[schaqfu]

Quote:

Originally Posted by Dreadhead /img/forum/go_quote.gif I wish that someone with measurement head and some time to measure the voltage at the headphones (not at the plug) would clear this all up.

AGREED!!!!

I am shocked, given that balanced-vs-unbalanced is practically the new holy war in the headphone enthusiast community, that there isn't an extremely detailed, definitive sticky out there that puts to bed the technical debate. Frankly, my theory is that the best way to accomplish that is through a Wikipedia page dedicated to it -- because multiple people can edit it back and forth, the debate happens in a way that sticks, rather than each new entrant simply leaving a new message that doesn't build on the previous.

One thing though, Dreadhead: again, it's all way beyond me, but I thought I read Elias (somewhere buried in that 10,000 pages of dialog) to be arguing that in fact the slew rate is not doubled. But maybe I'm mis-remembering that and mixing it up with his argument that distortion is increased. Oh well. I remain sufficiently interested that when I come into serious money (any decade now!) I will want to try a top of the line balanced setup and judge for myself.

 

[Dreadhead]

Quote:

Originally Posted by schaqfu /img/forum/go_quote.gif AGREED!!!! I am shocked, given that balanced-vs-unbalanced is practically the new holy war in the headphone enthusiast community, that there isn't an extremely detailed, definitive sticky out there that puts to bed the technical debate. Frankly, my theory is that the best way to accomplish that is through a Wikipedia page dedicated to it -- because multiple people can edit it back and forth, the debate happens in a way that sticks, rather than each new entrant simply leaving a new message that doesn't build on the previous. One thing though, Dreadhead: again, it's all way beyond me, but I thought I read Elias (somewhere buried in that 10,000 pages of dialog) to be arguing that in fact the slew rate is not doubled. But maybe I'm mis-remembering that and mixing it up with his argument that distortion is increased. Oh well. I remain sufficiently interested that when I come into serious money (any decade now!) I will want to try a top of the line balanced setup and judge for myself.

Hi,

Slew rate isn't doubled if the amp only has 2 amp circuits which some "balanced" amps do. Most high end balanced amps have 4 amps though and hence the slew rate doubles for each channel (+ve increasing at n v/ms and - decreasing at n v/ms gives 2 n slew rate). At least that's the way I see it.

Cheers

 

[schaqfu]

Quote:

Originally Posted by Dreadhead /img/forum/go_quote.gif Hi, Slew rate isn't doubled if the amp only has 2 amp circuits which some "balanced" amps do. Most high end balanced amps have 4 amps though and hence the slew rate doubles for each channel (+ve increasing at n v/ms and - decreasing at n v/ms gives 2 n slew rate). At least that's the way I see it. Cheers

Oh, I didn't know that about 2 vs 4 circuits. That's very interesting! That would explain why balanced may work in general but not from the DAC1, since I can't imagine it has four circuits. Heck, for that matter, I wonder how it creates its balanced output in the first place.

 

[pabbi1]

Quote:

Originally Posted by schaqfu /img/forum/go_quote.gif Oh, I didn't know that about 2 vs 4 circuits. That's very interesting! That would explain why balanced may work in general but not from the DAC1, since I can't imagine it has four circuits. Heck, for that matter, I wonder how it creates its balanced output in the first place.

Actually, both my balanced amps have 4 circuits - and amp stage for + & - for R & L. The gain is actually 4x SE, as I am told, which is perfect, as older incantations of this amp clipped awfully - even as much as I loved the signature, I could not abide the clipping.

 

[Dreadhead]

Quote:

Originally Posted by pabbi1 /img/forum/go_quote.gif Actually, both my balanced amps have 4 circuits - and amp stage for + & - for R & L. The gain is actually 4x SE, as I am told, which is perfect, as older incantations of this amp clipped awfully - even as much as I loved the signature, I could not abide the clipping.

It's 2X SE for the same gain settings not 4X; a SE amp has 2 amp circuits.

Cheers

 

[eweitzman]

Here are some numbers for you that will show why driving balanced headphones from the DAC1's line outputs will result in distorted frequency response. This says nothing about how a balanced amp -- with very low output impedance designed for driving phones -- will sound driving your Senn 650s.

To keep the numbers concrete, let the output voltage from the amp be a constant 10 volts at various frequencies. I've picked points at the inflection points of the Senn 650's impedance curves: 340 ohms @ 20Hz (340R@20Hz) (at the low end), 490R@80Hz (at the resonant peak), 340R@600Hz (near the end of the peak), 300R@1kHz (where it's "flat"), 300R@6kHz (where it stops being flat), and 360R@20kHz (where it's been rising).

