DIY floor standing speakers – dual woofer – beginner friendly

Speaker plans for tower speakers

The point of this article is showing you how to make a pair of DIY floor standing speakers. The advantage of DIY is that you can tailor the speakers to your liking. Sometimes get it done cheaper, and of course you get the satisfaction that you have built something yourself. The main characteristics of this loudspeaker are the following :

• Low price. The loudspeaker uses budget drivers from Dayton Audio.
• Fun sound. This is not your audiophile grade speaker design. It has a linear sound for mids and highs. However, it also has a slight boost in bass. Who doesn’t love bass?
• Minimal crossover components to keep the cost, and build difficulty, down. 2nd order filters for each individual driver. An additional notch filter is used for the midrange.
• Flexibility. I give different build options to match your skill level. Also, the crossover features quick changes for different sound signatures.

In conclusion, I present to you a pair of cheap DIY floor standing speakers. The goal is to have a linear sound, down till the lower octaves. There, we will have a more pronounced bass. This is done by having a dual woofer setup. Furthermore, the crossover is designed with this in mind. If you fancy less bass and a more linear sound (on all the frequency bandwidth), a simple polarity switch will do the trick (more on that later).

Parts list

Here comes a long list of parts. This might not seem cheap after all, but bare in mind it’s a dual woofer tower speaker (how cheap can you go?). Sometimes I don’t find an exact match, in the link. I mention this, if it’s the case. However, the item in the link will get similar, if not identical results.

• Speakers (Amazon affiliate paid links) :
• • Tweeter – Dayton Audio DC28F-8 – x 2
  • Midrange – Dayton Audio RS125-8 – x 2
  • Woofer – Dayton Audio SD215A-88 – x 4
• Crossover parts :
  • Inductor (Amazon affiliate paid links):
  • • 4.7 mH, Iron core, 1.2 mm, 0.31 Ω – x 2
    • 3.3 mH, Iron core, 1.0 mm, 0.36 Ω – x 2
    • 0.62 mH, Air core, 1.4 mm, 0.24 Ω – x 2 (tad lower inductance in link)
    • 1.5 mH, Air core, 1.0 mm, 0.65 Ω – x 2
    • 0.27 mH, Air core, 1.0 mm, 0.23 Ω – x 2
  • Capacitor (Amazon affiliate paid links) :
  • • 100 uF electrolytic – x 2
    • 10 uF electrolytic – x 2
    • 56 uF film foil – x 2
    • 8.2 uF film foil – x 2
    • 12 uF film foil – x 2
    • 6.8 uF film foil – x 2
  • Resistor (Amazon affiliate paid links) :
  • • 1.5 Ω , 25 W – x 2
    • 3.3 Ω , 25 W – x 2
    • 8.2 Ω  , 25 W – x 2
• Enclosure (Amazon affiliate paid links) :
• • 18 mm MDF
  • Mineral wool
  • Dayton Audio binding posts – x 2
  • Bass reflex port (2 options)
  • • Jantzen audio 70 mm – x 2, or
    • Precision port 3″ – x 2

Of course, you will need wires, and a board for the crossover circuit, but that is at your discretion.

Panel dimensions

The material I’m using is 18 mm thick MDF. So, when I’m going to list the panel dimensions, you will only see length and width. These are the sizes you need to cut :

• 1078 x 275 mm (front and back) -> 6 pieces
• 1042 x 359 mm (sides) -> 4 pieces
• 359 x 275 mm (top and bottom) -> 4 pieces
• 363 x 238 mm (internal braces) -> 6 pieces
  • 358 x 238 mm (if you don’t want to make grooves for the braces)

Here is a visual representation of the front baffle :

Just above we have the front baffle of our DIY floor standing speakers. The first sketch from the left, just shows the center of the circles. And since we have a double baffle (2 panels glued together), for added stiffness, we have 2 additional sketches. The rear part of the baffle contains 3 mm deep grooves to fit the braces. If you feel this is too much for you, or you don’t have the necessary tools, you can make the braces shorter and skip the groove process.

The rest of the panels are self explanatory. Just cut a big circle into the braces, so air can circulate. Do this for all the braces, except for 2. You need a panel to separate the chamber with the bass from the chamber housing the mid + tweeter. As a result, make sure you don’t cut a hole in all of them (just 4).

DIY floor standing speakers build

Here are some pictures with the actual build :

Above, you can see the baffle. It’s made by 2 boards glued to one another. The surface panel has the recessed steps for the driver cutouts. This way the speakers are mounted flush with the baffle. The 2nd panel has simple circle cutouts.

The grooves are 3 mm deep. Their purpose is to make a nice fit for the braces. Place them on the front and rear panel. When I say front panel, I mean the interior panel of the double baffle. For this job an Emerson tool and router is an excellent choice. Align all the 4 panels which need grooving, so you make the grooves in the same spots. Leave the extremities of the panels untouched (18 mm on each side). That’s where the panels fit together, and you don’t want holes there.

Above, you have the 6 panels used for bracing (3 for each of the DIY floor standing speakers). Leave 2 of them untouched. Just drill a small hole through them, so you can route the cables from the tweeter and mid-bass to the crossover. For the rest (4 pieces) of the panels, make a large hole in them. Even though you can find the exact diameter in the schematic at the beginning of the article, the exact size of the circle doesn’t matter.

I’m sure you find the pictures above self explanatory. As a finish, I applied 0.8 mm rosewood veneer using contact adhesive.

