Why do we use horns?

[Matt Riley]

So I was hanging out with a friend of mine, who does a lot of studio/mastering work and he asked me an interesting question, to which I wasn't able to give a particularly satisfactory answer. His point was that in a decent acoustic environment there should be no need for horns, and actually that they introduce a number of detrimental issues as well as solving some, and was specifically directed to the live monitoring context. One of the points that he asserted when making his argument was that a dome tweeter has a consistent 90 degree pattern, and so actually the benefits gained were simply those of efficiency.

 

My answer was that a dome tweeter, by design, will have a directivity dependent on the frequency it's reproducing at the time, where a CD horn may have more consistent directivity over the whole frequency range it is reproducing. I also contested the 90 degree claim. The final point I made was that in live environments, because of the size of rooms, it is almost impossible to get a room with good enough acoustics that you don't have any need to keep sound off the walls, and the issue of driver interaction and arrayability is still very relevant. The other issue I raised was that of the voicing of a horn loaded HF section was potentially advantageous in the monitoring context of getting vocals to cut through the stage noise.

 

So, over to the clever people... why aren't all the monitors we see on big festival stages loaded with big ATC dome tweeters instead of horns for the HF?

 

M

[Brian]

...why aren't all the monitors we see on big festival stages loaded with big ATC dome tweeters instead of horns for the HF?

Because 90 degrees is too wide for monitoring?

[Matt Pengelly]

...why aren't all the monitors we see on big festival stages loaded with big ATC dome tweeters instead of horns for the HF?

Because 90 degrees is too wide for monitoring?

 

+1

 

In the scenario you talk about on a big festival stage, it's completely plausible that there might be a dozen or so wedge mixes, with maybe 20 wedges reproducing them. If all of those wedges are chucking out HF at 90 degrees, that's one messy-sounding stage!

 

Also, dome tweeters do not provide the same highly sophisticated SDDS® (spilt-drink-delivery-system) technology as a horn; without which there is a very high chance that some of the lead vocalists pint may not find its way into the guts of the compression driver. That kind of waste is just not acceptable in professional touring circles where rider budgets are extremely tight.

 

Added to that, despite the protestations of your friend, I can't think of a single venue/space that I have worked in where I've felt that the theoretically superior sound of a dome tweeter would be worth removing any and all control over the dispersion of the PA.

[Simon Lewis]

Matt,

 

You've pretty much answered the question....

 

Efficiency and controlled directivity. You could easily be looking at an extra 10 to 20dB output with a suitable horn / compression driver. The output of a dome tweeter will indeed vary with frequency.

 

Simon

[robritchie]

Surly the increased dB could, in theory, be overcome. However the control and consistency of a CD horn could never be compensated for especially in a stage monitoring situation.

[Simon Lewis]

Surly the increased dB could, in theory, be overcome.

 

If you've got a method to achieve this, the sound reinforcement loudspeaker manufacturers would love to know about it ;-) Using a horn allows the impedance mismatch between cone and air to be improved. However, it can also introduce distortion - which is probably why less efficient direct radiating HF units still hold sway in critical listening situations.

 

Simon

[TimmyP1955]

The dispersion of both direct radiators and horn loaded drivers is much less consistent - and at high frequencies much more narrow - than most manufacturers would like us to believe - hence a lack of multi-frequency polar plots from most makers. With horn loaded drivers, pattern flip is an added complication - one that I've seen only one manufacturer talk about. The higher efficiency and pattern control of horns makes them very useful for many applications where direct radiators don't have the necessary output and/or control. Once multiple drivers and/or and crossovers are added into the mix, things like lobeing come into the picture. Both types of drivers have their own particular types of distortion.<br /><br />In the end, it all comes down to the needs of the user, and the skills of the manufacturer as to not just the type, but the particular model of loudspeaker that is best suited for the job.

[J Pearce]

Another important consideration is listening distance, critical listening is nearly always near field, our work is most often outside the near field, where dispersion control and pattern consistency becomes more important that +/-1dB frequency variations.