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Old 21st October 2005, 19:26   #1
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Smile Designing a Home Theatre System

Nearly two years ago when I was preparing to return from USA to India for good, I went through great pains to design a Home Theatre System for my new home in India. After that I published some articles on the web based on my research. Some of the figures may be old, but the information is mostly is useful. Therefore, I thought of publishing those articles with minimal changes.

Here goes... [This was originally written in 2003]

Designing my THX Select Home Theatre System
I recently finished designing the Home Theatre system for my home in India. While this thread may be too technical for those uninitiated to Home Theatre, it may also help them learn.

I am a former Bose Home Theatre owner and I have helped many friends and family setup their Home theatre systems. As I learnt more and more about Home Theatre systems, it became very important to get rid of my Bose satellite HT system so that I can design a good HT system from ground up. Bose speakers are mysterious since their specifications are never published except for power and impedence which are meaningless without futher info (more on that later).

I want a THX Select certified system, at least approximately. It would be sweet to have THX Ultra or Ultra2, but I can't seriously throw around that kind of money. BTW, THX is a surround sound standard for Movies developed by Tomlinson Holman (Tom Holman's eXperiment) for Lucas Films. Ultra is for commerical use and Select is for home use. THX certified systems are great for movies (DVDs), but not so for music listening (CD). Since I use my system mostly for DVD movies, that's fine with me. However, THX Ultra2 (which I can't afford) has fixed that short-coming.

Based on my budget, I aim to get a THX Select system that can reasonably handle THX certified DVDs. To achieve this, I need three major components, DVD player, A/V Receiver and 7.1 speakers. If I lots of money to burn, I would go for THX certified DVD player, A/V receiver and 7.1 Speakers. As noted before, I can't do that. However, there is one component that has to be THX certified to ensure all the four THX processings are done correctly. The four processes are THX Re-Equalization, THX Surround Decorrelation, THX Timbre matching and THX Subwoofer Crossover. These processes are done by the THX certified A/V Receiver. Regarding DVD player, you can get away with a decent non-certified player. However, non-certified speakers have to be chosen carefully to take care of the THX requirements. This is how I went about doing it.

DVD Player: Since there are no THX requirements, I considered following specs:
1) Support for both NTSC/PAL DVD and output in PAL. Yes, TVs are multi-system, but can't expect the same from A/V Receivers. I don't want the A/V Receiver to choke on NTSC.
2) Support for CD,CD-R,DVD+R/RW,MP3 and VCD apart from usual DVD.
3) Progressive scan possibly with 3:2 pulldown (for NTSC). Yes, there are TVs with progressive scan, however DVD player line doublers are known to have better circuits.
4) Nice to have DVD-Audio capability and Faroudja DCDi circuits; Okay, now I am going overboard.

I found Yamaha DVD-S540 to be the closest to my requirement and available via Yamaha dealers in Bangalore. Missing features are 3:2 Pulldown and DVD-Audio, and I wasn't really hoping for DCDi circuits.

A/V Receiver: This had to be a THX Select certified system with 7.1 outputs. The requirements are as follows:
1) Seven independent amplifier outputs with atleast 80W of power.
2) Subwoofer pre-amp output, which is given.
3) THX Select processing on the decoded signal.
4) Decoding for THX Surround EX, Dolby Digital 5.1/6.1, DTS-ES (Matrix/Discrete), DTS Neo, etc.
5) Upgrading all video signals (composite/S-video) to component video with 480p support.
6) Support for future formats including DVD-Audio pre-amp inputs.

Until a month back the cheapest available THX Select certified 7.1 A/V Receiver in India was Onkyo TX-DS898G at Rs.123,000. Therefore, I had given up on THX and was thinking about buying something cheap for now and wait for couple of years. Then I came across Yamaha RX-V1400 which is a THX Select certified 7.1 system for Rs.56,000 in Bangalore. It is only $600 in USA, but I want the 220V version and local support. It has all the features I wanted and more, even better than the Onkyo model that costs twice. It also has the 6 channel pre-amp input for DVD-Audio player I might buy some day.

