Is this Altec Driver Good For An IB

[jimbutler]

HI All,
I am new to the cult forum and have completely enjoyed the site. After years of cabs and various subs I find myself comtemplating an IB. My question is about an vintage Altec driver, the 411A. I have four of them and want to know if they would do well in an IB application. They would be venting into my 1400 sq ft basement.

The T/S parameters are:
xmas: .28 inches
RE(ohms): 6.80
Vd(cu.in.):35.70
Fs: 18.30
Vas (cu.ft.): 31.76
Ref (%) 1.40
Qts: .33
Qms: 2.71
Qes: .37
Vid:.20

Altec recommended that a 411A's best alignment is in a sealed 8 cu.ft. cab. I have a couple of these and they are great, but the extreme low end resolution the IB promises is really tempting me.

Any opinions and info would be greatly appreciated.

Jim Butler

[ThomasW]

I think you'll run out of suspension travel too soon if they're put in an IB

[jimbutler]

Thanks for the info. I thought it might be the case.

I am trying to educate myself about possible drivers to use through the various posts on IB driver selection. Unfortunately it seems there isn't a huge selection out there.

Has anyone done real world spectum analysis of the PE IB 15's? I couldn't find any in the various threads. It would be interesting to know how they perform considering their low price point.

[ThomasW]

Just sit tight because Ascendant Audio is about to launch their new line-up of drivers. This will include a ~$200 18" specifically designed for IB use.

I haven't seen a spectrum analysis of any of the drivers we use. We have 5+ yrs of anecdotal evidence regarding which drivers work well. Drivers like the PE-IB15 or PE DVC-12/15 are descendants of the original Shiva/Tempest, and are made by Eminence.

[dewardh]

The 7mm Xmax (and corresponding Vd) means that they will not produce the same max acoustic output as drivers with a higher Xmax (true in any enclosure), but that does not mean that they will not make a lot of noise <g>. They can produce the same output in the listening area in IB as they would in any box enclosure, with lower power input required at the low frequency extreme. You can, though (as with any IB mounted driver), easily push them to (or beyond) Xmax at low frequency, where the driver is "unloaded" and not protected by enclosure compliance. Rumble filter and peak limiting is *always* advised with an IB to protect the drivers, as output below about 25-30 Hz. (and especially below resonance) is almost always excursion limited. An amplifier that can produce Xmax at 100 Hz. can (and eventually will <g>) throw the voice coils into the next County if driven to the same (electrical) output at 10Hz.

Nothing is lost by trying, since you already have the 411A's. Build the IB mountings, either manifold or line array. If the 411A's play loud enough to suit then you are done, if not replace them *in the same mountings* with higher Xmax drivers. Even if you contemplate moving to 18" drivers all you have to do is make the initial mounting board(s)/manifold(s) large enough to accomodate the bigger holes should that happen. A fundamental advantage of IB construction for the DIYer is that the IB itself is not "tuned" to the driver in any way . . . any changes you might want or need to make with different drivers occur entirely in the (programable) crossover/equalizer.

If you have any choice in location it is a good idea to consider the effect on room mode excitation . . . unlike boxes which can be moved arround relatively easily (even if practical considerations won't let you leave them in the best spot) IB tend to stay where you build 'em . . . <g>. Line arrays have a theoretical advantage in this regard . . . a point source in a corner is worst.

dewardh

[ThomasW]

Those new to the forum won't be familiar with the trials and tribulations of "vintage" driver owners wanting to use their drivers, only to find the VCs slamming into the back plate. So on general principles we don't recommend experimenting with them.

BTW, very few IB owners use rumble filters.....

One fundamental advantage to an IB sub is their inherent ability to play lower than other subs. Those with 'smaller' IBs are encouraged to do so, but they're the exception not the rule.

With the release of newer DVDs with 3Hz content, some of the owners of larger IBs are now experimenting with 10Hz rumble filters.

[dewardh]

> DVDs with 3Hz content

One has to wonder what they are thinking . . . mechanical chair-shakers perhaps? No practical loudspeaker (except maybe that modulated fan thing) can produce significant acoustic output at that low frequency, and a driver in an IB that tries will self-destroy. The only things stopping excursion will be spider/surround elastic limits and/or mechanical stops (or voice coil "departure", hopefully with a controlled (centered) "re-entry"). If IB owners are not protecting their drivers from that with LF (rumble) filters there's going to be a booming (pun intended <g>) market in replacement drivers . . . since the resulting "thwak"ing sound will often be masked by or mistaken for something intended in the main channels (until it's too late).

[ThomasW]

Both Batman Begins and War of the Worlds have significant 3Hz content per the spectro plots.

The infrasonic content for movies like these is added by a special effects company using 22 Bag End subs for their monitors. There have been threads on couple forums discussing this...

People lacking the common sense gene are killing their standard subs not realizing the content of these movies. One of our folks had a minor bottoming incident with WOTW. He's now testing whether or not the 10Hz filter provides adequate protection. His second playing of WOTW with the 10Hz filter was uneventful.

Paul W's 18-15" driver IB clipped his amp for the first time with WOTW. He has the output setting lower than full throttle as a form of protection since he's actually more concerned about blowing out the window glass in the room

[jimbutler]

Interesting reading
I will sit tight for the new 18 inchers by Avalanche.
As regards the infrasonic info of the new movies (and some Telarc Cd's) I look forward to hearing, er, feeling this with and IB.
Thanks

[jimbutler]

Sorry..meant to write Ascendant 18 inchers.

[billgree]

admin said:

With the release of newer DVDs with 3Hz content, some of the owners of larger IBs are now experimenting with 10Hz rumble filters.

Hi

New member here. Is there any discussion of the rumble filter here (or elsewhere). Had a look but could not find anything.

Cheers

Bill

[ThomasW]

The only thing we're experimenting with for that is THIS

[billgree]

Thanks

I had seen that thread but didn't make the connection - had it in my head that you were referring to a DIY filter.

[ThomasW]

We can't scratch build one for the cost of the EQ. So if it works it's a bargain. If not I guess we'll design one from scratch.