Axiom Home Page Forums General Discussion Home Theater bi-amping with m80s

I am getting a onkyo tx-nr5007. At a 145w per channel at 8ohms, can I bi-amp my m80s?

http://www.axiomaudio.com/tips_biwiring_and_biamping.html

yes you can but I don't know if you will see a difference, I try with my m80 and Onkyo receiver but didn't notice too much of a improvement

Hey, you must be a regular. You posted that before any of us long termers did!

sorry just bored at home and spend too much time on the forum today!!!

How the heck do you think I got 13815 posts?

ok cool. Theoretically what would the advantage be? I'm not going to be using all 9 channels, so I figured it wouldn't hurt.

lol sorry just noticed the link.

Well we know it's not because having two kids leaves one with little to do all day. Which begs the question... how HAVE you racked up 13815 posts exactly???

Alex, you said you didn't see "too much" of a difference, what difference could you tell?

Well theoretically speaking, some advantages I can think of are :

A. You will have the peace of mind in knowing there aren't any more wires that you could be running to your M80's.

B. In case a tornado rips your house apart, your M80's will be better secured to your reciever than those of us who do not have our M80's bi-amped.

C. You can remove those gold connectors between the 4 posts on the back of your M80's and use them as ear rings.

I am not a expert , some guy here a pretty good here, I can not even tell, I try both and didn't see enough improvement to stick with the bi-amp, the best improvement I did with m80 was when I try with a amplifier (outlaw mono block)

Alright. I have always heard that doubling the watts to the speakers only raises its max output by one db, so I never really cared all that much about power to the speakers Lately tho I keep hearing about "headroom". Can't say I really know what people are talking about with that, but I figured if a 145w gave you more headroom than 100w, wouldn't bi-amping give you more, and wouldn't that be better?

This doesn't give you any more headroom, and doesn't double the power. There are several good discussions of the math on this if you do a search on biamping. Look for posts by ClubNeon.

sorry SteveP using your thread

heih! Kcarlile, can you explain me (newbie) what Headroom mean!!!

Thank

no prob man, was going to ask myself, thought I'd try and look it up first tho.

Ah I can't believe you regulars just don't scream when people like me ask questions that have been asked a thousand times. Poor Johnk. I just read like 20 different posts of him explaining bridging and bi-amping, for people like me. From now on I will search the forums before asking questions. Thanks everyone.

Steve, we can always make it 21. No, you can't bi-amp with a receiver, despite the terminology that some of the manufacturers shovel out. A receiver has only one amplifier with several channels of output transistors to distribute that power. Distributing the power through two sets of output transistors rather than one doesn't double the power as some imagine and can't increase the power available from the one power supply section in any amount.

lol I'm sure youve done it more than 21. I got it now. learned a lot tonight. Just learning ohms law answers a bunch of questions I had in my mind. Just in case any other newbs are reading this - search the forums first. I didn't even notice that you could before tonight. Anywho thanks again everybody.

as long as your receiver is rated for the 4ohm load and you have an extra set of speaker cables, then go for it. your manual will tell you how to do it; it will be in the speaker setup or type in the receiver menu. you will be giving up a pair of speaker outputs, usually the surround backs but with this new receiver you may be able to choose the height or width channels. you will either like what you hear or you won't or you won't hear anything but as long as your not hurting any of your gear, it's your stuff, don't let folks talk you out of it or try to make you feel bad for wanting to try it.

if you do try it, let us know what you think, you have to either like it or not, no one else!

No. Your manual will clearly state not to bi-amp 4Omh speakers.

Headroom means the spare power (JohnK, ClubNeon, and FredK will kill me over my explanation here) that is available over average power usage/volume level/program material. In other words, how much power is available for peaks in the material.

Actually, I think thats a great explanation. Most would agree that headroom is a good thing. Some just think you need a lot more than you usually do.

Sure, Ken; that's fine. Unless the source material is one of those uniformly loud pop CDs with practically zero dynamic range(such as the one described in the study in my AES Journal that I've mentioned before), there has to be more power capacity than the 1 watt or so which is used at a comfortably loud average level. But if say 20dB(100 times the power)of headroom is enough for even the most dynamic classical or other material, buying still more is meaningless. Unused headroom is simply that: unused.

