What is Room Equalisation (EQ) and why should you care?

The Perfect Loudspeaker

Loudspeaker design nowadays is advanced to a point where loudspeakers have a pretty much flat frequency response between 20Hz to 20Khz, which are the lower and upper boundary of human hearing. In an ideal home cinema, the main speakers reproduce frequencies from 80Hz up while the subwoofer is reproducing frequencies from 80Hz down (in simplified terms). Sounds below 80Hz cannot be localised by human hearing (that is you cannot tell where the sound originated from) and because of the complexities of sound waves interacting below 80Hz in small rooms, it is best to have only one (or more) carefully placed subwoofers reproducing these lower frequencies.

Here Comes the Room

It’s great we have such advanced loudspeaker design, but once you put the speakers into a room, things get messy. The sound waves will reflect off the surfaces of the walls and furnishings and interact to create drips and peaks in the frequency response, making some frequencies louder, others quieter and yet others to echo and ring as they decay.

Example of frequency response of a loudspeaker in a room

What is even more upsetting is that this is not uniform in the room. As you move your head, sit somewhere else or walk around, the dips and peaks change. If you have just spent 100’s or 1000’s on speakers, the situation is rather unacceptable. You obviously want to get the most out of your equipment.

EQ to the Rescue

There are two main ways to combat the above: digitally using equalisation and with acoustic treatments. The former is somewhat easier to implement and a lot more wife (or for our lady enthusiasts, husband) friendly.

Digital Room Equalisation is built into most receivers nowadays. Some are more effective than others. Let’s have a look at some of what is currently on the market:

Audyssey MultiEQ XT and MultiEQ XT32: Audyssey’s technology deals with the most problematic frequencies below 200Hz very well, especially when it comes to MultiEQ XT32. At the same time, higher frequencies may not sound natural to some listeners. Some manufacturers (such as Denon) allow you to apply it to only the bass frequencies for this reason. MultiEQ XT32 was also available in standalone products as SVS AS-EQ1 and Audyssey’s own branded subwoofer equalisers. They have been discontinued, however. It’s worth picking up a used one if you have a receiver that lacks a good subwoofer equaliser.

Yamaha YPAO and YPAO R.S.C: Yamaha YPAO and YPAO R.S.C are discussed in detail here. They both do a great job with frequencies above 80Hz. Fortunately, the implementation in most recent Yamaha receivers is fully editable using Parametric EQ, which gives you enough resolution to tackle most issues. The only exception to this is ringing of the modal frequencies (see below), which is important for subjective sound quality.

Parametric EQ solutions: a fully parametric EQ solution, such as the ones from MiniDSP, allow you to target the modal frequencies in the room precisely, therefore allowing the reduction of ringing / echoing of sound in the lower frequencies. A good parametric EQ is therefore essential for frequencies below 80Hz and good to have below 200Hz. Neither Audyssey or YPAO tackle ringing at these problematic frequencies.

Dirac Live: Dirac is at the forefront of audio equalisation research and seem to be overtaking even Audyssey. Their impulse response correction algorithms seem to be gathering great reviews. More recently, they are also available in MiniDSP NanoAVR DL product, which makes it affordable. It is also very easy to use for those with not a lot of experience in equalisation, but who want to get the most out of their equipment. The highest end home cinema kits feature Dirac Live.

How to EQ?

If you’re new to home cinema, at the very least read your receiver’s manual and run the automatic calibration routine with all its feature set. If you’re more adventurous, you can supplement your system with a fully configurable parametric EQ for your subwoofer to tackle the modal frequencies in your room. For this, you will need:

A parametric EQ connected between your receiver and your subwoofer
The free Room EQ Wizard (REW) software from HomeTheatreShack.com.
A compatible USB microphone.

