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Old 2nd June 2010, 03:03   #16
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Default Class AB vs Class D

Quoting from diymobileaudio.com

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Before we get into a numbers=numbers debate and clinical test bench measurements lets put both an AB and D into the real world... a car trunk.

I prefer class D. I think the transients and dynamic capabilities are better in an equal power standpoint. Here's why... efficiency! a class D amplifier is going to sag the supply much less, the supply WILL sag, I don't care what you have under the hood, how thick of cable you are running, etc.... it's GOING to sag! This cannot turn into a regulated/un-regulated debate either, the regulation in those power supplies cannot "look ahead" and Will not till they get digital inputs or some serious DSP to delay the output and actually adjust for power supply demands "before" the output waveform. Like look-ahead limiting on pro audio processors.

So we have a single kick with a nice sustain, or better yet (gasp) the infamous Roland 808 kick drone (for you hip hop fans) with an AB the initial attack will be just fine, the internal filtering/storage will account for this draw, but what happens when the caps are depleted for the sustain or drone? That's that "tongue-out blaaaaaw" you hear in street beaters.... the sound of a power supply frantically trying to catch up with a limited input voltage to the amplifier. The sound of money for me as I increase my Mouser order for new switching FETs for the poor sap. A class D amplifier will exhibit LESS of this issue, at WOT.

We are talking about running amps hard here, not loafing along. I challenge anyone to hear a difference in modern topologies in the LF domain under light operating conditions, But when you drop the hammer I feel that the difference can be heard (felt), not BECAUSE of the amplifier DESIGN but because of the outside operating conditions of 99.9% of the vehicle power supplies that WE will be running. Class D is better at getting the required power for the job from the battery to the voice coil, remember, it's an amplifier, that's it.

This debate has gone around the pro audio circles for decades now, First with the most popular G/H designs that Bobby Carver made popular in the PM series, all the way up into the more modern Lab Gruppen, Powersoft, Peavey DPC, QSC Powerlights. Early on it was a pretty much traditional output section Class AB, G, H, we were pretty much cool with that, BUT what was discovered is that a traditional power supply (Iron and lytic) making an amplifier way close to 80 lb, sounded more substantial on the bottom end than a switcher supply. Granted the switcher was light and saved money in gas and labor. It also made our AC distro's happier. But for some reason the oldie, recharging beer can caps at 120 times a second, just seemed to do a better job at conveying authority On the bottom octave than a high speed switcher charging a bank of smaller caps thousands of times a second. You saw the switcher PS's on top boxes and sometimes lows, crest 8001's /9001's, Crown MA3600's and 5000's, and QSC EX's still prevailed as choice sub amps. We made a deal, things were still lighter.

Then along came class D output stages. Hmmmmm, with AB the low end was warmer under stress than class D , but you could get TREMENDOUS power on a whim out of class D, it just seemed to control the driver better... and it did with extensive feedback, at this time the power supply Field was evened out, the Crown K series used a traditional PS and a class D output stage, people liked them, then Gruppen and powersoft started the all PWM amps and they still sounded good. A revolution was born, Crest discontinued the 8001's and 9001's, times they were-a-changin!

Of course us road-tired whiners could not go without bitching, we did not like the top end of early class D designs. Under stress the output filtering would drift around from heat. Artifacts made the output sound "harsh" this was compounded with ultra low inductance coils that were just getting lower with technology. Again a preference was born, no class D's on mids and highs, but a PWM power supply was still acceptable there. But to prove us Nancy-whiners wrong.. technology! Component production quality is advancing, switching FETs got faster in the time it took me to write this and better filtering technologies were invented/tweaked. Now you still have whiners but the advantages of class D amps and PWM supplies FAR out-weigh the traditional workhorse design. These attributes are: Insane efficiency numbers, HUGE peak power capabilities, lower weight and smaller chassis saves transportation costs, happier crew, less copper in the distro's, less line sag all around.

And the most important thing that I have always said while embracing the technology that I will adapt in a few words for car audio.

There is no way you will walk into a venue (or a car) and go "hey they have switchers, I can hear it", it just ain't gonna happen. Yes there are different attributes under heavy loading and at the ragged edge, but there is no way in hell you will be able to tell without knowing the room (*car) like the back of your hand and having something to directly compare it to for a good period of time. After saying that and adhering to this theory there is no reason to NOT embrace modern amplifier technology no matter what it is.

Chad
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Old 2nd June 2010, 10:32   #17
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While you do get high power and efficiency from Class-D amps, remember it works at its best at narrow range of frequencies, instead of the full spectrum. Hence the reason why most of the subwoofer amps are made of class-D.

If you require full range of frequencies to be amplified, you'd be far better with a ClassAB/Class-H.

Nitin.
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Old 2nd June 2010, 13:07   #18
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Quote:
Originally Posted by ph03n!x View Post
I am confused, as I remember reading this a while back where @navin had said Class D full range amps fall short of traditional Class A / AB amps.

