Certified THX Technician

I think the point is being missed here... that sub placement, along with room treatment, seating position etc are keys to having smooth bass response for the listener...NOT how good the sub is etc ...The best sub in the world, with perfect frequency response, will still cause problems in any room if not placed properly, and the room treated properly etc ....THX Certified gear means it was manufactured to meet rigorous engineering requirements and will perform up to THX standards at Reference levels with minimal distortion etc ... The only reason most people think it is a marketing tool is because they really don't know anything about it (either did I before I was certified). Yes, there is some gear that will hold up to THX engineering and performance specs that did not attempt to pass THX certification, but most won't because they were not built and engineered from the ground up in the first place to meet the THX performance standards. THX actually works with the manufacturers to build their products. Most of the specs are just very good engineering and design principles, but usually are not adhered to by manufacturers due to their own beliefs and due to manufacturing costs. However, many products that are brought in for testing, expecting to pass due to the "greatness" of the product, simply cannot meet the standards when push comes to shove and they do not pass the certification tests. It's up to them at that point to further engineer the product to meet the requirements or to simply sell it as is.

And it is not THX Certified ...and for good reason .... I will try to address this in my other thread on Subwoofers and proper placement.

\ I was wondering the same thing...... It entails spending some cash and taking a 3 day course on THX, all their technologies, how and why they work etc....a lot of it is hands on calibration, testing etc...and a lot of it is theory and calculations ...people on the course range from home theater installers who want to learn how to do things a "better" way, manufacturing engineers from speaker and receiver companies, sales guys ...you name it .... then you have to write a test and pass with a certain grade to become certified. Then you have to re-write the test every 2 years or so to keep your certification current and valid.

The left sub then should go in the middle of that entire wall, including the back room ...the standing waves first dip will be in the middle of that wall, and that is also where your first row is roughly ....then put the other sub across from it on the right wall, slightly ahead of center. You can then try moving the sub on the right wall to exact center and across from the other one to see which provides smoother response on that side. Non square or rectangular rooms are hard to control the bass properly. You don't need a wall behind you subs...they should be out at least a 6-12" from the wall....this helps reduce the Boundary Gain (buildup of frequencies on the wall...artificially boosting the signal) . I'll get back to you more on this tomorrow and with proper height for your surrounds etc ....also key is to make sure your SPL is the same from all speakers in the centre of the two rows of seats.

Yes, but the subs should be exactly in the center ...the look a little more towards the rear (I know it's only a rough diagram). Is the red line your curtain and does the actual room extend to the back behind it? if that left wall is actually longer and the signal passes through the curtain to the back that will affect the placement and sound as well.

Just a couple observations here ...I just started a new thread on subwoofer placement ... 1. Place your subs in the middle of each side wall across from each other....directly in the middle of the length of the side walls, one on each side. You could do front and back as well, but your would have to put the rear sub into the wall since you have seats there. THX recommended spec for 2 subs is opposite each other on opposing walls in the center of the wall. Face the drivers inwards towards the center of the room. 2. Your surround speaker placements are backwards. You should have your RS-42's at the sides, with the null between the two rows of seats and the 2 RB-51's on the back wall for the rear's, 30 degrees each off center. This is also THX recommended spec. Surrounds should be bi/dipole speakers and rear's should be direct radiating (front firing). I can explain this in much more detail with the how's and why's if you like by email. But trust me, you should reverse your surround speaker placements. Your setup is very similar to mine ...what is the height of your surrounds (side and rear) ? I will also let you know what height they should each be at.

This is a new thread on proper subwoofer placement according to THX standards. Some of the info in here will get pretty in depth, however, see the "6 spots to put a single subwoofer" to help you out. I will also mention dual sub, and quad sub configurations.

Gonna start a new thread on Subwoofer placement based on THX standards.....made some adjustments to my numbers in my above posts after referencing my notes .... Please direct any sub questions to the new Sub thread. Thx

The sub's driver should face the listening location, as do the speakers. if the sub is on the side wall, it's driver will face inward towards the room even though your mains will face perpendicular to that ..... See my previous post above on the 6 spots to put your sub ...I just checked my training notes and made some adjustments. If you move your sub into one of these positions it will help with the standing waves and even out the sub response. even if you have to move it a foot over, it will make a difference.

