7 inch 2-way
40 Liters Double Chamber Reflex

by Michael Chua

Measurements by LMS version 3.0
LMS is manufactured by LinearX

This design is free for DIY. Not for Commercial Use.
This article may not be published in part or full without the express permission of AmpsLab.

Merlin Test Box

What is a DCR?

DCR is short for Double Chamber Reflex. It is a little known variation of a Bass Reflex. Unlike a conventional Bass Reflex, where a single port determines the lowest bass, a DCR has two ports, one for the lower bass and the other for the upper bass.

The manner in which this is accomplished is by way of 2 internal chambers. In the larger chamber where the woofer is located, the main port fires outwards for the lower bass. Simultaneously, an internal port fires into a smaller chamber below. A third port in this secondary chamber then fires outwards for the upper bass.

It is this added complexity that separates the bass performance of a DCR from a Bass Reflex. With the assist of a secondary chamber, a DCR is much more articulate in the upper bass. It is equivalent to boosting the upper bass with an equalizer. Instead of doing it electronically, a DCR does it acoustically.

In the Near Field Response on the right, the outputs of the 2 ports are clearly defined. The green plot centered at 45Hz, is the output of the lower bass. The violet plot, with a slight peak at 80Hz, is of the upper bass. Note how well it bridges the gap between the lower bass and the roll off of the woofer (red plot).


Click Pictures to Enlarge

Double Chamber Reflex Plans

DCR Near Field Response

The face of Merlin

The Merlin is designed as a stand alone mid tower of 40 Liters. No subwoofers are required as it reaches down to 40Hz (-3dB) effortlessly. It is sensibly contoured so that mids are not emphasized or recessed. Vocals are transparent and clearly identifiable, a trademark of all our speakers.

This is accomplished by a high order asymmetric crossover that guarantees seamless integration of mids with the highs. In our raw, unsmoothed Gated Plot on the right, no evidence of phase cancellations are observed in the critical crossover region.

Due to our optimized crossover, string instruments are particularly well reproduced in the Merlin. Acoustic guitars exhibit the right tone and attack. Violins are a joy. No screech. Simply exquisite.

Jazz lovers will find the Merlin seductive. Intricate upper bass tracks are audible and detailed. Lower bass has "body" and "tautness".

The essence of the Merlin is in the naturalness of rhythm. Everything is in step. Timing is perfect. This is what makes music enjoyable.



Speaker Type  2-way Mid-Tower Double Chamber Reflex
High Frequency Transducer  Seas 27TDFC 1" Fabric Dome Tweeter
Low Frequency Transducer  Dayton RS180s-8 7" Aluminum Cone Woofer
Crossover Frequency  2,500Hz
Crossover Network  Butterworth Low Pass (12dB/oct)
   Butterworth High Pass (18dB/oct)
 Frequency Response (+-3dB)  40Hz-25kHz
 Sensitivity (1 watt / 1 meter)  85dB
 Nominal Impedance  8 ohms
 Enclosure Internal Volume  40 Liters
 Enclosure Internal Dimensions (WHD)  7-1/2" x 28" x 12"

LMS Thiele Small
Gated Crossover Response
No Smoothing Applied
System Impedance

High Order Crossover Network

60 Downes Street | Calais | ME 04619 | USA