Internal Diffuser

[Ron E]

Wow, this is a complex philosophy.

Deftly done!

 

[lucadelcarlo]

So what effect then might a miniature quardatic diffuser surface (peaks and valley variation of several millimenters) along the walls of a spherical type enclosure possibly have, if anyone would care to speculate? With the process I'm using, the surface could be modeled with as fine or exact a pattern to correspond with what's happening behind the driver and inside the enclosure as needed. Judging from the discourse, perhaps it should seem obvious on the face of it that the effect should be expect to be nil, but the question still stands

 

[crazyhub]

He tries very hard :
6moons audio reviews: Audiomanufacture Boenicke W20
....I tried all kind of diffusers inside speaker enclosures and the effect is minimal. Damping material is much more efficient. I put only that amount of damping material inside so that the small blimps in the phase of the impedance curve disappear.

Do you think porous cross-cut cardboard as used by Boenicke could have the same effect than traditional damping materials but without killing as much spl in the low frequency range?

 

[lucadelcarlo]

Surely there's been experimentation similar to Boenicke's out there somewhere - I'm intrigued as well.

 

[moray james]

you know if you brace and stiffen your cabinet with plenty of stringers to tie all the panels together well you will generate lots of diffusion inside the cabinet. That is a lot of work I cannot imagine attempting to build in diffusor panels into a cabinet. Fiberglass works so very well in sealed cabinets and is inexpensive and more than enough work to install if you use high density material. Best regards Moray James.

 

[lucadelcarlo]

Such intricate bracing to stiffen cabinets and possibly provide some internal diffusion certainly must involve significant work when conventional wooden construction methods are used. I'm curious what effect a very intricate filigree or lattice-like internal structure might have (imagine something akin to Eiffel-like forms on a very small scale) within a cabinet, in terms of diffusion. The Boenicke example comes close to what I'm imagining, but there must be other similar experiments. Has anyone seen such? Any more thoughts on the effectiveness of Boenicke's design in this area?

AHLM design for your ears

 

[AllenB]

Fibreglass will easily remove the higher frequencies that such a diffusor might work with. The question might be: do you want these higher frequencies at all? Much of the time it would be best if the back-wave would just go away, except for loading the driver through resonance of course.

 

[NATDBERG]

I tried all kind of diffusers inside speaker enclosures and the effect is minimal. Damping material is much more efficient. I put only that amount of damping material inside so that the small blimps in the phase of the impedance curve disappear.
In closed boxes for subwoofer use i stuff more because you can get an effective virtual doubling of the internal volume. Here glass wool or rock wool is most efficient.

I realise this is a little thread hijack (but seeing as nothing's been said for 8 months it prob. won't matter)..

Is the "effective virtual doubling of internal volume" easy to work out?

I have some big 150 litre cabinets housing 2x15" drivers which were built by someone else. An expert calculated on back of an envelope that they should be 300 litres and hence why I wasn't getting much bass from them.

Can I correct the design simply with internal damping choices ( I think it is minimal, light open fibrous stuff on the walls only) ? 300 litre cabinets would be rather large..

 

[lucadelcarlo]

3D Printed Acoustic Cloak

A very interesting new study released by Duke University researches on the use of metamaterials as acoustic cloaking devices to hide objects from sound. The research may have applications for loudspeaker construction (internally) and/or acousticians.

Acoustic Cloaking Device Hides Objects from Sound | Duke Pratt School of Engineering

 

[Moondog55]

Wasn't the old recommended solution to this problem to have the back wall at an angle to the front wall and still use stuffing

Nat the effective increase is about 20%
If you need a big box a big box is needed usually but try a combination of acoustic fiberglass and open cell polyurethane egg crate foam

 

[moray james]

A preliminary search did not return any useful result on this topic so...

Is there any argument to be made in favour of utilising a an internal soundwave diffuser within an enclosure to break up standing waves or to any other benefit? Just to be clear, a diffuser role is understood not to absorb soundwaves, but merely change or sufficiently randomize their angle of reflection to break-up standing waves and resonant frequencies. In a studio or theatre environment, the panels can be quite large and cover a significant area. Lower frequency waves are longer than the longest dimension of most any speaker enclosure, but what of the mid to high frequencies, or harmonics – could these be addressed by an internal diffuser, or, as mentioned, could there be, any other possible benefits?

Here is hoe I deal with diffracting standing waves inside if cabinets. I install plenty of strong brace work and tie the whole box together. The brace work will take care of any standing wave along with the drivers inside the cabinet and plenty of quality damping material. See the link for some pictures of the inside of a set of Klipsch Heresy 3 with brace work installed. Hope this is of interest. Best regards Moray James.

Heresy 3 Brace work... - AudioKarma.org Home Audio Stereo Discussion Forums

 

[RyanC]

QRD's require space to work, minimum ~1x of lowest diffused wavelength. So if you are hoping to diffuse 100hz inside your box it would have to be ~9ft deep.

But a QRD that is effective at 100hz is already quite big. I suspect it doesn't matter that much because the inside of a (typically sized) speaker box fits the modal model much more than the ray trace one. IE Schroeder frequency inside a speaker box is quite high, probably above 500hz or even 1k...

 

[NATDBERG]

Nat the effective increase is about 20%
If you need a big box a big box is needed usually but try a combination of acoustic fiberglass and open cell polyurethane egg crate foam

Thanks for that response. I came up with another solution - they are/were ATC units and I found some proper ATC SCM150 Pro cabinets for £150 so will instead turn them into single 15" driver passive ATC SCM150s instead.

However I do want to build some bass cabinets with a Volt B2500.1 to complement some Esotar drivers so will be trying out the same technique to keep the cabinet volume down to a minimum with infinite baffle.