How to Mix Better with Poor Room Acoustics?

In India, most of the of events are happening indoors, and the concrete multipurpose hall is actually a nightmare for the sound engineer.

It is an undeniable fact that many of these concrete bunkers have such modest acoustics, which is actually disgusting for the sound engineering technician and a factor that takes away the fun of working.

While it scares us, the audience expects – quite rightly – a transparent, professional sound.

What to do?

Howdy SEA Fans, Welcome to another tiptuesday blog post and the topic we are discussing today will be beneficial for those who sound engineers who are doing sound setup in ca onfined atmosphere and here are some practical tips to avert the sonic disaster.

What is bad acoustics?
There are several parameters that can be used to capture the acoustics of a room.

Among the best known are the cryptic abbreviations RT60 and STI.

RT60  describes the reverberation time of a room.

This is defined as the time interval at which the sound pressure has dropped by 60 dB after the silencing of the sound source.

The Speech Transmission Index, STI for short, arranges the quality of speech transmission between 0 (obscure)  to 1 (excellent).

The problem lies in the detail as always, because the optimal RT60 and STI values are program-dependent.

Thus, a classical orchestra in a room with a long RT60 time (over two seconds) and a low ST index (below 0.5) copes much better than a rock band with PA.

The appearance of an Iron Maiden cover band in a historic concert hall thus represents a challenge in terms of sound engineering.

However, not only classical concert halls or sacred buildings but also modern multi-purpose halls often serve many purposes – but not to provide music sound with useful acoustics.

This is often the money because cost-effective construction and dry room acoustics are difficult to reconcile.

While talking one of the acoustic consultant and sound engineer here in kerala, he told that there are many big halls and sacred buildings in the state, which are not acoustic friendly and those who are gathering inside the building are not able to hear it properly.

Those who are constructing the building will be spending a huge amount for erecting the building and decorating it and a marginal amount is being spent for sound installation and acoustics and that will reflect in the overall sound output.

The reason is that most of the builders are not taking care of the acoustics part while construction. Even if the building construction is acoustically perfect the sound will not be audible if the audio setup is imperfect as room acoustics was not taken into consideration while setting up.

Buildings made of concrete and glass, in which walls and ceilings are at right angles to each other, can be erected quickly and cost-effectively.

The fact that you create spaces that have virtually no sound-absorbing surfaces and throw sound back directly into the room, the task of the sound engineer hardly facilitates.

1. Room Acoustics

Too much reverberation sounds awful, everyone knows that.

Our goal is, therefore, to prevent as many direct reflections as possible.

You have to distinguish reflections by PA and stage.

Our work starts on stage because reflections make it hard for the musicians to hear each other clearly.

This, in turn, leads the musicians to turn their amps louder, to play louder and as a consequence demand a louder monitor sound.

So the FoH technician gives more steam to the monitors and at the same time more levels to the PA.

The result is an unnecessarily loud FoH sound that creates further reflections.

What the sound engineer can do is, the stage should generate as much direct sound as possible and as few reflections as possible.

But what to do if it sounds like the thunder dome?

A cost-effective solution is to hang the stage on the sides and over the entire width of the back with heavier material as possible.

Of course, only flammable materials may be used.

Usually, Stage Molton is used.

Even better is the stage velvet.

The heavier, the better.

In addition, you should attach the fabric with some distance from the walls and not smooth, but hang in folds.

This causes not only high but also medium frequencies to be absorbed.

Ideally, the ceiling over the stage is suspended with fabric.

Even better: professional absorbers or acoustic ceilings are used.

The latter is up to the hall operator and not the touring band.

The idea behind it is to create an open-air-like acoustics on stage.

There the backline noise literally dissolves in the air as there are no reflective room boundaries.

If you hang the stage on the sides, on the back wall and the stage cover generously with Molton, you also get a reflection poorer environment.

The musicians listen better and are not tempted to trick the room acoustics over loudness.

The FoH sound also benefits, as it provides more design options due to the quieter stage.

As a rule, it is only possible for large professional tours to hang as many reverberant surfaces in the auditorium as possible.

2. Setting up and adjusting the PA

The RT60 curve of a large church or bare concrete hall shows that the reverberation time increases with decreasing frequency.

Low-mids and basses are particularly long in the room and like to superimpose the important vocal range.

In addition, the lower the frequency, the more complex it becomes to achieve a directivity with loudspeakers.

Nevertheless, a targeted sound distribution is important, especially to effectively use the only significant large absorber surface, which is available to us.

The tops should only cover the public area and not encourage walls or ceilings.

The easiest way to do this is with a flown PA, with the top parts or line array aligned to the audience area.

If this is not an option, speakers or tiltable stirrups are recommended for the tops.

Subwoofer, however, reduces it to a minimum and works best with a directed array.

With a cardioid setup, you can compensate for the bass on stage.

A tactic of small steps. You should be cautious with extreme system equalization, especially if the hall is empty during the sound check.

Overpowering room modes can be lowered with a sum EQ in the sum, beyond that it becomes difficult.

Of course, it would be nice if a bad room acoustics could be straightened out with the EQ.

But that’s just treating the symptoms, not the cause.

In addition, the sound at the FoH position may be improved by massive EQ use, but if one leaves his mixing port, one often discovers that too many frequencies are missing in the near field of the PA.

soundman behind a mixer at concert

3. Mix Backward

Backward is the new forward, at least when mixing in acoustically difficult spaces.

The main problem is to make a not too loud mix that still has an acceptable definition.

And that stands and falls with the singing.

If this is not understandable, it usually does not take long until one is allowed to answer questions and answers at FoH-Platz.

Therefore, it makes sense to start the soundcheck with the vocals.

We need a vocal sound that is understandable and sufficiently loud for each genre.

With extremely poor acoustics, the telephone receiver sound is often the last resort.

One generously uses the low-cut (like up to 200 Hz) and turns the hi-cut (up to 9 kHz) so far in that the vocals just do not sound too dull.

Then you build the band around the vocals.

Very important: once we have checked the vocals, we leave the vocal microphones open as we level the rest of the band.

The crosstalk in the vocal microphones decides whether we need to optimize the band or stage setup.

A look into the dynamics section is also helpful.

DJs often find it easier to offer a transparent sound in difficult rooms than a band.

This is because the finished music was mostly compressed and has little residual dynamics.

Thus, there is hardly a place where a snare or vocals prominent from the song.

But precisely these impulses sustainably stimulate an acoustically problematic space.

It creates reflections that mix with the direct sound and thus worsen the sound.

4. What the band can do?

The biggest influence on the sound are the performers.

Arrangement and tempo of the songs also have a not inconsiderable part in the good sound.

Some bands shine in a reverberant arena with good sound, others not.

Since large rooms in the bass range are sometimes faded out over several seconds, they are the natural enemy of metal bands with consistent double-bass attacks.

The song selection can influence the sound.

“More ballads, fewer ball pieces” is not a bad idea.

In addition, the FoH man is happy about the lowest possible stage volume. Because: less crosstalk = less room excitation.

So rather use in-ear monitoring as floor wedges and put plexiglass discs in front of the drum set.

You can turn over guitar boxes or combos and let them shine in the backdrop instead of in the audience.

A Kemper amp or Axefx is often a better choice than a full stack from Marshall.

Of course, that’s what the musician has to decide.

After all, the listeners want to hear the typical sound of the band.

Therefore, the tips and tricks presented here are to be understood as a suggestion for an emergency.

Hope you have found the tips useful and don’t forget to share your perspective on the topic as a comment below.

We are looking forward to hearing from you.

Happy Sound Engineering !!!

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