Startup Decibel Test
07-12-2019, 10:05 PM
#1
Rennlist Member
Thread Starter
Startup Decibel Test
Just for fun, we pulled out the decibel meter to test cold starts. We put the meter 15' from the car for no real reason. GT3 has stock engine/ECU, with fabspeed exhaust bypass pipes.
Cold start @15' hit 99.5 dB. Gonna try 20" tomorrow.
-td
Cold start @15' hit 99.5 dB. Gonna try 20" tomorrow.
-td
07-12-2019, 11:22 PM
#2
Rennlist Member
Sweet. The 996 GT3 is an awesome car.
07-13-2019, 08:26 AM
#3
Rennlist Member
Sound pressure level (SPL) drops by 6 dB each time the distance is doubled.
You can use this calculator to figure out the expected value.
Where you place the microphone and surrounding surfaces impact SPL because of reflections, too. This can drastically complicate measurements and one of the reasons that speakers can sound great in one room, but like s**t in another.
You can use this calculator to figure out the expected value.
Where you place the microphone and surrounding surfaces impact SPL because of reflections, too. This can drastically complicate measurements and one of the reasons that speakers can sound great in one room, but like s**t in another.
07-15-2019, 02:34 PM
#4
Pro
Using the calculator I get 119.5 db at 20". That is pretty darn loud, if true. I suspect that the your method of measurement, with the car in the garage, is affecting your reading.
120 db is borderline painful, so probably not accurate.
120 db is borderline painful, so probably not accurate.
07-15-2019, 04:00 PM
#5
Rennlist Member
Thread Starter
What do you mean by affecting the measurement? (GT3 is very loud @20” - 107.5 dB)
Personally, I don’t think the garage impacts anything - the car is basically 3” from being outside and we measured the inboard side, so there’s no reflection. Also, we’re using a decibel meter not an iPhone reading, so I suspect it’s pretty close to accurate, even if it has a margin of error.
FWIW, my spec boxster measured over 120 dB and the R8 does as well, so 107.5 for GT3 is totally reasonable.
-td
Personally, I don’t think the garage impacts anything - the car is basically 3” from being outside and we measured the inboard side, so there’s no reflection. Also, we’re using a decibel meter not an iPhone reading, so I suspect it’s pretty close to accurate, even if it has a margin of error.
FWIW, my spec boxster measured over 120 dB and the R8 does as well, so 107.5 for GT3 is totally reasonable.
-td
07-15-2019, 04:10 PM
#6
Pro
I don't refute your readings. I do think the garage has an affect, but it might be small, or nothing, or something. Just my observation.
120db is loud, no question, I wonder what it is at full song?
Where did the 107.5db come from, your post says 99.5 db. I think that would be too loud for me for the street. Loud pipes are pretty annoying in a lot of situations, the track is not one of them though.
120db is loud, no question, I wonder what it is at full song?
Where did the 107.5db come from, your post says 99.5 db. I think that would be too loud for me for the street. Loud pipes are pretty annoying in a lot of situations, the track is not one of them though.
07-15-2019, 04:22 PM
#7
Rennlist Member
Thread Starter
The 107.5 video is in a separate thread. https://rennlist.com/forums/996-gt2-...5-degrees.html
I’ve rum bypass pipes on the gt3 for almost 10 years now. Street, track, trips, it’s not that bad. At least too me. I’m pretty sure it’s over 120 dB at at 100 feet @WOT. Even the boxster was, and it had a small engine. R8 sounds like an old F1 car. It’s crazy loud. 120 dB st startup.
-td
I’ve rum bypass pipes on the gt3 for almost 10 years now. Street, track, trips, it’s not that bad. At least too me. I’m pretty sure it’s over 120 dB at at 100 feet @WOT. Even the boxster was, and it had a small engine. R8 sounds like an old F1 car. It’s crazy loud. 120 dB st startup.
-td
I don't refute your readings. I do think the garage has an affect, but it might be small, or nothing, or something. Just my observation.
120db is loud, no question, I wonder what it is at full song?
Where did the 107.5db come from, your post says 99.5 db. I think that would be too loud for me for the street. Loud pipes are pretty annoying in a lot of situations, the track is not one of them though.
120db is loud, no question, I wonder what it is at full song?
Where did the 107.5db come from, your post says 99.5 db. I think that would be too loud for me for the street. Loud pipes are pretty annoying in a lot of situations, the track is not one of them though.
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07-15-2019, 06:29 PM
#8
Rennlist Member
What do you mean by affecting the measurement? (GT3 is very loud @20” - 107.5 dB)
Personally, I don’t think the garage impacts anything - the car is basically 3” from being outside and we measured the inboard side, so there’s no reflection. Also, we’re using a decibel meter not an iPhone reading, so I suspect it’s pretty close to accurate, even if it has a margin of error.
