I decided to write this Instructable after spending way too much time trying to find good quality, complete information for building HiFi speaker cabinets that didn't assume extensive experience or expertise. There are some great Instructables already published on this topic but there are still lots of tips and tricks not mentioned elsewhere that I found very useful so I thought I'd pass them on.
This Instructable is not meant to offer a specific design but hopefully will be useful for anyone, especially first time builders like myself, building speakers from the numerous kits available.
The aim of this project was to build an "audiophile" speaker set I would be happy to have on display in my lounge room. So I came up with a few goals:
- the project must cost less then the equivalent retail product. (Hopefully a lot less!)
- the finished speakers should look like they were professionally built. (At least in the right light!)
- the design must be the best I could find for my budget. (Not easy when you have no idea how the result will sound.)
My "workshop" is a garage with a small tool bench and an old coffee table. So I had to stick to techniques that don't require a comprehensive wood-shop. Whilst I have done electronics projects before this was my first serious attempt at cabinet making, indeed woodwork of any kind really so the learning curve was steep.
Any tools I didn't own I planned to hire, borrow or buy along the way.
TIP: Practice any new technique on scrap material! At every stage I first used spare pieces to practise everything before I did anything on the "real thing".
After much consideration I settled on the ZRT design by Zaph Audio and purchased the necessary kit through Madisound. The kit contained the electronics, drivers and acoustic foam materials required. I just needed to build the cabinets.
Step 1: Cabinet Design and Materials
The speaker kit came with a simple plan showing the overall dimensions of the cabinets suggested by Madisound. I was building the cabinets from scratch so I had to convert the basic plan into detailed drawings showing every piece with its individual dimensions. I also converted everything to metric.
Butt joints are far easier to achieve than mitred ones and will look the same when covered with paint or veneer.
- If you have not done this before remember to allow for the thickness of the timber including veneer, in your calculations.Example; if you are planning to veneer the top/sides of your cabinet, over-size the front panel by 1mm in each direction that overlaps the top/sides to allow for the added thickness of the veneer. You can trim the front to match precisely once the veneer afterward.
The critical aspects of a speaker cabinet design are;
- the placement of the drivers and any ports in the front and rear panels.
- the dimensions of the front baffle (front panel).
- the internal volume of the cabinet.
In addition, to ensure the best sound possible, your cabinet must be solid enough to prevent any extraneous vibration of the panels. This is achieved by;
- using substantial (thick) non-resonant material such as MDF or plywood in all panels.
- ensuring all joints are airtight and as rigid as possible.
- adding internal braces placed asymmetrically to minimise the chance of standing waves ("resonance")
Most speaker designs also suggest:
- mount the drivers flush with the front baffle.
- round off the edges of the front baffle.
- use flared ports (flared on both inside and outside ends)
- using acoustic stuffing and foam as directed in your design rather than makeshift materials.
I decided on 19mm MDF for everything except 25mm MDF for the front baffles. I made some modifications to the Madisound design that I felt would not affect the outcome. I moved the internal shelf braces so they were all unevenly spaced and none were positioned at any ratio of the overall cabinet dimensions(eg: 1/2, 1/4 way). I added a small brace behind the tweeter not included in the original design. I decided not to rebate the shelves into the cabinet walls. Most significantly instead of using the front baffle for access to the cabinet, I decided to use the bottom. This meant I could make the front baffle joints as strong as the other joints and I could join the front baffle to to the internal shelf braces - not just around the edges, stiffening the entire cabinet. It also meant I did not need any screws on the front baffle which I thought would detract from the final appearance. The removable bottom panel would be screwed on to allow access to the cross-overs. A foam gasket and the weight of the speakers would seal it airtight.Access to the rest of the speakers would be via the mounting hole for the bass driver.
Because I wanted to resulting cabinets to be "perfect" I decided I would not cut the pieces myself. It was cheaper to have a custom wood shop do it for me than buy the necessary tools and learn how to use them. If you use a shop you will get a much better response if your plans are organised and accurate - it costs time (ie money) to "fix up" poor plans for input into a CNC machine.
Step 2: Cabinet Construction - Preparation
Whilst the cabinet pieces arrived precisely cut to size there was still a bit to do to have them ready for assembly.
The shelves had to be drilled with a hole saw to allow air flow. I could have had the wood shop do this but I could do it at home with a hole saw. The holes don't have to be perfect.
TIP: When drilling MDF use the holesaw to score the wood to show where the hole will be. Then drill a hole or two with the pilot bit of the holesaw on the circumference of the holesaw cut. These holes will allow sawdust from the holesaw to escape preventing excessive friction and clogging of the holesaw. This simple tip turns MDF from cement to butter!
Then I prepared all the cabinet joints. There are several ways to do it and one way may suit you over the others. Here's my thinking:
- Glue/screws: cheapest and easiest but you have to ensure everything is held square whilst each joint is done. Battens maybe added inside the cabinet to the joints to increase their strength. If you want to hide any screws on the outside of your cabinets afterward so ensure they are countersunk.
