Homemade budget sub for movie

Why all this was done?

For a long time I thought about making a “BUHalki” for a movie in the form of an active subwoofer on the LFE channel.
As LF 30GD-2 (LF from S90), as such are available and are lying idle in large quantities (well, there are pennies in the right places, so it's not a pity). Well, I am a rogue :), I feel sorry for a decent sub more than 15 000 p. give away. According to calculations, I decided to choose a 6A bandpass. Only he gives a very decent return and low boundary frequency. According to the estimated frequency response -3db - 24 -63 Hz. Assembled sub looks like this.


The quality of the photo is mostly terrible, since I photographed it on the phone (well, I didn’t have a soap box or a mirror at that time).
Who cares welcome under cat. There are a lot of phot.

Design

The overall design is very similar to the well-known structure in the internet.
This is an example of the appearance from one site (I will not mention the authorship of the picture, because I don’t remember where I took the photo, if anyone knows, write in a personal, put a link). Naturally sizes will be completely different.

For the manufacture of structures you need to know or get the parameters of a particular speaker. They are called Thiel's Parameters — Small . If you don’t know what it is, then google and wiki help you, everything is measured quite simply, the software and methods goof with a bang. Not all software is free, but I will say that you can measure it with an accurate voltmeter, accurate scales, clay, generator and amplifier. Googled by the "method of added mass". I used the method of additional weight, but I automated the measurements with the appropriate software (the name is not indicated because the software is paid, but we in Russia who need that one will find everything;)).
It makes no sense to bring the measured parameters, because each speaker is unique and the assembly of the structure according to “alien parameters” will not lead to anything good. How to say about the dynamics of the times of the USSR, so as not to be rude ...
I have 4 woofers and all have completely different parameters, although they are of the same brand.
For those who want to point out and “say” that you cannot achieve “high-quality” sound from the bandpass, I would repeat once again that the sub was going to watch movies and sound the LFE channel, in which basically only effects occur.
')

Calculations

Here are the design drawings of the hull and the estimated frequency response, all designed for a specific speaker.
Calculations coincide in 4 known programs.
I took as the main calculation program Bass box pro



Calculations on the loss of the useful volume of the body

“Saw, Shura, saw”

After all the calculations, I ordered a chipboard cut in one company that deals with furniture, everything was very cheap.
Here is the middle partition for mounting the speaker.



Side walls

In the background you can see the drilling tool, oh and I hesitated to drill.

Side wall with bars for reinforcement and fasteners.


We are trying to collect everything in a single structure.



Example Phase Inverter from sewer pipe


Cover the walls with a sound absorber


And so with the speaker

Electronic filling

Pre-amplifier collected according to the scheme www.electroclub.info/samodel/sub_pred.htm
He drew a signet for smd resistors and reduced it in size. If it is interesting to someone, I can put it in Sprint Layout format.
As the terminal amplifier chose an amplifier on the TDA7294 with adjustable output impedance.
Scheme and description here . Signet used by the author. In order not to get far from the original scheme:


The process of making signets will not describe in detail only the finished result. Made by LUT (Laser Ironing Technology). As material for the transfer - cut sheets of the magazine PC Week.
Pre-amplifier board ready for pickling and after pickling in ferric chloride.


Terminal Board TDA7294



He collected almost completely the ULF, a pair of ohmic resistances and one oxidizer were missing and assembled a preamplifier with a subsonic filter and a low-pass filter with a variable frequency and phase switch. There is also a Linkwitz corrector on the board, but it is not decoupled, since it is not needed for processing a bandpass. On the pictures, the boards are not washed off from the flux, so these are “beautiful”.

Terminal amplifier


Preamplifier



Kit pick up the subwoofer


Take a piece of aluminum mark and make the back panel of the amplifier unit



Do not forget about the fusible insert, as a radiator, something from the stocks from AMD


Terminal amplifier board


Made all connections


Food from some old trance, again motannogo themselves. The transformer in ancient times stood in some kind of tube TV until it came into my hands and was not rewound for some kind of amplifier, it was a long time ago). Power on terminal + - 35 V.


Since this look is not pretty, then we paint everything with matt black paint from a can



Put the sweaters perdelki


The rub subwoofer should stand on the spikes. The spikes were ordered by the father to the turner. These turned out


An example


And fix them

Do sub moderately beautiful and cute

Let me give you to start pictures of the intermediate result. From them it is clear that such a sub will not decorate the apartment. Well, nothing we will fix it.


Without cover


He took out a vibrating grinder, putted holes in the screws, leveled the casing and began to glue the adhesive on the light wood. At first I bought a self-adhesive for pasting in one layer. Initially, the idea was a light body and black matte details. After the first layer, it became clear that one layer is very small.
First layer


I tried to cover the bottom with varnish, it became clear that one layer just shines through.


I had to go to the store again for the film. The second layer stuck more fun, as the wife helped. Four hands glue much easier.




After two layers, the film began to varnish. I do not remember the brand of varnish now, I remember that it was quick-drying and seemed to be diluted with acetone. It cost about 50 rubles per jar because it is overdue :), but we don't care about rogue.
Two coats of varnish



After drying it looks like this.


Nearer

How much does it cost?

600 r - sawed me the details on the case + material + delivery to the house.
100 r - screws.
120 p - timber
250 r - pipes of fazikov + the connector for connection in the end turned out to be superfluous and there are many pipes, 50 p. Would be enough.
50 r - sealant (expired)
50 p - plasticine
200 r - 2 pcs TDA7294 (one burned by stupidity by confusing polarity)
200 r various small parts of which were not available.
120 p variable resistors with handles
50 r varnish (overdue)
200 r 5 meters of self-bonding
100 r skin
85 r paint black matte
70 r sewer pipe

Total 2160 p., Like I forgot nothing

free - brought a cardboard tube for a fazik
free - woofer
free tool

Some calculations and reflections

The design pressure is about 109 dB in the operating range, with a power input of 50 watts. I have long believed I can lie. Calculations in haste

70 watts pressure here, as you can see there is a slope as the din actually works below the resonant frequency, but according to the schedule it does not go beyond the limits of the allowable stroke even by 20 Hz



100 W the situation is the same



I looked for the sake of interest that it is possible to pump into a din and 200 W and there will be no travel limit at 20 Hz. You can get up to 18 Hz to play a pipe. But is there a natural question? Do you need such power? On impressions when there was no separate amp swinging it with a 25-watt industrial amp, if done fully, it is very, very loud. I only switch it on to full when I want to show someone all the power to boast. So to say ChSV to amuse :) But in this mode you will not listen for a long time, all that can be shaken and glass jingles, powerfully in one word.

PS The constructions have been made for a year already, I did it for 3 months in my mood, for my pleasure.
Was it worth it or not? I think yes. The bass is very low and deep. Because of the design, the sub is played very softly, he cannot play a sharp attack, and he doesn’t need it, but all the LFE effects are just to cheer, all listeners were wildly delighted. Despite the fact that the sub is spiked, the walls and floor still vibrate noticeably creating an effect not worse than in cinemas (it would be better to remove the glass bounce).
Recently, I donated a dynamic head from an autosub, I will do one more, but this time a closed case and with Linkwitz proofreader.