Single dipole sub users: does response change when you move around? - diyAudio
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Old 14th July 2012, 12:04 AM   #1
OllBoll is offline OllBoll  Sweden
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Default Single dipole sub users: does response change when you move around?

Hello all, and especially you who have a single dipole sub or have tested one.

What I'm wondering is if the side nulls caused by a single dipole sub are hearable when you walk around the room or if the reflections make them unhearable and in practice you get equal bass response everywhere in the room.

If this is a problem I have one idea to "solve" it, but before I go down that path I thought I'd check with you people
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Old 14th July 2012, 08:37 AM   #2
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Yes, response varies within the room, mostly because of room boundary reflections.
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Old 14th July 2012, 10:19 AM   #3
OllBoll is offline OllBoll  Sweden
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Ah, then let's present the idea I have been toying with:

What about flipping the dipole sub such that outputs are upwards and downwards and the null is on the horizontal plane? Shouldn't the bass then spread in the horizontal plane more like a monopole, and be much easier to equalize evenly in the room?

What made me think was my H-frame midbass test, I investigated building a normal such frame and placing an omni ontop of it but I ofc got a dipole response so when I moved to the side of the speaker the I got much less midbass. After a while I realized it didn't integrate well with the omni and after a little time more I tried in desperation to mount the H-baffle upwards instead and it worked better than I ever thought it would. It worked so well my next step is to test to build an upwards mounted U-frame for the midbass.

And if it works for midbass, then shouldn't it work for subbass also?
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Old 15th July 2012, 01:15 PM   #4
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We have two opposite poles of high pressure sitting very closely, much-much close than half wavelength. Thus, there is strong leak between them. It is the cause of low efficiency.
hframedipole1.jpg
As far as the wave moves away, this leak is decreasing.
hframedipole2.jpg
So, any restrictions and limitations along axis of wave propagation will decrease the efficiency.
As we speak about wavelengths comparable with room size, the best place for dipole subwoofer is center of the room. Something like this.
hframe placement1.jpg


There is zero node at perpendicular axis of the dipole.
hframe placement2.jpg
But we can hear it because of there are variations of pressure while the wave shape is being converted by room.




Placing in this way works too but there is problem, one of the speakers is always out of phase.
hframe placement3.jpg
I have ripole in small room. Small size allows it to be placed between wall and sofa.
limitedripole.jpg
So, partially they restrict to the leak between poles. In other words, this space works like long, leaking, additional frame.
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Old 15th July 2012, 01:24 PM   #5
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I may be wrong, but I seem to think that the standing waves inside the room and the modes that relate to that will have the greatest effect upon the measured results and how a sub sounds as you move around the room.

Aiming the sub "up", which in this case is a dipole causes greater coupling to one side of the sub than the other, to the floor. That may or may not be an advantage.

But there is a problem. Mechanically, the cone is not designed to work against gravity for long. It will sag over time. You could decide to flip your symmetrical speaker cabinet over, invert it every 30 days or so, and be ok. Don't forget now!

The response wrt the floor coupling is just a gut feeling...

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Old 15th July 2012, 02:37 PM   #6
OllBoll is offline OllBoll  Sweden
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Cone sag wouldn't be an issue since I would do an W-frame, the cones are still mounted horizontally while the openings would then be upwards and downwards.

My regular speakers are upwards mounted omnis so what I'm trying to achieve is to make the horizontal dispersion pattern equal in all directions. If I loose a little output by sitting in or close to a null that's ok as long as I get the dispersion I want.
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Old 15th July 2012, 03:53 PM   #7
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Quote:
Originally Posted by OllBoll View Post
What about flipping the dipole sub such that outputs are upwards and downwards and the null is on the horizontal plane? Shouldn't the bass then spread in the horizontal plane more like a monopole, and be much easier to equalize evenly in the room?
The whole idea is flawed in my opinion.

Flipping the speaker 90 degrees will not change the fact that you still have a room with standing wave modes and boundary reflections.

You could also flip the room 90 degrees. It would be just about the same.
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Old 15th July 2012, 05:56 PM   #8
OllBoll is offline OllBoll  Sweden
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Quote:
Originally Posted by StigErik View Post
The whole idea is flawed in my opinion.

Flipping the speaker 90 degrees will not change the fact that you still have a room with standing wave modes and boundary reflections.

You could also flip the room 90 degrees. It would be just about the same.
Yes but the 90 degree nulls on the woofer would instead of being in the horizontal plane be moved to the vertical plane. Shoulnd't the response then change less when I move around than if I had a normal horizontal version and moved into the null angle?

Like in my awesome picture here =) The angle difference between two different listening positions would be very similar fairly independent of where in the room I would listen if the sub was vertical.
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Old 15th July 2012, 07:00 PM   #9
cbdb is offline cbdb  Canada
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Quote:
fairly independent of where in the room I would listen
The room at these freqs has much more influence than you think. If this had the effect you describe we would know about it by now. Is there really a null (no sound), or is this just theory in an anechoic chamber? This is an easy experiment for someone with this kind of sub, any volunteers?
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Old 15th July 2012, 07:14 PM   #10
OllBoll is offline OllBoll  Sweden
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Quote:
Originally Posted by cbdb View Post
The room at these freqs has much more influence than you think. If this had the effect you describe we would know about it by now. Is there really a null (no sound), or is this just theory in an anechoic chamber? This is an easy experiment for someone with this kind of sub, any volunteers?
At the moment I only have my midbass to test with and a null it is, but only a null if I put my ear next to the side.

While I don't hear a true null further away I still hear a difference in the frequency response when moving around in the room. When I tested with my H-baffle and flip it this disappeared and it sounded much more like my omni. And my theory is that it's because to truly hear a difference and the null I have to change listening height, which is fairly constant.
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