stupid questions? yep
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is on axis and off axis simply a result of whether or not the speaker is pointed AT you or not direcltly at you? is off axis response a good thing? does beaming occur only on axis? what exactly does beaming sound like?
JimJ
5,000+ posts
Tangled Up in Blue
Yup.
Yes. A speaker that throws a wide soundstage and is more forgiving where you sit is a very good thing.
Beaming is a very narrow on-axis response. Move beyond that, you start hearing it drop off...
Being too far off axis to a speaker can result in some funky things...Fostex and Lowthers, for example, have a very nasal and honking characteristic if no phase plugs are used and they're placed facing away from the listener.
I presume you mean something like.....a single 10" driver vs. an array of 3" drivers accumulatively totaling the same Sd as the single 10"?
Line array's aren't my forte.....but my guess would be that beaming for the array would occur at the point that it would for the single individual smaller driver.
I'd have to do more research to actually back that up, however.
Nothing in my post is written in stone, there is a tolerance for error just
in case one of those line array scientists intrudes on the discussion with
esoteric response. Try to keep the understanding the line array simple,
then it all becomes easy. Don't cloud your mind with too much science
otherwise you'd never build one.
Jim Griffin's line array document.
http://www.audiodiycentral.com/resource/pdf/nflawp.pdf
If you use cone drivers there is a formula to give you a maximum
recommended crossover point to minimize comb filtering.
It's
13560/driver center to center spacing.
If you want to make line array with 4 inch midranges and the center to
center spacing is 4.5 inches, plug that number into the formula and
you get 3013hz or ~3khz is the maximim recommended low pass to use
on the 4" drivers.
If you want to use 8" mids, with 8.5" center to center spacing, then
1595hz is the max recommended crossover point.
Are these numbers written in stone? .... no
You can cheat. If you increase your listening distance cheating doesn't
sound that bad.
Re: Beaming. Horizonal dispersion is limited to the performance of the
single driver. If your 4" drivers @ 3khz crossover has better off axis
performance than an 8" driver @ 1.6khz then the 4" will be have higher
horizontal dispersion.
But if you use a 1khz crossover point for the 4" and 8" then you may not
be able to tell the difference.
Beaming is over-rated if you are building a system just for you and not
an audience because you can design your loudspeaker to be toed in
for sweet spot listening. The NSB/PT2 array I made has a turntable mechanism
so I can rotate the array for whatever listening position I'm in. If I'm sitting
on the couch in the center, I toe in both arrays equally so the drivers are
pointing at me for optimium sweet spot. If I sit on the left side of the couch,
I toe the left side less and right side more. This is an array with 4" drivers
crossed over at 1.7khz, so because these drivers are not operating at very
high frequency there is less beaming and the tweeters are really the focal point
of the system. So, the sweet spot is really based on the tweeters not the NSB's.
On the other hand, if you designed your array where the midranges are doing
higher frequencies then aiming those midranges might be more important.
When you make a vertical line array from floor to ceiling, stacking drivers on top
of each other and obeying the generic comb filtering rules, it would give you
the illusion of having very high vertical dispersion because you can hear the
sound whether your head is low to the ground or way up high near the ceiling.
Comb filter is hard to grasp for some people. The best way to describe this is
to visualize it. Get two 15" subwoofers and place them 3 feet apart. Stand in
front of one of them and move towards the other sideways, did the sound change
or did you hear the same amount of bass? Most likely it sounds the same.
What if you spaced those woofers 500 feet apart? Yes, you can hear a difference
as you move from one woofer to the other.
Do this same test with two tweeters. Get two tweeters spaced 3 feet apart.
Stand in front of one and listen, then move your body sideways to the other
one. Did the sound change? Probably, because when you stand in the 'line of fire'
staring at the tweeter the sound is in your face, but as you moved away you
heard it less and started to hear the other one more. This is like comb filtering.
To minimize this perception you need to place those tweeters very close together
so you don't hear the 'voids'. You can see how lower frequencies are more forgiving
to distance than the higher frequencies. That's why if you make a line array with
domes that have excellent dispersion, it's best to keep the center to center close,
ideally less than 1.5". If you use planars or ribbon type of tweeters, because they
have weak vertical dispersion, you can just stack them and the void between
elements isn't as critical, but at very close range you will be able to hear the combing
effects. The ideal planar or ribbon is contiguous, ie buying a one piece element that
spans the whole floor to ceiling instead of using stacked smaller tweeters.
