907
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| posted on 25/5/09 at 06:06 PM |
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Testing the dB of cans
Hi All.
First of all, a BIG BIG thanks to Dan (Danozeman) for bringing his car over to act as the test bed.
It's a 1.8L Zetec running 2L cams and ZX9 bike carbs.
The object was to test the noise level of various size and types of can that I have made and hopefully learn something.
We used the SVA type test, i.e. readings taken at 1m distance, at 45deg to the can outlet. See Pic.
The cans were the normal design, that is a 2" perf titanium tube inside various size stainless bodies.
They were all packed with Acousta-fil wadding.
The results were....
115mm x 500mm long = 95.9 dBa
130mm x 500mm long = 88.6 dBa
130mm x 600mm long = 89.9 dBa
150mm x 600mm long = 88.8 dBa
Also tested was an R & D can that is a totally maintenance free jobbie.
95.1 dBa. (power loss tests to come)
The engine was held at a constant 2/3rds max revs and all the readings were 2dBa below the max reading, but increased
to max reading when the power was shut off and the engine speed started to fall ???
Why should this be ? I'm puzzled. 
I also expected a difference in the readings between the 130mm diameter and the 150.
Again, I'm puzzled.
Can anyone shed any light ?
Cheers
Paul G
 
Rescued attachment can-test-s.jpg
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nstrug
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| posted on 25/5/09 at 06:25 PM |
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For the record, SVA test is at 0.5m, not 1m
Nick
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David Jenkins
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| posted on 25/5/09 at 06:30 PM |
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Paul,
Also, the engine revs should have been 3/4, not 2/3...
The 3/4 of max power speed and 500mm distance was also in the SVA...
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907
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| posted on 25/5/09 at 07:12 PM |
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Bu**er
Dans car was tested at 3500rpm and 1m at SVA.
If an engine is not standard then this is when the 2/3rds max revs comes in, possibly?
O well, it was a nice day for a play, and I did learn a thing or two about size. 
For me, the most important thing is how good is the packing, and Dan now has this in his own can.
I'll re-do the tests at a later date.
Cheers
Paul G
[Edited on 25/5/09 by 907]
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craig1410
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| posted on 25/5/09 at 09:19 PM |
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Hi,
I think when max power RPM is known you need to test at 3/4 of this RPM but when max power RPM isn't know then you test at 2/3 of red line
RPM.
My Rover V8 3.5 was tested with one of your cans (one of the original batch you did a few years ago). I think they are probably 115mm but not sure if
500 or 600mm long. It was tested at 3000RPM and I'd guess it was 0.5m rather than 1m from memory. Noise level was just under 99dB (98.6 I
think).
Sounds like a bloody Messerschmitt out on the road when you open her up!!! 
Love your work!
Craig.
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907
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| posted on 26/5/09 at 12:22 PM |
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Hi All
To give an idea of how the different test methods would change the results of yesterdays tests
my son (Gaz 1977) brought the MX5 round. It has quite a fruity exhaust note.
We did a series of measurements using the 2/3rds, 1m (wrong) method and then a series using
the 3/4, 500mm (correct) method. We then took an average.
At 3500rpm and 1m away the average reading was 84.65 dBa
At 4200rpm and 500mm the average reading was 90.65 dBa
I realise this isn't scientific but I deduce that by adding 6 dBa to my original figures I will be nearer to the mark.
Proper tests will follow.
115mm x 500mm long = 95.9 dBa ..... now becomes 101.9 dBa
130mm x 500mm long = 88.6 dBa ..... now becomes 94.6 dBa
130mm x 600mm long = 89.9 dBa ..... now becomes 95.9 dBa
150mm x 600mm long = 88.8 dBa ..... now becomes 94.8 dBa
From this (and from Craig, cheers) I would think that the 115 dia is only suitable up to 1.6L cars
or cars in a lowish state of tune. The others seem OK.
Now, who's got a Blade or an R1 to test the big'un.
Or indeed anyone who fancies a cuppa & a sticky bun and can spare an hour or two.
Cheers
Paul G
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SJL
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 posted on 26/5/09 at 01:04 PM |
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You can test mine if you want,I was going to contact you about possible fabricating one for me anyway.
09 Megabusa if it helps.
Steve
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907
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| posted on 26/5/09 at 03:32 PM |
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quote:
Originally posted by SJL
You can test mine if you want,I was going to contact you about possible fabricating one for me anyway.
09 Megabusa if it helps.
Steve
Hi Steve,
Where are you?
Please don't say John O'Groats
Cheers
Paul G
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MikeRJ
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| posted on 26/5/09 at 04:23 PM |
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For SVA noise test the engine RPM is 3/4's of the maximum power RPM, not the red line! The default value is 2/3's of red line RPM if
maximum power RPM is unknown.
Note that A weighted (dBA) sound readings are rather inappropriate for high sound levels due to the frequency weighting which was originally developed
for low level sounds. Unfortunately, this means far more emphasis is put on high frequencies, so comparing results between different vehicles is
going to be very difficult. It also means any high frequency noise generated by components other than the exhaust could significantly affect the
accuracy of your measurements. Some kind of baffle, e.g. a large sheet of plywood with a hole for the exhaust, could help to get more repeatable
results.
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craig1410
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| posted on 26/5/09 at 05:17 PM |
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quote:
Originally posted by MikeRJ
For SVA noise test the engine RPM is 3/4's of the maximum power RPM, not the red line! The default value is 2/3's of red line RPM if
maximum power RPM is unknown.
Isn't that what I said above? 
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disco_biscuit
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| posted on 26/5/09 at 05:41 PM |
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I have an R1 MNR Vortx and need a new silencer, i'm in kent so would you be interested in fitting one and you can use it for testing?
Roy
Obviously i'll pay for it ;0)
[Edited on 26/5/09 by disco_biscuit]
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SJL
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 posted on 26/5/09 at 06:54 PM |
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Hi Paul,
I am based near Gatwick Airport.
Whats best shall I call you?
Steve
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907
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| posted on 26/5/09 at 07:56 PM |
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Hi Roy and Steve,
Yup, I'm up for trying both of those.
I'll U2U both of you my home number and we can discuss.
Cheers
Paul G
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procomp
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| posted on 27/5/09 at 06:59 AM |
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Hi
Static testing is good for passing the SVA ect. But for the guys wanting to quieten there track day cars you would be aiming to get them down to below
98Db whilst accelerating hard through the gears.
Only problem with that is that you will want to be testing a car that has already quietened the induction down to eliminate that from your test
readings.
Cheers Matt
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907
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| posted on 30/5/09 at 09:52 PM |
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First of all a big thanks to all on this thread.
I take your point Matt about other contributing noise but I'm not sure if I dare ask in the wood merchants
for a large sheet of ply with a small hole in it Mike.
I had a nice drive out today, well apart from the ten mile que for the Dartford bridge, and met up with Roy
and his R1 powered beastie. A very nice well finished car I must say.
He screamed his engine to 7.5k for me and at 500mm (Yup, I now know the dimension )
and the figure we came up with was 103.8 dBa.
There is room for a much longer can so I'm going to knock one up.
I just knew my 4 foot rollers would come in handy.
Cheers
Paul G
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