Quote:
Ricci wrote:
 I've come across something interesting in Illka's tests. I was running through the DIY subs that were tested and simulating them with WinISD to see how closely the predicted max output matched up with what was the actual real world results that were measured. Most of them are quite close, which was actually a bit of a surprise.
All of the subs had the most deviation from the theoretical down at the lowest freq's 12.5 & 16hz. The 2TC subs... TC2000 and LMS5400 were extremely close to what WinISD predicts. The TC2000 was short a maximum of 2.1db at 12.5hz from predicted in the 270L vented design. The LMS was off a maximum 0.9db from the predicted max output at 16hz in the 100L sealed  ! Seems like what you simulate is pretty close to what you will get with TC's subs.
The SDX subs on the other hand were way short of the predicted max output in both the dual driver 140L and single driver 100L sealed. They are both really close down to 25hz, and the 100L sub is only -2db off at 20hz. The 100L is 4db short of the predicted output at 16hz and 5.9db short at 12.5hz. The 140L dual driver sub is even further off from the predicted output...it is -6.5db at 20hz, -5.8db at 16hz, and -9.4db at 12.5hz  from what is predicted. I wouldn't think anything of this if the 2 TC drivers weren't so close to what is predicted.
Anybody have any thoughts on this? Seems like maybe the SDX really doesn't quite have 30mm of useable xmax? Perhaps the distortion just gets way out of hand even though there may be output left? Maybe the enclosure volume was too small? The 100L performed much better than the dual driver that only had 70L per driver... I'm just guessing here. |
Hi Ricci,
You can't really compare the CEA-2010 max output figures with the WinISD "max output figures" because the CEA-2010 numbers are THD limited (please see
this PDF for explanation on the CEA-2010 standard) and are using a burst signal instead of simple sine wave approximation of the WinISD. Also the WinISD approximation is only a function of the maximum power handling of the driver (Pe) or the maximum "linear" excursion (Xmax), whichever is reached first at each frequency. In other words it's EXTREMELY simplified approximation which basically doesn't always (ever) add up with the real word tests, even when not using any THD limiting or burst signals. Simulations are only simulations based on small signal T/S values which change a lot with larger input signals. Also basic simulations don't simulate the effects of any non-linearities (power compression etc.)
But when it comes to the SDX15, the CEA-2010 output down low is limited by the high 2nd order distortion component. This means that the compliance (Cms) non-linearity is quite high i.e. the suspension is causing a lot of distortion which limits the CEA-2010 numbers at the low end. The 3rd order harmonic is quite low which tells that the Bl related distortion is low, thanks to the XBL^2 motor.