Musicality of IB Setup?

[jstrahn]

Hello all. I am reading a lot about IB setups and thinking of possibly giving it a go.

One question I have is how well IBs do with music as opposed to movie sound effects. I do quite a bit of music listening in my theater so this is a concern.

The other question I have is how many drivers I would need for my setup. I was thinking of starting with two 15s.

The theater room is approx. 2100 cubic feet and the utility room adjacent is around 2800 cubic feet.

I was running a Mission 700AS and it did an OK job but I'd like a bit more output and definitely ability to hit lower frequencies.

Appreciate any input on my questions.

[JeremyG]

Forgive me, you all who are smarter than me, for answering.

If you've never listened to an IB setup then it's hard to explain. I consider myself a music guy. I don't listen to organ music or classical, I listen to jazz and rock. I key on drums, and only an IB can keep up with a double kick drum. But I tell you, organ music sounds real good on an IB (Thanks, Chrisbee). The stand-up bass on good jazz recordings will also defy your preconceived notions of a subwoofer.

I set up an IB four years ago based on the info in this forum (in its older form) and the help of a home theater/electronics guru. He had spent years building a pair of monumental cylinder subs. The best sounding subs I had heard, and I've listened to many. After the first listen of my IB, he moved the subs to a back room and built a quadruple 18" IB for himself.

But please, don't take my word for it. Read through this forum and see all the positive reactions. If you can, track down someone who has one and give a listen. Like a car, take a test drive. You will not be disappointed.

Jeremy

[jstrahn]

I appreciate the response. That is what I was looking for. A real world review with tight quick bass.

My concern was that since an IB can produce the low sweeping bass of sound effects that it wouldn't reproduce the kick drum type stuff in rock music.

[ThomasW]

If you have a picture of the room or even better a floorplan that will make it easier to make suggestions about drivers.

[jimcant]

I concur wholeheartedly with Jeremy

If you have not already done so, read Chrisbee's IB blog.
His description of the IB's musical capabilities should set your mind at rest, and have you itching to build one.

I too, mainly listen to music, and the IB excels in this area, like you would not believe

[chrisbee]

Don't encourage me, Jim!

I do listen to a lot of organ music but I also listen to plenty of other stuff. The IB's USP is that it sounds so real. Even thunderstorms sound more real than the real thing! I once turned off the system to protect it when a thunderstorm came up on a film without any visual clues on the screen. Only when all fell silent did I realise that the storm was recorded! ;D

The detail in the bass from an IB is stunning. The weight phenomenal. The total lack of colouration or muffling startling. The lack of compression mind boggling. The subtlety with which it paints the tone and timbre of very deep sounds is worth the entrance fee alone. You hear so much more from an IB than any other subwoofer merely capable of reproducing the same frequencies. The IB adds nothing to mask the vital fundamental. Other subwoofers play the lower frequencies but know nothing of tunes, timing, timbre or tone. The subwoofers which others rave about on other forums are soon discarded like chaff. Blown before the winds of the IB.

An IB needs good stereo/Main loudspeakers to support it though. Having huge power and bottomless extension from an IB is pointless if your Main/stereo speakers can't keep up on dynamics. The speakers are protected to quite a degree by the vital crossover but still need to be able to move some air an octave below the crossover point. If the IB swamps the speakers then the system goes loud in the bass but not at higher frequencies. I'd think in terms of 100dB @ 40Hz from your speakers to be able to keep up with a modest 4 x 15" IB.

Thomas will put you right on IB design but from my own experience I'd always recommend a minimum of 4 x 15" IB drivers just to have the necessary safe headroom. Most of the time with 4 x 15" or 2 x 18" you won't see any cone movement at all. Now and then you will see some serious cone movement and two 15" may not have the headroom to cope with the excursion demanded of them.

Muting any two of my four 15"s is very dramatic indeed. The bass just disappears. I just muted each pair in turn on some Vierne organ music and it's as if the IB is suddenly switched off! It really is that noticeable. No doubt somebody with 8 x 15" would say that muting four has the same effect.

