Good stuff!

Thanks for checking in and giving us some background about your earlier remarks.

I realize that if you read all of the literature on near field line arrays (or choose most any other speaker type if you wish not just line arrays), you likely would not take the time to design or build one. Line array downers (examples, are Lipshitz and Vanderkooy's AES Convention paper from 1986 and more recently Earl Geddes' "Audio Transducers" book dated 2002) would not inspire your confidence that near field line arrays will produce pleasing sound. However, I would urge you to read more of the recent line array articles that I referenced in my earlier reply in this thread. The L-acoustics work is especially noteworthy.

If one takes the time to adequately design and build a near field array for home usage, you may find it to be a rewarding experience as I detail in my white paper. There I detail is a specific set of criteria that can result in a pleasant listening event. My goal was to avoid or limit the near field chaos that would be haunting to a less exacting design.

I would like to reply on your reference to the John Meyer's magazine article. First of all, the 'cylindrical waves' statement is true to a degree. But in the near field the vertical wavefront (created from overlapping outputs from the drivers) is concentrated between the ends of the array--very little energy impinges from the floor and ceiling surfaces. The near field energy flow radiates parallel to these surfaces versus the normal spreading flow from a point source. Furthermore, Meyer's own data does support an average of 3 dB per doubling of distance sound falloff if you look at his data in Table 1 for the 4 and 8 meters distances (practical in-home near field distances unless you live in a castle). Furthermore, John's concerns about high frequency extension are difficult to mitigate for a high power pro sound line array but can be easily overcome via readily available small ribbons and such. Bottom line is that pro sound and in-home line array design/usage are vastly different issues. John's article is good magazine material for a pro sound line array audience but can be a misleading interpretation for an in-home near field array.

Thanks again for the posting.

Jim

Thanks! I agree that Lipshitz and Vanderkooy, and Geddes as well paint a pretty bleak picture of near-field line arrays (NFLA). I don't think they're THAT bad - clearly enough people enjoy them that their strengths carry a lot of weight with lots of people! And I've perused most of the other references (although I have not spent in-depth time); my understanding is that most acknowledge the acoustical issues when operating in the near-field, but feel these can be shaded down so that listener preference is positively influenced.

I've built quite a few arrays, and I've always found that in the near-field, I simply don't like the sound. Far-field, well, they can do some really cool things...;) But I just don't like the near-field. Likewise, I'm not a big fan of large, near horns either. Dynamics are great, and you can have great accuracy in terms of phase and frequency response (like the Unity horns). But to my ear, they sound like wearing a really big set of headphones - image is all left, right, or middle - nothing in between. I think the extreme dispersion control removes too much of the reverberant field of the room that I believe is fundamental to the creation of a large and open image.

Personally, I've designed NFLAs for clients, and will do so in the future too! If the client is happy, then I'm happy. I may not like what the results are like personally, but then again it's not for me. I do the same with drivers, amps, and other audio products all the time.

And I hope that no one assumes that because I personally do not enjoy listening to near-field line arrays that I automatically relegate NFLA adherents to the lunatic fringe or dismiss them! Preference is, IMHO, inviolate. Those who find their path to sonic nirvana should pursue it, but also allow others to follow their own path. Preference for a different path does not make anyone's path lesser or greater.

However, I also believe that the more we can tie hard physics and acoustics to preference (Tolve's 1989 article in JASA is, IMHO, a landmark work on the subject) the better off all designers are. And to do this means that everyone needs to fully acknowledge the strengths AND drawbacks of their path. Knowing how the path for you is set allows you to extend it even further and faster... Those who are in to extreme dynamics should know what they really like, and go after it. Those into extreme flat frequency response likewise. Those into broad images, the same. It's about learning the stones that make your path, and the underlying physics that creates those stones, and searching out ways to make more...

Thank you and everyone here for the cool, level-headed place to discuss this! Definitely class acts! And if there ever are questions anyone has about my likes/dislikes and experiences with arrays (line and circular), just ask!

Dan Wiggins

I find this interesting. Can you elaborate more on near-field behavior of line arrays? Do the lobing effects you and Rybaudio
described still exist at frequencies with a larger wavelength than the center to center spacing between the drivers?

Do you know if there are off-the-shelf tools to do the simulations shown by Rybaudio? (I'm posting this here to avoid creating an account on yet another fourm.)

Thanks,
-Josh

Please see my message to you in the car audio section.

Thanks,

Kramer

There's lots of programs that will do the simulation, but they tend to be quite expensive. You're probably better off rolling your own program. Here's one page with the equation for a single piston:

http://www.silcom.com/~aludwig/Physics/Exact_piston/Exact_piston.htm

You want equation P7. Here's an image of the output, using the equation:

http://www.silcom.com/~aludwig/Physics/Exact_piston/Cone_near_field_phase.gif

It's quite accurate (also the same equation as derived in Fundamentals of Acoustics). Examining the equation, you can see there is a linear dependency on wave number k, so at lower frequencies the problems are reduced.

With arrays the issue still exists until the wavelengths are longer than the longest center-to-center distance in the array. For example, assuming an array of ten 4" diameter woofers packed with centers 5" apart, you have a maximum center-to-center distance of 50". You'll have interference patterns (which is really what's going on, in Rybaudio's images) with wavelengths less than 50" long (about 270 Hz).

Now, the interference is reduced as the wavelengths approach this size; and any resulting lobes tend to be at high angles, so they really do not affect the direct field, even in a 45 degree vertical coverage (sit down/stand up test). They can affect the total power response, though, so if you are in the reverberant field of the speaker, it will affect the perceived tonal balance.

Dan Wiggins

Given a 5" long ribbon; approximate d is 12cm or so (length of the ribbon). At 3000 Hz, the wavelength is approximately 4.5 cm, so the near-field is (12^2/4.5) 32 cm away. To reach the typical 2-3m listening distance (assume 2.5m), we'd need to reproduce frequencies with a wavelength of (12^2/250) 0.58 cm, or (13560/0.57) 23.8 kHz.

It's the d^2 thing that really kills you as far as near-to-far-field transition is concerned. The larger the effective radiating diameter/length, the further the near-field. A single 5-6" long ribbon isn't really a concern in terms of near/far-field response differences until you're closer than ~2.1 meters (7 feet or so). Doubling up on the ribbons doubles the effective radiating length, which quadruples the near/far field transition.

Dan Wiggins