Missile nosecone for a sub box?

Robs Ears

Novice Member
Aye, as per the title - I have here a Dassault nosecone of some sort, came from a military scrapyard/army surplus kind of place before anyone gets too keen...

I was just wondering what I could do with it, maybe make a bit of a feature of it or something. But what...?

Well, its translucent orange fibreglass under the paint, light shines through reasonably well for a start. But I was thinking of replacing my llittle Mordaunt Short sub in my front room, for something a little bigger...

This thing measures about 80cm/32" tall and is 37cm/14.5" round at the base. Initial thoughts? Stark raving bonkers? Or could there be something in it?

It needs to sound good, so I was thinking (maybe naively) that the shape would at least stop standing waves, reflections etc? A 12" cone would easily go in there along with an amp/power supply. Considering pulling my MS308 to bits to try it out.

What do you think guys?
Please try it keep it semi constructive...

DSC02701(Medium).JPG


DSC02703(Medium).JPG
 

AngelEyes

Distinguished Member
Looks like an interesting idea but good luck working out the volume :)

Adam
 

Howard0000

Active Member
Looks like an interesting idea but good luck working out the volume :)

Adam

That's easy.. Fill it up with water and then empty it into canisters of a predetermined volume ;)
 

Nimby

Member
Probably an excellent enclosure. Is that constructive enough? :)

Cylindrical objects tend not to distort under cyclic internal air pressure. This thing also avoids internal standing waves.

Two would make excellent enclosures for bass speakers.

If you are going to move your components over from a commercial sub I'd be very careful about volume. Subs (and speakers) are tuned by their volume. It helps them avoid over-excursion and to achieve an efficient match with the driver for a reasonable response. It is a careful balance.

I wouldn't cut the nose-cone for a plate amp or you may regret it later. Difficult to seal properly anyway to such a strange shape. Just have a couple of speaker terminals for your driver to connect to and seal the amp in an electrically-safe external enclosure.

You could make it downfiring by fitting dowel legs just outside the driver rim to the circular baffle.

A tuned port might lose the point of your cone but add another possible dimension to your bass. :cool:
 

Howard0000

Active Member
I can imagine that actually being really easy to work with, as you don't need to build it from scratch. The "cap" for the end can easily be made out of 20mm MDF a-la the DIY sonotube things people have made, and then it's just a case of bracing it a bit internally
 

Nimby

Member
I wouldn't give bracing a second thought for something this shape. :)

The round baffle for the driver is really all you need.

There is literally nothing to resonate where the radius is constantly changing from one end of the cone to the other.

The dimensions are also too small for sympathetic vibration from a subwoofer driver with an 80Hz crossover.
 

AngelEyes

Distinguished Member
That's easy.. Fill it up with water and then empty it into canisters of a predetermined volume ;)

Heh, well that just shows why I buy subs and not build them :blush:
 

paulst10

Distinguished Member
you could sell it as a shiny hat to an svs cylinder owner .. ;)

does look like a large helmet from the planet of the apes movie
 

Howard0000

Active Member
Heh, well that just shows why I buy subs and not build them :blush:

Well I was gonna quote Nimby's post above yours saying pretty much the same thing ;)
 

Robs Ears

Novice Member
Ok...

Good point re pulling my little MS308 sub to bits, besides, that little fella would be great in my kitchen.

Well our kids got my electric sander, so thats on hold today. Going to have a look at 12" subs once Ive measured the volume (aye, water is useful stuff eh?) First thought was to look for a car audio sub, but you guys have encouraged me enough to go for something a bit better... if only I knew what better might be... any recommendations?

I was going to go for a downfiring cone as has been mentioned, it makes no sense to start cutting the cone up, besides, itd be real hard to accurately mark and cut shapes on this thing.

3 spikes for feet would be the best bet I think, giving about 4 inches "ground clearance" to keep the proportions about right. There are bolt holes in the aluminium rim on the base, Ill use some of those to mount the spikes/feet with a bit of luck. Does the distance from the cone to the floor matter that much, so long as it has room to "breathe"?

Getting ahead of myself there tho - theres nothing to say the speaker has to be right at the end of the nocecone is there? By positioning it further up I might be able to create a perfect volume... maybe...

Having said about cutting though, Im thinking a ported box may be better as the sub is used for films as well as music (from the Kinks to Sasha & Digweed), but then again, a sealed box of this size should go pretty low with a 12" in shouldnt it?

Ill go get measuring.

ps - I should still be able to get more nosecones in varying sizes/shapes/diameters... Ill find out next weekend.
 

Member 96948

Distinguished Member
Just done some quick maths (based on treating the nose cone as a cylinder, 1/3 x pi x r2 x h) and I came up with an internal volume of 28L. Allowing for the fact it's clearly bulgier (is that a word?) than a cone, an internal volume of 40L approx would seem about right. In other words , broadly similar to the internal volume of a sub with the external dimensions of 15" cubed (SB-12?). A 12" sealed would look like a reasonable bet to my inexperienced self.

It makes you realise how space efficient a cube is.

It's obviously extremely strong to deal with the extreme pressures it would have to survive in it's brief operational life, but I'm just wondering how acoustically dead something that thin can be?

Either way, it'd be good fun finding out.:smashin:

Russell
 

Robs Ears

Novice Member
I'm just wondering how acoustically dead something that thin can be?

Good point.

Its only 2.5 - 3mm of fibreglass type material. It could well be kevlar, well, it has a yellow weave rather than the regular white colour if that makes any odds. But it is very strong, strength from form and all that.

Thinking I should maybe stick some Dynamat equivalent in there?
 

Robs Ears

Novice Member
Volume of the nosecone is 48 litres.

I now have wet feet.
 
