This article based on past article.
This time, I considered about the “muffler sound”.
Good muffler sound is very difficult. Because it depends on individual preference, “good sound” is completely different.
But, my favorite sounds is F1 sound (*'∀` *)
like this!!
It ’s the best!
However, these cars have different numbers of cylinders in the first place, and the revolutions per minutes(rpm) also different, so such a high sound (high Hz sound) appears.
However, from the desire to get as close as possible to this sound, I wondered if there was anything I could do to get a high tone.
In general, there are several ways to make the muffler treble
1) straight pipe
2) the pipe diameter reduction
So, why does these could make a high tone? ?
①Why does the straight pipe make high tones?
First of all, a sport muffler generally absorbs sound in a cotton-like material called “glass wool” to mute it.
Reference of this page.
In summary, the exhaust pressure is reduced by glass wool, so the sound pressure is suppressed and the result is that the sound is muted.
What is important with this structure, the high tone sounds are easily absorbed, and the low tone sounds are not easily absorbed. If you often heard a sports muffler sounds, the bass sounds of “bow-bow-bow-” that couldn't be silenced by glass wool.
So, if not using glass wool, of course, the sound pressure is high, and if it is a straight pipe, the high sound is emitted as it is without being absorbed.
Along with this, how can I turn off the bass sounds? There is a silencer (baffle) that often thrusts into the muffler end.
Like this.
About this, upper reference page says
> Speaking of baffles, most of them are installed at the end of muffler, but if you have heard the difference in sound quality between installing and not installing it, you can feel the difference that ... , Only the bass sound is pressed down(muted). If you say it, it will sound like a “pas-pas-pas…” like a fart sounds.
It was written. I think so too this is such a sound on the street.
This is efficient to have done in a multi-stage expansion type silencer has been adopted well, such as genuine muffler.
BADMOON racing
With this structure, it ’s not a dream to turn off the bass and create a dream-like muffler that leaves only the target sound range!?
However, it is quite difficult to have such a structure in a after parts muffler. Because it is costly and there is no sound chamber volume calculation know-how to control the target sound range. I watched at the facilities of the Honda S2000 muffler manufacturing company on web, but I remember that it was a very big research facilities.
By the way , I using GP-SPORTS EXAS EVO TUNE has strange structure.
(GP SPORTS is major after-parts brand in Japan. The company usually make DRIFT parts, also muffler, knuckle, arms, catalyzer, suspension and more.)
The image says “power chamber”. But it seems to be generally called “Helmholtz resonator”.
In F1, it is sometimes used to balance pressure according to the opening and closing of the accelerator.
In GP-SPORTS, it seems to use for reduce the volume of muffler sounds.(it might be use reflected shock wave in the muffler)
② Why does a high tone sounds come out when the muffler pipe diameter is reduced?
I think the dual pipe muffler sounds a little bit high-tone sound, right??Most of AE86 muffler sounds are extremely high-pitched, but looking at the muffler is extremely thin(narrow).
(*AE86: TYOTA SPRINTER TRUENO. It is a major DRIFT machine in Japan. It is main car of InitialD animation. And most of AE86’s are NA and implement a high-rpm engine, so they make awesome high-tone sounds.)
First, I have a inquiry about “Why are they make high-tone sounds?? Because there is not only from high-rpm engine, but also from narrow muffler should have an effect!!”
So I understanding of them, studying the “structure of the whistle” to solve this inquiry.
The sound of a high tone often means that the Hz (hertz) is high.
In addition, there are two types of whistle structures, open tube type and closed tube type.
This is an open tube type
this is a closed-tube type
image from the vibration of the air column
It is also written in the above-website. The acoustic wavelength λ seems to be a little longer than the tube length.
The open end correction value is about 0.6 times the pipe diameter, which means that the open end correction changes depending on the pipe diameter.
Since the muffler of the car is an open tube type, I solved it a little. (But different from the actual muffler conditions, we believe as the sound of the fundamental vibration)
3.5m(meter) of the pipe assumes a muffler as a condition to be used, at the speed of sound 340m/sec, how it changes of fundamental vibration(Hertz ) emitted by different diameters.
A) In the case of an 80Φ tube, which is often implemented in a turbo car
Open end correction = (80/2) x 0.6 = 24mm
Wavelength = (3500 + 2 x 24) x 2 = 7,096mm
Hz = 340 / 7.096 = 47.91 (Hz)
In case of 80φ(mm) pipe might make 47.91Hz.
B) In the case of a 60Φ tube, which is often implemented in a NA car
Open end correction = (60/2) × 0.6 = 18mm
wavelength = (3500 + 2 × 18) × 2 = 7,072mm
Hz = 340 / 7.072 = 48.07 ( Hz)
In case of 60φ(mm) pipe might make 48.07Hz
When the diameter changes by 2cm, the change of sound Hz is only about 0.2Hz… (ToT)
The number of Hz is very slight, but this is just the fundamental frequency. And the engine frequency is multiplied here, so the human can distinguish the difference of sound.
By the way, it is often said that when titanium is used, a “dry muffler sound” will be heard.(*As an expression of titanium muffler sound in Japan)
It is the sound speed(sound velocity) in the above formula changes depending on the
sound velocity = √ metal elastic modulus (Pa) / density (kg / m3)
Stainless steel (SUS430) has a longitudinal elastic modulus of 204KN / ㎜2 and a density of 7.7g / ㎝3, while titanium has 106 and 4.51, respectively, so the sound speed seems to change slightly.
- Conclusion -
In order to acquire high-tone sound from the above and to produce a good sound
・ Straight pipe rayout(or structure without using glass wool) ⇒ I tried it
・ Try to make a narrow pipe’s muffler
・ Use of good material for sound velocity
However, it is not possible to make a straight pipe to run on the general road, and it seems to be a slight thing although there is a difference even if you use narrow diameter of pipe or choice to the material. I would like to make a multi-stage expansion silencer if possible, but I can't calculate that precisely (ToT).
Then, I came up with a new idea. If I could raise up the frequency(Hz) of the sound. . .it might get good sound??
If you do not think about the cost and exhaust efficiency, you can get a higher sound…? It is no dream to make the engine sound of the straight 4 into the sound of 8 cylinder !?
However, I learned about sound more… and I found that it is very difficult to make 8 cylinder sounds…. If you interested in and want to read more, please read next article.(It is still Japanese article. So please press “translate buttons” )
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