Cardioid Subs in a Smaller venue.

[Jay Barracato]

Re: Cardioid Subs in a Smaller venue.

I think this may have more to do with acoustic impedance and may even be fixable. However, I agree that the biggest problem with cardioid setups in small venues is when the environment seen by the rear woofer is dissimilar from that seen by the front woofers, e.g. too close to a wall. Seems that about 2M spacing from any boundary is sufficient, but that close small distance differences can have a large effect.

Part of what I have experienced with a rear boundary and seems to be supported when I have tried to model it, is that even with the subs further from the wall, say up to 20 feet, the line at which the cancellation becomes significant seems to be further back than when the subs are in the open. That means if the subs are at the front of the stage and the band is pushed to the front of the stage, they are not performing where the cancellation really is.

I have never seen it really supported in any practical writing, but my theory is wave cancellation as we know it really isn't occuring in the nearby space to the driver (within the range where the driver does work on the air molecules), but instead if two drivers are trying to do work on the same molecules at the same time, no wave is formed. You may remember the Syn Aud Com discussion "Black Hole Sum" from a couple of years ago. The discussion was about what is happening when two subs are out of polarity with each other and the greater likelyhood of burning up speakers due to the change in impedence. My interpretation was based on conservation of energy: i.e. the amp is putting energy into the speaker, the speaker is not doing work on the air molecules, so the only place for the energy to end up is as heat.

 

[Guy Graham]

Re: Cardioid Subs in a Smaller venue.

{snip}

Since we've switched to cardioid subs(D&B B4s), the stage noise has decreased significantly. The bands don't crank their amps as much, the monitors don't have to run as hot, and best of all no complaints from the neighbors.

That being said, when bigger acts come in we've been known to throw cardioid out the window because we do lose some energy out the front. For most events(corporate, galas, weddings) we don't need in your face bass, but I haven't heard a cardioid sub or configuration that's really wow'ed me.

With the B4 being (if memory serves correctly) a box passively driven, it only uses one amp channel and relys on the difference between the direct radiating front speaker and the smaller rear bandpass-type loaded speaker to achieve its cardioid character, as does the V and Vi Sub and I'm sure some various others also.

Hence you can't "throw cardioid out the window" with those type of boxes. However my query is (as I've not enough experience with these boxes, nor chance to experiment as yet) when you do want to get "in your face bass" and don't have old C-type normal boxes available (plus also may want to stretch your D12s to get the most sound out front possible), can you deploy subs like the two big J series boxes, and simply short the rear-firing speaker whilst connecting up the two front 18s/21s, if you were in a pinch and that was all inventory allowed?

I appreciate the situation is very convoluted and unlikely to happen in real life, if one already has such good quality kit available. But I'm curious to know if actively-driven cardioid designs like the d&b J series subs could be used with little or no ill effects, in a situation where D12 amp channels were urgently needed elsewhere so as to cause the operator to not connect up the rear-firing driver, but still give power to the front-firing speakers.

Would this design of sub still perform to a standard closely resembling the spec? Or is the design inherently compromised by not fully connecting it up, and so performance is then compromised by not powering each driver in the box as designed?

 

[Tim McCulloch]

Re: Cardioid Subs in a Smaller venue.

Would this design of sub still perform to a standard closely resembling the spec? Or is the design inherently compromised by not fully connecting it up, and so performance is then compromised by not powering each driver in the box as designed?

No. Yes.

 

[Guy Graham]

Re: Cardioid Subs in a Smaller venue.

No. Yes.

Thank you!

My posts could probably benefit from your style of brevity - something to bear in mind for the future ;-)

 

[Bennett Prescott]

Re: Cardioid Subs in a Smaller venue.

Thank you!

My posts could probably benefit from your style of brevity - something to bear in mind for the future ;-)

The thing to remember is that the rear driver is not only providing cancellation behind, but also creating addition in front. Turning it off will actually cost you output. In my experience putting these types of subs too close to a boundary behind may wreck the pattern (reduce cancellation) but doesn't seem to impact addition out front.

 

[Dave Barnett]

Re: Cardioid Subs in a Smaller venue.

The thing to remember is that the rear driver is not only providing cancellation behind, but also creating addition in front. Turning it off will actually cost you output. In my experience putting these types of subs too close to a boundary behind may wreck the pattern (reduce cancellation) but doesn't seem to impact addition out front.

How close is too close?

 

[Bennett Prescott]

Re: Cardioid Subs in a Smaller venue.

About twice the front to rear driver distance seems to be a good rubric IMHO.

 

[harrybrilljr]

Re: Cardioid Subs in a Smaller venue.

I appreciate the situation is very convoluted and unlikely to happen in real life, if one already has such good quality kit available. But I'm curious to know if actively-driven cardioid designs like the d&b J series subs could be used with little or no ill effects, in a situation where D12 amp channels were urgently needed elsewhere so as to cause the operator to not connect up the rear-firing driver, but still give power to the front-firing speakers.

