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Class D Subwoofer?


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DYohn 
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Joined: April 22, 2003
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Posted: October 23, 2006 at 12:44 PM / IP Logged  
No such thing.  A speaker is a speaker -especially a subwoofer - and anything else is marketing hype.  "Class" refers to amplifier topology.
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master5 
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Posted: October 23, 2006 at 2:14 PM / IP Logged  

Hi nouse and everyone else,

I wrote an article on this very topic a few years back, it is edit to be easy enough for anyone to understand the basics of amplifer classing.

Introduction:

Amplifier classification (A,B,AB,C,D etc.) can be misleading due to the fact that manufacturers have been known to periodically invent their own classes or, as a selling point, misapply existing classes. Additionally, the subject matter is quite technical. The premise of this article is to simplify the theory and to help you to understand and define the audio amplifier classification system, which basically describes circuitry types, as well as the advantages/disadvantages of each. I will only deal with the more popular classes, as the others are not generally utilized in our industry.

Amplifiers are divided into several classes of operation which are determined by two attributes: How inherently linear (low-distortion) they are and how effectively they convert voltage into power to drive speakers (efficiency).

Modes:

The nomenclatures of the most common amplifier classes (Class A, Class A/B and Class D) do not necessarily pertain to sonic quality like a test score, in which one is better then the other. In fact, high quality amplifiers are manufactured using all modes of operation. These modes are commonly known in the field as “linear” and “switched”. Amplifiers in classes A, B, and AB operate their output transistors in “linear” mode. Class D amplifiers operate their outputs in “switch” mode.

Class Examples:

Class A: This class is the least efficient of the categories I will cover, (about 25% efficient). One advantage of a class A amplifier is that it offers very low distortion. However, its inefficiency inherently causes it to use a large amount of current, which in turn generates a large amount of heat. With this class A “linear mode” amplifier the output transistors never actually turn off and will even consume full current with no audio signal, possibly as much as with a speaker connected to it when operating at maximum power. This means that a class A amplifier will operate hot even when playing at very low volume, as well as at high levels. Because of all the heat generated, class A amplifiers require very large heat sinks on the amp casings and usually incorporate fan cooling.

Many audiophiles claim pure class A amplifiers sound better than other classes. Although at one time this may have been true, in actuality amplifiers should not produce any “sound”. They are designed to increase power only hence any quality amplifier should perform that function well enough so that even the most critical listener will have difficulty telling one design from another by ear.

Class B: There is no reason to delve into class B amplifiers since it is not generally used for audio. In a class B amplifier, there is a small part of the waveform that will be distorted. Distortion, when describing audio equipment specifications, is any unwanted variation in a signal (compared to the original signal).

Class AB: We realize that a class A amplifier is very inefficient. In most cases this is not the best choice for a car audio amplifier. (It will use excessive power and operate hot). Class B amplifiers will have too much distortion, which is not good for any audio amplifier. The class AB amplifier was designed to be a compromise. A class AB amplifier is more efficient than a class A (about 50%-60% efficient) but without the distortion of the class B.

Some car audio amplifiers that claim to be a class A amplifier are just a “high bias” class AB design. These amplifiers are only class A at very low power output levels. This is not to say that true class A amplifiers do not exist. There are a few high quality (and expensive) mobile amplifiers that are a true class A design.

Class D: Class A amplifiers are very inefficient. Class 'AB' amplifiers are also inefficient but are more efficient than class A amplifiers. Class D, also called switch mode or digital amplifiers, is the most efficient method (up to 90%) and is the least linear, unless it employs sophisticated corrective signal processing. It is predominantly used in less critical applications where fidelity is not as much of an issue but power output is, such as with dedicated subwoofer amplifiers or “mono blocks”. However, there is a new breed of digital amplifiers that use Class D (or variations thereof) for high-end applications.

Summery:

Although I did not cover some of the more technical aspects you should now at least have a basic understanding of the differences between amplifier classes. This general information can come in very handy to promote to the customer your professionalism and product knowledge. However, keep in mind that the ear of the subjective listener is the final judge of what sounds good, not the specification sheet.

Copyright © 2003 by Ron Gold. All rights reserved including reproduction in any form, whole or in part, without expressed permission of the author.*

*any or all of this info may be shared publically or privately without recourse for educational and/or non-profit purposes only.

aznboi3644 
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Posted: October 23, 2006 at 4:01 PM / IP Logged  
Anyone here heard of CLASS T amplifiers???? This amp claims to be a class T
http://www.techronics.com/index.cfm?fuseaction=product.display&Product_ID=1110
master5 
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Posted: October 23, 2006 at 5:26 PM / IP Logged  

Hey aznboi..waz up?..haven't seen ya in a while.

Yeah..a class "T" amp. The T stands for Throw your money away..

lol, jus kidding, I will look into it.

I am reminded of the days of "Y2K compliant"..Remember that hooey? I think everything from wrist watches to coffee mugs had "Y2K compliant" stamped on the package..what a gimmick ,all in the name of capitalism..but you gotta love it. I think marketers are almost as bad as laywers...it's a close call.

Another sham..."Digital ready Speakers," I think I still see this one.  Unless you were a cyborg (perhaps way in the future) you wouldn't really get much enjoyment out of listening to digital information. It appears we mammals are designed to hear and enjoy analog information.

