Cardioid Sub Deployment

[musicman7722]

I have been researching this subject for some time now.

My system is a pair of Bose FH1 tops and a pair of QSC Ks112 subs.

The tops are amazing, the subs are small mainly because as a 70 year old solitary sound company I need boxes I can both lift and get in my van. These subs are great for me.

So moving on I was fascinated by the idea of running a cardioid sub array to reduce the low end wash on stage.

My solution has been to either stack my subs where possible or place them side by side when height matters.

I reverse the bottom sub when stacked or either of the subs when side by side. The subs DSP allows me to set a delay which is the depth of the sub. In my case it is around 2.9 feet. Then I purchased polarity adapter to throw the rear facing sub out of phase with the front facing box.

The final product reduces most of the lo end wash on stage with out losing any of the effect of having two subs.

I suggest you go to YouTube and search for this video "Two Subs, Six Setups"

By Michael Curtis

 

[bassdeal]

Very educational. Thanks for posting!

 

[musicman7722]

Thank you for reading and then commenting

 

[aglide]

Nice work. I recently acquired a sub for my K12.2 tops for the first time, and opted for the KS212C, which has two 12" already configured for the cardioid setup. It's really nice having the bass not punishing the front of the stage behind the sub and I would recommend it to anyone who is in the market for subs. It's cool that you were able to achieve the same thing with the modular setup you already have.

 

[musicman7722]

Excellent. when I first put my PA back together after Covid the 212C wasn't available. Of course it waights 88 pounds too

 

[Wasnex]

(Space allowing) I believe you will get better results by placing the cabs back to back (wheels to wheels); thus, increasing the effective spacing between the subs.

Here is a relevant post I wrote awhile back.
Subwoofer Placement/configuration

Assuming a 100hz crossover and ~40hz low frequency cutoff, the workup I did in the message linked above suggests spacing of 4.02', delay of 3.6mS, and polarity reverse of the rear sub.

The spec sheet for the KS112 says the cab depth is 24.25 inches (including wheels). So depth of two cabs wheels to wheels is 48.5" = 4.021'...which is pretty much perfect. As if they planned it .

One potential problem with this workup is AFAIK a gradient array only has an effective range of 1 octave. Ref: A_Practical_Guide_To_Bass_Arrays.pdf (sounddesignlive.com) Since 40hz to 100hz is more than an octave, the performance will be degraded at both ends of the operating range. If I remember correctly, I believe the output is reduced if you exceed the lower frequency limit and the dispersion becomes chaotic if you exceed the upper limit.

So you may further improve performance by optimizing the sub configuration for an octave operating range, for example 40-80hz or 50-100hz.

 

[musicman7722]

A lot of good info in that thread - thank you.

I have two outdoor shows next week and I will give myself some extra time to try your idea.

 

[Roxbororob]

Sub'd. No pun intended (but appropriate nonetheless).

 

[walterw]

i'll be honest here, with a pair of single 12 subs covering an outdoor event, too much low end on stage (or anywhere else) seems like an unlikely problem for anybody

 

[Wasnex]

i'll be honest here, with a pair of single 12 subs covering an outdoor event, too much low end on stage...seems like an unlikely problem for anybody

A single KS-112 is rated 128dB peak. I believe this would equate to 122dB continuous. Add a matching KS-112 and you get ~128dB continuous. Many vocalists will not want to be near that level of bass.

Consider center packed subs and a band on a portable riser.

 

[Wasnex]

A lot of good info in that thread - thank you.

I have two outdoor shows next week and I will give myself some extra time to try your idea.

Here's another potentially helpful idea from my notes:

Element Drive Level and Woofer Count. In practical gradient arrays, it has been found that minimum rear radiation occurs when the output of the rear element (often called the “steering element”) is approximately 6dB less than that of the front element. This result is due to cabinet shape effects. In practical terms, this means that the number of rear woofers can be half of the number of front woofers.
​

Ref: Microsoft Word - wp - Subwoofer Arrays v04 .doc (electrovoice.com) This is almost a direct quote of the second to last paragraph on p. 20.

Rog Mogale's Delta Array leverages this idea.

​

Image from A_Practical_Guide_To_Bass_Arrays.pdf (sounddesignlive.com) Fig 79, Top left corner of p. 15.

With the Delta array all cabs are actually producing the same SPL. The idea is the combined output of A+B is +6dB over the output of C.

With your two cab array, you would set the rear cab to be -6dB with respect to the front cab.

 

[musicman7722]

Would this setup require me to still delay and invert the polarity?

I could fit a third KS112 in my van But that is another $1200 investment.

 

[Wasnex]

Would this setup require me to still delay and invert the polarity?

I could fit a third KS112 in my van But that is another $1200 investment.

Yes the Delta Array requires the same processing.

My intended point was optimum rear cancellation occurs when you set the rear sub -6dB with respect to the front sub. This achieves the same thing as the 2 to 1 ratio of speakers in the delta array. It's just another tool you can use if the situation warrants.

But of course if yo have the means and desire to get a third KS112, .

 

[musicman7722]

@Wasnex
At my show last night I didn't have as much room as I thought so I opted to retain my stacked subs in my OP. I did take your advice and reduced the delay distance to 24" AND dropped the reversed subs volume back a bit over the front facing sub. I couldn't really figure out if it was a 6db drop or not. I also raised the low end on my system EQ from 40hz to 50hz.

I have to say the change was amazing. This was a large area and spread out quite wide but the subs were very consistent and seemed to carry quite far afield. I obviously can't say if any single item made this change because I did them all at once.

All I can say is thank you.

 

[walterw]

reduced the delay distance to 24" AND dropped the reversed subs volume back a bit over the front facing sub.

I have to say the change was amazing. This was a large area and spread out quite wide but the subs were very consistent and seemed to carry quite far afield.

so reducing the level of the reversed sub seemed to free up more low end out front?

did you get any sense of how the band perceived the low end on stage, whether it still reduced the lows up there?

 

[musicman7722]

@walterw

I did another show last night to about 200 peeps. I used the exact same set up and changes. I can easily say the subs carried twice as far as before. As I walked the audience area from the middle and then the back it was consistent and usable. Especially for a gazebo type gig. I had to do a number of band member line up changes and was on stage quite a bit. I also popped around back of the stage a number of times and discreetly walked the stage checking monitor quality. There was not noticeable low end onstage from the FOH. Band was very happy with the monitors.

Color me happy