Systems List › Velodyne › DD18+
NotesAfter running through the full series of tests with the big Velodyne having its servo set to max and at minimum it is obvious that the higher setting performs better. With the minimum setting the response is less flat and rolls off towards the top end which is probably due to driver inductance and is the natural shape of the DD18+ response. With it set to its maximum setting of 8 the response is considerably flattened out and the top end is extended better. That alone would be enough to recommend it.
Initially it was assumed that the higher servo gain setting would reduce the maximum output achievable. After testing the DD18+ both ways this has been proven wrong. The maximum output achievable is virtually no different between the two.
The last aspect of performance to look at was the distortion performance. Here there is a notable difference and it favors the highest amount of servo feedback. If the THD comparison chart is looked at, the deep bass distortion shows a large improvement at the same output levels with the servo gain cranked up. At the top end it might appear at first glance that the lower gain setting actually produces lower distortion but that would be misleading as the output is greatly rolled off over that frequency range when the servo gain is at its lowest setting. Thus the DD18+ is being asked for less output at those frequencies when configured that way. The deep bass distortion improvement from setting the servo gain all of the way up is impressive and validates the Velodyne claims for the servo technologies distortion improvements in my eyes. It seems to be more effective at the deepest bass frequencies. The overall distortion levels I consider to be quite good considering the output levels involved.
There have been some suggestions after the DD18+ results came out that the distortion is ridiculously high and deflates Velodynes claims. There have been some people throwing around distortion test results from other subwoofers taken under completely different scenarios, in room, lower drive levels used, close mic'd, different equipment, test signals used, etc, etc...Which are completely incomparable to a test such as these but yet they are being touted as better, or compared against the DD18+ THD results here.
Distortion test results from methods other than outdoor groundplane, with calibrated drive levels and known equipment, simply cannot be fairly and should never be compared, to those taken under the aforementioned conditions. If you want to compare distortion results from subwoofers compare them to only those measured in the same manner. In other words compare Data-Bass results to Data-Bass results. Otherwise it will not be apples to apples in any manner. Looked at in that light compared with other sealed subwoofers and subwoofer alignments measured in a similar manner, the DD18+'s distortion results are rather good. As far as validating their claims of 1% THD under typical use I don't see these results as proving or discrediting that as we have no way of knowing what Velodyne considers typical output levels and what environment the subwoofer might be in at the time. Also consider that there are a lot of other offensive noises that speakers emit when driven hard in a reflection free environment that do not show up on harmonic distortion charts. The DD18+ was completely free from any of those.