Introduction: 2-WAY BOOKSHELF SPEAKERS
please bear with me as English is not my native language.
This pair of bookshelf loudspeakers made using already own drivers and crossovers.
I had laying around some AUDAX speakers in particular a set of HT130K0 mid/woofers and a set of AW025S3 tweeters. AUDAX France was one of the major speaker manufacturers worldwide producing Hi-quality products for many loudspeaker company manufactures.
I am not sure if you can find them in the market any more but similar or better products are plenty around to purchase.
Step 1: SPEAKERS
The HT130K0 is a 8 Ohm woven Kevlar 130mm or 5 ¼ inch cone driver rated 40 WATS with resonance frequency (Fs) at 44 Hz and all that at 90 dB sensitivity which makes it a great driver for a small bookshelf loudspeaker.
The AW025S3 is a 8 Ohm shielded aluminum alloy 25mm or 1 inch dome driver rated 80 WATS with resonance frequency (Fs) at 1150 Hz and all that at 92 dB sensitivity.
Also had the crossovers ready made. Those are 2-way second-order crossovers at 2500 Hz.
The volume of the enclosure is approximately = 9.2 Litters and tunned at about 80Hrz.
Step 2: SPEAKER ENCLOSURE TYPE
The goal for the loudspeakers was to be lightweight, relatively easy to make, good looking and most important good sounding.
As mentioned above the main driver is only 5 ¼ inch (13cm) in diameter, which is not capable of producing deep low frequents like an 8 inch woofer but it can surely fill the gap of a sub woofer.
I have chosen to make the classic compression cabinet which is supposed to reduce part of the reflections in the cabinet. Next was to decide between sealed or ported design.
Sealed cabinet means there is no opening for the air to move in & out as the cone moves the airmass. The advantage here is the control of the cone's movement thus more accurate sound but with loss of the lowest frequencies the driver can produce which is a disadvantage especially for small drivers. Ported cabinet or vented or bass reflex allow for an extended bass response resulting in deeper bass tone which in this case is our goal.
Front or rear bass reflex?
Rear bass reflex requires distance from the wall and can be from 10cm to meters depending on the loudspeaker requirements. Front bass reflex on the other hand take advantage of the free space in front of the enclosure thus it can be placed near the wall which is suitable for bookshelf loudspeakers. So, this is the way to go.
An other thing in consideration is the shape of the cabinet. Rounding over the cabinet edge reduces peaks and troughs in frequency response around the baffle step diffraction frequency.
Step 3: CHOOSING ENCLOSURE MATERIAL
In an imaginary world a pair of speakers would reproduce the real life sound waves as they are but unfortunately there is no such thing as absolute sound reproduction system.
The current technology and materials have there limitations. The most common material speaker cabinets made of is chipboard, a wood derivative.
CHIPBOARD – the cheapest of all
Chipboard, also called particleboard, is made from a slurry of wood scraps, sawdust and glue that is dried in sheets and pressed into boards. Moisture and water is the real enemy of chipboard and it is the less strong / stiff material of all. Widely used by manufacturers from speaker to kitchen cabinets because it is cheap, NOT because is the best out there. Also is the most resonant material of all.
MDF – cheap
The reason why speaker enclosures are made from MDF is because it's cheap and relatively easy to work with and definitely stronger than the chipboard is. MDF contains a mixture of wood solids, wax, and resin bonded to gether under high temperatures and high pressure to create a uniform wood-like product that is far cheaper than real wood. Just because it's made from small parts it can be easily damaged plus is not very good at handling high moisture levels.
PLYWOOD – relatively cheap
Plywood is made from layers of solid timber veneer that are usually about 3 millimeters thick. Because it is made in layers it is incredibly strong, lightweight, resists cracking, bending, warping, and shrinkage making it a great material for speaker cabinets especially when weight is an important factor for bookshelf or huge speakers.
RAW WOOD – expensive
Panels made from scrap wood glued on each side.
