Do sealed back drivers need an enclosure?

[Bon]

1. I would assume that if significant diffraction effects on the axial frequency response occur below 4 kHz it will only get worse from 4 kHz upwards.
2. The mid-range 400 Hz-4000 Hz is where the human hearing is most sensitive and it is reasonable to expect it is where diffraction artefacts are most audible.
3. The enclosures in Figs 7, 11. 12, 13, 14 of the Olson paper, are of minimal depth. Not quite "beefy picture frame" but it is reasonable to infer that the diffraction effects are caused by the primary sharp edges closest to the driver and the depth of the enclosure has little bearing on the diffraction.

I have no desire to push my opinions on diffraction control. It is only a side issue of my OP.

 

[AllenB]

1. I would assume that if significant diffraction effects on the axial frequency response occur below 4 kHz it will only get worse from 4 kHz upwards.

They could increase or decrease, depending on where they are. With the Olson baffles, low frequencies aren't much affected as they don't significantly see the baffles. High frequencies are less affected because they are significantly supported by the baffles before encountering the step.

 

[Bon]

it is reasonable to infer that the diffraction effects are caused by the primary sharp edges closest to the driver and the depth of the enclosure has little bearing on the diffraction.

The thread

4

Thread 'Baffle edge diffraction with dipole radiation'

2015-01-03 6:44 am

Nearly all dipole speakers use either a flat baffle, U-frame, or H-frame. All these baffle types have in common a sharp termination separating the front and back sound waves. What is it about dipoles that eliminates the edge diffraction, or does it exist and people simply ignore it?

Roundovers are common and highly recommended for monopoles, but when it comes to dipoles, no one bats an eye at thin sharp edges. Do the opposing waves really totally cancel out the edge diffraction? Probably not, because we know that the shape of the baffle affects (at least) the response around and above the...

• 454Casull
• Replies: 91
• Forum: Multi-Way

is concerned with diffraction effects of panel speakers which are properly can be described as "beefy picture frame". It has interesting contributions from some of the loudspeaker heavy hitters on this forum.

 

[AllenB]

Would it interest you to know it's been shown that rounding the rear corners of a typical box can make a difference?

 

[Bon]

Given that the spherical baffle (Olson Fig 6) produces the least diffraction artefacts in the axial frequency response, it does not surprise me that rounding the rear of a typical box makes a difference.

 

[Bon]

Fig 11 and Fig 12 of Olson's paper, show the axial frequency response of two enclosures. The first is a truncated cone with driver at the cone apex. The second has an identical cone joined to the back, again driver at the apex of the first cone. It is not unreasonable to think of the rear cone enclosure Fig 12 as a "smoother rear" version of Fig 11. They both have nearly identical axial frequency response artefacts. Of course these are not typical boxes but it shows that the baffle edge diffraction effects may overwhelm other diffraction effects.

 

[AllenB]

it is reasonable to infer that the diffraction effects are caused by the primary sharp edges closest to the driver and the depth of the enclosure has little bearing on the diffraction.

I would not. It depends on how much diffraction needs to happen at any point and how much is being allowed to happen. You should guide the wavefront until all the guiding is done, otherwise you have to diffract it.