Live Sound & Production

[abzurd]

So Don, "boomer".... now "boomer2" in this forum,  pointed out in the old forum the specs about the horizontal pattern narrowing to 50 degrees above 5 Khz. At a wedding we did last night I finally got to use the system by itself and validated this is the case, which is disappointing. Between this and the 20 degree vertical coverage, you can't put the "best sound" everywhere. Dance floor coverage remains a challenge because both the horizontal and vertical are not really covering the near field.

2 columns per side would allow for more options. Stacked they would cover the vertical issue as you'd get another cluster of tweeters much lower than when using one box. The downside is this configuration allows for bodies to stand direcly in front of the speaker, which effectively blocks those highs.They can also be offset 30 degrees when stacked, which could be useful at times I suppose.They could also be splayed I suppose, but that negates the aesthetic of the unobtrusive single column.

Sound wise, when you're in the sweet spot it's very good with fantastic detail and clarity. As mentioned before, the mids can be a bit much so cutting back 3K is a must. Also, adding a little beef in the 250-400 range fattens things up.

As for the dropping off less than a point source speaker, that's a yes and no thing. It's doesn't really seem keep the volume over distance any better than anything else I've used, BUT it does keep the balance of the sound over distance way better than anything else I've used or heard. The highs come along for the ride which is pretty cool. I've heard stuff like JBL SRX ground stacks carry well in a large room or outside, but when you're up close, especially indoors, the highs are sheering your face off and the room can't usually take the volume needed to carry highs to the back. With the FBT it pretty much sounds the same whether you're 10 feet away or 60. Up close the snare and hi-hat isn't making you wince with every hit, yet you can hear it crystal clear far back. 

At 1/2 the size of the other small subs we were using, the subs do a pretty good job and are so small they look more like a stand base than a speaker. I ended up using preset 4, which is a 180 Hz crossover with emphasis on "punch". This put out a spike at 125Hz, which has nice impact, but sounds a bit like hitting a large plastic bowl. I knocked it down so it didn't stick out and it still had the punch without the "thunk" sound. Still not going to rattle bones, but SPL is not an issue and they are insanely portable.

[dboomer2]

" Feedback wise, the multiple drivers do help that. I walked in front of a column several times last night and no hint of feedback. "

Don't drink the Kool-Aid.  Feedback happens because the level of the speaker gets back through the mic at the level it goes in.  It's not smart and it cannot tell how it got there.  You didn't get feedback because you were below that level.

[abzurd]

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dboomer2 wrote:

" Feedback wise, the multiple drivers do help that. I walked in front of a column several times last night and no hint of feedback. "

Don't drink the Kool-Aid.  Feedback happens because the level of the speaker gets back through the mic at the level it goes in.  It's not smart and it cannot tell how it got there.  You didn't get feedback because you were below that level.

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But isn't the energy spread out more in a design such as this so the acoustical distance from the mic to the speaker is a bit longer than the physical distance of a single point source? If not, then why does nearly every column design marketing department claim tolerance to feedback it better than a tradtional point source? Is there no truth to this whatsoever?

Also, I don't know exactly what's occuring, but "preset 1" uses DSP with "sequential filtering" on 3 of the 6  4" speakers to smooth out the mid frequency horizontal coverage. Is this phase? delay? volume shading? "Preset 2" has all woofers firing the same for maximum SPL.

[OneEng]

It is a bit more complicated than that.

The number of open microphones, their pickup pattern, the spread pattern of the speakers, the damping of the room, and tons of other factors all contribute to feedback.

It is quite possible that different speakers would cause less feedback, although generally the microphones have more to do with it.

[dboomer2]

Is there no truth to this whatsoever?

None ... if ... you get the same exact response from 2 speakers at a given point (where the mic is) you will get the same feedback.  The threshold will be exactly the same.  

The fact you didn't get feedback is because you are not getting all the sound from the "line array" as from the "point source".  When you truly get apples to apples they will both feedback the same.