Uh oh; typing lag has reared its ugly head again.

agreed, that's why i said make sure it was rated (in everyway you need/want to use it at 4 ohms) and that it wasn't going to harm the receiver or anything. that's also why i like to say folks need to do research on their gear, i.e. reading the manual.

so i'm with you on your response!

We all gotta die of something Ken. Might as well be by an angry JohnK/Clubneon/FredK mob rushing your HT room with torches screaming, "BURN THE HEADROOM BELIEVER, BURN HIM"!!!!!! Then stringing you up by HDMI 1.4 cable to make an example out of you for the world to see.

At least that would be an original death.

John (or anyone who knows),

Can you elaborate on this some? I've always had trouble wrapping my head around how this actually works. If an amplifier's roll is to increase the amplitude of signal that represents sound in a channel, how do these transistors play into this when there are several discrete channels with their own independent signals? And how does the newer Denon receivers with assignable amplifiers fit into this?

The transistors are valves which let the central pool of current flow from the power supply to the speaker behind them. So one pool of power, but multiple outlets. If you open all the valves at the same time the single power supply may not be able to feed them all.

The newer receivers with assignable channels, just have multiple speaker connectors behind one output device. A relay selects which connector gets the power.

So the transistors work like flow control valves then? Where do they get their command signal from? What does the amplifier do? I always thought the amplifier was the control point for power to the speaker, by your description, I obviously wrong.

depending on the configuration, transistors also amplify the signal as well as controlling the flow...

Yeah, Mike; the output transistors can be viewed as valves. They have no power of their own, but their function is to apportion the required amount of voltage from the central power supply section out to the speaker. Amplifiers have a fixed gain, generally around 28-30dB, which means that the incoming voltage is amplified about 25-30 times. Let's say that a particular one has a gain of 29.03dB, an increase of 28.3 times. If at a particular instant in time 0.1V is input on a channel, the output transistors have to add enough voltage from the power supply section for the designed amplification factor, and the output to the speaker is 2.83V. If the impedance of the speaker is 8ohms, this results in 1 watt being used(Ohm's Law, power equals voltage[squared]/impedance). As the voltage input varies constantly during music, so does the amount of voltage that the output transistors have to draw from the power supply section.

Those receivers with assignable channels(not assignable amplifiers)can just change what source of voltage is sent to the assigned set of output transistors. For example, the usual back surround channel can instead be sent the front channel voltage signals. The designed amplification then takes place as usual.

it's called a biasing signal. to forward bias a transistor....

here is a 57min lecture on the topic

http://www.youtube.com/watch?v=PSdHf6yozyc


i skimmed though the lecture, it seems to answer most of the amplifier questions i have been seeing on the board as of late.

I studied transistors as a teenager and from what I remember, it's a 3 wire gadget where one wire is for the control voltage which is a very small current. The 2nd wire is for a higher voltage. The 3rd wire is a common wire for both, which is also the output wire from the transistor.

If no current flows in the control wire, then no current flows through the 2nd wire to the output. When current flows through the control wire, the transistor causes a copy of that current to flow through the 2nd wire to the output wire, but at a much higher voltage, thereby causing amplification.

I'll watch the video when I get some spare time Dakkon, thanks.

This is starting to make more sense to me, but I'm still fuzzy around the relationship between the amplifier and the transistor(s).

Which one gets the signal from the pre-amp section; the amp or the transistor? Or, in this case (channel output controlled by transistors) is the 'amp' just used for volume / gain control?

If I were to draw a block diagram with the ins / outs, what would it look like from the sine wave representing channel frequency to the speaker driver?

I searched "mosfet" at Wiki and am trying to get through that.

Thanks for the clarification on the assignable channels. I have not read the manual yet, but kept seeing "assignable amps" in the big AVS threads for these AVR's.

OK, you've made me curious.... Why would a teenager do this?