Speakers: Now that I had the A/V Receiver I wanted, I seriously started looking for speakers that can satisfy base THX requirements if not certification. This was one component I could take from USA since it has no format or voltage dependency. This was also one of the most tricky selection since wrong speakers can totally spoil the Home Theatre party. My first choice was to look at 7.1 speaker packages. Yamaha which makes THX 7.1 A/V Receivers didn't make any 7.1 speakers, they stopped at 6.1 speakers, which was really odd. Then I considered buying a 5.1 speaker system and adding two more speakers, which is reasonable. As I went deep into speaker characteristics, I started getting uneasy about buying packages. Here were some of my concerns.

1) The power handling vs performance of speakers can be very misleading. The sound level produced by a speaker doesn't just depend on the power, but also on the speaker sensitivity. For example, a speaker with 83dB sensitivity driven at 100W will produce the same sound level as a speaker with 86dB sensitivity driven at 50W. For every increase in 3dB sensitivity, the power required to produce the same sound is halved. In other words, 83dB speaker running at 100W sounds same as 95dB speaker running at 6.25W power. Amazing, isn't it? So, what do you think about the Bose speakers that claims to handle 200W while shying away to mention the sensitivity. What does that really mean without sensitivity value?

2) Almost all non-THX speaker package systems use direct radiating or monopole surround speakers. THX requires that all the four surround speakers should be dipole/dipolar speakers in order to diffuse the sound all around the audience. If you hear the surround speakers directly, it is not THX. The direct radiating speakers center on a small sweet-spot, if you are sitting away, the effect is lost on you. The diffused surround sound will create much expansive sweet spot.

3) THX requires that all the bass is handled by the Subwoofer. That means the center/front(L/R)/surround(L/R)/rear-surround(L/R) should only produce mid-range and high frequencies. Only Subwoofer will handle all the bass. I saw lots of speaker packages providing bigger front/surround speakers to handle bass, which may be okay for CD listening, but not for movies.

4) Since our Bangalore apartment is small, my wife wanted all the speakers to be compact and cute like the Bose satellite speakers and also match the wall/ceiling colors if mounted. I too agree with that logic. This was probably the only feature most HT satellite speaker packages met.

Based on the above concerns, I dumped the speaker packages and started designing a 7.1 speaker system, one speaker at a time.

1) Surround speakers: Many speaker packages offer the same speaker type for front/center and surround speaker. While this is fine for a direct radiated surround system with tiny sweet-spot, it is a big no-no for THX systems. Therefore, I started hunting for dipole surround speakers. Because of the living room design at my apartment, I have to wall mount all the four surround speakers, which means they have to be satellite speakers. Besides, THX doesn't send any bass to surround speakers, therefore they can be small with only mid-range and tweeter drivers. Finding a good satellite dipole surround speaker was quite a challenge. Finally, I found them at Cambridge Soundworks.

2) Center/Front Left/Front Right: These three have to perfectly matched to avoid variations in sound. When a car moves from left to center to right, you should hear it move naturally, no jump up or down in sound level due to speaker mismatch. The best way to achieve this is to use same make/type for all the three speakers. As before, I wanted these to be small speakers in order to fit the apartment. Since bass is produced only by the Subwoofer, this shouldn't be an issue with THX. Again I found a good front/center speaker from Cambridge Soundworks.

3) Subwoofer: This is a very important speaker since all bass will be produced by the Subwoofer. In fact, this can be called just a Woofer for that reason. This will be powered, therefore has to be in 220V version. Therefore, I will be buying this in India. Since Subwoofers are really heavy, all the more reason to buy it in India. The speaker sensitivity has to be matched with the other speakers and it's crossover frequency has to overlap with that of the other speakers so that we won't lose any sound. The Subwoofer crossover frequency will be set in that overlapped area.

My System:
Center: Cambridge SoundWorks Newton Series™ MC300 Main/Center Speaker (review)
Front(L/R): Cambridge SoundWorks Newton Series™ MC200 Main Speaker (review)
Surround (L/R/BL/BR): Cambridge SoundWorks Newton Series™ S100 MultiPole™ Surround Speaker
Yamaha RX-V1400 THX Select Certified AV Receiver
Yamaha SW315 Sub-Woofer

I picked the more expensive MC300 for center since MC200 is not known to be a good center speaker, but pretty good for front left/right. The tonal characteristics of MC300 and MC200 are perfectly matched, atleast according to the tech guy in Cambridge Soundworks. I was still wondering about that, then he pointed out that their home theatre package is designed that way using MC300 as center and MC200 as Main L/R. That closed the issue.

