Designing & Building Cherry Wood Speakers From Scratch

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Introduction: Designing & Building Cherry Wood Speakers From Scratch

This guide covers my build of the cherry wood speakers. These can be made by anyone who has access to basic wood power tools, no specialty tools required. These were built from scratch meaning that I designed the size for it by learning about audio design, I cut out the panels using basic power tools, and bought the speaker drivers from an online site. This guide will cover a brief audio theory overview, the CAD design for the speakers, discussion of how I cut the pieces, assembly, and finishing. Additionally, I provide background to allow builders to easily derive different version or approaches of this speaker design using things different like the tools, speakers, or the wood finish.

Supplies

Materials:

Tools needed:

  • CAD software or pencil and paper (If modifying the design)
  • Drill
  • Circular saw/Jigsaw/table saw - I only used a circular saw, table saw would provide better cuts
  • Router + bits
  • Random orbit sander + sanding discs
  • Large Paintbrushes
  • snap-off knife (best for cutting veneer)
  • Taper measure/straightedge/framing square
  • Soldering iron/wire cutters & strippers/crimping tool

Step 1: Picking Your Speaker Drivers: Basic Audio Theory

To choose the speaker drivers means delving into the world of audio theory, and this can get very overwhelming, so I don't recommend it unless you are really wanting to learn. However, I will point out some of the basics I learned. For more detail, please check out the references below. If you follow my exact design you can skip this section.

These are some great references:

  1. DIY Audio & Video: https://www.diyaudioandvideo.com/
  2. Sealed enclosure explained in detail and calculator: http://audiojudgement.com/sealed-enclosure-closed-...
  3. And a textbook: Loudspeaker Design Cookbook 7th Edition by Vance Dickason (Audio Amateur Pubns, 2005).

To review some basics, when picking out a speaker you will see a frequency response diagram. Small diameter speakers (tweeters) are much better at producing to high end of the frequency, large diameter speakers (woofers) produce the lower end. The human ear can hear approximately from 20 hz to 20,000 hz. The diameter is directly related to where the speaker has the best frequency, IE, the large the diameter you get, the lower the frequency it can produce, albeit the lowest frequencies aren't exactly heard as much as felt and are considered the sub-range of speakers. Additionally, some speaker designers opt to add a mid range speaker that reproduces the mid range the best; however, this comes at additional complexity and cost. For this design I opted to go with a dual driver setup, one tweeter and woofer per speaker.

The above datasheets outline specifications for the speakers. They include the frequency response tables, speaker geometry & dimensions, and some of the audio specifications. One of the audio specifications is sound pressure level (SPL) which measures the sensitivity of the speakers in decibels (dB) which is approximately the average dB on the frequency response chart for the applicable frequencies of the speaker. dB is a measure of sound level on a log scale. A 3 dB increase for instance is approximately twice the "loudness" of sound. A higher SPL means that the speaker can produce a louder sound with the same power input, so higher is typically better. Another specification is RMS, which is the maximum amount of power you can drive into a speaker. Now this is split between the tweeter and woofer, however more power is typically needed by the woofer. You need to make sure your amplifier does not go above the maximum power of the speaker drivers. The wattage listed on an amp is similar to RMS. Another important concept is impedance which needs to be the same typically between all the speaker drivers you choose. A higher ohm speaker can produce more sound at the same power. Although you can switch between 4 ohm and 8 ohm by wiring two of the same speakers in parallel or series as desired. Qts and Vas are used to help size the speaker box in the equation below.

Speaker driver choice & matching is very important and it is important you match the tweeter and woofer so they both have similar sound pressure level (SPL) as shown in the datasheet. This ensures the high and low frequencies have the same "loudness". If the woofer and tweeter SPL don't match, audio designers can double the the number of woofers or tweeters to raise the SPL by ~3db in order to match. Alternatively, designers can also lower the SPL using what is called a driver attenuation circuit or L-pad, usually with the tweeter because it takes much less power relative to the woofer. Impedance also needs to be matched with both tweeter and woofer with typical impedance being either 4 or 8 ohms. Lastly, you also want to make sure the RMS is high enough for your application and amplifier. When choosing the speakers above, I reviewed many different speaker drivers to find the best match that I liked within my price range.

In the datasheets you can see the frequency response for each speaker and notice where each speaker drops off. Sometimes the datasheets give a suggested range, but it is better to look at the frequency graphs to see yourself where the curve falls off or breaks apart. The range that is considered good for a speaker is where the frequency response is flat. The point where it falls off or is no longer flat are the ends of the applicable range for a given speaker.

