FRANKENSOUND

A lab-created monster made by a madman. These are my monitors that I've come to love so much.

General Overview

I was drawn to the openness and clarity of electrostatic drivers and a dipole system.

I chose to build the large coffin-like subwoofer enclosures so that the 15” drivers would be capable of reaching mid-range frequencies and the lowest ends of human hearing.

The coffin look is both interesting and functional as unusual shaped enclosures diffract frequencies and help disperse stored energy.

Design Goals

My first and foremost desire was for monitors that had enough bandwidth, clarity and accuracy to be used as mixing monitors. The electrostatic drivers came with clarity and accuracy so I wanted to design enclosures that could match this and supply the rest of the frequency range needed. I wanted to cover the range of human hearing from high to low accurately.

Design Objectives

Even full-range frequency response
Low harmonic distortion
Dipole system
Original design

Key Features

2-way crossover with potential for 3-way
Passive crossover with potential for adding an active in the future
Dipole sub/mid woofer enclosure for extended low frequency response and "air"
Electrostatic tweeters
Coffin-shaped design
Chalkboard paint

Technical Specifications

Bandwidth 25Hz to 25kHz, +-4 dB
Max SPL 85 dB with 20 dB headroom
f3 30Hz
f10 16kHz

Cabinet Construction

My cabinets are made out of 3/4 inch 13 ply baltic birch plywood and 3/4 inch MDF, this was done to keep the structure solid. Plywood was chosen because of its construction with alternating grain. The MDF’s density helps deaden the cabinet.

The Subwoofer cabinets were designed to be large so as to achieve lower end frequencies. The larger the box was, due to its dipole characteristics, the more resonance it had at lower frequencies. This was done to achieve low frequencies with just a 15in driver instead of using larger drivers and sacrificing mid-frequencies.

The coffin design is an irregular shape which helps to disperse stagnant energy held within cabinets. It also fits my personality.

Tweeter

I chose the Final Sound electrostatic speakers and built the rest of my system to fit it. I chose these drivers because they covered high frequencies and high midrange, which would save me costs in midrange drivers. I also chose these drivers because of their dipole nature and incredible transient qualities.

Though the driver wasn’t the flattest in response I believe this can be cured with acoustic tuning of the room that they are placed in. Unfortunately, a standard crossover would not work on these because their impedence nature had a completely different curve in testing. They were left with the natural crossover that they were manufactured with.

Subwoofer

For the subwoofer I went with the only infinite baffle designed drivers I could find. The Dayton IB’s were specifically engineered for dipole use and their sound is incredible. Unfortunately the drivers themselves were designed to reach 40 Hz which didn’t fit my requirements. This is why I built such large boxes and gained another 15 Hz lower.

Cross-over

As I stated before, a standard crossover would not function on the electrostatic drivers and were left to function with their natural manufactured crossover. This implies that I only needed to build a crossover for one driver and the crossover was the simplest crossover to create. I used a 1st order Butterworth at 100 Hz.

I chose this frequency because it was roughly where the electrostatic ended and where the subwoofer began to slope downward slightly. Though the total frequency response of the system looks a little rough, I plan to correct a lot of it with acoustically treating its environment and experimenting with black-hole fiberglass/foam.