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Discussion Starter · #1 ·
Thanks to Special Guest Russ Herschelmann for his help in lining up this one. Greg Miller is one of the owners of Gold Line, a leading manufacturer of audio test gear. He has written on audio measurement for Sopund & Communications, Sound & Vision Contractor, Custom Home Electronics, and is an Associate Editor at Electrical Contractor magazine. He served as an Instructor at the 2000 Home Automation Expo, where he taught the section on Home Theater Calibration. He also has appeared as guest lecturer at numerous workshops on audio calibration. Starts Nov. 4th.


This will be a good one!


------------------

Steve Bruzonsky




[This message has been edited by Steve Bruzonsky (edited 09-28-2001).]
 

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Greetings from Greg Miller and all of us here at Gold Line. Sweeptime is my long time moniker. In TEF audio analysis, the "sweeptime" is the time that the filters take to sweep across all of the frequency bands being measured.


I am headed out to Chicago in a few days, where we have 70 Audio Consultants coming in from the US, the UK and the Netherlands to spend three days discussing human perception of speech. Dr. Herman Steeneken is coming in from the Human Perceptions Group at the Dutch National Labs-TNO as a Keynote lecturer, along with D.B. Keele of Harman and Peter Mapp, who heads up the AES Section on Intelligibility in the UK. Professor Doug Jones is our Sr. Instructor and moderator for the event. This is the third year we have run the program through the TEF Division of Gold Line, and it is always a little intimidating to be in the presence of so many of my personal heros.


I was at the Dutch National labs a few months ago, and the facility is just amazing. They have chairs mounted in anechoic chambers, with two axis of concentric circle mounts. These are motorized so they can move a loudspeaker to any position in relation to the listener. I have long been told that humans become irrationale when deprived of stimulus by placing them in a anechoic chambers and turning off the lights. So of course I had to try it. If you find me irrationale currently, I can use it as an excuse.


After a half hour of listening to the sounds of my own heart, blood in my vessels and other things that gurgle, I turned on a small flashlight so I could let myself out. When I emerged, everyone seemed to be speaking quite loudly and their voices had a very high pitched metallic sound. The human brain constantly filters out background noise, and in doing so the sound is altered. In the silent chamber, the filters disappeared, and what I was hearing was presumably the true frequency response of my ears. It was a very strange experience and not altogether pleasing.


I look forward to speaking with all of you next month. I am a good source of information on use of analysis equipment and the interpretation of data from instrumentation. I happen to work for a company that makes this type of gear, but I am more than happy to talk about whatever gear you happen to own. We have a policy of not commenting negatively on anyone elses products, so please don't ask me questions like whether mine is better. As to objective standards of what we do in measurement, and how we do it, glad to share the few tidbits I have learned over time.


Tony Grimani while at Lucasfilm THX, once said to me, that while the setting of a sound system involves quite a bit of science, that we must never forget that it is the emotional response that is the objective. Music is part of the vast complexity of the human soul. I like to think of my business as one of bringing joy to people. I know that my involvement in the industry has brought great pleasure to me. Now if I could just find some way to explain to my wife why it is not really dark in my listening room while the music is on.



Best wishes,


Gregory J. Miller

TEF Division of Gold Line


 

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Since Gold Line has been more in the background of our industry rather than in the public/retail eye, many may not be aware of the range of products they provide. Members should go check out their website at http://www.gold-line.com/ . Gold Line manufactures the hardware and software of the 1/12th Octave RTA which Russ Herschelmann has been refering to in his posts. Note that these devices are quite capable. There is even a demo program for download to show how things work. Since I'm expecting that Greg won't be available as a guest until the conclusion of a professional workshop they are running, a good start for forum members would be to read through an article Greg has written directed at home theater installers. The article explains how audio analysis equipment is used to obtain optimal sound performance in a home theater environment, and can be found here:
THE ART OF EQUALIZATION FOR CUSTOM HOME THEATERS


What should be of equal interest to AVS forum members is the new "EQ2" Digital Parametric Equalizer. I had a chance to look over the product at CEDIA and was quite impressed with its capabilities. More importantly, this is a digital parametric EQ that has a very justifiable cost of $1250 for the 2 channel unit. You can find more info here:
EQ2


What readers might not be aware of is that Gold Line also manufactures the TEF measurement system which is used in a wide variety of advanced acoustic measurements and is used by respected consultants, system engineers, and manufacturers.


