Practical Outline of DIY Speaker Design

[Swerd]

Occasionally someone asks questions about building his first DIY speakers. They usually are inexperienced and are clearly unfamiliar with the design process, although they may not know it. Some of their ideas are going to lead to trouble and frustration.

I was inspired when I recently read a post by Jeff Bagby where he describes some common misconceptions about crossover design. I realized as I read his excellent post that many DIY newbies (including myself at one time) had no idea of what steps were involved designing speakers.

So, here is an outline of the various steps in designing your own speakers. (To keep things simple, I will limit this to a 2-way speaker.) These steps are the way I learned from two experienced designers who were kind enough to teach me. It probably isn’t the only way to go.

My intention here is not to publish a comprehensive guide to DIY speaker design, but to provide a general outline of the process, in the order in which they may be done. I hope this helps someone who is considering it for the first time to see how well prepared they are. It is also why I usually recommend that DIY newbies build a kit or a published design done by an experienced builder.

1. Choose a woofer: Design the cabinet based on woofer T/S parameters. You can rely on manufacturer’s values, or measure them yourself. Often woofers can vary at least ±10% from the manufacturer’s specs, so measuring the woofers you have is always better as these parameters play a major role in cabinet design. Will the cabinet be sealed or ported? The T/S parameters allow calculations to help decide whether a woofer is more suited to a sealed or ported design (see chapter 1 in Ray Alden’s Speaker Building 201), bass tuning frequency, cabinet dimensions. Various box design calculators (available online or in simple box design programs) can predict frequency responses for a given woofer in a sealed or ported design.
   
   Zaph Audio has published his measured T/S parameters of a large number of woofers available for DIY builders. These numbers can be useful as you decide which woofers to buy. If I had to choose, I’d rather rely on these T/S values than those published by the manufacturer. They are also useful to learn which manufacturers publish reliable numbers and which do not.
   
   
2. Choose the crossover frequency: This will depend on the woofer’s high frequency performance, both on-axis and off-axis. For a detailed explanation, read this article. The choice of woofer and its crossover frequency has a major effect on a speakers ability to create a believable stereo image.
   
   
3. Choose a tweeter: Once a crossover frequency is selected for a woofer, it is easier to choose a tweeter. A crossover frequency lower than 2 kHz usually requires a more ruggedly built and more expensive tweeter.
   
   
4. Build a test cabinet: Once cabinet volume and dimensions are settled, build a test cabinet. This can be a simple prototype, or can be an unfinished version that can later be veneered or painted. The important features for speaker design are volume, speaker mounting locations, and external width. If you change these, it can affect the frequency response, so settle on these before designing the crossover.
   
   
5. Mount woofer & tweeter:
   Locate the woofer and tweeter as close as possible to each other. Some tweeters or woofers have truncated frames, allowing closer placement. Other designs have a flush mounted tweeter and a non-flush mounted woofer, where the woofer’s flange overlaps the tweeter’s flange. Decide if the tweeter will be centered vertically or slightly off center. Changing these locations can affect the frequency response, so settle on this before designing the crossover.
   
   Attach long wires to each driver’s terminals and allow external access to these wires. If a ported cabinet is involved, it is easy to run these wires out of the cabinet through the port. If the cabinet is sealed, some creativity will be needed. I have drilled holes in the back of the cabinet (where I will later mount the input terminals) and run the wires through these holes, temporarily sealing them with a bit of silicone caulk.
   
   
6. Design the crossover: Measure the unfiltered response of each driver (read Jeff Bagby's article if you haven't already). To avoid damaging the tweeter with low frequencies at full power, it may be necessary use a single capacitor (~10-20 µF) in series with it.
   
   The complex crossover design process is best done with computer software (LspCAD, SoundEasy, Speaker Workshop, or others), a measuring microphone, and a full-duplex soundcard, that can send computer generated signals to the speakers and record the sounds coming from them at the same time. It requires an initial investment of money and plenty of experience to use these design tools correctly.
   
   
7. Build a test crossover: Mount it outside the cabinet using the wires mentioned in 5b. Listen to it and try tweaking individual components by trial and error (see Curt Campbell's article, scroll down to where it says The Tweaks and Additional Tweaks).
   
   
8. Build and finish the final cabinets and crossovers

 

[highfigh]

We could probably make this list overly complex but one thing I'd like to add is:

The listening experience is the only part of speaker design that's subjective and everything else can be measured objectively. That being the case, don't try to make the drivers do what they can't. The parameters will determine the box. Period. Wanting it to be different won't make it so.

2) "Choose a crossover frequency"

This really can't be done until the driver tests are complete. If the drivers won't work well/live long with the chosen crossover point(s), the design won't work.

Good job.

 

[lsiberian]

Could we get this stickied. I really like the post and plan to use it as a reference on future projects myself.

FYI if you really are too lazy to design a crossover Madisound does have services that are reasonably priced.

