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.

vergleich-absorberExample 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:

  1. A parametric EQ connected between your receiver and your subwoofer
  2. The free Room EQ Wizard (REW) software from HomeTheatreShack.com.
  3. 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:

  1. Install all the software
  2. Measure the room response (in this case for the subwoofer)
  3. Calculate the EQ filters automatically or manually in REW
  4. Input the filters into your choice of EQ
  5. Re-measure the altered frequency response
  6. 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 - beforeWaterfall 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.

How to build a $300 screen that performs like a $2000 one

Now you can order pre-mixed paint from us. Please contact us for more.

The difference a screen makes

You can project onto a white wall and get a really great picture, but if you’ve spent more than $500 on a projector, you will notice a marked difference with a purpose built screen. The benefits of projecting onto a great screen include the following:

  1. Increased sharpness / perceived resolution of the image
  2. Increased contrast
  3. Better ambient light rejection (when using a grey or silver screen as below) which means you can watch TV, movies or Sports with some ambient light on without completely distorting contrast

Enter Projection Paint

There are some – may I say – rather expensive paints on the market that you can use to build a DIY screen. In this article, I will show you how to get the materials yourself, mix the paint, paint the screen and hang it.

Please note that this is a fixed frame projection screen, which means it is not really possible to paint a roll-up screen with the below method.

Getting the screen

There are a few options on where to paint the screen.

  1. If you have the wall-space you can paint the screen on the wall with a black frame or even paint the whole wall with the paint mix below to create an invisible screen… until the projector is turned on that is.
  2. If you cannot paint the wall, you have the option of getting an MDF sheet to paint or even better…
  3. Paint on 3-5mm foamex / forex PVC sheets. These sheets are really light and easy to work with. You can nail them to a wooden frame for hanging or even nail them to the back of some bookshelves.
  4. Any other rigid material that is paintable.

imagesForex Sheet

You can calculate the screen size you need at http://www.projectorcentral.com/projection-calculator-pro.cfm and get the materials cut to size, leaving enough outer rims for nailing and hanging.

Getting the paint

The paint mix is called Black Widow. I will show you how to mix and variate the colour shade of this paint mix to get the desired results. For now, let’s look at the base, no frills mix, for which you will need the following:

  1. A matt white water based paint. Any will do such as the Dulux Wash and Wear Matt white. The most important thing is that it is water based and matt. 2L is plenty for upto 140″ screen.
  2. You will need to ask the paint to be tinted using black paint to a grey to a shade of N7.8. If this is not possible an N8 will provide the right shade of grey also. If your trade centre doesn’t know how to tint paint using the N tint codes, ask them to call Dulux or a Dulux Trade Centre.
  3. You will need Auto-Air Colors 4101-16 Aluminum Base Fine paint, which is a water-based silver paint formula. You will need 4 parts white paint to 1 part Auto Air Colors. If you’re using 2L of white paint, this will mean 480ML of Auto Air Colors. Be sure to buy the “fine” coarseness.
  4. A short nap roller
  5. Fine sandpaper

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Auto Air Colors

You will mix the above together using a drill and paint mixer head for 2-4 minutes

Painting the screen

  1. Using the paint mix, you will paint the surface with the roller in one direction only (vertical or horizontal) using quick movements. Go over it once quickly.
  2. Do NOT go over the surface again until it has dried.
  3. Once the first layer has dried, use the fine sandpaper to remove any imperfections from the surface.
  4. Remove any dust created by the sanding using a duster or a dry cloth.
  5. Repeat until you have at least 4-6 coats and a smooth even surface.
  6. Let the screen dry out completely before using it.
  7. Enjoy!

Variations on the above mix

The mix above comes out to a light to medium grey that is perfect for rooms with light coloured walls and bright projectors. It rejects ambient light well and has great contrast characteristics with the lights off as it rejects reflection from the light coloured walls.

If however, you are building a dedicated home cinema room with dark or black walls and you don’t intend on using the projector in ambient light, and you have a projector with great contrast (such as a JVC), you will want to mix a slightly lighter mix.

For a lighter mix, simply tint the white paint closer to N8.5, N9 or even N9.5. For 3D projection, which needs a lot of light, you could even try mixing with only a white base, as opposed to grey.

How to choose the right display?