I am confused as ever, can some one drop in a word? @navinji, has things improved out there?
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Hope you didn't take offence - I linked to post #10 in this thread, as I thought you might have missed it
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While you do get high power and efficiency from Class-D amps, remember it works at its best at narrow range of frequencies, instead of the full spectrum.
1. I am not a professional. I was a relatively active DIYer from the mid 70s to the mid 90s. Still that is over 15 years ago.

2. Like all technology I do expect Class D to improve over time. The gains to be had from the increased efficiency are just too good to pass up. As of today (June 2nd 2010) I would still say a good Class AB amp will sound nicer than an equally expensive Class D amp especailly at the high end (think DLS Ultimate, Audison Vrx, etc...). At the mid end the difference will be less clear just like a $100 CD player will outperform a $100 record player but a $1000 record player will outperform a $1000 CD player.

Some years back the same debate raged between tubes and transistors. A Krell KSA 50 (class A SS) for example was compared to an equally expensive Audio Research VT150 (tube) and many prefered the liquidity of the 150 to the clinical presentation of the KSA 50 but in the mid end (Adcom, B&K, Quad etc..) there were few $500 amps that could compete with the B&K ST140 (Class AB SS) etc..

So yes Class D will get better over time just like it took time for CD Players to get better and in the mid end who knows Class D might already be equal to their Class AB counter parts (I have not heard the Kappa). If we dont keep an open mind and willing ear we will never know.

Lastly that article refers to a lot of Pro audio ear. In Pro audio weight and reliability out weigh SQ.

Last edited by navin : 2nd June 2010 at 13:09.
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Old 2nd June 2010, 13:52   #19
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This could be one of the endless debate. Class AB or Class D it all depends on how much power one has, what is one looking out for from the setup, SQ, SQL or SPL. SQ could be achieved even with mere 200-250RMS class AB, SQl could go anywhere above 500RMS with either class AB or D, SPL could be rated at 1000RMS or more. With greater output its the efficiency that play a major role.
Sound quality wise there wouldn't be much difference between Class AB or Class D. But it all depends on the setup. Class AB amps could sound little more cleaner as compared to the Class D when the subs are crossed anywhere above 80hz and have better low freq. output. Class D amps if not installed right can add a bit of floor noise at times. For example Alpine PDX amps have been notorious to floor noise if not installed right.
Lots of change in circuitry since the time Class D have evolved. These days Class D amps have higher signal to noise ratio, lower THD, better power supply and can sound as clean as the AB.
However I have always used Class AB since last 15yrs on the sub have run'd the sub at 4ohms. Have noticed that the same sub with class D din't that well defined and clean compared to the Class AB. Ofcourse its the quality of the class D amps that also matters.
More important its the right setup of the sub, enclosure and the amp that matters the most. Someone having a Class Ab with low output could do well with the sub that has higher sensitivity. With 250rms class Ab power paired with a sub that has 90db1w/1m sensitivity would sound as loud as the sub with 87 db1w/1m sensitivity powered by 500RMS class D. There is very minimal difference between two but if one has ear for perfection will know what its like.

Last edited by Invinsible : 2nd June 2010 at 14:02.
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Old 2nd June 2010, 14:09   #20
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Thanks folks! @navin, it is your experience that we look up on - no education or guiding star can beat that!

Well, am equally torn between the Kappa Four, Alpine PDX (Both Class D), and Boston GT4100, RF T600-4 (Class AB), and a hoard of others out there. Auditioning these amps before buying would be great, but can't seem to find anyone with them!

And to think I gotta choose components after that... If only life's choices were simpler!

Edit: Did I say am getting a Boston g5 10" to go with my Alpine PDX 1.600 ?

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Old 2nd June 2010, 14:19   #21
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Originally Posted by ph03n!x View Post
Thanks folks! @navin, it is your experience that we look up on - no education or guiding star can beat that!

Well, am equally torn between the Kappa Four, Alpine PDX (Both Class D), and Boston GT4100, RF T600-4 (Class AB), and a hoard of others out there. Auditioning these amps before buying would be great, but can't seem to find anyone with them!

And to think I gotta choose components after that... If only life's choices were simpler!

Edit: Did I say am getting a Boston g5 10" to go with my Alpine PDX 1.600 ?
I wouldn't suggest the Alpine PDX amp for either to power the comps or the sub. PDX does have loads of power but quality isn't that great. Plus there have been issues with noise floor.

Class AB will always be better for the comps. Boston amps are good. You could also look at JL audio HD amps, just that they are pricey.
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Old 2nd June 2010, 14:57   #22
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Edit: Did I say am getting a Boston g5 10" to go with my Alpine PDX 1.600 ?
I dont get it, are you saying that you are planning to get this combo ?
IIRC, the Boston g5's are sold out.
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Old 2nd June 2010, 19:33   #23
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I wouldn't suggest the Alpine PDX amp for either to power the comps or the sub. PDX does have loads of power but quality isn't that great. Plus there have been issues with noise floor.

