Subwoofers~SVS vs Tapped Horn vs Fitzmaurice THT

[CECAA850]

READING

[CECAA850]

From the FAQ

7) How many drivers should I use?

This is a difficult question to answer accurately given the variables involved. To error on the side of safety, we recommend using at least double or more the Sd of that needed by a box sub used in the same room. In a small room 2-15"s should be adequate. For larger spaces or for high output, multiple 12"s, 15"s or even 18"s are desirable. People should understand the IB bass is much different than the bass from a standard 'box/tube' sub. Because of that, we recommend use of more drivers than one would normally associate with a 'normal' box sub. Please note, the primary function of using significantly more drivers is to maintain extremely low distortion and protect the drivers, not to create insanely high SPLs.

7a) Why do I need more drivers in an IB than a standard box sub?

The enclosure (for a small sealed box) functions as an acoustic high-pass filter. That acoustic filter acts to protect the driver from over excursion at lower frequencies because it rolls of the output as the frequencies go lower. Since an IB has no 'box' per say, it doesn't benefit from the protection from the acoustic filter. This lack of protection from the acoustic filter also means that an IB easier to drive at lower frequencies. As a result it's easier to hit the limits of the suspension because IB subs play so low.

[StephenM]

Something else to demonstrate why you need more drivers for an IB:

http://www.baudline.com/erik/bass/xmaxer.html

As mentioned, the SVS PB13U has been measured to put out 105dB at 16Hz with a 13.5" driver, at 2 meters ground plane, equivilent to 1 meter anechoic.

A single 13.5" driver in an IB installation would need a little over 42mm of one way Xmax to provide comparable dB. That's over three inches of peak to peak travel.

[CECAA850]

Using your calculator (pretty neat) a single ficaraudo 18" IB driver would best the mighty SVS. It has about 30mm xmax and runs about $250. 4 of them would loaf along at a little over 5mm of travel for the same SPL.

[artto]

OK, then lets say I can get three 18" or 21" drivers mounted in the wall under the stairway. Most of the subwoofer drivers I'm seeing have an Fs of 22Hz to 30Hz and the spec'd low end frequency response (for what that's worth) down to 22Hz to 30Hz also. I suppose in an IB situation that doesn't matter quite as much since the back wave is open to an isolated large area? (larger than my listening room) This is still going to go down to 16Hz without EQ?

[CECAA850]

16 Hz shouldn't be an issue at all. You'd need to EQ if you wanted FLAT to 16 Hz as IB's roll off similarly to a sealed sub. I've got about a 10dB drop off from 20Hz to 10Hz on mine. I don't use EQ to flatten it out. 20 to 16 Hz would most likely only drop off a couple dB but I haven't measured it.

EDIT, the Fs on my drivers is 17Hz but you can't get them anymore.

[StephenM]

Using your calculator (pretty neat) a single ficaraudo 18" IB driver would best the mighty SVS. It has about 30mm xmax and runs about $250. 4 of them would loaf along at a little over 5mm of travel for the same SPL.

Remember though, the calculator is giving you 1 way xmax (don't know if Ficar is giving 1 way xmax or not in their specs), so you're still talking about a cm of total travel for 4-18" woofers.

[artto]

THNX guys ~ great stuff []

What are you using for EQ? Most everything I know of only goes down to about 30Hz or so center frequency. I realize that any EQ will most likely be used for cut (as opposed to boost).

If I go this route I may just buy a Crown XLS1000 with the built-in DSP so I can use it's low-pass filter which I think the lowest Freq. is 50Hz. I'd like it a little lower, but....

[CECAA850]

I use a BFD but don't mess with anything below 20Hz. I mostly use it to handle some nasty room peaks.

I'm sorry I'm not familiar with your gear. There's no lowpass filter anywhere in your chain? Have you looked into a minidsp?

[DrWho]

Hey Art,

For your application, you're going to need the lowest distortion subwoofer you can find....that's automatically gonna move you away from the THT and the SVS.

The tapped horns have good distortion numbers, but have a different kind of sound to them. But if you're doing organ stuff, then I think they're gonna work out really well for your application.

Are you familiar with the "data-bass" that Ricci has been putting together? That guy has been busy comparing the subwoofers out there:
http://www.data-bass.com/data?page=systems&col=1&type=2&sort=desc&mfr=-1

You can sort the various designs he's tested by clicking on the headers and whatnot, and then there's links to the measurements and build information.

The Gjallerhorn may be a good fit, but don't overlook the simplicity (and smaller size) of the direct radiator with passive radiator. Not in Ricci's list is the LMS-5400 with dual 18" passives. Illka did some measurements though:
http://www.hometheatershack.com/forums/subwoofer-tests-archived/6015-index-subwoofer-tests-manufacturer-model.html
(One thing to note is that you can always lower the tuning of the passives by adding some of the washers they come with)

In the range below 100Hz, the LMS-5400 actually has less distortion than the khorn for the same SPL.

Anyways, there's a lot of great info and other designs available on those two links. One thing to keep in mind though is that the way the tapped horn "taps" the acoustic impedance, you're really not going to see any benefits from room gain.

