## Comment Re:Price is key... (Score 1) 207

Who said he was going in the same direction as the truck?

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Who said he was going in the same direction as the truck?

Don't forget that heat in a chimney is often not wasted energy. When burning fuel, you can lose more in the reduction in burner efficiency, caused the lack of draw that results from a cool chimney, than you gain from 'recovering' energy out of the chimney.

There are a lot of German-engined cars that can beat this already, while driving at 80 MPH. Audi A3/A4 2.0 TDI, BMW 320D, Golf 2.0 TDI, and others. These are by no means slow or underpowered cars, either (despite the extra weight of safety features that some posters have deemed excessive). I don't have experience of them, but something like a Citroen C3 diesel can probably acheive a similar efficiency level. My Skoda (VW engine) can easily acheive over 60 MPG in non-'highway' driving, and again is certainly not lacking in power when required.

All of this today and without any special hybrid technology. Who knows what might be possible in another decade's time. It seems to me that a lot of the objections towards the push for more efficient cars are basically unfounded.

All of this today and without any special hybrid technology. Who knows what might be possible in another decade's time. It seems to me that a lot of the objections towards the push for more efficient cars are basically unfounded.

Thanks for these interesting posts. Is there a book you would recommend that covers these issues in more detail? And perhaps a book that makes a reasonable attempt to counter some of these points? Cheers.

Let's have a look at the numbers.

Having heard that road wear is proportional to the fifth power of axle weight, I thought I would see what wear proportion that works out as, given that there are presumably more cars than trucks, and the differing mileages of these types of vehicle. As I write this, I have not done the final calculation. I will use a couple of papers and some government statistics.

Looking at a couple of papers (The economic and environmental benefits of increasing maximum truck weight: the British experience, Alan C. McKinnon, 2005. The cost of relying on the wrong power—road wear and the importance of the fourth power rule (TP446), Richard Johnsson, 2004, Impacts of Increased Goods Vehicle Weight Limits - A European Case Study, Proceedings of Fourth International Symposium on Heavy Vehicle Weights and Dimensions, 1995, the exact proportion of axle weight to road wear varies depending on factors including road surface type, anywhere from 3rd or 4th power of axle weight, all the way up to the 9th power. I chose 4 as a lowish-average.

Taking a Heavy Goods Vehicle (HGV) weight of 15 tons and an average of 4 axles (HGV maximum weights: a brief guide gives a maximum for HGVs of 44 tons over 6 axles, and I don't have a good source, but the minimum to count as a HGV is 7.5 tons, presumably with 2 axles), this gives 3.75 tons/axle. For cars I assumed 1.5 tons and two axles; 0.75 tons per axle. The ratio of these figures is 5. 5^4 = 625 times as much road wear per axle.

Traffic statistics are in vehicle-kilometres, so to use these we need to multiply this back up by the number of axles per vehicle. 4 for trucks and 2 for cars gives 625*(4/2) = 1250 times as much road wear per vehicle per kilometre.

Keeping with the euro theme, I got transport statistics from the UK department for transport. 240 billion miles driven in the UK in 2011 by cars/taxis, heavy goods vehicles 16.4 billion. 240/16.4 = 14.63 times as many miles driven by cars, compared to heavy goods vehicles (I have deliberately left out 'vans', or other vehicles that carry smaller loads than the HGVs that my axle weights are for). So now we have 1250 times as much road wear per vehicle for HGVs, divided by 14.63 as the ratio of cars-HGVs, gives 85.4 times as much road wear by HGVs. Take the reciprocal and subtract from 1 to get that as a proportion, 0.988, or 98.9%.

Wow, I really didn't expect to get so close to the GP's guess. My estimate for axle weight for HGVs I think is low if anything; I could easily have gone for 20 tons over 4 axles, which would have given 99.6%. I have also assumed that HGV weight is evenly spread over the axles; it strikes me that the rear axles will carry more weight, and so since the road wear varies with the 4th power of this, the real figure is probably higher.

Having heard that road wear is proportional to the fifth power of axle weight, I thought I would see what wear proportion that works out as, given that there are presumably more cars than trucks, and the differing mileages of these types of vehicle. As I write this, I have not done the final calculation. I will use a couple of papers and some government statistics.

Looking at a couple of papers (The economic and environmental benefits of increasing maximum truck weight: the British experience, Alan C. McKinnon, 2005. The cost of relying on the wrong power—road wear and the importance of the fourth power rule (TP446), Richard Johnsson, 2004, Impacts of Increased Goods Vehicle Weight Limits - A European Case Study, Proceedings of Fourth International Symposium on Heavy Vehicle Weights and Dimensions, 1995, the exact proportion of axle weight to road wear varies depending on factors including road surface type, anywhere from 3rd or 4th power of axle weight, all the way up to the 9th power. I chose 4 as a lowish-average.