Class AB will always be better for the comps. Boston amps are good. You could also look at JL audio HD amps, just that they are pricey.
I already have a PDX 1.600, so will be using that. Let me look up the noise floor issue- IIRC, it is to do with improper installs. For the 4-Channel, let me look up the JL too - I couldn't find anything interesting in my budget when I checked last. Thanks a lot for the suggestions.
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I dont get it, are you saying that you are planning to get this combo ?
IIRC, the Boston g5's are sold out.
I have the PDX 1.600, and am going to get the G5 - am getting them from the US and a few a out there (did I let the cat outta the bag?!! ).
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Old 2nd June 2010, 22:11   #24
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I have the PDX 1.600, and am going to get the G5 - am getting them from the US and a few a out there (did I let the cat outta the bag?!! ).
Getting a G5 from the states, lucky you. I tried to get one for myself but couldnt as its too heavy and big. Are you very particular abt the G5 if not why dont you have a look at the JL W6 / W7 subs.
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Old 2nd June 2010, 22:15   #25
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Originally Posted by ph03n!x View Post
And to think I gotta choose components after that... If only life's choices were simpler!

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Boston amps are good..
I second Invisible's recomendation. Of the 4 you have listed I'd take the Boston.
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Old 2nd June 2010, 22:56   #26
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Originally Posted by ph03n!x View Post
I already have a PDX 1.600, so will be using that. Let me look up the noise floor issue- IIRC, it is to do with improper installs. For the 4-Channel, let me look up the JL too - I couldn't find anything interesting in my budget when I checked last. Thanks a lot for the suggestions.

I have the PDX 1.600, and am going to get the G5 - am getting them from the US and a few a out there (did I let the cat outta the bag?!! ).
1. I'm sorry for the gentleman who's carrying the 13kg subwoofer for you.
2. Get the G512-44. I'll exchange it with my Brand-new-in-box G510-44.
You like it compact. And I like it l-o-w. What say?
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Old 3rd June 2010, 00:26   #27
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Getting a G5 from the states, lucky you. I tried to get one for myself but couldnt as its too heavy and big. Are you very particular abt the G5 if not why dont you have a look at the JL W6 / W7 subs.
Would a W6 / W7 come at a deal (steal) as low as a G5? And would they fit a 0.5 cuft sealed enclosure? Let me google again...
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I second Invisible's recomendation. Of the 4 you have listed I'd take the Boston.
Boston it is... Let me look for a deal and a carrier then!!! Any other choices in the same range / budget?
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1. I'm sorry for the gentleman who's carrying the 13kg subwoofer for you.
2. Get the G512-44. I'll exchange it with my Brand-new-in-box G510-44.
You like it compact. And I like it l-o-w. What say?
Its not the gentlemen who carry stuff all the time, sometime it is even those who smoke Black cigarettes You really wanna do the deal? Then I have to talk up some (no, a lot) more to the gentlewoman, ISD charges be damned!!!

Btw, you bugger, never told me you have a Brand-new-in-box G510-44!!!

Edit: Change ya sign, and make it "torque rox!!"...!

Last edited by ph03n!x : 3rd June 2010 at 00:32.
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Old 3rd June 2010, 06:38   #28
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I'll exchange it with my Brand-new-in-box G510-44.
How abt a used pioneer 305 F in exchange
Wish i could bite that G5 off your hands. Incase you plan to get rid of it in future, put me first in line.
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Old 3rd June 2010, 10:14   #29
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Here are a few more 4 channels I am looking at:

JL Audio 300/4 v2 (THD: 0.03%, SNR 109 db, 4x75wrms @ 4 ohms)

Soundstream Reference 4.400 (THD: 0.02%, SNR 115 db, 4x70wrms @ 4 ohms)

Boston Acoustics GT-475 (THD: 0.03%, SNR 100 db, 4x75wrms @ 4 ohms)

I honestly do not know much about the numbers (except the technical description google / wiki throws at you!). But I am somehow liking the JL 300/4 here - I can bridge it to 150x2 wrms and run only the front using it.

I am now all the more scared to start my search for component speakers, what with tearing off so many strands of my hair in one night!!!

EDIT: How is this one? Soundstream reference 4.760

The problem with most amps, apart from everything else is - where will I install them?!! I dont think I can put a 22" long amp under the seat (or can I?), and add the monoblock to it! I am worried for my car's boot space now!

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Old 3rd June 2010, 10:57   #30
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If your budget permits have a look at the Arc Audio KS 300.4. Its great 4ch amp (a Robert Zeff design) with a decent footprint.
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