sound meter used at competition

[diesel_truck_man]

does anybody know the brand/model of the meter they use in detroit? I would like to do some research on the specific one to find the specific frequencies it does and doesnt pick up on, so we can tune our exhaust system accordingly.

Thanks

[diesel_truck_man]

does anybody know the brand/model of the meter they use in detroit? I would like to do some research on the specific one to find the specific frequencies it does and doesnt pick up on, so we can tune our exhaust system accordingly.

Thanks

[Buckingham]

Their meter will pick up whatever your engine puts out. You won't have very much luck trying to "trick" their meter. If you are actually going to try and tune for a specific frequency, I would suggest the fundamental frequency of your engine (firing frequency). Then again, if you are actually going to try and tune specific frequencies, I would imagine you already have access to sound spectrum analysis equipment, in which case you would already know exactly what frequency band to tune for.

[Igor]

I would hazard a guess that a sound meter is just an RMS meter, meaning it won't miss any frequency.
However, if the rules state the level as dBA (I don't know if they do though), the frequencies are weighted by the A bandfilter. In this case you can try to shift your frequencies toward the lower bands.

Igor

[-]

The meter used a the FSAE competition is a top of the line B&K (Bruen and Krueger I think) sound meter that cost a few grand and covers the entire sound spectrum. From what I remember asking the sae committee about it last year is that they have a B&K rep at the competition that is there to either do or help with the testing.

Like the other guy said, you are better off making your engine quiet enough either making a good muffler and getting the job done or by analyzing the frequencies that come out of the muffler and lowering the high ones. From what the work I did last year I remember that if you can lower the key high frequencies (with packing, exhaust design, or baffles in the muffler) you can easily lower the sound level of the exhaust.

Good luck.

[Chris Boyden]

I think that they may run the meter in both
fast and averageing modes.
edit:
rules
say 110 dBA, fast averaging.

[jsmooz]

As stated the meter is a B&K. I forget what model tho. I'm positive it's a B&K because the guy that does the measurements at compeition is in the Detroit area and said he could stop by our shop before competition, since we also are in the area. It's good to see the support isn't just at compeition.

[James Waltman]

The company is Brüel & Kjær (the proper spelling may help you find some information).
The only picture I have of the meter is not very good:
http://dot.etec.wwu.edu/fsae/HostedPics/James/BruelKjaer_Sound_Meter.JPG

One of our graduates does NVH stuff for boats and immediately recognized the model from that picture. He said it was a pretty high end unit.

Rather than tuning for frequencies, you may try tuning for the rpm that the test is conducted at. http://www.sae.org/students/fsaenoisetest.doc

[osubeaver]

Our school has a very nice spl meter that we brought with us to competition (i believe we let a couple of schools borrow it before sound check). We brought it with us to the sound check and set it to the same settings they use (dbA, fast, etc..), and they were happy to let us do a side-by-side comparison with theirs and we got basically the same results, which was reassuring. As for the frequencies, I beleive it does pick up on everything (relatively speaking). I beleive that different standardized frequency weighting scales can be used, but they tell you what settings they use, so you can test all of this before competition.

Another thing to keep in mind is the air intake. Our air intake pointed out the rear of the car last year, and our sound level measurements indicated that the hissing sound of the air through the venturi had a significant effect on the sound level reading at the rear of the car, where the judges take measurements from.

[markocosic]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by James Waltman:
Rather than tuning for frequencies, you may try tuning for the rpm that the test is conducted at. http://www.sae.org/students/fsaenoisetest.doc </div></BLOCKQUOTE>

At the 2005 UK competition there was a rule change - noise tests were conducted over a sweep from idle to 3/4 of maximum rpms rather than at a fixed single number of rpms. Presumably this was to prevent the above kind of fudging or to accomodate the 'industrial' engines that were not capable of meeting the required piston velocity. I'd expect to see the same at all 2006 events?

[Tech Guy]

FGYI, the Noise Test Event Captain works for B & K. The meter(s) used at the US events are Class 1 (the best) units, either B & K 2250, 2236 and/or 2238 SLM models.

As far as tuning for a specidfic speed is concerned, I suggest you read the 2006 Rules! The Committee has closed that door, as the last paragraph of 3.5.4.3.A Noise Test Procedure says "The car must be compliant at all engine speeds up to the test speed defined below."

[Jetser]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">At the 2005 UK competition there was a rule change - noise tests were conducted over a sweep from idle to 3/4 of maximum rpms rather than at a fixed single number of rpms. Presumably this was to prevent the above kind of fudging or to accomodate the 'industrial' engines that were not capable of meeting the required piston velocity. I'd expect to see the same at all 2006 events? </div></BLOCKQUOTE>

That's strange we just need to run the engine at 7000 rpm.

[flybywire]

Well actually, the 'A' in dBA means the "A-weighting curve." In other words it tells you the frequency response of the meter. The "Fast Response" means an effective average over ~1/8s.

Look here http://www.ptpart.co.uk/noise.htm or google.

Now, if someone has some nice frequency response data for various mufflers it might be very interesting to stack those curves up against the meter curves.