Subwoofer design
The housing, input jacks, output terminals and regulators were used from the original converted car amplifier. The “Level” (Volume) regulator with a resistance of 50 kOhm is connected in the usual way between the output of the adder-filter and the input of the power amplifier. Heat sinks for transistors of the pre-final stage are not needed. Resistances marked * are replaced with tuning ones and their resistances were selected directly during tuning, to “hear” in the absence of any distortion at all volume levels. It must be said that despite the simplicity of the circuit, the quality and power of the sound turned out to be at a high level and all the needs of the “music lover” were fully satisfied! Although not 2000 watts, of course.
The assembled amplifier in the housing was placed directly inside the subwoofer “box”.
Fine tuning
So, a place for a new component has been found. The time has come to fine-tune the subwoofer to acceptable levels of bass and volume relative to the overall system. To achieve this, all modern subs are equipped with at least two adjustments: volume level and cutoff frequency.
Effective and large-scale scoring of what is happening on the screen is important for cinema. It is also important that the subwoofer and other system components interfere with each other as little as possible. This is where the internal functionality of receivers comes to the aid of movie theaters. Use the crossover built into the receiver to cut off unnecessary frequency range from the front and rear speakers.
If your acoustics are floorstanding, set the lower limit for it to approximately 80 Hz. If you use bookshelf speakers, leave them with sounds somewhere from 100 Hz and above. For the subwoofer, in turn, set the same upper limits: 80 or 100 Hz, respectively. Regarding the subwoofer volume level, first set the control to a third of the possible power. Further, already in the “field” conditions, you will understand whether you need to add volume to it or, on the contrary, take it away a little.
In a Hi-Fi system, the subwoofer setting is different. First we need to find out what frequency range is available for the specific speaker that we want to combine into a trifonic. We are interested, first of all, in the lower threshold of the AC. We are guided by it: if it is, say, 40 Hz, first try to set the subwoofer cutoff to 40–60 Hz so that a kind of “overlay” is formed and a smooth connection between the frequencies of the subwoofer and the acoustics. You can experiment and raise the cutoff frequency even higher - up to 100–120 Hz.
Here the result will depend on how tightly your speakers can play at a particular frequency in the lower register. As a result, you can get both an excess of upper bass and its pleasant compaction, better physicality and fullness of sound. But as a result of this setup, most likely, you will need to reduce the subwoofer volume level. And this, in turn, will lead to a weakening of the sound of the lowest frequencies that your sub is capable of.
There is also an alternative setting option, when the subwoofer cutoff is set to its minimum position, and fine tuning occurs by adjusting the volume level of the subwoofer relative to the stereo pair. In this option, the lowest hertz sounds better - the subwoofer will not take on the burden of the speaker, or it will only take a small share of it. This method is recommended by one of the subwoofer manufacturers.
Ultimately, in terms of tuning, the “reference” is considered to be such a combination of sound when the subwoofer and acoustics complement each other and become “one whole” by ear. But no one canceled taste preferences: in any case, the main thing is that you personally like it.
Speaker size
Let's start our story with emitters or diffusers, or rather, with the choice of speakers. All future modernization depends on this. Below is important information you need to know:
- So, if the speaker model is small in size (8/10 inches), then the diffuser inside will be lighter.
Note. You should know that lightweight diffusers have low inertia. On the one hand, this is good, because it is easier for the amplifier to control them. But the low output in the deepest bass negates the entire advantage of such a speaker.
- In contrast, large speakers larger than 15 inches have a heavier and more inert driver. It will be much more difficult for an amplifier (see How to connect an amplifier to a car radio: you are your own master) to swing such diffusers, but if you choose a more powerful device, it will cope with a speaker of 18 inches or even larger;
- In a word, in this case we are talking about an impulsive characteristic. Indeed, the ability of the speaker to clearly follow the electrical signal of the diffuser, which comes from the amplifier, is such a characteristic.
Tuning interior, subwoofer and much more
Note. Small subwoofers have better impulse response than larger ones. On the other hand, if the music collection the user is listening to does not include hip-hop or R&B, fidelity takes a back seat. The ability to effectively transmit bass, especially the lowest bass, becomes more important. And the larger the speaker, the better it copes with this task.
