GoodSoundClub - Romy the Cat's Audio Site

In the Forum: Horn-Loaded Speakers
In the Thread: Infinite Baffle Implementation and "Compression Sub-bass"

Post Subject: Infinite Baffle Implementation and "Compression Sub-bass"Posted by skushino on: 11/20/2016

I'm of the opinion that listening room aesthetics play a big role in enjoying music at home. This is self-evident, but over the many years playing with audio, my listening room has become incrementally cluttered with "audio detritus". It's ugly and cluttered. I'm working to get stuff out of the room. I believe this is also an opportunity to improve some aspects of my playback.

Let's start with sub-bass, because those cabinets are the largest objects in the room. I'm considering replacing the tapped horns with an IB design. Why IB? The design is elegant: similar to a sealed cabinet sound, without the box, without the heroic effort needed for massive volume and bracing, without room clutter, with much higher efficiency, and potentially better bass sound. Bottom line, an IB may sound good (won't know until I build), while being simple to implement in comparison to alternatives. The sole downside I anticipate is no positioning flexibility after I cut holes in the floor.

So far so good. My idea is to build two manifolds with 2 x 18" low Qts drivers each, mounted opposed to each other to offset movement caused by vibrations. I know where I plan to cut holes based on years of listening in this room. One left and one right manifold positioned in the floor at the boundary with the side walls.

The IB "guidelines" online suggest a manifold opening greater than or equal to the total Sd. In the case of 18" drivers, Sd = 192 in^2, implying an opening ~ 400 in^2. What would the effect be if the manifold opening was smaller, say only ~200 in^2? In the CD world, this would be analogous to a CD with 2:1 compression ratio. I'm wondering if mildly "undersizing" the manifold opening results in benefits normally associated with horns and compression drivers. After all, we already do this on our midbass horns, using a conventional direct radiator driver in a compression environment. At sub bass frequencies, I wonder if using the 18" drivers in a compression environment, but without a horn / waveguide, makes good sense. Bass is omnidirectional.

Anyhow, many IBs are built with undersized manifold openings and supposedly sound fine. I'm considering building this with purpose, to capture dynamics usually associated with compression drivers.

Anyone reading with first-hand experience to support or shoot down?

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