Updated January 18. 2009

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Building a Home Theater & Listening Room

.... and getting the acoustics right

Ready for Lord of The rings?

Front row. Sofa to the back still missing.

I have for a long time had a dream of building a real home theater. I'm fortunate to have a room that can be dedicated to music listening and movie watching.

I knew very well that the sound could be improved a lot in the room. In the house we had before the speakers sounded much better. Here in this room, the bass was boomy, and the mid and high very sharp and aggressive. Before I started the project one wall was all glass .... not the most optimal material for a listening room, as it is very hard and reflective.

The room is not too big, only 3.2 x 5 meters, which means that the standing waves or room modes, that you find in all rooms, are not widely spread and therefore quite audible.

I wanted this room to be optimal for both music listening as well as watching movies, and therefore I didn't want to make it very dampened. If the room was for movie only, you could get by with just a lot of absorption, as the 5.1 track will create the sound of room, but for music the sound will be very dull and lifeless if you put too much absorption in the room. Additionally, an room with too much absorption will actually not be very comfortable, just step into an anechoic chamber to verify this. You will feel as if there is a pressure in the ears, and the room will feel very small.

Therefore I wanted to treat the room modes with some localised absorption and use diffusers to spread out reflections.

I still have a small project left, to treat the 1. reflection points on the side walls just in front of the main speakers. As the speakers are very close to the walls, there will be a comp filter effect as the reflection from the wall meet the direct sound. This will result in a very jaggy tweeter response and the stereo image will suffer. I have tried to treat the reflection points with absorption, but this makes the sound more dull and less musical. therefore I will build some diffusers instead.

So what is the result of all the work?

Well you might think you get an improvement by upgrading to a better amp or CD player, some even think they hear big differences by changing cables. Compared to this, the improvement I have got by treating my room is light years beyond!!!!

Most noticeable is the improvement in the bass region. The boomyness is gone. The bass seems to go way further down in frequency, which is because the information in this region is not masked by the room modes anymore.

Better bass means better feeling of room in the recordings. Our brains uses the bass sound to determine size of room, and now this information is more accessible. This also improves the imaging.

The sound is much more relaxed and stable. You can now better pinpoint the instruments etc. The high frequencies is much better defined, and much less aggressive.

Another way it becomes clear that there is a huge improvement is the sound level at which it is comfortable to listen. In the new room I can play 10 db higher before the sound becomes uncomfortable. The sound is simply more clear and with less distortion.

The improvement is comparable to changing your speakers to something mush better.

So all in all, if you want better sound, stop buying expensive cables and snake oil, and start doing some real improvements to you room, it is worth every effort, and will bring out the best of any equipment you have or will bye in the future.

Many people believe that you can now just bye a room correction unit and get the same. This is simply not true. DSP units like that, will correct the frequency response, which will help a lot in the bass (remember that the in room response in the low end will have mumps of more than 10 db, this is normal and don't let anyone make you believe otherwise) but it will not be able to do anything about the decay of the room modes, that is how long it takes for these frequencies to die out (very visible on a waterfall chart). Real treatment will also help with the decay.

I knew it would help, but that the effect would be this big is amazing.

Take a look at the construction page to get more info on how it is all made.

Side Panels

   

Side panels houses two large Helmholtz resonators in each end and a middle piece og 150 cm that works as a perforated panel absorber. The frequency target was 110 Hz. Placing the absorbers in the corner of the room gives the highest effect as this is where the sound pressure is highest.

For more information of how to calculate and treat rooms, I can only recommend the book by A. Alton Everest "Master Handbook of Acoustics" which I have used through the whole project. It is easy to read and understand, and gives a lot of hands on information. A must have.

Helmholtz Resonators

 

Each end of the side panels houses a larger Helmholtz resonator. The target was to dampen the resonances at about 70 Hz.

I have used a tuneable bass reflex tube as to be able to fine tune the working frequency. I have tried to measure the tuning frequency by placing a microphone in the chamber, but due to the setup, I couldn't get rid of some feedback problems, so I had to abandon it.

To be honest I can't say how well these are actually working. I also tried to block all tubes, but I couldn't hear any difference, and was not able to measure any difference either.

Afterwards I have talked to a friend, who says that the actual damping takes place in the tube, which must have a porous surface (damping foam) ... mine doesn't and that is maybe why it doesn't work that well.

Anyway I haven't pursued it as I think the room has been cured of any bass problems anyway.

Corner Cubes

   

The corner cubes are meant to give a very broad band absorption. Placed in the corner to give the largest effect.

These are made of medium heavy fibre glass and covered with some nice black felt. These cubes are 30 cm on all sides, and are glued to wall and ceiling.

The result is very good, but it was not that easy to make. Think I would maybe go for some premade cubes if I was to do it over.

