Sub arrays for even front to back coverage

[Jon Pusey]

I work in a club which would be approx 1000 capacity standing, approximately 40 meters front to back. The boss is concerned that the front to back sub coverage drops off too much and that there is not enough punch from about halfway down the room.

The stage is approx 20m wide, about 0.8m high. The layout is a pros theatre with audience terraces rising up about 5m front to back. There is a narrow balcony at about 7m. The club runs another venue which is similar in size and layout but outdoors. I have not heard the outdoor system but my boss has expressed the same concerns.

In the indoor club there are two, two wide stacks of subs about 20m apart, below a line array flown at approx 9 meters. The system also exhibits severe non-uniform coverage left to right, but this is of less concern to the owner. Due to the layout of the audience area the subs do fire into the edge of the first terrace about 5 meters away.

Everything I have read about sub arrays seems to focus on uniform left-right coverage, with little on front-back coverage. For this application, it is not the end of the world if the response skews towards the bass end towards the back of the room.

In an almost ideal world, assuming that subs can be flown next to the arrays if necessary, but that the array height cannot be raised, what would be sensible steps to achieve this coverage?
If you flew a long line of subs next to the array, could this be enough to even out the coverage? Could you use delay to steer the pattern of the sub array up, or would you lose impact and create noticeable problems around the crossover to the mains?

If anyone has any pointers on what solutions to investigate I would be most grateful.

 

[Ivan Beaver]

Re: Sub arrays for even front to back coverage

The only way to get more even front to back coverage is to fly the subs.

Inverse square law is fighting you and you will lose.

The issue also has to do with wavelength. It depends on how much height you have to fly the speakers.

Subs do not have to be as close together as higher freq devices in order to get directional coverage and for coupling.

If we knew what sort of height you have- how many and what type subs your have that would help.

Maybe some photos would help.

Would you be open to flying the subs in some sort of configuration in the middle of the room?

It doesn't matter what might work in a model-if the actual space does not allow it-so we need to know the limitations of the space or it is a waste of time.

How low does the main PA without subs go-freq wise? That makes a difference on where the upper end of the sub range is and where you can crossover into them. The higher it is-the more localization you have to the subs.

The problem is that whatever you do it will be a compromise and with a left/tight configuration of the PA there is only one place to get a "proper" alignment and everywhere else will be off.

 

[Jon Pusey]

Re: Sub arrays for even front to back coverage

The outdoor venue is the venue where the bosses are looking at making immediate changes. Currently there is no system, so it is starting from a blank slate. Max trim height is about 7m on a ground support stage roof here, but it is possible to fly both subs and tops. I have seen two specs for systems for this venue and they both have subs flown next to the array, but I know they did something similar last year and still had some problems.

In the indoor venue we have two types of sub, logic systems nd315, 3 a side which are flyable, and 3 logic systems nd218 a side which are not flyable. the array is logic systems va. I don't know the crossover frequency. The trim height of 8 - 9 metres ish is as high as possible and close to the roof. The system is set up for live performance and sightline / decor issues mean a flown centre cluster isn't an option.
,

 

[Ivan Beaver]

Re: Sub arrays for even front to back coverage

The outdoor venue is the venue where the bosses are looking at making immediate changes. Currently there is no system, so it is starting from a blank slate. Max trim height is about 7m on a ground support stage roof here, but it is possible to fly both subs and tops. I have seen two specs for systems for this venue and they both have subs flown next to the array, but I know they did something similar last year and still had some problems.

In the indoor venue we have two types of sub, logic systems nd315, 3 a side which are flyable, and 3 logic systems nd218 a side which are not flyable. the array is logic systems va. I don't know the crossover frequency. The trim height of 8 - 9 metres ish is as high as possible and close to the roof. The system is set up for live performance and sightline / decor issues mean a flown centre cluster isn't an option.
,

The basic issue is distance. The distance to the furthest listener does not change (enough to be considered) whether the subs are flown or on the ground.

But the distance to the closest listeners changes quiet a bit (depending on height) between ground and flown.

So the rear SPL stays the same-the only thing you can do is to try to reduce the near SPL-so they are more balanced.

This can be done in a couple of ways- Get them up high- or try to do a directional array by spacing the subs so that most of the energy is going towards the rear of the room and less is on the close people.

It is not just a matter of what the array "looks like" but also rather how it is processed.

It is one thing to complain about something-and then quite another to start putting restrictions on what can and can't be done to try to fix it.

It is all a matter of compromise.

 

[Ivan Beaver]

Re: Sub arrays for even front to back coverage

The outdoor venue is the venue where the bosses are looking at making immediate changes. Currently there is no system, so it is starting from a blank slate. Max trim height is about 7m on a ground support stage roof here, but it is possible to fly both subs and tops. I have seen two specs for systems for this venue and they both have subs flown next to the array, but I know they did something similar last year and still had some problems.

In the indoor venue we have two types of sub, logic systems nd315, 3 a side which are flyable, and 3 logic systems nd218 a side which are not flyable. the array is logic systems va. I don't know the crossover frequency. The trim height of 8 - 9 metres ish is as high as possible and close to the roof. The system is set up for live performance and sightline / decor issues mean a flown centre cluster isn't an option.
,

I have been doing some modeling-using your 7M trim height limit.

At that height there is very little that can be done (that I can see quickly) that would affect the overall sub region (30-80Hz).

Yes there are some alignments (physical and/or delay) that will affect a single freq-but not enough to be concerned across the band.

Hence the reason it is IMPORTANT to look at more than 1 freq when doing models-or you can easily be lead into believing something that is not useful.

If you had more height available-then there are some options that would work-but that is not an option.

 

[Glenn Adams]

Re: Sub arrays for even front to back coverage

Agreed, you have to get the subs up. Anything else is mud city. People, bars and tables block and will take abite out of your lows, and a delay of subs anyplace in the club will add or cancel in some very odd places.

I am going back in my way back when machine but I remember a place in Wildwood NJ that had a quadrophonic PA.
it had ground stacked stuff all round the dance floor and it did work. I was never out on the dance floor, where I can only imagine blood flow from ones ears, but everywhere else sounded OK with good low end. Still cancel city here and there, and with lobes off KingKong.

 

[Jon Pusey]

Re: Sub arrays for even front to back coverage

Thanks for the help. Have told my boss that whatever system he wants to go for he should try and get a structure that lets him fly the speakers higher.

 

[Tim McCulloch]

Re: Sub arrays for even front to back coverage

Thanks for the help. Have told my boss that whatever system he wants to go for he should try and get a structure that lets him fly the speakers higher.

True. Trying to say "Captain, I can't rewrite the laws of physics" to your boss will likely get you a blank stare...