IB Subwoofer

[JimGore]

Good morning!

Been busy climbing in and out of the roof this weekend - started building my IB at last.

Climbed into and out of the roof about 900 times over the past two days.  Managed to get 3 sheets of plywood in there so far, but that will be increasing quite a bit before the project is done.

I am going with two manifolds, each with 2x 15" drivers.  Amplifier is a crown XTI 1000.  The amp can do 700w RMS per channel into 2Ohms, and has a USB port at the back with which you can set crossover points, DSP, parametric EQ, phase, gain, delay, etc.  Very nice.

I had quite a nightmare trying to find drivers that would work for the IB.  I looked at FiCar in LasVegas as well as Acoutic Elegance (AE).  Both companies were willing to ship drivers to me but the cost would have been insane.  These things are seriously heavy...

I started doing some homework on local drivers, measuring just about everything I could get my hands on.  I eventually found a driver that would work, and it was in the most unlikely candidate (in my mind) of them all:

Starsound 15" SVC from autostyle (SSW 381 SVC).  Free air specs (run in) measured by my as follows:
*  Qts - 0.445
*  Qms - 5.299
*  Qes - 0.485
*  Re - 3.401 Ohm
*  Fs - 21.53 Hz
*  BL - 13.3 N/A
*  Le - 3.59 mH
*  Mms - 186.7 grams
*  Vas - 282.9 lit
*  SPL - 89.54 dB
*  SD - 825.4 cm^2

Compare to AE's IB15 specs (from their website):
*  Fs: 16Hz
*  Qms: 6.8
*  Vas: 439L
*  Cms: .45mm/N
*  Mms: 220g
*  Rms: 3.239
*  Xmax: 18.5mm
*  Xmech: 25mm
*  Sd: 830sqcm
*  Vd: 3.07L (p-p)
*  Qes: .78
*  Re: 5.5ohm
*  Le: .33mH
*  Bl:12.49
*  Pe: 500W
*  Qts: .7
*  PL: 86dB

There is quite a difference between the two in terms of Fs.  I am sure this has to do with the Mms however.  186.7g vs 220g should drop the Fs from 21.53 to about 16Hz if need be.  Not sure this will be necessary, but the microphone will show the truth when the time comes.

The SSW 381 has higher sensitivity, lower Qts (I can increase this electronically if need be), similar BL strength, lower Vas.  I am sure the IB15 will have higher XMax, and surely has a better motor and basket as well as lower distortion.  That being said, the Starsound only costs R650 inc. VAT and is easily available here.

Some pictures of the build progress so far:

[oradba69]

Hats off to you. Working in such a confined space is literraly a pain in the butt. At least it looks cleaner in your roof than in mine.
Good luck with the rest of the build.

[JimGore]

The conditions in the roof are not pleasant to say the least.  I think I lost about 5 Kg in sweat up there because of the heat.

The roof isn't as clean as you think.  Serious dust and spiderwebs up there.

Next time I do this I will try my best not to build the enclosures in the lowest part of the roof.  What a mission!  To make matter worse the roof beams are not always as square or straight as you think they should be.  Makes for some interesting woodworking...

I will be building a bulkhead below the subs into which they will exit into the room.  Will probably put some aircon grilles or something to cover up the holes.

Any ideas where I can find aircon grilles?

Ian.

[Timber_MG]

Nice. Any indication of Xmax on this woofer?

[JimGore]

Unfortunately XMax is the one thing I have no way of measuring.  You also don't get any specs from the suppliers or manufacturers - you know how it is...

The surround and spider are definitely big enough & the voicecoil looks reasonably long.  I have given them quite a bit of power and they look like they are behaving.  More than that, who can say?

[Timber_MG]

You can always feed one too much power and find out with a vernier caliper.

[JimGore]

Thanks for that suggestion Martin    They are cheap, but not cheap enough to do that intentionally.

Got a little bit done today after work.  Not much, but every little bit helps.

Finishing off the mouth area.  The opening for each of the manifolds is going to be 580mm x 450mm.  Should be plenty for two drivers.

Some pictures at the bottom.

I will start with some of the bracing tomorrow if I have some time.

Ian.

[Vaughan]

Unfortunately XMax is the one thing I have no way of measuring.