Hopefully the above info will further help forum members in benefiting from Greg's presence.


Regards,


Mark Seaton


[This message has been edited by Mark Seaton (edited 09-28-2001).]
 

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Discussion Starter · #4 ·
Its almost Nov. 4th, so lets continue asking questions for Greg Miller of Gold Line.
 

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Reality check. Sunday morning is supposed to be nice, so will head out on my Motorcycle for a couple of hours. Then with my head clear, and my system on, will sit back for some audio fun.


Couple of Ground Rules:


1. There are no stupid questions. None of us were born understanding how to calibrate an audio system. It may be hard wired into our brains, but our brain just knows when it is right, not how to make it right.


2. I will not comment on brands i.e. is a so and so better than a xyz. I learned long ago to make the best of what people have, and I will leave it to the mags to sort out the hardware.


3. If you saw the article in Stereophile Guide to Home Theater this month on the DVD we did with Tony Grimani on Surround Calibration, and have questions on how to use the disk, or general issues as to why we put tracks on the disk, glad to go into the story behind the selection of the 100 or so tracks. It was a fun project, but there is a lot you can do with the disk that is not in the documentation. We did not want to make it so heavy that we confused people, but for those who want to go deep, glad to do it.


4. I work for a company that makes audio gear, but no hassles if you are using someone elses. This is about education, so bring it on.


5. I work with all sorts of sound systems, from Concert Rock & Roll to Churches to Recording Studios to Audiophile. Each has a different set of possibilities, but it is all about the emotional experience of great audio. The science is in knowing how to create that experience, to respond to the expectations of the human brain. No small task.



Talk to you guys in a few days.


Greg Miller
 

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:p I'll kick this off with a series of questions. Curious as to how you guys and gals out there in the real world are handling these issues:


1. Have you ever thought about noise in your listening environment. Turn off your audio/video and just sit back and listen to what noises exist in your room. You may be surprised. Question is, what noises do you hear: Heating Ventilation, Clocks, Road Noise, Component fans or for you ultra high end people, your own heart beat......


2. Where are your front loudspeakers mounted: Floor, wall, stands....


3. How close to equidistant are you when you measure from your left front loudspeaker vs. your right front., and if surround same for your center. Are you equidistant.


4. How did you determine toe in for your loudspeakers i.e. where are they aimed.


5. If you have a sub-woofer, how did you decide where to place it?


6. Have you ever used any piece of test equipment, SPL Meter, Real Time Analyzer or TEF Analyzer?


7. Do you use any acoustical materials in your room, and where.



Greg Miller

aka Sweeptime


PS- Riding was great here in CT on Sunday. Changing leaves, 60 degrees, sun shining and miles of twisty back roads.
 

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1. Yes, hopefully will be somewhat corrected in new home we are building


2. Walls currently, only due to kid factor


3. Equidistant


4. Not toed in


5. Again kid factor on top of cabinet/hutch TV is in. Plasma or FPTV for new home


6. yes RS SPL. RTA on order however


7. None currently, possibly in new home


Having limited funds at what price point would you spend on equipment vs. room improvement? I realize this is open ended, but just curious where you feel the point of dimishing return comes in for various equipment (speakers, amps, processors, etc) and room improvement. And of course test equipment.


Thanks

Bob
 

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Welcome to the forum, Gregg.


1. Yep...mostly screaming kids, barking dog, and my sweetheart nagging at me. Other than that HVAC is a real honker (unfortunately the intake is 6 ft from the main listening area), the fridge back in the kitchen can be heard, and my grandfather clock sure does a lot of bonging around noon and midnight :D .


2. They're on the floor (35" towers)


3. Equidistant


4. Toed in for optimum listening at the "hot seat", and also for a little better general dispersion the rest of the way around the (offset) seating area. Used good ol' listening tests to position.


5. It's placed where it is cause that's the only place it'll fit (big son of a ***** - 18" driver) - well not really, the other location caused a little too much cancellation at the listening area.


