Floor mounted sub--slot questions

[homebuilder]

Hello! Need some opinions regarding suitability to build small subs into our floor.

Our living room (750 sf) has numerous 2" x 12" heating registers located around the 3 outside walls, in the hardwood floor. Beneath this room is a 4' crawlspace. We have installed ductless mini splits, and boiler fed underfloor heating, so the vents are no longer attached to any duct-work. I was planning to fill them in with hardwood to match the original floor.

It occurred to me that I might be able to make use of them to have multiple smaller subs fire up into the room. My first thought was infinite baffle, but also thought of slot loaded woofers.

Would that register space, 24 cubic inches, be enough to get any use-able amount of bass? Perhaps with something like 8" woofers? A person could enlarge them to use ready made wooden grills, if they are too small. There are 9 of these scattered around the room.

The architecture of this room is very unique, and my plan is to build a "stealth system" into existing cabinets and wall spaces.

All of the vents are in floor joists (2"x12") on standard 16" spacing, so there is plenty of room for a rectangular box. However, they are generally about 6" from the outside walls.

Any ideas are appreciated.

Thanks!

 

[Juhazi]

How is the crawlspace vented and isolated? Humidity might be a problem and corrode the woofers quickly. Perhaps a box is needed, but it should be large. Can you make wiring to several subs in the crawlspace?

IB means that the backdside "box" has infinite volume, or practically infinite for woofers. Most IB subs use a chamber (slot) to house 2-5 woofers blowing in the same slot.

My suggestion is to utilize the vents for multiple subwoofers, each having eg. 2 10" subwoofer drivers of modest price (Dayton DCS) . You don't need a high power amplifier either, because of huge cone area giving high efficiency.

I noticed that you have another thread asking for a modern console speaker/hifi system. In good 'ole days those were playing monophonic sound, but for stereo they must be quite wide. If you can have a wall of sound and you can place listening chair(s) symmetrically, you have much freedom to make good 3-way speakers inside.

 

[kipman725]

you could use the duct as part of the vent of a 4th order bandpass box:
4th order bandpass calculator - With subwoofer box design example
play around in hornresp a bit the calculations in that article are more like guidelines/starting point.

 

[homebuilder]

floor mounted sub

Juhazi:

The crawlspace is not vented, nor does it have a humidity problem. Just as a side note, vented crawlspaces are for the most part a very bad idea. Ours is insulated, heated and air conditioned, and has 4' of clearance from the bottom of the joists to the floor. I have ready access to get in there through a full sized door in a portion of the basement where it is normal, full height ceilings. My new audio room has 9' ceilings in the basement, with no beams in the way. But, I digress.

Years ago, I had considered large IB subs, because it is "open" to nearly 7000 cubic feet in the crawlspace. But, the reason I am asking about these subs, and as you pointed out, my interest in having a "console" like cabinet on the main floor, is due to the unique architecture. And, the fact that we have built a specific audio room in the basement, of 4750 cubic feet of space. Our first floor is more for casual listening, company, lounging, etc.

Kipman 725: The bandpass idea is a good one. I could accommodate those type of designs between the floor joists. I'll read up on those, and see what the existing vent spaces could accommodate. I'd prefer not to enlarge them, and cut into the original wood floor anymore.

Both of those ideas are attractive, and keep the subs out of view in the main room.

Juhazi: i saw a beautiful mid century walnut console about a month ago for sale really cheap, but missed out on buying it by about 20 minutes. It was 8' long, full of tube gear, and had 12" woofers in the ends. IF I find the right cabinet, I'll pull out all the gear and put my own in there. A lot of those cabinets are really ugly, but this one was a beauty. It got me thinking about how gorgeous the JBL Ranger Paragons are. Another related option is I can build all of the equipment into the end wall. Lots of room there.

 

[GM]

Strongly recommend one or more easy to design/build multiple driver manifold IBs, so dual opposed woofers at minimum. Thomas's 12 Dancing [Avatar/Adire] Shivas started an IB centric website/forum with a wealth of help/info: 12 dancing shivas manifold IB - Google Search

Cult of the Infinitely Baffled: Home | "Cult of the Infinitely Baffled" Hear The Bass, Not The Box The definitive online resource for Infinite Baffle subwoofer design Established 1999

GM

 

[daqvin_carter]

How many slots does the room have? I have infinite baffle with a pair of 18s in the ceiling and love it.
It seems like multiple 8 inch woofers would be great as long as you have at least four slots.

 

[Juhazi]

The problem with IBs can be resonances from the floor itself (and conducted to walls), if the drivers are not boxed. Here in Scandinavia we have totally different types of construction and heating systems, so this is just guessing...

 

[homebuilder]

Slot sub

GM: I have been looking at the Cult of the Infinitely Baffled for years now, which is what made me think of using the existing vent lots in the floor for and IB sub. On that site, they classify that type of system as the least desirable, but still "do-able". I'm wondering about the fairly small size of the slot, being 2" x 12" net. The positives are that there are a lot of them, scattered around the room. I don't mind building several relatively small and simple boxes, but buying a bunch of (for example) *" woofers will quickly add up in cost, versus a smaller number of bigger drivers, and less cabinets.

daqvin_carter: there are 9 slots around the room. 5 of them are on the South facing wall of glass that runs the entire 30 plus feet of the room. 2 on the far end of the room, 2 on the third side. None on the end where the equipment and speakers would be, although there is a long wall where things can be built into the wall itself. the room is 24' by 36' overall.

