Speaker enclosure

[Nelly111s]

I've been asked to make a speaker enclosure for use on the deck of a boat. The enclosure is about the size of a shoe box (size 10) and the speaker is a marine specific type. I'm making it from teak. Ideally, it'll be a) watertight b) have a removable base (or top). I'm going to construct it with the 4 sides dovetailed together.
Two questions I have, which I'd be grateful of any thoughts on.

1. I think I'll make the "lid" in which the speaker will actually mount as a floating panel, but fill the gap with sikaflex or similar to stop water ingress. Does this seem reasonable?
2. For the base, I'm less sure. I could just screw the base to the box with small enough brass screws and use a bead of sikaflex as a gasket. This works, but is it a little clumsy? If not that - what other construction method could I use?

Any thoughts appreciated?

 

[paulrbarnard]

If the speaker is a marine speaker I would not look to seal the box. Water will inevitably get in and it’s better to let it run out the bottom of it does.

 

[Nelly111s]

@paulrbarnard It is a Bose Marine 131 and the manual says to drill a hole in the case of the speaker itself to let water drain, so you may have hit the nail on the head. I'm still not sure how to fit the base to make it look good and be removable.

 

[Dlyxover]

If the speaker driver is is a marine driver it should be IP65 rated, it should be suitable for use in a sealed enclosure to maintain the IP rating.

You could maybe use a machine screw and a threaded insert as a drain point in case of water ingress.
Any holes in a sealed enclosure will more than likely make a annoying noise (from the air passing through it) which is annoying.

 

[Spectric]

A speaker is nothing more than a diaphragm that moves air, if you seal the box then the air behind the speaker is contained and the pressure will change with temperature, this may effect the speakers performance.

 

[Nelly111s]

@Spectric You're right. But this is for a customer who knows better!

 

[Dlyxover]

That is true.
Some speaker drivers are more efficient in a sealed enclosure, it all depends on what the Thiele/Small parameters are for the specific driver.

 

[sploo]

This is what I was trying to work out from a quick look at the driver in question; if you put a "normal" driver on a baffle (i.e. no box) and run it hard you'll tear it apart. If you put a driver in a sealed box (where the box volume is way outside the design range for the driver) then it'll either sound bad, or, for a really overly large box, tear itself apart.

Based on https://assets.bose.com/content/dam...peakers/131_marine_speaker/pdf/owg_en_131.pdf it does look to be a complete driver + enclosure, but ported. This means it'd be a really bad idea to mount one of these in the face of a sealed box; especially a small one. I.e. the design appears to be intended to be mounted to a wall of a boat, where there's plenty of open space behind.

If there were a desire to mount one of these with the driver showing through the face of a small box then I'd strongly recommend having no rear on the box, and ensuring the port/vent isn't within 5cm of the box walls; otherwise it might cause some odd sound issues.

 

[AFFF]

A speaker is nothing more than a diaphragm that moves air, if you seal the box then the air behind the speaker is contained and the pressure will change with temperature, this may effect the speakers performance.

This is a standard design for enclosures. Its called an infinite baffle and very common especially for small cabinets

 

[Nelly111s]

@sploo, @AFFF, @Dlyxover Thanks for your replies.
The customer in the case definitely knows best. He wants this speaker mounted in a teak box, initially this was to be partly made from an old teak tea tray, but that part I managed to dissuade him from. He want to pull it out from the hold and put it on the deck of his yacht in Barcelona, plug it in and play music. I know its designed for a mounting in the wall/bulkhead of a boat, but ...

I've also got another customer who wants a pair of speaker enclosures making, with drivers that are meant for surface mounting being recessed (by the depth of the flange) into the front panel.

I've come to the conclusion that the common denominator in all this is me!

 

[sploo]

The customer in the case definitely knows best. He wants this speaker mounted in a teak box, initially this was to be partly made from an old teak tea tray, but that part I managed to dissuade him from. He want to pull it out from the hold and put it on the deck of his yacht in Barcelona, plug it in and play music. I know its designed for a mounting in the wall/bulkhead of a boat, but ...

If the customer will accept a slot in the box then it could be built such that the driver is mounted to the top of the box, and the enclosure's port/vent aligns with a slot cut into the side of the box (i.e. the keeping the port free to "breath"). That means any air movement generated by the driver would be fine, so holes for water drainage in the teak box shouldn't affect the sound.

Mount the enclosure's port/vent flush with the outside of the box though (rather than the inside of the box); otherwise you're effectively extending the length of the port by the thickness of the box material, and that will affect the tuning of the port.

Or just do exactly what the customer wants, but do tell him it might sound a bit weird

 

[Nelly111s]

Or just do exactly what the customer wants, but do tell him it might sound a bit weird

This

 

[AFFF]

Forgot to say that if your designing the cabinet then be careful that you don't use the same interior dimensions (or exact multiples) for H, W or D. If you do then there's a very good chance that you will get resonant frequencies caused by standing waves inside the enclosure. This can result in very "boomy" speakers or excessive drop off in the mid/high end. Ideally its best to use golden ratios for the internal dimensions. Also, teak is not a very good material for speakers as it "rings" too much. You want something that is acoustically dead. MDF is a good option but probably not in a high moisture environment. Speaker cabinet design is, despite all the science available, a bit of a black art. Best of luck, please let us know how you get on

 

[curlywurly76]

Is the speaker for Hi fi frequency reproduction or just radio chit chat ie just for information exchanging.

 

[Nelly111s]

I’m not sure exactly what, but I think it’s so the customer can sit on his yacht in Barcelona and annoy has neighbours with his music

 

[Nelly111s]

So, this is the design I came up with. Using. reclaimed teak for the whole of it and a piece of ready made stuff made to look like a ship's deck for the lid. Made the lid about 3 mm smaller than the top aperture and the rebate depth to allow for movement and filled the gap with Sikaflex to stop the water getting in. The render is from Fusion 360 and I'll post some photos of the finished product in a day or two.