Part 5: On the Move

The audio system won’t sound the same in the garage as it does on the road, and you must consider this when creating a tuning in the car.

So what are the differences?

A moving vehicle makes a lot of noise – from the engine, the tyres against the road, and the wind as it hits the vehicle. Let’s not forget the internal noises like the fan and extraneous noises like other vehicles and changing weather conditions.

Most of these unwanted sounds are made up of low and mid-frequency energy. This means that the bass from the loudspeakers will be masked by the engine and road noise, and you should therefore tune the sound system with a bit of extra bass to compensate.

Look at these in-car measurements made at different speeds. You can see the noise rises with speed and affects the listening environment even above 1kHz.

Adding bass

How much bass should be added?

Each vehicle sounds different, so you need to test it out for yourself. Try following these steps:

  1. Listen to 3 pieces of music containing bass and sub-bass frequencies in static conditions.

  2. Drive the car at low speed, e.g. 30km/h and listen to the same pieces of music again. Write down the differences you hear

  3. Drive the car on the highway, e.g. 80km/h and listen once again. Write down the differences you hear.

  4. Think about how you intend to use the car – mainly for long-distance highway driving, or short-distance slow city driving? Concentrate on making the sound good for this conditions

Ask yourself the following questions

  1. Is the overall bass level enough?

  2. Can you distinguish individual bass notes?

  3. Do the upper mid-frequencies become more harsh or aggressive?

  4. Do mid-range resonances seem to stick out more?

  5. Do you feel pressure on your ears and a boomy sound?

Some vehicles have an automatic bass compensation algorithm that increases low frequency energy depending on the vehicle’s speed.

Reducing the upper mid-range

When you are listening with the engine off, and you spend hours getting the right balance of warm lower mid-range to upper mid-range detail and clarity. Speech sounds clear, violins and guitars cut through exactly the right amount.

The second you start the engine, this balance is out the window! The engine also masks a lot of low-mid energy and this dramatically changes your perception of the mid-range balance.

What can I do about it?

Strategy No. 1

When you are tuning with the engine off, aim for WARM and FULL. Perhaps it sounds a bit muddy or the voices sound too chesty, but this will produce just the right balance when you start to drive. Try to reduce your filters in the range 100-400 to let a bit of extra energy back in to this range.

Strategy No. 2

Listen to some content with a lot of energy in the range of 2-5kHz. For example, a bright sounding string quartet, some clangy guitars (e.g. With or without you by U2). Go for a drive. Is the sound fatiguing or aggressive? Do you feel like you want to turn up the system but when you do, it hurts your ears? In this case, you need to reduce the upper mid-range.

In my mind, upper mid-range consists of 2-5kHz, although peaks between 1 and 2kHz can also hurt your ears. Experiment by boosting the energy in this area to find the offending frequencies.

Pesky Resonances

Some resonances stick out a lot more when on the road. I can recall times where I have to reduce a filter by an extra 6dB compared to working with the engine off.

Which frequency range are these resonances in?

There is no hard and fast rule for this, although I find myself spending a lot of time working with the filters in the range 150-700Hz. Perhaps now that a lot of bass energy is masked by the road and engine noise, the lumps and bumps in the frequency range above this stick out more.

What can I do about it?

Listen to each filter again whilst driving to check you are cutting the energy by just the right amount. Turn the filter on and off and listen to the difference. If you experience some pressure on your eardrums, or you can still hear ringing, you need to reduce this frequency further.

You might also find that you are able to reduce the gain of some filters where resonances no longer stick out (i.e. reduce the amount you are cutting).

Speech

You have reached a point where you are happy with the overall tonal balance and the great job you did removing those resonances. Before you kick back, do a final listening test on the road to check speech intelligibility. Even though you might have tuned the system for music playback, the last thing you want, is to be driving on the motorway and discover you can’t understand the traffic reports! Put the radio on at a comfortable volume and listen to the news for at least 30 minutes. Try some different radio stations and maybe a podcast played from USB or your phone. Ask yourself the following questions:

  1. What volume step am I listening at? Is this higher or lower than it is for music?
  2. Do voices sound clear or do I struggle to hear all words?
  3. Are male voices easier to understand than female?
  4. Do voices sound harsh or “shouty” or “forced”? Do my ears become tired after a short time?
  5. Do voices sound tonally balanced or do some parts stick out, for example, “ssss” and “fffff” sounds?

If the system sounds harsh or aggressive:

  • Use one filter with quite a high Q factor, around 4 or 5.
  • Play the speech or audio file that hurts your ears, but not too loud!
  • Boost the filter and move the frequency slowly until you find the exact frequency of the harshness.
  • Now reduce this frequency until the voices sound smooth and natural

If you are unable to hear the details of speech:

  • Try adding a small amount of extra energy between 2-6kHz, perhaps 1-3dB
  • Listen to the same audio content again.
  • Is it easier to understand the voice?
  • Experiment with the frequency you boost

If you are missing the “ffff” and “sssss” sounds:

  • Try to boost the sound between 6 and 10kHz
  • Does this help? If so, try a smaller band between 8 and 10 kHz
  • Remember you only want to add energy where really necessary. Small steps each time!

Nearly there…

Your system must be sounding pretty good by now!

Remember these 5 tips for fine-tuning!

  1. Make small adjustments
  2. Give yourself time to listen to each change carefully
  3. Watch out that you don’t remove too much energy
  4. It’s a cyclical process, you’re getting closer
  5. Use the measurement but trust your ears!

That brings us to the end of our 5-part course.

What have we covered during the last 5 weeks?

Part 1 Setup: Basic checks, equipment and tuning conditions

Part 2 Tonal Balance: filter types, equalization techniques and target frequency response

Part 3 The Sound Stage: ideal setup, setting delays with measurements and your ears, optimizing bass performance

Part 4 Listening Loud: dynamic processors, controlling the system and loudness tunings

Part 5 On The Move: Differences between static & dynamic listening, adding bass, reducing peaks and optimizing speech

Thank you for following this course all the way to the end! You deserve a certificate, or at least a pat on the back.

Now, I’d like to ask a favour.

If you enjoyed the course or found it useful, please share it with someone else who may also benefit from this knowledge.

Thank you for following this course all the way to the end! You deserve a certificate, or at least a pat on the back.

If you have any feedback for me, or any ideas to improve the course, I would love to hear from you.
shelley@echo-friendly.com

If you would like to learn even more about car audio, training your ears or audio in general.
Then check out my training workshops

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