# Headphone Voltage Requirements



## Tomo

Hello,

 This is thread contains the calculation to determine voltage requirements for your headphones. 

 1. Efficiency of your cans:

 Efficiency of cans are usually 80~100dB/mW. You will never need more than 10mW to give you 800dB ... This is EXTREMELY HIGH volume. 

 2. How much AC current we are talking about? 

 Now use H=I^2*R

 10mW/600ohms = 1.67*10^-5 (A^2)

 You get 4mA thru the can. (This is AC value.) 

 3. Determine Voltage:

 Now use V=IR.

 4.08mA*600ohms = 2.45V (This also is AC value)

 So all you need +-2.45V voltage swing to get EXTREMELY HIGH volume. (I thank Todd (HeadRoom) and Chu for this information.)

 *Note the current-wise, I assume your output stage can supply ample amount of current. This is usually the case with most of the amplifier designs. Opamp fans should see your opamps should be able to supply:

 Sqrt[10mW/32ohms] = 17mA ...

 If you have more than 50mA capability you, opamp fans, should be fine.**

 **From studies done by several HeadWizers and HeadFiers, we know that for high performance you might want to add more current capabilities. ... It is true but I am not the expert in that. For my last project, I just pick high power opamps (high bandwidth and high speed ...) 

 ***Note this current capability I discussed right above are not related to quiescent current. ... So don't get confused. 

 Tomo


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## ppl

An informative doc on Headphone Power requirements can be found at http://www.rane.com/hc6hp.html this list several headphones and the Max SLP obtainable with rane's headphone Amps.

 A Schematic of the HC6 is at http://www.rane.com/pdf/hc6sch.pdf This is a 450 Mw output Pro headphone amp.


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## Joe Bloggs

Quote:


 Efficiency of your cans: 

 Efficiency of cans are usually 80~100dB/mW. You will never need more than 10mW to give you 800dB ... This is EXTREMELY HIGH 
 volume. 
 

I haven't read the rest too closely, but this part is wrong. If 1mW gives you 80dB, 10mW would only give you 90dB, and you'd need 100mW to reach 100dB and 1W to reach 110dB. This is because decibels are directly proportional to log (amplitude) * 10.

 If you have a 100dB/mW can and you want it to reach 800 dB, you'd need, um...

 1^70 mW = 1^67 W = 1^64 Megawatt = 1^61 Gigawatt = 1^58 Terawatt = ...


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## Joe Bloggs

Oops, double post, but I might as well add something here:

 An atomic bomb blast might or might not be able to reach 800dB


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## Tomo

Hello,

 Is that true?

 Kinda crazy, but unit made sense for a while so I skipped details ... haha.

 Ok ok. ... Let me try again.

 100dB = 10 Log[Amplitude]

 ...

 Unit does not make sense to me. I want the exact equation.

 Thanks,

 Tomo


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## PRR

Any good audio technology book has formulas and charts for computing dB. 

 Be careful about the distinction between voltage and power. 10 times the power is 10dB, but 10 times the voltage is 20dB (because 10X voltage makes 100X power). 

 Assume that is is "approximately true" that many headphones make 90dB SPL with 1 milliWatt, and that many loudspeakers make 90dB SPL with 1 Watt. If that is true, then headphone power in milliWatts is the same as loudspeaker power in Watts. 

 That's not quite true. First, most modern speakers make less than 90dB SPL/Watt; 87 seems typical. Quite a few headphones are over 90dB/mW, and some are 100dB/mW (but one is only 74!). Second, with headphones you may listen at lower volumes because outside noise is less intrusive; or higher volumes because your neighbors don't complain. 

 So no exact comparison is possible. But milliWatts in cans = Watts in speakers does give a useful place to start. 

 In loudspeakers, we know that 1-Watt table radios can make a lot of noise, and yet 400 Watt amplifiers are often used in homes with speakers of efficiency similar to a table radio (although the frequency response is very different). 

 Large changes in power do not give large changes in volume at the ear/brain. 

 If a 10 watt amplifer is not loud enough before clipping, a 20 watt amp is not going to be much better. When you don't have enough audio power, you probably want 4 to 10 times more power to make a real difference. 

 Most home hi-fi loudspeaker amps are between 10 and 100 watts. I have seen quite a few homes where 100 watt amps were run into clipping; these people should have 400 watt to 1,000 watt amps but the cost and power-feed issues become enormous at these power levels. 

