Help needed for high power coffee table subwoofer project

[Sixthofmay]

I want the subwoofer to be able to loudly and cleanly reproduce 20 Hz at 115 dB at 10 feet for playing pipe organ music and the deep rumbles in dark ambient music. I also would like decently tight and powerful drum hits in goth-industrial and rock music. The room is about 30 x 30 x 30 feet on concrete slab (main room in a Bucky geo dome home).

The plan:
I'm thinking I want to have lots of large drivers and power to keep distortion low. I'm thinking cone excursion should be kept to a minimum. But to get volume with low excursion, I need lots of piston area. To keep the motion tightly controlled, a sealed box, good sized voice coils, with a good effective damping factor from the amp/speaker wires.

Eight 18 inch drivers total in two separate enclosures. Four per sub wired in parallel for 2 ohms per channel. The Dayton's are cheap and look like they might be about right:

http://www.partsexpress.com/pe/showd...number=295-085

The amp is a Crown MA-3600vz wired to a 30 amp 120 volt circuit, so I should have 1800 watts per channel at 2 ohms or 3600 watts total. The amp will be about 20 feet from the subs. Based on the following page I should use some big wire to improve damping factor. I'm thinking 4/0 welding cable:

http://www.bcae1.com/dampfact.htm
http://store.weldingdepot.com/cgi/we...ot/R0040x.html

The plan is to drive the amp using my Echo (Event) Layla rack mount PC sound card with two of the channels driven off a custom low pass filter and multiband parametric eq I'm making using Synthedit, Audiomulch, and some VST plugins. The low end rolloff will be compensated/tweaked with the parametric.

The main speakers are Magneplaner MG 3.6 amped off a Crown MA-2400 hooked to the Layla.

I'm not very experienced in speaker design/building. I used WinISD to try to design a sealed enclosure. I've come up with 42 x 38 x 21 inches (LxWxH) for the internal dimensions (19.3 cubic feet) for each sub. The two will be placed end to end so it'll be like a 44 x 78 inch, 23 inch high coffee table. Four speakers will be on the left/right sides, and 4 more on the front/back sides. The enclosures will be braced 1 inch MDF, with polyfill stuffing.

I'm unclear about the Qtc of a sealed design and its effect. Some threads and pages have suggested .71 (my dimensions above with the 18 inch Daytons). Others say for deep bass, use lower, like .5. According to WinISD I get slightly more SPL using a larger box and lower Qtc. I've thought about using higher vmax 15 inch drivers in the same size enclosure to get a lower Qtc. But my previous experience with sealed enclosures (car stereo project) showed me having more total piston area and less excursion would give deeper cleaner bass than having less piston area but more excursion with the same size enclosure. And WinISD does show the 18s being a few dB higher in output than 15s in the same size box. And my hunch is that the distortion at 20 Hz from the 18s will be less since there's less cone motion. The transient response would be better with 15s (assuming similar motor as the 18s). But I think I'm more interested in clean massaging bass than drum kicks, so I'm leaning toward the 18s.

I haven't bought any drivers or MDF yet and would appreciate comments by others who've built high powered sealed enclosure subs. Like is my basic plan reasonable? What other brand drivers would be good? 15s or 18s? Larger box?

[johninCR]

With cabs that size and a big room I think you'd be much better off with a bass horn or two. I'm thinking a pair of Jensen Imperial Horn cabs as subs and mains too if you use a 15" subdriver and a 15" coaxial, OR a pair of Labhorns with mouth extenders for sub only duty. A horn is definitely your best bet for high output low distortion bass and you won't need much power or a bunch of drivers.

If I had the room, I'd build the Jensen Imperials and use them for mains and subs. Check out www.decware.com and look in the support forum for a ton of info about them. It's an old design, but a classic and not too difficult a build especially with a helper.

Note that your square room is going to be a real modal problem, so plan on some good bass traps and notch filters to get the optimum sound in those low frequencies.

[sreten]

JMO but using high efficiency 18" pro drivers
with only 6mm of Xmax is not the way to go.

A 15" with 20mm :

http://www.partsexpress.com/pe/showd...number=295-420

Cheaper but still 15mm :

http://www.partsexpress.com/pe/showd...number=295-190

Note that 8 drivers will be 9dB more efficient
than one so the 15's will be ~ 98dB/W midband.

sreten.