In order to stop the speakers from producing a sound outside its range, and/or doubling the amount of sound in the frequency range where they both can produce sound, a crossover is used. a crossover splits the line going into the speaker into two different signals. The audio designer must select a crossover that captures the tweeter and woofer as best as possible, while also giving a decent buffer on the frequency curve where it still is flat (IE don't pick the crossover frequency right where the speaker starts dropping out). For my design, based on the datasheets I opted for a 2000 HZ crossover. This also plays in part with the speaker matching above. This means that on top of matching SPL, RMS, and impedance, you also need to ensure there is a good amount of overlap between the speakers frequency range in which they operate well and a crossover that fits in the middle of it. One important note is that it is not a hard cutoff. Crossovers reduce the frequency per an octave, which can vary. An octave is referred to as doubling in frequency (40 Hz - 80 Hz is an octave). For the part I chose, the crossover reduced by 12 dB per octave. Using the dateset csv from the manufacturer's website, I plotted the frequency responses whilst implementing the 12dB/octave reduction in frequency per octave to demonstrate how the sound is reduced and to determine whether these speakers would work for my design in the first picture. By merging the two responses with the crossover in the first graph, a predicted frequency reponse chart can be created which is also shown above in the second picture. The best response would be perfectly flat, but it is very difficult to produce a perfectly flat response without paying for very high end speakers, so the response above I deemed acceptable.

Lastly, sizing of the speaker boxes is considered here. A common equation is Vc = Vas / [(Qtc / Qts)2 -1] with Vc being the volume of the box, Vas and Qts found on the speaker datasheet, and Qtc = 0.707 which is the ideal number to design for as outlined in the second reference above. The tweeter requires almost no volume and in this case is already sealed for optimum volume. Larger/Woofer speakers need the most volume, and if you use a mid range, the mid range sometimes need to be considered, but the woofer is the primary driving factor as it is the one that really requires the volume.There is also some science behind adding stuffing or foam to speakers to artificially increase the volume while not physically increasing the volume so you can make smaller speakers with the same driver as outlined in the second reference, however, I did not use this method. Using this equation for the woofer, I determined the box size needed to have an inside volume of 0.56 ft^3.

Step 2: Sizing the Sides & CAD Design

Using the 0.56 ft^3 volume required determined in the previous section and the drawings for the speakers from the datasheet I drew up a Computer Aided Design (CAD) representation using Solidworks. My drawings are included above if you would like to use them.

CAD helps with the sizing of pieces, and making sure everything fits together, however, a little math is typically required to size the sections appropriately, and good designers can get away without even needing to CAD the model. The main driving factor is volume. Depending on which thickness of material you use, you need to ensure the inside volume is maintained to the design volume needed. That means taking into account the thickness of the material so you don't accidentally design the volume to the outer dimensions. For instance the inner dimensions of my speaker come to 14.5" x 9" x 8" inches which is a volume of 0.60 ft^3. This is a little bigger to account for the volume taken up by the speakers themselves and the crossover on the inside to make the approximate volume on the inside to be 0.56 ft^3 . My final dimensions for all the pieces are outlined above.

To touch a little on material selection, the ideal wood for design is Medium Density Fiberboard (MDF) at 3/4" thick. This is much denser and stronger than particleboard and does not resonate. You could also use hardwood, but it can resonate while MDF deadens the inside of the box like a shock absorber. Using MDF doesn't typically provide a good finish, so many designers opt to cover it with paint, veneer, hardwood, carpet, or other materials.

For a more in depth explanation of box design please check out this reference here: https://www.diyaudioandvideo.com/Guide/BuildSpeake...

Step 3: Cutting Out the Boards

This section outlines how I cut the boards. I only have a router and circular saw, so I hope this goes to show, you do not need any fancy tools to make this project. Of course, if you have a CNC router, I highly recommend taking advantage of it and skipping all the parts below in this step.

I got the MDF and took some time to mark all the lines carefully using my framing square and tape measure based on my drawings frame the section above. I carefully then cut out the outer piece dimensions carefully and slowly with a circular saw (a table saw would be way better, but I did not have access to one at the time). Lastly I cleaned up the edges with a quick pass from sander (do not round edges). Stacking same dimension pieces next to each other and clamping them together when sanding can help equalize the dimensions across the pieces to they will fit together better.

For the circles for the speakers in front and square for the terminal in back I used a router. You can just mark the lines with a protractor and free-form the cut, however, I recommend a circle router jig setup like this one here: https://www.thisoldhouse.com/house-one/21221690/di... This keeps the router in a constant circle as to create a most accurate circle as possible. For the terminals from the tweeter they stuck out a little on the bottom so a free form cut to allow room for them was made. On the back side the square hole for mounting the terminal block was carefully marked and cut free-form with the router. Since all these holes will be covered by the dirvers or terminal plate there is pretty low tolerance required, so one can get away with free-form cuts it needed. When using the router I recommend a very small diameter bit with length long enough tho reach the thickness of the board, in this case 3/4" length with a 1/8" diameter. You can also use a shorter length bit and just do multiple passes.

Step 4: Assembly & Check

Now that all the pieces are cut, the boards can be assembled and speakers wired. The circuit board at the bottom of the drawing is the crossover discussed in the previous sections that splits the input signal to the woofer and tweeter.

