CSA Cardioid Sub Array   3 comments

So  I decided to do a little more research on what i know as a CSA array or Cardioid Sub Array. In the posts on this kind of an array before this one I was mainly interested in getting as much cancelling on the stage side and as much level possible in the audience area.

I will be updating this post but it’s a start. (if you have Mapp on Line installed on your computer here are the ZIP-files from MAPP used to do this post CSA cue2016-3 CSA 2subs cue2016-3 CSA 2subs mics front cue2016-3)

In this post I’ll take a peak at what happens at different mic positions at the back and not at just 1 mic close for getting the maximum cancel. So here we go….

So here’s the start: A front-back-front set-up (3 x 900LFC Meyer Sound)Start 5 mic's CSA

The front-back-front set-up consists of 3 900LFC with the middle one reverse (shooting back worth). The mic’s are positioned at 1mt 2mt 4mt 8mt and 16mt (so each time the distance is doubled).

The problem with this array: If you phase align the “back sub” with the front subs with the mic at 1mt from the array and then polarity reverse the back sub you’ll get a pretty good cancelation at that mic position but in the far field you get to deal with a level offset between the 2 front subs vs. the 1 back sub.

This means there is a 6dB offset between them so at the 1mt mic position you will see a pretty good cancelation due to the fact that the sound from the front subs has to travel around the array and assuming this is +/- twice the distance compared to the sound travelling from the back sub to the 1mt mic position you’ll end up with both parts of the array having matched level. Has to do with the Inverse Square Law (with each doubling of the distance the SPL level reduces with 6dB).

So with the”back sub” at 1mt and the front subs at 2mt the front subs will have 6dB more level but travelling twice the distance they also loose 6dB.

Within Mapp you’ll see the same thing at the 1mt mic position.

This is the predicted response from the 2 front subs at the 1mt mic position at the back of the array.0001a CSA strt mic1-1mt front subs

This is the predicted response from the back sub at the 1mt mic position at the back of the array.0001b CSA strt mic1-1mt back sub

And a compare between both responses (2 subs front and 1 sub back at the 1mt mic position).0001c csa strt compare mic1 sub front vs sub back

(you might notice the level differences between the first 2 screenshots and ”the compare screen shot”. This has to do with a Gaussian program algorithm implemented within the Mapp program. The screenshots in the first part of this post were done in 2 day’s so i ended up with slightly different levels in the comparing screenshots sorry).

Gaussian thing

Now let’s look at the 2mt mic position.

This is the predicted response from the 2 front subs at the 2mt mic position at the back of the array.0002a CSA strt m2-2mt front subs

This is the predicted response from the back sub at the 2mt mic position at the back of the array.0002b CSA strt mic2-2mt back sub

And a compare between both responses (2 subs front and 1 sub back at the 1mt mic position).0002c csa strt compare mic2 sub front vs sub back

This is the predicted response from the 2 front subs at the 4mt mic position at the back of the array.0003a CSA strt mic3-4mt front subs

This is the predicted response from the back sub at the 4mt mic position at the back of the array.0003b CSA strt mic3-4mt back sub

And a compare between both responses (2 subs front red trace and 1 sub back blue trace at the 4mt mic position).0003c csa strt compare mic3 sub front vs sub back

This is the predicted response from the 2 front subs at the 8mt mic position at the back of the array.0004a CSA strt mic4-8mt

This is the predicted response from the back sub at the 8mt mic position at the back of the array.0004b CSA strt mic4-8mt back sub

And a compare between both responses (2 subs front red trace and 1 sub back blue trace at the 8mt mic position).0004c csa strt compare mic4 sub front vs sub back

This is the predicted response from the 2 front subs at the 16mt mic position at the back of the array.0005a CSA strt Mic5-16mt

This is the predicted response from the back sub at the 16mt mic position at the back of the array.0005b CSA strt mic5-16mt back sub

And a compare between both responses (2 subs front red trace and 1 sub back blue trace at the 16mt mic position).0005c csa strt compare mic5 sub front vs sub back

So you see the level difference increase between the 2 front subs and the back sub as soon as the distance increases. This means that the cancel you get after aligning this array might look pretty cool at the 1mt mic position but at the 16mt mic position the cancelation is not going to be as deep as the “cool” mic position.