[SkinnyBoy]

thats not a coffee table... thats the size of a single bed base, with a matress ontop of it... lol

[Paradise_Ice]

Did you say a coffee table? it would have to be very heavy and braced like the Golden Gate bridge! or else you wont have any cups that will stay on the top with out being rattled off! but i have heard some Rel subs that can double as tables and honestly i think there better off againts a wall or close to a corner,IMO, in the middle of a room is not ideal for extra bass unless its firing down wards and even then, your to close to it to get the best effect. I could be wrong, there are some many factors, but a high X max woofer is needed in any case, 18's are better fo PA, not in a home audio system, a 15 is about your wack!

[BillFitzmaurice]

To mirror some other replies you're on the wrong track. The best that the driver will do is an F3 of 35Hz in a 7.5 cu ft VB; that gives a 1w/1m SPL of 72dB at 20 Hz, so even eight of them will give a sensitivity of 84dB/1watt/1 meter at 20 Hz and you're going to need well over three thousand watts to meet your 115dB/10 ft goal- one which, I might add, is way overkill for any home environment. That kind of power at that frequency is adequate to reduce your home to rubble. That, plus the total required box volume of 60 cu ft makes the project less than feasible.

Different drivers won't help, as higher efficiency drivers will also have a higher F3 and lower F3 drivers will have a lower SPL. The kind of power you want requires a horn loaded system, and the LAB is probably your best bet. Realistically speaking you should also consider scaling back the SPL requirement by at least 10dB, which will still leave it well above THX specs.

[SkinnyBoy]

4000 watts..... 1100litre box (39cuf) 3 metres (10feet) = 20Hz at 113dB before room gain, and there should be some....

[SkinnyBoy]

or

4 woofers... as opposed to 8...
2000 watts..... 1100litre box, tuned to 20Hz 3 metres = 20Hz at 114dB before room gain, and there should be some.... lol

[Sixthofmay]

I've been quite busy with my job and haven't had time to read the comments until now. Thanks everyone!

I hope standing waves aren't an issue as the room opens up to the upper level which is totally open. The diameter of the house is 45 feet with a 28 foot peak.

The goal is to have the sub(s) be semi-asthetically pleasing (girlfriend already thinks I have a screw loose..) and not take up too much space in the wrong places. Subs to the side are no go as there is no room (Maggies and other stuff are there). Poor efficiency is ok as I have 3600 watts available for the sub. What I want is low distortion massaging bass below 50 Hz reasonably matched with the 115 dB levels the Maggies can put out. 4 Velodyne HGS-15X are a bit out of my price range. Efficiency be damned. Ebayed Crowns and electricity are cheap!

Folded horns I originally found out about because one large night club I like uses a few walls of large ones (hooked to 100,000 watts of Crowns stacked 3 columns wide to the ceiling , earplugs are a must!), but they take up way too much space, and group delay problems with them keep coming up in my google searches. Granted they're very efficient but my room is relatively small and low distortion with massaging frequencies is my goal.

I normally listen at 70 to 90 dB. I specified 115 dB at 20 Hz because I figured if it sounds clean at that level, it'll sound really damn clean at 80.

I dunno.. maybe I should go with some higher excursion 15s. The box would be smaller certainly. But my TLAR thinking is the sound comes from only the driver in a sealed enclosure, and that more driver area moving less should be better than less driver area moving more. The movement is non-linear right? Which means it's more linear the less it moves. More linear is better right? And if the resonance frequency is high, it shouldn't matter because I have sufficient power and it's a sealed enclosure so I can eq it to sound right.

Worst case, I can always have chainsaw fun and a bonfire out back and start over with a different enclosure....

And if I ever become rich, a bunch of Velodynes.


Side notes:
I fully admit I have no clue other than TLAR, WinISD, and Google (which indicates that high power sealed multiple driver subs in the home are rare (I had no luck finding anything)), and everyone's actual experience is most important to me.

TLAR = That Looks About Right

[leadbelly]

Originally posted by Sixthofmay
I dunno.. maybe I should go with some higher excursion 15s. The box would be smaller certainly. But my TLAR thinking is the sound comes from only the driver in a sealed enclosure, and that more driver area moving less should be better than less driver area moving more. The movement is non-linear right? Which means it's more linear the less it moves. More linear is better right? And if the resonance frequency is high, it shouldn't matter because I have sufficient power and it's a sealed enclosure so I can eq it to sound right.

IMHO it sounds like you plan to hammer on a square peg with a jackhammer to make it fit the round hole. Why big power and big EQ to overcome the high Fs of a driver not intended for sub duty when there are plenty of good drivers for all budgets that are intended for that duty? Yes, high excursion contributes to distortion, but it's only one aspect of various design considerations. Linkwitz has some good guidelines:

http://www.linkwitzlab.com/x-thor-measmt.htm