[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?

[suniil]

nice progress pics! glad to see the number of screws used, that will definitely give peace of mind when driving the SPL beyond 100db

[Welwynnick]

Originally Posted by suniil

nice progress pics! glad to see the number of screws used,

You noticed, then! There's about 300 screws there. As you can tell, I don't trust glue, even though everyone else seems to use MDF and Evostick. I may not necessarily have done it the right way, but I'm confident with what I've done.

The amp and driver are now in, connected and working, so it's time for a couple more pictures:

I've had it running with high and low-level inputs, with music and movies, and with the cross-over done by the amp and the speaker. I haven't had time to try different settings or positions yet, so I think there's some way to go to get it set-up well. I see a lot of people being able to test in-room frequency reponses, and I'd like to find a way to do that. Probably better try the subwoofer forum for that.

For now, though, I find that I'm continually turning the overall volume up more and more, and listening for longer and longer. The bass itself is an (expected) novelty in my particular system, but it's the way that you DON'T notice it that's impressive. It seems to allow the main speakers to sing more clearly and freely, and particularly for the soundstage to open up into a large and effortless space that just seems quite natural. The success for me is that it doesn't sound like a subwoofer.

Nick

[velvitjester]

Originally Posted by welwynnick

You noticed, then! There's about 300 screws there. As you can tell, I don't trust glue, even though everyone else seems to use MDF and Evostick. I may not necessarily have done it the right way, but I'm confident with what I've done.

The amp and driver are now in, connected and working, so it's time for a couple more pictures:

I've had it running with high and low-level inputs, with music and movies, and with the cross-over done by the amp and the speaker. I haven't had time to try different settings or positions yet, so I think there's some way to go to get it set-up well. I see a lot of people being able to test in-room frequency reponses, and I'd like to find a way to do that. Probably better try the subwoofer forum for that.

For now, though, I find that I'm continually turning the overall volume up more and more, and listening for longer and longer. The bass itself is an (expected) novelty in my particular system, but it's the way that you DON'T notice it that's impressive. It seems to allow the main speakers to sing more clearly and freely, and particularly for the soundstage to open up into a large and effortless space that just seems quite natural. The success for me is that it doesn't sound like a subwoofer.

Nick

looks good

[Welwynnick]

Thought I would finish for now with some comments and lessons learned that have been bursting to get out.

Most of the customer examples on the Rythmik website show beautifully finished boxes, but my wife says mine looks like a packing crate. I just wanted to get to the point where it's working, so I can make sure there's nothing wrong with the amp and driver before it's too late to do anything about it. As it happened I did have a problem, and Brian bent over backwards to help me. I see why everyone says his support is so good. I just had a loose connection somewhere, so it's all good now.

I'm still not convinced that ply is the best way to make a speaker, but I thought with a bit of varnish and sanding I could get an acceptable finish without veneering. My plan is to skim everything with filler and flat it smooth before varnishing.

Martin Colloms from HiFi News and Record Review did some tests on speakers a while ago, and showed that the cabinet can generate more acoustic output than the driver itself at some frequencies. That convinced me that cabinet bracing and damping was important for full range speakers, and that large cabinets that have to work at mid and higher frequencies are generally not a good thing. However, I still doubt that is so important for bass speakers. I understand that even the best and most expensive Velodyne subs use neither bracing nor filling, and they must have relatively enormous development and BoM budgets. I think the explanation is that subs are essentially static, rather than dynamic devices. You can make them work in slow time, and they will still work in the same way, which you can't say for dynamic speakers.

Whether it's working at 10 Hz or 100 Hz, the sound wavelength is long compared with the speaker itself. That means that the air in the cabinet, and the cabinet itself, do not suffer from the consequences and effects of travelling waves. Where there is compression and deflection in the air and the structure, it is pretty much in phase with the driver. So where the driver is compressing the air at the front of the box, the air is also being compressed at the back. And when it's relaxed, it all returns together, so there is no appreciable storage. The air in the box compresses and expands with the motion of the driver.

My take is that problems occur when frequencies are higher, and there is a phase difference between logitudinal rear and reflected waves, and there's a need to damp the reflections and oscillations and resonances. My view is that this is a very real problem from a few hundred Hz and up, but not at sub frequencies.

Waves also travel around the cabinet at higher frequencies as well, and will interfere and resonate. Where any panel dimension is half the wavelength of a transverse travelling wave, the panel will go into resonsance and sing along with the music, adding colouration where there shouldn't be any. Bracing will force this to higher resonant modes and frequencies, and damping will attentuate the resonance and reduce it's Q. But again, I believe these are issues for full range speakers, and not for subs.

It's true that I put a lot of bracing in my sub, but this is my first, and didn't want to make any mistakes or omissions that I couldn't conveniently fix afterwards. I will experiment with stuffing that box with wadding, as that is quick, convenient and reversible. I don't expect to hear any differences, but I'll keep an open ear and mind on that until I see for myself.

This wan't expected to be my final DIY sub effort. I've learned a great deal with this effort, and will almost certainly do another (perhaps a 15") and do it differently. Next time I will probably use the thickest and heaviest MDF I can find, glue it into a simple, empty box, and probably make it forward-firing. I don't regret what I've done the first time round, as I have a scientific bent that is attracted to learning, and this has certainly been an enduring hobby-horse of mine. I would rather have had the benefit of hindsight with some of my other household DIY projects, such plastering, but this has been fun, and I would rather do this sort of work rather than have someone else in China or Vietman do it for me. (No Offence )

Best regards,

Nick

[Welwynnick]

I guess I'm slightly overdue to update this thread. Firstly on finishing the box, and secondly on sound quality. I wanted to avoid mdf because of the dust, and I thought I might be able to get an adequate finish from plywood. Well, that wasn't easy.

Firstly I covered everything in wood filler, and a right mess I made of it too. I plastered it on like - well - plaster, and instantly wished I hadn't. I just wanted the filler to give a smooth finish over the gaps in the basic packing crate, as my slightly disatisfied wife called it. It did do that, but I had to spend a long time getting most of the filler back off before I could see the wood again.

Secondly, I went through a process of varnishing and sanding to try and get a respectable finish, and like every element of this over-ambitious project, it was more difficult and time-consuming than I thought. I made the mistake of using a tin of varnish that I happened to have to hand. Sorry if this is boring, but it was critical to what I wanted to do, and I thought others might like to learn from my mistakes. The varnish was quick-drying medium volatile organic solvents varnish, with which you can conveniently wash the brush in water.

This varnish went on like paint, and just sat on the surface, instead of being absorbed into the wood. Every time I sanded down, I got a fantasic finish which was was lost with every coat of varnish. The best I could do was leave it to set in the cold in the garage overnight - slow drying seemed to give a better finish with fewer brush marks. I did about nine coats then gave up. You can see the results in the "after" pictures below.

I've got a bit of work to do with gain, phase and x-over, but the ingredients are there now. I won't say that I've got the best bass I've ever heard (I've experienced Mad Mr H's HT after all!) but it was a new experience for me at home. CD or BD, I can't get enough of it now, and even the family seem to enjoy the re-discovered element of the system. I'll try to avoid using the common superlatives, but you get the message, it really does deliver this time.

Heres a few pictures:

Nick