July 21, 2010

Bass horn room integration

There are two aspects of integrating a bass horn. One is a practical challenge of fitting it in your room physically. The other is acoustically getting it to work in your system and room.

Room loading

Ideally a bass horn should load into a corner. That allows the horn to be smaller as the corner becomes an extension of the horn. In an extreme design where the horn mouth takes up an entire wall, the horn sees more loading than a corner so the walls can become part of the horn.

If you create a raised stage as shown below, then you have a mix of loadings. Horizontally it sees more loading than a corner horn, but vertically it sees halfspace loading. A rough guess would be to treat it as half way in between - quarter space loading.

What is all this space talk?

Put a bass horn up in the air and the bass radiates in all directions. We call that full space. Put it on the ground and we've cut that in half so it's called half space. 6db acoustic gain in theory results, less in practice due to transmission and absorption through the enclosure. Add a wall next to it and we call it quarter space as the radiation is divided in half yet again with 6db more gain. A corner adds another wall so we call this eighth space. So if you took the bass horn seen above, which we will describe as quarter space, and loaded it into a corner it could be half the size. We could cut the platform in half and turn it up on it's side on the right or left wall running floor to ceiling. It would do the same job, although it would destroy summetry. Another option would be to extend the front wall which has the screen. The horns would each fire into the corners and not be quite as wide as the room. Which option is preferable depends on the room dimensions.

Room modes

It's important to keep in mind that while a bass horn can be an ultimate solution, it may require more bass sources to even out room response. Generally corner loading is needed and there may be a need to add a few more bass sources to get a smooth result. Typically you will see peaks and dips in the response and extra subs can fill in the dips, then you can use EQ to remove the peaks. So it should be kept in mind that a beastly bass horn won't give you perfect bass.

Measure your room

Before you build a bass horn, measure the room. You'll need a bass speaker which can play low enough to see what you are dealing with. Measure it with the mic right up to the cone, then measure the in-room response. That way you can see what the room is doing to the response. Imagine if you put a corner horn and get a -15 db dip at 60 Hz. You will give up all the headroom gained if you boost the dip.

Combining subs

A better idea is to measure the entire room, then place another sub so that it will remove the dip. You might get creative with positions and consider a coffee table subwoofer. You might also use a combination of front loaded and tapped horns. A TH for deep bass extension, then a midbass horn extending where it leaves off. You might add a smaller sub in a closer position to fill in some dips.

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