John Sayers' Recording Studio Design Forum Archive

Here it is, by popular demand, the first Do-It-Yourself project for the Speaking of Speakers forum!

This first project is called the Killatone(TM). It's an updated version of the once popular Auratone 5C "full range" monitor.

Design overview:

The Killatone is an inexpensive, easy to build, single driver, closed-box loudspeaker intended for use as a limited bandwidth reference monitor for recording. It uses the 5" Fostex FE127E magnetically shielded driver in a 3.6 liter sealed cabinet to achieve a low frequency -3 dB cutoff of 117 Hz. The "crossover" consists of a parallel impedance compensation network (R2, C1) along with a baffle step compensation filter (R1, L1).

A completed pair should cost about $130 US.

Construction:

The prototype was constructed of 0.75" MDF in accordance with the diagram below. The driver was offset from the center of the baffle and the cabinet corners were rounded over in order to minimize response ripples induced by edge diffraction. The inner driver opening was also rounded over to minimize air turbulence noise as well as to reduce standing waves that often occur in this vicinity. However, the construction method and materials are widely open to experimentation. The only critical dimensions of the cabinet are as follows:

Don't change these:

1. The internal volume - in order to maintain the correct low frequency cutoff and damping characteristics.

2. The front baffle dimensions - the baffle step compensation filter is designed to compensate specifically for the response shelf which occurs due to an 8" wide baffle.

3. The amount of fill - this helps achieve the proper low end alignment as well as reduces internal cabinet resonances. Even here the exact amount of fill is not critical, but you should try to get it approximately right.

Otherwise, build it as you like.

Modifications:

Besides building the cabinet pretty much however and from whatever material you want, there is one easy upgrade to the Killatone. The Fostex FX120 is a drop-in replacement driver and doesn't require any change to the basic design. It has a flatter and smoother high frequency response and 5 times the linear cone travel. However, the FX120 is not magnetically shielded. So, you'd need to build some sort of shield into the cabinet if you wanted to use it near a CRT computer monitor.

Suppliers:

Here is a list of suppliers where you can order some or all of the parts.

Madisound (USA) http://www.madisound.com/
Solen (Canada) http://www.solen.ca/
Hifi Sound (Germany) http://www.hifisound.de/
Hifi Kit (Sweden) http://www.hifikit.se/


Have fun and sorry about the English units!:D

Thomas


PS - Next on the DIY project list is an inexpensive two-way monitor designed specifically for soffit mounting. Stay tuned!

Here are the frequency response and impedance curves for the prototype. (Normalized half space measurement using LMS).

The response is fairly flat and neutral from the upper bass through the midrange. Like the Auratone I had originally envisioned the Killatone as a "cheap reference" for bottom of the line boom boxes, car stereos, and TV sets. I still think it will work nicely for this purpose. However, from my brief time listening, the Killatone seems as if it might also be very useful for isolating and illuminating what's going on in the midbass and lower midrange section of one's mix. The high frequency bumps turn out to be rather inconsequential because you literally need to be dead on axis with the driver to hear them. The 5" driver focuses those frequencies so narrowly that, unless your head is clamped on axis in a vise, the highs are actually rather subdued in most listening positions. And without the distraction of the deep bass you're essentially forced to concentrate on the midbass and midrange.

I need to live with them for a little longer to form some solid opinions, but so far I think they're well worth the effort!

Pics of the prototypes to follow.

Thomas

Here are pics of the first Killatone!

And here's the latest progress on Eric Best's Killa project!

And here are Eric's final pics and comments!:D

"They sound surprisingly good. Between my mains and my JBL near-fields they give me a great picture of what things sound like. Any mix that sounds good on all three has translated very well to any other system that I've tried so far. Thanks again." - Eric

S3 asked a very good question.

"How to magnetically shield the Killatone when using the FX120 driver?"

Here is a very simple method.

Go to your local independent building suppler and buy a coil of galvanized steel flashing. With tin snips cut a 2.5" (64mm) wide by approximately 3ft (1m) long strip of flashing. Clean the strip to remove any grease. Now wrap the flashing tightly around the speaker magnet like I've illustrated below. It should go around about 2 or 3 times. Tack the end down with hot melt glue. Also put beads of hot melt glue where the shield meets the speaker (as illustrated) to hold the shield firmly in place. The only critical thing in all of this is to make sure the neither the shield nor the glue sticks out too far radially. Otherwise the speaker might not fit through its mounting hole.

That's it!

Looking forward to seeing your pics S3!

Thomas