If you like classical music you will hear the double basses cut effortlessly through full orchestra. The tympani and bass drum are a revelation and exactly how the percussionist plays them and touches them clearly audible. The shortest sound is reproduced in all its detail from start to finish. Like a high speed camera catches the invisible, the IB exposes the normally inaudible. One hears the occasional mechanical sounds of the pipe organ as if in the same room. Bass guitar is so real and every touch so exposed to your scrutiny you will realise you have never really heard one before. Even small drums take on a new, more mature, masculine character. Pipe organ from an IB is so real it becomes an unbreakable addiction. Asteroids in collision and tossing icebergs are as nothing to the weight and majesty of an IB reproducing pipe organ.

Once heard you cannot do without the IB. One day all film tracks and serious music recordings will mastered on an IB. Because, quite honestly, nothing else is remotely up to the task.

Don't even get me started on what an IB does for films! ;D

[darrellh44]

Muting any two of my four 15"s is very dramatic indeed. The bass just disappears. I just muted each pair in turn on some Vierne organ music and it's as if the IB is suddenly switched off!

Don't you lose a lot of energy thru the undriven pair of drivers? I would think you would have to temporarily seal the unused drivers from the listening area and then do level matching between a single pair vs two pairs to make a fair (although non-instantaneous) comparison. I'm not trying the diminish the benefit of doubling or quadrupling one's IB displacement, but I doubt it's as dramatic as your quick and dirty comparison makes it out to be.

-Darrell

[chrisbee]

Apr 21, 2009 13:01:46 GMT -7 darrellh44 said:

Don't you lose a lot of energy thru the undriven pair of drivers? I would think you would have to temporarily seal the unused drivers from the listening area and then do level matching between a single pair vs two pairs to make a fair (although non-instantaneous) comparison. I'm not trying the diminish the benefit of doubling or quadrupling one's IB displacement, but I doubt it's as dramatic as your quick and dirty comparison makes it out to be.

-Darrell

The question is; how much is lost to the idle drivers cancellation and how much due to the removal of the two driver's own output?

It's much too late tonight but I will arrange a shelf at mid manifold height between the pairs of opposed divers tomorrow and get out the SPL meter.

I think one would expect an immediate drop of at least 6dB but it seems more than that. In fact I'll run some REW sweeps using different combinations of drivers to try and pin down the true difference in dBs for future reference. I'll report back tomorrow with some "all measured" REW nearfield graphs for confirmation of the figures.

[chrisbee]

As promised: A graph of my 4 x 15" IB with all drivers driven, with only the top pair of drivers muted and then with only the bottom pair muted. The EP2500 was set to maximum on both controls and then left alone. Muting took place at the 80Hz 24dB/octave, active, stereo crossover. The analogue preamp volume control was left alone once the original REW calibration had been accomplished.

My Galaxy 140 SPL meter was placed on a cushion on the floor with the capsule on a line with the wall surface and pointing straight into the manifold. I selected 100dB scale with C-weighting and Fast on the meter. The deliberately low position for the test microphone made it easy to spot which of the opposed pairs was active during the tests.

I had to rewire my drivers in opposed pairs per channel instead of left and right as I had done when wiring up originally. So my former muting activities had silenced the left pair or the right pair. Reaction forces may have contributed slightly to the sensation of much lower output when any pair was muted.

The plywood shelf was much longer than necessary to separate the manifold into two boxes one above the other. The shelf projected about two feet into the room. There seemed no point in cutting the shelf material down just for this experiment. The manifold was already braced with a heavy screwed rod so the shelf's added bracing effect was essentially nil.

The differences with and without the plywood shelf suggest that the shelf simply masked the driven pair from the SPL meter. The higher response curves of each pair are without the shelf. Which is the converse of the logic that the undriven drive units would behave like resonant dampers. I ran a few more sweeps just to confirm this result.

I could have arranged the SPL meter at mid manifold height (with some difficulty since I don't own a microphone boom) but I doubt it would have offered any fresh insights.

Nothing was touched in between running REW sweeps except the removal and refitting of the shelf. The four driven driver tests made before, during and after the tests confirmed no accidental changes took place during the test procedures. I had calibrated REW for 85dB to avoid masking any interesting effects by using SP test levels which were too low.

My conclusions:

As expected: Two drivers offer 6dB less output than four drivers.
Possibly unexpected: Muted drivers do not act as dampers.

Feel completely free to pick holes in my methodology or results.

