john banks

An admission - currently my amp is grounded by putting my 8 gauge cable end connector around the thread of one of the protruding screws from the left rear speaker plate (one of the three that hold the plate to the rear deck). I know this is heretical, but it has been temporary until I can do something "definitive". I don't know the resistance of the said screw and I suppose I should really sand the area around it and use a non-anodised star washer and a nut to secure the connection.

But three questions -
1. Is the rear deck connected well to the chassis of the car - I am presuming it is welded and so OK?
2. Is the body galvanised, so will sanding down to metal be any good?
3. The ground cable is not long and the amp sits at the back left of the boot on top of the sub. Any one discovered any good grounding points nearby? For those with professional installs, where have the geezers done their grounding.

I do get a good supply voltage at the amp terminals, but I have not tested it under heavy load yet and my ohmeter is not currently working. I am not suffering any noise problems (except I can now hear "hiss" on some CDs because of my new tweeters - I am amazed that many CDs still have noise on - I thought they would all be DDD these days! - this is obviously not the system's fault) and the amp seems to hit hard, but I want a good ground otherwise I won't sleep at night wondering if I am losing 2% of system performance - yes I am very sad indeed.

Replies appreciated from like-minded saddos.

Thanks, John.

Scooby Doc

John

In the past I have sanded down to bare metal - using bolts securing folding rear seats. I'll look in the boot later when it stops raining and post back.

Martin

john banks

Behind the "trim" in the left side of the boot I found a piece of sheet metal welded to other bits of car with a few holes. Sanded one down and put a bolt through it and the ground cable. Seems to be OK. Can't tell any difference from the old method though. A neighbor (who used to do some welding) assured me that any panel that was welded would be clean metal and then painted and hence a good ground point.

ScoobyDoo555

Hi John,
Sorry M8, can't help you with the grounding coz mine works fine!!
<I thought they would all be DDD these days!>

Hmm, <frown>, not as long as there are 'proper' engineers recording and mixing the music!! <grin>

Slightly off topic, but as you know by now, I ain't bothered LOL!!!

As you know, the term DDD actually means
Digitally recorded
Digitally mixed (onto DAT or PCM equivalent) & Digitally mastered.
Even though Digi sounds clearer, is actually only samples of the original (CDs are recorded @ 44.1Khz or 44100 samples) - still not the analogue waveform. Even at 96Khz, the soon to be new standard, this STILL won't be enough.
The whole reason for the 'standard' being 44.1KHz is down to Nyquist Theorum, stating that for any digital signal captured, the highest frequency has to at least 2x that being heard, in our case, the human ear can hear 20Hz - 20Khz, therefore a minimum of 40KHz has to be sampled.

This is the whole reason why some people would argue on how good digital actually is - the technology isn't up to speed yet....

The above is why most music is still recorded Analogue, mixed digital, and mastered digital. The analogue signal CAN be highly cleaned up using Dolby SR - this makes it almost comparable to digital in noise terms, but the analogue warmth is maintained :-)

The only other digital format that does sound slightly closer to analogue, is Minidisc, because of its data compression (V subjective opinion, admittedly)

Besides, to take advantage of an entirely DDD project, you'd need digitally active speaker in your car!!!!

Just some thoughts!!! :-)

Dan (I'm bored - can you tell?)

john banks

Interesting, so would 96KHz 24 bit for example be noticeably better quality through everyday "hi-fi" equipment - I mean separates in a lounge?

I am a little concerned with the move to digital radio/TV etc that there will actually be a loss of quality - certainly I think my analogue TV reception is better than the Ondigital equivalent from my box because it is so compressed - there are glitches in the audio and the picture is not so hot with fast movement and around the edges after a pan motion. I know my decoder is cheap(std Philips Ondigital one) but compression artefact is evident even with good signal strength. And as we commented before, digital glitches are so much more unpleasant than analogue ones in terms of distortion or compressed AV.

Scooby Doc

Sorry John

Spent the afternoon re-applying the dynamat to the bootlid that fell off. Didn't get chance to look at the earth and then the alarm locked the keys in the car.

You and Dan going to have another debate?

Martin

john banks

No debates. I am here to learn on this one. I'm interested in the need for higher sample rates etc.

ScoobyDoo555

Nah, no debates!!! LOL!!
96KHz/24Bit is MUCH better, and you can tell the difference, but presently, it's at a price :-(

The whole issue of compression is a sad one. SKY/ON digital all use data compression, purely because of the small bandwidth between channels - to overcome this, the broadcasters BLOCK out frames of information and use error correction to 'fill in the gaps' (just like CD/MD anti-skip & error correction). It's usually in the background where it won't be noticed.....

But yeh, same principles for all digital, only with TV, instead of talking Kilohertz, we're talking Megahertz (****eloads of information!)

Dan
PS crunched by bumper the other day :-( - got it fixed today for next to nothing
WeY HEY!!! :-)

john banks

So would MP3 style audio compression of a 96KHz 24 bit source that produced a compression ratio of 1:3ish so that it could go on an audio CD using the same space as 44ish Khz 16bit sound better than an uncompressed CD? Presumably then the expense would be only in improved DAC? I've heard about some of these super CD/DVD audio standards - I previously thought they were overkill presuming CD was "as good as it gets" but now I will be following developments along these lines more closely.

How do you get your bumper fixed so cheaply - was it a repair rather than replacement - more money for ICE bits now?

ScoobyDoo555

Hi,
<So would MP3 style audio compression of a 96KHz 24 bit source that produced a compression ratio of 1:3ish so that it could go on an audio CD using the same space as 44ish Khz 16bit sound better than an uncompressed CD?>

In theory yes. However, practically, it works out as follows:-

@44.1Khz (16Bit)a stereo file (L&R) works out at about 1meg per minute.
So a 96KHz (24Bit), will use up at least 2meg due to the higher bandwidth, and that's not taking into account the 8 more bit used.

So, even with a compression ratio of 3:1, you've reduced your storage space by halfish (I think - bit too early for this!!!)

Plus of course, you've still got the problem that it's compressed, so the sound (and the quality) will be affected :-(

When they do finally bring out 96Khz CDs, I'm intrigued as to how big they'll be!! So obviously, there will be a size issue (Isn't there always?)

The bumper was replaced with one from a broken up Scoob, along with a rear cluster light. Subaru - Bumper £200 +vat, Light £105 + vat
I got it for - Bumper £160 Light £65 Cash.
Subaru wanted 23 hours labour. Actually fitted in 1.5hours!!!

All done by a proper Subaru mechanic. Work is brilliant. Anybody want his number?

ScoobyDoo555

Just readging back through the posts and I've realised that I forgot to mention WHY Nyquist Theory si important.

Regarding that 2x the highest frequency thing, we need to capture at least 40Khz due to the transients and harmonics above 20KHz that affect the lesser frequencies..... Without 'em, the sound is changed...

Hope that makes it a bit clearer!!!!

Dan

dowser

Try removing the >22khz filters on a stock CD player....and replace the op-amp with a biased transistor (via an led) and hey presto....digital audio nirvana.

That's with all the 2nd/3rd order harmonics (that're supposed to destroy sound quality) intact, along with a bunch if hi frequency info we *can't* hear (allegedly ) - don't understand it, but it works!

Analogues still better though.....

Richard

GranTurismo

I used the smae ground as the rear light clusters and it works fine.