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In Reply to: What would be the perfect size and shape of room for audio? posted by fortysomething on February 22, 2007 at 21:06:12:
Bigger rooms generally have better sound quality.
Especially if dimensions are not multiples of each other.Any opposing surfaces less than 15 feet apart can set up a standing wave in the 40 to 80Hz. octave that's likely to cause a bass boom or null with kick drums (very bad if a kick drums booms) and/or bass guitar notes -- both instruments are very common in popular music.
The two main differences between small rooms (in homes) and large rooms (auditoriums and nightclubs) is:
(1) Early reflections at home may be 10-20 milliseconds after the direct sound, versus 100-200 milliseconds in an auditorium. One interferes too much with the direct sound (at home) while the other sounds much more like pleasant reverberation (in an auditorium, unless you sit in cheap seats near the back corners where the sound can be pretty bad)
(2) The bass under 100Hz. is very uneven in small rooms, with 3 to 6dB peaks typically 5Hz. wide ("room booms"), and -6 to -18dB narrow partial nulls that can be deep enough to make a bass note at the same frequency inaudible.
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Richard BassNut Greene
Subjective Audiophile 2007
Follow Ups:
If the sphere is large enough it can work quite well provided you don't overdrive the room in which case it goes to hell really quickly. With speakers about 1/3 of the way into the room and listening position near the center of the room the sound can be really good. I specified that the room be large enough because in my case first reflection points are 15 to 20 feet away from the listening position and the speakers are 7 feet away. A room like this with exposed hard surfaces would be awful.
"If the sphere is large enough it can work quite well provided you don't overdrive the room in which case it goes to hell really quickly."RG
If you know of any spherical room that sounds good, then tell us about it. I based my conclusion only on audio theories, as I've never been inside a spherical listening room.
Sorry, I forgot to add that my room is over 16,000 cubic feet, if you are thinking of how easy it would be to ovedrive the room.
Richard,My house is a 34 foot diameter 3/4 sphere geodesic. The widest part of the house is 6 foot above the main floor level. Each facet is a triangle roughly 7 foot on a side. The first side reflections, which are minimal because of the distance, get reflected up and not toward you. The maximum ceiling height is a bit over 21 feet. I run mine with the listening position about in the middle. The dome section is basically one great room. The only enclosed area is the bathroom.
I've been in bigger domes where the speakers were placed about 4 foot from the wall with the listening position about in the center. This is pretty close to what you get from a bandshell.
There are hot spots where the volume is higher than in other areas, especially if you are near the back wall and in the spot where several of the facets are focused. Similar to the sidewise first reflection points, any backwall echo is directed up and not back at you. Sound hitting the next tier of facets is directed down so it hits the floor behind you instead of coming to you.
In the northwest the Tacoma Dome is one of the better places to hear music. We stopped going to Seatle for live amplified shows unless the show is in the Tacoma Dome. You get reasonably good sound at most all of the seats. You have to be in the last few rows to get any kind of backslap at all.Please don't confuse the sound you are getting from a concrete structure with the sound you are getting from things being round. The Tacoma Dome is a plywood dome and sounds good. The King Dome was concrete and was possibly the worst sound on the planet. Someone here posted about using echoses in a storage tank as part of the composition. Casals used to practice in an old cistern because he liked the sound. His cistern was rock and so the inner walls diffused reflection instead of focusing them like a true circle would.
If the wall behind you is dead, or far away and multi-faceted, or non-existent (like a band shell) then a partial sphere can sound just fine.
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