All these speakers have 86dB sensitivity with 10-120W power handling. The frequencey response is at 100Hz to 20KHz. Therefore crossover frequency has to be above 100Hz, which is a little high for THX which recommends 80Hz, hopefully it shouldn't matter.

I have used many technical terms here that may be pure English to HT gurus and pure Latin to the uninitiated. You can find the explanation to all of them by googling those terms. Therefore, I won't try to explain those terms and further stretch this post.

Last edited by Samurai : 26th February 2014 at 12:51. Reason: some updates
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Old 21st October 2005, 19:31   #2
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Default How to buy a low-end but decent Home Theatre System

How to buy a low-end but decent Home Theatre System

This article is addressed to people who want to have a good home theatre system in a low budget, say within a $1000, excluding the TV. This is not for audiophiles or people with bigger budgets. I am only trying to address people who don't want to get into technical details, yet like to have a good home theatre system.

First let me deal with the Bose issue. With desis, Bose is a big attraction, don't know why, but it is considered a prestige to have a Bose Home Theatre system. Even if you have a 10 times better HT system, your desi visitors and friends will still say "Hmm, not a Bose". No matter how much you defend your system, you won't convince them. That's the power of brand name.

If prestige factor is important, you would want a Bose HTS, and your choice is simple. Pick a dollar figure for your budget, and then look for the most expensive system within that budget. You are done.

Now for people who are not merely swayed by brand name, you guys need to learn a little more and make more decisions. And for that extra effort and prestige sacrifice, you will get a better system for less money.

A Home theatre system is essentially a surround sound system. It was discovered in the 70s (by lots of experimenting) that the minimum number of speakers required to provide a true surround sound effect is five, which includes LeftFront, Center, RightFront, LeftRear and RightRear. The woofer provides the bass effect and is non-directional, it has no role to play in surround sound. Therefore, if somebody tries to sell you a 2-channel, 3-channel or even 4-channel surround sound, it is not true surround sound. Hence the name 5.1, five mid/full-range speakers and a woofer. You can better the effect by going to 6.1, 7.1, 8.1 or even 9.1 systems. Also, HT systems are mainly aimed at movie effects rather than music. If your fancy is mostly towards to music, a HTS is not your cup of tea. For once you may be better off buying a Bose stereo music system, afterall Bose created their brand by selling great stereo music systems.

There are 4 major components in a Home Theatre System.

1) Source component: These are equipments that provide the video and audio signals. For example, VCR, DVD player, Cable Box, Dish Receiver, CD player etc. You can have many source components in a single Home theatre setup, most have three namely VCR, DVD player and Cable/Dish Receiver box.

2) A/V Receiver: This equipment has three major functions. (a) Multiplexer: The receiver can take many audio/video inputs and will selectively give out only one video/audio output. For example, you can connect VCR, DVD Player and Cable to the receiver input and then connect the single output to the TV and the speakers. And the receiver will let you select any one of the inputs to be played at a given time. (b) Decoder: The receiver will decode the digitally encoded music like Dolby Digital 5.1, DTS or matrix encoded Prologic surround sound signals into separate channels as designed by the sound engineers of the original sound tracks. (c) Amplifier: The reciever will amplify each channel signals to provide high current so that it can directly drive the speakers.

3) Speakers: This one is obvious, you need to hear the sound, therefore you need speakers. As explained before, you need minimum five speakers for a true surround sound experience. There are different types of speakers, full range, tweeters, mid-range, woofers. The drivers or the cones that play high frequencies are called tweeters, the drivers that play mid-frequencies are called mid-range, and the drivers that play low-frequencies or bass are called woofers. Many speakers have mutliple drivers or cones. Lower the frequencies, bigger the cone the driver needs. If you fancy compact satellite speakers as main speakers, you will need a separate woofer to play the low frequencies. The speakers that have all three types of drivers are called full range speakers. If all your speakers are full-range speakers, you can pretty much leave out the separate woofer.

