[Samurai]

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...

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

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.