The subwoofer for the car. Part 4
Sitting beauty in prison...
...and on the street, in this case, only the tunnel bass reflex. Such is the lot itself is decorated beautifully dynamics, if it put in a bandpass loudspeaker (bandpass). In the history of our bass publications of this type of acoustic design subwoofers - saycause. And the point here is not that he is the last in quality. It is not so. Just in order to cope with bandpasses, and samostojecu and professionals need to "enrich your mind with knowledge of all those wealth..." and hereinafter who passed and remembers, of course.
Bandpass loudspeaker - the Moody design, which can be represented in the trunk of the car, and it applies to phase izgotovlenie, and, most importantly, to the work of the final product. As we let's show a little further scope for errors, generating a monstrous sound, unattainable in simpler configurations are huge. It is natural to ask - coy same shit will carry us on these galleys? The answer is simple - greed and love.
Greed to sound pressure. When any competent manufacturer bandpass by creating volume bass radiation defeats rivals even not by knockout, and for obvious advantage."
Love for the beautiful. Bandpass all their mighty decibel gives through the pipe, that is to say the bass reflex tunnel. The speaker is hidden inside and not for him need to look for places where it would radiate to the salon. To find a place to tunnel through the diameter rarely more than 100 - 120 mm is much simpler and design may be the most witty.
There is one benefit that I like to emphasize in some of the guides that I was silent, for it is imaginary. It is about that time, supposedly, the bandpass loudspeaker, he and the crossover is not trebuetsya. The savings of a kind! No, because it is required, but more on that later. Now in order.
Bandpass loudspeaker 4-th order consists of two chambers, one of which is closed, and the other is communicated with the outside space through the tunnel, like a normal speaker bass reflex type.
Speaker installed in the wall separating the the cameras. It turns out like I would have taken the phase inverter and put him "the face" closed box, or Vice versa, took a speaker in a closed box and supplied the burqa in the form of a phase inverter. Any of these models contains the great secret the meaning of bandpass, which boils down to the concept of balanced load. What the trouble with conventional direct radiation loudspeaker? That acoustic the resistance of the medium, which speaker should excite and lead to oscillations, very little. Small compared with the forces of elasticity and friction, raging in the mobile the system of the speaker. Summed energy to it almost all speaker extinguishes in the womb, turning in the final iothe into heat. In acoustic the energy goes from 0.2% to 0.5%. Wow efficiency? In a sense, this like trying to row a toy paddle attached to the excavator bucket. Noise and pant a lot, diesel oil flowing river, but it dies in oily mechanisms, because the environment is almost no resistance. You can, of course, to make the paddle a little more about what we have to do in bass speakers, where the role of the oars acts as a diffuser.
In normal dynamics - gated whether or bass reflex, behind the diffuser is fully or partially closed the space where the acoustic energy or dies, but before that, partly controls the oscillations of the diffuser in a closed box; or concentrates and spills out through the bass reflex tunnel, significantly increasing efficiency dynamics in the frequency band where it is 's going on. But, if these speakers for the "back" of the diffuser is some supervision, his "face" abandoned to their fate and tries in vain to cause vigorous shaking in a sluggish, almost weightless air mass.
The creators of bandpass, concluding speaker between closed volumes, and has ensured that both sides of the diffuser loaded quite vigorously resisting air mass, resisting, inevitably concentrate the radiated acoustic energy and give it "on the mountain" already in amplified form.
In real life it looks like. On the chart depicts the frequency response of the speakers in open space, built on the basis of the same head with the optimum for the given design parameters. In as a speaker for all these examples, a selected Infinity Kappa 100w.br.
This speaker is in its the parameters is almost the perfect compromise, allowing to realize on its base and closed the loudspeaker, and the phase inverter and polakovic. So it happens not very often, less in any case than this promise manufacturers, attributing unconditional bisexuality his creations.
Already this graph shows that below 90 - 100 Hz bandpass loudspeaker (red curve) gives an enviable head start phase inverter (blue curve), not to mention a closed box (green). Scary, though, a kind of Frank hump on characterization of bandpass, which is easy to suspect that polakovic with excellent impact will be desperate to chant on a single note. Especially because many actually created the design and make, what scares away many advocates of expressive bass (but pulled lovers of bass thunder). All so. Yes, it happens, chanting, not only because of this. Take a look at the second graph is the frequency response the same Trinity, but given the internal acoustics of the vehicle interior medium sizes for which and optimized features:
In these, actually real conditions Meloman favorite - closed box, makes a perfect, up to half a decibel horizontal AFC. The phase inverter is a noticeable hump in the "delicious" bass, which many prefer sterile horizontal AFC - not all in vain bass correctors on the amps, if you have tuned to a frequency of 40 - 45 Hz. And band-pass variant, with the same speaker and the same summing power issues 6 dB more SPL. This, incidentally, is equivalent to an increase power amplifier 4 (in words - four) times. Where is the hump? And missing, offset by the increase in returns at frequencies below the critical for selected in this example, the size of the cabin.
Well as hands itch? Wait a bit, wash something to relieve the itching and read again written just above: with optimal parameters. What are the optimal settings and what if they do not get? There room for maneuver and for the accident wider than the closed, for example, drawer, exactly three times, for as many times more the number of subject choice. Two volume (number of cameras) and configure tunnel in one of them. Still say Bose (thanks for the second tunnel is not allowed to do...
