Thinking I need a Sub...

To clarify re: "overloading the room".

That is not - and never has been - the issue for me.

When setting up strictly by ear, I always start by attempting to level match at the x-over point. I have generally been good to within +/- 5db in that job (the most critical set-up element IMO as smooth response thru the "hand-off" is critical to seamless integration). That result is always verified by measurement after the fact (and subsequently tweaked).

The issue with the approach is generally "lumpiness" - I've always had 10+db peaks and/or nulls without EQ - despite exhaustive placement optimization efforts. Sometimes there's a somewhat excessive bass balance overall, sometimes it's a little light overall. It's never particularly smooth - as measured or (more importantly) as heard in A/B comparison with subsequently EQ'd bass.

The issue is virtually moot with bass management software. The Audyssey set-up protocol involves setting the average aggregated sub output at 75db per measurement on a bass sweep. The resulting measured on-axis FR is essentially flat across the entire range of the system. The difference between pre EQ and post EQ is not overall bass level, it's freedom of peaks and valleys in the response. The audible difference is not in overall bass level, it's in articulation through the bass and mids.

While my subs have the capability of producing much higher SPL (the 75db start point results in the gain pots being near the low end of their potential travel), the benefit here is less driver excursion and distortion. A peek at measured distortion tests will reveal VERY large values (often well north of 30%) for most subs as driver excursion (and SPL) increases, but I'll pass on the debate as to the audibility of this phenomenon. I will only note that the remaining potential clean output of the subs that is foregone by my set-up ensures that I've minimized distortion - for whatever you think that's worth.

The bottom line is: this ain't about overloading the listening room

Listen for yourself. Wolf is an experienced professional sound guy and I respect that credential, but I've always been surprised by his emphatic stated preference for non EQ'd subs. As noted, in my book this is a black and white issue, but - as also noted - I appreciate that other people's books are different from mine.

As a side note, I usually have a guitar in my hand 3 to 4 hours a day and feel pretty good about the subjective side of this evaluation as well as the measured evidence, The good news is, this is a very easy, very clean A/B testing opportunity - as long as there's a good, high-end AV place locally. IMHO, everyone who cares should satisfy themselves on this one.

Wolf,

I thought my statement re: distortion was clear enough, but here's a link that should be crystal clear:

The REL R-305

http://www.hometheatershack.com/forums/subwoofer-tests-archived/990-rel-r-305-a.html

If you scroll down to the THD graph, you'll see that this sub produces +/- 30% THD at +/- 30hz at 90db (quasi anechoic). BTW, this is hardly crushing SPL and as you turn it up, the story gets worse. The direction of these curves says a lot about what happens to THD as excursion increases, which was the real point of my OP.

Hope that this clarifies precisely the frequency/output levels at which a familiar sub reaches 30% + distortion.

The mention of guitar was merely made to point out that my comments were subjective as well as empirical. I'm a musician (tho sadly not a terribly skilled one) and my subjective evaluations are based on many hours a day around live music (my own) - for whatever that's worth.

And, while I play more acoustic than electric guitar, if the distortion in your class A tube amp is anything like mine, it is to be treasured - talent in a box. Not quite applicable to the conversation at hand IMO.

I guess we do.

Well, at least you've kept your sense of humor.

Sorry if any post I've contributed here reads as condescending - that was never my intention. I've tried to keep it civil but on point. Guess I came up short. What can I say? Sorry.

You can doubt what you like, but these test results are completely consistent with pretty much every other published set of #s I've ever seen on subwoofer tests. I 've reviewed a lot of test results on a lot of sites over the years and they all show the same thing: Most subs (regardless of brand) produce large amounts of THD as excursion increases, which was my point.Have a go at Google, if you like. Maybe there's been an epidemic of poorly calibrated test mics out there - who knows? (Alright, that might be condescending - but you earned it.)

I chose a REL sub as an example, not because it fared poorly (tho most RELs did consistently fare poorly vs the pack back when I was current on the data), but because it's a brand you know. It was simply to limit the debate a bit. It's entirely possible that newer REL models fare better, but none will fare particularly well, because -other than a few absolute monster efforts in no holds barred design - no subs fare particularly well on this test.

That point isn't meant to be condescending. You made the observation about powerful subs, room overload, etc. In fact, that was the condescending statement in this thread. My response was only meant to demonstrate the reasoning behind running powerful dual subs at settings designed to minimize excursion. I still think it's a pretty reasonable point - neither humorless, condescending, nor "douchebag-ish".

As to the guitar amp comment - that was largely context for other readers here. So, give it a break.

I've never stated that my opinion as to best practices for subwoofer installation are gospel. I acknowledged your credentials and stated that qualified evaluators - like you - disagree with me. I've consistently stated that anyone interested in making a determination should try an A/B and decide for themselves.

You might want to reconsider before pointing fingers again.

Neo,

Since Bob and Wolf (both pretty convincing contributors here) are providing conflicting advice, I'd suggest that you find a good high end HT installer/retailer and do an A/B comparison with Digital Room Correction and without it. That's a simple bypass button and a very clean A/B.

You've got to find the right showroom so that the sub placement is optimized prior to room correction EQ. Then, you can decide for yourself.

For the record, I've done that in my dedicated listening room with two different pairs of subs (Rythmik and Velodyne) and in my HT room with B&W subs. The positioning of the subs in the listening room was optimized both by ear and - on a second pass - with the aid of a real time analyzer. In the theater room, the position of the subs was largely dictated by the room layout, so there was much less flexibility in optimizing location.

In all cases, room correction made a dramatic improvement - to my ear. In fact, by my reckoning, no other change to my system over the last two decades has come close. But there's a caveat.: Since Wolf's mileage seems to vary from that conclusion, be aware that yours may, too. Which is why an audition at a retailer who can do it right is probably your best bet.

Marty

As to the active/passive (distortion) debate, that's a tougher A/B since most systems (that I know of) kill the sub output entirely when you remove the active low-cut filter from the main speakers. That means you'll probably have to re-wire the system before you can compare active crossing to passive which makes the judgement more difficult IME.

I find the theoretical arguments for actively crossing a system pretty compelling, but my experience suggests that it's very much case by case dependent upon the main speakers. I've done it both ways and had good success with both - but the best results I've gotten have come from actively crossed systems. If in doubt, I'd say cross actively but would note again that YMMV.