Front subs @ the mic 2 3 4 & 5 positions0006a csa strt all mic sub front level

Back sub @ the mic 2 3 4 & 5 positions.0006b csa strt all mic sub back level

Now let’s phase align this array at the 1mt mic position.

1st the 2 front subs solo (red) vs. the back sub solo (brown). The phase trace from the back sub shows it needs to be delayed to match with the solo trace from the front subs. There’s a 120dg phase offset at 100Hz so i have to delay the back sub with 3.33ms (10ms =360dg so 120dg =1/3 of 10ms=3.33ms)0007a pre alignment front back sub

Back sub (brown) delayed with 3.33ms matches with the front subs (red).0007b sub back 3.33ms delay match sub front

Sum of both measured at the back shows +/- 6db addition at the back. This is not what we want so i have to polarity reverse the back sub to get cancelation.0007c sum sub front sub back 3.33ms no ø yet

By reversing polarity on the back sub the sum of all goes from 114.5dB to about 96dB (at some frequencies even deeper cancels 83 to 87dB).

This means a +/- 18.5dB reduction Knipogende emoticon (you can see the peaks settling around the 96dB line) 0007d sum sub front sub back 3.33ms delay ø rev

But this is at the 1mt mic position let’s take a look at the 2/4/8 and 16mt mic positions.

2mt mic position: 10dB reduction so still a pretty nice result but less reduction ((you can see the peaks settling around the +/- 98-100dB line).0008b sum at mic2 Sub front sub back 3.33ms ø rev

4mt mic position: +/- 8dB of reduction 0008c sum at mic3 Sub front sub back 3.33ms ø rev

8mt mic position: +/- 7dB reduction0008d sum at mic4 Sub front sub back 3.33ms ø rev

16mt mic position: +/- 6 to 7dB reduction 0008e sum at mic5 Sub front sub back 3.33ms ø rev

So watch out with putting such an array in to action because what might give you nice results in the near field can be misleading. The far field mic position shows less reduction and might cause problems regarding environmental laws (the fine on exceeding the levels on a open air thing in Amsterdam can run up to about 10000 euros trust me on that since i nearly got fined a couple of times Bedroefde emoticon).

So this is the prediction field from MAPP at the 1/3 octave point of a graphic eq.

20Hz0009a CSA 3subs 20Hz

25Hz0009b CSA 3subs 25Hz

31.5Hz0009c CSA 3subs 31.5Hz

40Hz0009d CSA 3subs 40Hz

50Hz0009e CSA 3subs 50Hz

63Hz0009f CSA 3subs 63Hz

80Hz0009g CSA 3subs 80Hz

100Hz0009h CSA 3subs 100Hz

125Hz0009i CSA 3subs 125Hz

Now let’s look at a CSA array of 2 subs.

Here’s the start.CSA strt 2subs no level offset

Front sub @mic 1 1mt 00001a CSA 2subs mic1 front sub

Back sub @mic 1 1mt 00001b CSA 2subs mic1 back sub

Compare of front vs. the back sub @mic 1 1mt (so a +/- 6dB more on the back sub)00001c Compare CSA 2subs mic1 front back sub

Front sub @mic 2 2mt 00002a CSA 2subs mic2 front sub

Back sub @mic 2 2mt 00002b CSA 2subs mic2 back sub

Compare of front vs. the back sub @mic 2 2mt (so a +/- 4dB more on the back sub)00002c Compare CSA 2subs mic2 front back sub

Front sub @mic 3 4mt 00003a CSA 2subs mic3 front sub

Back sub @mic 3 4mt 00003b CSA 2subs mic3 back sub

Compare of front vs. the back sub @mic 3 4mt (so a +/- 3.5dB more on the back sub)00003c Compare CSA 2subs mic3 front back sub

