12 inch subs x 2 + quieter than one... wtf

Questions about Car Audio
IZU069

Post by IZU069 »

Your not alone. But keep it in mind next time. Capacitors are purely wank factor, and for people to make a buck.

As I said above, a capacitor has Watt-seconds (or Amp seconds) whereas a battery has Watt-hours (or Amp-hours). A capacitor has thousands of times less stored energy at a higher price.

A battery is like a big capacitor but it also "generates" (ie, converts) its own energy (voltage/current etc).
phatty
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Post by phatty »

IZU069 wrote:I can assure you that a $25-$30 12V 7AH battery will be more effective.
so where can i get one for under $30?
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IZU069

Post by IZU069 »

[ ^d8 12Nov08 - fixed Dick's link ]
Most battery places...
But prices vary - eg Jaycar $29.95 vs Dick Smith $39.95 and others $39.95 like BatteriesPlus CenturyPS1270, Panasonic, Yuasa NP7-12.

Alas I forgot lead prices have quadrupled - last year Jaycar's 12v/7AH was$10 less @ $19.95!

Smaller batteries are fine - like 12V/1.3AH - they still have far more reserve than a cap. You'll just be less likely to jump-start you car! (I got a 1.3AH to replace a 12V drill's NiCad batteries - I might try it....)
But 7AH (7.2AH etc) is an extremely common size and thus cheaper than many smaller batteries.

For what it's worth, Sonnenschein are the ones to get for hot climates, but they are expensive.
Otherwise Yuasa are traditionally very good, and Panasonic get good reviews. And I'd expect Jaycar wouldn't stock s*#t (except for my "blue" NiMHs).
There are lots of crap batteries out there, but that's probably more for NiCads etc in cheap tools, hopefully not SLAs & Gels (only the Sonnenschein is gel).
Last edited by IZU069 on Wed Nov 12, 2008 6:03 am, edited 1 time in total.
modern bliss
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Post by modern bliss »

IZU069 wrote:Your not alone. But keep it in mind next time. Capacitors are purely wank factor, and for people to make a buck.

As I said above, a capacitor has Watt-seconds (or Amp seconds) whereas a battery has Watt-hours (or Amp-hours). A capacitor has thousands of times less stored energy at a higher price.

A battery is like a big capacitor but it also "generates" (ie, converts) its own energy (voltage/current etc).
x2 good to see someone off the 'buy-a-cap bandwagon' that seems to be going around the audio scene atm.
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IZU069

Post by IZU069 »

Good to see someone recognising it! Thanx.
I've commented in other posts etc but seem to get "skeptics of enlightenment".
And I'm not saying caps don't stop lamps dimming, but I'd rather do the alternator upgrade (and solve other problems), or fix the wiring, or use the superior battery instead.
I remember someone laughing at me because I had a $1,000 system in a $500 car - a Kenwood 10-stacker in my Florian (later the V8 killer).
I reckoned they just didn't get it. But I don't get $100's on a capacitor compared to the "as simple" but cheaper battery solution.

The audio scene bugged me for years until a finally bought a copy of a mag ("Australian Incar Entertainment" #76 Jan/Feb 2006) which supported my views - for some it's all about looks. Hence reversed speakers, SIZE, quantity, caps, gold fuses, OFC (especially power cables!), etc.

And the "experience" that led to comments like at a "power output at a supply voltage of 14.4V you get a much higher figure than you would if you measure it at a real-world of 12 volts. Also a cold amp has higher output than a warm one - lower distortion as well." (all sic! ie, verbatim; not cool)
Ha - isn't real world 12.6, or 13.8?
And yeah - 14.4V is 44% more power than 12V. That's high school maths - namely V=IR & P=VI, hence speaker power is proportional to voltage (or current) squared. Let's not mention RMS.