6. RTA & SPL, but no TEF, unfortunately.


7. Just stretegically absorbent couches, carpeting and the fortune of having my living area, dining, and kitchen all combined as one long room, so rear bound virtual sources are drastically reduced. That leaves me with side reflections and slight ceiling interactions due to the vaulted/2nd window vaulting 10 ft ceiling breaking up large reflections. Pretty good room in general - wouldn't want it much more dead (other than the aforementioned kids/dog/etc).
 

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Tony Grimani once said "life would be so much easier if people did not insist on having walls in theaters". He was of course kidding, but it does recognize that walls create a fair number of problems.


Your loudspeakers being mounted on the walls will interact with the "Boundary" which will effect the pattern of sound radiating from the loudspeaker. Whether this will be a serious problem depends largely on the design of the loudspeaker. In general big loudspeakers are more of a problem, as they typically are used to lower frequencies. The longer the wave length, the lower the directivity of the loudspeaker, and the more energy wrapping around to interact with the wall. This is somewhat generalized, but if the loudspeakers are small, and you are using a separate sub not on the wall, it is somewhat easier. Otherwise, some fairly thick acoustical materials may be beneficial on the wall surfaces behind and along side the loudspeaker.


There are also issues of cancellation. Cancellation occurs when the direct sound from the loudspeaker arrives one half wave length before reflected energy. One of the arrivals is trying to pressurize the air, while the wavelength a half wave back is in the de-pressurized portion of its cycle. When one adds a positive air pressure to a negative pressure, one gets less pressure, which is to say less sound at that frequency.


If the distance is short, the frequency will be high, and as loudspeakers are fairly directional at high frequencies, the wrap around is not much of a problem. A 1kHz a wave is 1.1' long, so a 6" offset would cause cancellation. The wave must go two directions, back to the wall and then forward, so if the driver was 3" path length from the wall, one would expect that it would cause a dip at 1kHz. A 100Hz wave is 11.3' long, so the distance would be nearly a yard each direction. The bottom line, is that if there is a problem, the answer is acoustical materials to absorb the reflection.


If the loudspeakers are in wall, manufacturers take all of this into their designs, and there is less of a problem. Reality, go ahead an try it. Assuming this is not a million dollar system, it may sound just fine.


As to toe in, you state there is none. That means that the loudspeakers are pointed straight back. The tweeters are very directional, but in modern systems they stack them vertically to get greater horizontal dispersion. This will probably cover your listening area. It is not ideal, as in my experience tweaters sound best when they are around 5-10 degrees off axis as referenced to the central seating area, but once again there are many variables. And, for home theater we often set them wider to get better coverage for side seats.


The Radio Shack SPL meters are a good start. They will allow you to see the relative levels between the loudspeakers. In home theater we are looking for 75dB C weighted SPL as referenced from the central seating location, ear level. I have found them to be wildly inaccurate for subwoofers. Obviously more expensive gear is more accurate, but they are a great starting point.


In addition to the reference levels in your Processor, there are a couple of companies which offer calibration disks. Some of these have 1/3rd octave band limited pink noise. With the RS ignore what it says above about 4kHz or below 100Hz, but in between they can give you a good idea of system frequency response. Alan Parsan has a CD, and Tom Holman and Gold Line have DVD with the sources.


As to the balance between dollars for calibration gear vs. audio gear, I guess the question is how do I balance my budget. This is purely my opinion, so remember I work for a manufacturer, and that some of the audio equipment guys and perhaps some of the people on this site my strongly disagree. Having said that:


1. Good Loudspeakers. I have done demo's using a really cheap CD transport with a non-name amplifier and some plain jane heavy gauge oxygen free copper wire connected to a good loudspeaker, and it sounded surprisingly good. If you can afford the really great loudspeakers wonderful, but if you do not like the sound of the loudspeaker, the game is pretty much over. So, that is number one on my check list.


2. Good Loudspeaker placement. I will take a set of $1,500/ pr loudspeakers and set them in the correct location in a room, and blow away a $100k set of loudspeakers poorly placed. And, big full frequency boxes are the most sensitive to location. One of the worst systems I have heard lately used the lovely B&W 801. Great loudspeaker, utterly wasted.