Auralex has some nice 12" CornerFills called Atom-12. Can be bought here for 66 ...... which first sounds expensive, but I can tell that, medium heavy fibre glass, felt and glue is not for free either. On the other hand I think my cubes will be the more effective due to higher density.

Mini SuperChunk

I would have liked to place some big broadband absorbers in the corners behind the main speakers. But due to the room size this is not possible, and I had to opt for some smaller corner absorbers.

These are about 15 cm deep, and made of fibre glass floor plates, with very high density.

The higher the density the better the low frequency absorption.

The best information on SuperChunks can be found at StudioTips Acoustics Forum, that also have some very good discussions and building tips on acoustics and room treatment.

Ceiling Polydifusor

 

The main purpose of the ceiling difusor is to reduce the reflections from the ceiling. It is 1 meter wide and 20 cm deep.

It will also help as an bass absorber and will also reduce standing waves.

To give the room a little extra feeling, I mounted a blue LED string on each side, same as with the side panels.

Front Polydifusor

The front wall is covered with a polydifusor. It is a bit more than 1 meter wide and 15 cm deep and goes from floor to ceiling.

Main purpose is to reduce early reflections from the front and thereby help stereo imaging.

It will also help as an bass absorber and will also reduce standing waves.

Completing the front and ceiling poly, gave the room a really new sound. It was noticeable from the very start. It gives a feeling of a more quiet room, but it definitely doesn't feel uncomfortable as is sometimes the case with rooms that are damped with absorbers.

It just feels quiet and relaxed.

Projector

The projector choice ended up with Sanyo's new Full HD Z700. It's a middle price projector, but it really delivers a picture that leaves very little left to desire.

In projectors things are moving really fast, and I think it's better not to spend all your money on a top line projector, better to go for a very good middle priced projector and having the option to upgrade it with a new middle priced projector in say 3 years time. I'll bet that today's top models will be more than surpassed in 3 years time by a new middle priced model.

 

The projectors long throw lens makes a shelf mount possible.

The projector is really quiet, and you only notice the fan noise in very quiet scenes.

The screen is a 170 cm wide 16:9 motorised and remote controlled screen from Quality Screens. It is white and has a gain of 1.1.

The screen size was chosen to match the front seats that are 2.5 meters from the screen. This gives a viewing angle of 37deg. THX recommends a viewing angle of 36 deg. (A calculator for viewing angle can be found here)

Back seats will be around 4 meters from the screen, giving a viewing angle of 24 deg. a little to the low side according to THX.

From the start of Bladeruner (DVD). Picture taken with handheld Canon Ixus 800 IS

Nice result from a DVD I think.

 

Equipment

 

Left: Right main speaker. DIY construction using 2 x 8" Peerless woofers, ScanSpeak 4" Kevlar midrange, and Dynaudio Esotec tweeter. The filter is a 2. order Linkwitz-Relly deviding at 400 and 2 kHz. You can see it standing to the left of the speaker.

Right: Denon DVD 3910, Yamaha RX-V 1200 and LC Audio "The End" power amp.

 

Left: DIY center speaker. Yes I still miss to make a proper stand for it. It houses a single Seas 6.5" coax driver.

Left: The subwoofer amp, powering the two 12" JBL drivers. It's a LAB Gruppen LAB 300 prof. power amp. It only gives some 100 watt but it seems more than adequate to drive the speakers.

 

Left: The DVD collection, handy in a single box.

Right The dipole side speakers JBL HT1D. If you haven't tried dipole speakers for surround, I can only tell that it so much better than conventional speakers. They really disappear in the sound stage, and is very hard to pin point, delivering only the right kind of surround effect. It's not that you don't hear the sound as coming from behind and from one or the other side, you really do, but it's more that you can't tell the position of the speakers, which you normally can with normal type of speakers.

I use two HT1F speakers as center rear (one in each side) when running Dolby EX 6.1 or DTS EX 6.1 material. These are actually meant as front speakers but I find my own speakers so much better that they have to stay at the back J I was lucky to get this JBL HT1 THX certified set for about 2500 DKR (400 USD), barely used. And they now serve me when watching movies as surround and subwoofers.

 

 

Left picture: My Sanyo Z700 projector. You can also se the back surround speaker JBL HT1F just beneath the corner cube.

Right picture: The 3 main outlets, cables taken directly at the inlet, having each it's own fuse. I the room I have 2 x 10A + 2 x 13A at 240 V ......... think that's enough for anything J

Subwoofer

The subwoofer doubles as platform for the second row sofa (yet to be bought). The drivers are 2 x 12" JBL drivers that used to be housed in the HT1 subwoofers. Cabinet size and tuning is identical to the HT1 subwoofer, at I found the sound to be really good and well suited for movies. 120 litter and the tuning is 35 Hz. They might not give the very low frequencies, but the impact of the T-Rex in Jurassic Park, the falling of Saurons helmet in the intro to LOTR or the depth charges in U-571 is felt in the chest ...... you simply don't think; "I need more bass"!