But I am a nerd. Herein I was told so because I used P=V*V/R = 1.5x1.5/1 = 2.25W meaning any speaker of 1 Ohm or more and 3W or more will tolerate a 1.5V battery for polarity testing.
I wrote that after a multi-page discussion on the issue. I agree that programmers etc might find that nerdy, but for people on this site that discuss lamp power, fusing, wiring, ignitions, gear ratios, etc I didn't think it would be that bad.
But compared to that audio installer that told me my Alpine would only tolerate 12V, no, 13.8V - and that's what it got AFTER alternator power went THROUGH the regulator, yep, I am a f*#cking nurd! (I gotta fix its damn display - I reset its power when wiring in a fuselink box and managed to switch on aux & sub etc. Either fix it, or get the sun shining on its dead display!)

Anyhow, I used to have an issue with people unknowingly getting ripped off etc. But over the past few years I have understood that this is the norm and is accepted by our role-model leaders etc. (Or it was until recently - ha f'n ha!)
But I still like to drop a hint now a again for those that don't have that knowledge.
Isn't that what this forum is for?
(If people think I'm only trumpeting, I'll get off and get back to the drums. :) )
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Post by DR_GEM »

Love your work IZU069

I have never EVER used a cap and ive had four amps in the one car producing over 1800w rms

shot two alternators in two months though and didnt have the cash at the time to keep throwing money into it so pissed one of the amps off and run a second battery in the boot

now dropped down to two amps and 8 speakers with a total of 750w rms

im all for METHODICAL approaches - ie use actual physics and general science rules for audio setup - after all, bling doesnt make the thing actually work does it.

ive never contemplated the idea of using the 12v battrey though - thanks for the tip

Mick
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SICKTG
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Post by SICKTG »

i'd like to see how long the battery would actually last someone test it out
IZU069

Post by IZU069 »

SICKTG wrote:i'd like to see how long the battery would actually last someone test it out
How do you mean?
There is nothing to test. It's already been shown that a 12V/7AH battery will hold up about 2,000-4,000 times longer than a 1F cap.
Add the usual engineering fudge factors like -30% /10 & another /10 and it's still 10-20x. And that's for $30-$40.

But if you do want to test, set up a system with a sub-test CD (repetitive) and just CRO the input voltage with (1) Cap & (2) 12V/7AH battery.

It's easy to do. And it's be done - it's just hard finding the results LOL!

Can you jump-start a car off a stiffener cap? (No?)
Can you jump-start a car off a 12V/7AH battery? (Yes)

Has FieldEffect got a thumper? (He's got a CRO.)

Otherwise if TxRotor is keen - and someone supplies a cap - I can do it (though I'll probably pinch my girlFs 1.3AH drill battery - just don't tell her!).
SICKTG
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Post by SICKTG »

reason i say to test is i dont think it will last as long as you think ill test it i have some 12v batterys from alarm systems we used to use spotlighting but i still think the cap will outlast the battery
IZU069

Post by IZU069 »

You reckon a cap will power a spotty longer than a battery?
100W-seconds for 1F? 100W for 10 secs for 10F?
Isn't it intuitive?
Can you jump start a car with a cap of say 1-10F?

Not that this is the type of test we are talking about. We want to compare the hold up time for a voltage sag caused by hi peak power (SPL).
Whilst this peak might be a few hundred amps, and the alternator can only supply 45-85A etc, the main battery has little problem supplying the rest.
But the auxilliary cap/battery is at the amp/sub end to compensate for voltage drop during the surge.
EG - 1V for 5m of 5AWG @ 200A (ie, a 1000W RMS amp).

And this is where the challenge is. Although a battery is a "supercap", how does its voltage retention behave above full voltage (~12.6V).
If charging at 14.4V, how will each dip?
But I reckon that with 1000:1 ratio of total power content, the battery's surface charge (that above 12.6V) should compete with the Cap.
Then there is the much higher ESR of the battery I'd be using, but we are talking sub frequencies - not hi-freq, ie - so 20-40 times slower response is ok.

Let me know how long the spots or whatever load lasts.
SICKTG
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Post by SICKTG »

nar im not saying the cap would be better for spottys im just saying i think the battery wont last long with the quick brst of power it needs to put out thats all
IZU069

Post by IZU069 »

Sick Sick! Phew! As I said, "long-lasting full discharge" is a different situation which the battery wins without question. (Intuitively? If nothing else, parallel plates cannot store what chemicals can store in the same volume.)

