stevie

Does it work?

***Exceptionally well!***

It sounds like a great way of integrating a multi-speaker sound system into a hostile environment. To do it justice you would need more sophisticated measuring equipment than a handheld RATA, however.

I'll have to try to listen to one of F1 systems some day (although I'd have to win the lottery before I could even consider one.)


***The pink noise that I'm running would be collected over a period of 5 minutes. But, there seems to be some wierd randomness in the levels itself. Now if I had a good B&K pink noise generator....****

All you need is a good recording. There are quite a few out there. I have a CD called Sound Check by Alan Parsons, recorded at Abbey Road Studios. I costs only a little more than a normal mucic CD and it has quite a few pink noise tracks and an excellent selection of test tones. Plus the obligatory 1000 mph jet fly by, tanks, and steam trains with which to impress your neighbours- It's quite readily available at places like Radio Shack in the UK. I would guess it's available in the US, too.

There's also a program called ETF, Room Acoustics Analysis System, which I've got but haven't used yet. It works in conjuction with your PC. It's more expensive but it allows you to do quite sophisticated measurements in the car. They have a Web site if anyone is interested, and there's a review at http://www.audio-ideas.com/reviews/etf.html. There's also a downloadable demo version that's restricted in its functions. Not for the beginner, unfortunately.


>I'd take take those measurements with a liberal pinch of salt.

***I'm betting that if I had a good pink noise generator and the 2260 B&K RTA observer (at nearly 7 grand) or even the PULSE B&K (at nearly 20 grand) that the results would come out close. Take a look at the B&K Pulse. http://www.bksv.com Very slick and it shows time decay as well as other goodies.***

Now you're talking like an engineer-. You don't need B & K gear to get good results nowadays. There is so much available that harnesses the power of your computer. For example, I'm using a microphone that costs less than a hundred dollars but is as accurate as a B & K at fifty times the price. How? My mic has been calibrated against a B & K to produce a correction curve. The computer superimposes the correction curve automatically every time I make a measurement. That's what I call progress.

The measuring system I use is called Liberty Audiosuite. It has all the functions of the B & K Pulse, except that it's not very portable:-(

The price of digital measuring equipment for loudspeakers is coming down all the time. The last time I looked you could buy a simple, useable setup for less than 200 dollars using your computer soundcard. I think there may well be freeware available with limited functionality. If I come across it I'll post the info here.

On the particular point you're making, all I can say is that a sine wave measurement on a loudspeaker in a room will look nothing like a third octave pink noise measurement; it will look like a mountain range. I can't speak for the car environment, however, as I've never carried out any measurements inside a car.

>I'd be very intested to learn what's causing this rolloff.

***So would I!***

If you have a look at the carrapps.pdf article on the LinearX page that you posted, you will see some response curves on p. 21 that have the same brick wall response just below 10 K that you are measuring. I wonder if that's just a coincidence?

We have a limited number of options here.

1. The CD/CDplayer/amp/speaker is filtering the signal above 10 KHz
2. The mic/measuring equipment is filtering the signal.
3. The methodolody is incorrect.

What concerns me is the possibility that the stock CD/amp is doing the filtering.


>19 KHz is exceptional. That would make you around 16 years old, then, Percy-

***31 and counting. Don't let the years fool you...I know lots of 16 year olds that are almost completely deaf.***

The only person I have known who could hear 19 kHz had 'golden ears'. He could hear things that just escaped me.

Seriously, those 16 year olds probably have SPL-type sound systems in their cars. I often wonder if these people appreciate just how horrible tinnitus us. There should be a health warning.

Stevie

Percy

[QUOTE]Originally posted by stevie
[B]Does it work?


It sounds like a great way of integrating a multi-speaker sound system into a hostile environment. To do it justice you would need more sophisticated measuring equipment than a handheld RATA, however.

I'll have to try to listen to one of F1 systems some day (although I'd have to win the lottery before I could even consider one.)

***They're 8 grand.***


All you need is a good recording. There are quite a few out there. I have a CD called Sound Check by Alan Parsons, recorded at Abbey Road Studios. I costs only a little more than a normal mucic CD and it has quite a few pink noise tracks and an excellent selection of test tones. Plus the obligatory 1000 mph jet fly by, tanks, and steam trains with which to impress your neighbours- It's quite readily available at places like Radio Shack in the UK. I would guess it's available in the US, too.

***Will have to look into it!***

There's also a program called ETF, Room Acoustics Analysis System, which I've got but haven't used yet. It works in conjuction with your PC. It's more expensive but it allows you to do quite sophisticated measurements in the car. They have a Web site if anyone is interested, and there's a review at http://www.audio-ideas.com/reviews/etf.html. There's also a downloadable demo version that's restricted in its functions. Not for the beginner, unfortunately.

