Besides Qts and Fs, Xmax of a driver I am trying to figure out the importance of Vas to help me decide on a driver selection.
Lets say we've got two different 15" drivers. Similar Qts Fs Xmax, what differs is Vas. This determines the compliance of the suspension. Correct?
We have a driver with 6ft^3 Vas and the other one 15ft^3 Vas.
For true ib sub, volume is not an issue, and so higher Vas driver seems preferable. Criteria being sound quality -- clean, punchy, detailed bass. Am I correct, or are the guys at parts-express correct when they say Vas is not important with ib?
Ok, I did read the link you provided. However, still I have a question. Below are three drivers by Dayton. I know they make a specific IB driver. But I am trying to figure out Vas importance and how it effects sound quality.
All have Qt between .4 and .5. Fs around 20Hz. Vas is what differs significatly. The first driver has the highest Vas by far at 12.59 ft^3.
Xmax is above 5mm for all drivers which is what I am looking for. I do not intend to drive these hard. In fact I do not want to drive the sub over 1mm excursion for the most clean sound. I will have to use about 20 of them, I realize, for an adequate output, but that is better than driving 4 hard, near xmax limit.
Does the high Vas value mean that driver cone will be most controlled by the suspension and exhibit a detailed sound, precise motion without overshoot? How will the highest Vas driver of the three sound compared to the lowest Vas (driven at low level)?
That is what I am trying to figure out before purchasing more drivers for a sound quality test.
I appreciate your reply. It's a personal taste thing I guess. I just don't know about those metal cone drivers... I am trying to stick to paper cones for my whole system, including the tweeters and the bass drivers.
Perhaps the Dayton woofers are not the best but maybe some AE woofers will be. I will unfortunately have to listen (purchase) to them to find out.
It's like eating genetically modified food. It may be technically good but the flavor is not the same (at least in my mind
Rather ironically, by choosing to use a lot of drivers, to limit excursion to some arbitrary level, you are deliberately making Vas an important factor.
Even with small Vas drivers they multiply very rapidly into a huge Total Vas as you keep adding drivers. Vas x 40 for four drivers. Vas x 80 for 8 drivers. Vas x 160 for 16 etc.
Do you have an open plan home and a vast roof space or cellar? As you add drivers you increase LF pumping efficiency. Unless you have a large listening room and similar volume for your IB enclosure you will push up the resonant frequency of your drivers. The room and enclosure will end up being cyclically compressed like an opposed cylinder piston engine (or pump) with a single crank pin.
Compression will be distinctly non-linear with an emphasis on VLF. This will boost infrasonics as if you had massive room gain. You might need to add a high pass filter just to avoid moving the furniture around. As the bottom end tilts up you will lose your upper bass as it sinks below the weight of the VLF. I made this mistake and felt that my 8 x 15" IB had no impact compared with my previous 4 x 15"s. I made the upper bass more prominent, by reducing the low end, so now I no longer think so.
You should be aware that even four 15" drivers hardly move on most musical programme material. Only very low frequencies require much excursion. Above 40 Hz you can easily produce 130+dB without any visible cone movement. That's with only four 15" drivers. Though film LFE will certainly get four drivers moving well at spirited levels. Much less so with eight 15" drivers.
I'm all for adding more drivers myself but have already reached the limitations of my own undersized enclosure. I am already losing the bottom few Hz thanks to the compression of my very leaky 600 cu ft enclosure. Those missing, sub-10Hz frequencies may be inaudible but they are seriously diminishing my bragging rights.
Balance is required in all things. Including IBs. Emphasis on one aspect will affect the entire installation. Not necessarily for the better.