The bottom line is. If you listen to your array at greater distances the more error your
design can have and stlll sound excellent. But if you don't have that luxury and want
to listen to your array .. lets say 5 feet or closer, then you have to pay attention to
comb filtering more so you don't hear these 'voids'.
in case one of those line array scientists intrudes on the discussion with
esoteric response. Try to keep the understanding the line array simple,
then it all becomes easy. Don't cloud your mind with too much science
otherwise you'd never build one.
Jim Griffin's line array document.
http://www.audiodiycentral.com/resource/pdf/nflawp.pdf
If you use cone drivers there is a formula to give you a maximum
recommended crossover point to minimize comb filtering.
It's
13560/driver center to center spacing.
If you want to make line array with 4 inch midranges and the center to
center spacing is 4.5 inches, plug that number into the formula and
you get 3013hz or ~3khz is the maximim recommended low pass to use
on the 4" drivers.
If you want to use 8" mids, with 8.5" center to center spacing, then
1595hz is the max recommended crossover point.
Are these numbers written in stone? .... no
You can cheat. If you increase your listening distance cheating doesn't
sound that bad.
Re: Beaming. Horizonal dispersion is limited to the performance of the
single driver. If your 4" drivers @ 3khz crossover has better off axis
performance than an 8" driver @ 1.6khz then the 4" will be have higher
horizontal dispersion.
But if you use a 1khz crossover point for the 4" and 8" then you may not
be able to tell the difference.
Beaming is over-rated if you are building a system just for you and not
an audience because you can design your loudspeaker to be toed in
for sweet spot listening. The NSB/PT2 array I made has a turntable mechanism
so I can rotate the array for whatever listening position I'm in. If I'm sitting
on the couch in the center, I toe in both arrays equally so the drivers are
pointing at me for optimium sweet spot. If I sit on the left side of the couch,
I toe the left side less and right side more. This is an array with 4" drivers
crossed over at 1.7khz, so because these drivers are not operating at very
high frequency there is less beaming and the tweeters are really the focal point
of the system. So, the sweet spot is really based on the tweeters not the NSB's.
On the other hand, if you designed your array where the midranges are doing
higher frequencies then aiming those midranges might be more important.
When you make a vertical line array from floor to ceiling, stacking drivers on top
of each other and obeying the generic comb filtering rules, it would give you
the illusion of having very high vertical dispersion because you can hear the
sound whether your head is low to the ground or way up high near the ceiling.
Comb filter is hard to grasp for some people. The best way to describe this is
to visualize it. Get two 15" subwoofers and place them 3 feet apart. Stand in
front of one of them and move towards the other sideways, did the sound change
or did you hear the same amount of bass? Most likely it sounds the same.
What if you spaced those woofers 500 feet apart? Yes, you can hear a difference
as you move from one woofer to the other.
Do this same test with two tweeters. Get two tweeters spaced 3 feet apart.
Stand in front of one and listen, then move your body sideways to the other
one. Did the sound change? Probably, because when you stand in the 'line of fire'
staring at the tweeter the sound is in your face, but as you moved away you
heard it less and started to hear the other one more. This is like comb filtering.
To minimize this perception you need to place those tweeters very close together
so you don't hear the 'voids'. You can see how lower frequencies are more forgiving
to distance than the higher frequencies. That's why if you make a line array with
domes that have excellent dispersion, it's best to keep the center to center close,
ideally less than 1.5". If you use planars or ribbon type of tweeters, because they
have weak vertical dispersion, you can just stack them and the void between
elements isn't as critical, but at very close range you will be able to hear the combing
effects. The ideal planar or ribbon is contiguous, ie buying a one piece element that
spans the whole floor to ceiling instead of using stacked smaller tweeters.
The bottom line is. If you listen to your array at greater distances the more error your
design can have and stlll sound excellent. But if you don't have that luxury and want
to listen to your array .. lets say 5 feet or closer, then you have to pay attention to
comb filtering more so you don't hear these 'voids'.
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