More giant sub box questions (1 Viewer)

[RayJK]

Once again I come to the experts for rescue. My storage room sub has grown! I thought the room was only 4' deep and once I emptied it out I found it was 6' deep. This means my room volume has grown to 2385 L taking into account bracing and a port volume estimate.

The questions I have are:

1) Should I do my speaker model based on the lowest flatest curve or should I take some room gain into account?

2) If I do account for room gain, are there average values to use or a formula to figure it out? My room is 16'3" x 23' 6".

3) On paper I've come up with some models that have an FB of 11.64 and an F3 of 10.57 but they are down 3db at 18hz. Another has an FB of 14.75 and an F3 of 13.3 and is only down 1.4db at 20hz. So what would be the better way to go, lower or flatter?

4) How in the world do you estimate QL? What is minor leakage at QL 5 compared to QL7 or QL10? How important is leakage in a box with 1100 sq cm of port anyway?

5) If anyone has a Fane Colossus 24 they will part with let me know. This driver gives me 100-12hz -.5 db with an F3 of 10.5. On paper it looks perfect for an 80+ cubic foot box. I haven't found anything else that is even close except the Tekton Infra 21 and I can't find any info on that except the TS parameters. The P. Audio 2450, Precision Devices 2450, and the Beyma 21L50 don't do as well as one would think in such a large volume.

 

[Chad Kuypers]

Why not use the 34" Audiobahn subwoofer? I am surprised that none of the bass-heads here have gotten their hands on one of those yet.
Chad

 

[RayJK]

Besides being used for high SPL applications it is also way out of my budget. Originaly I had a budget of $2000 for this project but it's down to $1500 at the moment, too much Xmas.

 

[MichaelAngelo]

A while back the Clarion 32" woofer was available used on Ebay for ~800.00, been a couple months tho.

 

[Mark gas]

The Clarion is only good for 60 to 40hz and down you will need some really strong midbass to go with them because they have a ton of output under 60 hz. Why not get a pair of CV stroker 18 subs with 2400 watts of QSC power. That should run you around 1200. The strokers are derived from there pro sound and movie theater subs so they should have a ton of output while maintaining good sq.

 

[MichaelAngelo]

The Clarion goes below 20 hz.....

 

[RayJK]

Thanks for the ideas but I've found plenty of subs that will go low or use up my budget or both. Making them work in the volume I have is the hard part.

 

[Dan Hine]

Making them work in the volume I have is the hard part.

Are you not allowed to use less space?

 

[RayJK]

Dan,

It's not that I'm not allowed to use less space but that things are so much easier if I use it all. Trying to build and brace a fake back wall instead of using the concrete block one doesn't make much sense to me and building a fake side wall only gets me a 17.25 Cu ft decrease for each side. That would still leave me with about 50 cu ft if I did both sides. Again, one wall is block so I'd rather leave that alone.

 

[Dan Hine]

Well, what I was getting at was why do you have to build it in this storage room? Is the rest of the room actually that crowded? Seems like it would be easier (and probably better) to just build a good sub instead of trying to fudge something together to fit in a 85cubic foot space.

 

[ThomasW]

I don't really understand the fixation with huge diameter pro sound drivers....

Also why not just use a few high-end 15"s in an IB?

 

[RayJK]

Thomas,

I'm not fixated on any speaker, it just so happens that the Fane gave a ruler flat response with the parameters I have. Because of that I thought I would look at other drivers of the same size. I'm open to any ideas and that I why I posted the questions at the beginning of this thread. If I could get some of them answered it would go a long way in selecting other drivers.

I know Dayton markets some 15" drivers for IB use specifically, do you have any other in mind?

 

[ThomasW]

A plenum or manifold array (roughly 20" cube) containing 4-15"s would give you tremendous output. See the Link Removed page for examples.
Trying to model room gain at 10-15Hz is problematic; given that low bass just walks through most construction materials.
Also there's virtually no software (CD's/DVD's) available with info at 10Hz

 

[MichaelAngelo]

RayJK,
good luck on the sub. Consider an array of 15" subs, or Adire is supposed to have an 18 inch version of their Brahma available in 2003, maybe a couple of these would fill the bill.
Again, good luck.
The Fane sounds sweet.

 

[RayJK]

Thomas & Michael,

If somebody would answer my first two questions it would make the speaker selection easier. I don't think I have enough volume to use 4 15" drivers in an IB but maybe 3 or 12" ones instead. I do get some nice curves with a sealed design but I don't know how much to plan for room gain so response will be relatively flat at 20hz or less. I'd like the design to be close before I start to EQ.

 

[MichaelAngelo]

Ray,
80 cu ft is more than enough for 4 15s, although that may stretch the literal definition of IB a bit.
It would *kill*
From what I've seen and read, the Dayton is your choice for IB setup. However, if the critical para is the Qts being ~.60 or so, then many drivers would work.
As for question 1, I'd build it flat. Its been said that its easier to EQ out a hump in response, than EQ one flat. Like ThomasW said, trying to model room gain would be difficult, so it would be too much a variable, IMVHO.
Question 3, is one that plagues this as a hobby. Lower or flatter? "I can get 4 hz extension for 2 db up top." It'll likely bug you until you've tried both, just to "see". Again, IMVHO, build it flatter. If the sound is there, I want to hear it, not much material at 10-12 hz, but when its there, and your sub hits it right,THATS why you built it!
Hope this helps.
BTW, have you checked out the Cult of the Infinitely Baffled? See the link in a post above.....

 

[RayJK]

Michael,

I did check out the link above, some pretty wicked installs and good info too.

I ran 4 Dayton 15" IB drivers in Unibox 4.02 and it shows I hit Xmax at 26 hz in a 2365L volume with only 100 watts per driver. Even when I expand the volume to true IB standards (25,000L) Xmax is reached at 25.6 hz. What am I missing in this workup? I would have thought that Xmax would be reached at a much lower frequency in an IB setup.

 

[ThomasW]

If somebody would answer my first two questions it would make the speaker selection easier.

Actually it probably won't make any difference in the choice of drivers but here's the answer.
Yes you can certainly model both for flat and for room gain. But since you have no control over room gain; it tends to be a mute point that one must deal with after the fact.
To correctly model room gain you need to know the reflective/absorptive characteristics of the boundry materials, ie drywall, concrete, brick, etc, etc. And the the placement of the sub in relation to those boundries. A program like LspCAD is designed for this.
Yes the closet is a bit small for a true IB but it's big enough that you can use a manifold or line array with 4-15"s and see what happens.
Given the size of the closet I'd use the PE-DVC 15"s instead of the PE IB 15"s, since the DVC 15"s have a smaller Vas. Don't worry about the lower Qts, it won't be that audible. You can always put in some insulation to 'fake' a larger space
Don't fixate on trying to model the performance of an IB. The drivers are suspension limited not thermal limited like a standard 'box' sub.
As for trying to figure out the Xmax at a specific frequency and power input (in other words can I blow down the house/crack plaster?).... If this is really important then email Jerry McNutt (jlmcnutt@sky1net). Jerry's a loudspeaker engineer/designer at Eminence Loudspeakers (Eminence build the DVC/IB drivers for PE). Jerry has used an IB sub with the prototype DVC drivers for several years. Another option is to talk with Paul at PE tech support 1-800-338-0351 or post your question here