- Dowel joints: stronger than glue/screws and gives precise results but requires accurate drilling to do so.
- Biscuit joints: all the best features of a dowel joint with the advantage that if used properly the biscuit joiner makes accuracy easy. No screws to hide afterward.
I have never done it before but went with biscuit joints and hired a joiner for the weekend to cut the slots.
TIP: (refer to diagram) Mark the inside of the cabinet pieces and orient them so you are consistent with biscuit joiner to ensure your edges line up precisely.
MDF dust is toxic, consisting of both sawdust and resin. In fact MDF is banned in school wood shops in Australia due to its toxicity. Wear eye and breathing protection, use a dust extractor or vacuum and ensure members of you family are not subject to exposure.
Step 3: Cabinet Construction - Assembly Part 1.
After everything was prepared and I had done a dry test fit it was time to get out the glue and clamps.
- Clamps with plastic pads mean you won't need to juggle scraps of wood to protect the MDF.
- Get more clamps than you think you'll ever need - you'll need them!
- Quick release clamps such as Irwin Quick Grips are perfect.
Work in manageable stages rather than all-at-once.
My planned to do each cabinet in three steps:
First; glue the top and shelve braces to the sides.
Second; glue the back on when they had dried.
Third glue the front baffles after all the finishing was done and the damping foam and Acoustistuff was fitted.
For step 1 I masked the front and back panels where they would be in contact with the sides and braces so they would not get stuck. I then glued the top and braces to the sides forming a "ladder". I put the front and back in place without any glue and clamped everything. The next day I glued and clamped the back panel again using the masked front panel to ensure everything was aligned.
Step 4: Cabinet Veneering
After looking at a lot of options I found what turned out to be a fantastic product; iron-on wood veneer. No messing with contact cement or heating glue. I used American Walnut. It went on brilliantly. I started with the least important surface - the back. I glued a short edge and let it set as an anchor point then worked my way long ways down the board. Once the back edges were trimmed I veneered the sides, trimmed them and finally completed the tops. I borrowed a router and trim bit for the edges. It is by far the most reliable way to get a clean edge without splitting the veneer or causing it to lift. Make sure you test first to ensure no unexpected results! I found the bit was rubbing the sides so I added the blue masking tape to prevent it from marking them.
I did not veneer the removable bottom panels but painted them instead.
TIP: Iron on veneer: Whilst the instructions suggested a hot iron I found too much heat causes the timber veneer to curl and warp leaving "waves" in the finish. You only need enough heat to completely melt the backing glue. Put paper under the iron so it slides easily. Using a cork sanding block or similar, rub hard behind the iron as you go. You want to ensure the melted glue completely fills the space behind the veneer. Atmospheric pressure will hold it in place until the glue dries and you'll have a perfect finish.
If you do get cracks they are easily fixed with wood filler. Use a darker colour than the timber to make it look natural. Apply small amounts and use a flat scraper to remove the excess before it dries. You can always add more later if there is not enough first time round. You do not want to be doing a lot of sanding on your very thin veneer.
Step 5: Cabinet Finishing - Danish Oil
There are many options for finishing timber. I considered varnish, stains waxes and other options before settling on Danish Oil. It proved a great choice. It was easy to apply and there were no bubbles or other imperfections to worry about. I did 4 coats one or two panels at a time ensuring the cabinets never rested on oil that wasn't fully dry. I gave everything a light sand with 0000 steel wool to knock of any imperfections before the final coat. It took several days but it was worth it.
- Follow the instructions! Follow the instructions! Follow the instructions!
- Clear any dust from your workshop before you start. I vacuumed and aired out the garage thoroughly and let everything settle for a day or 2 before I opened any cans.
- Buy new brushes, rollers etc and buy the best you can afford.
- Be clean, organised and patient. Ensure you have the right thinners/solvent/clean-up gear close at hand.
Step 6: Cabinet Construction - Front Baffles and Speaker Grills
The rear of the cutouts for the base drivers had to be chamfered to allow unimpeded airflow in the cabinets. I used a router with angled bit for this.
The cutouts had to be enlarged carefully to ensure the drivers were a perfect fit. The drivers were slightly bigger then their spec's said due to tolerances so the holes were just a little too tight. Light sanding with a curved block and 240 grit soon had that fixed.
I marked the position of the speaker mounting screws and drilled pilot holes to prevent the self-tapping screws cracking or distorting the MDF. I also tested the screws before fitting the speakers and found the MDF bulged even with pilot holes so I sanded the bumps flat to ensure the speakers would seat properly against the baffle.
I did not want to use additional gaskets because the speakers were sitting flush to the baffle without them. If my mounting holes were too deep I would have added gaskets to bring the drivers forward slightly to make them level.
Next step was to build the speaker grills. I could not find a suitable kit or instructions on line so these are completely original:
- I wanted the grills to be a slim as possible.
- I wanted them to be child proof. Kids are hypnotically drawn to expensive speaker cones.
- I wanted minimalist fixings - in line with my project goals.
TIP: If you are planning close fitting grills, check the "maximum excursion" of your bass driver to ensure your grills won't interfere with it whilst playing music.
