Hybrid H-Frame, OB and nude driver

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I don't think we're very far off from each other on this, especially if half the power in a music program is below 300hz.

I've seen many different takes on "power response" halving or doubling, and whether you're talking to the amp guy or the speaker guy.

Below 60hz is mostly felt and not heard, and with a dipole being a velocity source it can't pressurize the room like a monopole down there. I have built huge dipole subwoofers that you could feel in your gut, but they're the size of a coffee table and used as a stand for equipment.
 
"The typical box speaker, whether vented, band-passed or closed, is omni-directional at low frequencies and becomes increasingly forward-directional towards higher frequencies. Even when flat on-axis, the total acoustic power radiated into the room drops typically 10 dB (10x) or more between low and high frequencies. The uneven power response and the associated strong excitation of low frequency room modes contributes to the familiar (and often desired :-( ) generic box loudspeaker sound. This cannot be the avenue to sound reproduction that is true to the original.

The directional response of the ideal dipole is obtained with open baffle speakers at low frequencies. Note, that to obtain the same on-axis sound pressure level as from a monopole, a dipole needs to radiate only 1/3rd of the monopole's power into the room. This means 4.8 dB less contribution of the room's acoustic signature to the perceived sound. It might also mean 4.8 dB less sound for your neighbor, or that much more sound to you. Despite this advantage dipole speakers are often not acceptable, because they tend to be constructed as physically large panels that interfere with room aesthetics, and they seem to suffer from insufficient bass output, critical room placement and a narrow "sweet spot"."

Room Acoustics

I think we're all in agreement here
 
Well I said a dipole puts 1/3 less to the room than a monopole, but the way SL is looking at it here, he's saying the dipole only needs to put 1/3 of the monopole's power to the room for the same on axis spl, so 2/3 less.

Makes Charlie's point about the difficulty of mixing dipole and monopole in the same speaker even more significant. Many companies have tried with limited success, and if you did it, you're better off going with dipole on the low end, and monopole up where it's becoming directional.
 
That’s 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 (in²) x pressure (psi)
 
That’s 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 (in²) 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.
 
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
 
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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