4) Television: This is one item where most people don't need much advice or at least think they don't need any advice. If you like the picture quality and the screen size, and one can safely buy it. Still, I would like to give some advice. If you are buying Plasma, DLP or HDTV, you can't go wrong buying based on size and picture quality. However, my advice is for people buying normal TV. Please make sure it has progressive scan with 3:2 pulldown correction. It makes a huge difference in picture quality. Go to circuit city and compare a TV with and without progressive scan with 3:2 pulldown correction. One will be smooth and have no visible horizontal lines, guess which one.

Most aspiring HTS owners already own TVs and DVD players and VCRs. Therefore, let's keep them out of the scope of this discussion. So we have entire $1000 or less towards the A/V Receivers and Speakers.

If you are really on a shoe string budget which is below $500, then are you not going get a good HT system. That's really very low. If you still want to have a HT system, you could buy one of those Home Theatre in Box kind of deals. However, most of them fall short of producing good surround sound. But hey, you may get lucky and land a good system in some sale, you never know.

The segment I am addressing here not techie enough to study every aspect of HT and design a good system. Therefore, let me make it simple.

A/V Receiver:

1) It should at least decode Dolby Digital 5.1, DTS and Prologic II.

2) It should drive at least 100W of power in each separate channel.

3) It should accept both Optical and Coax digital inputs. Some DVD players have only Optical output and some have only Coax. If you change your DVD player, you don't have to end up buying a new receiver. This did happen to me once.

4) Look for speaker output rated at 8 Ohms since that will match most speakers.

5) Try to pick from companies well known for their HT audio hardware like Yamaha, Onkyo, etc.

6) Know this, you can't easily spoil the speakers by sending more power than they are rated. However, you can easily spoil the speakers if the Receiver maxes out and sends distorted signal. Therefore, always try to have a Receiver whose power is rated higher than the speakers.

Speakers:

1) If you don't know much about speaker selection, you are better off with speaker packages that have 5 speakers and one subwoofer. And they are cheaper than buying individual speakers. Plus, you don't have to worry about speaker matching.

2) Make sure each speaker can handle at least 80W max rms. Don't be fooled by PMPO (Peak Music Power output) power specification. Divide the PMPO by 1.414 to get the real RMS power value.

3) Make sure impedence rating of speakers match the rating of the A/V Receiver. Usually 8 Ohms is a safe bet.

4) Go listen to the speakers at a showroom. Remember, you don't measure speakers by their loudness. Look for lack of noise, crispness, timbre. Pick the kind of movie with lots of sound effect and play it through that. Look for clarity if you can't make out anything else.

Speaker wire: Many speaker packages do provide speaker wires, although most are rated between 18 to 24 guage, lower the better. However, if you have to buy it, go with 16 guage. You can buy 100 ft of 16 guage for 20-30 bucks. Don't worry about monster cable, it's very good, but that's one more overpriced brand.

Home theatre systems are not primarily designed for music, although it could be a decent stereo system. Recently many music tracks are encoded in Dolby Digital, which are very good. The songs of Hindi movie Taal on the DVD sounds heavenly on the HTS, and sounds flat if played from a CD on the same HTS. The difference is that DVD version is encoded in 5.1 and the CD version is 2-channel stereo.

If you want to play music files on the computer via the HTS, it can be easily done. Connect the Line-out of the computer sound card to one of the audio CD input of the A/V receiver using a Y cable. However, that music will only be 2-channel stereo.

Now, if you still want a Bose and want to have a good HT system, you can strike a compromise, a good one. Buy a Bose speaker package that only has 5+1 speakers and none of their DVD/CD/Tuner modules. Get a A/V Receiver from a different company and set it up. Then, you will have a Bose Home Theatre that actually sound good. Your Bose-happy friends will only see the speakers and not the Receiver, that will keep them happy or should I say envious...
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Old 21st October 2005, 19:33   #3
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Samurai thats awesome. It's worth for a PhD in Home theaters
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Old 21st October 2005, 19:39   #4
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All I can say is

Can you customize your article in Indian context with approximate price points? It will be even more useful.
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Old 21st October 2005, 19:48   #5
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Quote:
Originally Posted by satish_appasani
Samurai thats awesome. It's worth for a PhD in Home theaters
Thanks. BTW, by any chance are you a VC of an University...