[darrellh44]

Thanks for the response and running the experiment. The 6dB drop for half the drivers is certainly expected (as it would for any speaker). The only reason I commented is that your original post made it sound as if the difference was much greater than the expected 6dB drop ("it's as if the IB is suddenly switched off"). I simply misinterpreted what you were saying and I apologize if it sounded like an attack.

Thanks,
Darrell

[chrisbee]

Apr 22, 2009 6:26:04 GMT -7 darrellh44 said:

Thanks for the response and running the experiment. The 6dB drop for half the drivers is certainly expected (as it would for any speaker). The only reason I commented is that your original post made it sound as if the difference was much greater than the expected 6dB drop ("it's as if the IB is suddenly switched off"). I simply misinterpreted what you were saying and I apologize if it sounded like an attack.

Thanks,
Darrell

I do tend to use "flowery" language. Leave no cliché unturned. ;D

You made a perfectly valid point to which I had no answer. I always welcome food for thought. It would be awful if nobody questioned a statement they thought was obviously wrong. There'd be no progress. I spend my entire life online expecting somebody to question my posts or offer constructive criticism. It's not that I am particularly insecure. Simply that there are always those far more expert than I in my many interests. Specialism has its benefits. I'm spread too thin.

I had really no idea if muted drivers behaved as resonant dampers. From my results I would say not but I do have quite a large manifold. The loss in output may well measure only 6dB but subjectively it always seemed like a considerable reduction.

[ThomasW]

Yes nonpowered drivers in a manifold will operate as passive absorbers decreasing output.

If the VCs of the drivers not powered are shorted with a piece of wire, they're somewhat less of an absorber. Be sure and disconnect the amp if attempting this...

[jimcant]

Chris,

With respect to reply #5, can I just say, you sure do have a way with words, and if did not have my own IB, that I can vouch does exactly what you are talking about, I would be busting my buns to have one

Now, where is the OP?

He is probably already making sawdust

Good onya for undertaking this experiment, as well as the ongoing humor and lateral thinking ;D

Cheers,
Jim.

[chrisbee]

Thanks, Jim

Fortunately, none of us are likely to have dead drivers sitting in our IBs unless we overdrive a two x 15" driver set up.

The point I was trying to make, before all this palaver with REW graphs and shelves, was that two x 15" is not nearly as good as four x 15" with regards to output and headroom. It was just easier to use REW and a shelf than build a 2 x 15" manifold to prove it.

6dB is not an inconsiderable difference in SPLs. Those without IBs would love to have that much extra output on tap. I still maintain that 4 x 15" is a much safer minimum number of drivers than 2 x 15". I believe the extra cost of two more drivers should be thought of as a vital, one-off insurance premium.

[norpus]

Apr 22, 2009 23:24:33 GMT -7 @chrisbee said:

Thanks, Jim

Fortunately, none of us are likely to have dead drivers sitting in our IBs unless we overdrive a two x 15" driver set up.

Did someone call me? ;D

May I just say that 2 x good 18's are way better than 2 x average 15's .... oops

They have a better sound too - more musical, cleaner, lower and you can typically use much less eq

Regarding unused IB drivers becoming passive radiators, I can attest to that. Even though I don't use the rear IB any more (it was an experiment and frankly the neighbours don't need the 2nd one). it does act as a passive radiator. When I sit at the dinner table (it is floor mounted) I swear it sounds like it is operating (even when amp is disconnected). Being 6mtrs away from the front IB, I don't believe there is pressure cancellation like would be expected if they are in same manifold. If anything, it enhances the experience - perhaps for a 12mtr wavelength in particular
Thomas, is there a theoretical advantage in having passive radiators around the room? You'd need a lot of them for bass trapping for sure!

[ThomasW]

Thomas, is there a theoretical advantage in having passive radiators around the room? You'd need a lot of them for bass trapping for sure!

Probably more practical to go with standard diaphragmatic (resonant membrane) bass traps

[norpus]

Thanks for the reply Thomas
Can you advise a link where this diagram/design came from? I'd like to learn more of its capabilities
Thanks

[cngbrick]

Try this spot first for bass trap info:

home.comcast.net/~thomasw-2/SubwooferSetupandEQpage9.html

Richard