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Cardioid Subs?
Cardioid Subs?
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Old 6th December 2018, 04:31 AM   #1
Cableaddict is offline Cableaddict
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Default Cardioid Subs?

I'm surprised that a search on this topic turned up nothing.

I always thought that you needed three subs to do this, but I guess I was wrong. After reading some info from Presonus on how they do it with only 2 subs, it's starting to sound like something to consider. It seems simple enough, using plate amps with DSP. (Or a processor with enough outputs)

Supposedly, all you have to do is put 2 of their powered subs side-by-side, face one backwards, then set one for out of phase, plus adding their pre-set delay to it. (Delay equal to the depth of the cabinet.)

(There's another method also, which supposedly is more effective, but it requires twice the stage depth in front of the band / DJ, so not something I'm interested in.)

So how come this hasn't been discussed to death on this forum?
--------------------------

I have one primary concern with doing this, other than the obvious need to invest in new amps or whatever:

* Does it sacrifice any dB out front?
- Or more importantly, does it require more amperage to maintain the SAME dB out front that you had when both subs were omni?

It seems to me that all that phase-cancellation could possibly do this.
Or not:
If the direct-radiating power stays the same, but all you lose out front is the stuff bouncing off the back-of-stage wall, with all it's phase smear, then I could live with that.

Does anyone have a definitive answer?

Thoughts in general?

--------------------

FWIW, there is one other possible downside, for me at least: I always use earbuds for monitoring, as does my entire band. Most affordable earbuds don't have a lot of bottom, and even if they do, it's not bottom that you feel in your body, viscerally. I really LIKE having a lot of LF on stage!

So... I dunno if this would be a good thing or not.

Last edited by Cableaddict; 6th December 2018 at 04:35 AM.
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Old 6th December 2018, 08:44 AM   #2
TBTL is offline TBTL  Germany
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Cardioid subwoofers are not useful below the Schröder frequency as you are listening to room modes, so directivity loses its meaning. Neither can you speak of sound bouncing off the back-of-stage wall. Think of a room of a box that supports standing waves. What you hear depends on to which modes your ears couple and by how much these modes are energized by the subwoofer.


Yes it sacrifices output. You can calculate the loss from the spacing between the drivers and the frequency. You lose 6 dB / octave below some frequency that depends on the spacing. At home audio you easily lose 10 dB. At pro audio the frequencies are higher and spacing is larger, so they do not lose that much. Pro audio 'rooms' also are larger (or the event is outdoor) so the subwoofers play above the Schröder frequency, where directivity matters.

Last edited by TBTL; 6th December 2018 at 08:48 AM.
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Old 6th December 2018, 08:48 AM   #3
chris661 is offline chris661  United Kingdom
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When you start trying to cancel out sound, you automatically lose SPL. Think about it for a moment, and it should be perfectly obvious.

Cardioid sub setups usually have lots of compromises. Most will only give a good cardioid shape over a fairly narrow bandwidth. The ones that do well are things like end-fire arrays, which use lots of cabinets to do it well.

Chris
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Old 6th December 2018, 03:38 PM   #4
tmuikku is offline tmuikku  Finland
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Cardioid Subwoofers | Fulcrum Acoustic

You need only one
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Old 7th December 2018, 09:33 AM   #5
epa is offline epa  Netherlands
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intrested on how this is achieved.
imho not possible ,yet here whe are.

whe always use endfire setup on the side of the stage centered around 40 hz 2 mtr spacing.
no loss in db in forward dirction ,and max lf rejection to the back.
whe us the monitors for lf on stage.
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Last edited by epa; 7th December 2018 at 09:41 AM.
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Old 7th December 2018, 10:08 AM   #6
Windforce85 is offline Windforce85  Poland
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Gradient-type cardioid is substractive method. It tries to remove radiation energy from the space around it. Leaving acoustic energy at the front is the side effect.
+ optimum pattern over a range of frequency
+ small physical distance over radiating components
- 6dB/oct efficiency drop below 'tuning' frequency
- requires large displacement drivers with high level of linearity
- bad time domain response, bad wavefront, step response is flipped over

Endfire-type cardioid is additive method. It tries to add radiation energy to the space around it. Removing acoustic energy from the rear is the side effect.
+ constant efficiency at the front which is the sum of efficiences of radiating components as monopoles
+ right time domain response, preserves wavefront coherency, unaltered step response
+ works well with any kind of driver
- optimum pattern over single frequency
- requires more distance between radiating components

Cardioid are only one discrete form of unipolar radiation. There more such a forms, supercardioid, hypercardioid, etc.
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Old 7th December 2018, 07:35 PM   #7
Cableaddict is offline Cableaddict
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Quote:
Originally Posted by chris661 View Post
When you start trying to cancel out sound, you automatically lose SPL. Think about it for a moment, and it should be perfectly obvious.....

Chris
Yeah that's what I was suggesting, above. But the question is:

Are you losing USEFUL energy, or energy that isn't getting to the audience anyway (outdoors) or energy that is bouncing off the stage wall then back to the audience at diminished volume and with massive phase smear?

Re the third option, I don't get why @TBTL wrote, "Neither can you speak of sound bouncing off the back-of-stage wall." I'd love a clarification on that.

-------------------

It might be a bit like PPSL: Some folks like the diminished distortion, why others dislike it because the muddy distortion feels like volume out in the room.

Last edited by Cableaddict; 7th December 2018 at 07:38 PM.
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