Wood panels have a higher density so are harder and more durable than any wood derivatives and the less resonant of all above making the best material for speaker cabinets. Also, they are the most expensive of all. In my humble opinion, unless you are a serious manufacturer making a state of the art loudspeakers or an individual engineer with the know how in depth there is no reason to spend money for hardwood enclosures. Imagine spending 100 Euro for drivers and crossovers while the cabinets could cost 300 Euro or more. But in the end it's up to you to decide!
For us, the DIY enthusiasts with more or less experience and knowledge in the field of loudspeaker engineering the MDF is a good choice as it is strong and cheap but it is a heavyweight material. Next is the plywood which seems to be the best solution as it is lightweight, easy to work with, strong, definitely superior to chipboard in many ways and cost effective plus is the next most uniform product after the wood as far as i know. That is why plywood is a better choice than chipboard in my opinion.
Step 4: CABINET STUFFING
Because black polyester soft foam loses its consistency in time better use sheep's wool felt or synthetic damping material or polyester fiber Stuffing or a combination of them. I have made some tests for these particular cabinets / speakers and found that 20mg of polyester fiber Stuffing at the upper part of the cabinet and an other 20mg at the lower part are more than enough.
A rule of thumb in the construction of speaker enclosures: a stiffer cabinet will simply color the sound less. Less glue, less staples, less screws, less thickness, less bracing and overall less detail will result in poorer speaker cabinet.
Step 5: TOOLS
Electric router tool
Compass swivel knife
Electric drill, dits
Pair of scissors
Electric Jig saw / Circle hole cutter
Step 6: MATERIALS FOR TWO (2) ENCLOSURES
Plywood 18cm thick (enclosure)
Wooden solid angle beading = 2m
Self adhesive PVC roll = 3m
Speaker Terminal plate = 2 items
Threaded inserts 5mm = (8 for the woofers, 8 for the back panels)
Threaded screws 5mm = (8 for the woofers)
Socket cap screws 5mm = (8 for the back panels)
Penny washers 5mm = (8 for the back panels)
wood screws = (8 for the tweeter)
Vinyl leather = 1.5mm thick /1m
Spray adhesive for vinyl based products = (3M spray adhesive 77, Minos spray adhesive)
Joiner biscuits = (36 for the enclosures)
Speaker stuffing = polyester fiber Stuffing (100mg)
Step 7: ENCLOSURE PARTS X2
All panels are made from 18mm thick plywood.
(A) front panel = H(33,1cm) x W(19,1cm) x2
(B) back panel = H(33,1cm) x W(19,1cm) x2
(C1) side panel = H(33,5cm) x W(23cm) x2
(C2) side panel = H(33,5cm) x W(23cm) x2
(D1) top panel = H(15,5cm) x W(23cm) x2
(D2) bottom panel = H(15,5cm) x W(23cm) x2
(E) bass reflex panel = H(15,5cm) x W(21cm) x2
(F) compression panel = H(15,5cm) x W(25cm) x2
Wooden solid angle beading = measure, cut and fill every interior joint of the cabinet.
Step 8: COST OF MATERIALS FOR TWO (2) ENCLOSURES
All parts are from local stores.
Plywood = 24 Euro
Wooden solid angle beading = 5 Euro
Speaker Terminal plate = 4.5 Euro
Vinyl leather 1m = 10 Euro
Self adhesive PVC roll 3m = 3 Euro
Spray adhesive = 7 Euro
Screws, washers and etc = 5 Euro
Speaker stuffing = 5 Euro
Total cost = 68 Euro
Step 9: CONSTRUCTION
An important note to adhesives. Be careful wilh what you are going to use because some contain pretty harsh chemicals which can actually deteriorate vinyl based solution products.
Vinyl leather thickness is important here and must be known because we are going to fold it between the wood joins for better stability in time.
For that purpose there must be a gap between the joins so the vinyl can fit in between and at the same time to allow the rest part of the plywood panels to contact each other to be glued.
