There are no really lazy people, just uninspired ones - Berry Gordy




40 years after the Apollo landing on the moon, and 5 years after building my original Delta speaker (and starting this website), the time has come for the next step forward in the pursuit of the ultimate loudspeaker system.

My 2009-2010 Apollo project incorporates the following features -:

1 - "flat panel" (shallow & wide) design, inspired by the wide Boston Acoustics designs of the 1980s, and Sonus Faber's Stradivari Homage. Wide, flat baffles reduce the listening room acoustic signature. i.e. they tend to bring the listener into the musicians room, rather than the musicians into your room. They also require less baffle-step compensation to negate the loss of bass that occurs as longer wavelengths wrap around a typical narrow enclosure.

2 - new high performance tweeter with particulary powerful low frequency performance i.e. low compression and harmonic distortion.

3 - a new 4" neodymium underhung specialist midrange.

4 - a new 6 1/2" neodymium underhung bass-midrange driver to cover the fundamental range of the human voice, whilst increasing power handling and sensitivity.

5 - a new wideband 12" (sub)woofer, actively driven, extending the bottom end to 25Hz (-3dB).

6 - time-aligned (stepped) baffle with separated enclosures (for isolation & weight managementl)

7 - highly-rigid bass enclosure for minimal cabinet resonance

8 - attention to driver rear ventilation, i.e. inside the enclosure

9 - improvements to general cabinet construction techniques and accuracy

10 - invisible grill mounting using high-strength neodymium magnets

11 - variovented lower and upper midrange enclosures

12 - first order, linear phase design (as close to as practical)

Design influences


Wide baffles, 1st order filters, 4-way, diffraction control.

Boston Acoustics A150 Boston Acoustics A200 Sonus Faber Stradivari Homage

Vandersteen 5A

KEF Maidstone Passlabs SR-1

Apollo will be a truly full range speaker, getting to below 25Hz and thus avoiding the need for nasty, poorly specified bass-management from a surround processor (and its undesireable phase effects).

To achieve this, it will be bi-amped, using 1 amplifier to drive the woofer, and a 2nd amplifier to drive the mid/tweeter section. The active woofer section will include equalisation, lowpass filtering and amplification to achieve the desired target. The "satellite" section will use standard passive high-level crossovers (the low level passive HPF shown in the diagram below is optional but only recommended in a very high power system).


Driver Selection
Seas T29MF001 E0047 Magnum (or Crescendo)
25mm magnesium dome tweeter
4 ohm, 92dB, 90W
Sd 8cm^2
Xmax 1.4mm p-p

Mms 0.35g
Intended frequency range 3kHz-20kHz
Scanspeak 12MU/8731T00
Paper cone, neodymium magnet, underhung motor system, coated foam surround, open basket , titanium former
8 ohm, 87.2dB, 800W
Sd 58cm^2
Xmax 6.8mm p-p
Mms 4.7g
Intended frequency range 800Hz-3kHz
Scanspeak 18WU8741T00
Paper cone, neodymium magnet, underhung motor system,
titanium former
8 ohm, 85.4dB, 60W
Sd 154cm^2
Xmax 12mm p-p
Mms 18g
Intended frequency range 200Hz-800Hz
Morel UW1258
12" paper cone
5.1" Hexatech voice-coil
8 ohm, 87dB, 800W
Sd 437cm^2
Xmax 25mm p-p
Mms 105.5g
Intended frequency range 20Hz-200Hz
Scanspeak flow resistor
Aperiodic vent that will be used to reduce the impedance at resonance by over 50% (midrange drivers), and also to reduce rear-wall reflections. Physical dimensions here .

Preliminary modelling.


Room and cabinet effects.


18WU 12MU
Power handling
Preliminary crossover simulation
Enclosure design

Apollo construction

Apollo crossover

Gatti Audio