Me thinks we all should have studied this as a teenager (in high school) and then there'd be more than 3 or 4 people on this board who have a clear grasp of the way it all works! Lol

I think amp is probably the total unit of power supply+output transistor, not a specific component in relation to the output transistor. Am I correct in that?

So what JohnK has been saying is that power amps (ie, not integrated or receivers) have one power supply per output transistor?

Some power amps are designed with a supply per output device, but others (like the A1400-8) aren't. There's nothing inherently wrong with a design based on a single power supply. But more often than not, the single supply isn't big enough, and dividing it among several output devices isn't ideal. But then some multi-channel amps, use one power supply per channel, but in an effort to squeeze that many transformers in one chassis, they are all under-sized.

It's all about the over-all design, and there are many ways to do it wrong.

Ken - I had the same epiphany a little while ago while I was recovering from a near death experience trying to run a mile under 6:30 (didn't make it either, dammit; 6:34).

The epiphany being that the "amp" per John's description, is the whole process: power supply, transistors, power rails, etc.

But regardless of that, a multi channel system will still need a controlling device to regulate power to each channel's output, dependant to its own discrete input signal.

Study? As a teanager? You mean like with, gasp...books and stuff?

michael_d,

The controlling device is your (stereo or multichannel) preamp--either a separate one or the preamp section inside your AV receiver.

The level control in the preamp meters out the low varying voltage to its pre-outs, depending on the level setting, then to the amplifier inputs. Where you set the "volume" control adjusts the preamp circuitry to send a signal that will vary (with the dynamics of the music signal) from a few millivolts to perhaps 1 volt or more. As JohnK mentioned, most amplifiers have 28 to 30 dB of gain, which means that if the amp section in your outboard power amp or inside your AV receiver is getting a 1-volt input signal, it will be close to delivering its full output to the speakers.

Alan

If this is correct, it makes John's argument merely one of semantics and fairly misleading, at that.

I agree with him that biamping in the receiver makes no sense, but not because it's drawing from a single power supply. No, it makes no sense because biamping with ANYTHING not including an outboard crossover doesn't really do anything.

It's funny, I never read assigned books, or did my home work as a teen (heck, pre-teen). But I was always studying something. All my teachers told my parents the same thing, "Chris could get straight "A"s if he'd just apply himself." The thing was, grades didn't motivate me, an A meant nothing. I'd rather be learning something which interested me. I'd pick up the Math, or English, or whatever as I needed it (to understand my own experiments*, or when writing stories).

*I invented Trigonometry one summer when I was trying to figure out how to programmatically rotate a camera by only using 3D coordinates of it's location, and where it is looking in space.

Lets break it down how well designed, multi-channel amp with a single power supply differs from a well designed, multi-channel amp with multiple power supplies differ when "bi-amping".

An amp with a single PS can provide X number Watts into any one channel, but divides those Watts between all available channels when more than one is active. If your goal is to put more power into a speaker, it isn't going to happen. You get X/2 Watts at most to each channel when driving two outputs at the same time (so X/2*2 or X).

An amp with multiple PSes can provide X/C Watts into each of it's channels, where X*C is the max it can pull from the outlet. If you bi-amp in this case, you can get X*2 Watts into the speaker.

If you're comparing something like the Axioms A1400-8 and Outlaw's 7700, the numbers work out like this:

A1400-8 driving one channel at max, it's getting 1400 Watts.
A1400-8 driving two channels at max, they're each getting 700 Watts for 1400 Watts total.
A1400-8 driving seven channels at max, they're each getting 200 Watts for 1400 Watts total.

7700 driving one channel at max, it's getting 200 Watts.
7700 driving two channels at max, they're each getting 200 Watts for 400 Watts total.
7700 driving seven channels at max, they're each getting 200 Watts for 1400 Watts total.

Is that making sense?

It makes sense, but it still makes John's argument a red herring.

Also, there's no way a tweeter's going to take 200 watts. It would probably catch fire and melt (hell, a midrange might too), which is my understanding of why bi-amping doesn't double the amount of power to a speaker.

