Harry Flatters Posted April 30, 2002 Share Posted April 30, 2002 Last Saturday week, I popped down to Goodwood to get my new engine/exhaust configuration noise checked. 99db the nice man said and he also said that they would let me on track with that level on a 98db day but monitor the drive-bys. On the strength of this I went home and booked a track day with BookaTrack for yesterday (29/4). Braved the weather, arrived, signed in, got a noise check - 104db!!. Where the f*** did that come from? The man checked it again - 103db. No supertraps available for my 3" tail pipe so nuts!! no track day and £160 squits out of pocket. I drove home (seething) and popped over to SBD (their exhaust system) and with their brand new noise meter re-checked my exhaust. Three readings which never got above 99db and one was 97db. Yes, it was done at 45 degs and 1m from the tail pipe. So where is the volume control that got inadvertantly yanked up while I was at Goodwood?? What could cause such a huge difference in readings? Any ideas?? Steve Mell PTM 88 Edited by - Steve Mell on 30 Apr 2002 10:06:02 Link to comment Share on other sites More sharing options...
EFA Posted April 30, 2002 Share Posted April 30, 2002 Steve, The equipement at Goodwood is regularly calibrated to ensure the sound measurements they take are accutate (local gov red tape & all that) I had a long discussion with the man down there as I was formulating a plan to somehow get K2 RUM back on Goodwood. Needless to say I only made 106db's when I told them of my 8000rom red line - so your car is pretty noisy! SBD's equipment is likley uncalibrated or if it is, it'll be a bit like their dyno - with a 9% reading correction! Fat Arn Visit the K2 RUM siteid=red> See the Lotus Seven Club 4 Counties Area Website hereid=green> Link to comment Share on other sites More sharing options...
Big Brother Posted April 30, 2002 Share Posted April 30, 2002 I was recently informed by an acoustic engineer that there is a level of inacuracy built into all noise meters of around +/- 3dB Apparently this is to allow for reflective irregularities???? Steve www.Se7en-Up.co.uk id=green> Link to comment Share on other sites More sharing options...
ashaughnessy Posted April 30, 2002 Share Posted April 30, 2002 Arnie, Steve said that the first noise check was done by the people at Goodwood. How come two readings at the same place with the same equipment on different days give a difference of 5dB? See also the Oulton Park thread on chitchat - Richard Ince says nearly all the R500s failed an initial noise check but after a silencer repack and a different testing person a subsequent noise check showed them about 7dB lower! Anthony Link to comment Share on other sites More sharing options...
stevefoster Posted April 30, 2002 Share Posted April 30, 2002 Were you reading fast or slow? Link to comment Share on other sites More sharing options...
EFA Posted April 30, 2002 Share Posted April 30, 2002 Steve, On different days things like cloud basa nd barometric pressure will make a difference, but only slight. If I was selling silencers I'd be sure my meter didn't over-read!! Noise checks should not be carried out on a hard surface and any reflective surface should be at least 20m away. Fat Arn Visit the K2 RUM siteid=red> See the Lotus Seven Club 4 Counties Area Website hereid=green> Link to comment Share on other sites More sharing options...
1400rs_0of30 Posted April 30, 2002 Share Posted April 30, 2002 Steve, I attend Goodwood regularly coz its me local, to get on track simply lie smile.gif I have to blag that my red line is 6000 rpm, I have always got on, and never been taken off from a drive by. The only advise then is not to thrash it, and assume a read line of ~6500 ish To be honest most of the caterham guys I talk with at goodwood do the same Sean The original 1400 K Series Roadsport Prototype My Caterham Website Link to comment Share on other sites More sharing options...
Harry Flatters Posted April 30, 2002 Author Share Posted April 30, 2002 Arnie, SBD's noise meter is brand new and fully calibrated. Regardless, if Goodwood's meters are so accurate, how come I got a 5db difference form one week to the next? Steve Mell PTM 88 Link to comment Share on other sites More sharing options...
Harry Flatters Posted April 30, 2002 Author Share Posted April 30, 2002 Sean, I told them the redline was 6k so it was checked at 4.5k and still it failed! Steve Mell PTM 88 Link to comment Share on other sites More sharing options...
