Frequently Asked Questions



These are some basic questions you might have concerning the design and construction of custom built loudspeakers. Also, you might want to invest in a book or 3 that will help you better understand the physics involved in dynamic speaker systems. Recommended reading includes "Advanced Speaker Systems" by Ray Alden, "The Loudspeaker Design Cookbook" by Vance Dickason, "Building Speaker Systems" by Gordon McComb*, and "Great Sound Stereo Speaker Manual" by David B. Weems**, to name a few. A good source for reference materials is the Audio Amateur Corporation.

For information not covered here, check out the Audio Corner DIY Forum on this site, where you can post questions and help others out with information on speaker and subwoofer building, car audio, and all aspects of audio applications.

Brian Steele has The Subwoofer DIY Discussion Forum for the amateur speaker builder.

Madisound Audio Discussion is yet another good forum for your DIY questions and answers.

Also, check out Pacific Audio & Alarm Discussion Forum for your Car Audio questions.

All are excellent sites where you can post your questions and everyone who reads the page can offer answers.

*Only available at Radio Shack stores.
**Available from Crutchfield.

What are the three most important factors in building a good sounding system?

Enclosure! Enclosure! Enclosure! The quality (and quantity, to you bass freaks!) of bass you get is totally dependant upon the quality and accuracy of the enclosure your drivers are mounted in.


Yeah, but can I really build quality sounding speakers myself?

Yes! It is not difficult to actually build a better sounding speaker for far less than a comparable model from a quality manufacturer. All it takes is patience and a willingess to learn about the theories involved, and you can be quickly on your way to designing your own custom speakers!


What type of enclosure is the best one to design for my speakers?

There is no one perfect enclosure for every application, and every enclosure type has it's advantages and disadvantages. Check out the "Audio Glossary" for descriptions of each type of enclosure. Also, different types of drivers work better in specific enclosures, so decide what you like best and purchase accordingly. You can use the EBP of your driver to help guide you in this endeavor. If you are interested in a ported or sealed box design, check out the article Enclosure Dilemma: Ported vs. Sealed. Remember that quantity is no substitute for quality! And one modest woofer in the correct enclosure can outperform 2 bigger drivers in a poorly designed chop-box with randomly cut "holes for air." :-)


I am building a speaker/subwoofer system for home/car. How big a box do I need for good bass?

Check out the "Software" section elsewhere in my website to download programs that can help you figure this out. If you are OK with math or a scientific calculator, I have listed some formulas in the "Useful Conversions and Formulas" section that will let you figure the optimum sized enclosure for sealed, ported, and single reflex bandpass.


OK, I've decided what I want to build. Do I need special tools to construct my own enclosures?

You will need at least a skill saw (or preferably a table saw), an electric drill, and a jig saw (for cutting circles). These are the only required power tools, although it is nice to have a powered screw driver and electric sander. Normal screwdrivers and other tools will be necessary to assemble the enclosure. You will need paint, varnish, stain, or carpeting with which to cover the enclosure.


Are there any specific tips to successfully build good enclosures?

Lots. First off, keep things as simple as possible. The simpler the design and construction, the higher the probability for success. If this is your first speaker system, don't go off the deep end and try to build that ported isobarik 6th order bandpass with the triangular enclosure (that comes later) ;-]

For car sub enclosures, try and use at least 3/4" medium density fiberboard. This is an excellent material for any enclosure, although you might find a high quality veneer laminate plywood more convenient for home speakers.

If you use plywood, make sure the plys are bonded tightly and the initial sheet you work off isn't warped. You can find quality plywood with hardwood veneer on one side, which makes an attractive surface to paint or stain.

When building the box, you can use PVC pipe for ports which can be painted to match the enclosure.

Make sure and seal the enclosure with a good silicone based caulk, and use proper bracing for large enclosures.

Any enclosure can also benefit from the addition of 1" fiberglass acoustic insulation sheets stapled or glued to all interior walls (except driver/port mounting board). Some people don't like using fiberglass in ported designs, since there's a chance the fiberglass fibers may find their way out of the port and into your lungs (use polyester batting instead).  Do yourself a favor and stuff ANY sealed box about 70% full with some sort of insulation. A good rule is to use 1 - 1 1/2 pounds of material per cubic foot of volume.

