Subwoofer for home and family. Part 2 - Start the Assembly!
We will need:
- ANY program for the calculation of Saba (software),
- primitive skills joiner (particle Board sawing, ability to work with a jigsaw and a drill),
- consumable material: silicone, screws, particle Board, drill 3 mm.
this will be enough...
Now let's begin the Assembly supermegaultra Saba.
Desperately searching for a program for the calculation of the housing Saba. The singular difference no: all the same primitive
Software for Saba
As we have seen, the calculation of acoustic parameters registration for the bass head is not a simple one. Indirectly this the statement confirms the existence of specialized software software (software), which can significantly facilitate the work the installer. Such programs currently there are several: Blaubox, WinSpeakerz, Term-Pro, JBL SpekerShop etc But they very similar. You can pick up a case for the existing dynamics or, on the contrary, to pick up a bass head already constructed box. Such programs allow you to compare the performance of a loudspeaker in buildings of various types. Most likely, in the database you will find the right you loudspeaker listing all of the required characteristics. If no, the database can be supplemented by the parameters of your driver, which you supplied manufacturer, and then to count all the necessary characteristics Boxing for optimum frequency response and the power of the subwoofer. Enter the parameters of the speaker and get the enclosure volume.
At this stage I have a serious problem - I don't knew most of the parameters of the speaker.
Have any two solutions to this problem:
the first is to find a brand Soligo dynamics in the Internet,
the second is to calculate yourself.
The first didn't fit because too large differences between different sources. Went the second way.
The measurement of Thiel-small at home.
Remember! Below is an effective technique only to measure the speaker settings with the resonant frequencies below 100Hz, for higher frequencies, the error increases.
The most basic parameters that can be calculated and to produce acoustic design (in other words - the box) are:
- The resonant frequency dynamics of Fs(Hz)
- Equivalent volume Vas(liters or cubic feet)
- Full quality factor Qts
- DC resistance Re(Ohms)
For a more serious approach will need to know:
- Mechanical q factor Qms
- Electrical q factor Qes
- Piston area , Sd (m2) or the diameter Dia(cm)
- Sensitivity SPL(dB)
- The Inductance Le(Henry)
- The Impedance Z(Ω)
- Peak power Pe(Watts)
- The mass of the moving system Mms(g)
- The relative stiffness Cms(meters/Newton)
- Mechanical resistance Rms(kg/h)
- Motor power BL
Most of these parameters can be measured or designed at home with the help of not very complex measurement devices and computer or calculator, able to extract the roots and involute.
For a more serious approach to the design acoustic design and characteristics of the speakers I recommend to read more serious literature. The author of this "work" does not claim special knowledge in the field of theory, and everything presented here is a compilation of a variety of sources - both foreign and Russian.
Measurement Of Re, Fs, Fc, Qes, Qms, Qts, Qtc, Vas, Cms, Sd.
For measurement of these parameters you will need the following equipment:
- The signal generator audio frequency
- Powerful (not less than 5 watts) resistor of 1000 Ohms
- Accurate (+- 1%) resistor 10 Ohm
- Wire, clamps and other trash to connect all of this in a single scheme.
Of course, this list may change. For example, most generators have their own scale of frequency and frequency not is in this case a necessity. Instead of a generator can also to use the sound card of the computer and appropriate software software capable of generating sinusoidal signals from 0 to 200Hz the required power.
Here is the diagram for measurements
First we need to calibrate the voltmeter.
For this instead of a speaker is connected a resistance of 10 Ohms and the selection voltage, supplied to the generator, it is necessary to achieve a voltage of 0.01 volt. If the resistor value, the voltage must correspond to 1/1000 nominal resistance in ohms. For example for calibration of resistance 4 Ohm the voltage should be 0.004 volts.
Remember! After calibration to adjust the output the alternator voltage is NOT till the end of all measurements.
Now, instead of connecting the calibration resistance speaker and putting on the generator frequency near 0 Hz, we can to determine its DC resistance Re. They will be the voltmeter reading, multiplied by 1000. However, Re can be measured and directly with an ohmmeter.
Finding Fs and Rmax
The speaker in this and all subsequent measurements should to be in free space.
The resonant frequency of the speaker is at its peak impedance (Z-characteristic). To locate smoothly change the frequency generator and look at the voltmeter. The frequency at which the voltage on the voltmeter will be maximum (no further change in the frequency will result in a voltage drop) and will be the frequency of the main resonance for that speaker. Speaker diameter 16cm this frequency should be below 100 Hz. Don't forget to record not only the frequency, but the voltmeter. Multiplied by 1000, they will give resistance dynamics at the resonant frequency Rmax needed to calculate the other parameters.
