When I first met Neville Thiele, well over 10 years ago now, he told me that one of the things he wanted to do more research in was how to reproduce LF properly in rooms so that it had the directionally we normally hear.
So it would seem that at least he never believed that mono was enough below 80Hz, and anecdotally, I've never thought that bass was omnidirectional. Pressure loading a room at LF is another matter, as Eric points out. Richard Lee has often written about his trousers flapping with LF, and again in my experience having bass (even merely in 1st order) decoded properly can certainly give the impression of bass coming from different directions. Indeed, the wave-front approximation of a large thump from the rear or side of the listening position is very impressive and it seems the LF gives a greater impression of the (large) space being reproduced. Paul > > from psychoacoustics we cannot really hear directions of sound below 80 Hz >I know that it is frequently written, but it's not true. Of the two >localization >mechanisms active at low frequencies, Interaural Time Differences (ITDs) are >the >ones that give useable localization cues in free space. The time difference >depends only on the direction of the source and not on the frequency. >Unofrtunately there is very little information in the psychoacoustical >literature about low-frequency localization. They consider 250 Hz to be 'low' >and 100 Hz to be very low. Maybe some day I'll do some research on that... > >It is true that the threshold of hearing rises substantially at low >frequencies, >and for that reason localization acuity decreases. > >Here's what I think really happens. For low frequency sounds reproduced in >ordinary rooms, the first arrival at the listener's two ears naturally has ITDs >that correspond to the direction of the source. After a short period of time, >reinforcement of the sound by reflections from the room boundaries changes the >phase of the sounds at the ears. This can be more easily seen by considering >the modal structure of the room at low frequencies. The room has relatively >few >modes and the sound wave quickly becomes constrained to travel in the modes. >Because of the relative energy of the transverse, oblique, and tangential >modes, >the sound effectively "comes from" the direction of the mode, not of the >source. In practice, large ITDs AND ILDs are seen at the listener's ears. As >a >result, the percept will probably be that the sound is coming from a direction >other than its actual source. This is what I actually hear when using low >frequency test signals in real rooms. > >But there's more going on that that. Almost always, the low-frequency sound >has >actually a fairly broadband spectrum. With that sort of signal the auditory >system clearly evaluates several cues as to the source direction and gives a >best estimate of the actual direction of the source. > >There are good reasons to use several subwoofers in a multichannel reproduction >system. At least the following two papers support that idea. > >[1] Subkey, A., Cabrera, D., Ferguson, S.; "Localization and Image Size Effects >for Low Frequency Sound", AES preprint 6325 (2005 May) >[2] Martens, W., "The impact of decorrelated low-frequency reproduction on >auditory spatial imagery: are two subwoofers better than one?" presented at the >AES16th International Conference, Rovaniemi, Finland, (1999 April) > >Having said that, I only have one (large!) subwoofer in my multichannel >listening room. But the reason for it has more to do with $$$ than my >believing >that one is enough. > >Eric > > >----- Original Message ---- >From: Bo-Erik Sandholm <[email protected]> >To: Surround Sound discussion group <[email protected]> >Sent: Wed, May 4, 2011 4:41:02 AM >Subject: Re: [Sursound] Minim AD7 for sale - Speaker configs. > > >Yes, I have a few woofers available BUT according to what I understand >from psychoacoustics we cannot really hear directions of sound below 80 Hz, >as the ear/brain is changing method of decoding soundwaves between 80 to 100 >Hz? >So do I really need more than a pair driven in mono (or 4) to even out the >excitation of the room modes? > > >If I where to add a low frequency decoder how should I do that? > >Is it not so that the speaker feed to all of the 10 speakers are in phase for >frequencies lower than > >Some "undefined" frequency? >That is using Ambdec? > >Should I have a highpass filter before or after the decoder for the 10 "small" >speakers, >if I add a low frequency feed, either mono or decoded? > >Bo-Erik > >-----Original Message----- >From: [email protected] [mailto:[email protected]] On >Behalf Of Peter Lennox >Sent: den 4 maj 2011 11:32 >To: Surround Sound discussion group >Subject: Re: [Sursound] Minim AD7 for sale - Speaker configs. > >Quick suggestion: - as