3. Good Processor- Life is tough, but a good processor still sounds a lot better than the bargain shelf units.


4. Room treatments. Few of us have perfect rooms, or the ability to choose perfect loudspeaker locations. Think of acoustical treatments as passive EQ. Well placed to take care of boundary problems and first reflections, a little material does wonders. Use too much, and the room gets dead.


5. Now I really get into trouble. I would much rather have a $1k analyzer, then $1k of fancy wire. If you can afford both, great, but $ for $ I think calibration is much more important in sound quality than 9x sterling silver conductors with magic connectors. There is nothing wrong with fancy wire, just if one has to decide, I would rather have the tools to set up the system, before I spent big dollars on interconnects.


6. Noise Reduction- This is surprisingly important. Take that battery operated tick tock clock, and give it to the kids. Get small LCD clock that makes no noise for your sound room. Also, when you turn down the lights, there is no distracting lights. I am a bit of a fanatic. When really listening, I take off my noisy mechanical wrist watch. If your watch is electric, might not be a problem. Mine, however, is audible. Hate that.


OK- I've opened the flood gates, just remember this is supposed to be fun, so don't get too offended if you disagree, and glad to discuss differences of opinion. That is what this is all about.



Greg Miller
 

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Thanks Greg for the response. I know my setup is far from ideal currently. My speakers are small, Atlantic Technology T70 system with Outlaw 1050 receiver. Everything is up high on the walls ~5ft because the room doubles as the playroom. I initially toed in my speakers and angled them down toward the sweet spot. This did improve the sound of the sweet spot but seemed to make the sound on the second couch worse. So I left them straight. I also initally had the sub on the floor but you could definitely identify what material came from the subs compared to the sat. Moving it up on the TV hutch helped make it more seemless. Anyway, this will probably be my bedroom system in the new house and I'll put all the speakers on stands then and the subwoofer back on the floor.


In your response about balancing your budget you list speaker placement as your number 2 priority and an analyzer as number 5. My question is wouldn't you need the analyzer to assist in proper speaker placement?


Thanks again for your detailed response.


Bob
 

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This is what I consider stage II. You have the gear, you have done the basic set up work and it is probably sounding pretty good. So the question is what is next? Big powerful systems are famous for energizing sympathetic vibrations i.e. rattles in rooms. Ceiling lights, HVAC, Pictures on walls and brick brack are all famous for rattling when the audio energy excites the resonant frequency for the object.


Time to slowly sweep a sine wave through the audio system, and see what rattles show up. You may not have noticed you have a problem, but I am willing to bet you will find lots of them once you start to look. There are a couple of ways to come at this test. The first is to use a sine wave generator. These can range from little battery operated units like our TS3, to slightly fancier 110 units with digital displays like our TS1 to full blown Hewlett Packard lab standards. The other alternative is a test disk that has a slow sweep on it. Needs to start down around 20 Hz and slowly sweep upwards. On our DVD the sweep is two minutes. There are plenty of other disks, what you are looking for is really slow sweep. When something starts to rattle, find it, and do whatever is necessary to make it stop rattling. Little bits of foam insulation work for cool surfaces. For pictures the moldable wax they sell for hanging pictures works. For metal ducts, little flexible magnets can add some mass. And sometimes, it is just a matter of better mounting the existing hardware. The key is to find these problems and fix them.


This is part of the psycho-acoustic realm. You may not be aware of the fact that you have rattles, as your brain filters them out of your conscious experience. The process of filtering, however, takes up limited brain power, and reduces the audio experience.


Those of you who have the ability to do this test, try it and let me know what you find. I have swept hundreds of rooms, and with the exception of the big dollar stuff Russ builds, they all rattle. A little work and a dramatic improvement in the listening experience can be made.


Greg Miller
 

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An analyzer is a great tool. At the professional level we all have them. And, as I make my living selling them, I don't want to be acused of bias, so here is my best attempt at a balanced response.


1. Placement of subwoofers can be largely accomplished with a sine wave generator to evaluate the room modes. There are also spread sheets to assist with this task.