I usually just go with an existing design. Why reinvent the wheel? Some other Genius figured it out already, but I'm not a big EE guy yet. I'm more into the woodworking part.

 

[highfigh]

Could we get this stickied. I really like the post and plan to use it as a reference on future projects myself.

FYI if you really are too lazy to design a crossover Madisound does have services that are reasonably priced.

I usually just go with an existing design. Why reinvent the wheel? Some other Genius figured it out already, but I'm not a big EE guy yet. I'm more into the woodworking part.

I don't think it's reinventing the wheel, more like tweaking it to personalize it. People do it with cars, bikes and houses- why not build a set of speakers and do a little "What if..." with the crossover? WinISD and some of the other freeware has crossover design, although this link has notch filter, Zobel network and L-pad pad calculators, as well as 1st through fourth order crossover calculators:

http://www.the12volt.com/info/diagrams.asp

Scroll down to the first two sections below the Fluke meter.

 

[Swerd]

2) "Choose a crossover frequency"

This really can't be done until the driver tests are complete. If the drivers won't work well/live long with the chosen crossover point(s), the design won't work.

I agree with your comments. I could have worded this better. Instead of saying:

Choose the crossover frequency: This will depend on the woofer’s high frequency performance, both on-axis and off-axis. For a detailed explanation, read this article. The choice of woofer and its crossover frequency has a major effect on a speakers ability to create a believable stereo image.

Choose a tweeter: Once a crossover frequency is selected for a woofer, it is easier to choose a tweeter. A crossover frequency lower than 2 kHz usually requires a more ruggedly built and more expensive tweeter.

I should have said:

Choose the woofer's low-pass crossover frequency: This will depend on the woofer's high frequency performance, both on-axis and off-axis. Look for a frequency at least an octave below any break-up or resonance noise, and where the 30° off-axis response is no more than 3 db below the on-axis response. Not all woofers can do this. This choice of woofer crossover frequency has a major effect on a speakers ability to create a believable stereo image.

Choose a tweeter: Once a low-pass crossover frequency is selected for a woofer, it is easier to choose a tweeter. A good rule of thumb is to look for a tweeter whose resonance frequency (Fs) is at least half the crossover frequency. So, if the woofer needs a crossover at 2200 Hz, look for a tweeter whose Fs is about 1100 Hz or less. This works well if your crossover slopes are 3rd or 4th order or steeper. If your goal is shallow slopes, such as 2nd order, you will be better off choosing a tweeter whose Fs is 1/3 the crossover frequency. So, for a 2200 Hz 2nd order crossover, look for a tweeter whose Fs is about 700 Hz. Lower Fs values for tweeters usually require a more rugged build and cost more.

 

[Warpdrv]

Nice Job... Now someone STICKY this to the top...

 

[highfigh]

I agree with your comments. I could have worded this better. Instead of saying:
I should have said:

Choose the woofer's low-pass crossover frequency: This will depend on the woofer's high frequency performance, both on-axis and off-axis. Look for a frequency at least an octave below any break-up or resonance noise, and where the 30° off-axis response is no more than 3 db below the on-axis response. Not all woofers can do this. This choice of woofer crossover frequency has a major effect on a speakers ability to create a believable stereo image.

Choose a tweeter: Once a low-pass crossover frequency is selected for a woofer, it is easier to choose a tweeter. A good rule of thumb is to look for a tweeter whose resonance frequency (Fs) is at least half the crossover frequency. So, if the woofer needs a crossover at 2200 Hz, look for a tweeter whose Fs is about 1100 Hz or less. This works well if your crossover slopes are 3rd or 4th order or steeper. If your goal is shallow slopes, such as 2nd order, you will be better off choosing a tweeter whose Fs is 1/3 the crossover frequency. So, for a 2200 Hz 2nd order crossover, look for a tweeter whose Fs is about 700 Hz. Lower Fs values for tweeters usually require a more rugged build and cost more.

Re: tweeters and x-over points, 3rd and 4th order filters sometimes make it hard to "knit" the speakers in the system. More phase shift and finding the right f3 is more difficult although the availability of more test equipment is making this more practical because trial and error is a PITA. 2nd order (12dB/octave) still requires inverting the driver's connections because of the shift. Higher order filters also have more insertion loss. I like to stay as far from the Fs as possible.

 

[audiohonic65]

Thanks! This is really informative, just forwarded to few of my friends who never used to figure out the right way to do it.

 

[lsiberian]

It seems to address 2-way design, but how about 3-way design

I'm thinking you'd select a midrange unit that crosses out of the sensitive range on both ends. Perhaps something like a full-ranger. I'm still going through drivers to see some possible suspects in the budget range.

 

[WmAx]

It seems to address 2-way design, but how about 3-way design

I'm thinking you'd select a midrange unit that crosses out of the sensitive range on both ends. Perhaps something like a full-ranger. I'm still going through drivers to see some possible suspects in the budget range.

Usually, 'full range' drivers do not give any advantage for higher cross over ranges, if you include dispersion as the critical factor.

-Chris