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[Scott Helmke]

I am not sure what you were trying to say about multiple arrival times being "part of the sound of an exciting rock show".

Multiple arrivals appears in spirit, if not in letter, on basically every rider out there. Stereo speaker systems are standard in rock, even though stereo is obviously not something that scales up well.

[Roland Clarke]

Yes and no. 

(By the way, I don't see any of this as debate, just informational)

A room that has reflections which cause comb-filtering problems can certainly be a challenge but we have no control over the room unless we designed it.
Purposefully employing effects in a recording is a choice to change the sound.
In a PA system from the output processing/DSP through the amplifiers and the speakers we are attempting to re-produce sound accurately with the acoustical output being faithful and accurate to the electronic input.  If effects or coloration of the sound should be required this is the function of Mic and Mic placement choices, effects units or plug-ins, overdriving pre-amps, etc.  It is not a wanted or desireable function of the speakers themselves.

Lee

I fully understand all this. Just making the point that it's not always that simple.  Case in point.  Get a small orchestra to play in an acoustically "neutral" room.  Probably sounds like crap.  A more reverberant space along with comb filtering galore can make it sound wonderful.

Of course I'm playing Devils advocate, however, whilst all that Ivan states is correct, subjectively, things change for all sorts of reasons, hence why many manufacturers doing very different things can provide solutions that in given situations work.

It really does depend!

[Peter Morris]

In simple terms we live in a world of multiple arrivals, and for the most part it doesn’t matter as much as you would think, our hearing / brain sorts a lot of it out.  That’s why something that’s sounds quite clear when we are listening in a room will sound bad when we listen to a recording (free field) made in exactly the same space. 

The recording and play back system does not contain the information our brain needs to sort things out. An extreme example of what our hearing can do is the “Cocktail Party Effect” https://en.wikipedia.org/wiki/Cocktail_party_effect

In terms of a speaker recreating the original, it’s more or less not possible.  An orchestra for example is made of many separate sources each with their own non – symmetrical and unique polar responses. Unless we recreate each of these, and experiments have been done along these lines, then it will be different.

However, if we can create is something that inspires a similar emotional response to the original, we will have been successful.

Speaking of line-arrays and multiple arrives, some are much better than others. I would suggest that if a line array can produce a good stereo image, things are fine. Many line-arrays cannot produce a good stereo image and as such they have multiple arrival issues. Unfortunately for Ivan, the latest generation of line- arrays are getting much much better.

You also have to remember that the aim of any speaker manufacture (for this forum not the installation forum) is being able to provide a contractor with a flexible scalable solution made of components that are easily movable and not breach the occupational health and safety laws if they have to be manually lifted in to place.

The way I see things regarding this discussion at the moment is a bit like – scalability & flexibility, cost effective, sound quality / minimal multiple arrival issues … pick any two.

[Justice C. Bigler]

So how do you start? I can't afford a Smaart rig and class but I'd like to begin learning about measurement. Will a cheap measurement mic, USB interface and REW get me into something I can use?

REW is a good platform to start with. It's free and will get you into the measurement world.


A Dayton Audio EMM-6 is a decent mic to start with and cheap enough that you can buy two or three and compare them to see which is flatest.


Any 2 channel USB audio interface in the $100-$150 range will be fine for measurement work. I'm not sure how REW handles multiple measurement sources so I don't know if it's worth it to buy a multi-channel interface and a lot of the Dayton mics to try to do multiple measurements at once. Plus it's probably easier to just start with one measurement source and one signal source anyway.

[Keith Broughton]

Get a small orchestra to play in an acoustically "neutral" room.  Probably sounds like crap.  A more reverberant space along with comb filtering galore can make it sound wonderful.

True, but that comes under "unless we designed it" point.
I know we all think Ivan is on the "line array problems" soap box all the time but that is not the only type of speaker system that suffers from multiple arrival time issues.
There are many installed, and portable, systems that have this problem.

[David Winners]

REW is a good platform to start with. It's free and will get you into the measurement world.


A Dayton Audio EMM-6 is a decent mic to start with and cheap enough that you can buy two or three and compare them to see which is flatest.


Any 2 channel USB audio interface in the $100-$150 range will be fine for measurement work. I'm not sure how REW handles multiple measurement sources so I don't know if it's worth it to buy a multi-channel interface and a lot of the Dayton mics to try to do multiple measurements at once. Plus it's probably easier to just start with one measurement source and one signal source anyway.