- The ideal option for improving and further installing a subwoofer in a car is not an 18-inch or even a 15-inch speaker, but a 12-inch one. The fact is that tuning will require the manufacture of the body. For 12 inches, the body can be made of acceptable dimensions (so that it does not take up much space in the trunk) and the radiating surface area will be acceptable.
Subwoofer under the seat
Note. To be fair, it is also worth noting that large subwoofer speakers do not provide the punch and bite of sound that is so valued by rock lovers. For this reason, the choice of 12-inch speakers is also the right choice.
Input stages - adder and filter
The circuit below was used as a summator of the signals of the left and right channels, as well as to isolate the low-frequency component from the general signal:
The circuit is one of many similar circuits that are published on various radio sites and perform one function - summing signals and isolating a low-frequency signal with the ability to adjust the cutoff frequency. However, some changes were made to this scheme:
- at inputs L and R, capacitors with a capacity of 1 mF (film) were added in front of resistors R1, R2 for decoupling from a possible DC component from the signal source;
- the capacitance of capacitor C1 is increased to 3300 rF;
- the resistance of the OS adjustment resistor R3 is increased to 100 kOhm;
- The resistance of the cutoff frequency adjustment resistor R5 and R7 (dual) is increased to 100 kOhm.
Power to the op amp can be taken directly from pins 4 and 7 of the 140UD708 power amplifier microcircuit, or you can assemble a simple stabilizer using limiting resistors and zener diodes, as for the op amp of the power amplifier (in the photo it is present in the form of a small separate scarf). Also, if desired or necessary, you can add a subsonic filter, which is usually a simple 2nd order filter and “cuts off” frequencies below 10-15 Hz, but this is ... if desired. In this regard, many different opinions are expressed, in particular about which order filter is better - first, second or third, and other subtleties and circuits also exist in a large variety - passive, op-amp and transistor. In this article I will not be able to fully cover this topic and this question, again, if desired, everyone can study on their own at their leisure)) Given the level of “quality” of car music, the presence or absence of a subsonic node is hardly critical.
How to make computer speakers with your own hands
How to make speakers with an isobaric subwoofer for a computer yourself
There is a good book written by S.V. Gaponenko, called DIY acoustic systems. The book is written in a fairly accessible and simple language, but it is not boring; there are clear examples and explanations.
In it you can see information on making a homemade calculation for creating columns. Anyone who has already dealt with similar things may disagree with the author in some ways, but overall the book is recommended for reading.
There are more boring books on this topic, for example, S. Bat, called amateur loudspeakers. Let's look at how to make a subwoofer for a computer yourself at a small size.
What is needed for making
From the tools you need to prepare a saw or sawing machine, a jigsaw, a chisel and a hammer, nails and glue, a drill, a compass and a screwdriver, you will also need a tape measure.
To create a subwoofer you will need chipboard plywood, you can use the remains of unnecessary furniture, a speaker, screws and wire, nails, and the required dimensions.
You will need to cut out square parts of the following sizes. Parts in the amount of 4 pieces, dimensions 355 mm X 203 mm X 20 millimeters from chipboard, two pieces of parts measuring 360 mm x 360 mm x 20 mm, make one from plywood measuring 330 mm x 330 mm x 25 milliliters. Also, make 8 parts from chipboard measuring 20 mm x 20 mm x 196 mm.
Where to begin?
Once the tasks for the sub are determined, consider the device that is responsible for the amplification in your system. If it is a receiver, such devices already have a dedicated subwoofer output. It is most often indicated by a corresponding inscription near the connector.
If your system uses a stereo amplifier, most likely it does not have a separate output for a subwoofer. In this case, the selected subwoofer model must have a so-called “high-level input”. This input allows the subwoofer to process and correct the outgoing full-range signal from the stereo amplifier.
With this option, the subwoofer is connected to the speaker terminals. It is preferable to use the “-” terminal from one channel and the “+” terminal from the other. But there have been cases when experimenters connected a subwoofer to the terminals of one of the speakers - this option is quite acceptable, but remains at your discretion.
There are also subwoofer models that are equipped with two pairs of terminals for your acoustics. In this option, both channels from the stereo amplifier are connected to the corresponding inputs on the subwoofer, then the signal from the subwoofer is supplied to the stereo pair.
This allows the sub, using the built-in crossover, to unload your speakers from low frequencies. But in this way one more link is introduced into the sound path, and I don’t think that fans of “direct drive” and similar buttons will prefer this option.