2. Placement of Front and Satellite loudspeakers can also be accomplished to a lesser degree with a sine wave and pink noise. If the sound is interacting with boundaries to create a series of cancellations (Comb filtering), then walking across the pattern of the pink noise will tend to be heard as a shifting frequency. This can also identify the effects of lobes from the loudspeaker designs. I recently did a room with the little Wilson Watt 5 Pups. When we had the distance, toe in and placement correct they sounded pretty good, but I suspected there was more to be had. We started playing with the seating height, and the sound stage just opened up with a great phantom image. We found this by looking at the response with an analyzer. Having said that, if you do not have an analyzer, listen. I always finish up my analysis of the seating position, by moving my head on all three axis by about six inches, to see if I can find a sweet spot.


3. One of the nice parts about having an analyzer, is that you have an objective standard. Lars Fredell lives down the street from me, and Lars keeps one set up all the time. He has a really good data base of his room, and when he changes anything, he imediately compares the data to the base line. He indicates this has allowed him to make significant progress, and I have to admit that his system sounds really good.


4. Once again, it is a matter of priorities. There is no replacement for a good set of ears. An analyzer, however, is good at identifying the nature of the problem. And, if you are using EQ, an analyzer will save hours.


5. If people want to discuss EQ, glad to go into the topic.


6. Finally, we may be in deep trouble. Looks like the Galactic Overlord may be coming up on this site. All I can say, is if he comes, listen. Will not give away who he is. And, if you think his comments are outrageous, think very carefully before flaming. This guy is heavy. Looks like a few others hiding out there in the wings. Some big sticks in the neighborhood. This should be fun.


Greg Miller
 

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Thanks for being here Greg,

Quote:
If people want to discuss EQ, glad to go into the topic
Please go into detail about your approach and recommendations about EQ'ing a dedicated home theater.
 

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Modern Digital EQs are amazing devices. Parametrics provide us with 100s of potential center frequencies, and tremendous control over the width of the filter. And, they manage to do this with far less shift in phase than was possible with traditional analog units.


Having said that, an EQ is not a silver bullet. They are used to correct specific types of problems, and when used with a degree of thought can provide significant improvements in sound quality. Routing the pink noise to the correct channels is difficult unless you have a calibration DVD. It can be done by running a generator to individual channels at the amplifier, but you will need trims to control the levels from the amplifer. Reality, use a disk with multi-channel pink noise. If you are using a TEF, then you can control the output from the TEF, and would go to each of the channels. In either case, turn off the sub(s), before seeking to EQ the front channels.


I start the EQ process by first measuring the frequency response of the Center loudspeaker. Remember that ~70% of dialog comes from the center channel, so this is arguably the most important loudspeaker in a home theater. First I look at the shape of the curve to see if I have the crossover set appropriately. I should see the frequency response roll off below 100Hz, as the low Frequency energy is being sent to the sub-woofer in a typical system. If the microphone is placed vertically at the "Money Seat", I will also see a roll off above 6.3kHz as the short wavelengths and pattern of even an omni mic are directional. This is fine. I am looking for a smooth curve from 100Hz to 6.3kHz. There is normally a smooth plateau of energy around 1kHz, and I use that to define my reference level. I then look for the areas which are above reference, and ask why. Often times I will take a thick pillow or a piece of acoustical material, and try placing it around the loudspeaker to see if the energy comes down. If it does not, then I am going to consider using some EQ to bring the level down closer to the reference level. A modern analyzer should have an overlay mode, so I first plot the base line with no EQ. Then I set the filter frequency for the center of the problem region, and with a 1/3rd octave filter pull it down 3dB. I then overlay a new measurement to see if the filter was effective. From the overlay I can see whether my filter was too narrow or too wide. I will then adjust the filter width "Q" to get the best fit to the data. Next I will add or reduce the amount of cut until I get close to the reference line. This is somewhat tricky as there is not a perfect answer. In most cases, in order to get the peak down, you will still have the skirts of the filter pull down more of the adjoining filters than would be ideal. If I can end up with the peak within 2dB on the plus side, I will put up with the skirts being a dB or even two down to get there. Having said that I rarely use more than 5dB of cut, as the swing in phase from the filter begins to adversely effect the sound in my opinion. Others claim that the phase change is less audible, and my response to each of you is to listen.


