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audio alignment and test cd

Basic Tutorial: How To Adjust A Room

This page is in response to the many people who've asked for assistance. "I'd like the audio test CD - but what do I do with it ?" Detailed steps are outlined further on in the document.

Forward:

Let me begin by saying that this is not intended to be a critically technical document, but merely a layman's approach to getting the best out of a sound system. We're not worried about thing like THD ( total harmonic distortion ) or SPL ( sound pressure levels ) or complicated formulae like SPL = 20 log (Ap/Apo)

Our Goal Is To Make Your System Reproduce Faithfully What The Producer Intended You To Hear.

This means we'd like to make speaking voices sound as if the people are in the room with you, musical instruments are properly spaced and responding with their full spectrum of sound, and imaging of sound ( where's it coming from ) is correct. While you can certainly use our audio test CD for critical measurement purposes as the tracks were digitally created, we know you'd much rather get on with the dial tweaking so you can boast about your system's purity and enjoy the reality of a well-tuned audio system.

We'll skip around and group the tracks by purpose - although you may feel free to use them any way you see fit. This is not meant to be a 'step by step' guide, rather an outline to aid in achieving the goal of perfect sound.

In my opinion, the most important alignment you can make in a typical audio system is to flatten the room. Flattening a room is the process of adjusting your Equalizers, Crossovers, and placement of speakers to cause the entire audible frequency spectrum ( 20-20 000 Hz although this varies greatly from person to person ). We flatten a room to hopefully have the audio produced by the system match what was heard during the production of the recorded audio you are playing through your system.

A flat system will also be less annoying over long periods of listening. It's very common practice for most people to adjust their Equalizer like a smiley face.

EQ Smiley Face

The human speaking / signing voice concentrates it's power in the 1khz range ( basically ). A Smiley EQ buries voices, accentuates the low and high ends to extremely un-natural levels , causes booms, screeches, high end clipping, pronounced "S" when speaking, low end resonant vibrations ( you know, when the wall seem to vibrate in an annoying manor ). This also tends to hurt your ears after listening for extended periods and may cause temporary loss of high end hearing. Yes, you heard me right - temporary loss of high end hearing.

How To Flatten A Room

Step 1 - Establish A Focal Point.

Pick a spot in the room that represents the most common place you'll be listening from, a focal point. This will probably be the center seat of your couch, or your easy chair. This is done because there are thousands of facets in the shape of a rooms that affect sound and it is simply impossible to adjust every spot in the room to sound identical. If you're in a movie theatre on the left aisle near the "Dolby Surround" left speakers, you'll mainly hear that speaker. When they set up the theatre, a focal point was selected to align the system to which is generally the center of the theatre. The next time you go to a theatre, try sitting dead center - you'll find everything "sounds" better.

Step 2 - Rough Imaging.

Use track 22 to verify right is right and left is left. It seems simple but thousands of systems are wired backwards. Stand at the focal point facing the audio system or video screen. Make sure when the voice says "left", it's on your left and "right" is on the right.

Step 3 - Verify Your Hardware.

In this step, we just want to make sure everything is functioning.

Most systems are either traditional 2 speaker systems with the woofer, tweeter, and midrange speakers in the same cabinet. Other systems are isolated types where the woofer is in a bass enclosure, midrange is perhaps a single 6", 10", or other in it's own cabinet, and the Tweeter ( horns ) are in 'satellite' enclosures. DJ's and Professionals in the field generally have 3 way or 4 way external systems with separate power amps and active crossovers. Let's just say this discussion is geared towards home users, but the basics still apply to the professional environment but I'm assuming anyone who owns an active crossover knows what it's for.

Before Playing the first test - Set the volume LOW - TURN DOWN THE AMPS !!! Then begin playing track 1. This is the 30hz test and will shake the house if used on a high power system. Gradually turn up the sound and you should hear , or 'feel', the 30 hz signal. If you hear and/or feel it - your low end is working. If you can't hear it, your system has serious limitations or the woofers are not hooked up. Use track 5 instead as not hearing the 30 hz signal MAY be a response problem. I know of several book shelf stereo systems that can't reproduce the 30hz test tone. If you can hear the 100 hz signal but not the 30 hz signal, assume you have inferior equipment and consider an upgrade.Note: the 100 hz signal will most likely be louder on most systems - this is part of what we're trying to adjust later in this process.

Next - check the midrange with track 7 ( 1 khz ). Then check tweeters with track 9 ( 10 khz ) . This tells us all the speakers work properly. If you hear distortion in any speaker enclosure, verify it is the speaker by swapping it with it's mate. If the problem stays with the speaker, get it fixed!. If the problem stays on the wire ( both speaker sound bad on the suspect channel ) then it's time to check your wiring or the amplifier itself.

Phase: For each test above ( low, mid, high ) you should also run the 'out of phase' version of the track. This will test wiring ( + / - ). When properly wired, the 'in phase' tracks should sound louder because both speaker are 'in phase' and the sound pressure is additive, as opposed to wiring the speakers 'out of phase', where one speaker 'cancels' the other. If the 'out of phase' tracks sound louder than the 'in phase' tracks, you'll need to check your wiring. It may even be inside the speaker cabinet where + and - may be mis-wired.

