22 August 2007

Bruce’s New Listening Room

Bruce Heran writes:

Unless you are a headphone audiophile, you are handicapped by the room you listen to music in. I was faced with the dilemma of listening in an acoustically poor space. Others may disagree on this, but I feel that the room has at least as much to do with sound reproduction as any other component. I had a 3.5 by 4.5 m unused space, so after convincing the spouse that an extra room would be nice, I got out my tools and went to work.

What I do want to relate is some of the planning and features that make a space better for audio. I decided that there were some key factors that would affect my listening pleasure. In no special order, they are room resonances, sound reflections, background noise levels, ugly wires dangling everywhere (like my old room), power considerations, ease of making changes, and general comfort.

The first step was to search for information on room resonance, for which there is plenty of information available.

Basically, the length and width of my room were OK, but the ceiling was problematic, as it was too low. As luck would have it, the roof over that section of the house is sloped. If I changed from a level ceiling to a sloped one that followed the roof line, the situation was much better. The slope is about 15 cm across the length of the room. I feel it is necessary to mention, that it is probably impossible to have a space (in a normal house) that doesn’t have some resonant frequencies and some nulls.

The next step was to damp out reflections. This was accomplished using a thick carpet with a thick under pad, acoustic ceiling tile, wall coverings and overstuffed furniture. Clearly you don’t want to get rid of all reflections, just the excess ones. You might ask which ones are they? Well, they are the ones that make music and voice sound strange to you. So how much damping you use is a personal thing. In my case, the main speakers (Parts Express Aluminum/Silk Dayton MTM) tend to sound best about 10 degrees off center.

The floor was made extra sturdy out of 2 cm exterior grade plywood. Joists were on 45 cm centers with concrete supports every 60 cm. The floor is solid and non-resonant. To cut down exterior noises and further reduce the possibility of resonances, the walls and ceiling were stuffed with insulation. One thing that I think is very important was that nearly all the construction was done using 10 cm “deck” screws. This makes a very strong structure that can be easily disassembled later. Another hint is to use many screws. It will save grief later when you discover that something resonates. All heating and cooling equipment is located out side the room to cut down ambient noise.

All wiring was installed overhead above the ceiling. In each corner I installed a section of foam pipe insulation to use as a conduit to the floor. It works like a champ to hide the wires and you can easily add or remove wires. Having enough electrical outlets was always a problem in the old room. I installed several above the ceiling and had some remotely switched. Concealed lighting and central power switching was also installed. I have a separate 120 VAC power feed to the room (20 amps), a dedicated 12 VDC supply that comes from a trickle charged 85 amp-hour deep cycle battery, a FM antenna drop, a CATV drop and provisions for a 120VAC UPS.

In the past, I had equipment scattered over several shelves and interconnects tangled every which way. So to solve that, I built a single shelf above the HDTV and speakers. All the equipment is in a single line and with careful placement, all the interconnects are short and untangled. As a side benefit, the high shelf helps conceal the wiring and keeps kids and short people from messing with it. The only difficulty I have encountered is loading discs into the DVD / CD player.

If you look at the HDTV mount photo you will see it is a DIY job, as I was appalled at the price of HDTV wall mounts. It consists of two small blocks of wood, a cross piece of wood and two metal pipe hanging brackets for a total cost of about $6US. The brackets fasten to the holes in the rear of the TV and are folded over at the top to hang on the cross board.

My turntable is just on the other side of my half height dividing wall (partially visible in the construction photo). It sits on 8 full size concrete blocks (20 X 20 X 40 cm) on a concrete floor. The wiring is a bit longer than I would like at 2 meters, but the arrangement is as solid as you can get.

There are some things I didn’t do, and some I may still do. I originally planned to build in the home theater (HT) 5.1 speakers. I planned to use Fostex FE126E speakers for the front, rear and center speakers and a pair of 38 cm subs to go with them. I built spaces in the walls for them, but have not use them (yet). If you look at the finished rear photo, the rear HT speakers (Radio Shack ceiling speakers 17 cm woofer and 2.5 cm tweeter) are hidden behind the picture frames. Power to the subwoofers is controlled by a DIY electronic relay control from the HT amp. I am using a pair of DIY Dayton BR-1 bookshelf speakers from Parts Express for the fronts and an Infinity MTM for the center.