Quote:
Originally Posted by RX135
Can you customize your article in Indian context with approximate price points? It will be even more useful.
Oh, sorry about that. I am really out of touch with the Indian prices now, and don't really have a reason/motivation or time to research.
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Old 22nd October 2005, 00:16   #6
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If I was a VC of an university, 50% of the tbhp members could be holding a PhD for their knowledge in cars, car audio etc.
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Old 22nd October 2005, 11:33   #7
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Quote:
Originally Posted by Samurai
3) Subwoofer: This is a very important speaker since all bass will be produced by the Subwoofer. In fact, this can be called just a Woofer for that reason. This will be powered, therefore has to be in 220V version. Therefore, I will be buying this in India. Since Subwoofers are really heavy, all the more reason to buy it in India. The speaker sensitivity has to be matched with the other speakers and it's crossover frequency has to overlap with that of the other speakers so that we won't lose any sound. The Subwoofer crossover frequency will be set in that overlapped area.
A sub is the easist to DIY and in fact offers some great advantages to the DIYer.

If I were you I would research some good subwoofer drivers (see www.diyaudio.com for more there is a Loudspeaker section in which there is a section just covering subwoofers) and good amplifiers (plate and otherwise) and get them to india only leaving for the box to be built by an good local carpenter in india.

The advantages:
Since the subwoofer is the most boundary depedant speaker you can make one that works best in your room and location.

for example only if you DIY can you make a sub that is 8 feet tall but only 8" deep and 15" wide. So as a DIYer you can build the subwoofer to fit inside, under or behind furniture and take advantage of boundary reinforecement from the walls of your room.

I have even seens subs that were built into walls in india. A friend of mine for example tore down a brick wall (no beams and.or colums were touched) and replaced it with a wall that is made of marine grade ply. the sub box then effectively became 8.5 feet tall, 6 feet wide and only 6.5" deep. He has 4 Peerless 12" (830845) XXLS woofers doing duty as subs in the space. The wall is obviously well braced.

If you have more depth available i'd recommend these as they have rubber sounds v/s the foam surround of the Adire Tumult subs.

http://www.soundsplinter.com/rls_sup...r_drivers.html
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Old 22nd October 2005, 14:29   #8
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Navin, you gave some pretty good ideas, woofer inside furniture/wall, cool . BTW, my article is nearly 2 years old, I finally bought Yamaha SW315 after moving to India, very happy with it.
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Old 9th November 2005, 01:06   #9
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Samurai, The article is too good and very informative. I was actually looking for a sound advice on HTS and your article is exactly what i was looking for. I actually liked the idea of mating the Bose 5.1 speakers with a good A/V Receiver (diff brand). Can you suggest any particular models of a/v receivers that might work well with a bose 5.1 speaker system?
-Chaxy
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Old 9th November 2005, 11:04   #10
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Originally Posted by chaxy
Can you suggest any particular models of a/v receivers that might work well with a bose 5.1 speaker system?
-Chaxy
There is another thread on HTS where all the recommendations are being done. Therefore I'll make my reply in that thread (The Home Theater thread). The purpose of this thread is to impart knowledge on HTS rather than make specific recommendations.
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Old 19th November 2005, 17:37   #11
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hi, just saw this post - maybe my inputs will be helpful. or maybe they'll just open up a can of worms!

IMO, THX is fraught with much more problems than it aim's to solve - on both, a practical and a theorectical level.

...The basic problem with thx is the requirement for speakers. Because of the vertical directivity consideration (where speakers must radiate their sound energy into the room and not into the walls), all thx speakers must have 3 drivers for the satellites. viz 2 mids placed vertically over a central tweeter. This is commonly known as the D'appolito configuration or also an MTM (midrange - tweeter - midrange)

The idea is that, in such a configuration - the speaker acts as a point source and all the sound appears to come from the centre of the cabinet viz the tweeter. This configuration also provides vertical directivity by increasing the energy in the frontal plane of the radiation, thus reducing floor and ceiling reflections.

While this confiuration is not bad in itself, the issues that they throw up are tremendous. For the configuration to work correctly, the speakers have to be centred at the ear level of the listener and all the 3 speakers have to be placed at the same height. these 2 conditions can never be met in a typical home - for the simple reason that the centre speaker has to be placed above or below the tv. In a theatre, this is possible because the 3 speakers are placed behind an acoustically transparent screen.

