Dave_Gib

time correction

I have some hybrid line arrays, a line of mids matched up with a single compression horn tweeter.

I know that the difference in intensity between a line source and point source gets more dramatic the further away you get. Does the rate of propagation change? The speed of sound is still the speed of sound, maybe I'm just thinking of sound as a liquid which would be wrong?

here are the speakers in question, never mind the center channel, watching movies isn't as important to me as listening to music



Would I need to put an amp on my tweets and a separate amp on the mids, use something from the prosound world to x them over and play with time correction. Or speed of sound is the same no matter what and just build the horn lenses out further to align the coils?

maybe this is wrong sub-forum, I have no idea if there is such a piece of gear with time correction in the home theater world

chuckg

Re: time correction

As you say, the speed of sound is the speed of sound...The time difference in the mids and tweet is only the position difference between the tweet driver coil/center and the mids coil/center. That could only be quite a bit less than one millisecond.

What is the problem you are having?

You do have some real time delay issues with line sources, though. the delay between sound from a mid near the center of the array and a mid at one end of the array can be substantial, especially in the near and mid field. For that reason, line arrays will always have nasty lobing problems vertically. That horizontal center array will have nasty lobes in the horizontal.

--ignore the man behind the curtain

Dave_Gib

Re: time correction

I got it, sound waves in a line array have no special propagation characteristics.

I have no problems at all. I got a new head unit for my truck with time correction it made a really big difference, just thinking of something for the house.

I could build a crescent moon enclosure to take care of the lobing, but then you'd lose all the benefits.

JohnRice

Re: time correction

The speed of sound does in fact change across the audible frequency, and there are speaker designers (some extremely prominant ones, in fact) who believe that there is a benefit to staggering the vertical alignment of drivers, with the tweeters furthest back. So, "the speed of sound is the speed of sound" is not correct. Of course, staggering drivers only works 100% at a predetermined listening distance.

All that said, I agree with Chuck that your greatest issue is the relative delay between all those mids, which would be a particular problem on the center. Of course, speakers have been designed that way from such prominant designers as Polk and even Mark Levinson.

Also, if you want to dispute that sound speed changes with frequency, or that it takes too great a shift to matter, explain why the sound of a siren drops suddenly as an ambulance passes you. It is due to the change in speed of the sound traveling toward you between the ambulance approaching and moving away from you.

They flutter behind you, your possible pasts.
Some bright-eyed and crazy, some frightened and lost.

Dave_Gib

Re: time correction

yeah, the doppler effect.......doesn't have anything to do with higher frequencies traveling faster....if they do.....


What I was looking to eventually do is play with time correction on the horns for different listening positions. For a long room, I play the Wii game system about 5 feet from the TV, watch movies at 13 feet from the TV and have a card table behind that where people end up congregating during social gatherings. I know the sound from the tweeter will fall off after about 15 feet, but from what I read in this article today it wont be delayed with regard to the mids. http://www.meyersound.com/support/pa...ray_theory.htm
According to that article I don't need to use time correction at all.

I was looking for a piece of home audio gear that could do this, but I don't think it's out there.

Wouldn't the lobing be more prominent with the towers, seeing how they are longer thus the difference between the center and edge speakers being greater than with the center.

I don't want to make the line arrays sound like a PS speaker, like how some electro-statics delay from the inside out, or a bessel config.

All speakers have pros and cons, I'm really happy with these lines, they suit my needs well. I'll upgrade to a full line of tweeters when my child is old enough to know not to press the domes in.

Dave_Gib

Re: time correction

John, it just came to me, I think what you are talking about with these speaker builders putting the tweeters further back has more to do with higher frequencies transitioning to the far-field further down range than freqs coming from the mids.

It sounds interesting, I'll have to look into something like that for my next build. This would do better in the ADIY sub-forum now.