For this assembly we will not yet glue anything together, rather just use wood screws. Make sure to mark appropriately and drill pilot holes as MDF is very easy to split I recommend at least 1.5" away from the edge of MDF to help avoid splitting. Screw all the front and sides pieces together, but leave the back open for wiring for now. You may need to sand down edges if pieces aren't fitting together well. It is important to have a good seal for audio quality. Gluing together in the future steps will help with this, but that will only go so far.

At this point you need to mount the speakers, crossover and terminal plate. Speakers and terminal plate will typically have a foam gasket to help seal the speaker. Make sure to mark the placement of the speakers whilst making sure to center them as best as possible before screwing them in. I used some black top small wood screws to mount my speakers from a hardware store. The crossover was simply screwed to the bottom of the speaker box.

For wiring, you can either solder everything or use crimp terminals. Crimp terminals may be easier so you can easily remove speakers if you ever need. I opted for a combination of both (soldering speakers, crimping the end that goes into the crossover). Make sure to ensure the polarity is maintained between all connections when wiring, in order to avoid any phase shift between the Left & Right Speakers and Tweeter & Woofer.

Lastly screw the back side and top pieces on. At this point you can test the speaker using your audio system to ensure it is operating properly. Every other step following this is aesthetics.

Step 5: Gluing Together, Edging, and Sanding: Prep for Veneer

This section outlines the prep work before veneering the speakers. At this point you have your speakers assembled for testing. You can now disassemble, or skip the previous step if your confident in your dimensions & design. Make sure to remove speakers as well to protect them, however you do not have to remove the rest of electronics if you do not want.

Once back in pieces, apply some wood glue to each side you are putting back together piece by piece. You can reuse the screw holes from the previous step to clamp all the wood pieces together while drying instead of clamping and waiting for one edge to dry at a time. Repeat for all sides and let dry.

Once dry, You can remove the screws if you want and you can add any creative edges you want with a router, I opted for a chamfered edge on each side to keep from having sharp corners in the front. For that edge I had to remove the screws, chamfer the edge with a router, and fill in the holes from the screws with wood filler.

Lastly, before veneering you must clean up all the edges and sand. If there are any major gaps or imperfections in the wood, add wood filler and let dry. Then sand the entire speaker with a random orbit sander, using 60 grit. Make sure to keep the edges sharp, do not round over edges as the sharp edges are needed to ensure a good veneer job.

Step 6: Adding the Veneer

This step overviews how to add the veneer. This is just a general overview, I recommend looking up a veneer instructable to better inform you of the nuances in veneer.

First step is to cut out the veneer sheets. Using the drawing from step 2, cut out the veneer sheets with an extra 0.5" added to each dimension. The second image shows all the veneer cut out, I veneered the bottom, but you don't have too as it will not typically be seen. I also did not veneer the back. For any chamfered edges make sure to cut out veneer for that. Veneer can also bend a bit if you want to do a rounded edge, however I recommend a minimum of 1/2" rounding (even then that might be pushing it) with the veneer grain direction going up and down if the curve is at the same place as the chamfered edge I have.

To attach the veneer, start with the top and bottom, since you will be laying one veneer sheet over the edge of the previous one, the last sheet attached should be the front one, so the edge will point sideways and not be easily seen. To attach veneer, contact cement is typically used. Make sure to follow the instructions of the bottle (IE brush on both sides, wait before attaching). This stuff sticks immediately so make sure you are very careful when placing it on as you cannot reposition. This is why there is an extra 0.5" recommended. you can maybe reposition if it has only touched a side edge, but as soon as you lay it down on any portion of surface it will stick fast. allow 2 hours to dry. Once dry, cut of the edges with a snap of utility knife. These knives specifically work well because they have a small form and a long strong and slightly flexible blade. This means you can use the edge to help bend and guide the blade and still provide enough force to cut the material. Place the speaker box new veneer side down and cut ensuring the blade is as perpendicular to the veneer as possible, while not angling inwards so there is no gap later, (this is where the bendy blade and small form helps as you can use the edge to force the blade to be perpendicular). Once cut, sand the edges so the edge of the veneer and next surface to be veneered are completely flush. Repeat this until all sides are added. The final veneer job before the protective coat is seen above.

Step 7: Finshing Coat

This is the final step, a finishing coat for the speakers. For these I used a polyurethane coat to both bring out the natural color in the cherry and to provide a protective layer from damage. You can also add stains or other coats as desired, but if you have a good quality veneer all you need is a protective coat which brings out the color in the wood.

For this step I followed the instructions on a polyurethane semi-gloss to add 3 layers on the speaker. Then once finished and dried, I reconnected and re-added the speaker drivers.

Congratulations! You have finished your own homemade speaker drivers!

If you want to check out any of my other projects like the resin river table they are sitting on, please check out my website at: https://ryanogilvie.weebly.com/

Happy listening!

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    3 Comments

    0
    rcarmier
    rcarmier

    1 year ago

    Enjoyed the breakdown on sound theory and audio hardware selection. Excellent! Want to make one but I'm curious if I would be able to laminate the faces of the MDF with hardwood without it interfering and adding resonance.