So if you pick some preset and you get less feedback it is because they filtered out some peak.  But if you filtered the point source speaker they same way you would also get the same result.

[abzurd]

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dboomer2 wrote:

Is there no truth to this whatsoever?

None ... if ... you get the same exact response from 2 speakers at a given point (where the mic is) you will get the same feedback.  The threshold will be exactly the same.  

The fact you didn't get feedback is because you are not getting all the sound from the "line array" as from the "point source".  When you truly get apples to apples they will both feedback the same.

So if you pick some preset and you get less feedback it is because they filtered out some peak.  But if you filtered the point source speaker they same way you would also get the same result.

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Actually the filtering was a separate question. I was just curious what it (sequential filtering) is.

As to the feedback,  I undestand that there's a threshold for feedback and it's the same no matter what the sound source is. What I've read, and maybe it's wrong, is spreading the acoustic energy over a larger distance means less energy coming from any one area of the speaker column. Therefore the threshold is less likely to be reached if the sound is spread out along a 3 foot distance.

As a consequence of the characteristics of the design, I know for sure that it's less prone to high frequency feedback when standing next to the speaker. For better or worse, if I can't hear any highs the microphone can't either.

[dboomer2]

What I've read, and maybe it's wrong, is spreading the acoustic energy over a larger distance means less energy coming from any one area of the speaker column. Therefore the threshold is less likely to be reached if the sound is spread out along a 3 foot distance.

 If the sound is spread out then your audience can't hear it the same as one that isn't.  So you have to turn up and then you'll have feedbackbecause you've now reached apples to apples.

Think of this.  Set your mic on a stand say 5 feet directly in front of both speakers pointed at the speakers.  Assume perfect, identical frequency response from both speakers.  Now as you raise the level of both speakers (one playing at a time) the same spl will set off feedback no matter which speaker it comes from.  If it's otherwise it is because one or the other speaker isn't putting out the same level at frequency so that speaker is deficient to your listener ... right?

So yes, speaker coverage will vary from speaker to speaker and if you put your mic where you're sitting in a hole you won't get feedback and if you sit on a peak you might.  But there is nothing happening with column speakers (aka- lie arrays) except maybe up very close ... very close and why would you ever be that close?

[abzurd]

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dboomer2 wrote:

....  But there is nothing happening with column speakers (aka- lie arrays) except maybe up very close ... very close and why would you ever be that close?

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Well there's the thing. As I mentioned originally, for some unknown reason, and despite me telling everyone I hand the microphone to NOT to do it, a great number of people start pacing around and decide directly in front of the speaker is the best place for them to stand. There's probably some psychology to it, but the result is they are less than 3 feet from the speaker.  I have no issues otherwise.

[dboomer2]

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abzurd wrote:

There's probably some psychology to it, but the result is they are less than 3 feet from the speaker.  I have no issues otherwise.

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No psychology ... just level.  At less than 3 feet the drivers have not converged so yes at less than 3 feet there might be a difference.  But since providing sound at closer than 3 feet is not usually the job of a speaker  I wouldn't consider that.  Why in the world would anyone stand less than 3 feet from a speaker box?

Still betting you are just not comparing apples to apples and when you do both apples will squeel 

[abzurd]

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dboomer2 wrote:

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abzurd wrote:

There's probably some psychology to it, but the result is they are less than 3 feet from the speaker.  I have no issues otherwise.

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No psychology ... just level.  At less than 3 feet the drivers have not converged so yes at less than 3 feet there might be a difference.  But since providing sound at closer than 3 feet is not usually the job of a speaker  I wouldn't consider that.  Why in the world would anyone stand less than 3 feet from a speaker box?

Still betting you are just not comparing apples to apples and when you do both apples will squeel 

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It's psychology that people are drawn to the speaker like a moth to a flame. That's what I mean. I haven't now, nor ever had any FOH feedback issues. Heck, if anyone has FOH feedback issues there's all kinds of things likely wrong.