There are so many brands, makes and types of displays on the market today that it is rather difficult to choose one for your living or home cinema room. In effect, there are 3 major things you need to look for when evaluating the quality of a display:

Black Level & Shadow Detail Performance

One of the most important aspect of perceived image quality is not resolution, as display manufacturers would like you to believe, but black level performance. A great proof of this is the switch from old CRT TVs with great black level to the then top of the range flat panel displays, which had rather poor black levels in comparison. Normal low-resolution TV broadcast looked better on the CRTs, while the new higher resolution flat panels needed specialised DVD players and trickery in signal processing to make images watchable.

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The difference between poor and great black level performance.

Black Level: how dark or deep the blacks look on the screen.

Because of how displays work, black level needs to be evaluated on dark as well as bright images and in moving from dark to bright images. The better the black level performance of the display, the more three-dimensional the images will look on the screen.

Shadow detail: how good a display is at resolving detail in darker areas (shadow) of the image.

If a display has dark inky blacks but it fails to resolve the subtle details in the darker areas of the image, the image will look flat especially on dark images or movie scenes. It is important that great black levels are married with great shadow detail performance to give a three-dimensional image regardless of the material.

Did you know that the brightness setting on your TV affects the black levels while the contrast setting affects the bright areas of the image? Just test the controls and notice what areas of the image change.

Brightness Performance

Even before resolution, how bright a display can go while maintaining its black levels contributes greatly to perceived image quality. The brighter the image can go, the more contrast your eyes will perceive – the contrast between the black and light areas of the image. The human eye will even perceive an image as higher-resolution simply because of the brightness of the image.

bright

In flat panel televisions, brightness is usually pretty average from display to display, but in projectors brightness plays an important part dependent on what kind of light control you have in a room.

In a normal living room with imperfect light control and light walls, projector brightness is more important than black level performance. While in a completely light-controlled room with black walls, black level performance becomes more important than brightness. Ideally you want a display that can do both.

For 3D performance, you will want high brightness again.

In flat panel displays, black level performance is more variable than brightness performance, therefore you should be paying more attention to that.

Resolution

There are three things under resolution you need to look our for.

Native Resolution

Native Resolution: the actual number of pixels available on the display.

Please refer to the diagram below regarding the type of resolutions currently available on displays.

resolutions-ultra-hd-4k-1080p-720p-dvdResolutions of modern displays

The amount of pixels you need to keep the image looking great depends on your viewing distance from the screen. As a guide, at the average viewing distance of 3 meters, you will notice the benefit of:

1080p / Full HD panel for any display above 30″ (display size is measured in inches diagonally).
4K for anything larger than 70″.

This means there is no actual benefit of buying a display with a resolution below those sizes at the distance of 3 meters for the average person.

Scaling Performance

Another area you need to look out for is how the display handles scaling.

Scaling: the transformation of an image from one resolution to another. For example, a DVD or TV image which has a maximum native resolution of 576p to 1080p.

Although most new material is now on Blu Ray and therefore 1080p natively, we still watch content on lower-resolution formats such as DVD and broadcast TV. The display needs to be tested regarding how well it handles this scaling. Some displays do this poorly but otherwise they perform well. In that case, you can still buy playback devices such as DVD players or set top boxes that do the scaling to the display’s native resolution to improve the image to bypass the internal scaling of the display.

Motion Handling / Motion Resolution

The last aspect of resolution is motion handling. It is also called “motion resolution”.

Motion Resolution: how well a display maintains image sharpness with moving images.

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Display manufacturers understand how important motion resolution is, so much so that they employ digital trickery  called frame interpolation – to reduce motion blur to keep image sharpness. You will want to turn any such trickery off and evaluate the display’s native ability to switch its pixels on and off using the same source device, such as Blu Ray player.

How to correctly evaluate a display?

This is the tricky part: as much as the above areas can highlight a display’s native performance, it is actually an interplay of the source device AND the display that will give you the end result. What does that mean? You need to evaluate the display’s ability using similar playback devices that you will be using at home, such as DVD players, Blu Ray players, TiVo, Gaming Consoles, etc.

Also, you need to set these devices up correctly to get the best performance out of the display: settings such as output resolution, output frame-rate, colour system, etc.

Which display technology?

So which display technology excels at all areas? It turns out some do better in some areas than others and it depends on your preference and situation as to what’s going to serve you best. The best thing to do is look out for the three areas above and trust your own eyes.

Flat panels:

Normal LCD Displays:

  1. Great native resolution, brightness and colour reproduction
  2. Below average black levels
  3. Below average motion resolution

LED and OLED Displays:

  1. Great black levels
  2. Great brightness
  3. Great all-around resolution
  4. Motion-resolution dependent on manufacturer and product

Plasma Displays:

Yes, they are still around, although in small numbers.

