Subwoofer: Does this make sense to you guys??

[Stevepaul]

Hey folks,

I am in the planning stages on my subwoofer project and want you guys to run a reality check on my ideas, plans, etc.

I have two Meniscus SW1238R 12" subwoofers:
Xmax: 13mm (one way)
Fs: 18hz
Qms: 10.04
Qes: 0.41
Qts: 0.395
Sd: 500 cm2
Vas: 170l
Le: 2.0
Nominal power handling ability: 200W
Re: 3.10 ohms
# of voice coils: 1

I have a closet that is behind the wall of the room my system is in....and it is in the corner of the room. I can utilize 17ft3 of the closet to place a sub enclosure (wife OK'd that space). I can net about 14ft3 of internal volume after bracing,ports,etc once I put a box in the closet. I would front fire the drivers and ports out from the right hand corner of the room near the floor (through an opening in the drywall). My room is 18' x 22' with 10' ceilings.

Wiring the drivers in series gives me Re=6.1 ohms. I run some various numbers though the latest version of 'Unibox' and I chose the following alignment:
Net Enclosure Volume: 400 liters (14ft3)
# of ports: 2 (3" x 17"/each)
Fb: 14 hz
max output (without room gain) at 20hz: about 110 db (excursion limited)
Power needed to reach 110db at 20hz: 260W
Port air speed: Only gets objectionable at 15hz.

I plan to use the 80hz low pass xover of the HT receiver for right now.

This alignment gives me a gentle 5db rolloff from 80hz to 17hz....which, with room gain should give me relatively flat response, in-room, down to 14hz. Response drops like a stone at 14hz. In reading JonM's discussion of 'room gain' and flat bass response, he noted that a 5db rolloff from from around 100hz to 20 hz usually gets a system bass close to flat, in-room. This alignment doesn't seem to require a special plate amp with their 'boost' circuits...from what I can discern, no boost is required.

I own a NAD amp that I can bridge to 400W into 8ohms, I have the woofers, I have the wood, and I have the wife's OK to build it as planned, I don't have to spend any money.......I am ready to start making sawdust.

Am I making good decisions here? :huh: I don't want boomy bass OR thin bass....I want bass as it should be. Please don't suggest other drivers or amps, I have this stuff on-hand and am trying to do the best I can with what I have.

Any thoughts from anyone......any at all? Please...feel free to give your thoughts/observations/opinions. :T

Many thanks,
Steve Paul

[taz13]

Try the Cult

Here
either in the gallery or FAQ there is a closet used for an IB sub, check it out. I know I just put in an IB sub and love it :T I was directed there by this site and I listened and am very glad I did.

[ThomasW]

No need build a box or use a port. As suggested go with an IB, pretty much the finest sound quality available

You'll need more displacement than that provided by a pair of 12"s

Regardless of the computer model, all subs benefit from the use of EQ, even if it's just used to cut the peaks.

[Stevepaul]

....not enough volume

I have considered an IB, but, I don't have enough volume to work it in. My wife has given me about 1/3 of the closet to work with....not the entire closet!

The Vas of each of my subs is 170 Liters. In reading the IB site, it is mentioned that a minimum of 4X the Vas is a minimum, with 10X (or more) being optimum.

2 drivers x 170liters = 340Liters x 4 = 1,360 liters minimum (3,400 liters optimum).

My wife has given me about 17ft3 or 481 liters to work with......So, I am afraid I just don't have the room for an IB.

Thank you for your response!

Steve

[ThomasW]

We're not fixated on IB's as the only solution. We just recommend them when possible.

Lets get back to a normal design.

I don't think that a pair of modest excursion 12"s are going to have adequate output for a room as big as yours.

What's the budget for drivers? Perhaps we can suggest something more appropriate to the size of the room and the available space in the closet.

[Stevepaul]

Actually, I already have the 2 - 12" drivers. I didn't pay for them and they are normally $150/ea. I imagine I could sell them for half price. I could throw in another $200....giving me a total of $350 available for drivers. I already have the wood to build the enclosure.

I have a space in the closet that is 40" tall, by 23" deep, by 33" wide. This gives a total of 17.6 ft3 'gross'. After deducting all the wood for the enclosure & bracing, the ports, drivers...etc, I figure I'll have about 14ft3 'net' available volume to work with.

I won't have money for an amp or BFD at the moment (I just built this house), so I will be using the 80hz cutoff on my HT receiver and utilizing my NAD amp. The NAD can be bridged 8ohm to 400w, or each channel can be run 330 watts into a 4ohm load. It is a very stable amp at low impedances (I will be upgrading to a BFD and new amp in the future).

So....I have $350 for drivers and 14ft3 to work with.

Thomas........what would you recommend? Maybe these new XBL drivers coming out in November? Or, maybe you have something laying around your shop you wouldn't mind selling off?