I am very cautious with using boost, as dips in frequency response are often caused by cancellation which cannot be corrected with an EQ. A trick I use is to measure the base line, then put in 3dB of boost, and then re-measure. If it is cancellation, you will get very little additional level. If this is the case, the solution is acoustical materials to absorb the reflection, or to change the loudspeaker position. If you are using a graphic, do not feel that you have to set every filter. In a normal system, four or five filters per channel is pretty much my max.


Another caution is that while EQ often have 12dB of boost, that is 16 times the power. So if the system is running at 100 watts, when you get to that frequency you would need 1,600 watts. This tends to toast loudspeakers, amplifiers and such. So, avoid the temptation to use large amounts of boost.


Once I have the center channel fairly smooth, then I set that as an overlay on the analyzer screen, and compare it to data from the left and right. I am looking for similar response from all three front loudspeakers, so the frequency does not change as the image pans across the front.


I am not super picky about surrounds, but once again, we are just looking to correct dramatic peaks.


Subs are tricky. Remember that they should roll off above ~90Hz. Many subs produce little energy below 32Hz. You cannot fix this with an EQ. Subs use ferocious amounts of power, so I am very cautious about using any boost from an EQ for a sub. Even 3dB of boost doubles the power requirement.


Unlike the problems with absorption seen at higher frequencies, the low frequencies are dominated by modal energy. These tend to be very narrow bands, and I always use 1/12th octave analysis. A 1/3rd octave analyzer blends too much of the energy into the wide band, and makes it very difficult to work with subs. Same comments as to EQ. If it does not have at least 1/6th octave resolution, it is unlikely to be useful with a sub.


One trick that I use is to slowly sweep the filter center around the area of the peak, and watch the response. Modern digital EQ can achieve spacings which are as small as a 1/2Hz. Start with filters at a 1/3rd Octave, and then start to sharpen them until the best response is achieved.


Finally, EQ will effect your overall levels, so when you are done you need to re-set your 75dB(c) from the processor test tones with an SPL meter. Most analyzers have high quality SPL meters included.


If one has a TEF Analyzer, the basic procedure is the same, but one can monitor which way the Phase is going as one changes filters. In most cases where EQ will be effective for the mid-high frequencies, the phase will be moving towards zero.


Not sure how deep you guys want to go, if you want more, I am prepared to go deeper.


Greg Miller
 

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Thanks Gregg,


I am sure I'll be calling you when my RTA arrives! I am curious what exactly a TEF analyzer does. What does TEF stand for? I am guessing some type of phase/ time analysis.


I plan on adding a parametric EQ (not digital) for my subwoofer in my new system. I think the cost of EQing every channel would cut too much into my budget for overall equipment. Hopefully I can tame any other peaks reasonably with room treatments.


Here are some questions for quieting a room. In my new home I already planned on staggering studs for the walls and attaching the drywall to hangers for the ceiling. The house is to be heated with FHW. Anything I can do tame that noise? I've already made sure that no ther plumbing or extra electrical is to go through that room. What else can I do during construction phase to help isolate that room that isn't going to cost thousands?


Bob
 

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There is not a simple answer to your questions on construction. You are on the right track watching what penetrations are made in the walls, and assuring that they are properly sealed.


Think about where you HVAC vents are going. These can pass sound to other parts of the house, and if the vents are close to seating areas, can be the source of turbulence noise from the air flow. In general you want big ducts with low air speeds. And, you want them as far as possible from seating locations. There are all sorts of products which can be used to treat ducts to reduce noise in them, plus adding right angles and such will reduce the direct flow of sound down the path. The Vibro-Acoustics web site has a lot of good materials on noise and duct works. Their URL is www.vibro-acoustics.com . I have no relation to this company, and have not worked with them. Their site, however, has some great stuff, and I see them at some of the trade shows.


As to TEF, it stands for Time, Energy & Frequency, the three domains of audio energy. TEF is one of our Trademarks, and the machine is based on a patent by Richard Heyser, who prior to his untimely demise was with JPL. It is a system that uses a tracking filter locked to a swept sine wave to measure sound. It provides the user with the time that the energy arrived, the direction from which the sound arrived, the frequency response, the phase and many advanced features such as prediction of intelligibility, distortion and post processing of data to show the directivity of a loudspeaker.