To know more about how to measure your room and configure a Parametric EQ, the MiniDSP or HomeTheatreShack websites offers some good guides, but in essence you will have to:

Install all the software
Measure the room response (in this case for the subwoofer)
Calculate the EQ filters automatically or manually in REW
Input the filters into your choice of EQ
Re-measure the altered frequency response
Repeat until you get satisfactory results

Modal Frequencies and What to Do with Them

Modal frequencies in effect are frequencies excited or affected by the size of a room. The modal region is the region below which modal excitation happens. This is normally somewhere below 250Hz for medium to large home cinema rooms. What happens in the modal region is that certain frequencies – very accurately predicted by room dimensions – will combine and re-enforce each other or cancel each other out in a way that creates big differences in loudness and decay time of the frequency. This will make the rest of the frequency spectrum – especially frequencies close to the mode – smeared, masking detail and transparency of the sound reproduction. To resolve this, the modes need to be calculated and measured using REW using the Room Simulation module, then checked using a frequency sweep and waterfall diagram. Once the offending frequencies are found, Parametric EQ filters need to be designed to EXACTLY match the mode’s frequency and Q to rob the mode of its energy. This will help reduce decay time also and make the waterfall diagram more even.

Waterfall plot showing increased decay time in the modal region. The most offending modal frequencies are clearly visible at 29.6Hz and 71Hz. Interestingly, speech intelligibility is affected by a modal at 83Hz, even though it is not as visible on the diagram.

We have really only touched on some basic concepts when it comes to equalisation. Nevertheless, the topic deserves the attention of anyone serious about home cinema. Learn it or get a friend or consultant who has the knowledge. It makes more of a difference to the perceived sound quality than your choice of speakers or amplifier. This is because the tonal quality that you like in your speakers is a lot to do with the above graphs. Even cheaper speakers can sound fantastic with the right equalisation and a good quality subwoofer.

Recreating the cinema experience: Yamaha’s Cinema DSP

Cinema versus Home

Movies are designed for the big screen and movie soundtracks for the big auditoriums of cinema multiplexes. When played back through a home cinema system in a smaller room, the perceived tonal balance of the soundtrack changes.

Tonal Balance: in simple terms, it is the amount of perceived bass, mid-range and treble present in a soundtrack.

All modern receivers have a way to combat this through equalisation of the speakers / room and filtering of the high frequencies which removes the perceived treble push of smaller, undampened spaces like your living room. However, you may notice that even after such equalisation, something is missing no matter how loud you play your equipment. This is because the big cinema auditoriums have different reflection and reverberation of the sound as it bounces around the room than in a smaller room.

This is what Yamaha went on to solve using their expertise in musical instruments and sound recording. Enter Yamaha Cinema Digital Soundfield Processing (DSP),

Yamaha Cinema DSP

Yamaha knew about this issue before all other manufacturers and they went onto recording and analysing the real-world behaviour of sound in cinema (and other) spaces. The extensive amount of data collected allowed them to digitally recreate the spaces using digital signal processing and in 1985 they released the Yamaha DSP-1, a standalone processor that could re-create cinema soundtracks as if they were being played back in a cinema.

Fast-forward almost 30 years and Yamaha’s Cinema DSP is in all Yamaha Home Cinema Receivers and have advanced to a point where it requires serious attention from anyone interested in home cinema.

What you need

You will need

A recent Yamaha Surround Receiver with at least 7.1 channel capability. Although Yamaha’s lower end units can do virtual Cinema DSP through a 5.1 set-up, it is not nearly as effective as having separate speakers.
An additional two speakers that will be used for the Front Presence speakers. They can have lower power handling and efficiency than your main speakers. Small bookshelves or satellite speakers will do with a frequency response from 100Hz to 20Khz.
More wires

Speaker Configurations

In essence, Yamaha’s Cinema DSP reproduces the reflections and reverberations of the cinema spaces through 2 height speakers at the front called Front Presence Speakers. Although you can use the front left and right speakers to reproduce the soundfield (called Virtual Cinema DSP), it produces a muddy and indistinct sound and does not compare well to the real set-up.

