F.A.Q. How to make a super-budget sub.
Hi all. I finally digested all the information and finished my experiments on a very interesting topic. I will tell you right away without intrigue. I want to offer you an idea of a sub with a small price, capable of working without an amplifier directly from the head unit and thus possessing a very good sound and able to compete on equal terms with many budget subwoofers in sound volume and quality. From the point of view of newbies, this sub has only one drawback. You will have to tinker with it, think, read and figure it out. If the above described is not about you then forget about the rest of this stuff. You do not need it in hell. The rest of you, I suggest that you read a bunch of crampons below. The essence of my idea to use design called quarter-wave resonator or Voight tube. In a nutshell it differs from boxes with phasics by the fact, that the box at the speaker is not present at all. The loudspeaker is cut right into the tube of the phaser.
Pros of this design: – The efficiency of such design is 300% higher than with a closed box! – PB reduces resonance of the driver. In a phasic or a woofer, for example, the speaker starts to play higher and the CV on the contrary reduces resonance. – The design of the HF has a very low drop below the tuning. For example a subwoofer in a phasic below its tuning dramatically loses volume with a steepness of 24dB per octave and practically doesn’t sing there. The B&W has a drop of only 6dB per octave! Lower than a closed box. In simple words, in the cabin of the car below the tuning frequency it can not only not lose volume, but also increase it! Accordingly, there is no need to tune the B&W low. And he does not like it. -Bass speed in the HF is quite comparable to the speed of the bass in the CY! That is, the bass is quite musical and fast. – HF is extremely easy to calculate and requires only the diameter of the cone (from the middle to the middle of the suspension) of all the parameters of the speaker. The calculation is done by two simple formulas. Of course different speakers will sing differently in the VC, but it will not affect the size of the VC. Just make a box once and change speakers, listen. – Not too demanding to the crookedness of your hands. If you screw up a centimeter or two somewhere it won’t dramatically affect the result, while the crooked saw cut will be compensated by plenty of sealant.
Disadvantages: – rather difficult to produce, you will have to be patient and use your brain. – the box comes out rather big. – The travel of the speaker in this design is LARGER than if you were to turn on the sub without the box at all. This means you won’t be able to get as much power into the speaker as possible, and with a lot of overdrive there’s a risk of ripping the speaker. However, before the speaker rips, it will start to rattle and crackle desperately. The overloaded speaker is audible at once (although for me this is a plus).
Hopefully intrigued and interested)
Almost any loudspeaker is suitable for the construction of the HF, from mid-bass to loudspeakers from old music centers, computer speakers, old Soviet speakers, etc. Preference should be given to speakers with a larger suspension size. Diameter and number of speakers, the more the better, but here you need to consider that the size of the box will grow appreciably. So you should think about the size of the box on the paper first. Will they suit you or not. For subwoofer work from your headset, I advise you to use a pair of speakers 13-16cm in diameter, 20-25w of power. Connect them to the rear channels, and that’s it. You can make a box from old cabinets, nightstands, etc. 15mm chipboard will be enough for our purposes.
Now let’s do the math on some cv’s. Let’s say there are two 13 cm speakers. We measure the diameter from the middle of the hangers. That’s 11.5 cm. At school we were told in geometry that the area of a circle is pR^2 (radius squared multiplied by the number of PI). If the diameter is 11.5 cm then the radius is 5.75 cm and the area 3.14*5.75^2 = 103.8 cm2 Since we have two speakers then multiply 103.8*2 = 207.6 cm2 This is the effective area of our speakers. For the partial frequencies, it is optimal to take a cross section one and a half times larger than the area of the cones. If you do more, then the speaker will exceed the stroke faster and if less, it will lose its efficiency. In short, let’s not be too sophisticated and take one and a half cross-section. Now we can choose height and width of our port. Choose these dimensions depending on how you are going to put the speakers. I used to put it in side wall at the beginning of pipe and dance on depth of speaker in order it would fit in. If you saw into the end of the beginning of the tunnel, look that the speakers fit in diameters. Let’s say we put speakers in the side wall of the tunnel like this: but the depth of the speakers is not big. Then we just take a square with cross section of 17,7 cm. (17.7*17.7=313.29cm2) turns out almost what we need (311.4cm2). Now determine the length and setting. It is recommended to tune it as close as possible to resonance of speakers (Fs), but my experience showed that for very small speakers you shouldn’t tune chv above 50-55 Hz, otherwise it will be useless. If its resonance is 55 and lower then build port in resonance of the speaker. If it is higher then tune it to 55 Hz. For simplicity let’s take chv tuning at 50 Hz. The length of the port is determined by the formula: L tunnel in meters = (343/F tuning)/4 In our case (343/50)/4=1.72 meters.
At first glance, of course, the figure is healthy, but who prevents triple or quadruple the port?