Near Field Line Arrays. Pros and cons?...

  • kyriakos

    kyriakos

    Administrator

    I copy-paste from the old phpBB Forum an interesting discussion, regarding Line-Arrays:

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    skaloumbakas - Wed 24 Aug 05, 10:44
    Post subject: Near Field Line Arrays. Pros and cons?...
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    I have found a very interesting paper (PDF document), regarding 'Design Guidelines for Practical Near Field Line Arrays', written by James R. Griffin, Ph.D.
    - link (pls, D/L)

    I insist you print and read it. It starts with:

    - 'It is widely recognized that tall columns of speakers comprising a line array (of woofers and tweeters) have significant benefits, when properly implemented...'

    This is also worth viewing also:
    - link (pls, D/L)

    • What do you think?
    • Have you ever come across any other relevant links?
    • Do you have different opinion?

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    trouble - Sat 27 Aug 05, 1:07
    Post subject: Re: Near Field Line Arrays. Pros and cons?...
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    I have tried to read this article, and have found too many givens for it to be taken seriously, although the author is a Ph.d.

    I believe that due to various variables (such as the recording! for ONE!) which are not taken into account, the anova statistical range would vary thus making all charts go off the wire due to inconsistencies. WE do not live in a world, where everything is constant, and equal, this is not micro or macro economics, rather a living organism, in that it seems to change as the weather does (metaphorically of course)…

    I would like to quote what the PDF has:

    2. Listening Position Coverage. Consider also the listening position and whether you desire to cover the sitting position (slightly less than one meter (39.4”) above the floor at ear level) only or both standing (typically up to 1.8 m (70.9”) height) and sitting positions. Hence, for many situations a tweeter line height would need to be grater than one meter to adequately cover both sitting and standing positions. Also note that for single ribbon or small ribbon/planar tweeter arrays any tweeter length significantly below the sitting listening position or above the standing position may not significantly contribute to the sound heard by the listener. If you listen while lying flat on the floor or are over two meters tall, then you may wish to appropriately increase the tweeter length.[/QUOTE]
    As one can simply deduce, one might not be able to increase tweeter LENGTH!!!
    also:
    [QUOTE]Driver Separation
    The goal in determination of the spacing between drivers in a line array is to position them so that you approximate a continuous line source as closely as possible. This would yield an constant phase front (isophase condition). We will consider three cases: circular (cone and dome) drivers, slot (rectangular) drivers, and ribbon/planar drivers.[/QUOTE]
    ...which makes sense to me, yes, if it is in isophase condition, does it increase near field listening and decrease the power of any line array? And what if the SPL is different, how does it affect a small room compared to a large area?
    And last, again quoted from the author:
    [QUOTE]Summary and Listening Impressions
    A near field line array provides a different listening experience versus point source
    speakers. Among the distinctions that characterize line arrays are:
    • Near constant sound levels throughout the listening room
    • A wider soundstage
    An image ʽsweet areaʼ and not a ʽsweet spotʼ
    • Recreates live event sound dynamics[/QUOTE]
    The underline is mine just for us to look at, and if indeed we do want to have this or not?
    This is a great topic in itself!!!

    skaloumbakas - Sat 27 Aug 05, 12:55
    Post subject: science and practice

    If you want to get more scientific download those:
    -** 'Wavefront Sculpture Technology'**, October 2003
    AES Journal, Vol. 51, n°10.
    link (pls, D/L)
    ABSTRACT
    [QUOTE]The Fresnel approach in optics is introduced to the field of acoustics. Fresnel analysis provides an effective, intuitive way of understanding complex interference phenomena and allows for the definition of criteria required to couple discrete sound sources effectively and to achieve coverage of a given audience geometry in sound-reinforcement applications. The derived criteria from the basis of what is termed Wavefront Sculpture Technology.[/QUOTE]
    - 'Wavefront Sculpture Technology'
    AES Convention Paper #5488
    Article presented at the 111th AES Convention, New York 2001
    link (pls, D/L)
    ABSTRACT
    [QUOTE]We introduce Fresnelʼs ideas in optics to the field of acoustics. Fresnel analysis provides an effective, intuitive approach to the understanding of complex interference phenomena and thus opens the road to establishing the criteria for the effective coupling of sound sources and for the coverage of a given audience geometry in sound reinforcement applications. The derived criteria form the basis of what is termed Wavefront Sculpture Technology.[/QUOTE]
    - 'Sound Field Radiated By Arrayed Multiple Sound Sources'
    AES Convention Paper #3269
    Article presented at the 92nd AES Convention, Vienna 1992
    link (pls, D/L)
    ABSTRACT
    [QUOTE]How to know whether it is possible or not to predict the behavior of an array when the behavior of each element is known? Our purpose is to describe the sound field produced by arrays in such a way that criteria for “arraybility” can be defined.