you're having to use more than 8 channels anyway, you're >likely to be using a 16 channel card; thus, you would have some channels left >to >decode (horizontal only) to 3 or 4 subs > >Dr Peter Lennox >School of Technology >University of Derby, UK >tel: 01332 593155 >e: [email protected] > > >-----Original Message----- >From: [email protected] [mailto:[email protected]] On >Behalf Of Bo-Erik Sandholm >Sent: 04 May 2011 08:09 >To: Surround Sound discussion group >Subject: Re: [Sursound] Minim AD7 for sale - Speaker configs. > > > >I still want to suggest a setup that I will soon have in operation, I have >written about it before. >It uses 10 channels, it is a hexagon in the horizontal plane with a speakers at >front back. >The Z is handled by for speakers, placed where the 4 hexagon side speakers will >end up if the > >Hexagon is rotated 90 degrees around a axis through the front and back hexagon >speakers. > >Fons A has created a ambdec for me of this setup. > >I have the possibility to have all speakers except the 2 floor speakers >permanently mounted due to > >my room geometry. I have the 2 floor speakers mounted on a long wooden plank >letting me getting them in place quickly. > >I have been rethinking my amplifier setup and will now use 3 modules of 4 >channel sure swiched amps instead of 2 Home theater amplifiers. >The shure amp modules (4 x 100W) cost 98USD including a switched power supply, >an will give 30 watts per 8 ohm speakers, >I will only be using 2 power supplies so the total material cost is at the >moment 3 x 44 US + 2 x 48 USD, that is less than 240 USD. >http://www.parts-express.com/pe/showdetl.cfm?Partnumber=320-302 > >I will be using second hand Kef KHT-2005.2 "Eggs" as speakers. > >It is a bit of a "bother" that 10 instead of 8 channels are used, when it comes >to the sound card setups... > >Regards >Bo-Erik > >-----Original Message----- >From: [email protected] [mailto:[email protected]] On >Behalf Of Aaron Heller >Sent: den 3 maj 2011 20:04 >To: Surround Sound discussion group >Subject: Re: [Sursound] Minim AD7 for sale > >On Tue, May 3, 2011 at 10:14 AM, Fons Adriaensen <[email protected]> wrote: >> On Tue, May 03, 2011 at 07:15:29PM +0530, umashankar mantravadi wrote: >>> >>> in fact angelo recommended that i arrange the eight speakers as two >>> crossed squares. two speakers in front and back, and four speakers >>> mid bottom left and right and mid top left and right, the only >>> problem is i do not see a readymade decoder >> >> A variation on this is an horizontal rectangle, 1 unit wide and 1.73 >> deep, and a vertical rectangle in the YZ plane 1 unit high and 1.73 wide. >> Or the same rotated 90 degrees. Looking from above you see an hexagon. >> >> This somewhat improves the rE for horizontal directions (not much), at >> the expense of all others. Anything outside the +/- 30 degrees >> elevation region will become very fuzzy. > >I had one of these set up at home for a couple of days and found it better than >a horizontal hexagon. The impression of height is a >welcome addition to the sense of envelopment. I had a fader set up >in Bidule so you could change the Z gain to compare horizontal-only with >periphonic. The entire listening panel (my son and I) preferred having the >height info, but the rest of the family didn't appreciate having a couple of >ladders in the living room. I also tried it with the vertical rectangle in the >XZ plane. That works too. Contact me off list if you want the Ambdec config >files I used. > >Aaron Heller <[email protected]> >Menlo Park, CA US >_______________________________________________ >Sursound mailing list >[email protected] >https://mail.music.vt.edu/mailman/listinfo/sursound >_______________________________________________ >Sursound mailing list >[email protected] >https://mail.music.vt.edu/mailman/listinfo/sursound > >_____________________________________________________________________ >The University of Derby has a published policy regarding email and reserves the >right to monitor email traffic. If you believe this email was sent to you in >error, please notify the sender and delete this email. Please direct any >concerns to [email protected]. >The policy is available here: http://www.derby.ac.uk/LIS/Email-Policy >_______________________________________________ >Sursound mailing list >[email protected] >https://mail.music.vt.edu/mailman/listinfo/sursound >_______________________________________________ >Sursound mailing list >[email protected] >https://mail.music.vt.edu/mailman/listinfo/sursound > >_______________________________________________ >Sursound mailing list >[email protected] >https://mail.music.vt.edu/mailman/listinfo/sursound _______________________________________________ Sursound mailing list [email protected] https://mail.music.vt.edu/mailman/listinfo/sursound
