Building IB box

[peteaimee]

After studying the greatness of IB subwoofer systems, I am keen to make a set up that i hope will work. In the land of Aussie, these designs are unheard of, so after searching E bay and many other on line shops, i have found a couple of stand alone 350Watt RMS amps, and will fit 2 X 15" subs. Lucky the amps run off the mains and will feed 4 ohms, so i can use a set of car subs. I know this is not optimal, but am on a budget, with projectors etc to come jet. Room is devoted theatre, with mojo ceiling(nearly black) and dark brown walls. I have a pioneer amplifier, 6.1. the walls and ceiling are sound proofed reasonably well. Insulation throughout the whole house's ceiling. The problem i have is can I split the RCA single channel into two so i can run two amps? will i still have enough pre - out voltage? any info or advice appreciated. only running a stand alone 10 inch sub from dick smith right now so i think this would improve it heaps.

[Otto]

peteaimee wrote:

The problem i have is can I split the RCA single channel into two so i can run two amps? will i still have enough pre - out voltage? any info or advice appreciated.

Hi there,

Splitting your preamp level output will cause no trouble. The high input impedance of the amplifiers will cause very little voltage drop, and both will work the same.

You will enjoy your IB -- it'll be a huge improvement over a single 10" sub!

Good luck!

[collo]

You're probably going to need more than two 15inch drivers for an IB. What is the Xmax?

An IB uses less power than a conventional box - excursion is the limiting factor.

Running a pair of amps would let you run 4 drivers per amp in a series / parallel arrangement.

If those amps are the Jaycar 350W models, bear in mind that the 6dB boost@35hz won't help you get down low. Check your design in WinISD. Sing out if you need a hand.

regards
Collo

[peteaimee]

- Continuous output power: 350 watts RMS into 4 ohms
240 watts RMS into 8 ohms
- Frequency response: 20 to 160 Hz
- Adjustable crossover: 50Hz to 160Hz
- THD: <0.1%
- S/N ratio: >95db
- Bass boost: 6db @ 35Hz
- Input sensitivity @ max vol.: 120mV,
-Line out: 200mV @ max vol.
- Power: 240V 50Hz
- Module cutout approx 240W x 285mmH
- Remote receiver cutout 125W x 65Hmm.
BUY WITH CONFIDENCE !!

this is the unit i was looking at. Not sure on the drivers yet, figure i would go to autobarn etc and find a couple of open air subs. You mentioned Xmas, what does this mean and also you mentioned that power requirements are a lot less in this type of arrangement. I build a few bandpass boxes for my cars over the years, all sound good. these subs usually require a fair bit to drive them. Sorry about the ignorance but am only new to this style of bass reproduction. Very interested though. However just build the house and another kid on the way, so i do have to be restrained a little with cost. any drivers that you know of that you would reccomend?


- Continuous output power: 350 watts RMS into 4 ohms

[peteaimee]

just to add a little info, I'm savi up for a projector, have a set of Audioline 3 way with 2 12" drivers each, pioneer 6.1 dts amp with pioneer hdmi DVD player, feeding amp through optical lead. pretty simple but it packs reasonable punch.

[collo]

That sounds like the Jaycar amp - I've got the same specs here: http://www.subwoofer-builder.com/amps-all.htm

Xmax is the one-way excursion of the driver, and in conjuction with the area of the cone Sd, determines how much air you can move. To get decent SPLs at low frequencies, you need to move heaps of air.

The Americans are blessed with affordable high excursion drivers, but we Aussies are not so fortunate. Jaycar used to stock a 15 incher CS-2345 with a usable Xmax of 12.5mm but the mongrels have discontinued it!

At the moment, there doesn't seem to be an affordable IB driver for us. I had hoped you had stumbled across one, but it appears not.

If you think you're up to building a hi-pass filter, you could go for the ported design on this page
http://www.subwoofer-builder.com/driver-CS-2246.htm

That amp driving a pair of the 12 inch drivers in a 190litre box tuned to 30hz with a 16hz hi-pass gets you around 117dB peak output.

[toecheese]

I don't know why the US is so blessed with high-excursion- maybe for all the road-going boom-boxes?

Since the Mach5 drivers are sourced out of China, it shouldn't be too hard to convince them to make a stop in Aussieland at some point? The ones we make locally however, are cheap, especially since the dollar has fallen so much. Shipping is what kills it, I'm guessing.

As far as IB, don't bother unless you have high excursion drivers, or a lot (like 8) medium excursion ones. Box subs- when properly designed- are fantastic for the amount of sound they can put out. And you can build them like a HT- build the box in the ceiling if need be.

[peteaimee]

one of the reasons i wanted to go IB sub is because the box is hidden in the ceiling. Like mentioned, there is no reason why i couldnt fit a good sub box in the ceiling. Would be more affordable as well. will investigate this some more.

[Chrisbee]

I have to reinforce the message over the minimum Xmax requirement for IB.
2 x 15" car audio drivers in a house IB will disappoint and probably get wrecked on the first film you watch. I'm serious!
I searched for suitable IB drivers for ages in Europe without success.
In a car you get masses of low frequency gain. That's free bass by the bucket full. 2 x 15" in a car is great fun. But not in a house!
Using average 15" car audio drivers for an IB you'd probably need at least 8!
Only if you can get really long throw drivers with a stated Xmax of 22-25mm (or more) should you risk coming down to 4 15" drivers in an IB.
A box sub would be much safer and probably save you money.
If you share your driver specs the experts here will design you a great one!

