Os parametros mudaram um pouco em relação ao 308, olhem esse comparativo das versoes D4, destaque para a sensibilidade, materiais usados na fabricação, frequencia de ressonancia e resposta de frequencia e parece que a serie D2 saiu de linha, agora so tem 309 (free air), 309S (bobina simples) e 309D4 (bobina dupla).
TS-W309D4
* Maximum input power 1.400 W
* Nominal input power 400 W
* Impedance 2Ω / 8Ω
* Frequency response 20 - 220 Hz
* Lowest resonance frequency 37 Hz
* Sensitivity (1W/1m) 94 dB
* Woofer size 30 cm
* Woofer material IMPP Composite Seamless Cone
* Voice Coil type Dual
* Dual 4Ω voice coils: 2 or 8Ω Yes
* Voice Coil bobbin type Aluminum, diam.2 inch (48mm)
* Pole Yoke Type Extended and Vented pole yoke
* Magnets Double-stacked, high power
* Terminals Push-type
* Recommended sealed enclosure 24,1 - 49,5 litres
* Cut-out Hole 283 mm mm
* Mounting Depth 153,1 mm mm
* Surround Dual Layer, Fiber Reinforced Elastic Polymer Surround
TS-W308D4
* Maximum input power 1.400 W
* Nominal input power 400 W
* Impedance 4Ω
* Frequency response 20 - 180 Hz
* Lowest resonance frequency 34,5 Hz
* Sensitivity (1W/1m) 92 dB
* Woofer size 30 cm
* Woofer material Interlaced Basalt / Aramid Fibre Reinforced IMPP Composite Cone
* Dual 4Ω voice coils: 2 or 8Ω Yes
* Voice Coil bobbin type Phenol resin coated glass cloth bobbin
* Pole Yoke Type Extended and Vented pole yoke
* Magnets Double-stacked, high power
* Terminals Push-type
* Recommended sealed enclosure 24,1 - 49,5 litres
* Surround 3-Layer Fiber Woven Radial Surround
No meu ver tem tudo pra ter ficado melhor (teoricamente), agora é testar na pratica .
Abraços!!