FWIW, my spec boxster measured over 120 dB and the R8 does as well, so 107.5 for GT3 is totally reasonable.
-td
Personally, I don’t think the garage impacts anything - the car is basically 3” from being outside and we measured the inboard side, so there’s no reflection. Also, we’re using a decibel meter not an iPhone reading, so I suspect it’s pretty close to accurate, even if it has a margin of error.
FWIW, my spec boxster measured over 120 dB and the R8 does as well, so 107.5 for GT3 is totally reasonable.
-td
Exhaust sound is a pressure wave of various frequencies. But for simplicity, let's just consider it as one. Think of it as dropping a pebble in a tank of water. Waves propagate outward, then strike a surface like your garage wall or ceiling. They are reflected back, too.
When a reflected wave meets a wave from the source (or even other reflections) it can be either in phase, 180° out of phase, or something in-between. If they are in phase, the amplitude of the sound at that point of intersection will be twice as powerful (+3dB) as the source (antinode). If they arrive out of phase (node) they can cancel. Think of a noise cancelling headphone. That's how they work.
Reading the recommended test setup requires objects and persons to be at least so many feet or meters from the vehicle just for that reason.
07-15-2019, 07:28 PM
#9
Rennlist Member
Thread Starter
Not quite following. The meter was 20” away unobstructed.
-td
-td
Yes, it can.
Exhaust sound is a pressure wave of various frequencies. But for simplicity, let's just consider it as one. Think of it as dropping a pebble in a tank of water. Waves propagate outward, then strike a surface like your garage wall or ceiling. They are reflected back, too.
When a reflected wave meets a wave from the source (or even other reflections) it can be either in phase, 180° out of phase, or something in-between. If they are in phase, the amplitude of the sound at that point of intersection will be twice as powerful (+3dB) as the source (antinode). If they arrive out of phase (node) they can cancel. Think of a noise cancelling headphone. That's how they work.
Reading the recommended test setup requires objects and persons to be at least so many feet or meters from the vehicle just for that reason.
Exhaust sound is a pressure wave of various frequencies. But for simplicity, let's just consider it as one. Think of it as dropping a pebble in a tank of water. Waves propagate outward, then strike a surface like your garage wall or ceiling. They are reflected back, too.
When a reflected wave meets a wave from the source (or even other reflections) it can be either in phase, 180° out of phase, or something in-between. If they are in phase, the amplitude of the sound at that point of intersection will be twice as powerful (+3dB) as the source (antinode). If they arrive out of phase (node) they can cancel. Think of a noise cancelling headphone. That's how they work.
Reading the recommended test setup requires objects and persons to be at least so many feet or meters from the vehicle just for that reason.
07-15-2019, 09:22 PM
#11
Racer
I think what Marv is indicating is that the sound (pressure) waves emanating from the source (your exhaust tips) are being deflected / reflected / absorbed by the garage walls / ceiling / doors etc before it reaches your meter.
The meter may be in a "clear" zone but the source is not....
The meter may be in a "clear" zone but the source is not....
07-15-2019, 09:52 PM
#12
Rennlist Member
True, but the sound is a succession of waves, not a single pulse. The pebble in the tank is not quite a perfect analogy. Instead, think of a buoy bobbing up and down for along period making waves. That's the exhaust note playing over time. Even though the mike is 20" away, reflected sounds will make it back to the mike, albeit at a later time, but the exhaust is still playing the same "tune", so to speak.
You may find that running the same test in an empty and open parking lot may produce a different result. Again, I am using the words 'may' and 'maybe'. It could be academic, but if you want to be sure, the open parking lot is the better way to do it.
You may find that running the same test in an empty and open parking lot may produce a different result. Again, I am using the words 'may' and 'maybe'. It could be academic, but if you want to be sure, the open parking lot is the better way to do it.
07-16-2019, 09:58 AM
#14
Rennlist Member
Thread Starter
Yeah, I suppose it might. But this wasn't a scientific test, or an experiment with a control. It was a "cool, look what we can do test." If it's off 1%, 2%, or even 10%, it's not really important. At the end of the day, I suspect the test is probably close to a very rigid test, subject to the accuracy of the equipment.
-td
-td
True, but the sound is a succession of waves, not a single pulse. The pebble in the tank is not quite a perfect analogy. Instead, think of a buoy bobbing up and down for along period making waves. That's the exhaust note playing over time. Even though the mike is 20" away, reflected sounds will make it back to the mike, albeit at a later time, but the exhaust is still playing the same "tune", so to speak.
You may find that running the same test in an empty and open parking lot may produce a different result. Again, I am using the words 'may' and 'maybe'. It could be academic, but if you want to be sure, the open parking lot is the better way to do it.
You may find that running the same test in an empty and open parking lot may produce a different result. Again, I am using the words 'may' and 'maybe'. It could be academic, but if you want to be sure, the open parking lot is the better way to do it.