So now we get to the crunch,
How does surface charge "capacity" of the battery compare to the "over full-batt voltage" capacity of the capacitor? ...and...
How does ESR of batteries (sealed/gel/AGM) effect performance compared to ESR of Caps?

Despite asking for comparison of the above, I have yet to see anything. And because I'm not into it (I'm into copious sound quality), it's stuff I haven't investigated much.

Through Boony's Yahoo query I found that Caps boast ESRs of .002 & .0016 Ohms (aka 2mR & 1.6mR or 1R6m).
I know that AGM batts are typically 7mR and normal lead-acid & sealed SLA batts (and gels?) are double that at about 14mR.

And I know the "ESR" of wiring - eg 5mR per meter for 5AWG.

I still don't know the impedance of typical amps.
I'd expect "12V" amps to be higher than batteries, but higher voltage amps (those that run 30-80V DC etc internally) could be very low.

So it may be left to testing.

Audiophiles would probably offer the data if caps were best. But they haven't. But that might be because there is so much crap like this going on but no-one finds it. :lol: (Though I am surprised by what of hear get "others" that have hit my posts at this site!!)

Of course even if caps prove to be better than batteries, then there is the issue that the Cap never recharges "high" if the alternator output is less than the amp draw.
IE - 80A alt. Amp is over 100A. Hence alternator cannot maintain its 13.6-14.4V output.
The voltage will drop to 12.6V and eventually flat batteries of ~11.6V. The the car dies. (Or amp low-vollts cut-out and the batts re-charge.)

But that is a no-brainer. The cap merely smooths out the voltage ripples - it won't extend the discharge time (except by seconds, and we are talking hours overall).
Only auxiliary batteries will extend the time from 12.6V downwards.
And those same batteries have the same "capacitance" as Cap for the voltage filtering (subject to our testing etc above).

Of course then there's the biggest rub: If you run caps to avoid clipping because the voltage drops say 1V from 14.4V to 13.4V, or 13.8V to 12.8V, then what the fk will happen when running on a voltage of only 12.6V? Note - this assumes the alternator output is LESS than the Amps average/RMS current/power demand (plus other car loads).
That's what I really love when reading and seeing some of these big systems! But if it's all for looks, it doesn't matter.
I have however been shocked that car amplifiers do NOT run higher voltage rails - I could never understand why the need for 1R & 2R speakers (that's a car audio thing - it wasn't initiated by the audio industry AFAIK).

But one step at a time. First is just the basic question - is a batt better than a stiffening cap as far as performance is concerned?
If it isn't, let's get rid of that rippoff and spend the money on better amps instead!
SICKTG
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Post by SICKTG »

or just get 200 amp alts and an optima battery :wink: ps im keen to try it this weekend ill let you know how i go
IZU069

Post by IZU069 »

The battery is secondary.
It's the alternator that is key. Without it you operate at under 13V.
That's from 1V to 3V less than charging voltage.

That drops output power by about 13% (full battery) to 35% (flat battery) if charging voltage is 14.4V.

And clipping - how do you rate that? 1-3V "more" clipping??
IZU069

Post by IZU069 »

phatty wrote:so where can i get one for under $30?
I just bought a Yuasa NP7-12 (12-7AH) AGM battery for $35 from the Century-Yuasa office in Mulgrave Vic.

That's almost or is cheaper than SLA & Gell Cells but for a much better battery.
I got it to replace a smaller NP4-12 alarm battery which only lasted 23 years (it passed its previous capacity test a few years ago).

I used to love Yuasa back in the old motorcycle wet-cell days, but 23 years!

FYI - the NP7-12 has 25mR internal resistance which is LOWER than a lot of "supercap" specs I have seen!!! (It has 210A ShortCircuitCurrent; and will probably jump-start your car.)
Even the same priced but smaller NP4-12 (4AH) at 40mR beats most caps!
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