Please direct questions to the Ask a THX Technician post ..... we are clogging up Steve's original post and getting off topic (which is partly my own fault).. I love to educate, and can take criticism as well ....I'm just here to make your gear sound it's best!

What I meant was if you cannot put your sub on the front wall with the mains and center, and you have to put it on the side wall...if you choose to put it at 1/3 or 1/4 the length of the wall, put it on the part of the wall that is closest to the front wall ...the side of the wall, not the side of the sub. Sorry for the confusion. The sub's driver, if front firing, should face you no matter where you put it ...same direction as your speakers do. Hope that clears things up. And I realize everybody does not have a dedicated room etc ...all I'm saying is here are the principles so that you can try to apply them to your space. The more you can adhere to the standards, the better your sound will be. Even a cheapo two speaker stereo system can sound better by applying the standards, toeing in the speakers towards the listening position, placing at proper height, proper sound levels etc ...all the THX standards can be applied to any type of system to make it sound it's best. I haven't even begun to dig into Room treatment..things you can do to eliminate echoes, reflections ...where to put bookcases, what kind of seating, flooring and materials are best etc to make your system sound better..... I'll save that for another day : )

To help clarify .... Best Spot to Put Your Subwoofer (single) 1st Choice - Front wall - 1/2 way (center) 2nd Choice - Front wall - 1/4 or 3/4 along length of wall 3rd Choice - Front wall - 1/6 or 5/6 along length of wall 4th Choice - Side wall - 1/2 way (center) 5th Choice - Side wall - 1/4 or 3/4 along length of wall (on side nearest front wall) 6th Choice - Side wall - 1/6 or 5/6 along length of wall (on side nearest front wall) This provides the first 6 spots to try and place your sub based on the first three modal harmonic frequencies which will help provide smoother bass response. One of these should work in almost all situations.

bigdaddy...I hear exactly what you are saying and that is true. when people ask me "where should I put my sub" ...well, I tell them, but that may be where their tv sits etc and all their gear ...you still have to work within the environment you are given. So that is why the 2nd and 3rd positions (1/4 of the way or 1/6 of the way along the front wall) work well as a second choice....it puts the sub usually beside the gear, away from the corner, and still helps with the 2nd or 3rd octave frequencies. Like I said before, you CAN stick it anywhere....it's just that anywhere is not the best spot for it. There is always somewhere better that it could go which will hopefully help out with the sound AND the aesthetics. The reason THX states to put the screen so close is because to truly have the home theater experience, similar to an actual Theater screen, the screen horizontally should take up 40 degrees or less of your forward view (20 degree from center to each side). So from where you are sitting , if your corners in front of you are at roughly 40-45 degree angles, the screen should be almost half the width of the wall. "This provides the greatest combination of visual impact with sharp detail". Watching a 52" HD LCD from 20 ft back, although clear, hardly puts you into the action or gives you that theater experience. Again, there are calculations based on SD and HD specs and visual acuity (what the eye can actually make out at a certain distance) to figure out seating distance and screen size. Also, screen height is also calculated, so that the viewer should not have to look up more than 15 degrees to see the top of the screen. This makes your neck and eyes more relaxed for extended viewing etc. Most TV's will never meet this spec though. You would have to sit 2-3ft infront of a 32" TV to get the desired affect or 6ft infront of a 65" TV. So again you have to make due. The main idea though is to have the image take up a large percentage of your vision to wrap you up in the picture and what is happening. The bigger the better. With Projectors , it works out perfectly. And also with computer monitors, as the larger 22 and 24 models are now out, you can achieve this as well sitting at a desk. THX home theater specs are just guidelines and best practices all based on sound engineering and design principles to help maximize the theater experience at home. But you have to do what you can in your space as well. That is why whether there are 10 changes or 1 change you can make to your setup, there is always something you can do to make it technically better, performing and sounding better, and more enjoyable. You wouldn't beleive the installs I've seen, that are tens of thousands of dollars, and the speakers or screen is totally in the wrong spot. Now, to somebody going for looks, it looks great and they don't care about the sound at all as long as they can hear it. But to an audiophile, it won't sound great or the best it can and the gear should have never been put there in the first place. So you have to cater to the client and design it best for their needs and wants since after all, it is their system and they have to be happy with it.