If the speakers are not placed at ear level, severe phase cancelations occur, due to 2 radiators (the 2 mids) giving the same sound but from asymettrical distances. In addition, all centre speakers in homes i've seen are placed horizontally - again a no-no for clean sound, but a standard placement constraint in all practical rooms.

These two factors itself kill the thx format in homes. also, these factors are never highlighted by thx themselves - because then their system becomes impractical.

How many people with thx speakers place the left right centre at the same level, at ear level, and then place them all vertically? No one! Then, bye bye thx, hello phase cancellations and bad sound!

Dipole surrounds suffer the same fate - to be used accurately, the listener has to be placed optimally in the null radiating field of the dipole. For more than 1 listener, this is impossible unless all listeners are seated in the same horizontal line! That's why all dipole speakers today come with a dipole off switch...so that they can act as monopole or point sources for 'practical' placement.

The concept of 7.1 thx takes these absurdities to a higher plane!

Remember, creating a sonic illusion is what good sound should be all about. Visually, to see an illusion, it means that an image appears to be floating around in the air - not created by anything practical that we know of, like a tv etc. Seeing a 3 dimensional image from a 2 dimensional plane is also an illusion - because it is beyond the practical.

The same with sound - if we hear sound from a position where a speaker is not present - that's a sonic illusion. if sound comes from the same spot that the speaker is in - that's electronics. So, the more the speakers, the less the possibility of a sonic illusion.

Besides -with all the practical constraints of home listening environments, getting 5 speakers to be placed correctly is a far cry, let alone 7 speakers being optimised for placement in terms of position, phase, delay, level etc - it's almost impossible. a sonic illusion is even more impossible with a 7.1 system than with a 5.1 system.

At the end, good sound is about an immersive iilusion. If a scene in a movie has the sound of rain, obviously, the engineers at dolby will send the sound to all the speakers and the rain will come appear to be all around you - because the speakers are placed all around you. But when you hear the rain coming from the ceiling, you feel the movement of the clouds overhead and you almost see the spots of wetness in your room, when you shove your arms together and huddle up because of this rain sequence, that's an illusion.

If a scene like this makes you want to open up your umbrella as you continue to sit on your sofa - that's what good sound is all about - if not, you're missing out on the real 'theatre experience'!

Any more coments about the accuracy of the thx format (even when all speakers are actually placed and configured correctly) is a topic for another day!

As it stands today - stereo (2 speakers) is the ultimate illusion, because it effectively takes into account (perhaps by fluke even), the psychology of human hearing and the psycho-acoustic aspect of a human beings (2) ears!

cheers
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Old 21st November 2005, 10:25   #12
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Man, you are confusing me with facts...

Ok, I am not as technical as you, after all you do this for a living. Yes, keeping the surround speakers at ear level was an issue, especially since I couldn't find walls at the right places. Ceiling mounting was the only choice. Therefore I mounted all the four surround speakers on the ceiling, but angled the di-pole speakers so that the null spot points to the loveseat right in front of the TV. Given the room shape, I didn't have any other choice. BTW, in the new HTS room, all viewers will be sitting in the same horizontal line.

Calibration was my next problem, initially I thought of spending hours of time at it with a sound level meter which I planned to bring from US. Then I got practical and used the following feature from Yamaha A/V Receiver.

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Old 2nd December 2005, 12:11   #13
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Originally Posted by cream
hi, just saw this post - maybe my inputs will be helpful. or maybe they'll just open up a can of worms!

IMO, THX is fraught with much more problems than it aim's to solve - on both, a practical and a theorectical level.

...The basic problem with thx is the requirement for speakers. Because of the vertical directivity consideration (where speakers must radiate their sound energy into the room and not into the walls), all thx speakers must have 3 drivers for the satellites. viz 2 mids placed vertically over a central tweeter. This is commonly known as the D'appolito configuration or also an MTM (midrange - tweeter - midrange)

The idea is that, in such a configuration - the speaker acts as a point source and all the sound appears to come from the centre of the cabinet viz the tweeter. This configuration also provides vertical directivity by increasing the energy in the frontal plane of the radiation, thus reducing floor and ceiling reflections.

While this confiuration is not bad in itself, the issues that they throw up are tremendous. For the configuration to work correctly, the speakers have to be centred at the ear level of the listener and all the 3 speakers have to be placed at the same height. these 2 conditions can never be met in a typical home - for the simple reason that the centre speaker has to be placed above or below the tv. In a theatre, this is possible because the 3 speakers are placed behind an acoustically transparent screen.

