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Old 27th April 2012, 10:08 PM   #1
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Default drivers offset issues

Hello,

I'm planing to build a floorstanded speaker using a 10" mid-woofer and 1.2" tweeter. Hoped Fx will be around 1.2kHz steep slopes.
For floor boundary reasons I want the woofer center to be 11.6" above floor. For listening axis reasons I want the tweeter center to be 28.9" above floor.
Simulations of diffraction/boundary/room-gain are really nice.

But...the 17.3" distance center woofer/center tweeter is actually more than the wave length at 1.2kHz_11.26".
I know this fact will create frequency response cancellations but wish to know how harmful they will be sonically at say 10 feet listening position...

Any thought/experience about?

Thank you very much.

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Old 27th April 2012, 10:45 PM   #2
jim1961 is offline jim1961  United States
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What tweeter are you using that you can crossover at 1.2k ?

Typically, you want the tweeter close to the midrange, which in this case is your woofer.

Last edited by jim1961; 27th April 2012 at 10:47 PM.
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Old 27th April 2012, 10:50 PM   #3
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Originally Posted by jim1961 View Post
What tweeter are you using that you can crossover at 1.2k ?

Typically, you want the tweeter close to the midrange, which in this case is your woofer.
- SB29
- I know...thus my question...I'm avare it's quite a challenge
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Old 28th April 2012, 02:05 AM   #4
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How about lowering the tweeter height and sloping back the baffle so it aims at the 3m listening position?
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Old 28th April 2012, 08:32 AM   #5
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Originally Posted by samadhi View Post
How about lowering the tweeter height and sloping back the baffle so it aims at the 3m listening position?
Yes, I thought about but then it would be some 8" below the ears listening height; so wouldn't this be detrimental on imaging?
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Old 28th April 2012, 09:17 AM   #6
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edit: regarding the dimension of the woofer frame I could place the tweeter 26.8" above floor, thus limiting the drivers center to center offset to 15.2" so less than 3" more than wave length at 1.2kHz...And probably the 1.2kHz emission in a 10" woofer isn't at its center, so the one wave length rule should be almost OK...
Thus the only question remains about having the tweeter 4" below listening height...Could make the trick, no?
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Old 28th April 2012, 06:36 PM   #7
AllenB is offline AllenB  Australia
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I don't think that 4" will make that much difference. I looked at this thread this morning (but was distracted). If I remember rightly your lobing will give you a null at around 14 degrees above your listening position, and this is if you match the phase to suit your 4 degree vertical listening angle.
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Old 28th April 2012, 07:27 PM   #8
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AllenB, thanks for your input but I'm not sure to understand what you mean...
Why are you telling about "14 degrees above my listening position" ?
My ears will be at 2.9 (6.4") above tweeter H axis and 9.6 (21.3") above woofer H axis.
I will design the filter to match drivers phases at Fx by placing my mic at listening height (33") and 59" distance from speaker (this is where I can windowing before first reflexion).
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Old 28th April 2012, 08:59 PM   #9
AllenB is offline AllenB  Australia
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As you move above your listening position your woofer will become further from you until it is a half wavelength further than your tweeter causing a cancellation. The further apart your drivers are at the crossover, the shorter this distance will be.

Anyway, I think you should have no problems with this. I mean it would not be ideal but you should be able to get good sound this way.
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Old 28th April 2012, 09:41 PM   #10
GDO is offline GDO  Spain
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Supposing an LR xover, vertical beamwidth is given by:

Arcsin ( λ / 2d )*2 where λ is wavelength at xover F and d is vertical offset ( see Linkwitz for more about this). Which gives in your case about 22*2=44.

So that whether your offset is ok or not depends on your vertical coverage needs. 1/2 wavelength is for 90, 1 wavelength for 60, but do you really need so much?

Imho 40 is fine enough.
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