From: owner-bass-digest (Bass Appreciation Digest) To: bass-digest@lunch.engr.sgi.com Subject: Bass Appreciation Digest V2 #149 Reply-To: bass Errors-To: owner-bass-digest@lunch.engr.sgi.com Precedence: bulk Bass Appreciation Digest Friday, April 21 1995 Volume 2, Number 149 Important Addresses: Submissions to the list: bass@lunch.engr.sgi.com (or reply to this message). Adds/removes/archives: bass-digest-request@lunch.engr.sgi.com Real, live person: owner-bass@lunch.engr.sgi.com Topics: Re: Home wiring bass in rear channels Center Channel Dispersion, Part N bass on TDC Re: vertical dispersion Re: Home wiring Delaying the back wave from dipolars Re: Center Channel Dispersion, Pt. Ib Re: SPDIF, computers, ethernet, etc. Re: bass in rear channels RE: bass on TDC ---------------------------------------------------------------------- Date: Fri, 21 Apr 1995 13:44:13 -0400 (EDT) From: petroca@acasun.eckerd.edu (Chris A. Petro) Subject: Re: Home wiring > I know I wouldn't like to get across the output of an amp with > +/- 70 volts on the rails, much less the family pet or a > teething infant. Could anyone shed some light on this or am > I just concerned about nothing? I used to test our big Yamaha amps going to the bass cabinets on the stage that way. just grab the two wires and have someone turn it up all the way... it's pretty easy to tell if it's the amp or the cable/plug that's gone bad. 8^) I wouldn't stick them in my mouth, though. I tend to stick everything in conduits so that I can pull something else through real easily without worrying about the cable getting stuck. I don't know about the actual regulations, and would also appreciate hearing about what they might be... _____________________________________________________________________________ Christopher Petro | -- Partner, Tampa Bay Media & Data Services -- Box 975, 4200 54th Ave South | * Professional audio, video and lighting St. Petersburg, FL 33711 | installation/setup 813-824-0405 | * Computer hardware, software and networking petroca@eckerd.edu | solutions for PC & Unix platforms ------------------------------ Date: Fri, 21 Apr 1995 11:45:52 MST From: wmeckle@PrimeNet.Com (William Eckle) Subject: bass in rear channels Hi All: In light of the recent discussion of THX etc. thought the following might be of interest: Subject: Re: Measurements of Low Freq in Surround Channel I agree with Greg Roger's findings indicating strong surround channel bass content and I'd like to describe an experiment I've conducted that substantiates the notion of intentional rear channel bass. The experiment conditions and results I'm about to report were submitted to both Peter Mitchell and Gary Reber last year. Peter reviewed my work, conducted his own investigation and published a series of three articles on the topic. His articles appeared in "Audio/Video Interiors", "Stereo Review" and "Stereophile". Gary Reber also began monitoring L+R and Surround channel outputs with 1/3 octave analyzers and reported in his excellent publication "Widescreen Review". In both cases, Mitchell and Reber used separate 1/3 octave analyzers to look at Front vs Rear spectral content. While it is possible to verify with this set up that bass in the surround channel does exist, and can exceed the amplitude of the L+R subwoofer output, it is not possible to prove that bass signals were intentionally placed there. What follows is a description of an analysis technique I have used since 1984 to investigate spatialization of program material. As my research was conducted with the intent of developing competitive commercial products I have not widely publicized my findings. Rather, my work was incorporated as proprietary knowledge in Kintek surround sound processors, subwoofers and surround loudspeakers. The Experimental Set Up - In order to differentiate between intentional and "stray bass" (Thanks, Roger Dressler) in the surrounds, it is nesessary to measure the simultaneous inter-channel phase of the Lt and Rt signals and simultaneously measure the amplitude of the L+R and Surround outputs. As you know, a Lt, Rt inter-channel phase relationship of 0 degrees will cause a signal to be decoded into the Center channel. A Lt, Rt inter-channel phase relationship of -180 degrees will cause a signal to be decoded into the Surround channel. By observing Lt/Rt phase, L+R and L-R amplitude and watching for visual program material cues it is possible to see where bass effects were intended to be heard. (I know I've repeated myself, for emphasis). I begin an analysis session by connecting the Lt/Rt outputs of a laserdisc player to the inputs of a two channel low pass filter set. Both channels of the low pass filter track each other and can be adjusted over a range of 20Hz to 200Hz in a single sweep. The outputs of the filter set (Lt/Rt now low passed) are sent to a continuous-reading analog phase meter calibrated in 2 degree steps from 0 to -180 degrees. It is now possible for me to observe the instantaneous phase relationship of bass signals on the Lt/Rt lines and determine placement along the Front/Surround axis. While I am monitoring the low-passed Lt/Rt