 In headphones, I suspect that a 10 milliWatt amp is suitable for soft listening levels and/or high sensitivity phones. Many users will want more, maybe up to 100 milliWatts. But overall size and power is less of a problem in headphones than loudspeaker amps, and excess power provides reserves for peaks, so as much as 500mW-1,000mW might be interesting. I do believe that *most* listeners will be entirely happy with 1-mW-100mW; the 1,000mW case is indeed like having a kilo-Watt amp on loudspeakers. 

 I have used the two extremes of 10mW and 1,000mW and made a little chart. 100mW would be between these extremes. 

  Quote:


 
 

All values are RMS. Multiply by 1.4 for Peak, by 2.8 for Peak-to-peak. 

 Some comments: 8 ohm phones are now rare, and most of them would die if they saw a 1,000mW amp. So we never need 350mA RMS.

 The higher impedance phones are (for historical reasons) almost always high-efficiency, and 1,000mW in them would be an insane amount of power. So we never need 24 or 45 volts RMS. 10 V RMS will drive all of them well over their rated power. 

 For driving 32 ohm phones, we want at least 18mA RMS but probably never need more than 176mA RMS. 

 For driving 600 ohm phones, we often want more than 1 volt but 10 Volts RMS will be ample in almost every case. 

 Yes, a 50mA peak (35mA RMS) chip will give 20mW in 32 ohms, which is enough for some users, but others may want more. The number of people using paralleled opamps or buffers suggest that one opamp isn't enough for them. (But they may be fooling themselves; few people really know how much power they need.)

 -PRR


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## Joe Bloggs

So, say you feed an amp 30V DC, split into +15V and -15V rails--would the opamps be able to output just 15V peak to peak--or 15V peak, ie. 30V peak-to-peak?


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## tophu

With +/- 15V, you would be able to output close to 30V peak to peak. Exactly how close depends on the opamp and how much current you are drawing.


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## Joe Bloggs

That's strange--since P = V^2 / R I thought the 1000mW voltage figures on the right would just be the voltage figure on the left * sqrt(100)

 ?

 edit: uh, yeah, sqrt(100) is 10. What was I thinking? That's what I get for typing at 3 in the morning...


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## dvw

Guys;

 PRR has two very imformative analysis threads over at Headwize's DYI forum.

 Tomo;

 I think you are confused by the spec ; n dB/mW. It is not per mW but rather at 1 mW


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## PRR

> _PRR has two very imformative analysis threads over at Headwize's DYI forum._

 Yes, but it must be noted that they ask: "How can we ensure *high* level into *any* common headphone impedance?" 

 Many people do not need levels this high, 100-500mW. 

 Many people have a cherished set of phones, and have no interest in other impedances. 

 Since the threads have scrolled off the top page, here are links (I hope this syntax works): 

http://headwize.powerpill.org/ubb/sh...num=3&tid=2432

http://headwize.powerpill.org/ubb/sh...num=3&tid=2521

 -PRR


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## ppl

PRR has indeed done his homework. he should have came to this fourm long ago. I found similar relationships with different headphones. I also found that some headphones like lot's of damping grado's and most Sony's. I went real crazy at one point and used a 1 Amp Buffer to use with Grados. this sounded better not only at loud volumes but also at listning levels of normal conversation. One may wonder why would 1 Amp of output Current be Needed to get the Punch grados are capable of. maby output impedance? maby less of a change in the Buffers output impedance in the 5-10 Ma output range? The result was and is a noticeable improvement in Dynamics using low impedance phones at all Volume levels.

 An interesting case regarding Loud was in an Amp i made for a DJ using the 24 ohm MDR-V700's alot of the time he would complain about most headphone Amps distorting on loud bass Notes. as con be seen from the Rane App note referenced hear and by PRR on headwize i can see why maby 2-3 watts of RMS power into the V700's may be needed. So i put together an Amp for Him based around a stack of (4) BUF-634's and He was very happy, Plenty of Volume without distortion. I still wonder how long someones hearing would hold up under sutch conditions but that's the relm of disclaimers (MAY CAUSE PERMANENT HEARING DAMAGE OR COMPLETE HEARING LOSS IF PLAYED AT LOUD LEVELS) 

 For quality sound on most headphones at normal loudness i have found that for Impedances of 100-200 ohms that an output stage capable of 100 Ma RMS is needed. and for 24-75 ohm phones at least 500 Ma and sometimes more is needed. and that (3) BUF-634's or (6) EL-2001's or (1) EL-2008 & EL-2009 operating from at least +/- 10 Volt Rails, will drive any Headphone i have tried not only to Loud levels! But will also have the Punch at low volumes. Some High impedance Low sensitivity Phones may require +/- 15-18 Volt Rails. This is at the Limit of opamps and Buffers so any more Voltage output will require another topology like a discreet component opamp or you can casscode an Opamp or buffer to operate at higher rail voltages and get more output voltage swing.

 This is the reason i have spent so mutch time on these fourms trying to Inform Folks that just an opamp is not the best way to power your headphones. This is what most Home CD players use and users still are wanting better sound so thay get an Outboard Amp to get Better sound, so i was confused as to why one would make or obtain an outboard Headphone amp that is nothing more than the Internal one on most home Units. I must say that the case of the Portable CD Player is where an Opamp only based headphone amp is far better than the High Distortion low Powered internal headphone Amp on most Portable Audio Products.

 we will not talk about Huge amounts of rail capacitence at this time.


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## Tomo

Hello,

 I agree. I get far more performance with my can amp than bare output of my CDP. I can hear differences.

 Lately, I have been working exclusively with my 600 ohm cans and never really gave a thought for 32 ohm cans. No wonder I never had current problems. All I really needed was clean gain which I do have. 

 I still wonder what loudness (dB) I get if I were pumping 10mW or 100mW into the 80~100dB cans. The unit, dB/mW does not make sense to me still. When I see "something per something" I immediately imagine linear factor. For example, I would assume that:

 N (dB/mW)* M(mw) = N*M (dB)

 Which I clearly absurd. I understand dB = 10 Log (P2/P1). This has been known to me. But I have not seen people actually use this unit in actual calculations. I want to know how this unit interact with the unite "mW." I know logarithmic and exponential natures. But they do not account for "per milli watt" part of the unit.

 Tomo


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## PRR

> _ an Amp i made for a DJ_

 One example of when huge power might be needed. And his ears may be exposed only for short times, if this is a stick-phone or if he whips the phones off to hear the main speakers and the roar of the crowd. And in any case, permanent deafness is an occupational hazard for DJs... if the phones don't blow their ears off, the LOUDspeakers will. 

 > _One may wonder why would 1 Amp of output Current be Needed_ 

 I hope that you have never put 1 Amp through headphones. And I doubt you have. 

 But maximum current isn't everything. 

 There is maximum current. There is output impedance, which may be different for small signals and large signals. And there is rise of distortion as the load impedance drops. 

 > _ just an opamp is not the best way to power your headphones._

 I too find that questionable. 

 A 40mA op-amp chip, fed 18V total supply, looks like it will make 100mW-200mW into 150-300 ohms. That's plenty of power for most people, and a fairly common impedance for non-WalkMan phones. 

 Into 32 ohms, the 40mA op-amp chip makes 25mW, good power but not great. But this is hard work for the chip. 

 Such chips have internal output impedances of 100 to 300 ohms. With feedback, you can make this look like zero ohms. But it is still there. And when a 300 ohm chip drives a 32 ohm load, the effective gain and available feedback is only 1/10th of what it shows on the datasheet for normal loads. These chips are really made for 2,000 or 600 ohms, NOT 32 ohms. 

 Also, to get low idle power consumption with high output current, the output stage is often "tricky". Mode of operation may shift dramatically between 2mA out and 30mA out. This means "small" distortions that don't show at the rated loads of 2K or 600 ohms. This may be a main reason why various "near-perfect" op-amps sound different, and people don't agree which is better. We are abusing them with loads far below what the designers intended or the spec-sheets spec. We are using them where we are not supposed to go, and each circuit and phone will abuse them differently. 

 You are not using the 1 Amp capability of the buffer, but the buffer inherently has an output impedance well under 10 ohms, and usually a well-controlled shift from idle to high current. Also buffers are usually very simple circuits without excess trickery. So even when only delivering the same 40mA current as an op-amp, they may do the job very much better. 

 So far I have mostly harped on getting "ample" power, especially over the wide range of headphone impedances. Many of the odd flaws of amps are simple peak-clipping. Some posted designs suck at low impedances, some suck at high impedance, and the power available at various impedances is rarely stated clearly. This situation would not be tolerated in loudspeakers. 

 But when you have enough power, you also have to ask: 

 Does it make that power cleanly? An op-amp specified for 2K load is probably not going to be happy at 32 ohms, or even at 150 ohms. 

 Does it have enough damping? Some headphones seem to care very little, but others really need low source impedance. And does it stay damped at all signal levels? While an op-amp can sometimes show "zero" output impedance for small signals, even when heavily loaded, when it gets up near its current limit the feedback will fail spectacularly and the output impedance goes to hell. 

 No disrespect to Cmoy and others, but to my eyes a single op-amp to drive headphones seems like a weak plan. For modest levels in 600 ohm phones, it could be great, though a 9V battery does preclude high levels. Many modern op-amps will do OK into 300 ohms. But 60 or 32 ohms on a standard op-amp just seems wrong to me. 

 -PRR


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## PRR

> _When I see "something per something" I immediately imagine linear factor._

 The way it is usually stated is "wrong" on several counts.

 "90 dB" is meaningless, there is no reference level. But for 50 years, acoustic measurements have been referenced to 0.0002 dynes/square centimeter, which can also be stated "dB SPL". They leave out the "SPL". 

 You should probably convert the "dB SPL" to "dynes/sq.cM.", a linear pressure. 90 dB SPL is 6.3 dynes/sq.cm. 100 dB SPL is 20 dynes/sq.cM. 110 dB SPL is 63 dynes/sq.cM. I'm not sure this really helps understand what's going on. 

 1 mW ---- 6 dyne/sq.cM.
 10 ------- 20
 100 ------ 60

 Power goes up as the square of pressure, as it should. But even I'm confused by this representation. 

 It isn't "per", it is "at". Put in 1mW, get out 90 dB SPL. The are not really saying what will happen at 2 or 10 mW; just what happens at 1mW. 

 dynes/sq.cM. is a pressure, mW is a power. So the math is screwy. We are apparently equating different units. To be meaningful in a strict way, we need to know another factor: volume velocity (air flow) or acoustic impedance. In a perfectly sealed phone, the velocity is about zero, impedance is very high, power is about zero, and efficiency is about zero. In open-air phones the velocity is high, acoustic impedance is low and reactive, reactive power is high but real power and true efficiency is about zero. 

 But we are stuck with the ears we have, and whatever impedance they offer; and phones can be designed to work fine either sealed or open. If we put 1 mW into the phones, pull the microphone out of our Radio Shack SPL Meter and stick it in our earlobe, and put on the phones, we measure 90 dB SPL. 

 A chart of power and dB: 

 Power - dB
 1 ----- 0
 2 ----- 3
 4 ----- 6
 10 ---- 10
 20 ---- 13
 100 --- 20
 1,000 - 30

 Given phones rated 90 dB SPL at 1 mW, here is a chart of what SPL you get:

 1mW ---- 90 dB SPL
 10 ------ 100
 100 ----- 110
 1,000 --- 120

 In everyday life, we may be exposed to sounds from 30 dB SPL to 130 dB SPL. 

 A quiet home is 30 dB SPL. My concert hall measures -4 dB SPL in the upper midrange (yes, negative SPL is possible, it just means the room is quieter than the average ear can hear) but 60 dB SPL at 50 Hz from fan-rumble (and this does mangle the music). 

 Standing in front of the speakers at a big rock concert can expose you to 130 dB SPL. The conductor of a big classical orchestra can be exposed to 126 dB SPL for a few notes of the loudest works. Levels I see in the front row of a more modest orchestra have not yet exceeded 118 dB SPL, but one Chinese Opera did go well over 120 dB SPL. And my meters may under-report the absolute peak several dB. I design my mike-amps for 126 dB SPL. 

 Levels for home loudspeakers rarely exceed 100 dB SPL average in the loud parts. The amp and speaker need to deliver 110 dB SPL at the peaks. Many people are quite happy with 90 dB SPL average (100 dB SPL peaks). Some like to run up to 110, meaning 120 dB SPL on peaks. 

 Above 150 dB SPL, things get strange. An air wave that swung from twice normal air pressure to zero air pressure -might- be called something like 194 dB SPL. Note that negative peaks can't be greater than this (can't have less than a vacuum) but positive pressures can be far higher in the area of an explosion. Even down at a "mere" 150 dB SPL, this non-linearity means that air waves tend to be asymmetrical and distorted. Fortunately we don't go there in audio (although the levels in a horn loudspeaker's throat could run into this problem).

 -PRR


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## ppl

Tomo:
 While most Headphones state the sensitivity similar to what Sony dose on my MDR-7506 and MDR-v6 as (106dB/Mw) this dose not imply 106 dB per Mw, rather it states 106dB@1Mw. Thus these Phones should produce 116dB@10Mw since as PRR states power is 10 log, while Voltage is 20 log. gives a more easy to understand spec. why thay do not spec Headphones like Loudspeakers are i can't say. 

 PRR:
 No i have never put close to 1 amp into my can's in fact since My most powerfull portable amp can output just over 7 Volts RMS into a 50 ohm load i could not evean get close to 1 amp through the cans at pull output. Most of my listening is done at under 0.5 Volts and for the most part at about 100-200 Mv. this one would think should be well within the range that most opamps can Linearly drive. real world Listening test at these levels show quite different results. these phones operating in the 100-200 Mv range powered from an opamp able to output 80 Ma into a short circuit sound Thin and bright to me. maby that impedance rise you mentioned. If i power these from an Opamp Buffer combo with the Buffer able to output 160 Ma into a short circuit the sound is alot better More full and warm with more control over the bass, however the bass still is not ideal since it is slightly bloated. By using buffers able to output 1.8 amp of current (EL-2008) the Bass gets real tight and quick. the Midrange takes on a nice sence of ambience that was missing with both the opamp alone or the 160 Ma buffer (EL-2001) and this is at low levels at higher levels the bass on just the opamp compleatly falls apart with total loss of control of the Driver. a scope monitoring this did not reveil any clipping. Using the El-2001 the Bass at high levels got alot better but was on the verge of losing it. the midrange also gets muddy as like the bass was modulating the Mid's. going to the EL-2008 and at the same high level 0.5-1.0 Volt Everything is great with nice and tight bass as well as the bass not messing with the Mids. My old Koss pro4AA rated at 220 ohms sound better with a good buffer than with just an opamp, but i must addmit it takes only (1) El-2001.

 Based upon my own listening test as well as measurements I have not found that just an opamp alone without some form of buffering to be sonicaly ideal. I look at headphone Amp design as it were a low powered Audio power amp so like any power amp should have an outout stage after the gain stage. now it is true that most opamps include an oiutput stage folling the voltage gain stage and thus an opamp could be considered a lowpowered monolithic Amp. so why follow this with an evean higher Current output stage. well like you stated the real open loop impedance of over 100 ohms vs a real open loop impedance of less than 10-20 ohms. But moreover the most critical reason for buffering is to Improve the Accuracy of the opamp and to remove load dependent tempature changes that can drmaticaly affect the Performance of the opamp. Opamp makers know this and that is why Buffers were made.

 To Conclude! It may be true that in tomo's case by using a opamp able to output more than 100 ma and by using 600 Ohm phones most of the Nonlinearities may be removed but the tempature effects are not. In addition consider the back EMF of the phones and what this dose to the feedback and why a low real output impedance is required. But also in tomo case finding a buffer to Follow a 450 MHz. Opamp is quite a task unless you want to use the Buffer outside of the opamp's feedback loop. in that case a Low distortion Buffer is required. and one of the lowest distortion open-loop buffers i have found is the OPA-633/HA-5033.


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## PRR

> _calculation to determine voltage requirements for your headphones._

 How much voltage? 

 Depends on headphone power sensitivity, impedance, and desired listening level, of course.

 On HeadRoom's site, they propose a level of 100 dB SPL as a guide, and publish the voltage needed to reach this level for the headphones they sell. 100 dB SPL is perhaps arbitrary: we know many people listen in the mid-80s, and others need more than 100 dB SPL. However, 100 is enough for most folks, and those who need more can do the math for their level. 

 Sadly, something in HeadRoom's webserver is busted: all the values are "0.0V". So I computed numbers from Rane's paper posted on HeadWise. 
  Quote:


 
 

Conclusion? If 100dB SPL is your goal, any headphone on this list (or similar) will reach that level with 3 Volts and 26 mA RMS (4.2V 40mA Peak). This is within reach of small chips working on 9V batteries. 

 If 100 dB SPL is not enough, you probably want to look for 110 dB SPL. Triple the numbers above (3^2=10, near enuff). 10 volts and 80 mA may be needed. 

 -PRR


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## ppl

PRR:
 Thanks for redoing rain's list to include Recent cans. Also i would like to point out that these are RMS levels and peak levels considering a 10 dB dynamic range of most music and Hope-fully more than that on Audiophile recordings, then the values you listed for power, will have to be 10 times larger. Also consider that the current limit on most Chips limit rather quickly so evean peaks will be limited.... Just a thought.


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## PRR

> _PRR: Thanks for redoing rain's list to include Recent cans._

 Well, but I didn't add anything to Rane's list. I did shorten some model numbers to fit.... if by accident they now look like new-models, it should be understood that they come from Rane's list. I can't find info on modern cans. 

 I am amazed at how many model numbers on that 20 year old list are still available. True, there may be refinements between a 1984 HD-600 and today's HD-600, but I suspect the gross numbers for impedance and sensitivity are about that same today. 

 > _these are RMS levels and peak levels considering a 10 dB dynamic range of most music .... the values you listed for power, will have to be 10 times larger._

 I understood HeadRoom's words to mean: "average" listeners should be sure the voltage needed to drive a phone to 100dB SPL is less than the maximum voltage available from the jack. 

 Allowing a little peak clipping for best battery utilization, we could say 10 dB headroom. Meaning HeadRoom thinks that 90dB SPL average will satisfy most buyers. 

 I agree: 90 isn't soft and won't disappoint most listeners. More might be nice, but in limited-voltage duty such as portable battery players, we can't go overboard. 

 However, most of HeadRoom's "Volts for 100dB SPL" listings are blank, and I could not find where they say what the typical output voltage is for different mass-market devices. 

 I computed some numbers for the headphones. And the most common portable player is the 2-AA cell WalkMan-type, which must make 0.5 to 1.0 volts available at its headphone jack. 

 The 32-ohm Sony phones probably work fine (loud) on 2-AA WalkMen. They need 0.1V to 0.3V to make 100dB SPL. The AKG 240 and its ilk are known to be unsatisfying on 2-AA WalkMen, and they need 3 volts to make 100dB SPL. So HeadRoom's 100dB SPL guide is probably a good starting place. 

 In live recording work I often need 110dB SPL (5 volts into AKG240 is not quite enough). In a quiet office, 75dB SPL average 85 peak might be ample for many listeners. So it is only a benchmark, not a golden ruler. 

 > _Also consider that the current limit on most Chips limit rather quickly so evean peaks will be limited.... _

 Current limiting on small chips is normally FAR faster than any audio transient. The only way to design is a chip that can make full current with ease. And many chips will get nasty at currents less than the limit. 

 Of course things like R-load or CCS-loaded SE amps just *won't* make more than a certain amount of current. (Tomo's thoughts grew out of a thread about such an amp.)

 Power chips may also have heat limiting. They may be slower. You can sometimes cheat them for an audio peak. But when they limit the amp goes wild or dead for many milliseconds. So we don't want to go there for good listening. 

 -PRR


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## ppl

PRR:
 Thanks for the clarification on Headrooms avg. 100dB Level, We seem to be in agreement on the Current limit issue and i would like to add that I have found that All IC output stages are sensitive to Heat and will limit sooner at higher temp's. the Burr Brown BUF-634 is a clasic example of this and is so stated on the data sheet, moreover I also agree that most IC output stages start to get real nasty at currents way below their max Current ratings. This may be yet another reason that high current Output stages sound better to me than low Current ones.

 Distortion also starts to get really high at currents more than 1/4 the Rated output Current. I measured the BUF-634 as a stand alone Buffer and the THD + Noise went from a nice 0.01% @ 20 Ma of output current @ 5 Volts RMS output to just under 1.0% at the rated 250 Ma of output Current. note>> the load impedance had to be reduced to get 250 Ma Flowing through the Load resistor. Evean at 50 Ma of output current & 5 volts RMS output the THD+ Noise was 0.6% also note that what could be considered exsessive heatsinking was needed to get these numbers (200 Sq. In.) for the To-220 package. I wouls suspect that similar results would also happen with other Buffers as well. Also i would suspect that Opamps would be worse behaved under High load conditions relitive to there rated output, However the Opamps would have the Bennifit of feedback so actual distortion numbers might be lower due the feedback reduction. 