Thank you Justice

[Lee Buckalew]

I fully understand all this. Just making the point that it's not always that simple.  Case in point.  Get a small orchestra to play in an acoustically "neutral" room.  Probably sounds like crap.  A more reverberant space along with comb filtering galore can make it sound wonderful.

Of course I'm playing Devils advocate, however, whilst all that Ivan states is correct, subjectively, things change for all sorts of reasons, hence why many manufacturers doing very different things can provide solutions that in given situations work.

It really does depend!

What you are describing is not comb filtering, per se, comb filtering is the exact same source being repeated at an offset.  When a reflection occurs in a room it is usually significantly below the amplitude of the direct sound. 
Multiple players or singers, even in unison, do not create comb filtering with each other.  Possibly Room reflections will create comb filtering but, the offset in amplitude usually negates or at least significantly decreases the affects of comb filtering and the room modes and anti-modes are what predominantly effect our perceptions.

Lee

[Ivan Beaver]

Plus it's probably easier to just start with one measurement source and one signal source anyway. [/font][/size]

When I got started in real measurement (I had hardware  RTAs before-but that does not count) it was with Smaart 3.6  on floppy disks.

I took it home and hooked up to my home stereo and started playing around.

Up close, at the back of the room, 1 channel, 2 channels etc, and then started asking myself-WHY was I seeing differences.

Then I brought it to work, in a much larger room, then started playing outside.

It is a PROCESS, NOT a do this, then do that and you are done type of thing.

The BIG KEY is UNDERSTANDING what is being displayed on the screen.

As long as I have been doing this, I still run into "fooled ya" just because it is on the screen and sometimes chase rabbits.

So don't be afraid to make mistakes-we all do.  And will continue to do so.

But LEARN from those mistakes.  THAT is how you get better.

[Ivan Beaver]

What you are describing is not comb filtering, per se, comb filtering is the exact same source being repeated at an offset.  When a reflection occurs in a room it is usually significantly below the amplitude of the direct sound. 
Multiple players or singers, even in unison, do not create comb filtering with each other.  Possibly Room reflections will create comb filtering but, the offset in amplitude usually negates or at least significantly decreases the affects of comb filtering and the room modes and anti-modes are what predominantly effect our perceptions.

Lee

That depends on where you are in the room and the path length differences.

Short differences in path length will often mean that the reflection is just as loud (or a dB or two lower) as the direct.  So it could mean massive cancellations.

A much longer reflection path would mean that the comb filter first notch is very low in freq.

A longer path "might" be lower in level.  HOWEVER, I have seen reflections that are louder (actually measured 9dB louder in one case) than the direct sound.

Mike and I were walking around a Church that had asked us to look at their sound system.  We had pink noise playing.

At one point in the center aisle we both stopped in our tracks and looked at each other DO WHAT? we said.  We pulled out the TEF and sure enough the reflection off of the curved balcony at that position was 9dB LOUDER THAN THE DIRECT sound.

OK-This is a "little" problem-------

It all depends on the particular room you are in.

[Lee Buckalew]

That depends on where you are in the room and the path length differences.

Short differences in path length will often mean that the reflection is just as loud (or a dB or two lower) as the direct.  So it could mean massive cancellations.

A much longer reflection path would mean that the comb filter first notch is very low in freq.

A longer path "might" be lower in level.  HOWEVER, I have seen reflections that are louder (actually measured 9dB louder in one case) than the direct sound.

Mike and I were walking around a Church that had asked us to look at their sound system.  We had pink noise playing.

At one point in the center aisle we both stopped in our tracks and looked at each other DO WHAT? we said.  We pulled out the TEF and sure enough the reflection off of the curved balcony at that position was 9dB LOUDER THAN THE DIRECT sound.

OK-This is a "little" problem-------

It all depends on the particular room you are in.

You are describing different results that are being caused by different factors yet attributing them to the same thing. 

You cannot have a longer path length from a single reflection and have a louder result but, as you said, a curved surface could create that as you are experiencing the result of a focused reflector.  This is actually multiple points of reflection focusing to a single listening spot.  It is not a single reflection getting louder.  You can often experience similar results when listening or measuring in symmetrical rooms along the axis of symmetry.  Two reflections from opposite directions meet in phase and magnitude to add along the common axis.

Longer vs. shorter reflected path lengths react two ways.  The longer the path, the lower in magnitude, relative to the direct sound, is the reflected signal and the lower in frequency is the first null.  The shorter the path the higher in magnitude, relative to the direct sound but the higher the first null. 

Again, not arguing, just wanting to make the distinctions between and among the various acoustical interactions that are being brought up here. 

Very interesting thread.

Lee

[ProSoundWeb Community]