phase, a parrallel connection from the unfiltered Lt/Rt laserdisc source is sent to a standard Dolby Pro-logic decoder. The Pro-logic decoder feeds an SPL-balanced system consisting of identical, full range loudspeakers. Separate spectrum analysers are used to monitor L+R and Surround outputs. The Results - A particulary clear example of intentional surround channel bass placement occurs in the first underwater scene in "The Hunt for Red October". This scene is about ten minutes into the picture, just after the Admiral call for a car for Jack Ryan. An underwater shot. Powerful rumbling of turbines and propellors. As the US submarine "Dallas" appears on screen the phase meter my phase meter indicates -180 degrees between Lt/Rt in the octave between 30Hz and 60Hz. An intentional surround bass signal that matches the visual information on-screen. The "Dallas" appears overhead, and low frequency sound is matched spatially to it. As the "Dallas" moves on-screen and moves in the direction of the forward vanishing point, my phase meter smoothly tracks the Lt/Rt bass phase from - -180 through 90 to 0 degrees. An intentional bass pan from surround to front. "Stray Bass" does not track a visual object from surround to front. Remember, the phase meter is looking at only the Lt/Rt bass in the 30Hz to 60Hz octave. Some additional observations about relative Front/Surround bass levels - The first scene that takes the viewer inside the "Red October" is a good example of how much bass there is in the surrounds, and how intentional this effect is. Ocaisionaly, I use a narrow-band FFT analyser instead of a 1/3 octave analyzer in order obtain a more detailed picture of spectral content. My Hewlett-Packard analyzer is capable of 400 spectral lines of resolution between the measurement start and stop frequencies. For bass content anaysis I set the HP with a bandwidth of 20Hz to 200Hz. I have measured surround channel bass at 40Hz that is up to 12dB greater than the average midrange level. During this time, the phase of the Lt/Rt is reading about -135 degrees and front bass level at 40Hz is 6dB less than the surround level. Both amplitude and phase measurements indicate intentional surround channel bass placement. Is it what the director intended? In dubbing theatres equipped with Kintek KT-340, JBL 8330, or John Allen's HPS-4000 surround loudspeakers directors can hear surround channel bass that is flat to 60Hz and down about 4dB at 40Hz. Unfortunatly, most theatre-goers are not so lucky. With the exception of a small percentage of high quality "B-chain" installations with high power amps and efficient full range loudspeakers used for surround arrays, most theatrical sound is bass-shy in the surround field. Exhibitors simply will not pay to upgrade loudspeakers. It is not a "visable" improvement. Many saw fit however to equip their plants with DTS and Dolby SR-D Digital format processors. Big, action pictures recorded in "Digital Sound" are a draw. The average consumer knows "Digital = Better", or THX = Better. So there really is very little insentive for exhibitors to upgrade to full range surround arrays that would allow film directors the chance to explore spatialized bass effects in the studio - and be assured that audiences would hear these effects with attenuation or distortion. But the likely acceptance of Dolby AC-3 as a consumer digital surround sound format could offer home theatre performace far beyond what is likely to be encountered at the multiplex. The Dolby AC-3 spec include data fields that allow producers to encode information about the nature of the mixing environment and their mixing intent. So if a producer monitors a project on five, identical full-range loudspeakers with an average dialog level of 80dB and a maximum M&E level of 110dB your system will know that. If you want to reproduce it that way or play it through a sub-sat system, it will be your choise. Michael Joly Director Consumer Products Kintek, Inc. Copyright 1994 Michael Joly, All Rights Reserved Re-transmission or copies may be made if this notice is included. -=Bill=- -=Bill=- wmeckle@primenet.com (or) wmeckle@aztec.asu.edu ------------------------------ Date: Fri, 21 Apr 95 16:48:41 EDT From: poe@keps.com (Bob Poe) Subject: Center Channel Dispersion, Part N - ----- Begin Included Message ----- > > B&W has one which has a single tweeter on top of the cabinet, Samsung > has a coaxial one, and so does KEF. Other than these (Tannoy might have > one too), you will be enhancing the ceiling and floor reflections > contrary to what THX claims and have a very poor horizontal dispersion > unless you use the center speaker standing up (go figure how you'll get > it to look ok). So stand it up! That's what I'm saying. If you care more about how it looks than about how it sounds, that's not my problem. Doug Dawson dawson@utpapa.ph.utexas.edu - ----- End Included Message ----- I would think that another possibility is available through some of the "sub-sat" systems. (This may apply even in the common situation, where the "sub" is not a *real* subwoofer, but just a separate bass module.) The typical satellite