First Time Speaker Build, Cabinet Advice

[Ken98]

Hi there I am about to build my first speaker. The Selah Audio Tempesta's.
They are a 3 way design with Raal 70-10d mids, Accuton C50 mids, and Scanspeak Illuminator 18wu/4747T00 Lows.

The Default Cabinet, Used In the Prebuilt Version is the Dayton Audio MTMC-1.0.

I have very little experience in wood working and cabinet making, but I do have some basic Autodesk Inventor Experience so I decided to Design my own Cabinet, using the front baffle dimensions provided by Rick Craig at Selah Audio. I have also tried to take some designs cues from the Dayton Cabinets.

I will be Constructing them out of MDF. Front Baffle Dimensions are:
9" (228.6mm) x 22" (558.8mm) x ~1"(25mm) (WxHxD)

I originally planned to make the the all the other sides of the cabinet out of 18mm thick MDF, but have since decided to go with 25mm, unless 18mm is fine.

The Dampening Materials I have choose are these:
http://www.foamland.com.au/shop-onli...tegory=5129238

and this for the speaker stuffing stuff : 650gsm Acrylic Speaker Dampening Material | Jaycar Electronics

If anyone has any objections to these, that I can source locally here in Australia, please fire away.

I also do have some questions on the Cabinet design.
firstly is 25mm thick MDF enough, I don't really want to go anymore than that as it would effect the total internal volume.

Speaker Dimensions are:

228.6mm (9in) x 558.8mm (22in) x 368mm

Secondly, I'm planning on getting the cabinet CNC cut, should I remove the screw holes in my CAD file and do them by manually once everything else is cut to scale.

My budget is pretty tight, I don't want to spend to much on materials, but at the same time I do want something that will last a long time.

 

I have uploaded images of my CAD design below, advice on whether or not it is a sound design would be appreciated, especially when it comes to advice on the cabinet bracing, something I have no idea about.

The Last 3 Images are of the Braces, with the 3rd last one being the front brace, 2nd last one the middle brace, where the Crossover's mount and the last brace is one that I did, that I can add later one, though I'm not sure if it is necessary.

I'm also planning on using finger joints for the cabinet sides, and dowel joints for the braces. Again any recommendations are appreciated. 

Any Help/Advice would be appreciated for a first timer.

[swervyn]

I wonder a bit on your choice of finger joints. Normally used on the same plane for butt joining timber.

 

Not sure about a 90deg joint, especially in mdf, I can see all the fingers breaking off

 

Might be a good idea to test run one first

 

Dont think I would bother with the dowels for the bracing either, will make it a pig to assemble. Just use plenty of glue and screw through the bracing into the side panels & top & bottom, maybe a timber batten if needed and if it doesnt effect the volume of the cabinet

 

Dunno, just my 2 bits worth

 

Where in Hobart are you going to get these cut with the finger jointing as well?

[Ken98]

Fair enough, using screws for the bracing would make it easier.What kind of joints should I use for the sides then.

 

I'm planning on getting a quote from xanderware. My friend who has some decent wood working experience may help if getting then CNC cut turns out to be to expensive.

[swervyn]

1 hour ago, Ken98 said:

Fair enough, using screws for the bracing would make it easier.What kind of joints should I use for the sides then.

 

I'm planning on getting a quote from xanderware. My friend who has some decent wood working experience may help if getting then CNC cut turns out to be to expensive.

Could try Euro Signs too, they have cut out mdf lettering for me before and were reasonably priced from memory

 

joint really depends on what finish you are going to use for the boxes and strength of course, looks from your rendering you are going to veneer them? Not really worth using fancy pants joints unless they are going to be a feature.

[Ken98]

I think I'll go with Dado Joints for the cabinet sides and yes I'm planning on trying to veneer the cabinets. Not really sure how much veneering them my self would cost though.

[Wozza_Lee]

Hello ken,

I am a novice in sp3aker building but have a lot of experience with woodworking, finger or tail joints are completely unnecessary inside the cabinet, just the ol pva and screws will more than suffice. For the main box (top, bottom and sides) a simple 90 degree or mitre joint again with countersunk screws and glue will also be enough.

As far as cnc, seems overkill for a project like this a circular saw and jig saw would easily cut it. If your conserned about thickness and cabinet resonance then anoth great option is to laminate 2 pieces of 18mm MDF together, if you want to get a bit more fancy try a rubber adhesive (contact adhesive) that will be thicker and hopefully add some inter sheet dampening.

Perwonalky i hate veneering, there are great ways of staining mdf to make it lookmlike wood, just check out YouTube

[Ken98]

Thanks for that advice. Some people seem to prefer ply over MDF. I have found a local supplier in my area selling birch and marine ply. I am thinking about going with that instead.

[Wozza_Lee]

Ply has higher torsion strength but lower shear strength (hence why you can bend 4mm ply but not 4mm mdf very well before it breaks) 

You would have to ask somone far more experienced than myself but my personal opinion is that mdf would work far better to reduce resonance as it has better dampening.. However the ply would leave you with a wood grain that you could finish/stain etc and make pretty easier 

 

Maybe do mdf inner cabinets and outside ply (if you plan on laminating as I suggest previous) 

 

Just my $0.02

Edited October 19, 2017 by Wozza_Lee

[Ken98]

How does the bracing in look in this photo. https://drive.google.com/open?id=0Bw3Wtypjaai0ejdRR2U2ZFRiaGc

I can always adjust the position of the last brace.

Still a bit torn on what material to use, MDF or Russian Birch Ply. Some seem to prefer Birch ply, others MDF. I will be keeping these speakers for a while so I don't mind spending a bit more for better longevity.

Birch ply is like 3-4x the cost of MDF though.