It is Optimal placement and it has nothing to do with the seating or how far you are from the sub. It has to do with the sub, the room, and standing waves. Here is a brief explanation of why. Standing waves are caused by the room dimensions. Unless you are using resonators and bass traps to reduce these unwanted frequencies in the room, sub placement is key to providing smoother bass response. The seating should ideally be placed in the middle of the waveform of the modal frequencies (and there are exact calculations to find where that is). Usually you have a little play with the seating. Even moving them a foot or two in the proper direction can make a big difference in the bass response at those seats. You can't always move the seats though, as you mentioned, but you place the sub at the proper spot to help reduce the affect of the buildup of frequencies where the seats are. Keep in mind most of these frequencies are below 200Hz. The room generates these unwanted standing waves regardless of sub placement. Each dimension (Length, Width, and Height) has a particular harmonic frequency at different octaves that will have an affect on the room as the sound waves reflect off the walls, ceiling, floor etc. The idea is to reduce the affect of these standing waves by proper sub placement, and moving the seats to a better spot if possible so you don't feel this affect. Without doing tons of calculations, by placing the sub halfway along the wall, it reduces the first octave standing wave frequency's pressure level, whatever that frequency may be based on the room dimensions. 1/4 distance reduces the second octave, 1/6 the third etc ...The first octave is the strongest one over the others, although the 2nd or 3rd octave may be the one that is producing the same standing wave as another wall, creating a large build up of that frequency which would then require putting the sub at 1/4 distance along the wall etc to reduce the peak affects of that frequency. So unless you do the calcs to know the exact frequencies and where to place the sub, rule of thumb is to put it in the middle as it will reduce the first modal frequency (the strongest one) and help smooth out the bass response no matter what. Then you do a bass test (hammer the crap out of the sub with specific trouble frequency) and walk around the room to see where the buildup of frequencies are. You will feel a high pressure zone, making your head worble etc ..then as you move a foot or so away, it will disappear etc....you want to find that spot in between the high and low pressure to put your seating ...ensuring you will get smooth bass response. Now to do this you need a tone generator and need to do the calcs to get the frequencies that will cause havoc in the room. The sub is non-directional and isn't easily localized so it doesn't matter where you put it to get bass. But it does matter where you SHOULD put it to get smooth and accurate bass. Perfect scenario is 4 subs, one in the middle of each wall. 8 is even better - 2 on each wall in opposite phase to each other - eliminating almost all standing waves. Even 2, 1 in the middle of the front wall, and 1 in the middle of a side wall, will help reduce 2 major frequency build ups and provide smoother bass response. Some installs have subs mounted halfway up a wall or in the ceiling etc ... but there are hard engineering principles behind why it SHOULD go in certain spots, whether you agree with them or not. The proof is in the pudding ...when they are properly placed, you can run tests and sit in the sweet spot and have perfect, smooth bass response at extreme volume levels ..not loud, rumbly, shake your head bass (which is NOT good bass response). Subwoofer placement and calibration is one of the biggest misconceptions in Home Theater. To properly place a sub, it requires a good understanding of the science behind it and why it works. I should really open another Post on this topic, as it is quite indepth and requires knowledge of standing waves, modal frequencies and how the room affects bass response. You will actually get better bass response with more smaller subwoofers, than with fewer larger ones. I am just trying to educate people in order to help them out. I know some people that don't care, and just throw the sub in the corner and crank it up. And that is their right to do so. But in a $100,000 custom theater, you don't just guess and throw the sub somewhere because it's aesthetically pleasing or convenient. You place it where it should go to provide the best bass response for that room. And to do this requires proper calculations and testing. I hope this wasn't too technical, and helps you to understand the theory behind proper sub placement.

are you pumping the video out as well to a TV or projector and want the surround sound to fill the room? or are you just sitting watching it on your laptop and want surround sound around you in front of your laptop?