Measuring a PA Setup to Make Sound as true to the original in a Room

This has been a hot topic in the industry for over 100 years.
If the sound was shit, then “the technician” is to blame. Nobody sees relevant backgrounds. But wait, why actually “the technician”?

Whether an ear does not like a straight line, or maybe it is, is an open question. but the ear only hears the sound!

It’s an old dream: to create a “linear frequency response” by simply looking at the third-octave spectrum on an analyzer and then raising or lowering the individual third-octave bands on a graphic third-octal equalizer. But this is very questionable.

Welcome to another tipTuesday blog post and today’s article does not deal with the sound of music, instruments, vocals, etc., but with the transmission characteristic in relation to the frequency response of an electroacoustic system.

It requires specialist knowledge, acoustic references, a good ear and appropriate technology, as well as a brain that can process all the relevant information in order to achieve the best possible transfer function of a PA in a room.

Considering the frequency response, there is then the phase curve and the decay, as well as a different dispersion in different frequency bands on the side of the PA above all the frequency-specific absorption and reflection of materials in space also plays an important role.

And only after all these influencing factors, the sound arrives at your individual listening position.

And two meters further it can sound quite different again. But that’s not what it’s all about, which is why a lot of experts are working to make the sound as true to the original as possible at every seat in the audience.

There are different approaches – even for loudspeaker developers – to what an “ideal” frequency response of a PA system should look like.

Some want a neutral tool, ie a loudspeaker with a frequency response that is as linear as possible.

The others prefer a loudspeaker that sounds more comfortable on its own.

What you like depends a lot on the listening habits, so that you can not just commit yourself to that.

It makes no sense, however, to create a linear frequency response by looking at the third-octave spectrum on an analyzer and then inversely raising or lowering the individual third-octave bands on a graphic third-octal equalizer.

The frequency response depends on the measuring position.

Especially when raising a frequency you should be very careful, so that not a frequency or a frequency band, which is slightly lower due to the beam angle of the speakers just at the measuring position in the level, is overemphasized everywhere else in the hall.

Also, the room has its influence – and this one measures with: The microphone absorbs the total sound level in the room. And this overall sound level includes the direct sound level from the speakers, the early reflections from nearby walls, etc., and then the infinite reflections that make up the reverberation of the room.

The reverberation, for example, falls to high frequencies; this drop in frequency becomes more pronounced with increasing room size and longer reverberation times.

So if you see a steady drop to the high frequencies during a measurement, that usually does not mean that the speakers are weakening and therefore the frequency response has to be raised, but rather that you can see the reverberation time of the room in the measurement.

Don’t mess up the PA

There are other reasons why measuring the perfect system is not even quick.

In any case, it takes some time and experience to adopt a PA system as optimally as possible to the respective spatial conditions.

Mostly it is well advised, at least first to try out what one of the system technicians on site makes available.

Most of the time you do not have the time or the equipment to do a real optimization of the PA system.

Often already competent people have already dealt with the customization and found a passable option for the present conditions, even if this does not sound ideal on the first note.

It should also be assumed that the developers of loudspeaker systems have been busy with the tuning of their speakers.

While there may be an opportunity to make settings in the system processor, it is not recommended to make any changes here in a hurry.

By contrast, the time saved by avoiding lengthy gauging can be used more profitably elsewhere: for example, place the speakers so that all listeners are well reached, keep order and system in the stage wiring, and the saved money is much better in higher quality microphones or speakers.

Do not forget the ears

The ears are a very extraordinary tool, because they do it quite naturally, which is difficult to visualize and difficult to interpret: the simultaneous evaluation of time, frequency and level information.

Measuring should therefore only support hearing, it may perhaps make one or the other auditory impression better generally definable and objectively detectable.

We hope that the topic we discussed above has been a matter of interest as well as a piece of valuable information on whether to rely on your hearing perception or not.
What do you think? Write us in the comments!

Happy Sound Engineering !!!

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