more questions - sound deadening?

[soundmanjim]

whoops did you get cut off?? put another 50p in the meter.

yes i've got it now. that makes much sense. i am going to try and align the club system when i get back over there next week - im sure the bass needs it.

is there a cd or a sound that i can use to align these by ear? i have a cd of pink noise and other sounds that i got off of a fellow radio ham.

[Simon Ryder]

Pink noise and smaart live, otherwise it's the tape measure and the mathematics.

I wouldn't bother trying to do it by ear. If you get it right, the sound kind of goes holographic. Its not as cut and dried as detecting peaking frequencies.

[soundmanjim]

okydoky.

[Simon Ryder]

OOOPS

I'm embarrased

I just reread my equation post with the benefit of a good night's sleep.

I got my equation the wrong way up.

Speed = distance / time

time = distance / speed

so:

measured distance / speed of sound = time in seconds

so in this case:

10 / 344 = .029 seconds or 29 ms


I have modified my original equation post to the correct version,

[shepz]

Yeah I had to set up delay lines before at a festival I was running the sound for - makes it all alot cleaner and the people in the front row don't get bleeding ears at the end of it all!

=]

[gingerbiscuit69]

altho flat out FOH, plus phat delays are always fun!!

[Rick Sarson]

Try creating a cardioid sub array with the back of the subs facing the problem punters house. You need a minimum of three subs driven by seperate amp channels and a delay line. Place the subs in a line one behind the other, all facing forwards. place them so that the fronts are exactly a metre apart. It looks really wrong because the front of one sub is facing the back of the next one. Delay the middle and front sub to the rear one. This is easiest to do by dialling it in using the metres setting rather than milliseconds on the delay line, one metre for the middle sub and two metres for the front sub. You will get +6db out of the front and better than -20db out of the back. You can use more than three subs if you have more amp channels and delay taps, but three is the minimum. The people at Meyer sound have been doing it for a while. It is proper sound voodoo, but is perfect for tent gigs. Whilst you are mucking about with delays try delaying the entire system to the back line/drums it tightens the sound of everything wonderfully! If you think about it, if for example the stage is 20 feet deep, when the bass player, guitarist, drummer hits a note or drum the sound comes out of the cabinet and the sound system at the same time and there is therefore a twenty millisecond(ish) delay between the two sounds. If you delay the sound system to the back line by that twenty milliseconds you will get a much more coherent sound which is also easier to mix because you are not fighting that delay. Try it, let me know what you think.

[Simon Ryder]

The cadiod sub array is very effective. However, if your subs have a greater depth than 50cm following Rick's method then it will be impossible to get the timing right. This technique also only works across a narrow frequency band, less than an octave. What Meyer and Nexo do is divide the frequency spectrum into slices and apply different delay times for each fequency slice, achieving a broad response cardiod pattern.

It is however still a very effective technique which we use to great success in noise sensitive areas when doing noise pollution consultancy.

If you play with your spacing between the cabinets and the timing it is possible to create cardiod response arrays, hypercardioid and even shotgun, though the latter is a little impractical.

[Simon Ryder]

If anyone wants to know the equation for doing it then:

Place one sub facing forwards, the other behind facing backwards. Space them so that the drivers are 1/4 wavelength of the center frequency of the desired affected frequency range. Next delay that rear sub by one quarter wavelength of that centre frequency.

This means that when the sound reaches the rear sub it is 180 degrees out of phase with the sound coming out of the rear sub and cancels.

To try this for a centre frequency of 63 Hz:

V=F*L

V= speed of sound
F = frequency
L= wavelength

344 = 63 * L

344 / 63 = 5.46

L = 5.46m

L/4 = 1.37m


To work out the delay time required:

L = VT

T = L / V

1.37 / 344 = T

T = 0.00397s or 4ms

So to sum up:

For a broad response, cardiod array you need your rear subs 1.37m behind your front subs (measured from driver to driver) and the delay set to 4ms.

NB:
you can have both subs facing forwards, one behingd the other Again measure from driver to driver but reverse the polarity of the rear sub.

Give it a try.

Have fun!

[Simon Ryder]

sarson said:

You will get +6db out of the front and better than -20db out of the back.

Unfortunately you will only get +1.5 dB in front. This is due to the forward waves coupling 90 degrees out of phase.

Even if both subs were in phase and sat next to each other that would still only give you +3dB

1x 1000W sub + 1x 1000w sub = +3dB
1 x 1000w sub + 9x 1000w subs = +6dB

the -20dB to the rear is roughly accurate, in fact across that operating range of the cardiod array, it will vary from a maximum possible of about -22dB (depends on many factors) to about -15dB. Outside the bandwidth of the cardiod array, the rear sub will have very little effect.

[gingerbiscuit69]

www.speakerplans.com/forum/forum_posts.asp?TID=9927