Myths about Pro Live Audio?

[RoadRanger]

Non-myth:

Point source speakers follow the inverse square law, -6db with each doubling of distance. Line arrays drop as little as -3db per doubling in their near field.

 

Myth:

Line arrays only drop -3db with each doubling of distance no matter how far out you go.

 

Non-Myth:

In a reverberant room speakers with less vertical dispersion will seem to throw further as they tend to keep sound off the ceiling so sound clearer at the back of the room and also can "throw" the sound over the front rows so are less loud up front = more even front-to-back in SPL. Also speakers with a narrower horizontal dispersion seem to throw further because they tend to keep sound off the walls so are also clearer at the back.

[RoadRanger]

Another myth:

Two or Three 60 degree trapezoidal tops have to be splayed at 60 degrees between each pair so give 120 or 180 degrees of coverage.

 

Non-Myth:

They are most commonly splayed at the angle of the trap cab's side = ~15 each so 30 degrees between two. That gives about a 90 degree coverage for two or 120 degrees for three in "real world" practice.

[Tomis17]

MYTH: Speaker cables are bigger versions of instrument. You can use them interchangeably. Heck, if you know how to solder, solder XLR ends on 12 gauge speaker cables and you've got yourself a heavy duty mic cable...yes, there are people out there operating this way.

[agedhorse]

It is true though that the same driver at the same power through a narrower horn will produce more SPL and thus "throw farther" because the horns are NOT starting at the same SPL. However, in practice, this doesn't usually come into play or work for our benefit.

 

 

This is correct, and may account for the "myths"

[dboomer]

Another myth: Two or Three 60 degree trapezoidal tops have to be splayed at 60 degrees between each pair so give 120 or 180 degrees of coverage. Non-Myth: They are most commonly splayed at the angle of the trap cab's side = ~15 each so 30 degrees between two. That gives about a 90 degree coverage for two or 120 degrees for three in "real world" practice.

 

 

Hard to say. It all depends but generally the less you splay them (in a plane), the more comb filtering you get. FYI ... comb filtering generally isn't as big a problem as people give it credit for.

 

You certainly could splay them 60 degrees and get roughly 120 degrees. The first problem is getting the drivers very close to each other, and that is usually limited by the cabinet.

[Coaster]

 

Maybe you should. I'm not inclined or prepared to debate the laws of physics, but, if you want more SPL at a distance than you need more SPL at the source. For example, A 60 degree horn producing 100dB will have the same SPL at 100 feet as a 90 degree horn producing 100 dB. There is a lot of info out there on this subject if interested.

 

 

if you use the same driver with the same power and change the horn from 90 to 70 degrees you will hear sound farther away.

 

also, its called inverse square law not inverse half law and line arrays do not follow "inverse half law" at 100% of frequencies and distances.

[dboomer]

if you use the same driver with the same power and change the horn from 90 to 70 degrees you will hear sound farther away.

 

 

Correct, except that you will be running away from the woofer which didn't change. So typically you would adjust the padding to the HF driver to maintain the balance. So it would be a benefit if you were designing a cluster, but not really if you are simply stacking boxes.

[sibyrnes]

if you use the same driver with the same power and change the horn from 90 to 70 degrees you will hear sound farther away. also, its called inverse square law not inverse half law and line arrays do not follow "inverse half law" at 100% of frequencies and distances.

 

 

I don't know where you came up with the term "inverse half law." That's a new one on me. I did mention the "Inverse Distance Law": http://www.sengpielaudio.com/calculator-distancelaw.htm

 

"A 60 degree horn producing 100dB will have the same SPL at 100 feet as a 90 degree horn producing 100 dB."

 

I'm quoting myself here, because apparently you're not grasping the point of my "myth" and you are more interested in just arguing. You see a 60 degree horn and a 90 degree horn are equally sensitive to the laws of physic, what ever you want to call them, - one does not project sound further than the other.

[JohnnyGraphic]

 

also, its called inverse square law not inverse half law .

 

 

Not to be confused with the "Inverse Half-In-Law", where you marry your mothers older twin sister who is also your daughter.

[6Imzadi]

OMG, that is just wrong. Tommy, tell him how is really works with the in-laws.

[Coaster]

 

I love that one, get it all the time! Here's one that I know is going to cause trouble: A 70 degree horn will project further than a 90 degree horn.

 

 

it will given the same driver and power. quote is yours, bold is mine

 

you say nothing about db or spl

[Coaster]

 

No. It would be nice if it where that easy to defeat the laws of physics, but that's why they call them laws. Sound follows the inverse distance law. If you double the distance, the sound level is cut in half. If you triple the distance you have 1/3 the sound level. The shape of the horn or the dispersion pattern cannot change that(on this planet, anyway;)).

