In Reply to: Re: Room modes sparse under 50Hz.? posted by AJinFLA on February 6, 2007 at 15:44:23:
I wouldn't want you to get too excited by saying "You're right!"In a typical 20' x 15' x 8' listening room
Stereo bass speakers summary:
Most benefits from dipoles are likely to be above 50Hz.
But if there is a first-order width standing wave with a particular song (bass must be louder in one channel than in the other), then stereo dipoles are a better choice than stereo monopolesMono bass speaker summary:
If there is just one mono bass driver (let's say up to 80Hz.),
then dipole is the best choice
Supporting "armchair analysis" comparing three bass driver choices:
(1) using one mono monopole driver on left side of room, or on right side of room
(2) dual left-right monopole drivers,
(3) dual left-right dipole driversAxial room modes analysis
28.25Hz. first-order length
(1), (2) & (3) = all strongly excite this room mode37.7Hz. first-order width
(1) = strongly excited (a single dipole would be better)
(reduced excitation if woofer is placed halfway between the side walls in the partial null)
(2) & (3) no standing wave forms at all if bass output from both speakers is identical, because the speakers are located out of polarity for this standing wave. But if bass IS louder from one side, there will be at least a weak standing wave, and dipole speakers will excite the standing wave 4.8dB less than monopole56.5Hz. second-order length
(1), (2) or (3) = all strongly excite this room mode
71Hz. first-order height
(1)= strongly excited (a single dipole would be better)
(2)= strongly excited
(3)= 4.8dB less excitation from dipole woofer75.3Hz. second-order width
(1) strongly excited (a single dipole would be better)
(2) strongly excited
(3) 4.8dB less excitation
(but even less excitation can be achieved from either monopole or dipole if woofers can be located at 1/4 and 3/4 of the room's width, in the partial nulls for this room mode)
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Richard BassNut Greene
Subjective Audiophile 2007
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Follow Ups
- Let's consider a typical 20 x 15 x 8 room -- maybe you may be somewhat partially right about monopoles below 50Hz.! - Richard BassNut Greene 09:41:08 02/07/07 (0)