registered: January 2001
Illuminati (33rd Degree)

My concern with this arrangement is not only with smoothing but with localization. Flanking subs necessarily have some low midrange content. So you'll be making some of your right and left signals panned towards the center, assuming the helper woofer is centered between the mains. Whether or not this is natural sounding, I don't know. Please report back after you've done it a while.

Re: Mono "flanking sub" [message #81629 is a reply to message #81624] Mon, 26 October 2015 12:05 Go to previous messageGo to next message
jonone is currently offline  jonone
Messages: 67
Registered: October 2015
Viscount
I was concerned as well, but surely vocals appear to come from the centre with a good stereo image?
Anyways mine is under the right speaker and I can't detect any blurring of the stereo image or a lopsided effect, but I don't claim to hove golden ears? Maybe the upper frequency's still steer the image?

Can you recommend a track or test that would show up any weird effect?

Thanks jon.
Re: Mono "flanking sub" [message #81630 is a reply to message #81624] Mon, 26 October 2015 15:06 Go to previous messageGo to next message
jonone is currently offline  jonone
Messages: 67
Registered: October 2015
Viscount
I have tried this quickly http://www.audiocheck.net/audiotests_ledr.php

Maybe it does pull it away from the l/r hannel slightly when the flanking sub is in line but it's pretty minimal, not really enough for me to worry about especially with the type of music I mainly listen too, but in a perfect world i agree stereo would be optimum.
I would like to see what others think if they summed a single flanking sub?
Re: Mono "flanking sub" [message #81631 is a reply to message #81630] Tue, 27 October 2015 13:23 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 18787
Registered: January 2001
Illuminati (33rd Degree)

That's good feedback. Interesting.

You're the only one I know that's done this, so it's useful to hear your impressions of that kind of setup.

Re: Mono "flanking sub" [message #81632 is a reply to message #81624] Tue, 27 October 2015 18:14 Go to previous messageGo to next message
johnnycamp5 is currently offline  johnnycamp5
Messages: 354
Registered: June 2015
Location: NJ
Grand Master
I am currently running a pair of 4pi's on my front wall.

Until I get the system in my basement, I have been using a single sub.

Initially, I had the sub located outside of either the left or right speaker, with my dac and amp centered.

With this configuration, I could hear/feel the somewhat lopsided bass response towards one side of the room (left or right), as Wayne has described.

I then centered the sub, (swapped it with the dac and amp) and the lopsided bass response went away.

Overall, bass response in my room sounds/measures relatively flat.
But I must say, I believe some of this improvement is a result of exstensive (compared to most) room treatments, not just to the centering of the sub.

In fact, before the room treatments in this room, I had a complete 70 hZ "null" (inaudible frequency), dead center in the room!

YMMV.
Re: Mono "flanking sub" [message #81634 is a reply to message #81632] Thu, 29 October 2015 04:10 Go to previous messageGo to next message
jonone is currently offline  jonone
Messages: 67
Registered: October 2015
Viscount
Thanks for the reply, can I ask what crossover point were you using? And if you had any eq applied?
You were not exciting a room mode less by placing the sub in the middle?
Jon
Re: Mono "flanking sub" [message #81635 is a reply to message #81624] Thu, 29 October 2015 11:24 Go to previous messageGo to previous message
johnnycamp5 is currently offline  johnnycamp5
Messages: 354
Registered: June 2015
Location: NJ
Grand Master
I use a plate amp that is attached to the sub itself.
I tend to prefer it set at 50hZ, which many find too low.
I believe the crossover (low pass 50 to 100hZ)slope is 12db.

I use no eq.

I come from a mindset/point of view where, you try to fix the room first (acoustical treatments in the form of broadband absorbers, bass/corner traps, Helmholtz absorners) instead of just throwing in multiple subs for correction.

Of course this can be quite tedious, and many view extensive room treatments as "killing ants with a hammer", since you can simply use multiple subs for correction, but I am set in my ways.

Things were not bad at all with the sub in the corner after the room treatments.
I centered it to make bass response in the room as even as possible throughout. In my opinion, there is no denying multiple subs work best, even in heavily treated rooms, but I simply do not have that option in my current listening room.
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