This makes no sense. You buy the amps with the boxes so you always have enough. Each box gets an amp.

Cancellation is timing specific, therefore it is location specific.

This is true if the elements of the array are spaced apart. The further apart they are, the more true this is. It's not really an issue when they are close together like in an all in one box or a CSA.

In Dave Rat's YouTube material he states that the primary reason he doesn't like/use cardioid subs is the detriment to sound quality that results from the sound in front of the stage, that is caused by the combination of the front firing sub in a cardioid array with the delayed out of phase bass coming from the rear-firing sub.

In a real-world situation where cardioid subs are deployed, is this impediment to the sound quality in the house as noticible as the theoretical combination of the forward sum of all the subs in the array, which ends up being a mix of the in-phase front-firing box combining with the out-of-phase rearward box signal?

In other words does the theoretical problem manifest itself in a noticeable degradation of sound quality, or in a real-world scenario are the benefits of using this bass-steering technique to clean up stage noise, reduce potential for standing waves and so forth, better to the point of negating the undesirable effect produced out front when mixed phase sub-bass frequencies are heard in the house?

In real life a 2:1 array where the elements are in close proximity, the rear driver has little influence on the sound out front. The benefit of getting rid of unwanted low end reflections from the rear wall that otherwise add in a destructive way to the energy out front outweigh small loss of impact (punch in the chest). In all 1:1 configurations I've used or tested where the rear is pol inverted and delayed, the sound out front was noticeably mushy. The waveform is smeared in time. All 2 deep front facing end fire arrays regardless of which driver is delayed are a compromise in sound quality and not my first choice. All stacked arrays with all drivers facing forward have more total output and sound better unless there is a reflection or interaction with another array that causes problems which could have been prevented with a directional array.

Yes it is the timing that CAUSES the top end rolloff.

If you measure one sub out front-then turn the "cancelling sub" on, you will notice that the top end (say 100ish Hz-give or take a good bit depending on spacing and delay added) will be lower than with one sub.

An endfire setup will not have this rolloff.-yet the same amount of delay is used-just on a different speaker and the relative polarities are the same-not reversed as in a cardioid setup.

 

[harrybrilljr]

Re: Cardioid Subs in a Smaller venue.

The easiest way to make a CSA is to stack 2:1 with 1 being rear facing and usually on the bottom but that can be experimented with. Place your measurement mic where you want the deepest cancellation to occur. Measure normally(with Smaart) with the front drivers on. Capture the trace. Mute the front. Turn on the rear. Do not adjust the reference delay in Smaart. Adjust the delay of the rear driver until the phase traces match. The levels are almost always super close, but you can adjust drive if you want them matched perfectly. Turn the front back on, and you should get close to 6dB more than before. Invert the polarity of the rear. The OP could do this with 1:1 by turning down the rear facing box to match the level of the front at the rear. This set up damages the front the least since the rear drivers add very little to the front.

 

[Spenser Hamilton]

The easiest way to make a CSA is to stack 2:1 with 1 being rear facing and usually on the bottom but that can be experimented with. Place your measurement mic where you want the deepest cancellation to occur. Measure normally(with Smaart) with the front drivers on. Capture the trace. Mute the front. Turn on the rear. Do not adjust the reference delay in Smaart. Adjust the delay of the rear driver until the phase traces match. The levels are almost always super close, but you can adjust drive if you want them matched perfectly. Turn the front back on, and you should get close to 6dB more than before. Invert the polarity of the rear. The OP could do this with 1:1 by turning down the rear facing box to match the level of the front at the rear. This set up damages the front the least since the rear drivers add very little to the front.

Excuse me if this is a dumb question, would something like the drum riser approx where the kick drum will live be a good spot for the measurement mic?

What about lead vox position?

 

[Jay Barracato]

This is true if the elements of the array are spaced apart. The further apart they are, the more true this is. It's not really an issue when they are close together like in an all in one box or a CSA

Harry,

My belief is that two drivers close enough together to couple are not creating two waves that combine but instead are both doing work on the same air creating a single wave. Therefore there is no constructive or destructive interference.

My main point is that when you have two waves overlapping at a point in time, whether it is from separation of sources OR reflection off a barrier, the possible cancellation at that point does not stop the wave from propagating and having different amounts of interference at other locations.

 

[Bennett Prescott]

Excuse me if this is a dumb question, would something like the drum riser approx where the kick drum will live be a good spot for the measurement mic?

What about lead vox position?

To measure what? It could be a good spot for a lot of things but perhaps not for creating a cardioid array.

 

[harrybrilljr]

Re: Cardioid Subs in a Smaller venue.

