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Author Topic: Line Array Intelligibility Distance  (Read 2643 times)

Luke Geis

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Re: Line Array Intelligibility Distance
« Reply #20 on: February 11, 2019, 02:58:00 pm »

I am not going to spell intelligibility 20X so I will use I instead, ok.

The I of a speaker is not a function of how loud it can get per se. If you have two speakers that are functionally identical and one gets 3db louder, the I of the two of them will be the same. Now the one that distorts first will have a lower I than the other and is what would make a speaker that is capable of more output have a higher I at higher SPL's if it doesn't distort.

Line arrays are horrible examples to use for the purposes of I. The smaller the array, the better the I should be in practical theory, but it is dependent on other factors though. If you imagine a long 30 box hang of speakers, you can easily see how at a far enough distance away, you would be in the coverage zone of all of them at once. From a point of incident standpoint, the top box would hit you later than the lowest box would. From that far of a distance though, the difference in time may only be a few milliseconds perhaps. Enough to potentially reduce the I of a system though. Now if you imagine that same scenario with a very small dash array, there are very few speakers and there is essentially no difference in distance change between the top and bottom box. You will hear them as one, but the sound will be affected by the length of that array.

Now we get into the deep and dirty stuff. A short array that is only 4' long does have directional control of frequencies down to about 1khz. This means that frequencies above 1khz should, in theory, beat the inverse square law. This means at far distances you will have an accentuated response in the high end, while the mids and lows are muted in comparison. This may actually help in increasing I for dash arrays that are set up appropriately to take advantage of that phenomenon. There is still nothing better than a single source though.

The distortion of a speaker at volume is the last factor. If a speaker is able to produce 10db more in output before distortion occurs than another speaker, that speaker will have better I over all distances. The final factor is the coverage control of the speaker. Most all point source speakers are essentially omnidirectional from about 500hz and below. This means that a lot of mids and low-end media is splashing off any other object nearby and smearing the sound with the reflected energy. So using narrow coverage speakers and speakers with better pattern control often prevail at having better I over typical speakers. Horn loaded speakers don't throw sound like we want to think they do, they just keep the majority of the sound pointed in the desired direction of interest.
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drew gandy

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Re: Line Array Intelligibility Distance
« Reply #21 on: February 13, 2019, 09:59:50 am »


For those who don't know Don, he was with Altec-Lansing and developed the graphic EQ and RTA after tuning systems with custom-wound filters and an o'scope displaying Lissajous patterns.  He and Carolyn went on to found Synergistic Audio Concepts, now run by Pat Brown and his wife.


Let me fix that for you.... 

"...now run by Brenda Brown and her husband." 
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drew gandy

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Re: Line Array Intelligibility Distance
« Reply #22 on: February 13, 2019, 10:12:29 am »

Now the one that distorts first will have a lower I than the other and is what would make a speaker that is capable of more output have a higher I at higher SPL's if it doesn't distort.


Now hold on.  We need to define what distortion in your sentence means.  If I recall correctly, the US military far far in the past used to have a "process" for speech signals to add harmonic distortion because it actually improved speech intelligibility!  Distortion is the enemy of a linear sound system but it's not necessarily the enemy of human perception. 

As far as volume levels go, signal needs to get over the noise.  So, a louder speaker at a distance might have better I than a quieter one if there is some kind of obscuring noise to contend with. 
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Ivan Beaver

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Re: Line Array Intelligibility Distance
« Reply #23 on: February 13, 2019, 12:51:40 pm »


Line arrays are horrible examples to use for the purposes of I. The smaller the array, the better the I should be in practical theory, but it is dependent on other factors though. If you imagine a long 30 box hang of speakers, you can easily see how at a far enough distance away, you would be in the coverage zone of all of them at once. From a point of incident standpoint, the top box would hit you later than the lowest box would. From that far of a distance though, the difference in time may only be a few milliseconds perhaps. Enough to potentially reduce the I of a system though.

The statement of "may only be a few milliseconds" is something that many don't understand.

Depending on how few is few, the resulting combfiltering that results from that delay can greatly reduce intelligibility.

Consider that 1ms=1000Hz.  So the combfilter first notch will be at 500Hz (1/2 of the difference in arrival time, and the resulting notches will be spaced at 1000Hz apart.

So for 2 signals that are arriving 1ms apart, you will have notches at 500hz, 1500Hz, 2500Hz, 3500hz etc.

NOW, lets, add that since there are more than 2 signals arriving to you (since the cabinets are all different distances from each other to the listener), you will have a new set of notches for each additional cabinet.

This is why combfiltering sounds like the sound is dull, because of all the notches.

But you CANNOT fix it with eq.  It is a TIME issue, NOT amplitude.

So the more cabinets you have, the worse the intelligibility gets, because of the multiple arrivals.

That is why I always say: "No matter WHAT cabinet, model or brand, a single cabinet will ALWAYS sound better than multiples.