I reply to every thread Posted April 30, 2002 Share Posted April 30, 2002 Packing? During my recent exhaust research I was told that some systems need repacking at lunchtime during trackdays in order to continue to comply with sound regs even though they may have passed at 8.30 am. I was told this by a fairly frank manufacturer. Still doesn't explain the difference between Goodwood & SBD though. I'd be pretty confident that the Goodwood meters are the accurate one of the two. If you made it clear that you needed an exhaust that would meet certain sound limits then no doubt SBD will do "The right thing"? Link to comment Share on other sites More sharing options...
Paul D Jones Posted April 30, 2002 Share Posted April 30, 2002 If you have a stack dash configer it to 3 cylinders for the noise test and lift at the drive by point changing to 3 cylinders shows the revs lower maybe wort a try. Paul. See My Car Here Link to comment Share on other sites More sharing options...
philwaters Posted April 30, 2002 Share Posted April 30, 2002 Hi Steve, Sorry to hear about your problems. It does seem very odd that you got a 5dB difference from one day to the next, and I would be writing a letter of complaint, not that it will get you far, but can help to vent the frustration. As an aside, you are not the only one... My starting problems wasn't my battery - not directly anyway. So a new starter and I am now down £160 also. Oh and the clutch release beaing on my tin-top went pop last night so thats another load... ferry leaves on Saturday and I don't know which car I trust to take! Phil Waters Zetec is in and running wink.gif Link to comment Share on other sites More sharing options...
stevefoster Posted April 30, 2002 Share Posted April 30, 2002 185K miles tin top vs 500 miles on new Zetec. A car you can fix yourself vs one thats harder to fix... The sun, the sun the sun... open top verses tin top with no AC. Hard choice mate! Link to comment Share on other sites More sharing options...
philwaters Posted April 30, 2002 Share Posted April 30, 2002 Too much stress with 7, trying to get it ready in time. I am not happy that it will always start when needed. Therefore I am taking the tin-top... therefore it decides to fail! Oh, and it is ONLY 181k miles... I don't know, just don't make them to last any more huh. (yes it is the original smile.gif) Phil Waters Zetec is in and running wink.gif Edited by - philwaters on 30 Apr 2002 13:36:36 Link to comment Share on other sites More sharing options...
Tony Martyr Posted April 30, 2002 Share Posted April 30, 2002 I do hope that some of the contributers to the recent thread on measurement of engine power are also reading this exchange because the theme is the same. Power measurement and generation from heat engines is, like noise measurement and noise generation are very complex and variable processes that are often, wrongly, reduced to an apparently simple integer, be it in kW units or dB. The units that both measurements should have been recorded in is dBA the A bit is an internationally agreed weighing system used in measurement systems to bias the results in such a way as to match the human hearing sensitivity. If one of the meters was not set to A weighing you need look no further for the anomaly. Meters used to be, and probably still are, graded into Types 1,2 and 3. Type 3 units are the low cost units that most nonspecialists like me use for site surveys etc. The accuracy are in the range of plus and minus 2% for most functions. Seeking the reason for the difference I would want to check meter setting, Microphone or pickup type matched and the test sites. Reflection is the major variable and the distance of the measurement from reflective surfaces is vital. Remember you are measuring power in a series of waves, you can get additive reflection and subtractive reflection. If you tip a sensor towards the ground you can generate some stange effects. The Goodwood measurements could be put into context by asking others if their readings were also higher than expected which would indicate a systematic error. Coming back to my first point we can no more say that a car produces 100dBA at 5000rpm than we can say the same car produces 140kW at 5000 rpm, each statement requires a detailed description of the experiment that produced the figures IF it is to be accurate Link to comment Share on other sites More sharing options...
Leadership Team Mcalvert Posted April 30, 2002 Leadership Team Share Posted April 30, 2002 What effect would angling the end of a side-exit exhausd downwards have? Would this reduce the noise because it would not be pointing directly towards the meter, or would it make it louder because of the reflections? I'd experiment if I had a sound-meter, but I don't! Regards - Michael. Link to comment Share on other sites More sharing options...