[OneEng]

If you look at it from a signal and system processing problem (which by the way it really is), then feedback is simply a response to a system that is under-damped and results in a continous increase of one or more frequencies.

In signal processing, there are 3 types of systems.  Over damped, critically damped, and under damped.

In an over damped system, when you kick the system, it doesn't ring at all.  In a critically damped system, it rings once.  In an underdamped system, it rings at a frequency.  In mathmatical terms this "kick" is called the impulse response.  If you keep kicking at the same frequency (or one of the frequencies) that the system rings at, it will continue to build at all of those frequencies until you turn it down, or something maxes out, or something blows up.

Each piece of your PA represents a part of this "system".  In order for a pair of speakers to be EXACTLY the same, they would have to produce the same response at all frequencies in all locations at all SPL's.  Additionally, they would have to react to the rate of change in energy at different frequencies exactly the same.

The only way for this to be true is very likely for the 2 speaker systems to actually be the same system

So of course your speakers have something to do with feedback.  Even if you have never studied the math involved, your ears would tell you this.

Ever tried to use one of those old JBL plastic **bleep** speakers with the cheepo tweeters as monitors?  Doesn't take much to get those things to feed back .... even with my FOH mains and microphones.

[agedhorse]

Incedent energy density is what creates the SPL portion of the cause of the feedback. There's also the phase response which is independant. The incedent energy is the SPL per unit area at the point the mic diaphragm is. With a columnar waverfront, closer than the critical distance, the energy density is less as you only see the SPL from the specific  part of the array that crosses the mic diaphragm's area. For an 8' column, with drivers that are suitably sized, you may indeed improve the feedback situation as much as 8-10 feet in front of the speaker. The other thing that is responsible for improving GBF is that the improved vertical pattern control increases useable SPL where it's needed and less is wasted in a conic section versus a columnar section. This keeps the inverse square law from killing you from the start. You can expect to gain maybe 3-6dB (rough back of the napkin guess) in practice.

[dboomer2]

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agedhorse wrote:

. The other thing that is responsible for improving GBF is that the improved vertical pattern control increases useable SPL where it's needed and less is wasted in a conic section versus a columnar section.

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While this certainly does have to do with articulation (and loss of it) it has nothing to do with feedback.  So yes you may be able to operate a system with better results at a lower level ... but that's pattern control ...and you could do that with a point source speaker as well. So what you actually comparing is a speaker better suited to a room to one less suited to a room.

My point is at any given point in space, feedback doesn't care about anything but level (per frequency) and phase.  Once you make those two things the same (at the mic) it doesn't matter how you generated them.

It doesn't matter whether you use gas or electricity to boil water.  When it reaches 212 degrees it boils.  Once you cross the unity threshold in phase (or close to it) you get feedback regardless of what speaker you used.  Lie arrays do not get to break the laws of physics (neither do line arrays).

[agedhorse]

Right, pattern control is largely responsible for getting the desired SPL to the audience and not to where it's not needed, and up close the crossectional area (that's a byproduct of the pattern control effect of the line array) helps with the SPL at the mic versus the SLP at the audience. Of couse it only works when the array is operating as a line source and not as a point source as that's where the pattern control equations dominate.

[OneEng]

My point is at any given point in space, feedback doesn't care about anything but level (per frequency) and phase.  Once you make those two things the same (at the mic) it doesn't matter how you generated them.

As I stated, I think there is more to it than that, but even then, the directionality of the speaker would have a good deal to do with that.

I have certainly seen the difference between microphones more than the difference in speakers, but I have seen that too.

Incidentally, can someone tell me how to quote someone?  Thx

[abzurd]

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OneEng wrote:

one tell me how to quote someone?  Thx

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There's a blue "quote" button in the upper right corner that you see AFTER you click reply (not quick reply).

[dboomer2]

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As I stated, I think there is more to it than that, but even then, the directionality of the speaker would have a good deal to do with that.