Make sure not to block ports with insulation! And speaking of ports, it is not all that critical where they are located on the enclosure as long as they are mounted a few inches away from drivers. Make sure your ports aren't so long inside the box that they come closer than 3 - 4 inches from an opposing interior wall.

Remember to account for drivers, ports, partitions and bracing when figuring the total box volume. To allow for this, add at least 10% over-volume to your enclosure calculations.


Do I really need to use acoustic insulation inside the box?

I have never met an enclosure that didn't sound better with some type of acoustic insulation inside. Damping material is necessary to absorb undesirable sound from the back of the cone that would otherwise bounce around the box interior and reflect out through the cone. Since this sound is out of phase with the sound emanating from the front of the cone, this causes cancellation and reduced bass response. Also, damping material can help to reduce peaking, providing a smoother response curve. Finally, damping material can help suppress cabinet resonances that would degrade bass performance. Use it!


Does acoustic insulation increase the box volume? How much volume can I hope to attain by stuffing my box with insulation?

20% is a realistic maximum figure for sealed enclosures. A sealed enclosure is almost never to big! So even if it is "optimum", it can still benefit from the damping. Damping material changes the operation of the box air from adiabatic (constant heat) to isothermal (constant temperature). With the isothermal process, the damping material absorbs and gives up heat which maintains a more constant temperature inside the box. This also has the added effect of reducing sound velocity, which shortens the wavelengths and makes the driver "think" it is in a larger air volume.

Don't stuff a ported system - just line the walls with fiberglass or lightly fill with polyester batting. Stuffing a ported box may decrease the speaker systems efficiency, and it is difficult to predict how much a large quantity of acoustic insulation changes the tuning frequency.


What type of adhesive is good for assembling the enclosure?

Liquid nails is a very good construction adhesive that permanently bonds almost any type of material. If you don't want to use screws in your home speakers, you can use wood blocks and straps to hold panels together while the adhesive cures.


Do I need a partition(s) to seperate multiple drivers?

Some say yes, others no. Like anything else, it depends. In my experience, partitions aren't neccesary with drivers tuned to the same frequency operating in the same Vb. Definitely partition open backed midrange/mid bass drivers in their own chamber if used in the same enclosure as subwoofers!


Should I flush mount the drivers?

Always a good idea for tweeters and midrange when possible to avoid diffraction, not really necessary for bass drivers.


What about crossovers?

You can use passive crossovers for any system, although many automotive amplifiers include adjustable built in crossovers. You can use an electronic crossover for car speakers as well, although passives will work just fine. The best multi-thousand dollar audiophile speakers ever seen on this planet use passive crossovers, so the logic just isn't there that they can't work well in your car. Blaubox has a good little passive crossover design utility, if you are interested in putting together your own.


What gauge wire should I use to wire the box?

When wiring your enclosure internally, use at least quality 16 gauge speaker type stranded cable. This should be good as long as you are powering your speakers by less than 200 watts RMS. Use 14 or 12 guage for very high power applications. Use a good quality 16 or 18 gauge cable for tweeters and mids.


What about connection terminals mounted on my speakers?

No problem, just make sure you use terminal pads that are small and don't require a large cutout. Large terminals have a tendency to resonate and buzz, and it is difficult to get a good airtight seal with these. If possible, find terminals that require simple holes to be drilled for mounting and speaker cable insertion.


Is there anything I can do to make my existing speakers sound better?

Yes indeedy. Take the drivers out of the enclosure and use a good quality silicone based caulk to seal all inner joints, lines, creases, and bends where two panels are fitted together.

Line the interior of the box with 1" sheets of fiberglass insulation on all inside walls. You can also stuff a sealed box with polyfill.

If you notice the wiring is small and puny, get out your soldering iron and rewire 'em.

These little, seemingly insignificant details can make a bad sounding speaker system sound much better, and a good sounding system sound great.


I spent lots of time and money and spilled my sweat, tears, and blood, but my system still sounds reminiscent of cats being slowly boiled alive!

So build you a new set of speakers! That's half the fun, after all. Finding the right combination of enclosure and driver is a labor of love, one that will take up as much time as you are willing to spend pursuing it. And remember to have fun! ;^)

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Revised: 11 Jan 2003 07:35:43 -0600.