But when "passive bi-amping", you're still using 200 Watts into both ends of the speaker. When driving the tweet/mid their high-pass filter is turning the low frequency signal to heat, and woofer side the low-pass filter is turning the highs to heat.

But you're NEVER using 200W!
Of course, we're in agreement here...

I think, as the unofficial, self-proclaimed, fearless leader of the M60's posse......it's time I chimed in here.
You all, are wrong. The term "bi-amping" when used in reference to the M80's, simply means: two amplifiers. One amp for normal use, and the other amp wired in, so when the first amp overheats, or shuts down.....with the flip of an A-B type switch, the second amp takes over, so no listening time is lost.

M60ti's, M60v2's, and M60v3's, all Rule!

In order to drive our M80's to 80 db's we only need about 1 watt of power. This is what has been explained to me on here, I'm not educated in the math that gives us this figure, so I'm just repeating what I've read. So using the 'water' model from the thread in the 'Technical Questions' forum, I'm picturing the faucet turned on just enough to let 1 watt flow down the pipe to my speaker. Which creates 80db's worth of output, so most people won't be opening that faucet (volume knob) much further than that.

However, if you turn the volume knob on your reciever up 100%, then the faucet is wide open, so if it's a 200 watt amp, then wouldn't there be 200 watts worth of power flowing through the pipe to the speaker?

If not then how could they call it a 200 watt amp?

I didn't completely understand his statement either. Most people won't use 200W, but it's possible some will.

The 1 Watt figure, isn't really math, it's a measurement. Axiom puts 1 Watt of power into the speaker, holds a mic 1 meter away, and sees how loud it is. It's known as the speaker's sensitivity. The M80s actually get 91 dB from 1 Watt.

Alan,

Thanks, but I’m still confused. When I referred earlier to the sine wave input signal I was referring to what you are, the pre-amp output to the “amp”. The “amp”, whether it is an actual physical device or component in the receiver (amplifier or transistor) or if it is working sum of all components is where my confusion lies.

John has stated that a receiver has one power supply and one amplifier. He also states (and so does Chris), that these “transistors” act as gates for current flow to each channel and that share a common “pool” of power which is supplied by the power supply.

I need a block diagram. Anyone know where one might reside on the web?

Oh fine, just ignore that statement.

What I meant is that RARELY will anyone be using 200W at anything more than a brief peak, if even that.

It is my understanding that the transisters "are" the amplifier. There would be one power supply that feeds the transisters that amplify the pre-amp signal. There would be one transister per channel.

Please correct me if I'm wrong.

The transistors do cause an amplified version of the input signal to be output, yes.

Technically, in Class AB, and D amps, there are a pair of output devices. One which handles the Positive portion of the signal and one which handles and Negative. Additionally, more than one pair can be used on high-output amps. You asked.

Ok thanks, but in the simplest terms what I said is correct then.

OK, I'm curious. Why would the negative be an output. Negative should be an input from whatever electrical user, for a path back to ground, no?

Ok, I see what you mean then.

If my room were about 4 times as big as it is, with lots and lots of room treatments, bass traps and the like, and I was throwing some huge party with tons of people dancing around drunk out of their minds screaming, "turn it up man"!!!! Then I could see possibly maxing out the volume knob on the Emotiva and really giving it everything it has. But under normal circumstances, then I'm with you, most won't.

But I wouldn't say NEVER either. After all Alan has already told it before on here why the A1400 was designed. Because Ian was tired of his Denon dedicated amps (which if they were the Ultra's, put out 300 watts into 4 ohms) shutting down on him at his parties. So he built an amp that wouldn't disappoint him.

Sounds like I need to be at his next party!!!

