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Flat panel loudspeakers and a crossover filter

2005-09-04

A week ago ago I recieved a bunch of loudspeakers for testing from Soundscape Studios in Trondheim a small company specialising at advanced loudspeaker and sound systems and installations. It were mainly a variety of Amina and Wharfedale nxt type panel speakers.

I’ve been testing them at my studio and I really like what I hear. They don’t work all the way down to the low frequencies and have to be complemented with a sub woofer. Mounting two panel speakers on opposite walls of the studio in combination with a sub it sounded really convincing. I have been testing with a variety of sound sources and switching back and forth between these loudspeakers and my regular B&amp W 602 speakers to test for differences. The frequency responce seems to be quite good a lot better than I expected. The speakers are not able to transmit phase information and I was unsure what the effect of that would be for the listening experience. The over all impression is that the sound is not coming from a distinct sound source functioning as a point in the room but rather gives the impression of being emitted from a continuous field surrounding the speakers. The sound seems to be “in” the room and “take” the room in a different way from regular speakers. It was no problem distinguishing stereo information but at the same time the sound is a lot more spacious. Turning back to the ordinary speakers the sound seemed to come from “out there” not “in here” as for the panel speakers. Also I tended to hear the sound of both speakers regardless of my position in the room. In comparisment one loudspeaker tends to become much more dominant as I get close to it canceling out the signal from the other when using ordinary loudspeakers. To wind it up: A very interesting experience.

In addition the loudspeakers look different and invite new and interesting ways of visually integrating the speakers in an audiovisual installation setting.

I’m planning on using this type of speakers both for the Generator.x installation and the White-out installation at USF with Kurt Ralske.

The speakers require a 24 dB per octave high pass filter at 80 Hz or higher. After a bit of investigtion a 4th order Linkwitz-Riley crossover filter seems to be the high end standard for this kind of crossover filters. I found equations for it here (as well as equations for a lot of other kinds of digital filters) and set down to code a filter external for MaxMSP to use. tl.crossover4~ doubles as a high or low 4th order Linkwitz-Riley crossover filter. It’s included in a new update to tl.objects version 2.1.2 uploaded the other day. It can be downloaded at

http://www.trondlossius.no/software

It’s more or less the first time I’m touching C-code and programming MaxMSP externals in four years time so I felt a bit rusty but I got it working eventually. So far it’s only compiled for MaxMSP 4.500 at OSX as I don’t have a Windows compiler. It’s released as GNU LPGL with source code included.

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