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

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.