If the vinyl is 1.5mm thick for example, from my experience a 2mm gap (vinyl + glue) is the optimal.
A 5mm space is enough to fold the vinyl and can be done using a router tool at the rear of the front and back panels.
Also, the front and back panels must be shorter at the vinyl thickness at height and width from all four sides.
First of cut all cabinet pieces. Mark and open the holes for the drivers using a Jig saw or the Circle hole cutter. Then, with the help of a router cut the outer diameter of the speakers to sit face to face with the plywood. Again, use the router to round over the cabinet edges from front and back panels.
Round one end from the bass reflex panels and from the compression panels.
Mark and open a hole where the speaker terminal plate is about to fit using a Jig saw.
To screw on the drivers to the front panels you can use wood screws or threaded inserts, personally prefer the last option.
It is a good idea to use Joiner biscuits if you can but it's not necessary.
You can glue up the panels and use butt joins or nails instead or simply use only glue. It's up to you to decide.
Cut the vinyl about 5cm more than the panels are from all sides.
Now it's time to attach the vinyl to the front and back panels. By far the easiest way is the spay adhesive applying a layer at the back side of the vinyl and to the front side of the panels from 10-15cm distance.
CAUTION: When done use a ventilated area, protect your clothes, wear protective goggles and mask, be away from things you and others care because tiny adhesive drops will spread all over the place and they are not the easiest thing to clean up. I have learned the hard way!
Read the manufacturer's instructions or in general, let cure the adhesive for about 10-15 minutes.
Spray one more layer to vinyl and immediately attach it to the panel.
Form the vinyl where needed by pressing it, fold and stretch it to glue up at the rear side of the panels. Cut where needed.
Measure all joints and cut the wooden solid angle beading to pieces.
Glue the side panels including the bass reflex, angle beads and compression panels in between.
Then use the router to round the edges from all four sides of the box.
Sand the surface using 400 sandpaper to make it even and clean / remove any dust.
Time to attach the self adhesive PVC roll. Measure the depth and the diameter of the box and cut a line of PVC. Place the box on a flat surface horizontally, this is going to help attaching the PVC in a straight line. Start from the bottom panel and pay attention for air bubbles as you attach the film.
Attach the crossovers to the panels opposite to the woofers where there is more space.
If you wish the back panel to be removable as I did, you can use wood screws or better yet threaded inserts. Place and screw the drivers to the front panels. Connect the plus & minus terminals to the crossovers and glue the front panel to the enclosure. Add glue to all joins inside the enclosures to seal them and glue the front panel to the box.
Leather is a worm good looking material but pale leather on a flat surface needs an extra tone in my opinion. By applying PVC at the front panel we can give some style to the loudspeaker.
Measure the exact diameter and the distance between the drivers with a ruler, turn the PVC sheet upside down and mark the distances. Make use of a drawing Compass to draw the diameter of the drives. Now draw an other circle 1cm larger than the drivers diameter and join the outer horizontal parts of the woofer and tweeter circles. Now, first cut half way the outer circles up to the join points using Compass swivel knife for best results. Cut the joining lines with a utility knife. Use the compass knife to cut the inner circles and carefully apply the PVC to the front panel. Done!
Remember, detail makes the difference!
Step 10: Worth the Effort?
This pair of loudspeakers are small enough to sit on a bookshelf or on a computer desk as long as there is enough space.
Can be driven by a home stereo system or by a small, cheap lepai amplifier for instance.
You can even make them active / blue-tooth if you include the appropriate components.
They might be small but loud enough to fill a room of 16 square meters or more even for a party especially if you combine a sub-woofer.
I am using the loudspeakers in my room with an active sub-woofer connected to digital multi channel amplifier in stereo mode and I'm very happy with the results.
Worth the effort. I have enjoyed every moment making them, they are cheap, unique, small, leather looking and sound good. Love them!
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