Juhazi; yes, this type of construction is quite different than from your area. I would personally never build a house with a crawlspace, but I wasn't in charge in 1952

As this idea develops, I'm looking much harder at the end wall, and building speakers into it. Being repetitive, that wall is actually a bank of 3/4 fir plywood floor to ceiling cabinets fastened together to form a wall. The side facing into the large living room is smooth with redwood plywood veneer. The other side are cabinets with doors. Reading on the site that GM mentioned, this layout would work for an manifold based IB system. Those cabinets also have access into the same crawlspace below.

If I can use the former heating vent slots located around the perimeter of the room, I can mount speakers in the end wall cabinets, and not have to use that space for subwoofers.

 

[weltersys]

I'm wondering about the fairly small size of the slot, being 2" x 12" net.

That exit size would not present any output problems with any size driver you are likely to consider, even including 15" or 18", other than potential for a bit of turbulence noise for huge displacements. The relatively small plenum/slot will have a resonance, but that resonance will be above the "subwoofer" range.

With as many placement possibilities available, you should be able to find locations that would result in a uniform low frequency room response.

Art

 

[daqvin_carter]

With a total of eight 8" woofers, you should be able to pull off a decent system.
You may only be able to use them up to 60 hz with that much spacing but they should also avoid room mode problems.

The next question is what sort of performance are you looking for. You could spend as low as $16 a pop for some decent closeout woofers SW830-PP 8" Poly Cone Woofer with Foam Surround 4 Ohm.

Or go with some thing like this and you would have more low end than you might tolerate. Tang Band W8-2022 8" RBM Subwoofer 8 Ohm


Also, sacrificing the cabinets is a noble idea.

 

[scottjoplin]

That exit size would not present any output problems with any size driver you are likely to consider, even including 15" or 18", other than potential for a bit of turbulence noise for huge displacements. The relatively small plenum/slot will have a resonance, but that resonance will be above the "subwoofer" range.

From Generic IB design, build and install page 1 "The downside to a manifold is that the outlets are never as large as the multiple openings in a line array. This results in a small decrease in sound quality.

The fundamental rules for manifolds are 1) make the outlet as large as possible, and 2) keep the manifold as short as possible"

 

[homebuilder]

Slot subwoofer

ScottJoplin:

So what do you think about this particular scenario? I have read that information, but don't know how to qualify it in my particular case. Is there a specific size/displacement woofer that will work better or adequately with my 24 cubic inch slots? Or should I enlarge the holes slightly?

I'd love to make this work, because I'm fascinated with the concept. I'm thinking of simple dual opposed manifolds because of spacing available in the joist cavities below. I do not want long boxes with 8, or 16 woofers hanging down close to the floor.

I'm going to read up on bandpass designs too. Have not had a chance to do that this week.

 

[scottjoplin]

I don't know, I was querying what Art said, I'm very interested in your project though and will be following, I've done a little experimenting with IB, a manifold through a slot in the wall and have been impressed with the results so far. I would suggest you experiment a bit before committing yourself, I'm not sure how the floor would respond to all that LF energy

 

[daqvin_carter]

I forgot about the manifold approach. I did not need to do that.
I am reconfiguring things so I can reach about 150 or maybe 200 hz so I can start with horns for the rest. Manifold would not work with that.

10 inch woofers would be mild compression and not likely to have much affect as far as being a slot. You would just want your manifold length and width to equal 50 square inches reducing to 24 square inches in the slot.

You just need to figure what sort of total displacement you want. Think of each woofer in terms of bore and stroke (xmax times cone area) multiplied by eight slots. You can easily compare a pair of larger woofers to your 8 smaller drivers.

 

[GM]

GM: I have been looking at the Cult of the Infinitely Baffled for years now, which is what made me think of using the existing vent lots in the floor for and IB sub. On that site, they classify that type of system as the least desirable, but still "do-able". I'm wondering about the fairly small size of the slot, being 2" x 12" net.

Not surprised, went down that 'road' with Thomas even before the forum IIRC and as Art noted, until the manifold gets long enough to be a TL in the sub's pass band where it needs to be damped like the TL it is, it's easily dealt with same as any other 4th order BP, i.e. critically damp the 'vent' via an impulse response test* to remove any 'noise', so at worst a bit of felt/whatever between grill and opening and/or need to relocate slots for whatever reason.

* REW measurement system or similar for spot on or the DIYer's 'trust your ears' tester: Click test: Click Test | GM210 | Flickr

GM

 

[homebuilder]

slot subwoofer dual opposed

What do you guys think of this inexpensive Goldwood woofer for a dual opposed box mounted under the floor slot (24 cubic inches) of area? The space between joists is 14.5 inches so I could build a decent sized box and mount one of these 10's on either side to fire up through the floor slot. I'm thinking 4 of these boxes around the room.

MODEL GW-410D
Thiele-Small Parameters, Voice Coils In Parallel
Parameter Value
Unit / Notes
Effective Piston Area (Sd)
344.9
cm
2
Free Air Resonance (Fs)
40.4
Hz
DC Resistance
(Re)
1.8
Ω
Mechanical Q Factor (Qms)
6.172
Electrical Q Factor (Qes)
0.680
Total Q Factor (Qts)
0.613
Voice Coil Inductance (Le)
0.3
mH/milli-Henrys
Equivalent Air Volume ( Vas)
56.9
Liters
Moving Mass (Mms)
45.7
Grams/Mmd + air load mass
Suspension Compliance (Cms)
340.995
μM/N/micro-Meters per
Newton
Force Factor (Bl)
5.512
Tm / Tesla-Meters
Sensitivity (SPLref)
95.7
dB/Reference 8
Ω
/2.83Vrms
Thiele-Small Parameters, Voice Coils In Series
Parameter Value

 

[HammerSandwich]

3mm Xmax per Parts-Express? Maybe the specs are wrong. The 10SW looks like a better bet, but its Sd of 140cm2 is obviously wrong as well...