I am intersted in opinions of electronic bass extension, specifically Greg Ball's design which can be found here:
This is a very thick topic. My short answer is... does Greg understand thermal compression?
Thermal compression is what happens when a voice coil is dissipating heat and the voice coil temperature rises. The resitance will rise when the heat rises and... viola' thermal compression happens.
First, In most rooms a sealed f3 in the mid-high 30s is about right. Other folks whom I respect in such matters agree. The room lift will correspond with the woofer roll-off and balance just perfectly. I do understand the room construction varies and rooms are VERY spotty with low bass. Most rooms start to have base nodes and modes below @300hz. Above 300hz, many rooms are relatively flat (massive reflections withstanding).
Second, I had a 25hz bass boost on my SCC300 subwoofer woofer with it's sealed F3 in the high 30s. I didn't like it. It sounded boomy and fat. I removed the bass boost and it sounded significantly better. The bass was nicely balanced. If someone else prefers the bass-boost for a SCC300 (or similar woofer), this is fine. But it is not my preference. I have been there and done that. I'll not do it again.
Third, it's possible to take ANY woofer system and equalize the bass to the desired level - no matter how insensitive the woofer. It's possible to make a 84db 4 ohm car audio subwoofer match a 90db 8 ohm monitor. However, the enerergy dissipated across the subwoofer doubles for every 3db of sensitivity gain and doubles when the impedance (8 ohms) is halved ( to 4 ohms). If the monitor is pushing 30 watts, the woofer needs 60 (97db), 120 (84db), 240 (4 ohms) watts. One industry guy commented that thermal distortion is the #2 cause of distortion in loudspeakers. I think the reasons are obvious.
Fourth, I DO understand that all loudspeakers suffer thermal distortion. However, the very best (and most expensive) way to accomodate this is by making the speaker more sensitive, and the cabinet resultantly bigger.
Once upon a time this was not true. High power amplifiers were relatively expensive, and bigger loudspeaker cabinets were relatively cheap. Most things were made in the USA, and shipping was a lesser concern. This isn't true today. Today's high power amplifiers are cheap, and the cost of shipping big cabinets sans damage is considerable. The cost of amplification is cheap, and the cost of shipping a high power amplifier from china is cheap. The latter are much more durable.
The only truly sad part of this is those big old speakers sounded good in 1 regard - dynamics. Anyone proud owner of speakers like these will convey this:
while these speakers are terrible in many regards, they succeed in dynamics. They have snap. This is simply because very little wattage is required to make the drivers move. It's a sensitive speaker and it works. So does the Tannoy Churchill.
There is a very small but very dedicated following for speakers with higher sensitivity using low power triodes. I believe there are many extremely valid reasons for their dedication, and wish to move in this direction. I will take a step toward this with my next project. I am confident that 40wpc is SE Tube is more than enough for my 85db 1801 speakers, so a 20wpc amp will commensurately be more than enough for a 89db 3-way speaker. It SHOULD be even better with a nice flat impedance curve. Please note that while this 3-way will likely shake most rooms with a bigger amp, this will not be my personal objective. I'll use the speaker on a quaint 20wpc SET.
On a personal note... I heard an amazing young gal sing this past weekend. She sang in an old Lutheran church with a wood celing and plaster/brick walls. The room was fairly quiet. There was no amplification, and she wasn't loud, but... oooooh it sounded good! The resonance of her soprano voice in that old church was sublime. Her control, enunciation and pitch were perfect. It brough tears to my eyes. THIS is good music.
