Subwoofer tuning in the car
The subwoofer is a good addition to the car speaker system. But it is worth mentioning that buying an expensive subwoofer does not guarantee high quality sounding, as this device needs to be properly tuned. In order to connect and adjust the subwoofer properly, you should have not only good hearing, but also deep knowledge of auto sound theory.
Of course, before setting up the subwoofer in the car, it is better to ask for help from professionals, and for those car enthusiasts who want to do it themselves, this article will be useful.
Where do I start to tune my subwoofer?
Subwoofer tuning begins with the making of the box. By changing the characteristics of the box (volume, port length) you can achieve different sound. At the same time, you need to know in advance what audio files will be mainly played in the car, as well as what amplifier will be connected to the audio system. When a subwoofer is already delivered in a manufacturer’s cabinet, the flexibility of adjustment is of course limited, although with the necessary knowledge it is quite possible to achieve the desired sound quality.
One of the important factors influencing the sound quality is the amplifier, we advise to read the article “How to choose an amplifier”.
Tuning LPF (lowpassfilter) filter
First of all it is necessary to set up a low-pass filter (LPF). Every subwoofer today has a built-in LPF filter. The filter allows you to select the threshold at which it begins to block high frequencies, allowing the subwoofer signal to mix naturally with the signal from the other speakers.
Setting the filter, like setting up an active subwoofer, consists of a lot of experimentation – there is simply no certain correct “formula”.
The subwoofer is designed to play low frequencies, it can not sing this is the task of the speakers. Thanks to the LPF low pass filter, we can make the subwoofer play current bass. You need to make sure that the filter value is not set too high, and the subwoofer does not overlap the woofers of your full range speakers. This can lead to over-emphasis on one frequency range (say, around 120 Hz) and a fuzzy sounding speaker system. On the other hand, if you set the filter too low, because then there may be too much difference between the subwoofer signal and the speaker signal.
The playback range of the subwoofer is usually from 60 to 120. Try setting the LPF filter at 80 Hz first, and then test the sound. If you don’t like it, adjust the switch until the speakers sound the way you want them to. On the stereo itself, the filter should be turned off.
Adjusting the subwoofer
Next, you must activate an infrasound filter called a “subsonic. The subsonic blocks out the ultra-low frequencies that naturally occur in some songs. You cannot hear these frequencies because they exist below the threshold of human hearing. But if they are not cut off, the subwoofer will waste extra energy playing them back. By blocking the infra-low frequencies, the unit can more effectively reproduce exactly those frequencies that are within the audible range. Moreover, it prevents the failure of the subwoofer coil due to the accelerated movement of the cone.
What is Bassboost for?
Many amplifiers also include a Bassboost switch, which can increase subwoofer power by setting a certain frequency. Some motorists use the switch to make the sound more “rich”, although it is usually used to distribute the bass evenly. If you set the switch to the maximum value, the subwoofer may burn out, however, it is not worth turning off Bassboost completely, as in this case the bass may be completely inaudible.
Input sensitivity adjustment (GAIN)
Some motorists don’t understand how to properly adjust the input sensitivity. Input sensitivity indicates how much signal can be applied to the input to get rated power at the output. It must be adjusted to normalize the input signal voltage.
It is very important to adjust the input sensitivity correctly, as this will help avoid signal distortion, poor sound quality, or speaker damage.
To adjust the “GAIN” you will need
- A digital voltmeter that can measure AC voltage values;
- A test CD or file with a 0 decibel sine waveform on it (it is very important not to use a weakened test signal);
- Subwoofer manual, which specifies the allowable output voltage.
First, you must disconnect the speaker wires from the subwoofer. Next, make sure that the bass, equalizers and other parameters are turned off on the head unit to get a clear sound. In this case the input sensitivity level should be minimal.
Make sure that the digital voltmeter can read the AC voltage and connect it to the speaker terminals on the speakers (you can fix it with a screwdriver). After that you will have to turn the sensitivity “knob” until the voltmeter will show the necessary voltage value, which was specified in the specifications.
Next, it is necessary to supply a recorded audio file with a sinusoidal waveform to the subwoofer, changing the volume of the audio system from time to time until the occurrence of interference. In the case of noise, the volume must be restored to its previous value. In the same way the sensitivity is adjusted. You can use an oscilloscope to get the most accurate data.
Most subwoofers have a switch on the back called “Phase” that can be set to the 0 or 180 degree position. From an electrical standpoint, this is the second easiest thing to do after the “on/off” switch. If you set the power switch to one side, the two conductors will carry the signal from the output to the rest of the electronics to one side. Just flick the switch and the two conductors change position. This means that the shape of the sound will be reversed (this is what engineers mean when they talk about moving the phase backwards, or switching it 180 degrees).
But what does the average listener get as a result of the phase adjustment?
The fact is that by manipulating the phase shifter, you can achieve the highest perception of the mid- and upper-bass during listening. It’s the phase shifter that allows you to achieve all the bass you’ve paid for.
It is also the phasing of the monoblock that helps you achieve that frontal sound. It often happens that the sound is unevenly distributed in the cabin (music can be heard only from the trunk).
Subwoofers tend to have small delays, and they are directly proportional to the size of the distance. For example, the speakers of the American manufacturer Audissey deliberately put more distance to prevent this delay. It’s worth noting that it is possible to tune the amplifier for the subwoofer only if you have an external processor, or a built-in processor. An indication that the subwoofer is causing the delay can be considered laggy bass, which sometimes spoils the sound. The purpose of the delay setting is to achieve simultaneous playback of the subwoofer and the front speakers (the sound should not be allowed to lag by even a couple of seconds).
Why is it important to dock the subwoofers and midbass correctly?
