You're looking at a classic case of diminishing returns. I have not had the privilege of hearing the 1812, but I will bet it's one heck of a sub! If someone had the disposable income and was inclined to spend that much of it on a sub, I would recommend they audition one even though I haven't heard it. For the more fiscally conservative (or obligated) I would point them in different directions.
"The 1812 contains - you guessed it, an 18 and a 12, each powered with their own DD-based amp and DSP-driven control circuitry. The cones are made of a Rohacell material that makes them lighter and stiffer, which is essentially the only difference in the drive trains from regular DDs.
The crossovers are pretty interesting (speaking of course, as the guy who coded most of it). The 18 handles from infrasonc up to about 60 Hz, and the 12 handles above that. This frees headroom for both units, and lets the unit get really, really loud - I say without exaggeration it is the loudest, cleanest thing we have ever tested.
The crossover point between the 12 and 18 units is not fixed, and neither is the slope. The crossover point slides up and down as the whole sub's crossover slides up and down. The trick in the crossovers is the phase and slopes. It's easy, by moving the system crossover and as a result moving the sliding crossover between the 18 and the 12, to have a big suckout (cancellation) at the 18/12 crossover point. So, we had to devise a special phase and slope table that keeps the 18 and 12 in phase and flat even as the crossover point changes. I'd lke to say we devised a special formula for the relaitonship, but the reality is that it was with not a small amount of trial and error that we finally got it tuned!
Anyway, I hope you like the sub. It is quite a beast.
I got this from a Velodyne forum and I guess it explains why it's so expensive.
Wouldn't there also be the advantage of being able to tune the two sub enclosures for better frequency response? Such as giving the larger sub up 60 hz a slightly more boomy sound to make sure the lfe on movies hits hard and low. Then use the 12 in maybe even a sealed box for good accurate bass for music. I assume if they got the tuning right? Could you accomplish the same thing with a tunable crossover and two home built sub enclosures for allot less?
That may be true, but the idea is to let the different sized drivers handle a more specific range of frequencies, and follows the same logic as having seperate drivers for the mid-range and high frequncies.
The VMPS Larger subwoofer operates in a similar way, allowing a lower moving mass 12" driver and a 15" larger-displacement driver to operate in tandem. There is no crossover between the two woofers, though. The Larger Subwoofer also features the adjustable-damping passive radiator which is slot-loaded. It does not use the servo control circuitry to extend its bass response. Indeed, Brian Cheney, designer of the VMPS Larger Subwoofer, has called the servo effect "decidedly weird". Yet, the unpowered subwoofer, which retails for less than $1500 and requires an external amplifier, has bass extension down to 17 Hz.
In reality you're all correct on some level. I'm not here to bolster the product, but in some ways it is a good thing, and some it doesn't offer much benefit. First, the HGS and DD series of Velodynes employ a lot of electronic correction which requires power and pushes the drivers quite far at low frequencies. They electronically protect the system to prevent damage. If you are always within this limit they work quite well. That said, the limit gets lower and lower at lower frequencies. If you drive the sub into significant limiting or protection, you can hear this, and it adversely affects anything else being reproduced at the time. Now realise this happens with almost any sub, the question is at what level for a given frequency. For as similar but more extreme action (the Sunfires have similar behavior), take a look at the response curves for the 21" Bag End in the July/August issue of Ultimate AV.
So, the down side to the 1812 is that you don't have much significant increase in output at any given frequency over the single 18". The benefit is that you can drive the snot out of the 18" without adversely affecting the upper bass output of the 12". This WILL result in a higher output capability on real program material. There is of course the other benefit in that naming a subwoofer the "1812" is a marketing department's wet dream with the 1812 overture cannon shot reference.
I just read that Stereophile AV sub shootout and had a question about the Bagend S21E vs the DD18. According to the article, the Bagend produced 20% THD at 20Hz while the DD18 produces only 1.8% THD at 20Hz according to Secrets of Home Theater review. Is this low THD due to the servo mechanism?
Hi Mark, The HGS and DD products do both use electronic correction, but the way in which they do it is dramatically different.
Both DD and HGS use an accelerometer on the cone to provide a servo loop which, contrary to popular belief, is not a dampening system - it ensures linear response down to the lowest frequencies. In fact, sometimes the servo causes the unit to drive a lot harder down low because the sub might otherwise roll off without this correction.
Both DD and HGS have "gain compression" that protects against overdriving as you describe, but that's pretty much where the similarities end.
While the HGS system is analog, DD is all digital, controlled by a Texas Instruments DSP computer. In a digital system, the speed at which you can effect cone correction via the (now digital) accelerometer and the precision to which you can tune the gain compression rise dramatically. The phenomenon you describe for HGS overstepping its gain compression is affectionately known as a "bruck". With DD, brucks are far fewer and not as severe because we can, via the software, trap overdriving much more efficiently, precisely, and proactively, and recover from it more gracefully. The result is the ability to push the limits of the driver and amp much closer to their physical limits and produce more low-distortion output. Not to mention the fact that the DD cones have 1/4" more excursion.
As far as the 1812 performance goes, I will tell you that we test subs here all day long. Freeing the upper frequency range form the 18 really does allow the whole unit to play louder - a LOT louder. The 1812 is a product I am honestly scared of.
Hi Len, Yes, primarily. With us it's all about the distortion. We patented the servo feedback system back in the 1980s and now that it's digital it has even more "loop gain" (that is, correction effect). We also use dual push-me/pull-you voice coils and other mechanisms to lower distortion.
Thanks for your reply, Bruce. Hope you didn't mind me quoting you.
I have a couple of questions. The dd18 has a frequency response of 14-120 Hz with less than 0.5% harmonic distortion while the dd1812 has a 15-120 Hz response and a less than 1% harmonic distortion. Do these specs mean that the dd18 is a slightly better sub?
The other question is why is the dd1812 385 lbs? How can anybody move it around by themselves?
Finally, I know this sub will be reviewed in the Sept/Nov issue of Stereophile AV. Any idea how it placed amongst the 12 subs reviewed?
One thing of interest is that the reviewer discovered that you can use a single DD series sub in conjunction with multiple other non-digital subs, and still reap the benefit of the digital e.q. processing. I find this is great news. I currently have two of Velodyne's older subs (ULD-15's), and was considering selling them, and buying two DD-15's. Now, I'm considering keeping the ULD's, and just adding a DD-18.
By "this sub", you mean the DD-18 of course. I honestly have not seen the copy, but even if I had Mr. Yates and company would be quite unhappy (and justifiably so) if I revealed anything about the review prematurely. We'll see!