Application note for

D1001-04 - L26ROYA high-end subwoofer featuring the Design by SEAS

L26ROY 10" subwoofer driver and SL26R 10" passive radiatorDesigned at the SEAS R&D laboratory.

Drive UnitsThe woofer is the SEAS Design D1001-04L26ROY. The target for this product was toachieve good low-frequency extension in a rel-atively small enclosure volume. Finding theright balance between moving mass, suspen-sion stiffness and motor force factor is impor-tant, and this is directly influenced by compo-nent selection and design.

To transfer the motion of the voice-coil to thesurrounding air we need a very stiff cone inthis application. The aluminum cone used inthe L26ROY is very rigid and is ideal for thistask.

This cone makes the loudspeaker free from res-onances in a very wide frequency range, sothe use of this driver is not limited to a sub-woofer. It will even perform extremely well ina 3-way speaker. The cone break-up starts atabout 2.5 kHz, so a crossover frequency up to500Hz should be possible with a passive filter.

The L26ROY use a long overhung 2-layer voicecoil, and together with the copper cap over thepole piece this results in very low inductanceand very little problems with inductance mod-

ulation. The measurement below is done withthe Klippel LSI module and show inductanceover a wide excursion range.

To get the force factor we need to achieve theright T/S parameters, we need an extremelylarge magnetsystem when using a 2-layer voicecoil. The driver is very heavy and must be se-curely fastened to the enclosure. The KlippelLSI measurements show us that we have a verylinear motor. The force factor is very symmetricdue to the FEA optimized magnetic circuit, and

SEAS, November 9, 2010

it has only decreased by 20% when the voicecoil has been displaced by 14mm in one direc-tion.

The suspension components have also been op-timized by the use of modern FEA software toallow for very long excursion, while keepingthe voice coil centered in the air-gap. Again,the Klippel LSI measurements confirm that thesimulation has been successfully converted to areally good performing product.

The D1003 - SL26R passive radiator is verymuch based on the L26ROY. The same cone anddustcap, and very similar suspension compo-nents make this the perfect match in the appli-cation we will describe below.

When designing a small vented box with a verylow Helmholtz resonance frequency you soonfind that it’s difficult to fit the reflex port insidethe box without reducing the area of the portso much that you get problems with port noise.Smaller port diameter leads to high air-velocity

in the port. High air-velocity can cause audi-ble turbulence and whistling noise when play-ing certain program material with loud low-frequency content. The solution to this problemis a passive radiator.

This solution is more expensive than the com-mon reflex port, but when comparing the com-pletely noise-free operation of the passive radi-ator to the chuffing and whistling reflex port,there is no doubt that the critical listener willprefer the passive radiator subwoofer.

Box design:The simulated half-space response of theL26ROY with the SL26R passive radiator in a40 liter box predicts a resonance frequency forthe passive at 25Hz. With a low-pass filter com-monly used in a subwoofer application, the -3dB point for the system is at 26Hz, and -10dBis at 21Hz.

We have chosen a cubic form for this box tokeep the internal standing waves well abovethe subwoofers operating range. The drawingalso shows a separate sub-enclosure for a plateamplifier. This is important to avoid air leakagethrough the adjustment pots, connectors andother holes in the plate amp. Such holes willcause annoying air-noise. The volume of thisenclosure is 6 liters. The dimensions for the am-plifier box is not shown, as this may vary fordifferent type of amplifiers.

Alternative box design:In the case of a bass-reflex enclosure of the samecabinet size, a port with an ID of 7cm wouldhave to be 38cm long in order to achieve aHelmholtz resonance at 25Hz. This leaves only1cm to the back wall if a straight tube is used,so we don’t recommend this.

Instead, we recommend increasing the cabinetsize to 50 liters. With a port diameter of 7cm,the length should be 30cm in order to have aHelmholtz resonance at 25Hz.

In a sealed box application the L26ROY couldbe used in a 20 liter box to have a Qtc of 0.707.The -3 dB point would be 54Hz, and the -10 dBpoint is at 30 Hz.

B-B ( 1 : 6 )

ROY-sub

bidland

03.11.2010

Designed by

Checked by

Approved by

Date

1 / 1

Edition

Sheet

Date

B B

415,0

415,0

n269,5

n238,0

207,5

207,5

415,0

Optional rounding of outside edges

8 x M5 knock-in inserts equispaced at ø256

6,0

Material: 25mm MDF

Sub-enclosure for amplifier