Now you're talking like an engineer-. You don't need B & K gear to get good results nowadays. There is so much available that harnesses the power of your computer. For example, I'm using a microphone that costs less than a hundred dollars but is as accurate as a B & K at fifty times the price. How? My mic has been calibrated against a B & K to produce a correction curve. The computer superimposes the correction curve automatically every time I make a measurement. That's what I call progress.

***B&K has something like this also. The newer stuff is literally plug and play (automatically detects the mic, s/n, cal chart for s/n, and the type of preamp and it's cal'd characteristics. Very slick, moocho bucks.***

The measuring system I use is called Liberty Audiosuite. It has all the functions of the B & K Pulse, except that it's not very portable:-(

***Can you measure the interior of your car with a mic extension at the headrest position? I'd be interested in the reading you would get.***

The price of digital measuring equipment for loudspeakers is coming down all the time. The last time I looked you could buy a simple, useable setup for less than 200 dollars using your computer soundcard. I think there may well be freeware available with limited functionality. If I come across it I'll post the info here.

***The thing that worries me with the soundcards is that they're not all linear from 20-20k. But, knowing the gurus out there, they probably have correction curves for this also.***

On the particular point you're making, all I can say is that a sine wave measurement on a loudspeaker in a room will look nothing like a third octave pink noise measurement; it will look like a mountain range. I can't speak for the car environment, however, as I've never carried out any measurements inside a car.

***Give it a shot...you might be very surprised.***

>I'd be very intested to learn what's causing this rolloff.

If you have a look at the carrapps.pdf article on the LinearX page that you posted, you will see some response curves on p. 21 that have the same brick wall response just below 10 K that you are measuring. I wonder if that's just a coincidence?

We have a limited number of options here.

1. The CD/CDplayer/amp/speaker is filtering the signal above 10 KHz

***I'd agree with option 1. ***
2. The mic/measuring equipment is filtering the signal.
***Not likely but always possible.***
3. The methodolody is incorrect.
***Keeping it simple here...***

What concerns me is the possibility that the stock CD/amp is doing the filtering.

***Yep...I'd definitely agree on that one.***

The only person I have known who could hear 19 kHz had 'golden ears'. He could hear things that just escaped me.

***Most "golden ears" are just people that actually LISTEN and HEAR, rather than just let the info pass by. With a bit of training a person with good hearing can detect these frequencies a bit more consciously. As long as your hearing isn't notched or if you've been firing pistols, rifles or in the military next to artillery.***

Seriously, those 16 year olds probably have SPL-type sound systems in their cars. I often wonder if these people appreciate just how horrible tinnitus us. There should be a health warning.

***I know a carpenter that has serious tinitus. He has to keep a fan running on "high" just to cancel out all the horrible ringing his ears/nerves produce.***

Percy

stevie

>I'll have to try to listen to one of F1 systems some day >(although I'd have to win the lottery before I could even >consider one.)

***They're 8 grand.***

I'd definitely have to win the lottery then-


***Can you measure the interior of your car with a mic extension at the headrest position? I'd be interested in the reading you would get.***

Yes, no problem. Once I have my new speakers installed I'll take some measurements and post them here. I should be able to get some interesting data, such as the rollof of the sub bass crossover, for example, and also information about the major resonances inside the car. I could also take some curves to show what's happening when you connect the rear speakers out of phase, or what affect the housing has on the HF unit - that kind of stuff.

I'm quite looking forward to getting to that stage myself.

***The thing that worries me with the soundcards is that they're not all linear from 20-20k. But, knowing the gurus out there, they probably have correction curves for this also.***

I'm not sure how they handle that. My system is based on a professional sound card with extremely low distortion and a perfectly flat frequency response. The system automatically correct for deviations in the response of the amp you use, as it's able to check input against output.

>On the particular point you're making, all I can say is that a >sine wave measurement on a loudspeaker in a room will look >nothing like a third octave pink noise measurement; it will >look like a mountain range. I can't speak for the car >environment, however, as I've never carried out any >measurements inside a car.

***Give it a shot...you might be very surprised.***

I will.

>What concerns me is the possibility that the stock CD/amp is >doing the filtering.

***Yep...I'd definitely agree on that one.***

You should be able to confirm that by listening to the sweep as it's happening. If it's true, it means that someone has deliberately designed a filter into the system. That would be really annoying for those of us who are using the stock amplification.

Stevie

engin_ear

iTrader: (1)

Geez, sorry I missed this discussion as it was happening, it is interesting.
I have a couple of things to contribute.