An amplifier is a combination of one power supply section feeding its voltage output through one or more channels, each with its set of output transistors(typically two per channel, running in parallel)to add the necessary voltage gain to the incoming signal at any given instant in time. So, both are parts of the amplifier, it's not one and/or the other. The gain is fixed, in the amounts described; there is no gain control in audio amplifiers.

source->pre amp->amp

pre amp->input stage of the amp which is the base of the transistor. as the pre amp voltage increases, the voltage seen on the base increases so the transistor conducts more, or becomes more forward biased..(this is shown in the video i posted) and this is why you can push the amp into cut off if the input voltage is to high, you will push the transistors into saturation(exceeding their normal operating permitters)...

the negative of the transistor, is often the common ground. which is also the (-) terminal on the amp. the (-) has to be an output, because you have to ground the speaker, and with the (-) as an output it puts the speaker ground or (-) terminal = to the amp ground.


as Chris stated the power supply is one of the most important sections of a home audio amp, that is where the power is.. so you can ONLY get the power that that power supply can provide... if you have a 500W power supply you will ONLY get a total of 500W out of that amp. even if the manufacture says each channel is "rated" for 500W..... this is why receiver ratings are misleading many times... the power supply for the receiver can not provide 135W X 7.. even though each amp in the receiver can product 135W, you WILL NOT get 135W to each channel simultaneously.

The speaker doesn't just push out, it pulls in too. The audio signal is alternating current. For parts of the signal which are above 0, the P output device is active, for parts of the signal below 0, the N output device is active.

Actually, the P device is run slightly into the negative (even though it is very inefficient to do so), and the opposite for the N. This minimizes zero-cross distortion.

between the few EE types of us Chris, i think most of the questions will be answered.....

I expect everyone to be building their own amps soon.

Electricity is so damn unique, nothing acts like electricity does. I wonder how long it took the guy who discovered electricity to understand it???

Wasn't he that guy with the kite and the key that tried to get hit by lightning.

I think it was the guy who tried to play with his eel.

He should've listened to his mother.

Thanks. I'm really not trying to be a pest and am just curious. I hope you don't think otherwise with all my silly questions.

Considering that, I've been trying to find information regarding the operation of a voice coil to describe just how electrical current flows through the windings to position the driver to the fixed magnet. I'm not having much success. Can someone either point somewhere, or explain this?

It's just an electromagnet, if you want more information, search on that.

An electromagnet, like any other magnet will attract differing poles, and repel similar. But an electromagnet has it's poles, and strength determined by the electricity flowing through it. More flow, a stronger field, reverse the flow reverse the field. So when it is next to the fixed magnet it'll either push away from it, or be drawn to it, with various strengths following the signal.

Mike, it depends on how much detail that you're looking for. Here's a very brief explanation. Here's more detail, although still not exhaustive.

Thanks John. I am familiar with electromagnets, but on a much larger scale; like multi mega watt generators. The whole reversing electrical current through the coil is what was throwing me off. I think I just need dakkon to refresh me on electrical theory.

Thanks for the links. They are very informative.

in a generator you have a constant 60hz, the frequency is dictated by the prime mover.... in the voice coil, the frequency is controlled by the source, the Cd, SACD, what ever it may be, and in the digital world, its a stepped DC, think of it like a constantly moving CRDM, the Digital-analong converters smooth the signal, basically a filter circuit. Actually the CRDM pretty much works the EXACT same way a voice coil does with the electro magnetic filed. but rather than the clamping force, you have the electro magnetic field, with a rare earth magnet behind it, for arguments sake when the electro magnet is + in respect to the rare earth magnet, it will "push similar poles" when it is - it will (pull dissimilar).. as it pushes and pulls it disrupts the air, creating noise...



now, i am assuming you still remember how CRDMS work :p

reactor control rod drive mechanism.... it's been a couple decades since I've been around one, but i have some recollection. thanks, that helps.

figured you just needed a familiar terminology

rods 'n acid man....lol - i don't feel so alone round here anymore.

most of that stuff is still fresh for me, as i just got out last august, so not even 12 months for me yet..... and on a Sub, the electricians knew almost as much as the RC divers did... also i was cross qualified to help the Rc divers out underway.....

they asked me one time to help with maintenance.... mind you ONLY 1 time, it was quite scary for them...

if you have a facebook account look up "Shit you don't say if you are a Submariner"

i'm sure you can appreciate many of those stories...

So if I get a certified letter proving that I've read through this entire thread (and all subsequent links) and send it in, can I receive some sort of degree in the mail?