Yes, multiples will get louder, but the sound quality goes down as you add cabinets.

The STIpa

 https://en.wikipedia.org/wiki/Speech_transmission_index

 measurements for intelligibility look at the notches that are a result of combfiltering as their basic methodology. So more reflections will reduce the intelligibility, which is also the same as more cabinets arriving at the same location.

The fewer the arrivals, the greater the intelligibility.  Simple as that.

STIpa does not say anything about sound QUALITY, just whether or not it will be clear.

So it is entirely possible to have a loudspeaker that sounds bad, to have a high STIpa score.

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Josh Dunaway

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Re: Line Array Intelligibility Distance
« Reply #24 on: February 14, 2019, 10:38:18 pm »

Well, for those following along at home, this is the second "stab" at the Line Array world by Josh. You may remember this thread from October, 2016. At that time, after the obligatory mention of Danley (haha, sorry, Mike!) there was a discussion about a "line" versus a "dash" and the fact that a line array isn't something you can do as a Box of the Month process. Josh was looking at four HDL10s per side.

A week ago, Josh then posted this where it sounds like he's decided on 4bx per side of HDL28As. I think that's still his current plan, although he's trying to figure out how to ground stack them without stacking on subs, and apparently either can't or doesn't want to fly them. (But now he also sounds like he's back to the HDL20s, instead of the HDL28As, so I'm getting confuddled. lol)

Tim then gave one of his usual insightful replies, repeating many of the things that we'd talked about back in 2016. You just can't do a line array piecemeal-- assuming that this is "stepping to the next level," and not just looking for a small increase of quality or convenience for your own enjoyment, you have to invest big to get the right results. A poorly deployed (or insufficient sized) line array is going to reflect poorly on you and your customer base, and probably yield negative results.

Two years on from your initial post about this, though, Josh... how are things going? Let's play "What If." If you'd purchased the 8bx HDL10 rig back in 10-2016, were there enough opportunities (not only in new shows, but also getting existing shows to pony up more money, as well as cross-rental opportunities) that you could have paid for this new system? Did you turn away any potential clients because you don't have a line array?

I mentioned this before- unless you're renting this size of system at least a couple times a month, or you're turning away one to two clients a month for a lack of this system, then it's possibly better to rent one in as you need it. Once you buy into this rig, it's going to be a minimum 18 months before enough people know you have it to really get the business flowing. If you purchase using a lease (which is what we did) then you have to realise that the leasing company is gonna want their money every month regardless of whether or not you've made any money with it. So, your existing income streams need to be sufficient that you can cover these payments each and every month.

Swinging back to the delay tower option: You do want it voiced the same as your main PA. So, if you're using RCF line arrays for your mains, you'd really want the same for the delays. Otherwise, you might run into a challenge where the delay zone sounds different from the main zone, and touring A1s will notice that. (And now we circle back to the discussion of a poorly designed and deployed system is a bad mark on your reputation.) We had a show last year where (by virtue of needing to scrape together extra capability) we had delay hangs that were simply processed differently (I-Tech HDs running v5 presets for the mains, and conventional I-Techs running v4 presets for the delays) and the A1 noticed the difference. Booked the show again for this year, so it wasn't BAD (and I explained why I needed to send the rig like this), but it could have ended poorly.

-Ray

Ray-

I have been fortunate enough to get by with the system I have until now. I was trying to have more rig before I ran out of rig in 2016.  The finances did not make since at that point after doing my research.

Fast forward to 2018- I had several shows that left me wanting more rig, fortunately my customers didn't realise there was ZERO headroom available and didn't ask for more.

I am now bidding out shows that are requiring a line array to cover the show / rider requirements.  I am a small fish in a small market, but growing rapidly.  I have been reaching out to companies in the region and found the HDL20's to be readily available to cross-rent as needed.  I have also heard mixed reviews on the 28's which also make me shy away from them (even though I would love to have FIR & RDNet)

I realize 4 per side won't give you all of the advantages of a "True Line Array" but it is better than not having enough coverage for an event that can't afford more, not to mention there are a vast a mount of production companies using this method for smaller events- even RCF shows it as a configuration option.

I do plan to have at least 12 if not 16 boxes within the year, but cannot afford to purchase all at once and have taken on a debt free, cash only, approach to my business (and personal life for that matter- paying the last mortgage payment of my life tomorrow).

As far as the Ground stack post- many companies will run a 4 stack on top of 1 or 2 double 18's- this is horrible sub placement.  I would rather have another easily deployed option available.  Prime example: I don't want to put my subs on stage on the side to get my boxes in the air and would like a less bulky, lighter weight, less expensive option compared to $5k 500lbs lifts that I can't always easily manhandle with 2 people.

Check out a suggestion from another member- very cool, clean approach to height and can get my subs where I want them.  They have weight plates available.
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Josh Dunaway

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Re: Line Array Intelligibility Distance
« Reply #25 on: February 14, 2019, 10:40:18 pm »

How many HDL20's were you planing to buy? How much distance do you need them to cover? What of what type music and SPL do you need?