Now, an ideal amp has 0 ohms output impedance. Here are the voltages, currents, and powers that would be delivered to the phones at each of the above frequencies.

Code:

[left]Ideal output impedance: 0 frequency impedance voltage current power variation ref. 1kHz (db) 20 340 10.000 29mA 0.29 -0.5 80 490 10.000 20mA 0.20 -2.1 600 340 10.000 29mA 0.29 -0.5 1000 300 10.000 33mA 0.33 0.0 6000 300 10.000 33mA 0.33 0.0 20000 360 10.000 28mA 0.28 -0.8[/left]

The variation with reference to the power at 1kHz looks pretty bad. That is, these phones consume 2.1db less power at 80Hz than 1kHz, but give relatively flat response (ie, constant SPL). How come? These power differences are combined with the mechanical behavior of the phones and give the 650s their more-or-less flat response. Thank the designers for this.

Now let's look at these values if the amp's output impedance is 0.11 ohms, the upper limit for the output impedance shown in the DAC1PRE manual.

Code:

[left]HPA2 output impedance: 0.11 ohms (less than 0.11 per DAC1PRE manual) frequency impedance voltage current power diff from ideal 20 340 9.997 29mA 0.29 0.0 80 490 9.998 20mA 0.20 0.0 600 340 9.997 29mA 0.29 0.0 1000 300 9.996 33mA 0.33 0.0 6000 300 9.996 33mA 0.33 0.0 20000 360 9.997 28mA 0.28 0.0[/left]

The power delivered to the phones is identical to the ideal case because there are negligible losses in the 0.11 ohm output impedance.

Now for the fun part. Here are the 60 ohm XLR outputs driving Senn 650s. The power delivered to the phones is very different from the ideal case, being roughly 2db down over the entire range. This power is lost in the 60 ohm resistor. But there is much more of importance in the last column!

Code:

[left]XLR output impedance: 60 frequency impedance voltage current power diff from variation ideal ref. ideal 1kHz 20 340 8.500 21mA 0.18 -2.1 -1.6 80 490 8.909 16mA 0.14 -1.5 0.6 600 340 8.500 21mA 0.18 -2.1 -2.3 1000 300 8.333 23mA 0.19 -2.4 -2.4 6000 300 8.333 23mA 0.19 -2.4 -2.4 20000 360 8.571 20mA 0.17 -2.0 -1.6[/left]

The last column compares the variations in power (2nd last column) to the last column for the ideal case. Look at the variation now! Whereas the power at 80Hz should be 2.1db lower than the power at 1kHz (ideal case) for flat response, the power at 80Hz is 3.0 db higher (0.6 - (-2.4)). That's a huge bass boost of 3db SPL. Similarly, the power at 20kHz should be 0.8db lower than at 1kHz, but is now 0.8dB (-2.4 - (-1.6)) higher, nearly 1 db of boost at 20kHz. You might not be able to hear 1db boost at 20kHz, but you will certainly hear 0.5db at 10kHz.

In general, the frequency response will become shaped like the impedance curve as the output impedance of the amp increases. It's just a matter of scale as to how big the deviation from flat becomes.

To complete the picture, look at the XLR line outputs driving a preamp with a fixed 20,000 ohm input impedance:

Code:

[left]XLR output impedance: 60 frequency impedance voltage current power 20 20000 9.97 0.49mA 0.005 80 20000 9.97 0.49mA 0.005 600 20000 9.97 0.49mA 0.005 1000 20000 9.97 0.49mA 0.005 6000 20000 9.97 0.49mA 0.005 20000 20000 9.97 0.49mA 0.005[/left]

The last two columns don't really matter, since the DAC1 isn't being called upon to deliver any current or power. All that matters is the voltage, and it is unchanged from frequency to frequency because of the constant load impedance.

Hope this helps!

- Eric

 

[eweitzman]

Quote:

Originally Posted by kool bubba ice /img/forum/go_quote.gif The 650/SA5000 sound better through the balanced out of the DAC1 then the DAC1 headphone amp.. Thats my & many others experiences..

I don't think my 650s sound very good with the DAC1's headphone amp unless the volume is turned up quite a bit. Then I'm really very pleased with the sound. Since I like to listen to music fairly loud (90-95dbC peaks), this suits me fine.

If I was driving them balanced from the XLR line outputs and got a 3db bass boost and 1db treble boost compared to the mids, it would certainly sound better to me at lower listening levels. This is exactly what the "loudness" compensation circuits in older preamps do, BTW. These circuits raise the bass and treble levels at lower listening levels, compensating for our ears' lower sensitivity at the frequency extremes. (See Fletcher-Munson equal loudness contours is you're not familiar with this.)