Edit: I've just read your blog and enjoyed your pictures.
I still can't understand why you can't feel the low bass.

[Sonnie]

If you cannot find or afford the right drivers for the IB install, you could consider the SLLT. You could get by with a couple of drivers for it. The best example we have here is the one Rodny did... the IB Makeover.

[NickTF]

If you are going to box it the only way i'd consider it is by porting or using a passive radiator. In my very limited knowledge of the subject I don't see any benefits a sealed system would have over an IB system considering the back wave is not used in either, but the IB system is much more effecient in the lower frequency ranges. I have a two 15/two 18 passive radiator sub in my house with 3600watts and am very impressed with it (but selling it currently to implement an IB) so something like the SLLT should be pretty neat output wise with your limited woofer displacement!

[peteaimee]

this is getting too complicated for me. Im thinking on the lines of sealed front facing drivers, i have measured the room i have for it, and i can go 17"deep by 59" wide, height is open slather. possibly with a port. I realize this is not going to be as good as some of the other designs, but it would look the part, 2 15" subs looking at you. What im not sure about and was always under the understanding of is that bass is generally non directional, so would it matter if i placed it in the side of the room? also, the amp measured above mentions 350W RMS at 4 ohm, 240W at 8 ohm. If these speakers are twin voice coils, therefore hook both terminals on one speaker in parallel to give me 2 ohm a speaker. Then, hook both speakers up to the amp is series to give me 4 ohm. would this work and how much watts would i feed into these?

[NickTF]

peteaimee wrote:

this is getting too complicated for me. Im thinking on the lines of sealed front facing drivers, i have measured the room i have for it, and i can go 17"deep by 59" wide, height is open slather. possibly with a port. I realize this is not going to be as good as some of the other designs, but it would look the part, 2 15" subs looking at you. What im not sure about and was always under the understanding of is that bass is generally non directional, so would it matter if i placed it in the side of the room? also, the amp measured above mentions 350W RMS at 4 ohm, 240W at 8 ohm. If these speakers are twin voice coils, therefore hook both terminals on one speaker in parallel to give me 2 ohm a speaker. Then, hook both speakers up to the amp is series to give me 4 ohm. would this work and how much watts would i feed into these?

Are you saying that you will have the sealed box out of sight, like an IB setup? If so with your limited amp power you really really need to consider the IB for it's much better effeciency.

[toecheese]

Define 'efficiency': for power-per-sound pressure, IB is the worst.

peteaimee: don't get discouraged- it would be easier to do one DIY sealed in the ceiling than two floorstanding boxes. At a later point when you get IB drivers, you could re-use the same box (unsealing it, of course).

[NickTF]

toecheese wrote:

Define 'efficiency': for power-per-sound pressure, IB is the worst.

peteaimee: don't get discouraged- it would be easier to do one DIY sealed in the ceiling than two floorstanding boxes. At a later point when you get IB drivers, you could re-use the same box (unsealing it, of course).

I don't understand how a sealed box can create more spl then a IB with the same input power given everything is optimal thier respective designs and execution. I do whoever understand how a sealed box's air spring can restrict woofer movement making it require more power to hit xmax. I'm not arguing, i'm asking the question in attempts to learn.

[toecheese]

No, you're absolutely right, I wasn't picking on sealed in general, but wanted to warn that IBs are not the panacea of subwoofers; there are some downsides. High SPL is not it for IB.

For example, an earlier post said "An IB uses less power than a conventional box - excursion is the limiting factor." And that is true. However, the actual sound coming out is less than half: for SPL, IB is inefficient.

If he's using drivers without the proper XMAX for IB, IB won't work, period: he'll hit the stops everytime without the air brake.

I wouldn't go sealed unless his speakers force him to be. (I'd like to clarify the 'unsealing' part of an earlier post- I meant 'increase the baffle').

[NickTF]

Oh, ok. I've made the attempt to make correlations in the past between different alignments and i'd say this much from what i've learned. You can compare a sealed box setup to an IB somewhat in output but the IB will become more effecient in lower frequencies due to no air spring. Also, because of no air spring the subs are in danger of over-excursion so some form of electrical limiting (eq, infrasonic filter, etc.) must be used if you are using enough power to hit your particular woofer's xmax and then some. Long story short, I'd think if you are happy with a sealed alignment using two 15s then you'd be happy with a IB alignment using the same drivers if you are able to prevent over excursion. Remember, the woofer recovers faster in an IB so you will miss some bloat and overhang associated with smaller sealed enclosures which some may call SPL.

Now, regarding ported/passive radiator alignments it seems to be a bit more tricky. I don't totally understand but at the system's tuning, atleast in a radiator setup, I believe you get the radiator's displacment capability which needs to be twice that of the active driver, but only at Fb and higher do you gain this displacement. Actually, in thinking while typing this it would seem the system is capable of displacing twice the amount of air as the active driver(s) (hence the requirement for twice the amount of radiator displacment of that of the active driver(s) in a passive radiator alignment) at Fb in ported or radiator alignments. Now I don't understand the exact relationship of how that diminishes as you get over Fb and i'm sure it's different for every alignment.

Long story short, if you want the most output for given amount of wattage, outside of a large horn enclosure, it seems a ported enclosure or passive radiator setup is for you!!!

[toecheese]

I don't think there's any case that a driver would be suitable for both IB and sealed. Two very different drivers.

In summary, I agree that he should use a ported or similar design.