 

First time that I finished a box in veneer. However, I’m quite happy with the result. Next time I’m confident I will do it even better.

Sound damping

I consider sound damping material to be optional, especially in a bass reflex enclosure. However, acoustic measurements revealed a standing wave. A nice way to eliminate it is to use mineral wool.

 

Use 5 cm mineral wool on sides and top. For the bottom, use 3 layers of 5 cm (15 cm thick pad). You can check out more details in this article.

Port tuning frequency

The port design that I will describe in just a bit, is for a 25 Hz tuning frequency. Some might consider it too low, and I won’t disagree. However, this type of tuning has its advantages. I, myself, aimed for a higher tuning frequency, but it seems I miscalculated something and I ended up with a lower box resonant frequency. Since I ended up here, I decided to leave the port like this. The advantages of tuning this low are the following :

• Better bass response below the resonant frequency of the driver.
• Smoother roll-off. In conclusion, better transient response.
• Less port noise. The driver cannot play efficiently under its resonant frequency. Therefore, there is less amount of air movement through the port. As a result, less air turbulence.
• “Subsonic” acoustic filter. Since the port takes the load of the speaker at that particular frequency, it makes sure it doesn’t crack down under the pressure of low octave tones.

Even though you have these advantages, having a higher tuning frequency, translates in a better bass response in an area which you will encounter on music more often (30-40 Hz). Not many tracks go under 30 Hz. But anyway, here are my port dimensions :

 

 

The Jantzen Audio port I used in 70 mm in diameter. The length is :

• 120 mm without flares.
• 190 mm with flares.

If you use the 3″ Precision port, that is 75 mm in diameter. As a result, if you use the same dimensions as I did, you will get a higher tuning frequency (because the diameter is a tad larger and the length is the same). If you keep shortening the port, you will get an even higher tuning frequency. Expect more air turbulence when going up in tuning frequency. However, the larger diameter helps in this regard.

Crossover design

To finish our DIY floor standing speakers, we need to  get into the actual crossover design. First of all, let’s talk about how to wire the bass speakers. Some might have issues here because the woofers are dual voice coil, and this might confuse someone.

Basically, you wire the coils in parallel and the 2 woofers in series. For a total of 8 Ohm load. Now let’s take a look at the actual crossover diagram :

Here is a brief descriptions of the crossover :

• on each speaker side there is 2nd order filter.
• the midrange has an extra notch filter. The response has a peak at around 1200 Hz. This is probably caused by edge diffraction. You could probably solve this issue by rounding up the edges and by placing the midrange and the tweeter off-set on the baffle (not in the center). However, this is not tested by me.
• Tweeter has an attenuation resistor.
• The capacitors on the woofer side are electrolytic. This is to keep costs down because an 100 uF cap is expensive. I wired 2 capacitors in parallel for a total of 110 uF. I did this because it’s hard to find a 110 uF cap. Furthermore, electrolytic capacitors have low power handling, and by wiring them in parallel, you basically double the power they can take.
• Big value inductors are iron-core, to keep the cost down. Furthermore, iron-cores have lower resistance to the equivalent air-core. As a result, L1 has lower resistance, and therefore more bass for the woofers. However, resistance of L2 is quite irrelevant.

Crossover tweaks

What is a pair of DIY floor standing speakers without tinkering? There are certain tweaks that can be made to this crossover, depending on your preference.

If you want less bass and a more linear sound, you can simply swap the polarity of the woofers (either in the crossover or where you connect the bass speakers). The crossover is designed with a bump in low frequency response. Fortunately, I noticed if I switch the polarity of the woofer(s), the response flattens on the bass side. I did not calculate this, it’s just a fortunate coincidence. If this is your cup of tea, make the change.

Another thing that might be relevant is the dip in impedance at around 1200 Hz. This is created by the notch filter to fix the peak in frequency response at 1.2 kHz.  Problem is that it’s getting closer to 2 Ohms. Many amplifiers cannot handle 2 Ohms. However, since it’s such a narrow bandwidth and pretty high in frequency, most amplifiers should handle this hiccup, no problem.

 

If you have a really crappy amplifier, it might shut off because of this. Simply increase the value of the resistor R2 until the problem goes away. As the resistor reaches 9 Ohms, the impedance curve doesn’t dip below 4 Ohms and problem should be solved. However, as you increase the value of the resistor, the peak in frequency response gets larger and larger (and ruins linearity). Anyway, most amplifiers will not have any issues here.

Frequency response

In the crossover design app you see the response only down to 200 Hz. This is because I used only far field measurements to model the crossover. However, after the speaker was finished, I included the nearfield measurements as well, to have a full frequency response measurement.

 

So this is how the response of our DIY floor standing speakers looks like. It’s without the inverted polarity of the woofer, so with a bass boost. As you can see. it has a linear midrange and top end. The lower octaves are higher in amplitude. You can also see the effect of low port tuning. The roll off is very smooth and still hits very low frequencies with decent output.

Conclusion

First of all, here is a picture with our finished DIY floor standing speakers :

Once again, I want to iterate that this not your audiophile pair of speakers. As a result, they are designed to give a fun sound, with above average bass response. They have physical presence in a room and look awesome with their dual woofer setup. Hopefully, this pair of DIY floor standing speakers will have a low build difficulty, as I mention in the beginning. Bare in mind, that these are tower speakers, and inherently are more difficult to build compared to a pair of bookshelf speakers.