I've never been able to afford high xmax drivers until just lately with the release of the SI HT 18. So I never really bothered taking the time to simulate the possibilities. As expected, this type of driver is not a good choice for high tuning. Even with the ~ average 16 hz tuning you can't really use all the available xmax without dramatically surpassing the rated power handling (which may not even be an issue since this driver is apparently able to handle much more power than rated). So I kept lowering the tuning until I could actually use all the available xmax but the port size requirements ended up unrealistic. So I tuned even lower, just for fun to see what would happen. This is what I came up with.
That's dual SI HT 18 drivers in a Gjallerhorn size (external) ported box tuned to 2 hz with 1000 watts applied. Above 16 hz the Gjallerhorn wins but below 16 hz the SI box wins. (Comparing SI simulation with Data-Bass Gjallerhorn measured results, so it's not completely fair or accurate but that's the way it looks.)
I was surprised to see that I could get by with a 2 inch diameter port! It's 90 inches long but who cares, resonances are clearly not an issue and the entire port only takes up 10 liters or so of the box volume. Obviously it will chuff - but only below 3 hz, and who cares about that? Besides, applying a roundover on the port will probably make it chuff-free down to 2 hz and below that chuffing really doesn't matter much.
This can be used without any high pass filter at all, although amp turn on thump at full power will ruin your day in a dramatic way if that's not taken into account. You can see on the excursion graph that with 1000 watts there's no excursion problem until 1.5 hz and down.
The only problem I see is in other simulation programs, they show higher velocity and the velocity peak at ~ 75 hz might cause audible chuffing.CONS
- large size (although just like a sealed box you can make it smaller and eq to taste)
- large excursion requirements (the high xmax, low cost driver takes care of that issue)
- it will chuff below 3hz (possibly 2hz depending on effectiveness of port roundover), and possibly at 75 hz alsoPROS
- I see lots when I look at the graphs above (the blue line in each graph is IB response for the dual drivers for comparison purposes)
I should probably mention that even without a high pass filter, most amps are not flat to DC, so 2 hz tuning is not necessarily required to get the advantages shown here, even 5 hz tuning might be passable.
Opinions? Comments? Criticisms? I've never tried anything like this before so I have no idea if I might be overlooking something.