Yamaha’s more advanced Cinema DSP called Cinema DSP HD3 uses an additional set of speakers for the back soundfield called Rear Presence Speakers. When using DSP HD3, the Front Presence Speakers are more important to install than the Back Presence Speakers. Please see the full configuration below:

Cinema DSP 3D and Cinema DSP HD3

Cinema DSP 3D only has the capability to use Front Presence Speakers. Yamaha’s lower and mid-range receivers have this version. The rear soundfield data is mixed into the surround speakers. For this reason, it works better if the surround speakers are not at ear height but at least half a meter or more above the listening plane.

dsp

Receivers of this class are capable of 7.1 or 9.1 channel output. For 7.1 channel receivers, the back surrounds will not output sound when the Front Presence Speakers are being used by Cinema DSP. The 9.1 channel receivers have the capability to power all 9.1 speakers at the same time.

Cinema DSP HD3 improves on 3D with two things:

An additional two channels at the back (Rear Presence Speakers) that only reproduce the CinemaDSP effects for additional clarity. This expands the speaker configuration to 11.1.
Double the processing power to calculate more precise soundfield data both in the frequency and the time domain. For example, this means that sound reflections are tracked in space for double the time than with DSP 3D providing even more clarity.

From Adventure to Sci Fi

When Cinema DSP is configured well, you will experience your walls literally melting away and your home cinema opening up to sounding like a big movie theatre. To configure it, do the following:

Ensure that the Front Presence Speakers are placed wider and higher than your front left and right speakers.
Run the YPAO automatic calibration even if you will not use the EQ function of your receiver. This is because higher end Yamaha receivers will adjust the Cinema DSP parameters dependent on the already existing acoustic characteristics of your room.
Select a Cinema DSP program (called movie) on your Yamaha Receiver.

There are 6 movie soundfields on all modern Yamaha receivers. Read your Yamaha manual to understand the differences between them. As a guide:

Select Sci Fi for any action or Sci Fi movie or where the soundtrack has lots of precisely steered effects.
Select Drama for movies with lots of dialog or for TV programs.
Select Adventure or Spectacle for older movies or movies with big musical scores.
Mono movie for – you guessed it – mono movies.
Select Standard when no other soundfield sounds right for the movie or when you want to leave the front soundstage intact.

In addition there are many parameters you can adjust for each soundfield to make it sound less or more spacious. It is rather difficult to configure these manually, so download the Yamaha iPhone and Android app to your phone that allows you to configure them easily.

I recommend this even if you have an older receiver that doesn’t allow you to configure soundfield data using your phone. You can simply use the app in demo mode and copy in the parameters using your remote manually.

What about other manufacturers?

Even though other manufacturers have started using DSP soundfield programs, they don’t have the sophisticated algorithms Yamaha uses. Most simply add echo or reverb to the soundtracks to create some kind of effect as opposed to precisely measured soundfield data. I recommend auditioning the difference between them.

How to choose the best positions for your Home Cinema Speakers

Positioning speakers correctly is important if you want to get the best sound out of your Home Cinema speaker system but it doesn’t have to be hard!

What is 2.0, 5.1 and so on

In surround sound, we refer to two types of sound channels:

Main or full-range channels which normally reproduce a frequency range between 80Hz and 20KHz
Low Frequency Effects (LFE) channels – or subwoofers – which reproduce anything below 80Hz

in the X.X notation, the first number refers to how many full-range channels there are and the second number refers to how many low-frequency channels there are. For example, in 5.1 there are 5 full-range channels and 1 LFE channel.

The symbol displayed on some DVDs and Blu Rays for 5.1 surround sound encoded on the disk

Channels versus Speakers

We refer to channels when we talk about how many sound channels are put onto a medium such as DVD, Blu Ray or TV broadcast.

We refer to speakers when we talk about how many speakers reproduce the sound that is being played. For example, did you know that you can play stereo (2.0) channels over a 5.1 speaker system and vice versa? An explanation of why and how to do that is going to be a topic of another post. For now, let’s position your speakers in your listening environment.