Step 4 - Leveling.

For 2 channel systems ( left/right speakers ) use track 24 ( whitenoise ) and make sure that the balance is set so that from your focal point, the left and right channels sound equal in volume.

For surround sound / multi-channel systems this will take a little longer and *may* required that you physically move speaker nearer of farther from your focal point. This is a very common problem in home theatre surround sound systems - the rear speakers are usually too far away and sound too low in volume. High End quality systems have separate amplifiers which facilitates easier adjustment of the volumes. Typical home systems may or may not have separate rear volume controls and in many cases will require repositioning. This explains the floor stands that many home systems have for their rear speakers.

Step 5 - Equalization.

This is the fun part. Not all systems have all the parts / pieces to perform a reasonable equalization. Ideally, each speaker group ( left, right, front, rear right, rear left, subwoofer ) should have it's own equalizer. You probably only have a main EQ for left / right.

ALWAYS start with a flat EQ - This gives you a starting point.

Flat EQ

Poor Man's Version: Play track 19,20, or 21 and adjust the EQ until you think you hear all the tones at equal level. This is not scientific and is perceived only, but is better than nothing.

High Tech Version:

Get a separate graphic equalizer with spectrum readout ( visible graph for each band ) or a spectrum analyzer and run 2 microphones into it. You can use a computer and analyzer software if you wish. If using an EQ, set it flat, as we're interested in what the microphones hear.

Place these microphones at the room's focal point where your ears would be. Play track 23 ( pink noise ) and adjust the ROOM's EQ ( not the analyzer's EQ ) until the display show flat response from 200 hz to 12khz. Ignore the low and high end in the first pass. Once the midranges appear flat, slowly adjust the low end towards flat response. You'll probably notice that the < 100hz range requires more gain. STOP - This is most likely caused by the microphones or the sound card if using a PC analyzer. You should NEVER have to make a SMILEY face EQ, although a little boost is normal. If the < 60 hz band seem to never fully adjust properly, leave them at the level of the last well adjusted setting. ( ie: if 120 hz adjusted smoothly, but 60hz did not, set the 60hz EQ to the same as the 120hz adjustment. )

Perform the same adjustments to the high end.

A typical flat EQ will look like this:

A Normal Flat Room EQ

Notes:

You will be tempted to boost the highs and lows - resist the temptation - when you over accentuate a range of frequencies, your system will become muddy, unclear, and generally annoying to guests. It's really a hard habit to break, but after a 2 hour movie you'll find that you've heard everything, the works, the locational cue's, etc. and you'll actually feel less stressed.

If you find your EQ setting is exaggerated like the image below, you'll need to go back to step 1. This indicates a gross hardware failure or misconfiguration.

audio eq exaggerated

I Sincerely hope this helps. Remember - an EQ is generally used to compensate for room deficiencies as most hardware is designed to perform flat from the factory. If you  need EQ to overcome speaker and amplifier deficiencies then it's time to consider new hardware.

Ken Anthony

TRACKLIST

Track Description Length
1 30 hz in phase 1:00
2 30 hz out of phase 1:00
3 60 hz in phase 1:00
4 60 hz out of phase 1:00
5 100 hz in phase 1:00
6 100 hz out of phase 1:00
7 1k hz in phase 1:00
8 1k hz out of phase 1:00
9 10k hz in phase 1:00
10 10k hz out of phase 1:00
11 sweep 30hz to 3k hz in phase 1:00
12 sweep 30hz to 3k hz out of phase 1:00
13 sweep 100hz to 5k hz in phase 1:00
14 sweep 100hz to 5k hz out of phase 1:00
15 sweep 1k hz to 10k hz in phase 1:00
16 sweep 1k hz to 10k hz out of phase 1:00
17 sweep 3k hz to 15k hz in phase 1:00
18 sweep 3k hz to 15k hz out of phase 1:00
19 10 band eq test

Bands: 32, 64, 125, 250, 500, 1k, 2k, 4k, 8k, 16k

5:00
20 15 band eq test

Bands: 25, 40, 63, 100, 160, 250, 400, 630, 1k, 1.6k, 2.5k, 4k, 6.3k, 10k, 16k

5:00
21 31 band eq test

Bands: 20, 25, 31.5, 40, 50, 63, 80, 100, 125, 160, 200, 250, 315, 400, 500, 630, 800, 1k, 1.25k, 1.6k, 2k, 2.5k, 3.15k, 4k, 5k, 6.3k, 8k, 10k, 12.5k, 16k, 20k

5:00
22 Stereo Imaging Test - Human Voice Identifies LEFT and RIGHT channels. Useful for tracking down miswired systems. 5:00
23 pinknoise 5:00
24 whitenoise 5:00
All tracks are recorded at 0dB Full Scale ( 0dBFS ) unless otherwise noted.

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