Subwoofer enclosure in steel?

[metalsculptor]

I am new to the the DIY Hifi stuff , so this is my first attempt and I thought a Sub would be a good start. The choice of steel is a style decision, The decor in my house is industrial and the sub should compliment that

I like curves and I have access to a lot of pressure vessels and light pipe bends which got me thinking about making a sub enclosure in steel. Most of the steel I see is 4 to 6mm wall with plenty of compound curves which I think should stiffen the enclosure. I am not sure about resonances other than that the transverse modes can be quite low frequency but they require asymmetric loads to excite them in a pressure vessel, pressure loads should be symmetric where the wavelength is many times the enclosure size. Constrained layer damping just in case ? I will use fill as this is to be a sealed enclosure operated below resonance.

The driver I am looking at is a PA driver 15" 98 db/w good for 500W RMS with an xmax of +/- 11mm Vas around 170l The intended use is home hifi to get 32 hz organ pipes and the thud of large Asian drums. Asian drumming is often fast paced and off beat I am thinking about crossing over at 55 hz I have about 300W RMS to play with.

Has anybody made a steel enclosure? Thoughts about using high sensitivity PA drivers? Good speaker design books? Should I use an 18" driver instead or maybe two 15" drivers.

[Aurality]

since your goal is purely asthetical and will be a first attempt why not just follow a conventional
and tested design out of wood/mdf then use the steel just to plate it. a metal veneer if you will..
That way you will have something that works well and looks like it has been entirely made out of steel.

[metalsculptor]

The steel design will be either cylindrical with ellipsoidal ends or a conical elbow, due to the difficulty of making curves of any type in wood let alone compound curves I never considered it, even concrete or FRP would be options except making the mould is no fun. The steel comes preformed to the shape I desire, I know I am lazy.

Unless you are suggesting build a square wood box inside a curved steel shell in which case I might as well use wood bracing to dampen any resonance in the steel shell and skip the box.

[sreten]

Hi,

Use a proper subwoofer, unless you planning on huge subs you will find
no gains in using high efficiency drivers, bass efficiency will be poor.
I cannot see the point of CLD at such low frequencies.

Two mono subs spread around the room are better than one bigger one.

download a similator, WinISDpro or Unibox and play with them.

rgds, sreten.

[pheonix358]

Have a look at Building in Stainless steel and timber!.

What you have in mind sound very good to me, the material choice is not an issue. Try to ensure that the wave front from the back of the woofer does not strike untreated metal.

As for your choice of drivers, most Pro drivers are not good at very low frequencies. Look at decent subs designed specificaly to go low.

Terry

[Andrew Eckhardt]

Being a sculptor perhaps you could do what it takes to make sure you have perfect cylinders and symmetrical ellipses, since that is what is required to load the vessel material with tensile and compressive force rather than bending. If you did that, there would be absolutely no way to match the volume or distortion performance of a 1/4" thick steel vessel with a wooden box subwoofer for a single 15 or 18. I would make a pair.

[Aurality]

Don't know what your room is like..but if you have a fireplace, I made subwoofer
in the last house I lived utilising the old chimney breast.. That Thing couldn't have
been Any better for the low organ frequencies you require .. or have been any more industrial

No need for a super duper woofer, excellent results can be had from a less capable, cheaper driver, since it will be
in it's own natural 20-30 foot solid concrete resonance chamber. which corresponds perfectly to
low 30 hz wavelength.

My setup was just plated underneath the chimney.. yours could then have an elbaroate
steel sculpture to hold the driver in place, leaving you much creative freedom..
Just an idea.


if not maybe some inspiration could be had from the RAAL requisite 'Eternity' OMNIS

http://www.raal-requisite.com/


.

[wakibaki]

I wouldn't agree that the material choice is not an issue. I suspect that steel is too lively a material to lend itself to loudspeaker enclosure construction. Wood and MDF are deader and more likely to provide good damping. 'Course it all depends on the thickness ratio, there's a big difference between a 6 inch cube with half-inch-thick walls and a 3-foot tall floorstander made of sixteenth-inch sheet.

w

[Andrew Eckhardt]

wakibaki I would recommend thick steel sheet in typical pressure vessel construction is nearly ideal only for a subwoofer. At higher frequencies things get more complicated.

As an aside I think when you're dealing with high performance pressure vessels the ends are usually spheric sections except for an interface bend so that high stress doesn't develop at the weld. For the relatively low pressure differentials of a woofer volume the stress there can be ignored and spheric/cylindrical figured optimum from a minimum surface distortion under drive standpoint.

[metalsculptor]

For the relatively low pressure differentials of a woofer volume the stress there can be ignored and spheric/cylindrical figured optimum from a minimum surface distortion under drive standpoint.

Exactly what I was thinking pure tensile load if possible Even thin walled (1.2mm) 2 stroke exhausts driven with pulses around 200db don't deflect much. A lot of industrial pipework is subjected to internal pressure pulsations with minimal sound radiating from the pipe surface.

As for the use of a high efficiency driver, is the problem due to the chance that the voice coil may leave pole piece area as the excursion increases? I could measure cone deflection vs drive current over the range of excursion but that would mean buying the driver just to find out. I have used loudspeaker motors as current to force transducers in the past and ended up using hifi ones because of their greater linearity. Are automotive subwoofers any good? low Xmax and plenty of snake oil doesn't inspire confidence.

Aurality I love that idea I bet no birds sat on your chimney Unfortunately I do not have a fireplace to convert. The Raal units are very attractive.

I will download a simulator, I am new to Ts parameters but understand the physics.