ProSoundWeb Community

Please login or register.

Login with username, password and session length
Advanced search  

Pages: [1] 2 3   Go Down

Author Topic: Plane wave from subwoofer array  (Read 8406 times)

Luca Rossi

  • Newbie
  • *
  • Offline Offline
  • Posts: 23
Plane wave from subwoofer array
« on: April 14, 2016, 08:57:37 am »

Hi all, as topic subject, is it possible to get a true plane wave from a small-medium subwoofer array? I know that it is frequency, distance dependent..

I read from an acustic manual that in a front plane wave, PVL and SPL are in phase, so the intensity of the active field is maximum.

Thanks!
Logged

Art Welter

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1578
Re: Plane wave from subwoofer array
« Reply #1 on: April 14, 2016, 01:03:43 pm »

Hi all, as topic subject, is it possible to get a true plane wave from a small-medium subwoofer array? I know that it is frequency, distance dependent..

I read from an acustic manual that in a front plane wave, PVL and SPL are in phase, so the intensity of the active field is maximum.

Thanks!
Luca,

A subwoofer array is a combination of individual omnispherical radiation patterns. An array small compared to the lower frequencies reproduced would not be a true plane wave. An array with a boundary larger than the low frequency wavelengths reproduced could be an approximation of a plane wave.

What is a "front plane wave" ?
What is "PVL"?
Is there a practical application behind your inquiry?

Art
Logged

Luca Rossi

  • Newbie
  • *
  • Offline Offline
  • Posts: 23
Re: Plane wave from subwoofer array
« Reply #2 on: April 14, 2016, 03:44:53 pm »

I mean that when the distance from the omnidirectional source is far enough, the front wave becomes planar. This is called far field, so the sound pressure level is in phase with particle velocity level. For high frequencies, far field, is closer to the source than for low frequencies.

I think that for feeling more low frequency impact we need to get a true plane wave, regardless of a high spl. I would think that this can be obtained from a well sized subwoofer array. So we can get the intensity of the far field at closer distance.
Logged

Stephen Kirby

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 3006
Re: Plane wave from subwoofer array
« Reply #3 on: April 14, 2016, 06:51:07 pm »

Actually it's the other way around.  At the transition from near field to far field the wavefront becomes spherical.  Meaning if you had a large enough planar source (world's largest Magnepan?) it would be a planar wavefront in the near field, but in the far field it will become a spherical point source.
Logged

Ivan Beaver

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 8889
  • Atlanta GA
Re: Plane wave from subwoofer array
« Reply #4 on: April 14, 2016, 11:20:05 pm »

As Art says- any subwoofer array is going to be a series of independent radiating devices.

Each of which has a spherical pattern.

What you want to end up with  is a spherical pattern-since that is the natural way sound propagates through the air.

THat is what will give you the best phase response.

When you have multiple devices arriving at a location, you will have phase interaction/cancellation etc.

This is not good for either the phase or the amplitude response.

A "flat" way can only be constructed by DESTRUCTIVE means.

Which means the output level will be lower-along with a lowering of the overall sound quality.
Logged
A complex question is easily answered by a simple-easy to understand WRONG answer!

Ivan Beaver
Danley Sound Labs

PHYSICS- NOT FADS!

Luke Geis

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1894
    • Owner of Endever Music Production's
Re: Plane wave from subwoofer array
« Reply #5 on: April 14, 2016, 11:34:04 pm »

Stephen, I believe Luca is actually correct in his understanding of wave propagation in the near vs far field. In the near field sound waves are more spherical than in the far field from a point of incident standpoint.

Stoke's law for sound attenuation explains why lower frequencies attenuate less over distance than higher ones. In the sense of a perfect planar wave ( technically impossible to achieve ) it would never attenuate, but in order for this to be possible the planar wave source would need to infinite. This point only presents the possibility that having a planar wave " like " output for only the low end would not be ideal since it already has less attenuation over distance than that of higher frequencies. Hear are several links showing what I mean:

Near Vs Far field waves

Stokes' law of sound attenuation

Does it apply to all frequencies ?

