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Author Topic: What is it which makes a subwoofer "omnidirectional"?  (Read 2295 times)

Mike Henderson

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What is it which makes a subwoofer "omnidirectional"?
« on: May 16, 2021, 09:37:29 am »

Hey guys, I am thinking of getting this sub for my garage:

https://av.loyola.com/products/audio/ev ... or-kw.html

Can you guys tell me exactly what it is which makes a sub omnidirectional please?

I have this one:

https://av.loyola.com/products/audio/ev ... i-sub.html

which is omnidirectional too but instead of trying to find another one, I am thinking might best to get the dual 18" version but these 2 subs look totally different in design which is why I am asking the question.
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Tim Weaver

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Re: What is it which makes a subwoofer "omnidirectional"?
« Reply #1 on: May 16, 2021, 10:11:20 am »

Hey guys, I am thinking of getting this sub for my garage:

https://av.loyola.com/products/audio/ev ... or-kw.html

Can you guys tell me exactly what it is which makes a sub omnidirectional please?

I have this one:

https://av.loyola.com/products/audio/ev ... i-sub.html

which is omnidirectional too but instead of trying to find another one, I am thinking might best to get the dual 18" version but these 2 subs look totally different in design which is why I am asking the question.


In this house we obey the laws of Physics!


It's not the mic of the kickdrum, it's the size of the wavelength.


Size doesn't matter. Until it does.
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David Morison

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Re: What is it which makes a subwoofer "omnidirectional"?
« Reply #2 on: May 16, 2021, 10:41:01 am »

Hey guys,

Can you guys tell me exactly what it is which makes a sub omnidirectional please?


All sounds have a characteristic called Wavelength, which is inversely related to frequency. Therefore low frequencies = long wavelengths.

If the source of a wave is much smaller than the wave itself, then the source will not be able to control where the wave goes, and it spreads out pretty much in every direction.

The wavelength of 100Hz is about 3.4m (and 30Hz = 11.4m), whereas common subwoofers might only be 0.5-0.6m wide (or tall if laid down), therefore the subwoofer definitely falls into the category of "small relative to the wavelengths being produced".

Wiki link if you want to get academic about it.

Cheers,
David.

PS: The links in your post don't work so I've no idea what subs you were referring to, but the general relationship between size & directivity applies to all subs, unless you move the goalposts by adding other sound sources to creat cancellations in the direction of the "unwanted" sound.
« Last Edit: May 16, 2021, 11:18:36 am by David Morison »
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Mike Henderson

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Re: What is it which makes a subwoofer "omnidirectional"?
« Reply #3 on: May 16, 2021, 11:50:57 am »

PS: The links in your post don't work so I've no idea what subs you were referring to, but the general relationship between size & directivity applies to all subs, unless you move the goalposts by adding other sound sources to creat cancellations in the direction of the "unwanted" sound.

Sorry, these links should work:
https://av.loyola.com/products/audio/ev-eliminator-i-sub.html

https://av.loyola.com/products/audio/ev-eliminator-kw.html

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Matthias McCready

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Re: What is it which makes a subwoofer "omnidirectional"?
« Reply #4 on: May 16, 2021, 12:46:11 pm »

Mike,

David is correct it has to do with Wavelength.

--

Fun experiment for you. Play some pink noise and use a low-pass so that you are only getting information under 200hz. Now place a normal speaker (not a sub) on a stick.

While your eyes are closed have a friend spin the speaker around, and see if you can hear when it is aiming directly at you vs away.

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John Roberts {JR}

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Re: What is it which makes a subwoofer "omnidirectional"?
« Reply #5 on: May 16, 2021, 01:23:39 pm »

Location matters, boundaries like walls, and corners will influence propagation... yes its physics.

JR
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Mike Henderson

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Re: What is it which makes a subwoofer "omnidirectional"?
« Reply #6 on: May 16, 2021, 02:25:59 pm »

Well here's my update and train of thought with this omnidirectional issue, guys.

One day last couple weeks I had turned on my system and no sound was coming from the EAW SB1000 Sub which is always at my back wall facing forward. So I took all the speakers off of it and placed them in the middle of the room. I then as first test plugged the speaker cable from the EAW into my EV's full range to test and was totally surprised the I was hearing the bass more evenly anywhere in the room and even at the one trouble spot which is right in front of the garage's side door.