If the speakers are not placed at ear level, severe phase cancelations occur, due to 2 radiators (the 2 mids) giving the same sound but from asymettrical distances. In addition, all centre speakers in homes i've seen are placed horizontally - again a no-no for clean sound, but a standard placement constraint in all practical rooms.

These two factors itself kill the thx format in homes. also, these factors are never highlighted by thx themselves - because then their system becomes impractical.

How many people with thx speakers place the left right centre at the same level, at ear level, and then place them all vertically? No one! Then, bye bye thx, hello phase cancellations and bad sound!

Dipole surrounds suffer the same fate - to be used accurately, the listener has to be placed optimally in the null radiating field of the dipole. For more than 1 listener, this is impossible unless all listeners are seated in the same horizontal line! That's why all dipole speakers today come with a dipole off switch...so that they can act as monopole or point sources for 'practical' placement.

The concept of 7.1 thx takes these absurdities to a higher plane!

Remember, creating a sonic illusion is what good sound should be all about. Visually, to see an illusion, it means that an image appears to be floating around in the air - not created by anything practical that we know of, like a tv etc. Seeing a 3 dimensional image from a 2 dimensional plane is also an illusion - because it is beyond the practical.

The same with sound - if we hear sound from a position where a speaker is not present - that's a sonic illusion. if sound comes from the same spot that the speaker is in - that's electronics. So, the more the speakers, the less the possibility of a sonic illusion.

Besides -with all the practical constraints of home listening environments, getting 5 speakers to be placed correctly is a far cry, let alone 7 speakers being optimised for placement in terms of position, phase, delay, level etc - it's almost impossible. a sonic illusion is even more impossible with a 7.1 system than with a 5.1 system.

At the end, good sound is about an immersive iilusion. If a scene in a movie has the sound of rain, obviously, the engineers at dolby will send the sound to all the speakers and the rain will come appear to be all around you - because the speakers are placed all around you. But when you hear the rain coming from the ceiling, you feel the movement of the clouds overhead and you almost see the spots of wetness in your room, when you shove your arms together and huddle up because of this rain sequence, that's an illusion.

If a scene like this makes you want to open up your umbrella as you continue to sit on your sofa - that's what good sound is all about - if not, you're missing out on the real 'theatre experience'!

Any more coments about the accuracy of the thx format (even when all speakers are actually placed and configured correctly) is a topic for another day!

As it stands today - stereo (2 speakers) is the ultimate illusion, because it effectively takes into account (perhaps by fluke even), the psychology of human hearing and the psycho-acoustic aspect of a human beings (2) ears!

cheers
cream,
i can't believe i read this post of yours just today. very well and simply explained point. Speaker positioning is of vital importance. Most folks spend oodles on "high end" systems and mess it up with lousy positioning.
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Old 13th February 2006, 20:36   #14
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Man, you are confusing me with facts...

Ok, I am not as technical as you, after all you do this for a living. Yes, keeping the surround speakers at ear level was an issue, especially since I couldn't find walls at the right places. Ceiling mounting was the only choice. Therefore I mounted all the four surround speakers on the ceiling, but angled the di-pole speakers so that the null spot points to the loveseat right in front of the TV. Given the room shape, I didn't have any other choice. BTW, in the new HTS room, all viewers will be sitting in the same horizontal line.

Calibration was my next problem, initially I thought of spending hours of time at it with a sound level meter which I planned to bring from US. Then I got practical and used the following feature from Yamaha A/V Receiver.

the YPAO is a handy tool that can callibrate sound levels and check polarities and distances and yes even the size of the speaker, but for finer tuning you do need a spl meter, a radioshack can really bring out more from your HTS
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Old 14th February 2006, 09:24   #15
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the YPAO is a handy tool that can callibrate sound levels and check polarities and distances and yes even the size of the speaker, but for finer tuning you do need a spl meter, a radioshack can really bring out more from your HTS
Actually I did buy a SPL meter from Radioshack ($86) for calibrating the HTS system for my boss (he paid), but I didn't get it back to India. My current setup is placed in a very inappropriate T shaped room with hardly any acoustic advantages.
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