QUICK GUIDEHOW TO...

Set up for a Live Sound Event

This document provides a practical guide on how to use NTi Audio instruments in a Live Soundenvironment.

What you need: XL2 Kit for Front of House— XL2 Analyzer— M4261 Measurement Microphone— Minirator MR-PRO— ASD Cable— Cable Test Plug
— Mains Power Adapters— Exel System Case
XL2 Kit for Front of House

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QUICK GUIDE

What to Do:
There are four areas where the NTi Audio instruments come in very handy,— Finding faults— Optimizing the frequency response— Identifying feedback frequencies— Ensuring compliance with legal requirements
Plus, if you have the requirement, you can— Set up Delay Speakers

How to Find Faults
Everything is set up and switched ON and you are ready for the sound check, but there is a hum on
the PA, or no sound from one of the microphones or instruments.

NO SOUND
To isolate where the signal path is being broken, choose a source point in the signal path, for example the microphone, remove the XLR connector and plug the MR-PRO into the down-line sectionof the path (towards the mixer).
Confirm that the line is providing Phantom power to the microphone if appropriate (the DC value should be 48 V ± 4 V).
Select an appropriate sound, such as “FILE, MESSAGES,Adjust”, and listen for the signal through the PA.

Interrupt the signal path at various points, plug the XL2 into
the up-line section of the path (from the MR-PRO). Select“SLMeter”. Press the speaker button on the XL2 and listen
for the signal from the MR-PRO through the XL2 internal
speaker. To adjust the volume, hold the speaker button andturn the wheel.

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QUICK GUIDEHUM
To isolate which component is causing the hum, choose a point in the signal path, for example thestage breakout box, and remove the XLR connector.
Plug the MR-PRO into the down-line section of the path(towards the mixer). Select “SINEWAVE, 1 kHz” and checkthat the down-line signal is balanced, because a missing
screen on the cable or an unbalanced line can often causethe hum.

At the same point in the signal path, plug the XL2 into theup-line section of the path (from the mic or instrument). Select RMS/THD, create a sound at the source (ask the guitarist to play or gently tap the microphone) and check that theup-line signal is balanced. Press the speaker button on theXL2 and listen for the hum through the XL2 internal speaker.
For tips on finding faults, see Appendix A

HOW TO OPTIMIZE FREQUENCY RESPONSE
Configure the system to deliver a similar response across the frequency spectrum for left and right(and center) of the PA.
Play Pink Noise from the MR-PRO through the PA.

Select “SLMeter RTA” on the XL2, measuring LZSlive. Select
1/3 Octave resolution, as this gives you 31 bands of resolution, matching most traditional equalizers. Position the XL2
microphone at the nearest audience position in front of the left
speakers. When you are satisfied that the frequency responseof the left PA has no significant spikes or dips, press pause onthe XL2 to freeze the spectrum reading from the left PA.

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QUICK GUIDE

Capture the “LZSlive” spectrum as your reference spectrum.

Recall this Capture spectrum.

Position the XL2 microphone at the nearest audience position in front of the right (or center) speakers. Release thepause to measure LZSlive. Adjust the frequency response
until the spectrum is similar to the reference spectrum of theleft PA (the left PA Capture is shown here in red).

Play the dynamic speech and instrument sounds of the MRPRO through the PA to get a feel for the whole sound.

Monitors
If you have frequency control over individual monitors, you can do the band (and yourself) a favourand configure each monitor to deliver a similar flat response across the frequency spectrum, using
the method for optimizing the PA as described above.

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QUICK GUIDEHOW TO IDENTIFY FEEDBACK FREQUENCIES
To identify the frequencies that are causing feedback, choose the SLMeter RTA page ( ) of theXL2. Measure “LZF hold3”. This will hold the feedback frequency for a period of 3 seconds after it
has occurred.
For tips on reducing feedback, see Appendix B.

XL2 Analyzer with M4261 Measurement Microphone

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QUICK GUIDEHow to Set up Delay Speakers
In order to determine how much delay should be added to the delay speakers, we need to measure
the difference in time, between the front PA and the delay speakers, for the sound to reach the audience position closest to the delay speakers.
NOTE: Before the Delay test, disconnect the measurement
microphone from the XL2 as the internal Voice Note microphone is used during this test.

Play the DELAYTEST signal from the MR-PRO connecteddirectly to the XL2 in order to synchronize the two instruments. When sychronised, the XL2 shows that you are now
ready to measure the delay with the word “Measure”. You
now have 5 minutes to measure the delay before anothersynchronization is required.