Couple in which direction? The distances I am calling close in this case are about a quarter wavelength. The drivers are spaced upstage to downstage. If they were all on the same amp channel the pattern would be between omni and bi directional. I have to admit, I'm just a dumb soundguy and your posts are a bit hard for me to read so I might be misunderstanding something. That being said we tend to over complicate things. One thing I like about Dave's approach is he just tries things and figures out what works where. Eventually we all end up in about the same place. Some will get stuck in minutia and never progress. Dave doesn't go in with preconceived notions. Spenser, how long is a string. I mean I don't know your situation. I like to have lots and lots of smaller subs so I can create arrays based on the situation at hand. It could be a different array everyday as those that have toured with me can attest. No 2 venues are alike. In many cases just stacking them high and wide on each side of the stage does the trick just fine. Arcing them around the corners a bit helps open it up. There is a reason ShowCo and Clair had 20 subs a side long before we were even having this discussion.

Harry,

My belief is that two drivers close enough together to couple are not creating two waves that combine but instead are both doing work on the same air creating a single wave. Therefore there is no constructive or destructive interference.

My main point is that when you have two waves overlapping at a point in time, whether it is from separation of sources OR reflection off a barrier, the possible cancellation at that point does not stop the wave from propagating and having different amounts of interference at other locations.

 

[Spenser Hamilton]

Re: Cardioid Subs in a Smaller venue.

Sorry for the confusion, my question was directly in reference to this.

Place your measurement mic where you want the deepest cancellation to occur.

I understand that every venue is different, just wondering if there are some starting points for those of us that are just starting to experiment with different sub arrays.

 

[Per Søvik]

Re: Cardioid Subs in a Smaller venue.

Sorry for the confusion, my question was directly in reference to this.



I understand that every venue is different, just wondering if there are some starting points for those of us that are just starting to experiment with different sub arrays.

Place your mike where the simulation shows max cancellation, or alternatively where you want to achieve max cancellation.

 

[Spenser Hamilton]

Re: Cardioid Subs in a Smaller venue.

Place your mike where the simulation shows max cancellation, or alternatively where you want to achieve max cancellation.

Thanks Per

 

[Jay Barracato]

Re: Cardioid Subs in a Smaller venue.

Couple in which direction? The distances I am calling close in this case are about a quarter wavelength. The drivers are spaced upstage to downstage. If they were all on the same amp channel the pattern would be between omni and bi directional. I have to admit, I'm just a dumb soundguy and your posts are a bit hard for me to read so I might be misunderstanding something.

Harry,

As I understand the cardiod sub array, it relies on three factors:
1. The delay caused by the physical spacing between the forward facing drivers and the rearward facing drivers. (Approx. 1/4 wavelength)
2. The electronic delay added to the rearward drivers (approx. 1/4 wavelength)
3. The polarity inversion.

I would add that the subs themselves are important (as opposed to considering them as an idealized point source) because they act as a physical barrier between the air that the forward facing drivers act on and the air the rearward facing drivers act on.

My idea is just that two drivers that are close together compared to the wavelength they are producing both act on the same mass of air creating a single wave which then propagates according to wave theory. If two drivers are far enough apart or have some sort of barrier between them that causes each driver to act on a separate mass of air, then two waves are formed, begin propagating, and then can interfere. An often repeated but completely wrong misconception I hear frequently is that the interaction of two waves at one point and time somehow changes the waves at other points.

I would not suggest doing this in real life, but as a thought problem, could you set up an equivalent array with all three drivers facing forward, and the delay caused by the physical spacing replaced by the equivalent amount of electronic delay?

 

[Per Søvik]

Re: Cardioid Subs in a Smaller venue.

Of course, the position will vary a bit depending on array configuration. So measuring/listening where the array is expected to have most cancellation is probably the best for fine-tuning a particular set-up. Measuring the response out front makes sense for obvious reasons too 8)~~

10:7 cardio array

Double endfire, 1.36m 4 ms delayed fronts, 3m spacing axis to axis

Double cardio 1.36m 4ms delayed and phase inverted rears -3dB, 3 m spacing

3 to 1 cardio, 1.36 m 4 ms delayed and phase inverted rear, 1.5 m spacing

 

[Per Søvik]

Re: Cardioid Subs in a Smaller venue.

An often repeated but completely wrong misconception I hear frequently is that the interaction of two waves at one point and time somehow changes the waves at other points.

That conception is actually true to a small degree, since air isn't a completely ideal gas, and the mechanisms that causes loss and dispersion will also cause some interaction over distance. A line array would be a lot harder to make if there was absolutely no sonic interaction. Of course, actual air-movement will cancel out or combine fairly completely.

 

[Per Søvik]

Re: Cardioid Subs in a Smaller venue.

I would not suggest doing this in real life, but as a thought problem, could you set up an equivalent array with all three drivers facing forward, and the delay caused by the physical spacing replaced by the equivalent amount of electronic delay?

No, you would then have the same effect in both directions. But you can of course achieve some steering effect with electronic arching if the whole group is wide enough to show some figure-eight directional properties. (1/3-1/2 wavelength between the outer cabinets). But the steering will be the same forwards as back. You could turn figue-eight into clover or Omni but it wont be useful in any but very strange situations.