At this stage though I'm leaning a towards MDF, just cause it is so much cheaper.

The drivers going into these speakers are very high quality so i want to do them justice.

 

I may laminate, but at the same time I don't want to complicate things. I also don't have that much in terms of equipment to construct the speakers with.

 

 

 

[swervyn]

MDF is cheap and a good place to start. Maybe knock up a couple out of MDF and see how they turn out. You can always bog up holes, sand and paint. The ply face is the finished surface so no room for error. 

[Wozza_Lee]

Won't take any tools to laminate, literally just wood glue and somthing heavy (i recommend a slab of corona). 

 

As far as the bracing goes I would consider only one vertically and another horizontally, strong in both planes and not just one. 

[Ken98]

Ok so instead of having both horizontal and vertical bracing like this (image below), I should separate the horizontal and vertical parts? and where should I place them.

 

Thanks for all the advice so far. 

[Wozza_Lee]

I would keep as much material as possible that won't interfere with air movement, personally I get a piece of mdf and punch as many holes in it (either a hole saw or spade bit) as possible (keep in mind that it will effect the internal volume a fraction. 

 

As close to half way as possible, if there is a driver in the way just do as much as possible 

[swervyn]

While I can advise you how to put a cabinet together, (30+ yrs cabinetmaker) the whole cabinet design factor is a specialised thing taking into account so many things including volume, drivers etc, a bit of science involved and way over my head. I have been looking for a project myself, just need to locate free drivers and a proven design for them lol

I would say stick to a proven design that you know works, looks like you already have researched that. 

 

dunno that getting a piece of mdf and punching as many holes in it as possible is a proven design

[Wozza_Lee]

1 minute ago, swervyn said:

While I can advise you how to put a cabinet together, (30+ yrs cabinetmaker) the whole cabinet design factor is a specialised thing taking into account so many things including volume, drivers etc, a bit of science involved and way over my head. I have been looking for a project myself, just need to locate free drivers and a proven design for them lol

I would say stick to a proven design that you know works, looks like you already have researched that. 

 

dunno that getting a piece of mdf and punching as many holes in it as possible is a proven design

Hahaha no, no it's not I was suggesting that for a brace, that is all

[THOMO]

I advise making up several  experimental cabinets made from different materials and thicknesses.That could include ply,chipboard,MDF and jarrah blockboard as sold by Bunnings.

Sometimes a very heavily built cabinet using thick MDF and lots of bracing will sound worse.It is the overall acoustic that matters and every box will have a sound.

[Al.M]

Experimental or test cabinet is a good idea or clad it later if it sounds good so that the work and materials are not wasted.

 

The enclosure is only about 50cm tall so it’s not so large that slabs of MDF will for sure resonate and cause undesirable vibrations. A single H frame brace with 4cm by 1.8cm MDF cross section in the middle would do but one that doesn’t have too many reflections and impede airflow. You might also want to glue damping matts inside to control vibrations, which you can find from engineering acoustic and vibration supply shops or simply find offcuts of 3-4mm thick commercial floor vinyl sheets or tiles and glue on with rubberised bathroom floor tile adhesive. Use a trowel scree to apply glue to form good contact.

 

Whatever you do don’t reduce the minimum design volume so allow for anything that will reduce it such as internal damping Matt’s etc. 

 

I would go with 18mm MDF unless the design says otherwise. 

 

The kit looks really good, I have heard the sound of those Scanspeak Illuminators and they do about the best tuneful and dynamic bass I ever heard and the magnet structure on them looks really nice. Spec wise they have 9mm cone excursion which is a lot more than the average for that size driver of around 5-6mm. The Raal ribbon tweeter and Accuton mid combo should be really good with incredible detail and imaging, good match with warm sounding bass driver.

 

 

Edited October 21, 2017 by Al.M

[Ken98]

Thanks for that, guess I'll stick with 18mm then. Is 25mm overkill/unnecessary?.

Is laminating 2 layers of 9mm MDF a good idea.

How about using a layer of ply and 1 layer of MDF.

I also plan to veneer them, with either, Blackwood, Blackheart Sassafras or Myrtle Burl.

[Al.M]

You should ask the kit supplier what they recommend for enclosure thickness.

 

I wouldn’t bother with sandwiching two 9mm MDF, just create work for yourself and no proven benefit of doing so. 25mm is OK to use with slight risk of it sounding quite sterile and the overall bulk appearance change. The Scanspeak illuminator woofer is quite a warm musical sounding unit so a thicker cabinet may not sound too sterile is my guess and happy medium could result.

 

There are many schools of thought on cabinet thickness and methods etc. Many of the classic UK sound speakers often use 12 or 18mm MDF or ply with 6mm thick bitumised pads glued internally, which gives the bass a nice warm and musical note. Many DIYers have tried to replace these UK speaker cabinets with thicker and more solid materials ending up with a sterile sounding result.

 

While in other country designs they have made very thick and solid cabinets and still achieved a good result with less bass warmth. It all depends on the drivers used, the bass tuning and final interaction.

 

I would go with 25mm front and sides/rear/top/bottom 18mm MDF, H frame bracing and vinyl or similar damping pads. Factor in the slight reduction internal volume taken by the pads and bracing.

Edited October 21, 2017 by Al.M

[Ken98]

I read that ply is better, because due to its additional stiffness it pushes cabinet resonances up higher, where they are more easily controlled.

25mm front baffle and 18mm for the rest is what I'm going to settle on.

[Al.M]

The ply can also be stained and lackered without need for extra finishes.

[Ken98]

True, but I love the look of Blackheart Sassafras and Myrtle Burl. Blackwood also looks very nice.

I'll be keeping these for a very long time, so I need them to look and sound excellent.