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Nope ... that's it and that's all there is.  There is a threshold that once you satisfy you will get feedback and the threshold doesn't care how it gets crossed.

There may be some small advantage if you are close enough that they haven't yet combined.  But unlike Andy's example they are not an 8' column.  There are 6 x4" drivers so the effective column is less than 3 feet.  There is also a column of tweeters but since they operate at a different frequency I wouldn't add much to it.  Setting a second column on top is questionable in adding length to the column because the tweeters are in the middle.  So maybe you'd pick up a little at less than 3 feet because the level there would not be quite what it would be from a single driver.  OTOH your speakers on a stick would likely be up a bit to where you also couldn't stand directly in front.  If that were the case it is likely the balance would swing the other way.

If you are arguing that the directionality of the speaker comes in to play , well yes it does.  But then you are not comparing equals.  In this case it would not be getting to your listener either so you would need to make that adjustment.  Once you make the adjustment to equal then the feedback threshold would also be equal.

As my point to Andy's point ... yes properly aimed speakers are a good thing compared to speakers which don't go where they are needed (and do not where they are not)

In the case of the speakers that are the subject of this thread;  yes you could employ additional speakers to cover the area you need.  But what are you now going to do with all that other lower frequency sound that will be spilling to where you don't want it.  That could likely give you the same problem that careful pattern control could solve.  You'll be creating sound that just causes reverb and echos that you now will have to fight to combat.

[OneEng]

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abzurd wrote:

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OneEng wrote:

one tell me how to quote someone?  Thx

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There's a blue "quote" button in the upper right corner that you see AFTER you click reply (not quick reply).

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Ahhh.  Thanks abzurd

[OneEng]

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dboomer2 wrote:

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As I stated, I think there is more to it than that, but even then, the directionality of the speaker would have a good deal to do with that.

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Nope ... that's it and that's all there is.  There is a threshold that once you satisfy you will get feedback and the threshold doesn't care how it gets crossed.

There may be some small advantage if you are close enough that they haven't yet combined.  But unlike Andy's example they are not an 8' column.  There are 6 x4" drivers so the effective column is less than 3 feet.  There is also a column of tweeters but since they operate at a different frequency I wouldn't add much to it.  Setting a second column on top is questionable in adding length to the column because the tweeters are in the middle.  So maybe you'd pick up a little at less than 3 feet because the level there would not be quite what it would be from a single driver.  OTOH your speakers on a stick would likely be up a bit to where you also couldn't stand directly in front.  If that were the case it is likely the balance would swing the other way.

If you are arguing that the directionality of the speaker comes in to play , well yes it does.  But then you are not comparing equals.  In this case it would not be getting to your listener either so you would need to make that adjustment.  Once you make the adjustment to equal then the feedback threshold would also be equal.

As my point to Andy's point ... yes properly aimed speakers are a good thing compared to speakers which don't go where they are needed (and do not where they are not)

In the case of the speakers that are the subject of this thread;  yes you could employ additional speakers to cover the area you need.  But what are you now going to do with all that other lower frequency sound that will be spilling to where you don't want it.  That could likely give you the same problem that careful pattern control could solve.  You'll be creating sound that just causes reverb and echos that you now will have to fight to combat.

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Just hasn't been my experience Don

[Bajazz]

My experience is that Line Arrays is no magic thing. Not the big ones, and not the small ones for smaller venues.

As mentioned by several here is that when the sound level exceeds a certain amount of db there will be feedback between the mic and sound source.

A point source (conventional speaker) with limited dispersion (typically 60x90 degrees) will cause the room to have varying spl depending on where you stand/sit. IME this will vary a lot from very close to the speaker and to the dead spots in the room. With a pair of speakers and thoughtful placement you'll mostly avoid feedback and get the sound spread OK.

But (again IME) not as even as a line array or alternatively 4 or more speakers (careful with delay here...) Because IME, the difference between max spl and minimum spl in the room is much less, you need to crank  it up less for everyone to hear. This is like having 2 hi-watt lamps vs many spotlights.