A wild guess but I think in the region of between 7-10mm. What are they charging you for the AE15 ?

Regards,

[JimGore]

The IB15 price was $500 for 4 of them.  Shipping was an additional $521.93

For that money I could buy 16 of the Starsound drivers.

Have to love being so far away from the US.

[Vaughan]

Well, you need a relatively robust driver in an IB. The stresses placed on them will be very high. The IB15 drivers are well designed and at least have decent 1-way excursion. 4 of them would do extremely well, that's what, like over 12L of displacement ! Since displacement is key in an IB, perhaps it might be worth trying out a pair of IB15 drivers and add in the other two (for the other manafold) at a later stage ?

With the Star Sound drivers, given their pricing and application, will most likely have very low Vd capabilities (don't quote me on that though, it's a hunch but it stands to reason, IMO   ); you'll presumably reach Xmech levels (never mind Xmax...) extremely easily, especially in an IB, which is obviously not good. I think, in my opinion, if you're going the IB route and have the means to do it (which you obviously do), do it right. I think you'll be glad you did.

Obviously, that's easier said than done, I admit. 

Regards,

[JimGore]

You know you make a very valid argument.

For the meantime I am going to try out these local drivers and will give feedback here on the forum on how they behave themselves.  I can always bring the IB15s in at a later stage if need be.  I am pretty confident that the SS drivers will fulfil my requirements for the short to medium term.

The alternative is to simply use more SS drivers so that the excursion for each drivers becomes less for a similar overall SPL.

The disign of the manifold I am doing is such that I can extend it quite easily to accomodate more drivers.

Unfortunately bass, like acceleration in a car is addictive.  What is good enough today might not be tomorrow.

Have a good afternoon.
Ian.

[Vaughan]

Hey, you could always buy 16 of them (8 per manafold). I don't think you will be able to reach Xmech with the amount of displacement on tap.   But seriously, I look forward to hearing your impressions once you have something cooking. I have a feeling you'll be very impressed.

Have you tested your frequency response in the position you're installing the manafolds ?

Have a good afternoon.

Thanks, you too. I'm still on leave actually...not complaining one bit...

Regards,

[JimGore]

Lucky fish!  I have been working straight through the festive season.  Obviously not on the public holidays.  It would be nice to have some leave so I can get this thing done sooner.

I moved the cone of the driver with my fingers a bit this afternoon.  Trying to see how much it is willing to move.  Not very scientific, I know.

These things might have more xmech than we are giving them credit for.  They can move quite a lot!  At some point I will hook one up to the amplifier and put a 20Hz frequency on it & see what it does.

I am not plannig to reach 120dB with this IB in any event - the people living in my complex will shoot me before I get near that.  After all the reading I have been doing on IB's I think that even a below standard IB install will still sound pretty good.

I did measure the response in the locations I am putting them in.  Placed a sub in my normal listening position and put the mic where the manifolds are exiting.  The subs are going to work where they are.  I will need to build two serious bass traps to put across the corners however.  Some floor to ceiling jobs.

Got a little bit done this afternoon after work - put some bracing in place.  I am sawing up a couple of roofing beams I have lying around for this.  Fortunately I have some decent machines so I can flatten, straighten, and smooth out the wood.

Pics below.

[Vaughan]

Thomas W at the Cult used to say that the key to good IB results was not only proper placement (as with any other sub) but to make sure that the manafold outlet was of adequate size. It needs to be as big as you can make it, within reason of course.

I've experienced 2 IB installs so far but each of them blew me away, for exactly the same reasons. It's like dipole bass; at first it sounds almost too dry, then you realize you're hearing bass as it was meant to be heard except here, you have all the extension you could possibly want and more.

Things are coming along nicely with your install. Once you've finished I would love to hear the end results. : )

Regards,

[Ampdog]

Unfortunately XMax is the one thing I have no way of measuring. 

This is where eyebrows will be raised a bit ....

I take a small hobby knife and make two slits in the bottom support near the edge about 3mm apart, cut that as well, and carefully lifts the 'tongue'. One can then measure Xmax by depressing the cone until the voice coil just reaches the magnet edge. Afterwards, careful pushing the tab back into position and with some contact adhesive, makes the cut almost disappear.