Loudspeaker information sought

[Macca]

93 litres is very large, are you sure?

[Barry]

If you ignore the slanted part of the enclosure, and just consider it as a simple cuboid of external dimensions of 1' high by 1.5' deep by 3' wide, that is a volume of 4.5cu ft. There are 28.32 litres in a cubic ft, so 4.5cu ft equates to 127 litre.

(1 cu.ft is 1728 cu.in. An inch is 2.54cm, and a litre is 1,000cm³. So 1 cu.ft = 1728 x (2.54)³/1000 = 28.3168 litre.)

Taking the pentagon prism shape into account, the external volume is 4.1cu ft, or 116.1litre. Again, assuming the internal volume is 20% smaller than the external volume, that reduces the internal volume to 116.1 x 4/5 = 92.88 litre.

The actual internal volume is yet to be determined, but it will be something like 92 to 100 litre. The real unknown is how to dampen and load the elliptical drive unit, with say 1" thick felt, or by stuffing the internal volume with loft insulation. Total fidelity is not required as the sub woofer is located away from direct earshot. A lot of room for experimentation.

[Macca]

Here's an image with a bloke for scale of a 100 lite cab - that's a big subwoofer!




Not sure that Phil's thinking of something that big if it's going under a desk/bench. But maybe he is...

[Barry]

The internal volume looks as though it could house 4.5cu ft. We will have wait for Phil to post a photo of his 'infinite baffle' enclosure.

[Phil M-W]

Barry, it might be a while, before I have anything to photograph, apart from the speaker. The guy who is making it for me is very busy. I did some rough calcs this morning and I came up with a volume of approximately 107 litres, but that was based on the external dimensions, so the 93 for the internal volume sounds entirely plausible.
Don't forget the eventual aspiration is to turn this into a transmission line speaker, so internal baffles are going to soak up some more of the volume. I was going to line the the inside faces of the panels with 6mm flooring felt, to minimise internal reflections and then strategically place other material in there to adjust how it sounds. I also theorised that having the speaker mounted at an angle, whilst it wont reduce reflections, from the panels behind will provide a variable path length so should remove, or more accurately, smear out the reflected wave over a range of frequencies, so (hopefully) preventing a standing wave between the back of the speaker and the back panel causing colouration at a specific frequency.
@ Macca, there is a big space under the desk which I can't really use for anything else. I suppose if I were younger and more agile, I probably could. Getting into the space isn't so bad, getting out can take a while. I have a 100 litre LPG tank in the back of one of the cars and it would just fit in there so that looks to be about right, and I'm sure I've heard somewhere, the more volume you've got for your speaker the better.
Phil

[Macca]

@ Macca, there is a big space under the desk which I can't really use for anything else. I suppose if I were younger and more agile, I probably could. Getting into the space isn't so bad, getting out can take a while. I have a 100 litre LPG tank in the back of one of the cars and it would just fit in there so that looks to be about right, and I'm sure I've heard somewhere, the more volume you've got for your speaker the better.
Phil

Indeed, make the cab as large as is practical.

[Pigmy Pony]

A box measuring 18" x 18" x "24" has a volume of 4.5 cubic feet, or 127 litres. Probably have an internal volume of about 100 litres, when allowing for cabinet wall thickness. So plenty of room to 'go big' under the table

[Barry]

Any update on the speaker enclosure being made for you Phil?

[Phil M-W]

Funnily enough Barry, I wasn't expecting anything this soon, but it appears the cabinet has already been started. I contacted him last week to mention another minor issue we had, and mentioned the increase in size of the cabinet at the same time. He came back saying he had already started but the change wouldn't be a problem. I haven't got an eta yet though, and as the other issue is trivial, and probably caused by the excessive heat we've had recently, it won't be high on his list of priorities.
It would be nice, once it's built, to find someone who could test and analyse both the speaker (driver) and the assembly - and has the time to do it. Just to get an idea of what I'm starting with and where improvements could be made.
You mentioned Walpurgis (flashbacks of Procol Harum there!) in an earlier post. Is this the sort of thing he (presumably not she) could do? I did approach Matt at Haycross Audio, but he is trying to focus on building speakers and wasn't very keen.

A quick p.s. Have there been issues with the forum recently. This is the first time I've been able to get on for a couple of days.

Phil

[Pigmy Pony]

I've had problems for about 4 days now, and yesterday couldn't get on at all. Dunno why.