As far as amplifiers, I would highly recommend steering away from the XTi series if you want extension below 20Hz. You'll want to look at different amplifiers / processing for this application...though that's gonna depend on which speaker you wanna go with.

[CECAA850]

Using your calculator (pretty neat) a single ficaraudo 18" IB driver would best the mighty SVS. It has about 30mm xmax and runs about $250. 4 of them would loaf along at a little over 5mm of travel for the same SPL.

Remember though, the calculator is giving you 1 way xmax (don't know if Ficar is giving 1 way xmax or not in their specs), so you're still talking about a cm of total travel for 4-18" woofers.

I thought all xmax figures were 1 way. Isn't that the t/s definition?

[CECAA850]

Hey Doc, I remember reading the Gjallerhorn build. Did he ever get the panel resonance handled?

[DrWho]

I don't remember - I've been outta the loop for the last few months. Life's just been way too crazy.

And you're right, xmax is supposed to be the one way displacement - and it's supposed to be to 70% Bl, although some manufacturers subtract the winding depth from the gap height.

[StephenM]

I thought all xmax figures were 1 way. Isn't that the t/s definition?

It's supposed to be, but that's never stopped anyone from fudging it either.

Edit: One reason why it's confusing:

http://en.wikipedia.org/wiki/Thiele/Small

X_max - Maximum linear peak (or sometimes peak-to-peak)
excursion (in mm) of the cone. Note that, because of mechanical issues,
the motion of a driver cone becomes non-linear with large excursions,
especially those in excess of this parameter.

[CECAA850]

I guess that would be the difference in xmax and xmech. As far as the ficaraudio drivers go, I've had great luck with them and they seem to run true to spec as far as I can tell. Here's a Q series driver.

[StephenM]

Looks like a meaty son of a gun for sure. Pricing is pretty impressive too, especially since they're US built.

[artto]

Geeez Mike, some of those are HUGE! I realize I have a generous amount of space, but I like the openess, and the way it sounds, that's part of the "effect". You've been here before. Maybe it's time for another visit. I've made a few changes since you were over. Maybe you could get a better idea of what I'm trying to get and need to get there without spending megabucks or turning half of the room (or house) into a subwoofer (I already have some issues with the neighbor on that side of the house). Since I've added stacked MegaLENRDs and some source and equipment changes, on some source material it seems to go down pretty low, just needs some boost down there that the Khorns were never intended to deliver. And who knows, maybe I'm just chasing after a lost cause. Sometimes "less is more".

EDIT: BTW, this all kind of started with a tapped horn. I was going to buy the one a Forum member had for sale but someone beat me to it by a day or two. I kind of liked the idea because I could put it under the record cases replacing the existing riser and not loose any real estate. But then I started thinking........and one thing led to another.

[DrWho]

Haha ya, horns that go low tend to be kinda big []

I agree that you don't want to give up any of that spaciousnes/imaging that you've worked so hard to achieve - I can see how a big box might affect that a bit. I recall your room being fairly wide? What if you did a custom tapped horn that ran along a floor/wall corner where it wouldn't affect the size of the room too much? Maybe something on each side of the Belle between the Khorns?

I definitely agree with the less is more approach, but getting good quality bass that keeps up with the performance of the rest of your system is gonna require a little brute force - them wavelengths are just so fricken huge.

Btw, my perspective is that tapped horns only save you money when the individual drivers are too cost prohibitive. In other words, building two vented boxes that take up the same space as the tapped horn is going to yield very similar performance (if not better in some regards). You're basically exchanging the cost of the extra driver for the cost of wood (and a more complex build).

Heck, why don't you just throw two dual opposed 18" cabs in the front of the room - one on each side of the Belle and call it a day? There's a ton of drivers out there that would play nice in this configuration.

[artto]

Heck, why don't you just throw two dual opposed 18" cabs in the front of the room - one on each side of the Belle and call it a day? There's a ton of drivers out there that would play nice in this configuration.

Yeah, then I'm kind of back to something I was considering a couple years ago, a pair of Bag End D18E-AD with their INFRA Integrator (or D12E-AD) on either side of the Belle or possibly behind the vertical panels, or one D18E-AD under the Belle. I still might go with the tapped horn like the one Tom (Quiet Hollow) built.

[formica]

Hey Art...

How have you been?… You’ve been getting pretty good advice already...

An Infinite Baffle subwoofer. It uses multiple drivers for low distortion. Mine will do 100dB @ 10Hz (corrected) at the listening position which is about 14' from the sub. My living room is not sealed and has 3 large openings. There's no sub in the room but the drivers must be mounted in a wall so that the back wave is wasted into an unused space (attic, basement etc).

Because of the low distortion and deep extension possible, I to went the same route as Carl, with an IB using six 15” inch drivers which is open to a large semi-finished storage space. Rather than compromises, it’s using physics in your favour...

http://community.klipsch.com/forums/t/64932.aspx?PageIndex=12

Since I was building the room ground up at the time I opted for this, I managed to wrap it around my center channel (which I’ve recently built a Cornscala variation). If ever you want to go this route, I agree with maximizing the number of drivers to maximize extension with minimal distortion.

ROb