How do various degrees vertically affect a speaker?

For performing musicians and engineers: stagecraft, engineering and gear.

Moderator: Moderators

Post Reply

How do various degrees vertically affect a speaker?

Post by zackp »

So I realize the horizontal dispersion is about getting the most sound thrown from left to right. Makes sense. But what about vertical? I’ve seen speakers with 100x100, 90x40, and all other random things. What does wide dispersion for you get vs small? I could see how the smaller dispersion would be more directional, but the wider might help through sound over heads?
zackp
Poster
Posts: 27 Joined: Wed Nov 30, 2022 4:47 pm

Re: How do various degrees vertically affect a speaker?

Post by Sam Spoons »

The ideal dispersion for a speaker system depends on the venue but, generally speaking a tighter vertical pattern is better as you are 'wasting' less energy into the ceiling and floor. The problem is that standard 'point source' speakers tend to radiate fairly similarly in the vertical and horizontal planes (this is due to physics not design) and only line array type speakers have a wide horizontal coverage with tight vertical dispersion. The other fly in the ointment is that dispersion is frequency dependent and higher frequencies are more directional than lower with sub bass speakers being almost omnidirectional (cardioid subs do get around this to a degree but 'normal' subs are typically omni).
User avatar
Sam Spoons
Jedi Poster
Posts: 19478 Joined: Thu Jan 23, 2003 12:00 am Location: Manchester UK
People often mistake me for an adult because of my age.

Re: How do various degrees vertically affect a speaker?

Post by Wonks »

As Sam says, the best dispersion angle depends on the venue.

Lets assume we're talking about a typical 8"/10"/12"/15" main driver + HF horn 'one box' PA speaker.

Consider yourself standing at a speaker position with your eyes at the same height as the speaker horn. You're looking out at the audience. Ideally your vertical dispersion pattern would be from the head of the nearest audience member to the head of the furthest audience member.

What you ideally want to avoid is a lot of the sound being sent up to the ceiling where it will be reflected back down and mix with the direct sound coming from the speakers, resulting in a measure of comb filtering affecting the sound quality. The more direct reflections bouncing off walls and ceilings, the stronger the reverb level in the space and the less clear the sound will be.

If you can direct all the sound at the audience and none at the walls and ceiling, then you'll get the best sound quality possible in that space. Unless you've got a big venue with enough space to install a carefully positioned line array system in it, it's very unlikely that you'll get anywhere near that ideal.

But it's still good to try and minimise the amount of direct sound that is being directed at the ceiling and walls. You can't do much about sound bouncing off the floor but assuming that you have a reasonably full venue, then the audience will reduce the amount of reflections from the floor, along with any carpeting or soft seating.

So selecting a coverage pattern that suits your typical venue will help to get a good PA sound.

Your typical fairly low-ceilinged pub/small club will benefit from a tight vertical pattern, so say 40° (or ±20° from the speaker's horizontal axis) Angling the speakers down (if possible) will help here. Some speakers have both straight and angled pole connections in the base. Or you can get angled adapters for speakers that only have a single pole socket. Angling the speakers in so the sound doesn't bounce off the nearest wall is also a good idea and helps improve coverage in the central areas.

A larger venue with either tiered seating or a balcony will benefit from a wider vertical dispersion, but again, you still want to minimise the amount of sound being directed at the ceiling and walls.

Note that the dispersion angle is normally measured as the point where the SPL has dropped by 6dB at 8kHz. So it's already down from the full on-axis level. You'll get some HF sound beyond this angle, but it will probably drop off quite quickly as the angle increases (this will depend on the HF driver+ horn design). -6dB is a physical halving of SPL/volume, though the ear tends to perceive it as a bit less than this. But still, you won't be getting the full frequency range of the mix at the edges of the dispersion pattern.

So you have to balance the wish to give as good a mix quality to as much of the audience as possible by having a wide dispersion angle, and wanting a narrow dispersion angle to curb unwanted reflections from walls and ceilings.

If you have PA speakers being used as floor monitors, then your requirements on 'vertical' dispersion angles may change. A 90°x40° dispersion pattern becomes 40°x90° if the speaker is on its side. The 90° vertical angle can then be beneficial in getting sound to the users ears, but the 40° horizontal dispersion can ether be useful or a hindrance.

Useful if only one person is using that monitor and they stand relatively still, but not so good if you've got say one monitor for three backing singers. A 40° angle at 5 feet away from the monitor give a coverage area that's about 3' 5" feet wide. You could get two people standing close enough together so that both get a decent sound from the monitor, but with three it would be impossible. So if you are using a PA speaker as a monitor in that instance, you would be better going for one with a 90°x60° or 90°x 90°dispersion.

If in doubt, try using a protractor to draw some different angled triangles on card, say 40°, 60° and 90°; cut them out and take them along to your next gig. Look along them (holding them both horizontally and vertically) and you'll get a better idea of in how wide a pattern the majority of the sound is spreading out from your speakers.
User avatar
Wonks
Jedi Poster
Posts: 16764 Joined: Thu May 29, 2003 12:00 am Location: Reading, UK
Reliably fallible.
Post Reply