Let's in order of receipt:
Volume rear (closed) Vr camera( defines, in essence, the "operating range" is ready bandpass. The graph shows that the greater the volume of the closed chamber, the lower become both borders of the working strip, and the lower the yield (efficiency) the loudspeaker. Of course, as in a closed box, with increasing volume decreases the maximum allowable summed power is lost because control over the movement of difusora. If the volume of the rear chamber to reduce all bell-shaped frequency response is shifted up in frequency, the efficiency increases, but the price narrowing the bandwidth.
When you change the volume of the anterior chamber (with tunnel) Vf extreme limits of the operating band remain in place, but changing shape of the top of the bell. The closer front camera, the lower the gain, but it is in the broader pojavljatsja the frequency band. Shown on the chart, the volume of the anterior chamber 8 l should to be considered critical, because at this point begins to "SAG" often average frequency response of the horizontal section. Further the reduction of Vf characteristic gain frankly the double-peaked shape and it has nothing to rectify.
Soft top their heads, achieved when configuring the front camera as expected, in the middle of the bandwidth becomes paintings, almost exactly the same figure of the Little Prince "a Boa constrictor swallowing elephant, with its trunk in one direction and then in the other direction. "No problem," say the optimistic reader, already done with the Laundry and ready prasowaniu wood, --"custom in the middle, under the prescriptions of doctors and enjoy masterpieces of Stanley Clarke's the envy of the rest". Yikes! Here here are just the main trap in which we, together with You almost got, and where many, alas, have been. The following specifications are for the free space, or at least to a large, say - residential the premise. But not to the interior of the car. Adjusted for internal acoustics, these three characteristics would look like this:
What was perfect in the infinite expanse (set to 55 Hz), appealed to rapidly sabaliauskas above 50 Hz the characteristic. To dock it with the midbass is absolutely unreal, because the frequency partition will have to choose 60 Hertz, so low and the midbass is not tightening. And if you do not proceed, there will be a pit just where are concentrated the most the expressive elements of bass - the lower midbass (80 - 100 Hz). But then, that looked weird to me in the previous image, has blossomed into a very worthy and a fairly flat frequency characteristic, without effort reaching up to 90 - 95 Hz, where it can marry even with a 5-inch midbass. (This bauble already seen in first chart - I had stashed away.) The characteristic configuration 45 Hz from the previous example does not even cite, not to frighten once again. But complement graph of what can happen when there is an error in the other direction - setting tunnel at 75 Hz. See narrow and nasty hump at 80 Hz? Here he is-and will be sickening chant, poisoning us life, and bandpass reputation.
You can say, "Well, badly designed the design is bound to produce bad characteristics and corresponding sounds. Right, but the cost of failure is somewhat different. Here's an example: for the same head Infinity Kappa 100w.br, placed in closed box, "make a mistake" in volume compared to the original 14 l in half, and then, where we did not disappear, even in a half. Custody for the volume of a box of 20 and 30 liters in free space at all almost do not differ, the cabin - go below 50 Hz, but remain more than favorable.
But with the volume we swung by more than half! More nervous reflex more averse to false in the configuration of the tunnel, but still retains a sense of propriety. For example - the results of the restructuring of the tunnel from 30 to 45 Hz at constant volume 29 L. Contorts AFC strongly, but still live can.
Here because of this "rigor in piloting and ruthlessness to errors of calculation, failed bandpasses created, it seems, more than good. Add to this the possibilities that would be the choice inappropriate dynamics - we operated with one of the best for the occasion. In General, life would simply not be able...
Another deterrent from bandpass element of its specificity is much more complicated and troublesome fabrication. Where speaker "looking outside", from the street you can install. All done, all seal, seal, and finally to pull the head. Here to put it have inside, and, therefore, at least one wall to make a detachable, losing stiffness and instead of buying a headache with the seal of the joint. The work "not for the boy, but her husband".
But... I do everything in life has its own "but". In addition, unless, migraine...
But bandpass gives unusual layout opportunities. Say: prosthechea konstruktivnaja implementation shown in the beginning article, looks like closed from all sides of the box, damage which is impossible, and, therefore, to fit within the trunk can "taste". If you go on the installation path of the two speakers, there are opportunities at all unique. Let's see: two identical bandpass can coalesce into one three-compartment, making common front-facing camera, and two tunnels to replace one of the doubled section. Then the whole structure can transmit the bass into the cabin through a single window not God knows what size, and attached, for example, in the center of the rear shelf or opposite the aperture of the rear seat armrest. Gracefully?
And Vice versa: to put the speakers back to back in the closed chamber, and the bass "exhaust" to organize through the tunnels, located outside the volume of the box and connected to the holes, the source intended for rear speakers.
In short, to be developed here can be very mentally, you just have to keep in mind: bandpass is a powerful thing, in fact, a powerful weapon bass attack. And these weapons are not for rookies, so if You, or even Your professional installer, there is enough experience of calculation, design, construction, configuration, and measure the characteristics of the subwoofer - it is better to choose something simpler. And if all of the above and You have "caught in the setting - invite to hear, huh?
Author: Andrew Elyutin, Autosound; Publication: www.avtozvuk.com, www.cxem.net