So I moved the EV's to the back wall facing forward to see if I would get the same result but no, it was the same as the EAW. Then thinking well, since the EV's were facing the side walls when I had plugged the cable in to them let me try facing them towards the side wall and this gave me the bass all around the room just as when they were in the middle of the room.

I then decided to add an EV Sub in the middle of the side wall to "flank" it and this doubled the bass all around the room. So right now with one full range EV acting as a sub at the back wall facing the side wall and the addition of the EV Sub on the side wall, I am now getting what I have been fighting for all these many years.

I am just wondering now instead of having the one EV Sub at the middle of the side wall if that Dual 18" Omnidirectional Sub can be placed at the back wall facing forward might give the same result I am now getting with what's mentioned. So, think this might work or should I leave the the 2 speakers where they are and get another EV Sub to replace the full range EV at the back wall and be satisfied with that?
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Caleb Dueck

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Re: What is it which makes a subwoofer "omnidirectional"?
« Reply #7 on: May 16, 2021, 03:58:14 pm »

Well here's my update and train of thought with this omnidirectional issue, guys. <snip>

What you experienced isn't directionality, but the effect of boundaries on low frequencies. 

Read up on standing waves and room modes.  What you're fighting with doesn't have to do with subwoofers, but placement within the room and all the interactions thereof. 
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Art Welter

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Re: What is it which makes a subwoofer "omnidirectional"?
« Reply #8 on: May 16, 2021, 04:13:07 pm »

Well here's my update and train of thought with this omnidirectional issue, guys.

 as first test plugged the speaker cable from the EAW into my EV's full range to test and was totally surprised the I was hearing the bass more evenly anywhere in the room and even at the one trouble spot which is right in front of the garage's side door.

So I moved the EV's to the back wall facing forward to see if I would get the same result but no, it was the same as the EAW.

I then decided to add an EV Sub in the middle of the side wall to "flank" it and this doubled the bass all around the room. So .. I am now getting what I have been fighting for all these many years.
 So, think this might work or should I leave the the 2 speakers where they are and get another EV Sub to replace the full range EV at the back wall and be satisfied with that?
Mike,

As Caleb mentioned (while I was typing my response..), what you are experiencing are not directional issues, they are room modes.
Room modes are caused by sound reflecting off of various room surfaces. There are three types of modes in a room: axial, tangential, and oblique. Modal activity occurs at frequencies which are directly related to the dimensions of the room.
 
Room modes  dominate a single sub's response in small rooms, causing huge variance in level and frequency response, dependent on location of both the sub and listener.

As you found, adding additional subs in a small room can both smooth the response in frequency and space.
The room's modes did not change, but the number of sources did, resulting in more even response.

https://mehlau.net/audio/multisub_geddes/

The EV Eliminator i "Sub" has little low end, and it's 50Hz Fb (Frequency of Box Tuning)will result in "flapping" if you try to get much low end from it.

For additional subs using the same processing as your SB 1000, look for units that match's its Fb of around 30Hz.

Art
« Last Edit: May 16, 2021, 04:15:33 pm by Art Welter »
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Luke Geis

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Re: What is it which makes a subwoofer "omnidirectional"?
« Reply #9 on: May 16, 2021, 07:39:04 pm »

A subwoofer is generally omnidirectional because the device that propagates the sound is significantly smaller than the wave it is producing.

Directional control of a wavelength is acquired when the horn, flare, baffle, or radiating path is roughly 4X the length of the frequency it is producing. In the case of low-frequency media, we are talking about wavelengths that start about 10' in length and go to as large as 40' in length or more. To have real directional control over those wavelengths you need a baffle, flare, or whatever you want to call it that would be effectively too large to even consider building or transporting.

The horn that is used on a typical speaker is only large enough to control the dispersion of perhaps only the last octave of frequencies from perhaps 3khz and up. Almost all speakers are essentially omnidirectional from about 500hz and below.

To sum it up though, a subwoofer, in general, is omnidirectional because the wavelengths it reproduces are too large for the size of the box that is producing the sound to control them.
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Re: What is it which makes a subwoofer "omnidirectional"?
« Reply #9 on: May 16, 2021, 07:39:04 pm »


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