Average SPL throughout a venue. Should your mix level be the same for every person in the audience?
With the advent of high performance DSP, improved amplifier and loudspeaker technology and the introduction of flexible design software, the major audio system manufacturers have given us excellent sets of tools for designing, adjusting and safely rigging large audio systems.
A systems engineer now has
the ability to design optimum sound coverage for the whole audience. Often this
is interpreted as ensuring that the whole audience area SPL coverage is within
+- 3dB and I have seen many system designs that have achieved that goal.
In my opinion the objective of the delivering the same SPL level across the whole venue is not the correct goal. Here are some discussion points that have persuaded me to modify my approach to what is a suitable mix level across the whole audience.
Sure, for an arena rock show getting a good rock mix to the back of the seating areas is necessary but that does not mean it has to be as bone crushing as it usually is down front. A good mix at 95 – 100 dB is still exciting and satisfying.
There is another really important issue here; not every show is a rock show. There are many other musical styles that tour regularly and attract significant audiences. Jazz, folk, broadway and world music all draw devoted audiences and add up to a significant number of seats sold annually. Furthermore the age range of the audience is much broader, many of these shows have a high percentage of significantly older attendees.
This is an another important point. Audiences with a higher average age are much more sensitive to high SPL levels and many complaints are lodged at venues about shows being too loud. Often older patrons will deliberately sit far from the stage to avoid what they consider to be high volumes. Jazz, folk, broadway and world music audiences can be very particular about the sound quality and sound style of the show. Like a rock or rap show, the sound style of these shows is a direct the result of the musical content, the sounds have to be appropriate for the music.
There is one other factor that is of major significance, ticket sales. Most shows do not need a sellout to make money. Not every show sells out and the empty seats are usually at the top of the balcony in a theatre or the nosebleeds at the top and sides of an arena. Of course these are the furthest points from the stage and probably have more energy directed to them from the speaker system to achieve that magic average loudness level throughout. The result of that is significant energy reflected back into the room which negatively affects the mix quality everywhere.
All these factors are real life for a lot of engineers on a daily basis, so how do you deal with them? Well here are a few answers that work for me when I am out mixing FOH on shows.
- Check seat sales before you do the speaker coverage simulation. Below about 85% sold you are going to have rows of empty seats at the back or the top of the venue, even allowing for walk up sales. Seriously think about not covering those areas or at least make them the soft edge of the coverage pattern.
- Check the SPL distribution and coverage of your
simulations very carefully. It’s OK to be -6dB at the back or edge of the
seating area compared with the average levels on the main floor, even for
quieter jazz or folk music shows.
- A good (albeit rough) rule of thumb is to point
your boxes at the audience in proportion to the seat counts in each area.
If 40% of the audience is in the balcony and the rest on the main floor
then point 40% of your boxes at the balcony and the rest at the main floor.
(There is a significant sidebar to this point but it will have to wait for
an upcoming topic).
- Consider using delays to cover the audience section
that is the last to sell. If the seats don’t sell then you can turn the
delays off without sabotaging your mix or coverage throughout the rest of the audience area.
- Make sure the edges of your coverage area are
starting to roll off in level, the last couple of seats at the end of the
side aisles do not need to be at the same SPL level as the centre of the seating
area, especially if there are hard side walls. This can be a difficult
objective with a fixed horizontal coverage line array and is significantly
venue dependent.
- For an audience that is predominantly older
having a gradual reduction in level further back in the venue is often
very welcome.
To sum up, think hard about what you are dealing with every morning when you walk into a new venue and start your setup.
The old axioms still apply, point the speakers at the audience, not at the walls, floor or ceiling.
Your audience coverage does not have to be +-3dB, it’s OK to have a 6dB drop in level at the very top or side edges of your audience area.
Reducing the amount of reflected energy in the room increases the critical distance for direct sound and overall improves the listening experience.
Don’t automatically juice up the top cabinets in your speaker arrays to get more level to the very back and top of the venue unless you are sure those are sold seats. Often an EQ tweak will achieve a good mix quality in the edge seating areas without throwing too much power up into the roof or onto the walls.
You know your artist and the audience they attract, I strongly recommend paying close attention to your simulation and adjust your coverage levels to suit.
Below is an example of a well designed distribution that reduces levels at the upper, less populated areas and does a controlled roll off at the edges of the venue.
Soundvision design for the outdoor old Roman Ampitheatre in Viennes, France
Note that the top 25% of the seating area is approximately 95dB compared with an average level of 100 dB in the lower bowl. The very top couple of rows are down to 90db. The shaded areas at the side extremes are covered by point source speakers that can be adjusted in level as needed.
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Clive Alcock - 2023