 

 

again, its inverse square law. square, not half

[Tomis17]

OMG, that is just wrong. Tommy, tell him how is really works with the in-laws.

I've learned to just let him learn. Two weeks ago he decided to use his rig for a Valentines event. He set his stuff up thinking everything was going to work great...wrong. The band came to do sound test and politely asked if they could use someone else p.a. He was pretty ticked and wondered why they blew him off like that. I just shrug my shoulders...

[WynnD]

A good soundman can make a bad band sound good. Or "It can be fixed in the mix".

 

 

I like this one. A good soundman can make you sound as good as you are. A bad one can only make you sound worse than you are.

[Dogoth]

Not to be confused with the "Inverse Half-In-Law", where you marry your mothers older twin sister who is also your daughter.

 

 

That would be called the "Inbread Half-In-Law".

 

 

 

myth) A Great mic pre will make "a world of difference" no matter what kind of mic or system it is attached to.

 

myth) Audio Engineer - D.J. there is no difference (they both make sound right?).

 

myth) Sound technicians can tune instruments from the FOH position (sans the Anteries unit :-)

 

myth) forget acoustics, physics and talent. Electronic wizardry can fix any mix.

 

myth) once you get a band mixed, you can take it from venue to venue and ALWAYS get a good mix "don't touch that dial!"

 

myth) Physics! We don't need no stinking physics! We got a sound guy!

 

truism) Good balanced monitors can help a band perform better (but they still can't tune their instruments :-)

 

truism) If you put the mic directly into the monitor or main speaker, it usualy will feedback.

 

truism) If the mic is already feeding back, you probably can't turn it up any more "Can I have some more of me?"

[stunningbabe]

 

I like this one. A good soundman can make you sound as good as you are. A bad one can only make you sound worse than you are.

 

 

Makes perfect sense to me!~

[sibyrnes]

again, its inverse square law. square , not half

Again, it's inverse distance law. distance, not square

I'm sure this conversation is getting old for everyone here, but you won't let it go. My statement, that you seem to have a problem with, is true. If we double the distance, the value for the sound pressure falls to a half of its initial value or about 6 dB. That is an established fact, easily verified. For example http://www.audiosonica.com/en/course/post/32/Decibels-Inverse_distance_law

What are you talking about?

[dboomer]

 

is true. If we double the distance, the value for the sound pressure falls to a half of its initial value or about 6 dB.

 

 

-3 dB would be half power. -6 dB is one quarter power. Inversely proportional to the Square of the distance

[sibyrnes]

-3 dB would be half power. -6 dB is one quarter power. Inversely proportional to the Square of the distance

 

 

Right, but I'm talking about sound pressure level, SPL, not power. You are correct in that as you double power you increase 3dB, but as you double distance you loose 6dB. And 6dB is percieved as 1/2 the SPL".

[dboomer]

Ok ... you would be correct for "pressure" and me for "intensity"

[sibyrnes]

:

Ok ... you would be correct for "pressure" and me for "intensity"

Yeah and the difference is hard to wrap your head around(at least for me!), but most here are familiar with the term SPL and it's what we hear.

Maybe we could use a little less pressure and intensity around here!

[jasps]

If one is using a point source speaker with a horn and you have the speaker angled correctly for the geometry of the room, you don't lose 6dB per doubling of distance, either.

[dboomer]

Doesn't matter whether or not a horn is involved. In fact it doesn't even matter if a speaker is involved.

 

You DO until you reach the critical distance line. From that point since the reflected sound is equal to or greater that the direct sound it basically remains constant from there. Now if you take that outdoors you will basically lose 6 dB per each doubling of distance if you are in an open field. It can change depending on reflections.

[sibyrnes]

Doesn't matter whether or not a horn is involved. In fact it doesn't even matter if a speaker is involved. You DO until you reach the critical distance line. From that point since the reflected sound is equal to or greater that the direct sound it basically remains constant from there. Now if you take that outdoors you will basically lose 6 dB per each doubling of distance if you are in an open field. It can change depending on reflections.

 

 

Interesting! Is it possible for the reflected sound to ever be "equal to or greater than the direct sound". It seems some of the energy of the refected sound has to be absorbed by the walls, furniture, people etc.

[dboomer]

Maybe I should have made a more complete explanation. It's not just the reflected sound at that point ... it is the combination of both the direct and reflected sound, so yes they can add and be 3 dB louder than the direct sound itself. It gets pretty complicated because of so many variables.