DohNut Posted April 30, 2002 Share Posted April 30, 2002 Tony As you mention IF the sensor is pointed towards the ground you will create all sorts of anomalies - ie all tests (I am pretty sure this was your point but worth re-iterating) I recall a conversation with Mr Whiting who during a noise test walked round the car with the meter (kept in a consistent orientation) and there was minimal variation in the dB level. This was attributed to the fact that all the alloy pannels can resonate and amplify the sound. Also that there is only a single alloy sheet to keep the general engine noise (not exhaust) in the engine bay. Fitting / re-fitting carpets could be one option to absorb some of the noise but fitting an undertray and lining the inside of the engine bay and bonnet with a sound deadening material may be one way forward. Most kitchen sinks have a small area of foam sheet / expanding foam sprayed on the underside of the bowl which does an excelent job of dulling the tinny sound. The most impressive bit is that the whole area need not be covered, just enough to change the resonance of the metal away from the exiteing frequency. I would be very interested to see if there is a fireproof version of expanding foam that could do this job. Any suggestions ? Nick Link to comment Share on other sites More sharing options...
Tony Martyr Posted April 30, 2002 Share Posted April 30, 2002 How about I bring a Type 2 Noise meter to the Stoneleigh Show and demonstate the variability of noise measurement, using somebody elses car of course? There you could try a test on grass which is absorbent and a road which is not. Nick is correct to point out that the whole vehicle is part of a vibrating system. However, as I understand it the noise test should be taken at 1 meter from the exhaust outlet pipe and 45 degrees from the plane of the pipe end. I had assumed, but may be wrong, that the correct alignment of the meter is parallel with the ground at, or about the level of the exhaust. The more directional the pickup the more variation will take place due to orientation. I have fitted a heavy adhesive silvered sheet to the underside of my bonnet to reduce sympathetic vibration from intake bark. The same principle is used by all car makers. There are fireproofing foams on the market that could be put in the void space near the exhaust and may make a difference to the brightness of reflected sound. Tony Link to comment Share on other sites More sharing options...
Ian B Posted April 30, 2002 Share Posted April 30, 2002 Not sure what effect the panel damping will have on an A-weighted reading as A weighting is biased to respond to the 500-10,000 Hz range. C weighting on the other hand has a flat response generally between 32-10,000 Hz. I know the Goodwood meter is an analogue 'needle' type and probably has both weighting settings, C is generally the default, so perhaps it had been set incorrectly? (or had been dropped!) I have a digital meter, with A and C settings, (and accuracy of +/- 2dB at 114dB) so if you are in blatting distance of Maidstone you are welcome to pop round and we can experiment. MI 5EVN Link to comment Share on other sites More sharing options...
Harry Flatters Posted April 30, 2002 Author Share Posted April 30, 2002 Cheers Ian, If it ever stops raining I may well take you up on your offer. I live about 5 miles north of the Reigate junction on the M25. Steve Mell PTM 88 Link to comment Share on other sites More sharing options...
Chelspeed Posted May 1, 2002 Share Posted May 1, 2002 Just for the record all MSA limits are at 45 deg to the exhaust outlet but at 0.5m and not 1m as discussed in a couple of posts above. Perhaps Goodwood were measuring at 0.5m and SBD at 1m...... Link to comment Share on other sites More sharing options...
Tony Martyr Posted May 1, 2002 Share Posted May 1, 2002 If the distance of the two readings was varied by 50% it would explain the anomaly. Noise intensity varies directly as the square of the distance from the source I seem to remember. We could copy the Roman civil engineers trick and make up a loop of string with 3 knots. When one knot is held at the centre of the pipe and the triangle formed one of the corners would represent the test position and direction of the meter as required by MSA, at least we might get consistancy. Link to comment Share on other sites More sharing options...
Harry Flatters Posted May 1, 2002 Author Share Posted May 1, 2002 Graham, you are right about the distance, although Ted Crouchers prong thingy looks longer than .5m to me. I can't vouch for the exact distance that SBD did the test but I would say that it was pretty much the same if not closer than Goodwood. Regardless, none of this explains the disparity of the two Goodwood readings one week apart. Steve Mell PTM 88 Link to comment Share on other sites More sharing options...
ashaughnessy Posted May 1, 2002 Share Posted May 1, 2002 Perhaps the tester at Goodwood didn't run the test in the same way each time? Perhaps he stood closer for one, or pointed the meter in a different direction, etc? Link to comment Share on other sites More sharing options...
millsn Posted May 2, 2002 Share Posted May 2, 2002 Anyone got nay zetec noise readings? Nigel Mills - 2.0 Zetec carbs Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now