Finding Qms, Qes and Qts
These settings are as follows:
As you can see, it is a consistent finding additional parameters Ro, Rx and measurement of previously unknown to us frequencies F1 and F2. It the frequency at which the impedance dynamics equal to Rx. As always Rx less than Rmax, then the frequencies will be two - one slightly smaller Fs and the other several more. You can check the accuracy of their measurements the following formula:
If the calculation result is different from the previously found more than 1 Hertz, you will need to repeat all over again and more carefully.
So we found and calculated a few basic parameters and able to draw some conclusions:
- If the resonant frequency dynamics above 50Hz, he has the right to apply for a job at best as midbass. The subwoofer on this the dynamics can be immediately forgotten.
- If the resonant frequency dynamics above 100Hz, it will not the long tail. Can use it to play medium frequencies in three-way systems.
- If the ratio Fs/Qts speaker is less than 50, this the speaker is designed for use exclusively in closed boxes. If more 100 - exclusively for use with vented, or bandpass. If the value is between 50 and 100, then there should look carefully at other options - what type of acoustic clearance speaker tends. It's better to use special computer programs that can simulate in graphical form of the acoustic impact of such dynamics in different acoustic design. Though in this case not do without the other, not less important parameters - Vas, Sd, Cms and L.
The so-called effective radiating surface the diffuser. For the lowest frequencies (in the area of the piston effect) it coincides with constructive and equal to:
Radius R in this case would be half the distance from the middle of the width of the rubber suspension on one side to the middle rubber suspension opposite. This is because half the width of the the rubber suspension is also radiating surface. Please note that the unit of measurement of this area - square meters. Accordingly, the radius of the need to substitute in metres.
Finding the inductance of the coil dynamics L
For this purpose the results of one of the samples from the the first test. Need impedance (impedance) audio coil at a frequency of about 1000 Hz. Because the reactive component (XL) separated from active Re at an angle of 900, we can use theorem Pythagoras:
Since Z (impedance of the coil at a certain frequency) and Re (coil resistance DC) is known, then the formula converted:
Finding reactance XL at frequency F can rasschitat and the inductance according to the formula:
There are several ways of measuring a volume equivalent, but at home it is easier to use two: method "added weight" and the method of "incremental amount". The first of these involves the use of several materials weights of known weight. You can use a set of weights from pharmacy weights or use old copper coins 1,2,3 and 5 cents, because the weight of this coin in grams corresponds to the nominal value. The second method requires air-tight box of known volume with a corresponding hole for the speaker.
Finding the Vas method and added weight
First you need evenly load the diffuser weights and again measure its resonant frequency by writing it as F's. She must be lower than Fs. It is better if the new resonant frequency will be less than 30% -50%.
The mass of the weights is taken approximately 10 grams per inch diameter diffuser. I.e. for 12" head need a weight of about 120 grams.
Then you must calculate the Cms based on the received results according to the formula:
where M is the mass of the added weights in kilograms.
Based on the results of Vas(m3) is calculated by the formula:
Finding the Vas method incremental volume
Need to hermetically attach the speaker in the measuring box. This is best done by a magnet to the outside, because the momentum is still with which side of his volume, and it will be easier to connect the wires. And extra holes with less. Volume of the box is designated as Vb.
Then you need to measure FC (resonant frequency dynamics in a closed box) and, accordingly, calculate Qmc,Qec and Qtc.
The measurement technique is completely similar to that described above. Then is equivalent to the volume by the formula:
With practically the same results can be used a simpler formula:
Resulting from all these measurements, data it is enough to calculate acoustic design low frequency level is quite high class.
Now we have to decide where you can enter a sub, t e to determine its form. I assure You she mozhit be any, on the quality sound she has no deterioration (not taking into account horn subs)
Now take a ruler, a square, a pencil and ACCURATELY mark up a piece of chipboard. Sawing, trying not to add to the sound of his own saws MAT. Collect sub with the help of beam 30*30 mm, which is inserted in the ribs. All this design is stitched with screws in increments of 5 cm at the edges. Jigsaw to cut out the hole for the speaker (NOT MISS). All seams inside promazyvaetsya silicone, and the outside putty. Day the body dries.
During this time, you need to get hold of candy!
Publication: www.radiokot.ru, www.cxem.net