And how many times I hear installers say they can't work on a car because it has a "fiber optic antenna". I guess they don't understand that AM and FM is transmitted in analog, but, such is this world we live in..the "mis" information super highway.

Oh...and the amplifier the size of a matchbox crammed inside with the CD mechanism, the tuner and other circuits puts out a clean 35 watts x 4. That is not true BTW, but so many think that when I am trying to explain to them why they need an amp on thier mids/highs.

Have a good one and I will see about this class "T" amplifier and get back.

haemphyst 
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Posted: October 23, 2006 at 5:37 PM / IP Logged  
Actually "Class T" is a true amplifier class. Manufactured (rather invented and licensed) by Tripath, out of San Jose, I do not actually know the differences between T and D, but there are significant differences. While it is a switch mode amplifier (Class D) at heart, it is diferent.
JVC licensed Class T from Tripath, and they truly did cram a REAL 35 X 4 into a head unit, and I might add, it sounds pretty damn good for a deck! If I am not mistaken, it uses the TAA4100A chip, and if you'll notice the 65W @ 2 ohms, saturated square wave specification, and if you'll remember back to our recent thread regarding low power blowing speakers, and the point made regarding "Crest Factor" in there, half of that is 32.5 wpc RMS. Yes, it can be done, I have heard it, and as I said, you'd be "wowed" by the overall sound of this deck.
It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."
master5 
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Posted: October 23, 2006 at 5:48 PM / IP Logged  

haemphyst got here before I did.

Was gonna post basically the same thing.

I have no hands on experience with a class t amplifier yet but hope to soon.

Seems to me it is a modified class D. The T has to do with the trademark "Tripath"

You can google "class t" and find a ton of info.

As far as that 35w rms crammed into a head unit and somehow not generating enough heat to melt the dash...well that is impressive. I have not used that particular JVC but I am a JVC dealer and like the product (no debates please, its just my opinion)

We do use a model of pioneer that you can hit a switch and do some programming and it ups to RMS power (so they claim, I can't really hear that much of a difference but it IS a nice sounding head unit)

When you program it for RMS you are supposed to cut a jumper acc wire and run it to the battery or a high current source (ie: heavy ga. @ ignition harness).

Amazing how much I learn everyday. Technology changes so fast I don't even think I should reply with advice anymore....nah, I will. Even if I am wrong it's still a learning experience.

But more than being "wrong" I really just find out something that I never even knew exisited.

Keep the info coming. Later all.

master5 
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Posted: October 23, 2006 at 6:14 PM / IP Logged  

Oh, another memory just came up. I think it was back when I was like 8 years old. I used to hangout at this high end shop near my house. I would sweep up and pass them tools etc. in exchange for being allowed to watch them.

I remember they were doing a system in some famous tennis players rolls royce corniche convertible. They were installing this system made by K-40. (yes, the same one that makes the radar detectors.)

It came with a small amp "module", 2 - 6 x 9 "subs", and 4 little mid/tweet pods.

The amplifier was so effiecient (so they clamed) that you did not need to connect at the battery, The little 18 ga. wire at the trunk light would suffice, as long as constant 12v was there.

The system operated at 1 ohm so this is a reason they claimed they were getting alot of power out of it.

I have not seen one of these since so can't vouch for the reliability.

I also remember our favorite company  BOSE (no highs, no lows) had a system you could buy for any car. It had a thin amp module you put in the glove box and it had slider controls for "spacial" and level etc. I think that was 1 ohm also, I don't remember much else about that.

At the time I didn't know what a pinswitch was. But that experience as a kid is what kept me interested in this field. I was close to changing careers a few times but am always drawn back.

I love the "controversy". Either that or getting to hack up all these cars?  It's all good.

aznboi3644 
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Posted: October 23, 2006 at 7:27 PM / IP Logged  
Whats up master...how've you been.
Well I haven't reran those wires yet as it is 35 degrees here in southern indiana lol..gotta wait till a warmer day
master5 
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Posted: October 23, 2006 at 8:20 PM / IP Logged  

azn, you have the opposite problem as me. It is usually too hot where I live to work outside.

Luckily, at least for now, our shop has ac. This is a good time of year for us. Only 80 degrees and lower humidity, But it doesn't last long and always a threat of a hurricane, although this year it's been quiet so far.

I did a side job sunday and the guy gave me a brand new 300w, 150w rms sub he had in his trunk. He just got the car and didn't even know it was there. I went online and found some specs and ts parameters..perfect for my next "experiment".

I am going to hook it up on my bench in a vented enclosure to a 60w, 30w rms @4ohm kac322 tiny kenwood amp I had lying around forever. With a 100a power supply to the amp I am going to use a test tone cd, and take some output readings (current, voltage etc) and using that with ohms law and watching the sub response find a frequency that "moves" that sub.

I am going to let it run full volume with the gain also full and see what I find in the next morning.

If that woofer is toast those who stated "you can NEVER blow a sub with a small amp" will have a little explaining to do.

But I have a feeling it will be playing still (the power specs on the amp/sub are so far apart that the amp should not "theoretically" be able to toast it from what I gathered recently on the topic)) or the amp will take a dump first. Should be interesting.

I'll keep you posted. If the sub survives maybe I can try it again with a class "T" amp. lol

see ya later

aznboi3644 
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Posted: October 23, 2006 at 8:46 PM / IP Logged  
Can't wait to see the results...but i'm sure that it'll survive.
Could you post the make and model of that sub??
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