If the subwoofer is poorly mated with the midbass, the sound will be poor and incomplete. It is especially noticeable on low frequencies, when instead of clean bass you get some nonsense. Sometimes such deplorable variants are possible, when the sound from a subwoofer will play independently at all. As a matter of fact, it concerns all kinds of music, not only, say, classical or rock music, where “live” musical instruments can be observed.
For example, in the tracks that refer to such a popular among young people genre EDM, the brightest bass is exactly at the junction with the midbass. If you dock them incorrectly, the low-frequency loud bass will at best be not so impressive, and at worst – will be barely audible. Since the amplifier needs to be tuned to the same frequency, it is recommended that you use a sound spectrum analyzer to get the most accurate data.
How do you know if your subwoofer is set up correctly?
If the subwoofer is properly connected, the people in the car simply can’t hear it, because it shouldn’t interfere with the main signal. If you listen to music at a low volume, it may seem that there are not enough bass frequencies. Lack of bass at low volume is a sure sign that the subwoofer has been connected correctly. Of course, there should be no noise, distortion or delay in the audio signal, and it makes no difference what type of design is used. The percentage of bass in each track must be different, i.e. the playback must be exactly the same as the original track recorded by the producer.
The next article we recommend you read is called “How the Subwoofer Box Affects the Sound”.
Video on how to set up a subwoofer
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Subwoofer tuning tips
A car subwoofer is an important element in the structure of acoustic systems. And it is important not only to select and connect the subwoofer correctly, but also to tune it.
It is important to understand that the subwoofer is a speaker for reproducing low frequencies, i.e. a bass player. In fact, the bass speaker has a cone that oscillates up and down, creating compression and rarefaction of air.
Bass is the lower range of sound (20 to 150 Hz). This is the frequency of oscillation for subwoofer cones as well as midbass speakers.
- Low bass (15 Hz to 50 Hz)
- Mid-bass (50 Hz to 100 Hz)
- Top bass (100 – 150 Hz)
After buying a subwoofer and amplifier, it’s worth starting by designing the box according to the characteristics of the speaker itself. Choose the style and type of music that will be listened to most often. The right approach allows you to get a good sound.
Setting the LPF filter
The LPF (Low Pass Filter) serves to remove high frequencies (vocals) from the subwoofer and leave only low frequencies. It is best to adjust the LPF on the head unit. This way you can get accurate setting values (we recommend 50 or 63 Hz cutoff). If it is not possible, then the cutoff is adjusted on the amplifier itself.
We do not recommend to use the filter on the amplifier and the head unit at the same time.
On the amplifier you need to turn LPF to the end, then turn counterclockwise (backward) until the subwoofer will not play upper frequencies. Since the frequency filters on the amplifiers are different (30 – 180 Hz, or 35 – 250 Hz), there are no recommended slider positions. Rely on your hearing or seek professional advice.
Adjusting the SUBSONIC filter
The ultra-low pass filter (SUB SONIC) is used to remove the lowest frequencies (20 Hz and below), preventing the speaker from exceeding its allowable range. Operating at these frequencies without a cutoff can noticeably increase the stroke of the cone, and the coil can come out of the gap and become damaged. Turning this filter clockwise makes it easier for the subwoofer to work, raises the volume limit at its normal frequencies and avoids the risk of damage.
Note that not all amplifiers have a subwoofer. It is advisable to immediately select an amplifier for the subwoofer which has the specified filter.
Adjusting the GAIN (LEVEL)
Setting the input sensitivity level of the subwoofer and adjusting it is done on the amplifier. The Level or Gain control allows you to match the signal level of the head unit with the amplifier to avoid distortion and interference with the speaker.
Note that the GAIN control is not a volume control. Do not be confused.
1. Setup on your head unit:
- The GAIN (LEVEL) control on the amplifier is set to zero;
- The audio signal with the adjusted frequency is input;
- Increase the volume on the radio until distortion occurs;
- Leave the volume at the distortion level and move on to the amplifier.
2. Tuning on the amplifier:
- Increase the signal level with the GAIN (LEVEL) control on the amplifier until distorted;
- Move the knob back a little so that the sound is clear.
An oscilloscope is used to fine tune the subwoofer. This solution allows you to adjust the levels flexibly, eliminating even subtle distortions.
Delays can only be set on processor-based boomboxes, or when an external processor is connected.
This setting is needed if the bass is “lagging.” Simply put, the front has already played, but the subwoofer is playing somewhat late, that is, with a delay. This is the reason why a delay adjustment is needed, to allow the front speaker and subwoofer to play back in sync.
Phase adjustment (PHASE).
The adjustment allows you to shift the sound from the subwoofer in phase relative to the main speaker – 180° in most cases. Phase adjustment eliminates phase mismatch, which improves bass quality.
Please note, when choosing an amplifier, it is desirable to buy with this adjustment, if it is not in the head unit.
Controls and sags
After all the adjustments, be sure to monitor the subwoofer’s performance and sags (lack of power from the car’s alternator). We recommend using a voltmeter to monitor the voltage. Be sure to connect to the input terminals of the amplifier. Normal voltage on the input of the amplifier should not be lower than 12.5V when operating.
Subwoofer operation is accompanied by heating of the voice coil. If the bellcup is warm, then everything is fine tuned. If the bell is hot, it means that the voice coil is getting very hot, because of which the subwoofer often and quite quickly fails.
Causes of rapid heating:
- Incorrect tuning;
- Poor design;
- Not enough power (clip);
- Bass amplifiers are used (bass boosts and not quality tracks);
- Weak amplifier (clip).
Pay attention , it is easier to control the speaker with more powerful amplifier. We recommend that you choose an amplifier that is 25 – 100% more powerful than the selected subwoofer in the impedance in which it will be connected.