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Hybrid H-Frame, OB and nude driver
Hybrid H-Frame, OB and nude driver
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Old 26th January 2021, 02:48 PM   #171
diypole is offline diypole  United States
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Quote:
Originally Posted by iamvalheru View Post
Thatís pretty interesting, I assume there is correlation between dipole drivers tending to be bigger than their monopole counterparts, meaning larger surface area/ air velocity generated and room energy.

This is true in fluid power (hydraulic systems); to generate the same force, a cylinder with a small surface area needs more pressure than a cylinder that has a large surface area.

Force (lbs) = area (in≤) x pressure (psi)
Well, it's true that a driver is a piston, and it's capability on the low end is going to be determined by the surface area of the piston multiplied by how far it can travel back and forth (Sd * x-max = volume displacement)

A driver's size relative to the frequency range you're using it in are power factors, as a larger driver will start to become directional at a lower frequency, so more energy to you, and less off axis.

However, let's take this out of the equation, and assume we're only using the drivers in their omnipolar range, or when the driver diameter is less than a third of the wavelength it's reproducing.

So we have a monopole and dipole 10" wide, and we're only using them below 450hz. The monopole is a pressure source and the dipole is a velocity source.

Now, the monopole needs to displace 4 times the air volume for every halving of frequency below this to keep spl constant, but the dipole, because of roll off due to front/rear wave cancellation has to move 8 times as much air.

So after compensation, you're actually putting a lot more amp power to the dipole to keep a constant spl.

All else being equal, and only used in omnipolar range of driver, the dipole is directional and the monopole is not.

So, if you were to point both the dipole and monopole at you with the on axis spl being equal for both, the monopole is putting 4.8db more sound to the room compared to the dipole, because the spl of the dipole is way down at 90degrees off axis to each side where the rarefaction from the rear is cancelling the compression wave from the front.

The monopole is equal loudness for 360degrees, the dipole is equal loudness at zero and 180 degrees, with nulls at 90 and 270.

Now if we start bringing driver directivity and chosen crossover points into the equation it gets more complicated, but if we're only using drivers in their omnipolar range, it's just that simple.

A cardioid is somewhere between a pressure source and velocity source, but the same holds true as for the dipole, only the null is to the rear at 180.
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Old 26th January 2021, 03:09 PM   #172
iamvalheru is offline iamvalheru  Canada
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@diypole

Much clearer now, thank you for the clarification, much appreciated.


D
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Old 26th January 2021, 03:16 PM   #173
diypole is offline diypole  United States
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You're very welcome. These threads always remind me of things I've forgotten or help to clarify issues.

I thought I'd be able to measure drivers in the shop today, but an employee at the gym has called in, so I have to put on my trainer hat.

Have a good day and best of luck with your project.

Jason
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Old 29th January 2021, 03:57 PM   #174
iamvalheru is offline iamvalheru  Canada
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Here is a stupid question, when simulating an H baffle in Basta (i.e. a flat baffle with wings extending both front and rear), I unfold it to be a flat baffle, but how do I determine the overall baffle width (i.e. acoustic distance)?


Taking the attached drawing as an example:

1. Is it simply the sum of the main baffle plus the overall length of the 2 wings: 20+16+16 = 42"

Or

2. The sum of the complete linear path from the acoustic center of the driver: 20+20+16+16+8.25+8.25+7+7 = 102.5"


Thanks

Denis
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Old 29th January 2021, 04:10 PM   #175
joensd is offline joensd  Germany
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Should be 1 but keep in mind that the baffle (unfolded h-frame) is not equivalent to the h-frame not only due to the resonance.
That said it should give you an idea at least.
I do the same thing in Basta as I donīt have access to the mathcad sheets of Martin King.
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