So, how does it sound? Very well, in my opinion. The detail is excellent as is imaging, there is a wide soundstage, with quiet background and the overall tonal balance is slightly warm. That is my preference and may well be a result of my use of a modified K-12 tube amp to drive the MTMs. You may have noticed that the MTMs are above what would be considered a standard height. This is also a personal preference as I like a sense of having the performers on a stage and this placement aids in the illusion. With the subs in the corners, there is considerable room gain as would be expected. This could pose serious balance problems if uncorrected. I handle it by using an active crossover with a 24 dB / octave slope. The crossover frequency is set at 50Hz and I use a separate amp for level control. I still have some fine tuning to do but the results are already worth the trouble.

Several things could go wrong with a project like this, the biggest being excessive room resonances and reflections (too few or too many). Loose wall panels that might vibrate could also detract from the listening experience. Bad ergonomics would certainly detract as well. I wanted a comfortable place to enjoy music and as a side bonus, the wife likes it too.

Good Listening,

Other DIY Audio Projects by Bruce Heran:

13 August 2007

Grado RA1 Headphone Amplifier

A while back I got the headphone bug and purchased a pair of Grado SR80 headphones [new model: SR80i]. I am very pleased with the inexpensive ($99US) headphones which deliver great value.  The Grado SR80 headphones have an impedance of 32 ohms, so I built a CMoy Headphone Amplifier in an Altoids mint tin to drive the somewhat demanding headphones. The results were surprisingly good, especially when you consider that one can easily build a CMoy Head Amp for about $20. The CMoy was a huge improvement to a portable media player and rivals the performance of the built-in headphone amplifiers on NAD C162 and NAD 1020 preamplifiers.
A while back, I was showing off the Grado SR80 headphone / CMoy combination to a good friend. He is the Walkman, Discman and now iPod type who typically lives with the factory supplied headphones until they die, replacing them with similar light travel headphones. He was stunned with the amazing sound quality, so I let him live with the Grado / CMoy combo for a while. Not surprising, he loved the sound quality, but found that the Grado headphones were too bulky and leaked too much sound for use on public transit.

While he found that the combo was not suitable for his daily commute, he was in love with the amazing sound quality and decided to spoil himself. He purchased a pair of Grado SR225 headphones and a Grado RA1 headphone amplifier for use at home.

For those of you who are not familiar with the Grado RA1 headphone amplifier, it is well regarded, runs off of two 9V batteries, is housed in a beautiful mahogany enclosure and retails for about $350US. A stock photograph the Grado RA1 is shown below.

Grado RA-1 Headphone Amplifier
Grado RA1 Headphone Amplifier

Recently I had the opportunity to visit and listen to his Grado SR225 / RA1 combination. Of course I brought along my little pocket CMoy headphone amplifier!

We both did some blind listening and in the end we pretty much had the same listening impressions. We thought that both the CMoy and RA1 amps sounded excellent and fairly similar, but we both gave a slight edge to the DIY CMoy amplifier. We were both a little surprised, considering you can build a CMoy for about $20 or buy an already built one for about $40 on eBay, yet the Grado RA1 rings in at $350.

After a few Google searches, we found that others had reported similar listening impressions between the two amps. That being, they both sound very good, with similarities between the two and the slight edge going to the CMoy.  

Dissected Grado RA1 Headphone Amplifier

But what I found most interesting were these two sites, one which showed the dissection of a Grado RA1 headphone amplifier and the other which also took apart and upgraded the Grado RA-1. The sites provide pictures of the inner details of the RA1 and also a schematic for the amplifier section.  The schematics below show the both the Grado RA-1 and CMoy headphone amplifiers.

Schematic - Grado RA1 Headphone Amplifier

Schematic - CMoy Headphone Amplifier
Both the Grado RA1 and CMoy designs use a basic non-inverting amplifier circuit using an operational amplifier (opamp).  For my CMoy, the opamp used was a OPA2132PA (Burr-Brown) which retails for about $5 and for the Grado RA1 uses a JR4556 that retails for about $0.50. Despite the fact that the JR4556 is a low cost opamp, the RA1 sounds decent, but not as good as a properly implemented CMoy headphone amplifier - (DIY lets you choose the gain setting).

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