- 30 litres volume (maybe up to 40 ltrs if stuffed properly),

- 8” woofer.

For the sake of quality of measurements I have decided to go for the closed box design.

One of my key targets is to use DSP to boost the bass to get possibly linear FR down to 25 – 30 Hz. I have been analyzing the topic for some weeks and for now I have come to a conclusion that one important factor is the maximum linear excursion, as this defines the max SPL for bass.

But an even more important thing for me seems to be using DSP bass boost as little as possible since this e.g. limits the overall dynamics of the speaker. So I thought the best selection criterion for the woofer can be the level of reference SPL in the 30-ltr-enclosure at some low bass frequency, say 27 Hz. I made some preselection and landed with the following woofers based mainly on their ( low) f3 in a sealed box, suitable Vbox, max linear excursion (in some cases) and reasonable pricing.

So the list is for now is:

- Visaton TIW200 XS, 12,5 mm linear exc. max

- Wavecor 223BD01, 10,5 mm

- Peerless HDS-P835026, 6mm

- ScanSpeak 8555, 6,5mm

- Seas L22RNX, 6mm

I calculated the reference SPL for each of the drivers using the formula that takes into account the differences in Re: 112dB +10*log10(n0*8ohm/Re)

where 112 dB – 1W radiated into semisphere at 1m

n0 = 9.64*power(10,-10)*Fs3*Vas/Qes

Because I factored in Re I think I am effectively making the assumption that I have power in abundance which improves a little efficiency for drivers with low Re, right ?

However this calculation did not help me a lot as a bit surprisingly most of these drivers land at 30 Hz at similar efficiencies (within 1,5dB, Scan 21W8555 being the best). This could actually speak in favour of more efficient drivers with higher f3 like Seas LR22 since it has at least noticeably higher efficiency at 40-50 Hz where significant bass energy is located (more than in 25-35 Hz) ?

I am also a bit unsure if the efficiency calculated this way (factoring in Re in particular) is really reliable enough since in reality amp power is pumped into the driver impedance not Re ?

What do you think of my line of analysis and conclusions ? What would you take into account on top of/instead of what I did ? What would be your drivers of choice for this kind of application ?

Regards, Pawel