7.1 Surround Speaker Placement

Front Left and Right Speakers – 2.0

This is real easy! You simply place the speakers on the left and right of you TV screen. All you need to ensure are two things:

They are ear height when you’re sitting down – unless you’re watching movies standing up for some reason!
If they are more than two meters apart, ensure the speakers are slightly turned inwards towards the listening position so they end up facing you.

Centre Channel Speaker – 3.0

The centre channel should go in between your front left and right speakers. Usually the best place for it is under or on top of your TV. Unfortunately, doing either could compromise dialog intelligibility. To avoid this, experiment with the following:

Try placing the speaker both under and over your TV screen and see which position you prefer in terms of sound
In each position, angle your speaker up or down to ensure it is firing towards your ears as you sit down in your normal listening position. To achieve this, you may need to wedge something under the bottom front or bottom back of the speaker to get the right angle. One way to do this is to buy some rubber stick-on feet like below on ebay and use those.

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Surround Speakers 5.1, 6.1, 7.1

Now this is a bit more tricky but it becomes easy as long as you know how many surround speakers you want to install.

2 surround speakers for a 5.1 set-up – Surround Left and Surround Right

If you have two surround speakers, it is best to position them as follows:

Height: about 1/2 to 1.5 meters high from your ears when you’re sitting down
Best Placement: about 1/2 meter back from where you are sitting to the left and right of you. This can be on the wall or on speaker stands or even hang them from the ceiling. You don’t need to have them at equal distance from you, so you could put them on the side walls even if your room layout is not symmetric AS LONG AS you account for this when you set up your AV receiver. I will show you how to do this in my next post.
Good placement: if you cannot position the speaker high or behind you, you can position them on speaker stands to the side.

3 surround speakers for a 6.1 set-up – Adding 1 Surround Back Channel

All modern AV receivers can process stereo and 5.1 channel (dolby digital and DTS sound-tracks) to extract 6.1 and even 7.1 channels. This provides a more stable surround sound stage and better movement (called steering) of sound effects at the back of the sound stage.

When you add a third surround speaker, you will need to:

Put it behind you on the wall or on a speaker stand at the same height as your Surround Left and Surround Right speakers.
Set your AV Receiver to mono Surround Back channel or 6.1 Speaker Configuration and ensure you connected the speaker to the correct speaker terminal. Most AV Receivers will ask you to connect a single Surround Back speaker to the Left Surround Back Speaker terminal.

4 surround speakers for a 7.1 set-up – Adding Surround Back Left and Surround Back Right Channels

You can also have stereo Surround Back channels, adding two speakers behind you instead of just one. To achieve this, you will:

Put both speakers behind you at the same height as the surround Left and Right Speakers.
Leave a minimum of 1/2 meter distance between them. The bigger your listening area, the bigger the space between them should be. For example, I use all my living room as my listening space so the surround back speakers are placed equal distance from each other and from the side walls.
You can measure your listening environment and make the same calculation: equal distance from each other and from the side of your listening area such as your couch while still respecting the minimum distance between the two speakers (1/2 meter).

Subwoofer – the .1 in X.1

Subwoofers can go anywhere in the room because the sounds they produce are non-directional – that is you cannot tell where they are coming from. Subwoofer placement is an art in itself and short of hiring an audio engineer, you can do a lot to get the best sound in your room with the following rules:

If you have only one place where your subwoofer can go, then easy: place the subwoofer there.
If you can put it both front and back, try it in the front of the room first then try it at the back and see which position sounds best.
If you can literally put it anywhere, and you just want to get THE BEST sound possible, you can do the follow – called the crawl test:
1. Place your subwoofer in the position where you normally sit. This may require shifting the couch and putting the speaker on a chair.
2. Put your favourite music track on with a lot of consistent base.
3. Now crawl around the room and mark any places where you consistently like the sound of the base – these are the “sweet spots” in your listening room.
4. Place the subwoofer in one of those “sweet spots”
5. Enjoy!

In spite of the above rules, first and foremost you should always trust your ears. Play with speaker placement and see – or rather hear – what sounds best to you!