1) The weighting curves vary based on loudness. The A curves are basically the inverse of the Fletcher-Munson ear sensitivity curves. As the sound intensity gets louder, the weighting gets flatter (hence the 'loudness contour' control common in stereo). If you've used pure sinewave test tones at different frequencies, the mic needs to see the same SPL (even though you're generating the same level electrical signal from the test CD) for each frequency to apply a FIXED curve, otherwise it could be all over the place if you're getting a ton of reflections, which you are. As far as the CAR's response linearity, a flat weighting will thus reveal the most. Why weight it until you get to the point where you want to actually correct the response? (or you're trying to match what IASCA is doing, etc, etc).

2) Allow me to suggest something strange: How about covering the entire interior with some good-quality acoustic foam? This would serve to dampen reflections to the point where what you are measuring is then dominated by the direct response (you'd still have some direct path interactions, though). The difference in the curves measured with-vs.-without the foam would approximate the contribution due to the interior acoustics. It would tell you more directly how the electronics are tuned. At first, this may sound silly, but given the amount of cash being spent on some of these systems, the price of foam would be in or near the noise. Even a reasonable job of covering glass, seats, door panels, deck, would likely be revealing. Foam can be wedged, temporarily taped, or even just laid in place, converting the car into a cheap anechoic chamber. Just a suggestion....

It is hard to believe that ANYONE would intentionally tune a response to look like the curve presented. Lexus would have to have been drunk, or on some serious drugs. It's like 'this is your response, and this is your response on drugs (see curve)' :-)

Jerry

Percy

[QUOTE]Originally posted by engin_ear
[B]Geez, sorry I missed this discussion as it was happening, it is interesting.
I have a couple of things to contribute.

1) The weighting curves vary based on loudness. The A curves are basically the inverse of the Fletcher-Munson ear sensitivity curves. As the sound intensity gets louder, the weighting gets flatter (hence the 'loudness contour' control common in stereo). If you've used pure sinewave test tones at different frequencies, the mic needs to see the same SPL (even though you're generating the same level electrical signal from the test CD) for each frequency to apply a FIXED curve, otherwise it could be all over the place if you're getting a ton of reflections, which you are.

***For the mic to see the same SPL throughout all the test frequencies would indicate that the response is flat. Definitely not the case here! I see what you mean by the response curves (ISO Recommendation 226) Fletcher-Munson differing from 40 to 80dB, but even with the different curves (epecially below 250hz) the peaks measured would still have been there. I'd guess an average of dB readings would be needed to fit it in the appropriate curve.***

As far as the CAR's response linearity, a flat weighting will thus reveal the most. Why weight it until you get to the point where you want to actually correct the response? (or you're trying to match what IASCA is doing, etc, etc).

***I'd rather use A weighting to simulate the ears response at lower sound levels. To use linear would have presented information below 1khz that would not have been accurate in simulating the "average" human ear response. I could go linear on the response, but the peaks would have probably been more magnified. ***

2) Allow me to suggest something strange: How about covering the entire interior with some good-quality acoustic foam?

***Now there's a sight! ***

This would serve to dampen reflections to the point where what you are measuring is then dominated by the direct response (you'd still have some direct path interactions, though). The difference in the curves measured with-vs.-without the foam would approximate the contribution due to the interior acoustics. It would tell you more directly how the electronics are tuned. At first, this may sound silly, but given the amount of cash being spent on some of these systems, the price of foam would be in or near the noise. Even a reasonable job of covering glass, seats, door panels, deck, would likely be revealing. Foam can be wedged, temporarily taped, or even just laid in place, converting the car into a cheap anechoic chamber. Just a suggestion....

***It would have to be done in a fashion that would literally resemble an anechoic chamber. Lots of foam in wierd configurations! Hey Stevie...can I borrow your computerized test equipment? ***

It is hard to believe that ANYONE would intentionally tune a response to look like the curve presented.

***You should listen to some of the other audio systems. GM '96 and below Grand Prix models. YUCK. A transistor radio sounded MUCH BETTER than the CD!!!***

Lexus would have to have been drunk, or on some serious drugs. It's like 'this is your response, and this is your response on drugs (see curve)' :-)

***They're breathing in too many fumes from the 4 liter v8!***

Percy

engin_ear

iTrader: (1)

"For the mic to see the same SPL throughout all the test frequencies would indicate that the response is flat. "

Yes. My point here is that because it is NOT flat, the variable weighting applies even more non-linear variation at low and high frequencies. I'd be looking for the unweighted response first.

And apparently those V8 fumes have caused those Lexus guys to do some other strange things as well --- now I understand! :-)