Designer:

Brian Stoller

Project Category:

Loudspeakers/Cabinets

Project Level:

Intermediate

Project Time:

20+ Hours

Project Cost:

$500 – $1,000

Project Description:

This design was loosely based on a ‘short line array ‘ aka SLA, a Bill Fitzmaurice design
https://billfitzmaurice.info

They sound great with much more clarity than my commercial array:
Galaxy Audio – Powered Line Array 
4- “5 Inch Spk 100W (500$ a pair)

A sub is still required for the full audio spectrum

Design Goals:

Nothing lofty here – I sold my 70’s Kustom Amp that had 3-15″ per cab that I used its speakers for my basement studio and wanted a better replacement.

Driver Selection:

Goldwood GW-4028/S 4″ Shielded Woofers 
Goldwood GT-302/S 1/2″ Mylar Dome 

6 Years ago, I’d purchased 6-Goldwood GW-4028/S 4″ Shielded Woofers 
and 8-Goldwood GT-302/S 1/2″ Mylar Dome tweeters to build a Bill Fitzmaurice designed center speaker for our TV but then felt the dimensions were just too large so I put the project aside.

After retirement, I decided to make two cabinets with 6-4″ drivers and 8-1/2″ tweeters w/ L-Pads to be used as monitors in my home studio.

Enclosure Design:

My interpretation of this cab used tapered sides as I thought it looked more aesthetically pleasing. 
The woofers and tweeters are sealed so the internal cabinet area wasn’t critical

Wood was 1/2″ Birchwood with the top and bottoms cut from a 2″x6″ for strength

34”tall
9” Front baffle
7-1/2” sides 
6” back 

Slow cure marine epoxy and wood glue used throughout.
Fastener only used in handles and speaker stand inserts.

Enclosure Assembly:

I think the only notable item was the baffle board. The front 9×34” 1/2” birch baffle was made into a sandwich a layer of carbon fiber and a sheet of 1/4” basswood back – see pics.

I initially cut the speaker holes and speaker recesses thru both wood sheets screwed together but with all the holes the 2 baffles were extremely flimsy. I added carbon fiber cloth in the center with boat epoxy. Cutting out the fiber after the epoxy set was easy. The baffle sandwich was like steel as it couldn’t be twisted, even slightly.

Crossover Design:

See products used section. I added a 2.7 uf capacitor and .13 inductor to the commercial HPF to make a 3rd order filter that cuts over in the 5k region. I know that’s on the high end but I kept reading these ‘inexpensive’ tweeters are best served in this region. Having 8-1/2″ tweeters with a L-Pad
really allows full control of the sizzle.

Conclusion:

I can’t ignore that this project, which I assumed would only take 50 to 100 hours, was probably closer to 300 to 800 hours. I started on May 13th do it’s been around 100 days putting in some 3 to 8 hours most days. With the woofers and tweets along with the hardware; handles, speaker stand inserts, jack plates L-Pads and paint and rollers and other sundry items there’s some +500$ of parts

Tips & Tricks:

Carbon Fiber sandwiched between wood with epoxy is amazingly had and dense. I’m planning to build 2 scaled down Tuba-45’s (another Bill Fitzmaurice design https://billfitzmaurice.info ) and use 1/4″ wood and Carbon Fiber.

About the Designer:

Bill Fitzmaurice has some amazing designs up on his site (various designers).

Project Parts List: