Dynamic Headroom?
Thread Starter
1000 Watt CAFz'r
Joined: Oct 2003
Posts: 1,783
I saw a thread on another forum that brought it up. The responses were...um....American. 
So I thought I'd post a similar question here to kickstart our brains and combat the winter blahs.
Lets get this rolling.
1.) What is headroom?
2.) How does it influence sound quality?
3.) How much headroom should a system have?
And we're off...
Adam
So I thought I'd post a similar question here to kickstart our brains and combat the winter blahs.
Lets get this rolling.
1.) What is headroom?
2.) How does it influence sound quality?
3.) How much headroom should a system have?
And we're off...
Adam
Guest
Posts: n/a
1. It's how much space you have for your head.
2. If you don't have enough your head has to be crooked thus skewing your image as one ear will be blocked by your shoulder.
3. enough so the above problem isn't a factor
[img]graemlins/@bow.gif[/img]
2. If you don't have enough your head has to be crooked thus skewing your image as one ear will be blocked by your shoulder.
3. enough so the above problem isn't a factor
[img]graemlins/@bow.gif[/img]
Head room is the amount of amp power the system has in reserve when you need an extra boost, for example a heavy bass note. Picture this:
If you drive a 4 cylinder motor at 8,000 rpm, it works but not very well. If you need more, to pass or go up a hill you can't. If the drive the car at 4,000 rpm you can still pass, go up hills etc.
That's why some systems have just as much bass at 1/2 volume, as 3/4 or full volume. The amp has run out of headroom. That's why level matching is so important, in SPL people "burp" their systems to maximize their amp, but if they run it for longer, there's no headroom, not getting anymore SPL.
Cheers, I hope this helps...
If you drive a 4 cylinder motor at 8,000 rpm, it works but not very well. If you need more, to pass or go up a hill you can't. If the drive the car at 4,000 rpm you can still pass, go up hills etc.
That's why some systems have just as much bass at 1/2 volume, as 3/4 or full volume. The amp has run out of headroom. That's why level matching is so important, in SPL people "burp" their systems to maximize their amp, but if they run it for longer, there's no headroom, not getting anymore SPL.
Cheers, I hope this helps...
Yankee
Joined: Oct 2003
Posts: 3,599
2.) How does it influence sound quality?
Head room, per say, is unused power and will have no affect 99% of the time (I am assuming that the operator is not trying to max out system volume). But when operating at a reasonably high output and a sharp transient comes to play (drummer hitting the rim, tympani, snapping of fingers, NOT cannon shots) there may be a need for more wattage than the amplifier rated for, the duration will be a brief period (WELL under 1 sec is a good SWAG).
This is where dBa can be discussed, 3 dB of head room would mean the amp would temporally provide twice its rated power. This is A LOT of headroom and if I were designing an amplifier I would give it maybe 1 dB of real headroom. When a discussion of watts or current is being conducted from a manufacturer’s point of view it is all about thermal management (engineer) and marketing (more headroom I can claim the more I will sell). To engineer an amp with more headroom that means better transistors (not more transistors) and better heat sinking (more heat transfer surface area near the transistor or a heat transfer grease is in order not bigger sinks). There are different ways to attack this issue from an engineering point of view, this is how I would given I want the device to remain affordable.
I am pretty sure there aren’t automotive headroom rating standards to fully define how long the transient will last so comparing headroom on brand y to brand x may be somewhat meaningless. This is claimed headroom and could fall into the category of false manufacturer claims unless we are talking about a company with an established engineering reputation that could be harmed by not meeting claimed specifications (McIntosh comes to mind, their brand name hinges on the quality of their products)
BTW there is no such thing as amplifier Wattage RMS it should be called average amplifier wattage rating, there IS such a thing as amplifier Voltage RMS though.
Yankee
Joined: Oct 2003
Posts: 3,599
3.) How much headroom should a system have?
My opinion 1 dBa of headroom is good enuf
50 Watt CAFz'r
Joined: Mar 2003
Posts: 309
So, wouldn't max power/peak power have some sort of influence on headroom?
If that's the case then Rockford designs their amps with around 5dB of headroom (if they actually do the peak wattage they print on the amp). 300W amp, 900W peak.
If that's the case then Rockford designs their amps with around 5dB of headroom (if they actually do the peak wattage they print on the amp). 300W amp, 900W peak.
Guest
Posts: n/a
I just don't understand it..
I have spent countless (and too many) hours trying to figure out how to get some of the power ratings that some of these companies print on their head units and amplifiers. I have created very application specific waveform tracks (a single 1kHz sine wave cycle for example) in hopes that perhaps the amp will be able to provide more voltage for an instant. But to no avail. In fact, all the testing has showed up is that most power supplies take a moment to catch up to the needs of the amplifier, and my AC/DC power supplies take even longer than the amp does.
Dynamic Power, in my opinion, is basically how far away from peak power you are at a specific listening level. If you have the system very quiet, you have more dynamic power left.
There are amplifiers, like Bob Carvers Sunfire home amps that use a stored energy display rather than an output display. The analog meter showed how many joules of energy were left in the amps storage capacitors. Given this though, then perhaps Dynamic Power is the energy stored and available to the outputs before the power supply can catch up and refill it.
The amount of power an amplifier can produce is limited by two things, How high the rail voltage is (or can go) and how much current the amp can supply into the load. Let's assume the load is fixed, and for arguments sake, is one ohm. If we have an amp with a rail voltage of plus and minus 50Vdc, then we have and output waveform peak of about 50V. There will be some minute losses due to the biasing voltage required to activate the output device and some losses through the various components of the amplifier, but we are going to assume there are negligable for now. So, we have a peak voltage of 50V for our sine wave. This means the RMS voltage is 35.36Volts, what you would measure with a True RMS voltmeter, and the only number you can use to calculate power.
As an aside and a reminder, Power is defined as:
The rate at which work is done, expressed as the amount of work per unit time and commonly measured in units such as the Watt and horsepower.
A Watt is:
An International System unit of power equal to one joule per second.
So, there we have it. The time basis for measureing power, represented in Watts is one second. So instantaneous power can't truly be measured in Watts, as they already have a time base of one second, not a portion of it.
Now, lets assume that I don't mind if we through the laws of physics out the window, and we decide that there is a chance that we can measure power at single instance in time. So, let's look at the point in time where a sinusoidal waveform has reached the 50V level. At this instant in time, we have an output of 2500VA (VA is Volt/Amps and is very similar to Watts, but without the one second time base).
If we were to use the definition of Watt though, we need to revert back to using the RMS voltage level over a given amount of time (one second). We get almost exactly 1250 Watts of power from an amplifier with a 50V rail, driven to the brink of clipping, into a one Ohm load.
So, back to the dynamic power discussion. I still don't know how to measure or quantify it, other than to say that some amps jam harder than other. But, there is more explanation...
The other limitation of an amplifiers ability to produce power is it's ability to pass current to the load. If the amplifiers power supply can't supply enough current to the load, the rail voltage will drop, just as your lights dim as your amplifier attempts to draw power from your electrical system.
If an amplifier design has enough reserve capacity (energy stored in capacitors for example), then it could draw on that energy to provide current to the load device before the power supply falls behind.
Anyways, I still don't know how to measure it, and trust me, I have tried and tried.
Oh, one last thought. There are some amplifiers that have power supplies with an output voltage that tracks (or tries to stay ahead of) the required output voltage. This reduces the overhead voltage, allowing the amp to run cooler. Mr. Carver calls this the tracking Downconverter.
I did some reading on the subject, while reviewing Bob Carvers Sunfire amplifier design and found out more about where this theoretical dynamic power comes from. In a side-bar from one of Mr. Carvers white papers, he mentions that 'testers' (clowns like me) will set the amp up with a dead short, the feed a pulse of 500 microseconds, 20 microseconds or even one thousanth of a second into the amp, the measure the output current. The current will be quite high, but not sustaneable (of cours. Mr. Carver refers to it as a parlor trick (which I just love!). He reminds us that power is the result of the square of current over resistance. Since the resistance in this example is functionally zero, the amp produces no power. However, testers go on to claim that the amp can produce huge amounts of current, and therefore huge amounts of power. Marketing and games... I read the rest of the Sunfire website.. very smart lad.
Anyways, I am tired, have more products to review and want to watch some Rally Racing. Goodnight all...
I have spent countless (and too many) hours trying to figure out how to get some of the power ratings that some of these companies print on their head units and amplifiers. I have created very application specific waveform tracks (a single 1kHz sine wave cycle for example) in hopes that perhaps the amp will be able to provide more voltage for an instant. But to no avail. In fact, all the testing has showed up is that most power supplies take a moment to catch up to the needs of the amplifier, and my AC/DC power supplies take even longer than the amp does.
Dynamic Power, in my opinion, is basically how far away from peak power you are at a specific listening level. If you have the system very quiet, you have more dynamic power left.
There are amplifiers, like Bob Carvers Sunfire home amps that use a stored energy display rather than an output display. The analog meter showed how many joules of energy were left in the amps storage capacitors. Given this though, then perhaps Dynamic Power is the energy stored and available to the outputs before the power supply can catch up and refill it.
The amount of power an amplifier can produce is limited by two things, How high the rail voltage is (or can go) and how much current the amp can supply into the load. Let's assume the load is fixed, and for arguments sake, is one ohm. If we have an amp with a rail voltage of plus and minus 50Vdc, then we have and output waveform peak of about 50V. There will be some minute losses due to the biasing voltage required to activate the output device and some losses through the various components of the amplifier, but we are going to assume there are negligable for now. So, we have a peak voltage of 50V for our sine wave. This means the RMS voltage is 35.36Volts, what you would measure with a True RMS voltmeter, and the only number you can use to calculate power.
As an aside and a reminder, Power is defined as:
The rate at which work is done, expressed as the amount of work per unit time and commonly measured in units such as the Watt and horsepower.
A Watt is:
An International System unit of power equal to one joule per second.
So, there we have it. The time basis for measureing power, represented in Watts is one second. So instantaneous power can't truly be measured in Watts, as they already have a time base of one second, not a portion of it.
Now, lets assume that I don't mind if we through the laws of physics out the window, and we decide that there is a chance that we can measure power at single instance in time. So, let's look at the point in time where a sinusoidal waveform has reached the 50V level. At this instant in time, we have an output of 2500VA (VA is Volt/Amps and is very similar to Watts, but without the one second time base).
If we were to use the definition of Watt though, we need to revert back to using the RMS voltage level over a given amount of time (one second). We get almost exactly 1250 Watts of power from an amplifier with a 50V rail, driven to the brink of clipping, into a one Ohm load.
So, back to the dynamic power discussion. I still don't know how to measure or quantify it, other than to say that some amps jam harder than other. But, there is more explanation...
The other limitation of an amplifiers ability to produce power is it's ability to pass current to the load. If the amplifiers power supply can't supply enough current to the load, the rail voltage will drop, just as your lights dim as your amplifier attempts to draw power from your electrical system.
If an amplifier design has enough reserve capacity (energy stored in capacitors for example), then it could draw on that energy to provide current to the load device before the power supply falls behind.
Anyways, I still don't know how to measure it, and trust me, I have tried and tried.
Oh, one last thought. There are some amplifiers that have power supplies with an output voltage that tracks (or tries to stay ahead of) the required output voltage. This reduces the overhead voltage, allowing the amp to run cooler. Mr. Carver calls this the tracking Downconverter.
I did some reading on the subject, while reviewing Bob Carvers Sunfire amplifier design and found out more about where this theoretical dynamic power comes from. In a side-bar from one of Mr. Carvers white papers, he mentions that 'testers' (clowns like me) will set the amp up with a dead short, the feed a pulse of 500 microseconds, 20 microseconds or even one thousanth of a second into the amp, the measure the output current. The current will be quite high, but not sustaneable (of cours. Mr. Carver refers to it as a parlor trick (which I just love!). He reminds us that power is the result of the square of current over resistance. Since the resistance in this example is functionally zero, the amp produces no power. However, testers go on to claim that the amp can produce huge amounts of current, and therefore huge amounts of power. Marketing and games... I read the rest of the Sunfire website.. very smart lad.
Anyways, I am tired, have more products to review and want to watch some Rally Racing. Goodnight all...
Yankee
Joined: Oct 2003
Posts: 3,599
Bumpin'Nova- there are a lot of confusing terms in manufacturer promotional literature, this is to sooth the jangled nerves of the prospective buyer to ensure him or her that they are buying a quality product (unless it is standard phraseology they can claim their product can do anything). There is Continuous Average Power- this is the power the amp was designed to run at all day without thermal overload, Max power should be the max peak to peak power (voltage derived I believe) or the point of clipping. The difference between those two points is headroom. A lot of these values are impedance sensitive so once again if there is no fixed standard for headroom measurement I would be surprised if companies use entertaining ways to derive max power/ headroom.
I like Rockford they made great car audio stuff for quite a while (their amps inspired awe in me in 1990 ... so much power into such low impedances!) Their 5db of head room works with the numbers shown only if it is a 150w x2 that maxes at 500w x2.
My desire for 1dB of headroom (30% over continuous rating) may not be reasonable in a car audio system (low impedances) and is based on my listening preferences and I want to amend that to 2 dB minimum. The first link below recommends a Minn of 3 dB with 10 desired. I do not think most SQ types bump all the time (but we all do once in a while) and the SPL burps certainly want to clip the crap out of their systems so the more headroom the merrier the burpers are. BUT the folks that would prefer to bump all day want a high continuous rating. Sound Quality folks don’t ever want to hear a ragged edge or have the possibility of ever flattening a waveform at any time in their semi adolescent lives.
Good dialog and technical breakdown, unsupported conclusions though
http://www.aes.org/sections/centrali...rown020206.pdf
Painful link to read but very informative
http://www.reed-electronics.com/ednm...ges/330071.pdf
I like Rockford they made great car audio stuff for quite a while (their amps inspired awe in me in 1990 ... so much power into such low impedances!) Their 5db of head room works with the numbers shown only if it is a 150w x2 that maxes at 500w x2.
My desire for 1dB of headroom (30% over continuous rating) may not be reasonable in a car audio system (low impedances) and is based on my listening preferences and I want to amend that to 2 dB minimum. The first link below recommends a Minn of 3 dB with 10 desired. I do not think most SQ types bump all the time (but we all do once in a while) and the SPL burps certainly want to clip the crap out of their systems so the more headroom the merrier the burpers are. BUT the folks that would prefer to bump all day want a high continuous rating. Sound Quality folks don’t ever want to hear a ragged edge or have the possibility of ever flattening a waveform at any time in their semi adolescent lives.
Good dialog and technical breakdown, unsupported conclusions though
http://www.aes.org/sections/centrali...rown020206.pdf
Painful link to read but very informative
http://www.reed-electronics.com/ednm...ges/330071.pdf
Yankee
Joined: Oct 2003
Posts: 3,599
Hi Dave! I was wondering how long before you visited us. 
Do you have the same high esteem of Bob Carver as I do? He has made some great products and some PPP but he is an Engineers Engineer. He proved with his amplifier null @ Stereophile a decade or so ago that you can change the sound of an amp till it sounds exactly like another amp.
His Sunfire products sounded excellent (auditioned B&W 802N with a reasonably priced Sunfire AV receiver)! And his stuff always has something new or at east unique and patentable in all of his designs.
I didn’t mean to offer a technical response after you did Dave I was typing for quite a while (I type like an old guy too) so I missed most of the Rally.
Dave I have only disagreed with you once and it was mostly semantics, I disagree with Dukk … well just because it is fun, but I don’t think I have ever disagreed with Dereck!? [img]graemlins/dunno.gif[/img]
Do you have the same high esteem of Bob Carver as I do? He has made some great products and some PPP but he is an Engineers Engineer. He proved with his amplifier null @ Stereophile a decade or so ago that you can change the sound of an amp till it sounds exactly like another amp.
His Sunfire products sounded excellent (auditioned B&W 802N with a reasonably priced Sunfire AV receiver)! And his stuff always has something new or at east unique and patentable in all of his designs.
I didn’t mean to offer a technical response after you did Dave I was typing for quite a while (I type like an old guy too) so I missed most of the Rally.
Dave I have only disagreed with you once and it was mostly semantics, I disagree with Dukk … well just because it is fun, but I don’t think I have ever disagreed with Dereck!? [img]graemlins/dunno.gif[/img]