K

kstrain

Guest
Good point.

Its only 2.5 - 3mm of fibreglass type material. It could well be kevlar, well, it has a yellow weave rather than the regular white colour if that makes any odds.

At sub fequencies it is very hard to absorb sound - what matters is stiffness. If the internal air pressure cannot deform the cone it cannot re-radiate the sound. Lining might not be such a good idea.

At some higher frequency the cone might ring quite strongly - I expect you already have an impression of the lower-limit to that from tapping the cone when one end is open. Hopefully that would already be quite high.

The weak point is the stiffness around the opening - you'll want to make sure it is *rigidly* fixed to the plate that holds the drive. Given the shape of the cone, the lowest vibrational mode will involve the wide end flexing in one of several possible ways, by fixing on a stiff end-plate the wide end will be constrained forcing the lowest mode up, perhaps considerably. The end plate will need to be sized quite accurately, and fixed on very solidly (glue all the way round, probably).
[Sorry if I'm stating the obvious here, I'm just writing as I muse.]



You could tap the in various places, record the sound and analyse (e.g. spectrum in Audacity etc.) to see the main resonance.

When you have a drive in there you can just play a slow sine sweep and feel for the resonances.

The resonances could be compared to the resonances in the panels of a typical MDF sub box of about 50 l (under 200 Hz, I think, so it matters more that they are damped).

Thin can work, at low frequencies, if stiff enough, and high Q (undamped) is not bad if the resonances are well out of band and the crossover works. In any case the mis-match between the cone and the end-plate will likely damp the resonances somewhat, except at rather high frequencies.



Ken
 

Member 96948

Distinguished Member
Volume of the nosecone is 48 litres.

I now have wet feet.
:rotfl: :rotfl: :rotfl:

40L wasn't too bad a guess then and I'll take money on it being Kevlar. Have you had any further thoughts on what driver you might use?

I do hope this doesn't get silly with prefered missile types being suggested for certain drivers. You know, Sidewinders for small 8" sealed designs, Pheonixs for 15" subterranean bass heads etc. Who'll be first to suggest a dual Skyflash system?:cool:

Russell
 

Robs Ears

Novice Member
Thanks very much for the thoughts, appreciated. Just wanting to get a really good sound has got me a bit out of my depth I think!

Its certainly very stiff, despite its thin skin, and the alloy ring no doubt helps a lot. However the cone does ring when placed on its tip and struck firmly with finger tips. I have no way of getting a good quality recording, but if I had to put a number on it then Id say somewhere upwards from around 200hz, depends with what and whereabouts I whack it though...

Regards to the opening, check the pics below for a little more detail. The little lip in the opening is only 3mm at the most, but good for locating a baffle if nothing else.

Not a bad shot at 40l at all! No idea with regards to a driver, Im much more familiar with in car gear Im afraid, any advice on drivers and how to run it and control it, would be great. 12" and sealed is sounding sensiblish to me so far though. I want to keep it as cheap as possible, obviously. But Im doubting I have any good options for under £120 all in?

I was thinking more of covering it in leather, trimming it with yaks hair, adding a pair of bulls horns and calling it Thor. Or maybe not... lets keep in on track, doing well so far. Thanks again guys.

DSC02705.JPG


DSC02706.JPG
 

Member 96948

Distinguished Member
I'm really no expert, but one of these might be worth a look. I've seen them used in sealed, vented and passive radiator designs. God only knows which works best.:confused:

Russell
 

Robs Ears

Novice Member
I heard flocking is the latest thing.

But enough for one night.

Thanks for the link russ, its looking like I need to double my budget to get this sorted properly. Hmm. Well I guess I can knock on with the enclosure and decide on a Module or whatever they are called, later on.

Wrong time of year to get extra hours at work though, new budgets and all that... Ill scour ebay etc tomorrow.

Pubs and clubs await!
 

micb3rd

Active Member
russ.will sugestion is good, it is too big for a XLS 10 but pretty much spot on for a XLS 12.
 

Member 96948

Distinguished Member
Pubs and clubs await!
You need to get older and boring. Just like me! If you want to know about cheap but bloody powerful amplification suitable for such a sub then the Behringer Europower 1500 seems like a good place to start. More than enough power for a single XLS-12.

In fact enough for two, but then you're talking about an arsenal and that's just offensive to a true blue.:mad:

Russell
 
K

kstrain

Guest
russ.will sugestion is good, it is too big for a XLS 10 but pretty much spot on for a XLS 12.

Although 40l looks a little too big for the XLS12 (830500) it certainly looks better than easily available alternatives: an XXLS12 (830845) wants 60l sealed or more or LAB 12 - again about 60l sealed or more. I can't immediately think of a perfect match.

With only 40 l EQ would be needed in any case to get a "real sub-woofer" response (in most rooms), and I suppose it is easiest to start with the over-damped response of the 830500 in 40 l (Q~0.4, definitely on the low side), rather than something underdamped and so boomy in the room-modes range.

Depending on room gain and desired response a boost of a few dB down around 25 Hz is likely to be needed - I'd consider a BFD (or equivalent parametric EQ).

Amp-wise I would be tempted to chuck a BK electronics sub panel like BSBPV500 (in a separete box). I've not calculated it, but I think this will reach excursion limits with the over-sized box (and maye even the 300 model would do that). One of these may give sufficient basic EQ to avoid doing a proper job of EQ (start with +6dB at 25 Hz perhaps).

You know, I'm sure, that this has to be for fun/uniqueness, as it will not end up wonderful value for money in pure performance terms. For starters: XLS12 ~ £150, BSBPV500 ~ £220: close to Monolith money and you won't approach Monolith performance.

But what else can you do with the nose-cone?

Ken
 

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