Play the Delay signal from the MR-PRO through the left delay speaker only. Stand at the audience position closest tothe delay speaker and press the XL2 Delay STORE function.
This sets your zero point.

Now play the Delay signal from the MR-PRO through the frontleft PA speaker only. Remain at the audience position closest to the delay speaker. Add 15 ms to the delay difference
shown on the XL2 (81 ms + 15 ms = 96 ms in this example),and apply this delay value to the delay speakers. Assuming
the speaker layout is symmetrical, apply the same value tothe right delay speakers, or measure again on the right.
Why do we need delay speakers? - see Appendix C

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QUICK GUIDEAppendix ATips on finding faults
There are several actions you can take before reaching for your test instruments:— Stay calm – blaming people or equipment will not solve the problem— Check Stereo – is the problem on one side of the stereo image? – fault is probably post-mixer.
— Be methodical – follow each signal path, rather than checking components randomly— Switch it out – consider changing multi-core channel, mixer channel with ones that are known tobe working

NO SOUND
Check the obvious— are all components switched on?
— is the channel muted on the mixer?
— are all cables in the signal path plugged in correctly?
— does a battery need replacing?
— is the input gain on the mixer too low?

HUM
Very often mains hum is caused by incorrect cabling of equipment— if your earth reference voltage is different from one end of the signal path than the other – plug allcomponents (mixer, instruments and PA) into a single electricity mains socket— if you run an audio cable through a load of coiled mains cable— if you use lighting dimmers on the same supply as your sound system supply
Earth hum can be very difficult to find, especially with very large PA systems. You can determine
where the hum is coming from by unplugging all equipment from the iputs of your mixing desk, andthen plugging in each piece of equipment one by one.

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QUICK GUIDEAppendix B
Tips on reducing feedback
Once your frequency response is optimized, you can identify potential feedback frequencies by ringing the system out. Push channels up individually, beyond the level at which you expect to operate
during the show, until feedback is heard. Use the XL2 “SLMeter RTA” page to identify the feedback
frequencies. Use a filter or an equalizer to reduce these frequencies.
Hint: Jingling car keys or clapping hands into the microphone can help trigger a feedback fortesting.
There are several actions you can take to reduce the likelihood of feedback:— Move the microphone, the monitor or the PA— Use a more directional microphone— Turn down the monitor volume— Turn down microphone gain and ask the singer to hold the mic closer to their lips
— Look for reflective surfaces that might be bouncing the monitor or PA sound to a microphone andadjust as above— Turn off microphones when not in use

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QUICK GUIDEAppendix C
Why do we need delay speakers?
If you can not cover the whole audience area with one speaker system, you can set up additional
speakers on each side of the venue halfway into the hall. These speakers then cover the back halfof the hall. All good. Problem is that the poor audience sitting just to the right (and left) of these
additional speakers will see the performance in front of them but hear the performance from thespeaker to the side of them. The result is that the sound experience for these people is not ideal – itis much more desirable to perceive the sound coming from the direction of the band. We can bring
the perceived direction of sound back to the front PA while still maintaining enough level to cover theback half of the hall.
The trick is to add a delay to the additional speakers (thus called “delay speakers”) so that the soundfrom the front PA arrives at the audience closest to a delay speaker at least 15 ms before the soundfrom the delay speaker arrives. As the first sound arriving is then from the front PA, the perceived direction of the main sound is therefore also from the front PA, while the sound from the delay speakeris perceived as a reverb, resulting in a rich sound experience. Further, it is now possible to increase
the sound pressure of the delay speaker up to 10 dB higher than the front PA without affecting theperception of sound direction.

Humans perceive direction of sound to be coming from the position from where thefirst sound arrives. If a sound from a second source (in this case the delay speakers)
arrives within 5 ms after the first source, then this second source also has an influenceon the perceived direction of the sound and the listener will perceive the sound to becoming from a position somewhere between the delay speakers and the front PA.
If a sound from the second source arrives between 5 ms and 35 ms after the first source, thenthis second source is perceived by the listener as a reverb and has no influence on the perceived
direction of the sound – the sound is thus perceived to be coming from the direction of the front
PA. If a sound from the second source arrives more than 35 ms after the first source, then thissecond source is perceived by the listener as an echo and the listener perceives two separate
directions of sound – from the front PA and from the delay speakers. Giving the delay speakers
between 5 ms and 35 ms (as a rule, set it to 15 ms) of delay allows you to bring more sound levelto the back of the room without altering the perception of direction of sound. This somewhat remarkable concept is known as the “Haas Effect”.

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