33.3% difference is not that small...
The bracing is also to divise the internal box modes amplitude towards several less powerfull ones?
As for the thicker vs the denser : the frequencies radiated & involved will not be the sames at iso weight. Best is to mix the layers as plywood, sandwichs. Also denser does not means each times stiffer... but at iso material.
There is a measurement of the Aberth M40 on Stereophile with 19 m mdf, no bracing but a lot of synthetic foams, targetting to put the ringings of he panel in a range which arms less vs 25 or 30 mm mdf according the designer (BBC old white paper). There was also at diya a long thread about the best material for cabinets...
The bracing is also to divise the internal box modes amplitude towards several less powerfull ones?
As for the thicker vs the denser : the frequencies radiated & involved will not be the sames at iso weight. Best is to mix the layers as plywood, sandwichs. Also denser does not means each times stiffer... but at iso material.
There is a measurement of the Aberth M40 on Stereophile with 19 m mdf, no bracing but a lot of synthetic foams, targetting to put the ringings of he panel in a range which arms less vs 25 or 30 mm mdf according the designer (BBC old white paper). There was also at diya a long thread about the best material for cabinets...
HF are not that much of an issue because there is less energy trying to move (relatively) thicker material. If one can push resonance up high enuff there is little energy to get thoese resonances moving.
dave
dave
But also less energy required to produce an audible output I think is Earl Geddes' conclusion, hence why he prefers damping.
Bracing is OK. Sandwiching of a heavy damping layer (with high internal friction losses) between two stiff layers, be it MDF or birch ply is way better. Point.
It is, but a more difficult build, and often for improvements that, in practice, can be made insignificant. Most boxes are not that well built/designed.
dave
And Geddes also points out that at higher frequencies, if the panels get going (very hard to do if the box is well executed), that any panel is going to output both in-phase and anti-phase rereadiation and most of it will cancel.
If the bandwidth of the potential resonance can be reduced sufficiently, there will rarely ever be a sustained tone at exactly the right frequency to light up the resonance. Something typically not in music.
So HF can be made moot when considering resonances.
dave
When I built my first pair of "big" speakers back in the early 90's, I was limited both in cabinet skills and tools. I made a 3/4 inch particle board box, and braced it as good as I could at the time. With the benefit of hindsight, I now realize that much of the bracing was not very effective.
Later, I wanted to tame the cabinet resonances and improve the aesthetics of these speakers... so I over-layed the particle board with 3/4 inch cherry veneer plywood. After several coats of Watco and sandpaper, the looks were greatly improved... but so were the resonances. Despite the poor bracing, the 1.5 inch wall thickness on all six sides really deadened the enclosure. It made the speakers very heavy, but this brute-force method did the job.
I would never plan to build a speaker this way today... but to correct a mistake, it has merits. Others have said to double up on the cabinet wall thickness.... I would go beyond that and use 3/4 (19mm) inch Baltic birch plywood, and rout the edges flush. Brute force...yes, but it will likely solve any cabinet deficiencies. It would also be an fast process for your cabinet maker to execute.
Later, I wanted to tame the cabinet resonances and improve the aesthetics of these speakers... so I over-layed the particle board with 3/4 inch cherry veneer plywood. After several coats of Watco and sandpaper, the looks were greatly improved... but so were the resonances. Despite the poor bracing, the 1.5 inch wall thickness on all six sides really deadened the enclosure. It made the speakers very heavy, but this brute-force method did the job.
I would never plan to build a speaker this way today... but to correct a mistake, it has merits. Others have said to double up on the cabinet wall thickness.... I would go beyond that and use 3/4 (19mm) inch Baltic birch plywood, and rout the edges flush. Brute force...yes, but it will likely solve any cabinet deficiencies. It would also be an fast process for your cabinet maker to execute.
Over here such CLD-sandwiched board sells right from the shelf, given the right supplier. About 1,5 times the cost of B grade birch ply and 20mm thickness...
I think everyone is saying the 12mm front panel needs beefing up. 😎
The rest can remain thin-wall, with maybe some light battens for strength.
Then apply some stuck-on damping to the side and top and bottom:
Harbeth Super HL5plus loudspeaker | Stereophile.com
Light speakers don't store too much cabinet energy, so have some advantages. Easier to move, as well. If it's reflex, you don't add much volume stuffing. How it works. 😀
The rest can remain thin-wall, with maybe some light battens for strength.