Front sub @mic 4 8mt 00004a CSA 2subs mic4 front sub

Back sub @mic 4 8mt 00004b CSA 2subs mic4 back sub

Compare of front vs. the back sub @mic 4 8mt (so a +/- 2.5dB more on the back sub00004c Compare CSA 2subs mic4 front back sub

Front sub @mic 5 16mt 00005a CSA 2subs mic5 front sub

Back sub @mic 5 16mt 00005b CSA 2subs mic5 back sub

Compare of front vs. the back sub @mic 5 16mt (so a +/- 2dB more on the back sub)00005c Compare CSA 2subs mic5 front back sub

And now the phase alignment. I moved this set-up a little to get the centre of the array in-line with the mic’s (so just checking).

Front Sub solo00007a CSA 2subs sub front pre phase alignment

Front & Back sub solo00007b CSA 2subs sub front sub back pre phase alignment

Front & Back sub 3ms delay on back sub to phase align with front sub.00007c CSA 2subs sub front sub back phase aligned 3ms

Front & Back sub 3ms delay+polarity reverse on back sub.00007d CSA 2subs sub front sub back phase aligned 3ms ø reverse

SUM (mic1-1mt from array) Front & Back sub 3ms delay+polarity reverse on back sub (solo front sub level 109.4dB goes to +/- 107dB so roughly 2dB reduction).00008a Sum CSA 2subs mic1 front sub back sub 3ms ø reverse

SUM (mic2-2mt from array) Front & Back sub 3ms delay+polarity reverse on back sub (solo front sub level 104.9dB goes to +/- 99dB so roughly 6dB reduction).00008b Sum CSA 2subs mic2 front sub back sub 3ms ø reverse

SUM (mic3-4mt from array) Front & Back sub 3ms delay+polarity reverse on back sub (solo front sub level 99.4dB goes to +/- 90dB so roughly 9dB reduction). 00008c Sum CSA 2subs mic3 front sub back sub 3ms ø reverse

SUM (mic4-8mt from array) Front & Back sub 3ms delay+polarity reverse on back sub (solo front sub level 94.1dB goes to +/- 84dB so roughly 10dB reduction).00008d Sum CSA 2subs mic4 front sub back sub 3ms ø reverse

SUM (mic5-16mt from array) Front & Back sub 3ms delay+polarity reverse on back sub (solo front sub level 88.4dB goes to +/-76dB so roughly 12dB reduction)00008e Sum CSA 2subs mic5 front sub back sub 3ms ø reverse

Most of the time a –6dB is implemented on the back sub in an CSA array of 2 subs but by doing a –6dB on the back sub the reduction in the far field will be less. Also you run the risk of the cardioid effect disappearing. If this set-up is run at maximum level the the limiters on the front sub will be activated while the back sub still has 6dB to go before it’s limiters are activated.

If you implement a CSA of 2 subs you have the choice. Maximum reduction on stage or maximum reduction in the FAR field. Take your pick Knipogende emoticon

 

There’s also another challenge. If you do not implement the –6dB on the back sub it will chance the response on the audience side of the array.

So here are the predictions at 1/2/4/8 &16mt.

CSA 2subs mic's front of array

 

Mic1-1mt000010a CSA sub array mic's at the front mic1

Mic2-2mt000010b CSA sub array mic's at the front mic2

Mic3-4mt000010c CSA sub array mic's at the front mic3

Mic4-8mt000010d CSA sub array mic's at the front mic4

Mic5-16mt000010e CSA sub array mic's at the front mic5

And the prediction field within MAP

20Hz00009a CSA 2subs 20Hz

25Hz 00009b CSA 2subs 25Hz

31.5Hz 00009c CSA 2subs 31.5Hz

40Hz 00009d CSA 2subs 40Hz

50Hz 00009e CSA 2subs 50Hz

63Hz 00009f CSA 2subs 63Hz

80Hz 00009g CSA 2subs 80Hz

100Hz 00009h CSA 2subs 100Hz

125Hz00009i CSA 2subs 125Hz

Hope this helps Knipogende emoticon enjoy……

Posted 03/01/2016 by timobeckmangeluid in Geen categorie

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