  1. Great black level performance
  2. Good brightness
  3. Below average motion resolution

Projectors

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DLP Projectors

  1. Class-leading brightness performance and motion resolution
  2. Great Colour reproduction – especially for 3-chip varieties
  3. Black level and shadow detail performance depends on manufacturer and product – goes from average to class-leading.

Recommended for brighter home cinema rooms as the high brightness will create a better perceived contrast. Also recommended for high-frame-rate material such as sports and 3D.

LCD Projectors

  1. Generally challenged black levels and shadow detail performance, although some manufacturers are better than others.
  2. Great brightness and colour reproduction
  3. Good but not great motion resolution.

Recommended when DLP projector is not suitable for viewers because of the DLP Rainbow effect.

XSDR – IDLA – LCOS

  1. Class-leading black level and shadow detail performance bettering even the best cinemas in the World.
  2. Historically low brightness over their lifetime more suited for dark home cinema rooms
  3. Motion-resolution has considerably improved but DLP still betters it.

Recommended for dedicated, light controlled home cinema rooms. The best cinemas use this technology for 2D viewing. DLP is still better for 3D.

How to wire up your speakers!

In my previous post, I explained how to position your speakers for surround sound. Next I would like to show you how to wire them up. This is something you do even before you plug your AV Receiver in.

It is really simple to do if you get the basic principles below.

Red and Black – Positive and Negative

All speakers will have two terminals: one for the positive and one for the negative side of the signal. They are usually coloured red for positive and black for negative.

  1. You will need to connect the red or positive terminal posts on your speakers to the red / positive terminal post on the AV receiver using your speaker cables.
  2. You will need to do the same with the black speaker terminals.

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Speaker terminals on the back of two different speakers

To aid in the above, most speaker cables will have one side of the wire labelled with a + sign, while the other one with a – sign. Sometimes, only one or the other is labelled but in all instances it should make it easy to connect them up to the correct post.

Choosing the right speaker terminals

Your AV Receiver will have the red and black speaker terminal pairs labelled with the speaker positions: Front Left, Front Right, Centre, Surround Left, Surround Right, Surround Back Left and Surround Back Right. To understand what these positions mean, refer to my previous post.

You will simply need to connect the red and black terminals up to the matching speaker. What you absolutely need to ensure is that the wires don’t touch – at either your speakers or at the AV Receiver. Touching wires will cause a short circuit and could damage your AV Receiver and your speakers.

To attach the cables, unscrew the jumpers and insert the peeled wires from the side of the jumpers ensuring none of the unpeeled wire is hanging out on either side. Screw the jumper back on while holding the speaker cable in place. Ensure it is screwed back on tight so the cable cannot become loose.

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Speaker terminal pairs on the back of an AV Receiver

Connecting your subwoofer

A subwoofer 99% of the time will have its own amplification, therefore it is not connected using a speaker cable and speaker terminals. It is connected to a pre-amplified signal output by your AV Receiver called a pre-out jack. You will find the subwoofer pre-out jack on the back of your amplifier under the area called Pre-Out.

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Pre-out jacks on the back of an AV Receiver

The cable you will need to connect your subwoofer with is called a single mono RCA to RCA cable or subwoofer cable. If your subwoofer has an LFE input, connect it to that input. If your subwoofer only has a line level input, connect it to that. These will usually be labelled accordingly on the back of your subwoofer. If there is only one RCA input, don’t try to figure out what it is, simply connect the cable.

To ensure the subwoofer is functioning correctly, set the crossover / high-pass filter to its maximum setting. This is usually a knob labelled ‘crossover frequency’ on the back of your subwoofer. This is needed because for home cinema, you need to let your AV Receiver handle bass management for this speaker. Lastly, don’t forget to plug the subwoofer in and power it on.

On higher-end AV Receivers, you may notice that all other speakers will have a corresponding pre-out jack. In an advanced post, I will show you how to use these for adding another amplifier as either an upgrade or for bi-wiring.

Bi-wiring

Some speakers have two sets of terminals connected by something called the jumper.

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Double speaker terminals for bi-wiring

The double terminals can be used to bi-wire the speaker. Bi-wiring means connecting the same amplified signal to both the midrange and high-frequency drivers (or sets of drivers) to achieve double the power and get a cleaner sound.

Be-wiring requires an AV Receiver that has this feature or an additional external amplifier. Additionally, it requires advanced set-up of said equipment. I will show you in an advanced post how to do this. For now, just leave the jumpers on the speaker terminals and connect the speaker cable to the lower set of red and black terminals.