Room Acoustics Forum by Rives Audio

RE: Room dimension question & door location

124.185.181.118

In Reply to: RE: Room dimension question & door location posted by vinyl survivor on June 28, 2008 at 06:31:43

I can't say how your speakers will work in the room. Driver integration, for instance, depends on the distance between the top and bottom drivers in the speaker and the smaller this distance is, the less space it takes for the sound from the different drivers to integrate. How much space you need between the speaker and the walls depends on their polar response pattern which shows how they radiate in a 360 degree pattern.

All one can guess from just frequency response is how likely you are to be exciting troublesome room modes and if your speakers have useable response down to 25 Hz that is quite possible. KlausR usually jumps in at this point and comments, correctly, that you only excite modes if the frequency associated with the mode is actually played and there's a lot of 'space' between the frequencies of musical pitches but percussion sounds are often 'unpitched' which means they contain sound at lots of frequencies, many not associated with actual musical pitches, and sound effects like explosions and the like in movie soundtracks are similar. If you use the system with soundtracks you'll definitely manage to excite all your room modes individually at various times and probably several of them collectively as well at times. How bad that will sound depends on a lot of things, and bad sounding explosions tend not to be a noticeable problem in many ways but acoustic treatment goes a long way to eliminating the room behaviour whether or not modal response is a problem and I find the reduction in reverberation time extremely beneficial in clarifying and making intelligible bass parts in a lot of music as well as letting one actually hear the clarity of legato playing at those frequencies.

I've got a 32" screen in my separate HT system and I sit around 6'6" away from it, actually 2 metres since I'm in Australia and we use the metric system. That's about the most distant of the recommendations I've seen for viewing distance which range from roughly 1.5 to 2.5 times the screen diagonal. At that sort of distance you could fit some surrounds a little behind you and to the sides which is the recommended position for those speakers in a 5.1 system.

Truthfully I don't know how much diffusion you will get from LP racks. You will get some absorption from the cardboard covers and the amount will vary depending on where the vinyl is at that point on the disc's height. Because of the circular shape of the disc you have no depth between spine and disc at mid height and roughly 6" depth at top and bottom of the disc. That will vary the absorption slightly over the height of the disc spine and introduce some diffusion into things but the amount of absorption and diffusion is hard to estimate. I definitely don't think there's enough absorption for use at first reflection points and I also think the room is too small for diffusion to be an effective treatment at those points since diffusion takes space in which to develop. I'd tend to place the LPs at the rear of the room and, depending on results and personal taste, might even consider placing some free standing panel absorbers in front of them.

I would be very careful of my centre speaker choice. It really needs to match the L & R front speakers tonally because my experience with using a couple of speakers that didn't match my fronts was that the tonal changes in voices that moved into and out of the centre channel was highly annoying. I preferred running without a centre speaker to using a speaker which was not a good tonal match in my HT system. I eventually bought the matching centre speaker for my fronts and find having a centre speaker preferable to not having one, provided you do get that tonal match. If you've got DIY fronts, trial any potential centre speaker in your system before you buy, and use a couple of movies with soundtracks where voices move into and out of the centre channel for your test material.

If you're using a 5.1 system and you have freedom to place the door wherever you like, my suggestion would be to place it on a side wall between the surround speaker and rear room corner, or along the rear wall. That lets you run speaker cable over the floor to the speakers and means people can walk into and out of the room without tripping over cables or having to navigate between speakers. Even if accidents are highly unlikely, avoiding situations where people need to remember to watch their feet at certain locations is a good idea.

David Aiken

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