speakers in these systems are small enough that they don't look too absurd in the vertical position on top of (or below) the video monitor. For instance, Cambridge SoundWorks has a 4-piece system, called "Ensemble", with stereo bass units. They also make a shielded version of the Ensemble satellite, called "Center Channel". One could configure 3 satellites (at least one of them shielded) and three bass units across the front of the room, to get nearly identical sonic characteristics from all 3 channels. The Center Channel speaker could rest vertically on top of the TV monitor, and the corresponding bass unit could reside below, without being too visually offensive. My own system is essentially like this, except that I don't have the center bass module . . . yet. It's not high-end, but it strikes a nice balance between the needs of music and the needs of home theater. Oddly enough, CSW usually shows the Center Channel placed horizontally[!] on top of a TV, even though it is asymmetrical in that position, being a two-way speaker. The company also markets the "Center Channel Plus", which is a (symmetrical) horizontal array. I auditioned the latter extensively in my home and found it decidedly inferior to my current configuration. I don't think I can attribute my dissatisfaction to the dispersion problems noted here, however. Rather, it seemed to suffer from a severe roll-off of the high frequencies (even on-axis) that prevented it from matching the L and R satellites. ------------------------------ Date: Fri, 21 Apr 95 15:47:00 E From: Lou Lung Subject: bass on TDC I was watching The Discovery Channel last night and on _Beyond 2000_ they had a segment on an experiment run at Georgia Tech (?). The research is on human perception and reaction to sound as it relates to sonic booms with the goal of trying to find a less annoying sonic boom. [The premise is that supersonic flight over land is in the near future so let's see if we can shape the sonic boom to be more pleasant sounding] For the research they had an array of rather large horn-shaped drivers outside a house with test subjects both inside and outside the house. Control sound consisted of everyday sounds like trucks, horns etc. At sonic boom frequencies, everything in the house rattled - doors, tables, etc. The system was capable of repoducings frequencies down to 3 Hz ! The low frequency drivers were labeled "servodrive" and looked like large vanes attached to a horn. Sure would make a cool sub :) -lou ------------------------------ Date: Fri, 21 Apr 1995 17:35:07 EDT From: eliot@MIT.EDU Subject: Re: vertical dispersion I am curious as to the differing opinions on vertical dispersion that have been brought up in this thread. The absence (or relative lack) of vertical reflections apparently increases clarity at the cost of ambience. However, the Carver ribbons, which likely have a narrower vertical dispersion that a D'Appolito type speaker, seem to have little such problem. Is this due to their dipolar nature and the presence of the reflections from the rear of the ribbons? If so, perhaps some of the acoustic problems in THX speakers could be alleviated by having them be 'switchably' dipolar, with essentially another speaker grafted onto the back. Since THX mains don't have to go that low if there is a sub, the cabinets wouldn't be _that_ much larger, and it would allow the same set of speakers to be used for music and theater. Eliot ------------------------------ Date: Fri, 21 Apr 1995 17:16:38 -0400 (EDT) From: kodis@daacdev1.stx.com (John Kodis) Subject: Re: Home wiring > I know I wouldn't like to get across the output of an amp with > +/- 70 volts on the rails, much less the family pet or a > teething infant. Could anyone shed some light on this or am > I just concerned about nothing? A few months ago, one of the audio rags reviewed a monster power amp. Possibly from NAD; I'm not sure. Anyway, one thing that the reviewer found irksome was that the binding posts had a hinged plastic cover over them which interfered with getting the cables attached and secured. The reviewer assumed that these were a safety requirement in one of those fussy European countries. In the manufacturers comments, the manufacturer confirmed that the binding post covers were indeed a government mandated safety feature, but that they were mandated by the US government. So there may be some literal justification for the descriptive phrase "a real killer of an amp". - -- John (Bzzzzt) Kodis. ------------------------------ Date: Fri, 21 Apr 1995 17:41:30 EDT From: eliot@MIT.EDU Subject: Delaying the back wave from dipolars Dipolars seem to have improved ambience over standard speakers. However, in all reports of them I have read, there is a substantial problem in room location or room size. The dipolars want to be a long way from a room boundary before they really work. I am curious if anyone has tried delaying the back wave from a dipolar loudspeaker ( it would have to be a dynamic type, for obvious reasons) so that the speaker could be placed closer to room boundries while still retaining some of the airy spaciousness of the dipolar radiating