Audio Engineers Handbook example 1.3.3


No matter how you cut it, you will not get a true planar wave sub, ever....... And would probably not be ideal even it were possible.

I would wonder more what creates the perception of impact with a sub speaker? Many feel that a horn loaded sub needs more distance for impact to be perceived. I have noticed that direct radiating subs have a similar effect too though. I think it takes time for the wave front to propagate from the source before it can be perceived truly. I am going to throw a spit ball, but my guess is that if it requires less than 1/4 wavelength between drivers to effectively couple, then why wouldn't it take at least 1/4 of a wavelength for a wave to begin to be perceived or recognized? If that is the case it may explain why you don't seem to get full frequency impact from a sub until you are several feet away?
Logged
I don't understand how you can't hear yourself

Merlijn van Veen

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 309
    • www.merlijnvanveen.nl
Re: Plane wave from subwoofer array
« Reply #6 on: April 15, 2016, 01:37:08 am »

Sunlight could be considered a planar wave by the time it hits Earth (150.000.000 km). The sun clearly is a point source. But the section of the arc of the wavefront that reaches us is only 0.002 deg and for all intends and purposes flat. Sunlight does not attenuate from Mt. Everest to sea level and casts parallel shadows proving that the light rays angles of incidence are virtually parallel to each other.

If you zoom in on the edge of a circle it eventually becomes flat.

Interesting topic.


Verzonden vanaf mijn iPad met Tapatalk

Luca Rossi

  • Newbie
  • *
  • Offline Offline
  • Posts: 23
Re: Plane wave from subwoofer array
« Reply #7 on: April 15, 2016, 03:24:10 am »

Stephen, I believe Luca is actually correct in his understanding of wave propagation in the near vs far field. In the near field sound waves are more spherical than in the far field from a point of incident standpoint.

Yeah, that's what i mean. 
Logged

Luca Rossi

  • Newbie
  • *
  • Offline Offline
  • Posts: 23
Re: Plane wave from subwoofer array
« Reply #8 on: April 15, 2016, 03:29:49 am »

I would wonder more what creates the perception of impact with a sub speaker? Many feel that a horn loaded sub needs more distance for impact to be perceived. I have noticed that direct radiating subs have a similar effect too though.

So yes, i would think horn loaded subs behave more like a plane wave, that's can be a reason why we get more impact, regardless of high SPL...

I think the goal is how the wave hits our bodies. Plane waves hit our body at the same time in all its size, while sphericals of course don't. Sure high SPL matters, but it is not the only.

« Last Edit: April 15, 2016, 03:38:18 am by Luca Rossi »
Logged

Ivan Beaver

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 8889
  • Atlanta GA
Re: Plane wave from subwoofer array
« Reply #9 on: April 15, 2016, 07:04:30 pm »


I think the goal is how the wave hits our bodies. Plane waves hit our body at the same time in all its size, while sphericals of course don't. Sure high SPL matters, but it is not the only.
So let's assume for a couple of seconds that you are correct.

Let's then look at the freq and the time periods associated with sub freq.

When you consider that, you will realize that the "different times that the sound hits your body" is EXTREMELY small when compared to the size of the sub waves.

And also consider that any "array" of subs is going to produce a different source of sound-at a physical different distance from you.

So what you have is MULTIPLE arrivals on your body (a different one for each driver), which is going to be larger/longer than a "planer" waver vs a normal wave.

Sorry-but I don't see any way that this makes any sense.
Logged
A complex question is easily answered by a simple-easy to understand WRONG answer!

Ivan Beaver
Danley Sound Labs

PHYSICS- NOT FADS!

ProSoundWeb Community

Re: Plane wave from subwoofer array
« Reply #9 on: April 15, 2016, 07:04:30 pm »


Pages: [1] 2 3   Go Up
 



Page created in 0.048 seconds with 24 queries.