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Old 12-09-2007, 04:09 PM   #41
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^^^NICE!!!

This is all from a book I'm reading called "The Scientific Design of Exhaust and Intake Systems"

They did a test using a perforated main tube silencer. The inside diameter of the silencer was 1.75, and the outside diameter was 4", 18" long. The results were a reduction in wave amplitude (volume) of 26%. The tested two of these silencers in series and recorded a 61% reduction in amplitude. They then say that the apparent noise redution is greater than the figures suggest, because of the elimination of the high pitched waves.

They suggest that perforated silencers are surperior for dampening sound. With the perforations facing the silencing material, they can funnel sound waves toward the dampening materials without hurting flow as much. They also say the thickness of the dampening materials should be no less than 1", but preferably over 1.5". An Oval shaped silencer would be the best design for a silencer where there are space constraints.

Basically the longer it is, the better. Doubling the length of the silencer will more than double it's effects. So, one long silencer would be desirable.
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Old 12-09-2007, 07:21 PM   #42
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I wonder about that, or if there's something to be said for using two a distance apart, you're selecting out a range of noise, then perhaps a tuned length between (I'd think around half the length of the following resonator) might help to make sure that your second resonator is only looking at stuff you're most likely to have left.

Overengineered for sure - the sort of experiement that would be worth doing if I were making more than one. :-)

BTW: Isn't intensity ("volume") proportional to the square root of the wave amplitude (which is why a 10 mW laser only looks twice as bright as a 3mW)? If so a 60% cut is pretty small in perceived volume - though as you said, if it's in the right place it makes a huge difference. Your ears don't respond linearly anyway, so it probably all balances out in the end, hence the "audio taper" in most potentiometers that are actually good for anything.
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Old 12-09-2007, 07:38 PM   #43
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I don't know, I pulled up Wiki and it says
Quote:
"The amplitude of sound waves and audio signals (also referred to as Volume) conventionally refers to the amplitude of the air pressure in the wave, but sometimes the amplitude of the displacement (movements of the air or the diaphragm of a speaker) is described. The logarithm of the amplitude squared is usually quoted in dB, so a null amplitude corresponds to -∞ dB. Loudness is related to amplitude and intensity and is one of most salient qualities of a sound, although in general sounds can be recognized independently of amplitude."

Your probably right, I said volume because I 'thought' that was the same as amplitude. However, they don't pay me to think, they pay me from the neck down and the waste up... Everything else is no good.
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Old 12-09-2007, 07:46 PM   #44
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- full 3" exhaust from downpipe out to rear bumper
- no muffler
- metalcore cat
- short resonator

loud and deep, not at all raspy. i'd describe the sound as "**** you I'm out"
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Old 12-09-2007, 08:10 PM   #45
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What's the resonator like?

I've heard cats do great things for chilling an exhaust note/volume the #%$& out. 'Course, they do the same to flow. You should put a test pipe in one day - you'll never go back. :-)
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Old 12-09-2007, 09:25 PM   #46
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i'm guessing you aren't familiar with my AbsurdFlow© exhaust/intake and my previous turbo setup. 15psi with the wastegate fixed fully open and full boost under 3k. that was with the IHI turbo out of an msm and the factory msm mani. now with my new AbsurdFlow© tubular mani and gt2560r i can't imagine spool will be a concern.

besides, i don't like to break the law.
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Old 12-09-2007, 11:12 PM   #47
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Not so familiar I wouldn't like to see some pics. You know what I'm bummed about? I picked up FM's intercooler kit, only to find out they have a bigger IC I didn't even know about. Sigh.

With my wastegate stuck open I still get a fair amount of boost, really I should open things up a bit. I did pick up a spring to ease some of the tension on my actuator, but I'm not convinced that's my only problem.
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Old 12-10-2007, 04:36 PM   #48
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Ok, I just got an Autozone gift card for my birthday, went to Autozone and got a 18" 3" cherry bomb. The tube inside is not very smooth but I dont think it'll hurt that much. It has the drilled teeth coming up against the flow. I may just install it backwards but then it probably wont help at all.
I'll post some pictures when I get it done.
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