Then apply some stuck-on damping to the side and top and bottom:
Harbeth Super HL5plus loudspeaker | Stereophile.com
Light speakers don't store too much cabinet energy, so have some advantages. Easier to move, as well. If it's reflex, you don't add much volume stuffing. How it works. 😀
I have seen that material. Even used it. Better than MDF, not as good as (good) ply IMO. getting the corners right is difficult.
dave
Chipboard could be better than ply but the corners are also difficult to acheive.
System7, you can find good pictures of Aberth internals also in the SixMoonaudio site...don't like this site BUT for the pictures...it's the PlayBoy of Hifi press imo.
System7, you can find good pictures of Aberth internals also in the SixMoonaudio site...don't like this site BUT for the pictures...it's the PlayBoy of Hifi press imo.
I do not see why one would discard proven materials (as in acoustically tested) and linger in discussions about ply, chip or MDF. All of them have significant resonances dependent of stiffness, weight per surface and surface/shape. And they do not differ that much. Only adding some material with high internal friction that will introduce losses and dampen resonances will help here (apart from double wall and air gap solutions). Basic acoustics here. Be it that it isn’t even that critical.
dave, I have had Barefoot MM27, so I know the real benefit of pp woofer. Their woofers are tightly connected each other using metal ring in the cabinet, and cabinet itself is still extremely heavy construction. (Sorry for off topic.)
12mm is definitely too little for the cabinet dimensions mentioned, I would negotiate with the carpenter to saw up another layer of 12mm pieces that can be glued outside the existing cabinet, it will be even better than a single layer of equal thickness of two thinner layers, and here's why....
Looong time ago I helped a friend building a woofer box for his car, and at one of the local supplier by chance had some 10mm thick particle board on sale for a relatively hefty discount so told my buddy I will saw up the pieces and build a double layer as it would be cheaper than using a single layer 20mm and the end result actually became very good, the interesting thing is that, particle board, and MDF too I think, the most outer layer is the densest while somewhere in the middle it's pretty porous, so choosing 20mm would have rendered in worse result than 2 x 10mm glued together, the end result was a better damped cabinet, and with the knuckle "knock test" revealing its quality, from my earlier loudspeaker building a single layer 20mm particle board box is that a double layer glued together have different properties because the wall becomes in its composition like: "dense-porous-dense-glue-dense-porous-dense", which will better scatter and absorb acoustic energy in the cabinet wall than a single layer thicker board "dense-porous-dense", in some way it is resembling CLD (Constrained Layer Damping).
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Hope I'm not being annoying by mentioning my personal "thing" again, but you can look beyond MDF and plywood.
I've used slate (stone) for 4 speakers, mostly because I like the look and it's actually *much* easier to use / finish than wood, but just looking at the measurements slate stone is pretty ideal for cabinet building.
Due to it's layered composition it's more than 200% better at damping than MDF is:
Boxenselbstbau - Gehausematerial - connect
20mm slate damps almost *twice* as much as 28mm MDF:
(In german - "schiefer" means "slate")
I've used 16mm slate for a pair of Needles,and 25mm slate for a pair of "Samuel HQ" speakers.
I've used slate (stone) for 4 speakers, mostly because I like the look and it's actually *much* easier to use / finish than wood, but just looking at the measurements slate stone is pretty ideal for cabinet building.
Due to it's layered composition it's more than 200% better at damping than MDF is:
Boxenselbstbau - Gehausematerial - connect
20mm slate damps almost *twice* as much as 28mm MDF:
(In german - "schiefer" means "slate")
I've used 16mm slate for a pair of Needles,and 25mm slate for a pair of "Samuel HQ" speakers.
If you learn enough about TL you'd be well accomplished at bracing. Bracing does have an effect and not all bracing is equal. The bracing of a TL is known to be adequate is it not? Part of that allure is tied to a certain TL configuration where dampening material is used very heavily throughout the cabinet. The other half is the line folding itself. Not only does it brace across the structure, it can raise the resonate frequencies out of the passband by way of internal dimension.
With that understanding you would always want to be building a well folded TL for all ported designs and a sealed TL for sealed designs. If that cannot be realized then bracing that is based off the concept would be next best.
Heavy dampening material and the use of Transmission line, sealed or vented....is one of the best performing ways to get rid of the "cabinet"....whether its coming out of the port, radiating through the cone, or box walls.
With that understanding you would always want to be building a well folded TL for all ported designs and a sealed TL for sealed designs. If that cannot be realized then bracing that is based off the concept would be next best.
Heavy dampening material and the use of Transmission line, sealed or vented....is one of the best performing ways to get rid of the "cabinet"....whether its coming out of the port, radiating through the cone, or box walls.
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