I don't want to toot our own horn to much, but let's talk about a time based analyzer vs. a real time analyzer as a general concept. The simplest analyzer has one axis- Energy averaged over time. We would refer to such a device as an SPL meter. It measures the Sound Pressure Level over a specified amount of time, and displays it as a total, referenced to a pressure of 20 micropascals =0dB. If we took the SPL, and rather than showing it for all frequencies within the audio range, divided it into groups of frequencies, we would call it a Real Time Analyzer. In the old days, we ran 1/3rd octave band limited pink noise, and measured the level. It took 30 measurements to measure the 1/3rd octave frequency response. An, RTA does all of these at once, which is why it was called "Real Time" analysis. The next axis would be to divide the energy in the groups of bands, and divide them up as to when they arrived. This allows us to see when sound arrives, to see how it reflects in the room, and then how long it takes to decay. As high frequencies are more easily absorbed than low frequencies, typically sound decays faster at high frequencies.


I was recently in the field looking at a small expensive home theater system here in CT. Nice stuff. Full Krell Rack. Arial Acoustics Loudspeakers. Expensive room treatments. The owner had a small table in front of the listening position, and there was a small overhang above the listening position. The sound was striking the overhang, bouncing back to the Rear Projection Screen, then bouncing forward to the listening position, causing a reflection that was quite destructive to imaging. Then the bounce off of the table was causing cancellation. The Loudspeakers were too close to the corners, causing summing of energy. The net result was a very expensive system that did not work. The solution was fairly simple, once we measured where the sound was coming from. Of course, we could have thought it through without analysis, but when one can see the data, one can quickly prioritize the significance of problems.


Greg Miller
 

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Fascinating! Go deeper, especially with respect to FFT measurements and such. Also, does your TEF analyzer software provide plots in a variety of formats, such as waterfall plots for freq resp curves?
 

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Quote:
Originally posted by Sweeptime
After a half hour of listening to the sounds of my own heart, blood in my vessels and other things that gurgle, I turned on a small flashlight so I could let myself out. .............It was a very strange experience and not altogether pleasing.
LOL. I would like to try that but I have a feeling it would freak me out. :eek:



are the instruments that you use to analyze a room calibrated in an anechoic chamber?
 

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Greg,


I have a few questions for you....


Everybody's budget SPL meter of choice is notoriously inaccurate at both frequency extremes, but is very accurate for the musical midrange.


In price comparisons, your SPL meter is mid-priced vs something along the lines of an Audio Control SPL/RTA meter. What type of accuracy does your SPL meter have vs. the Radio Shack product? How about vs. the Audio Control product?


There are definite advantages to reproduction chain calibration, where you use a DVD to calibrate system levels from DVD player through amplifier, rather than just using the internal tones from your processor/receiver. I am curious what formats the Audio toolkit contains. DD? DTS? Pro-logic? THX-EX? DTS-ES? Pure stereo? Obviously the more the better. So far I haven't seen anyone provide a disc that allows for DTS to be calibrated in this manner, and was hoping that your test disc might do just that.


In response to your earlier questions:

1) If the projector is on, I hear the fan until my hushbox arrives ;-) Other than that, I hear a small amount of outside noise depending on time of day, and HVAC noise when the heat or AC is running (a mild air churning type noise). On a very windy day, I hear that in the room as well.


2) I use floorstanders, they're planar hybrids, so they're also fairly tall.


3) Equidistant by measurement to Front L/R and the CC is equidistant as well. This assumes I should be measuring to the center of the speaker and not its comparable location on the floor.


4) I started with a mirror in the primary listening position and got the speaker to just show in the edge of the mirror, then tweaked by ear. A set of review speakers I currently have has taught my a lesson or two (which is good) and after they're gone I'm going to be working on imaging on my mains. You think it's good until you hear something better, you know? So I'll be moving them slightly closer together. They're aimed so that the drivers don't quite center on where my head is in the normal positions.


5) I went for the most practical location which gave me smoothest FR on a bass decade test via the RS meter.


6) Yes. But I'm going to be purchasing something better than the RS meter when the opportunity affords itself.


7) Yes, I use absorbers for the first reflection points of the mains, and these were placed using a mirror to spot the speakers along the walls. I have diffusors directly behind the primary listening position along the back wall.


Thanks for participating Greg!
 
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