FWIW In terms of intelligibilty the HDL30's are better than the HDL20's

I was hoping to cover up to 200' with 8-10 20's per side without delays.
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Peter Morris

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Re: Line Array Intelligibility Distance
« Reply #26 on: February 15, 2019, 09:11:44 pm »

I was hoping to cover up to 200' with 8-10 20's per side without delays.

8 - 10 boxes of a good line array of this size should cover up to about 200 feet.  I usually consider this the max distance for this tye of system - you can certainly hear it well beyond that but the quality drops.

To me the HDL20 is amazing value, but offers very ordinary performance.  The HDL30 uses a larger compression driver and has a flat phase response over the vocal region.  This allows a lower crossover frequency and better pattern control thought the crossover region but it does get a bit narrow around 670Hz.  The flat phase response also improves intelligibility and the separation between instruments.

You can easily hear the difference on this video clip.

HDL20  Vs HDL30 https://www.youtube.com/watch?v=e9UEeUWdruk

If you want to have a look at the GLL files for the HDL20 & HDL30 you can see some of the issues around the crossover frequency (horizontal pattern).  In comparison the dB Tech VIO and Adamson S10 are almost perfect though this region.

« Last Edit: February 15, 2019, 09:13:51 pm by Peter Morris »
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Jason Raboin

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Re: Line Array Intelligibility Distance
« Reply #27 on: February 16, 2019, 09:54:30 am »

Ray-

 but cannot afford to purchase all at once and have taken on a debt free, cash only, approach to my business (and personal life for that matter- paying the last mortgage payment of my life tomorrow).


You might want to pick up a book on business finance.  What is "right" and works for your personal finances may not be the right thing for your business finances.  Whether or not and how much debt to take on is an equally important question, if not more important than whether you buy HDL20's or 28's.  Interest rates are very low and an unwillingness to borrow money may be an impediment to growth.  Also, if you are about to pay off your mortgage that means you have collateral.  An equity line of credit would be very easy to obtain.
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Tim McCulloch

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Re: Line Array Intelligibility Distance
« Reply #28 on: February 16, 2019, 04:27:04 pm »

You might want to pick up a book on business finance.  What is "right" and works for your personal finances may not be the right thing for your business finances.  Whether or not and how much debt to take on is an equally important question, if not more important than whether you buy HDL20's or 28's.  Interest rates are very low and an unwillingness to borrow money may be an impediment to growth.  Also, if you are about to pay off your mortgage that means you have collateral.  An equity line of credit would be very easy to obtain.

^^^ THIS.

I've written previously (like a few years ago) about why debt is not inherently evil.  Jason, you're spot on that what might be appropriate for ones personal finances is not necessarily right for ones business.

For those playing along at home:

Being able to capitalize only a portion of needed investment means that investment really doesn't happen.  Understand that *strategic debt*, with a business plan, is better than missing the chance to expand business capabilities or provide a strategic advantage.

Parting shot - Jason's great advice above helps shine a light on the lack of business and accounting training held by many small business owners, and especially in our industry.  Seriously, write a business plan.. or several.  Do pro-forma cash flows to see what it takes to sustain a business at various levels.  And above all pay yourself for the job(s) you do at your business.  You owe it to yourself and any partners (business or domestic) in order to reflect the true cost of operating.  If you're doing a job that would normally be done by an employee, you should be paid to do that job, too.

Edit ps.  Cost Accounting.  Seriously.  At least read a book on it.
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Scott Holtzman

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Re: Line Array Intelligibility Distance
« Reply #29 on: February 17, 2019, 05:13:51 am »

^^^ THIS.

I've written previously (like a few years ago) about why debt is not inherently evil.  Jason, you're spot on that what might be appropriate for ones personal finances is not necessarily right for ones business.

For those playing along at home:

Being able to capitalize only a portion of needed investment means that investment really doesn't happen.  Understand that *strategic debt*, with a business plan, is better than missing the chance to expand business capabilities or provide a strategic advantage.

Parting shot - Jason's great advice above helps shine a light on the lack of business and accounting training held by many small business owners, and especially in our industry.  Seriously, write a business plan.. or several.  Do pro-forma cash flows to see what it takes to sustain a business at various levels.  And above all pay yourself for the job(s) you do at your business.  You owe it to yourself and any partners (business or domestic) in order to reflect the true cost of operating.  If you're doing a job that would normally be done by an employee, you should be paid to do that job, too.

Edit ps.  Cost Accounting.  Seriously.  At least read a book on it.
Great advice as always.

Many small business owners don't track loans to the company and often comingle funds.

We hit a neat milestone last year,   the company started to make payments on the debt back to me.  Every penny I have loaned the company is booked and accruing interest.

Sent from my VS996 using Tapatalk

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