I decided to use fine steel mesh for my child proofing and got some from a local supplier of fire-screens. It was the lightest, most open mesh I could find. I thought it offered the least chance of rattling or effecting the sound if the speakers were used with the grills in place.
To achieve the 10mm clearance I needed for the base driver and have the slimmest frame possible I built up the desired profile from pieces of beading which had to be glued together. Then the frames were put together carefully squaring each corner. With the frames assembled I glued in the steel mesh with epoxy.
To fix the grills I found some small neodymium magnets and metal dowel markers which paired perfectly. With the frames clamped tightly and compressed to prevent splitting I drilled the holes for the dowel markers in the corners with a Brad Point Bit.
Then I sealed the frames with the brush-on sealer and gave them a couple of coats of matt black with a light sand to finish.
I purchased grill cloth and glue from Queensland Speaker Repairs and carefully followed the instructions to fix it. Finally I glued the dowel markers in the corners. I positioned the grills on the front panels and pressed them down. The dowel marker points marked the baffle where I had to drill the holes to flush mount the magnets. I drilled the holes in the front panels with a Brad Point Bit to ensure precise holes and glued the magnets in with Gorilla Grip. I marked each frame and speaker so I'd know which way up the frames went and which was fitted to which speaker baffle.
Step 7: Cabinet Finishing - Painting Front Baffles
I choose Rustoleum Oiled Bronze for the baffles. To prep' them I brushed several coats of sealer on all the edges where the MDF had been cut and sanded it with very fine sand paper to ensure the texture of the rounded edges matched to face of the panels. I also applied sealer to the driver and port cutouts as a precaution against any moisture working its way in. Then I glued the base ports into the panels.
TIP: I learned the hard way some glues shrink. I suggest once you have your ports in position with wet glue, place the front panel face down on a clean flat surface. Apply weights to the baffle and the back of the port pressing both into your work surface. This will ensure the port stays perfectly flush to the baffle while the glue sets.
Next I primed all surfaces to be painted. Use the matching spray-on plastic/wood primer for your finish paint and leave it to fully cure. This will be quick on the MDF but may take several days on plastic parts.
TIP: To check curing spray some Primer on the back of the plastic port and once it is too hard to easily scratch off it's cured.
Then I sprayed several light coats of the Oiled Bronze to the front baffles. There was some splattering but I kept respraying until the finish was as I wanted it. It took more than 2 cans and several days to get right. I left the paint to cure for a week or so. (refer next section for more on that)
TIP: If you're spraying paint wear the right mask - not a dust mask!
I did not have an exhaust system so I left the garage as soon as I finished each coat and returned once the paint was touch dry to open all the doors and vent the fumes.
Step 8: Final Assembly
With the cabinets and baffles ready for final assembly it was time to use add the foam sheets and Acouta-Stuff filling supplied in the Madisound Kit. I glued the foam inside the rear and sides allowing room for the baffles to recess into the cabinets. I also added some foam around my extra brace but not the shelves. I did not put foam inside the baffles.
TIP: use a thick glue that won't soak into the foam too much. Test your glue as some are corrosive to the foam.
One tweak to the crossovers before final assembly. I thought I'd add sections of speaker cable to any circuit links directly in the signal path to augment the bits of wire provided. I am sure it worked wonders :)
I screwed the crossovers inside the bottoms of the cabinets. It is important to ensure the inductors do not interfere with each other - refer to the picture.
I then mounted the input terminals and completed the internal wiring.
With all the internal hardware in place it was time to add the Acousa-Stuff. I used a digital scale to weigh even amounts for each speaker and stuffed the spaces suggested in the instructions.
TIP: Acousta-Stuff needs to be teased out thoroughly to create an evenly dispersed "cloud" without knots and clumps before filling the cabinet. This way it packs in evenly and consistently.
I learned the hard way the baffle paint took several days to cure. I glued and clamped them after the suggested drying time only to have the cardboard pads I used inside the clamps damage the paint. No choice but to buff off the damage, carefully mask the veneered sides and driver ports and spray several more light coats of paint. It cost me a couple of days. Rustoleum support were helpful and at their suggestion I waited 2 weeks after touching up the paint to ensure it was ready.
Last of all I installed the drivers. Before I tightened the screws I did a quick sound check to make sure everything was correct. Yes! Carefully tighten screws and....Finished!!!
TIP: You don't need to use crazy amounts of force to tighten the screws. If everything is made carefully the drivers should be airtight without having to resort to brute force. If in doubt - add gaskets. You can make good ones from sheets of felt cut to size or just buy them. I would never use silicone to seal the drivers in place as it would make removing them very difficult.
In the final picture you can see the speakers on bases consisting of two layers of rubber floor mat sandwiched between felt to protect the floor and speakers. I know spikes are all the rage but this was simple and effective.
Did I achieve my goals? Absolutely. The ZRT's sound fantastic and I could not be happier with the way they look. Good luck with your speakers!!!
Second Prize in the
Audio Contest 2018