Seriously upgraded bass units !
The Mission 765's uses 2 x 8" (200mm) bass units per speaker, so the effect of getting this right was critical. Although the original units were good, they were of course built to a price and even new (according to Wilmslow) were not a high cost item. They looked good, sounded "ok" but not in the league of these beauties.
The SEAS L22's are a superb driver. Aluminium coned, so much better engineered in every respect and with a far higher capability in every aspect of loudspeaker design.
They were a mechanical straight swapout (of course, the crossover needed modifying) but in all respects, these bass drivers are a world apart from the polypropelyne units originally supplied by Mission.
Here's the spec:- Seas L22RN4X/P (H1208) Aluminium Cone Mid/Bass
The L22RN4X/P is an 8" mid/bass utilising an extremely stiff aluminium cone and natural rubber surround, which combine to produce tremendous bass precision. A large magnet system helps to produce good sensitivity, reasonably high efficiency and low Q. Whilst the extremely long 4-layer high temperature voice coil wound onto an aluminium former, gives a high power handling capacity.
The phase plug reduces compression due to temperature variations within the voice coil, eliminates resonances that would normally occur in the volume between the dust cap and pole piece and increases power handling.
The L22RN4X/P also utilises and extremely stiff and stable injection moulded metal basket, which keeps all the critical components in perfect alignment. Whilst the large windows in, above and below the basket, reduce sound reflection, air flow noise and cavity resonance to a minimum.
Frame diameter: 221mm
Sensitivity (2.83v/1m): 86,5dB
Nominal impedance: 8 ohm
Frequency range: 20Hz-1kHz
Free air resonance: 21Hz
DC resistance (Re): 6.1 ohm
Voice coil inductance (Le): 3.76mH
Effective piston area (Sd): 220.0cm²
Moving Mass (Md): 40.0g
Force factor (BL): 10.7Tm
Excursion (lin-max): +/-14.0mm : +/-21mm
Voice coil diameter: 39mm
Nominal power handling: 125w ( 300w max )
Speed, a very lucid midrange, almost no compression at high volumes ( I do like my dance music and also, to play at realistic volumes). Bass overhang was much reduced, precision increased. In other words, a serious upgrade.
Next up, the crossover - read here for details