I am open to suggestions..Thanks again for your help!

Steve

[ThomasW]

Well driver choice depends on how soon you want to start building. I imagine that the new XBL^2 drivers will be available close to the end of Nov.

If you want something now, the BP1503 is a nice driver, but act quickly, there are only a few still available. They work fine in a ported box.

[Stevepaul]

Jeez--o-peeete! That 18" XBL is nuts...

I just ran the numbers for the new 18" XBL^2 driver through the 'unibox' modeling program and stuck in my 400 liters that I have available. I tuned it to 16hz( Two 4" x 16" long ports).

At 500 watt input, we are at 117db at 70hz and 114db at 20hz. :E Seems to have a smooth & even rolloff from 100hz down to 15 hz of 5db. With room gain of 5db at 17hz, theoretically, I could achieve flat 117db response to 17hz. Xmax isn't reached until 12hz. Only 67% of total xmax is utilized anywhere between 80hz and 20hz.

My listening position is 13 feet away....which would reduce the level by 6db. But, 111db at 20hz is still nuts. I would still have the room modes to deal with so a BFD is in my future....but, this seems a solid start.

Whaddya think.......sound like a good plan?

Steve

[Andrew Pratt]

Seems like a better long term plan to me.

[ThomasW]

You're probably not going to be happy with a pair of 4" diameter ports. They'll huff and puff like a steam engine with that high excursion 18".

I use nothing smaller than 6" flared ports for high excursion 15"s. I imagine that 8"-10" diameter is about right for a high excursion 18".

And no I'm not joking .........

[Stevepaul]

Thomas,

Regarding the 8" port for the 18" XBL^2..........yep, it appears that you are correct again.

I went back to Unibox and looked at the port air speed graph, and also at the minimum port diameter suggested by the program. It suggested a port diameter of almost 8". Punching that diameter into the progam lowers the port speed to an exceptable level (again, according to unibox). The port size would be 8"diameter x 18.5" long. This is a friggin' sewer pipe! Luckily I do have the room for this size port inside the enclosure without altering my tuning too much.

Is there anything else you would suggest before I start cutting wood in preperation for a late November arrival of the 18" sub???

Does it make any sense to couple the enclosure to the floor via some heavy duty screws or bolts?? I have access to the area below the closet in my basement and could drive some screws/bolts up through the floor. (The closet has carpeting on the floor)

Thanks a million for all your help, Thomas. I truly appreciate it.

Steve

[Dennis H]

I have access to the area below the closet in my basement

Well heck, you have everything you need for an IB. Fasten a bottomless box over a hole in the floor and you'll be a certified member of the cult. :W And the good news for your wife is the box can be much smaller - just big enough to hold the driver and form a "duct" into the basement for the backwave.

Edit: okay I reread your first posting about how you want to mount it. So, mount the driver to the wall with a good MDF baffle. Cut a hole through the floor behind the driver at least as big as the driver's area. Build a 3-sided (triangular looking from the side) "duct" connecting the two. It should take 3-4 cu.ft. max out of the closet.

[cdwitmer]

It looks like you are going to be infinitely baffled after all. If you go over to the IB forum (http://www.f20.parsimony.net/forum36475/ ) you will see an announcement that Stryke is selling Lambda 15" drivers that are ideal for IB (you may be able to get away without any EQ). If my memory serves me correctly, the sale price was four drivers for $400.

[Stevepaul]

I would love to be 'infinitely baffled'........unfortunately, my basement is going to be 'finished' this winter and that area underneath the closet will be part of the family room. Not sure the wife would enjoy seeing a manifold hanging down into the room! :frypan:

I believe that Thomas has led me down the path of enlightenment with regards to my situation: 400Liter enclosure, tuned to 20hz with an 8" x 18.5" port.

I saw that a BFD is only $140....maybe I will ask the wife to get me that for Christmas!

Thanks again Thomas and everyone else for the great suggestions!!

Steve
(I will post pictures of my progress and finished project)

[Andrew Pratt]

Steve you should be able to get the BFD for $119 online at most places.

[Cam McFarland]

Steve,

Dont know if you bought your driver yet, but at 20Hz I get 107db (uncorrected) out of my BP1503 at my listening position which is ~13' away from the sub. Its enclosure is only 200 liters, with a 6" port. I am running 800w through it & they are pretty much bulletproof, trust me, I know...... ops:

[Chinook]

Hi Guys,

I've been reading your discussion..........what's a BFD ???? i've seen this abriviation in different other threads, but couldn't find what it is......

[Andrew Pratt]

Behringer FeedBack Destroyer

[ThomasW]

Behringer has a $25 rebate on the BFD until Jan 31 of 05

http://www.behringer.com/01_news/rebates_us.cfm?&lang=ENG