HiFi audio ramblings

How come audio professionals seldom speak about the cables they use?
Does it matter what kind of speaker cables you use?
Do you get better sound with more expensive cables?

Speaker wire, a history. Article by former Director of Acoustic Research for McIntosh Labs, Roger Russell:

How low does it go? The instrument that is.
What frequency do I cut to reduce sibilance?

The Interactive Frequency chart by Independent Recording Network gives you the answer:

Does it matter how and where I place my speakers?
Yes, it matters a lot! Here is a guide I have found helpful:

Setting up loudspeakers in a room, a guide by Audio Physic: http://www.audiophysic.de/aufstellung/index_e.html

Ethan Winer on room acoustics

Genelec on room acoustics

GIK acoustics primer

Headphone frequency response comparison graphs

MasVis, free software for audio analysis

Sonic Visualiser

Gnoosic: Find some new music that you will like!

Music Map: Find even more music that you will like!

Audio in my living room, measurements

Audio in my living room, using Room EQ Wizard (REW) and HOLMImpule for measurements and analysis. Optimizing the listening experience by taking measurements, adjusting subwoofer/speaker placement and hopefully avoiding any major acoustic pitfalls. Having fun and learning about acoustics in general is a great bonus.

The tools: Room EQ Wizard from HomeTheaterShack, HOLMImpulse software from HOLM Acoustics, a laptop computer, a Behringer ECM 8000 measurement microphone, the M-Audio Fast Track Pro USB audio interface with microphone preamplifier, a Radio Shack sound level meter, a camera tripod and some cables.




After having some problems (loopback input signal constantly changing) I finally got a good loopback signal and was able to make a soundcard calibration file in REW. Lesson learned: RTFM. The pictures below show the soundcard frequency response before and after calibration.


loopback frequency response



My front speaker placement in my living room is far from ideal. The left speaker is by a side wall and the right is not. There is (mostly) open space behind both speakers so I loose some bass. I use a surround receiver as preamplifier for stereo use and do some equalizing to get back what bass I have lost. Rear facing bass ports are plugged to get a uniform bass response. I have a carpet on the floor between the speakers and the listening position.

OK, lets get on with the measurements. The first two graphs show the left and right channel room impulse responses (made with HOLMImpulse). The reflection at about 75 centimeters is probably from my living room table. The reflections (on both graphs) at 125 centimeters are from the ceiling I believe.



It is really not practical to remove the living room table. I will probably try using some absorbing material on the wall though, or maybe moving my DVD shelves and using them as a sound diffusor. My flatscreen TV is placed between my front speakers. Ideally it should be placed further back to interfere less with the sound. I have tried moving my front speakers further out into the room, this cleans up some of the reflections, but intruduce other problems (not practical, speakers are blocking the passage through the room).

I am pretty happy with the sound now. The soundstage is wider and deeper than with my previous speaker placement (made without doing any measurements). I use track 6 (Late home tonight part 1) from the QSound mixed album Amused to Death by Roger Waters to check the stereo imaging and soundstage. The sounds of the droplets in the beginning of the track seems like they are coming from far behind my head on the left side. Check it out, it is way cool!

How about the frequency response? The next graph shows the frequency response in my listening position, both front channels driven (1/6th octave smoothing):



OK, lets add the subwoofer and have a look at the 15-200Hz area (no eq and no smoothing, this is with the best reasonable subwoofer placement I have found in the room after several tests). Overall I am very happy with this result.



What to do about the reflections by the left speaker?
Lets start with a fresh measurement, the green graph on the left below shows the impulse response with a bare wall. The blue graph on the right side shows the effect of placing a heavy blanket on the wall, what a great success!


left bare wallleft imp blanket


The peak after 75 centimeters is tamed and so is the peak after 170 centimeters. So, the peak at 75 centimeters was not from the table as I previously believed, but from the wall (confirmed by doing a measurement with the blanket covering the table, it made no difference to care about).


So, what to do? Leave the blanket on the wall? I think not. Get some ultra expensive, but nice looking professional acoustic absorbing material? I´d like to try something different first, I really need all the space I have for my rapidly growing DVD/BD collection. Lets use some DVD shelves as a diffusor. The red graph to the right shows the result. The peak after 75 centimeters is somewhat tamed, but another peak has emerged after 60 centimeters... Have a look at the peak after 170 centimeters, it is smaller as well.
left imp shelves


On top of my wish list now: A new high-end preamplifier? New high-end speaker cables? No, it´s a purpose-built dedicated listening room with acoustic diffusors and absorbents placed in the right positions. New house?

Audio in my living room, acoustic treatments

New arrivals: a pack of four Vicoustic Round Bass 360 Premium bass traps, seven lengths of heavy curtain, five slabs of 1200x600x80mm acoustic panels, six 1200x600x40mm acoustic panels. 10 meters of beige dekomolton, a staplegun and several cans of sprayglue. Let the fun begin!

You may ask: Why all this? Measured reverb time is up to 700ms(!) and the soundwaves are reflected all over the place.

In with the bass traps (all four placed in a corner). Behind the front speakers: a wall made by curtains hanging from the ceiling with four 80mm acoustic panels behind it blocking off the open staircase. An 80mm acoustic panel and five 40mm panels placed by the wall/window behind the listening position. Result: overall shorter reverberation time and a much better and tighter bass.



New speakers, new measurements, new software tools

New speakers set up in the living room, these are German Audio Physic Virgo 5 with two side mounted 7 inch woofers each. I use a Grace m902 as DAC/preamplifier and homemade Hypex monoblocks to drive these.

I plan to do digital room correction using my Squeezeserver with Inguz DRC and EQ plugin. I have tried Inguz DRC in the past , but I could not get the filter generation process to work very well. This time I will use Audiolense 2.0 from Juice HiFi to do the measurements and generate the correction filters.

Some new measurements done with Audiolense follows (no DRC applied yet). As you can see, my asymmetric and less than ideal speaker placement (left speaker by a wall, right speaker not close to any walls) gives me a slight boost in the bass from the left speaker:



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Last update: 15/10-2011