 This may be the reason that most folks seem to like Discreet transistor's as an output stage rather than in Monolithic form. I my-self also like these better. I also believe that current limit Hinders Performance on all aspects as well as on sound quality, however Current limit is a nessisary evil as every time the Phone plug is inserted or removed the Output is shorted and a designer can't expect the User to stop playing music prior to Pluging in or unplugging the Phones.


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## zorin

Can somebody wake up from the long hibernation ?
 What voltage would an amplifier need to supply to drive 600 Ohm Beyerdynamic T1 ? The telling feature of these headphones is a wide impedance spread between their nominal impedance  of 600 Ohm and a peak impedance of around 1250 Ohm of the bass end, centered on 100 Hz.
  





  
 So an amplifier would need to supply enough voltage to deal with the 1300Ohm peak. What would this voltage need to be ?
 +13V to 15V / - 13V to 15V for  a peak voltage of 26 to 30 Volts ?


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## jcx

the frequency response is usually measured with low Z Vsource - the amount of current at any frequency is determined by the Headphone Z at that frequency, so the power "absorbed" by the headphone varies verses frequency with constant V drive - but to no consequence for SPL vs frequency which is controlled by V alone if the amp output Z is low compared to the headphone
  
http://www.innerfidelity.com/images/BeyerdynamicT1.pdf
  
 with the T1 spec of 600 Ohm nominal Z and 102 dB re mW sensitivity/efficiency you need ~ +/-1.1 Vpk for 1 mWrms, giving 102 dB SPL (they state a 500 Hz ref frequency)
  
 for 120 dB SPL you would need ~+/-8.7 V from your amplifier output, with ~  +/-15 mA where the Z is close to 600 Ohm, but only 7 mA would be needed at the 100 hz Zpeak of the T1
  
 many monolithic op amp IC can manage that I, V when powered from more than +/-12 V supply, although some may show a little more distortion at 15 mA
  
 I'd look for those rated with at least 2x the output current or parallel a couple "A47" or O2 style
  
 the O2 output op amp has highish output current drive ability so just one JRC/NJM4556 would be happy with 600 Ohm or higher load  but the  dual "9V" battery may not be enough supply V if you really want >115 dB SPL clipping free
  
 some discrete SS amps, or buffers for op amps used in headphone circuits can't swing very close to their supply rails


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## zorin

Thanks for replying,....I am in a conversation with an amplifier manufacturer, he makes a very good transportable 'class A' hybrid amp but this amp's driving voltage is 5V, so its headphones optimal top driving range is 300 Ohm. - http://www.analog2p.com/product/tur06.html - By my reckoning this voltage is not big enough to deal with T1's peak impedance of 1250 Ohm [as measured by en.goldenears.net] / 1400 Ohm [as measured by innerfidelity.com] centered at 100Hz. He told me he can modify the amp in order to raise the driving voltage to 12V. I worry if this voltage is enough. By my estimate, as I do not have enough knowledge to do the calculations, a voltage of 13 to 15 Volt would be needed. If you say 12 V is enough I'll tell him to go ahead and make an amp for me. Since this amp would have to drive well both 42 Ohm W3000ANV which needs big current and 600 Ohm T1 which needs big voltage I think of suggesting to him doubling the number of op-amps in a 'cascade' mode. ALO Audio did this with their RX-Mk3B portable amplifier. - http://www.aloaudio.com/rx-mk3-b-plus - I just do not know enough details about Rx-Mk3B if those 'doubled' op-amps are of the same kind, to deal with either increased current or voltage requirements, or if they are different ones to deal, each with either current or with voltage requirements. What do you think about doubling op-amps to deal with higher voltages ? In a matter related to this, I saw a bit of an information that 'the Continental', a portable amp made [discontinued since 2013] by  ALO Audio to specifically drive Bayerdynamic T1, has an "output voltage" of 26V. This number seems to be too high to be +26V / -26V.


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