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    johnrtd - Sat 27 Aug 05, 17:58
    Post subject: arrays and/or sound fields
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    In the past I worked, as a sideline, on some professional outfits. One of the demands was having voices or solo instruments giving the same impression in the front of a concert hall and in the far away back side. So we used line arrays. Those bundle vertically and when positioned at a sufficient heigth (the lowest part of the array about 1 meter above the heads of the people in the front chairs) it worked satisfying. I then also constructed a big horn for the lowest octaves of a keyboard. Not an array but the result was the same. At the back side of the hall chairs were vibrating.

    But we're not in a hall together with some 1500 people. The bundling effect is not needed, or worse, it distorts your musical experience when moving up or down by sitting on various types of chairs.

    The same goes, to some extent, for the so-called D' Appolito way of construction. A lot of manufacturers use this in their "center" loudspeaker models.
    The advantage of D' Appolito is the relatively high output and widened horizontal spreading of the sound pressure, but at the cost of vertical spreading.
    Now those center constructors put the system on it's side. That's done because most customers want that thing upon their TV-sets. But when listening to it and moving your head sideways the image constantly changes and a source moving across the screen seems to "hop" from one loudspeaker to another.

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    skaloumbakas - Fri 04 Jul 08, 22:13
    Post subject: Thoughts, thoughts, thoughts...
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    According to the theory...

    The maximum separation (STEP, in mm) between individual sound sources must be less than 166.7/f (f being the highest frequency of the operating bandwidth of the source, in KHz) in order the individual sound sources to properly couple each other, without introducing strong off-axis lobes.

    STEP < 166.7/f

    For example, for a number of woofers to produce a line source, if they operate below 300 Hz, STEP is calculated to be 0.5m., so that notches will not appear. For woofers, it seems easy to make a line array.

    Doing the same with tweeters we can realize that for frequencies above a handful of KHz (e.g. 4000 Hz), calculated STEP becomes a few millimeters, which is difficult to obtain with the existing tweeters in the market!!!

    Any way, today, apart from:

    - link

    ... a Swedish Company named
    - link
    ... is designing speaker arrays and also the following companies employ to some of their speaker models the line array principal in one way or another...

    ...and more and more audiophile DIYʼers love to deal with line arrays projects (not a very easy task to be honest)

    1  22 Sep 2010  
  • Trouble

    Trouble

    ACA Member

    The great old days of having time and energy to really dwell into the unknown....take the chaos and make sense of it for us to understand.

    2  22 Sep 2010  
  • kyriakos

    kyriakos

    Administrator

    Regarding the definition of the near field, this is the field having a distance from the speakers: < H² / (2 * l)
    (H is the vertical height of the linear source, l is the wavelength of a particular frequency).

    We see that the extend of the near field, is dependent:
    [LIST]
    [*](a) on the wavelength (it does not extend to all frequencies at the same distance), and
    [*](b) on the vertical dimension of the emitting linear source, so the near field extends from a few tens of meters for the higher frequencies, to relatively close to the speaker (about 50 cm - 1 m) for the lower frequencies.
    [/LIST]

    What does this mean? It means that the sound from a line array obviously is heard at a large part of the spectrum within the near field area and the rest part outside.

    For the higher frequencies (inside the near field), this means that for doubling the distance from the speaker, we have a general decline in pressure over a 3 dB. For the lower frequencies for which the listening position is already in the far field, for each doubling of the distance the pressure is reduced by 6 dB.

    3  22 Sep 2010  
  • kyriakos

    kyriakos

    Administrator

    Trouble wrote:
    The great old days of having time and energy to really dwell into the unknown....take the chaos and make sense of it for us to understand.

    Come on Tony, you are still young enough to have energy, to take chaos and give something out of it!
    Or is it you are a married man now and...

    4  22 Sep 2010  
  • Trouble

    Trouble

    ACA Member

    Actually it is everything.

    It is not age maybe, but the accumulation of bad experiences in life which just drill the energy out of me.

    But I think the fact that marriage has changed me so much is evident in every moment of my life.

    I have NOOOOOOOOOOOOOOOO idea how you did it. Seriously. No joke. I do not know how you didn't go nuts with everything going on around you. A family, a full time job, an entire site, and and and...

    But I do realise that it was not the right thing to do. In the end, only you were the site, and others gave 1% of there time for the site and for the club.

    I know that when you want things done, you do it yourself, but I find it awfully tiring to beg others to do what they want done, but by others work, blood and tears.

    You know what I mean.

    5  22 Sep 2010  
  • Mikekan

    Mikekan

    ACA Member

    Trouble wrote:
    Actually it is everything.
    It is not age maybe, but the accumulation of bad experiences in life which just drill the energy out of me.

    Thats sounds cool, I'll steel it....

    Come on Tony, you're full of energy!

    6  22 Sep 2010  
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