characteristic? Apparently when they get too close to the back wall, the reflections from the back wave are too close in time to the original. This would be most easily done in a loudspeaker with DSP capabilities, but it might work in analog (Textronix manages to delay incoming signals an appreciable amount in their scopes using nothing more than a _long_ piece of cable coiled up inside the scope.) Anyone tried this? Anyone written about this? Eliot ------------------------------ Date: Fri, 21 Apr 1995 13:09:41 -0700 (PDT) From: Mike Ford Subject: Re: Center Channel Dispersion, Pt. Ib > > What I meant was in the following sense: > > The thing that I don't like about the Home THX loudspeaker spec, > aside from the obvious problem that you have a very limited number > of models to choose from, is that vertical dispersion characteristic. > I find that it tends to make such loudspeakers sound rather dry and > beamy, not to my liking. This is a quality that I've observed in > all such units that I've auditioned, and I'm inclined to attribute > it to that dispersion requirement, not that I have ironclad Interesting, so you prefer a more "Boselike" speaker with a higher level of reflected sound? I am wondering if limited dispersion may be a dominant part of the sound of dipole speakers. It has been said that limited dispersion improves clarity, could some of the technical types amplify on this point? How is the sound (measurably) different in the same room when sources of different dispersion are compared? Is the reverberation time any different? ------------------------------ Date: Fri, 21 Apr 1995 12:59:41 -0700 (PDT) From: Mike Ford Subject: Re: SPDIF, computers, ethernet, etc. > > This is getting away from speakers and/or bass but here goes: > > > > I think you mean a PLL stable enough is not a trivial exercise... a > > > crystal oscillator is pretty darn stable when divided down to 48 kHz. > > > > I meant what I said. When you define "pretty darn stable" in picoseconds you > > will find getting a "stable enough" clock at the DAC isn't simple, cheap, or > > easy. > > People argue both sides of whether jitter from one or another PLL > driven by the digital data is audible, so the effect is clearly on the > subtle side. Given that, a straight crystal oscillator will be much > easier to make much more stable than a PLL. > "Audible" is a can of worms. I look at 16 bits of accuracy and let others decide what they can hear. I also don't know what is the easiest or best way to get a stable clock, just that nobody sells one yet that I can afford. ------------------------------ Date: Fri, 21 Apr 1995 12:27:42 -0700 (PDT) From: Mike Ford Subject: Re: bass in rear channels A nice technical discussion of rear channel bass, but I have to say what a dumb concept. We are still arguing about mono or stereo bass (and I prefer mono at the moment) and this person is hawking five channel bass (his idea of bass ends about where mine starts 40 hz). Could it possibly be that he sells full range theatre surround speakers? ------------------------------ Date: Fri, 21 Apr 95 18:16:28 EDT From: ges6@po.cwru.edu Subject: RE: bass on TDC >For the research they had an array of rather large horn-shaped drivers >outside a house with test subjects both inside and outside the house. > Control >sound consisted of everyday sounds like trucks, horns etc. At sonic boom >frequencies, everything in the house rattled - doors, tables, etc. The >system >was capable of repoducings frequencies down to 3 Hz ! The low frequency >drivers were labeled "servodrive" and looked like large vanes attached to >a horn. Sure would make a cool sub :) > > -lou > Look at intersonics??? and phoenix gold. (503-288-2008) Phoenix has(had?) 2 servo subs for the car market. The brochure doesn't have much, but here it is: two units, MDU 15(vortex) and mdu10(cyclone) vortex looks like 2 iso mounted heavy duty 15 inch cones, except there is a big dc motor in between the cones. Looks like the volume between is ~2.25 ft^3, minus motor assembly. Clear plexi enclosure for this volume, looks like 1 inch plexi. nice looking. price: 3000, plus install and enclosure said to be equal to about 6 18 inch speakers, I think. 1 inch excursion. cyclone is smaller and unorthodox. Clear plexi tube, prob 11 inch diameter. uses the a dc motor still, but works sorta like awave pool-big vane rotates inside the tube, and there are openings in the endcaps. High excursion, obviously. price: 750, plus install and enclosure. Both are said to go really low with minimal distortion, but also not to sound right- this maybe due to the lack of distortion, or it may be transient response problems. don't know. may also have been discontinued-I don't see them in my current car audio and electronics directory. greg ------------------------------ End of Bass Appreciation Digest V2 #149 *************************************** A non-digest (direct mail) version of this list is also available; to subscribe to that instead, send the command lines: unsubscribe bass-digest subscribe bass end in the body of a message to majordomo@lunch.engr.sgi.com. Thanks and enjoy the list!