Long Overdue Rythmik-Audio Servo-Sub Project

[welwynnick]

My Life story: after graduating I worked in a shop before I got my first "proper" job. Not just any shop, though - they sold high end audio equipment, as luck would have it. So I spent a few months being paid to play with the best hifi gear there was, and I learned a few lessons on the way.

But one of my over-riding memories was of listening to the bass on various Level 42 tracks through really great systems. Not just deep and weightly, it also had great transparency and articulation, and I couldn't get enough of it. Sadly I didn't get any more, and had to go and earn a real living, but I've been looking forwards to hearing the same quality of bass ever since. And I've been disappointed for a long, long, time.

Multi channel audio systems have arrived and taken over, and tiny active subs have replaced huge passive speakers. The range of very expensive equipment has also mushroomed, and I've heard plenty of it at all the hifi shows. But none of it has ever come close to what I fondly remember from my days of happiness and poverty . Somehow, though, I noticed that active servo speakers were making an impression in audiophile circles, and Rythmik Audio were making waves in the States. I liked what I was hearing about the technical and subjective descriptions of the subs, and after a little research decided to join the cult.

That was the easy decision though, and while Rythmik only really specialise in servo sub kits, there were a few more choices to be made.

One sub or two?
15" or 12"?
Sealed or Reflex?
Small box or large(ish)?
MDF or plywood?
Veneer or varnish?

I decided to dip my toes in the water, and in the middle of last year I ordered a DS12CV servo kit for a 1.5 cu ft sealed box. I'm useless at getting my finger out (of the keyboard) and into the garage during the winter, but recently I've finally made some progress with the woodwork. It's getting close to the point where I'll have something working, so I thought it might be time to start a thread to capture and illustrate what I've been up to. I'll get the camera out tomorrow and show some really interesting pictures of some piles of wood. You never know, it might encourage some folks to do the same.

I just hope the years of anticipation won't be in vain when it comes to the big day.

regards, Nick

[ched]

Nick, hope you are busy with bits of wood and a camera. I for one am looking forward to the photos and to read your comments on the performance of the sub.

Good luck.

[welwynnick]

OK, here's a picture of a pile of wood. I decide to go for plywood rather than MDF, as I didn't fancy all the sawdust problems, and I stood a chance of getting an acceptable finish without having to veneer it

If only I could explain how long that took me to design, buy, mark, cut, trim, plane, smooth, glue and screw. I'm too tight to pay someone to do it for me, though.

There are two parts to the enclosure - the outer box, and the inner bracing, which looks like a sort of skeleton.

Now I have to figure out what order to assemble it. I think it's a matter of how the tolerances add up. Do I build the box, then fit the skeleton inside afterwards, or do I build the box up around the skeleton?

Nick

[ched]

Looks great. I bet it was huge amounts of work. I have made sub enclosures before and it is amazing the amount of effort that is required. It annoying that in the end people who hear the sub wont realise the amount of effort you have put in.

Well done and keep posting the picys.

[inzaman]

Originally Posted by ched

Looks great. I bet it was huge amounts of work. I have made sub enclosures before and it is amazing the amount of effort that is required. It annoying that in the end people who hear the sub wont realise the amount of effort you have put in.

Well done and keep posting the picys.

I agree with that, i also really enjoy seeing these sub builds; i am tempted to do one myself - keep the pics coming

[welwynnick]

Here's another picture with a trial fit before I put any glue on:

As you can see, I don't trust glue; or at least my ability to glue things together. The driver mounting was complicated because once I did the big cut-out (by jig-saw!) the strength of the panel vanished. I thought I needed to follow other people's advice and double up on the driver mounting, so there are two panels glued and screwed together, and very much stiffer for it.

The walls of the box are extended to make the feet. I wouldn't recommend that to anyone, as it's so much more difficult to get a good finish across the bottom when I can't simply saw and plane right across. However, it does mean the driver panel is inserted from below, so I fixed battens above and below it. I cut slots in the battens to allow the bracing to but against the base panel. The material, which was glued across its narrow edge to the base, fell away in my hands, so it seemed to me that the strength would come from the screws instead. I'm not sure that I trust plywood not to de-laminate when there is any tension on the surface.

There must be two hundred screws in that one panel, totally over the top, but it's very solid. It seemed to be important not to obscure the back of the driver by screwing it into double thickness material, which might impede airflow.

The end result is the driver looks like its rebated, which neat in itself. however, I didn't measure carefully enough when I cut the hole in the outer panel, and the driver wouldn't quite fit. I had to open up the hole with a hand-held jig saw, and made a terrible mess. Good jub it's down facing. I don't have a router, but if I did this again, I would certainly need to find a better way.

It's taken a long time to get to this stage, and it's a bit unfortunate that it's so cold and dark these days, but I'm glad to making some real progress. Won't be long now ...

Nick

[ched]

Its looking good. I take it that you have been sealing the joints with something to stop any air leakage?

Keep up the good work, it will all be worth it in the end.

[welwynnick]

Finished the gluing and screwing last night.

Fitted the driver and amp today and lots of pictures to come.

Will fire it up tonight, and quite looking forwards to it.

Nick

[ched]

Cool, tell us how it goes...

[chelsea.tone]

Nice job Nick, very impressed. I totally wouldnt have the patience or expertise to attempt this More pics m8

Tony

[ReTrO]

Looking good. I really must get on with my BK Monolith clones soon.

[welwynnick]

A few more pictures:

I fixed the external walls together first, to help ensure the joints were air-tight, then fitted the top panel.

I "fettled" the bracing to fit the box. It fitted easy but tight - I couldn't even twist it inside the box, making the glue difficult to get in the right place. In hindsight, it may have been easier to build the box around the bracing. Once the bracing was fitted, the box seemed somehow "quieter..."!

The driver mounting panel, last to go in. With glue round the edges, I had to push quite hard to get it down inside. It was a close fit.

This a view with everything together. It looks very complicated, and I'm not sure it's necessary to go to such extremes with box bracing for a modest-sized enclosure. The design is based on the Rythmik design for the 2 cu ft speaker, but I took about 4 in form the top. It brings the amp transformer close to the drive unit ....

Nick

[ched]

So come on then how does it sound??????

[welwynnick]

Originally Posted by ched

So come on then how does it sound??????

Sorry, after all that I dunno yet. I doing battle with the set-up menus on my SOny amp. I used to use my Acoustat hybrid electrostatics on full range, but I can't seem to switch on the sub output. Very frustrating; I'm going to have to read the manual. D'ohh!

Nick

[velvitjester]

any finished pics?