15" vs 18" subwoofer - which to buy?

I am interested in getting DD12. DO you guys use the speaker level or the line level input? And if using line input, is there benefit in using the line output back to the amp? ( increase dynamics vs lost in trnasparency)

Thanks

If you want to hear a musical sub, give a listen to the Bag End Infra-Sub 18. I've heard and owned many subs including NHT Sub Two[stereo pair] with four 10", and Vandersteen with three 8", B&K 15", A stereo pair of Onkyo THX from a $3000.00 speaker system[CRAP] and for 2 channel nothing comes close!!! Although its protection circuitry will shut it down if played loud for any length of time but I’m talking 115 db of dense bass

My gosh, I had to buy TWO gas masks for all the BS I smell in this thread. Talk of stereo bass, need for numerous 18" subs, small Velodynes as toys. The word NEWBIE is written all over this thread. For the umteenth time, it really boils down to just a VERY few things;

What size is your room?
How loud do you like to listen ON AVERAGE?
*if I asked most of you, you would have no clue (we're talking spl's here).
Is the sub capable of low distortion output?

That's all you need to know...period.

Will a larger DD-18 be able to play as well as a 15,12,10 etc. at lower levels? Duh: Of course. Will those other subs have the same low frequency extension as the 18"? Of course not.

As a general rule..according to Velodyne;

2 DD-10's will have slightly more output than a single DD-12, but also slightly less extension. (this extension thing can get a bit complex to explain)
2 DD-12's will have slightly more output than a single DD-15, but with less extension.
2 DD-15's will have slightly more output than a single DD-18, but with less extension.

As for the use of dual subs, there's really only one reason to do this, and that's usually because there's not enough output from a single. And actually, it almost always makes more sense to just get the next size up in subs. I had a DD-10 in my 3500 ft³ condo living room and it did just fine for both music AND movies. No, the low end did NOT have the impact that an 18" would, but damned well did just fine for living in a condo.
I recently moved up to a DD-12, and I couldn't wish nor ask for more. It produces MORE than enough ground shake and special effects for my needs...and I'm an experienced listener.

Like I said, it all depends on how loud you listen to your material. Most folks on these forums (and even folks from Velo) will convince you that you need massive amounts of subwoofing power, but once you get over the initial goofing around/testing it out/demos for your buddies, I guarantee you that you will very likely just "SET IT AND FORGET IT". Trust me, if you're making the most out of dual 18" subs in even a LARGE living room, you're probably doing damage to your hearing with your main speakers.

My buddy has had both a DD-15 and a DD-18 in his 4000 ft³ space and although he's kept the DD-18, he acknowledges that the DD-15 was MORE than enough for his room. He just happens to be the type of guy that needs to have the biggest, baddest, toy of ANY kind. Perhaps he's compensating for something else? :)

The smartest thing that any potential buyer can do is borrow any sub he's interested in and take it hope and play with it a little. Properly calibrate it to your mains and listen to all kinds of material, from music to HT. I'd be shocked if anybody in a 4000 ft³ space absolutely feels the need for 2 DD-18's, much less one. If I could tolerate the size, I know for a fact that a DD-15 would be the max I'd ever desire for MY room, but with my DD-12, I don't even feel the need for that. Then again, I don't listen to loud organ music.

Oh yeah, I forgot to mention the some folks use two subs in order to attempt to smooth out some of the peaks and nulls in the listening environment. Takes lots of time, practice, and measuring equipment to accomplish this effectively.

Truthseeker -

Funny comment:

"My gosh, I had to buy TWO gas masks for all the BS I smell in this thread. Talk of stereo bass, need for numerous 18" subs, small Velodynes as toys. The word NEWBIE is written all over this thread"

Kinda feel that is pointed directly at me since I am the one commenting on using a pair of DD-18s. You picked Velodyne why? You picked a DD-12 and then a DD-15, why?
You picked your main speakers, why? You picked you preamp, why? You picked you cables, why? You picked your transport, why? You picked your power conditioning, why?
I will give you the simple answer: Because you prefered it over another. This is no different than why I personally run a pair of DD-18s.

So many folks say bass is non-directional. Right. While this may be true below a certain point, 20hZ or whatever it is, a sub going from 60hZ (or whatever one has it crossed to) to 20hZ or less is directional and I personally can hear poiint out where it is coming from. Now, if I had a 30,000 sq ft auditorium, there is a much great chance of not being able to do so. Unfortunately, such a thing here in CA is about +$20M, albeit not much more than a home!

When properly set up and calibrated a pair will always sound better than a single.

Dan