A Big'un - the Audio Nirvana Super 15

[Melon Head]

I agree, you shouldn't need to do anything. Put the speaker in and have a listen, then start stuffing it with accoustic filling and listen. Get yourself a trolley to move that box around.

 

[Bigun]

Fate has shown it's hand. A chap at work, who knows I'm building this monster, phoned me up and offered me a big piece of carpet they were throwing out because it has the wrong logo on it. It's not been cleaned so I'll have to clean it yet but it looks just the ticket. About 2.5mm thickness of rubber and the carpet pile will provide further acoustic benefits, mostly at higher frequencies. In fact I may use this carpet as the only lining material and not install any felt lining - I'll put felt and batting on the braces to intercept sound waves inside the box rather than at the walls where air velocity will be lowest. Contact cement already purchased.

 

[Bigun]

I've also had a go at playing with some wood stains as I'd like to do something different than a gloss coating. But Birch is not that easy to stain - it blotches easily. I've found gel stains the least blotchy. But the colours are not optimized for Birch, most likely expecting people to use them on Oak. They tend to come out rather extreme. Birch has little grain structure to start with and it's easy to obliterate it. There's a patch of Amber shellac in there somewhere and apart from being too yellow it actually does a reasonable job.

Not sure how I'm going to proceed on finishing.

 

[GM]

Considering the rest of the construction, adding a rubber backed carpet will probably over-damp the driver somewhat plus it will reduce the cab's net Vb, though being sealed, the slight increase in tuning will probably be offset by the increased damping for a slightly [I imagine inaudible] net loss in performance when compared to just adding a bit of polyfil or similar to quell any HF reflections. Only one way to know for sure of course.

GM

 

[Melon Head]

Also consider lacquer without the stain. Not sure what it will look like, but it might turn out better than you expect. I will show you what I have done on a small boxed speaker

 

[GM]

But Birch is not that easy to stain -

Maybe this will help: Successfully staining birch

GM

 

[Bigun]

adding a rubber backed carpet will probably over-damp the driver somewhat GM

Sorry GM, I don't understand this part ?

... the rubber may help damp box wall vibration / colourations, how does it affect the driver ?

I will show you what I have done on a small boxed speaker

eagerly awaiting pictures !

 

[GM]

The cab's air mass is like a spring with a quality factor [Qa], so anything that alters its ability to act at this Q will lower it. This in turn impacts how it damps the rear of the driver, especially at higher frequencies and power.

Just because it's not some sort stuffing filling up the cab doesn't mean it's not acting the same way to a greater or lesser extent.

GM

 

[buzzforb]

I've also had a go at playing with some wood stains as I'd like to do something different than a gloss coating. But Birch is not that easy to stain - it blotches easily. I've found gel stains the least blotchy. But the colours are not optimized for Birch, most likely expecting people to use them on Oak. They tend to come out rather extreme. Birch has little grain structure to start with and it's easy to obliterate it. There's a patch of Amber shellac in there somewhere and apart from being too yellow it actually does a reasonable job.

Not sure how I'm going to proceed on finishing.

Look up how to stain soft maple. Similar problem of uneven absorption. water based pigments seem to be preferred as i the link GM posted. Prep is very important. A clear coat on Birch can be gorgeous. Look at Troels Quattro for a good example.

 

[Bigun]

The cab's air mass is like a spring with a quality factor [Qa], so anything that alters its ability to act at this Q will lower it.

so the rubber lining would absorb some of the energy from this 'air spring' and lower the Q - i.e. more damping. In post 16 you were concerned about use of a sealed cab being under-damped. Which effect do you think will dominate - or is this one of those 'suck and see' things ?

 

[Bigun]

Look up how to stain soft maple. Similar problem of uneven absorption. water based pigments seem to be preferred as i the link GM posted. Prep is very important. A clear coat on Birch can be gorgeous. Look at Troels Quattro for a good example.

yes, it's a very nicely finished speaker. Thing is, it's also much smaller. I have built a sub woofer and I finished that box with clear coat and it looks good. But the Big'un AN 15 box is much bigger and all that white wood is going to be a bit stark in my living room. At the very least, I need to tone it down.

The link GM posted contains a lot of recommendations which require spraying of coatings and I don't have the set up or equipment for that. The solution has to be applied by hand in my garage.

 

[GM]

Hmm, post 16 referred to your considering A-N's 13.6 vented cab, which would be under-damped, but now it's a ~12 ft^3 sealed, right? If so, it's ~ a max flat alignment.

Regardless, I was referring to the higher frequencies and higher power scenario. The rubber will reduce net Vb and doubtful it will do any useful panel damping to a constrained layer construction, especially since it's carpeted. The carpet will reduce net Vb a little also, but mostly will damp.

Right, only one way to know for sure except by comparison.

GM

 

[buzzforb]

yes, it's a very nicely finished speaker. Thing is, it's also much smaller. I have built a sub woofer and I finished that box with clear coat and it looks good. But the Big'un AN 15 box is much bigger and all that white wood is going to be a bit stark in my living room. At the very least, I need to tone it down.

The link GM posted contains a lot of recommendations which require spraying of coatings and I don't have the set up or equipment for that. The solution has to be applied by hand in my garage.

water based pigments can be applied by hand. Thinning is done by water for tone control. About same price as normal can of stain. be sure and practice of course.

 

[Bigun]

doubtful it will do any useful panel damping to a constrained layer construction

that's a good point indeed - I really have no intuitive feel for how effective my implementation of the constrained layer is providing and so if I'm honest with myself, I am simply assuming that more rubber can't be a bad thing for the little effort (and no cost) involved in gluing it in place.

 

[Melon Head]

First listen to it and try and see if you can detect anything unpleasant. Put your hand on the box while it is playing music and feel for vibrations. I think at best you might get another 5% improvement with further tweaking. You have already done an excellent job of bracing it.

 

[Bigun]

Good thinking Melon.

I'm gluing in a couple of corner strips to strengthen the joints at the bottom of the inner box since the outer box stops a couple of inches short from the bottom (by design). And I'm installing a frame-type shelf brace about 6" from the bottom and I'll glue on a short piece of ply on the back of the box up to that brace so that the bottom of the box is strong and closed all round. Then I'll sand the outer sides gently and start staining them with the Gel stain (it doesn't blotch).

So I'll start out with no lining and no stuffing just to see what I get. I need to sort out some bolts for the driver, I've quite a few in my collection but nothing suits the rebate in the driver - I may end up with temporary bolts where the bolt head is too big to fit into the rebate.

 

[Bigun]

now on to some sanding and a little black paint strategically positioned on the driver surround

 

[Richard Ellis]

I once built a single enclosure at 23.5 Cubic feet, with a 2.5 sub-enclosure inside.........Four HD casters, 153 screws & a quart or so of wood-glue, using One inch MDF........It would distort the carpet when I "tried" to roll it. Needless to say I didn't build the second one.........but it sounded great, too bad it took up so much space inside my tiny Apartment.

________________________________________________Rick........

 

[Melon Head]

Just tried varnish on a piece of birch ply. It did not have the effect I was hoping for. Definitely not blotchy but it needs some sought of stain to look good.
It does work very well on Tasmanian Oak though.
I will upload a picture later

 

[phivates]

stains

Look for stains with translucent pigment. Varathane was one when I was looking 2 years ago. I've settled on tinted shellac under evolved waterborne varnish, sprayed. The new products are vastly better than what we tried 20 years ago. Finishing wood is a challenge.