Taking a Heavy Goods Vehicle (HGV) weight of 15 tons and an average of 4 axles (HGV maximum weights: a brief guide gives a maximum for HGVs of 44 tons over 6 axles, and I don't have a good source, but the minimum to count as a HGV is 7.5 tons, presumably with 2 axles), this gives 3.75 tons/axle. For cars I assumed 1.5 tons and two axles; 0.75 tons per axle. The ratio of these figures is 5. 5^4 = 625 times as much road wear per axle.

Traffic statistics are in vehicle-kilometres, so to use these we need to multiply this back up by the number of axles per vehicle. 4 for trucks and 2 for cars gives 625*(4/2) = 1250 times as much road wear per vehicle per kilometre.

Keeping with the euro theme, I got transport statistics from the UK department for transport. 240 billion miles driven in the UK in 2011 by cars/taxis, heavy goods vehicles 16.4 billion. 240/16.4 = 14.63 times as many miles driven by cars, compared to heavy goods vehicles (I have deliberately left out 'vans', or other vehicles that carry smaller loads than the HGVs that my axle weights are for). So now we have 1250 times as much road wear per vehicle for HGVs, divided by 14.63 as the ratio of cars-HGVs, gives 85.4 times as much road wear by HGVs. Take the reciprocal and subtract from 1 to get that as a proportion, 0.988, or 98.9%.

Wow, I really didn't expect to get so close to the GP's guess. My estimate for axle weight for HGVs I think is low if anything; I could easily have gone for 20 tons over 4 axles, which would have given 99.6%. I have also assumed that HGV weight is evenly spread over the axles; it strikes me that the rear axles will carry more weight, and so since the road wear varies with the 4th power of this, the real figure is probably higher.

I also spent 4 years studying an EE degree, and although it was not especially focused on signal processing, I now work for a large pro audio company.

Some of the issues pointed to in this and other posts regarding oversampling and AA filters are not really relevant to the subject at hand, given the technology currently in use. A statement like 'oversampling at 192 kHz' shows a lack of knowledge regarding the kinds of audio converters that have been in use for a good while now. A Delta Sigma ADC running with an Fs of 48 kHz might often be oversampling at 3.072 MHz or 6.144 MHz. Anti aliasing filters that many people have mentioned are implemented digitally inside the converter (no need for external analog filters, which may well exhibit many of the problems mentioned), and actually have extremely good pass band ripple.

Look at datasheets for converters from manufacturers such as TI (burr brown), cirrus [page 36 here has detailed plots of 48, 96, and 192 kHz pass pand characterisitcs for the device, highlighting the fact that increasing the sampling rate does not improve pass band ripple for this device (also note the scale is 0.02 dB/div)], AKM, Wolfson micro You will find pass band pass responses that are flat to within less than +/- 0.05 dB over the audible range, and stop band attenuation in excess of 100 dB, whether sampling at 48 kHz or 192 kHz. If you can find anything in actual converter datasheets that points to better converter performance from selecting a higher sampling rate, I would be interested to see it.

All in all, the basics of sampling theory don't really help people to understant the real world issues in designing a moden high end audio device. And in the end, surely the proof of the pudding is in the blind tests, that never seem to show that anybody can tell any difference when moving to higher rates? Even*if* there were a few people who could hear this difference in some perfect listening envirmonment, would it really make sense for everyone else to go out and buy 192 kHz equipment?

Some of the issues pointed to in this and other posts regarding oversampling and AA filters are not really relevant to the subject at hand, given the technology currently in use. A statement like 'oversampling at 192 kHz' shows a lack of knowledge regarding the kinds of audio converters that have been in use for a good while now. A Delta Sigma ADC running with an Fs of 48 kHz might often be oversampling at 3.072 MHz or 6.144 MHz. Anti aliasing filters that many people have mentioned are implemented digitally inside the converter (no need for external analog filters, which may well exhibit many of the problems mentioned), and actually have extremely good pass band ripple.

Look at datasheets for converters from manufacturers such as TI (burr brown), cirrus [page 36 here has detailed plots of 48, 96, and 192 kHz pass pand characterisitcs for the device, highlighting the fact that increasing the sampling rate does not improve pass band ripple for this device (also note the scale is 0.02 dB/div)], AKM, Wolfson micro You will find pass band pass responses that are flat to within less than +/- 0.05 dB over the audible range, and stop band attenuation in excess of 100 dB, whether sampling at 48 kHz or 192 kHz. If you can find anything in actual converter datasheets that points to better converter performance from selecting a higher sampling rate, I would be interested to see it.

All in all, the basics of sampling theory don't really help people to understant the real world issues in designing a moden high end audio device. And in the end, surely the proof of the pudding is in the blind tests, that never seem to show that anybody can tell any difference when moving to higher rates? Even

"A car is just a big purse on wheels." -- Johanna Reynolds