But I don't want my headphones to have this distorted frequency response all the time. If I really wanted the boosts at lower levels at times, I'd use a loudness circuit or tone controls or an equalizer. My goal is to have phones that provide the most flat and undistorted playback possible to reveal what's coming from the source. I suppose if I always listened at low levels, going balanced from the XLR line outputs would be an acceptable alternative.

- Eric

 

[eweitzman]

Quote:

Originally Posted by kool bubba ice /img/forum/go_quote.gif you live in SJ Eric?

A couple of towns away...

Quote:

I disagree with Elias on the distortion factor. I notice non with my balanced headphone.. I will compare both when I get me a XRL male to 1/4 cable..

Well, I think you probably *do* notice the frequency distortion (ie, the bass & treble boost.) But as I wrote elsewhere, the other distortion mechanisms he mentioned are probably dwarfed by the change in frequency response.

- Eric

 

[schaqfu]

Quote:

Originally Posted by eweitzman /img/forum/go_quote.gif Here are some numbers for you that will show why driving balanced headphones from the DAC1's line outputs will result in distorted frequency response. This says nothing about how a balanced amp -- with very low output impedance designed for driving phones -- will sound driving your Senn 650s.

Holy crap, Eric! You're a monster!! What a great explanation! So good that it for the most part makes sense even to me!

Two quick follow ups: I didn't quite understand why it's normal and okay for the Senns to have such varied resistance at different frequencies, and more importantly why they remain audibly flat across the entire range in spite of those variances. Is that magic of the Sennheiser designers just in how they physically shaped the various parts of the unit? Wow.

Second: assuming one connected the DAC1's balanced outs to a true dedicated balanced headphone amp with exceptionally high input impedance (I think HeadRooms are all 70k ohms), and extremely low output impedance (can't find this for HeadRooms, but I'll assume it's good), is there any reason to believe that the balancing of the headphones would affect any of the numbers you shared above? Is there any negative tradeoff to balanced drive, or is it really all hot fudge and apple pie with no weight gain?

 

[schaqfu]

Quote:

Originally Posted by eweitzman /img/forum/go_quote.gif A couple of towns away... - Eric

Do you work in technology? I hope you work for Sun!

 

[eweitzman]

shaqfu,

To tell you the truth, I wouldn't mind someone double-checking my numbers.

But I'm pretty sure they're okay. I've worked this out for other things before and the number seem right. I'm pretty surprised at how little current the 650s draw, but the equations don't lie: 10 volts into 300 ohms pushes just 33mA of current. I guess they have a reputation for being hard to drive because they need a relatively high voltage before they accept appreciable amounts of current and power and play loud. They could be really sensitive and not need much power, but then they wouldn't have the hard-to-drive reputation.

To answer your questions:

1. Almost all speakers show this type of impedance curve: there's a peak at resonance in the bass, then the impedance rises as frequency rises. The bass peak sort of handles itself: at resonance, the driver needs less power to get consistent SPL, and with higher impedance, they accept less current/power. The impedance rises at resonance (I think) due to the back EMF essentially canceling some of the drive voltage. Somebody correct me if this is incorrect. Usually the HF rise isn't too noticeable and may even be desirable due to baffle and/or radiation pattern issues. Often it's corrected for by a filter in the crossover in speakers. I don't know how they deal with it in headphones.

2. The big thing that balanced connections get you when driving a headphone amp or power amp or just a preamp/processor from the DAC1 would be immunity to some types of noise. Any benefit would depend on your particular noise situation. (Any high current AC feeds nearby? Big electromagnets?)

I would hope that any headphone amp, balanced or not, would have a very low output impedance so that shouldn't be a problem with any headphone amp you buy. Sorry, but I don't know if balanced phones are that much better: never been able to compare apples to apples myself, and never looked at the technical arguments. If they really do reduce noise by giving each channel a quieter ground path, that would be a good thing. I'll probably get flamed for saying this, but until I know differently, I will continue to suspect it's just another round of techno-escalation in the headphone amp marketplace. IMHO of course... But if people want it, why not make it and sell it?

- Eric

 

[schaqfu]

Quote:

Originally Posted by eweitzman /img/forum/go_quote.gif Sorry, but I don't know if balanced phones are that much better: never been able to compare apples to apples myself, and never looked at the technical arguments. If they really do reduce noise by giving each channel a quieter ground path, that would be a good thing. I'll probably get flamed for saying this, but until I know differently, I will continue to suspect it's just another round of techno-escalation in the headphone amp marketplace. IMHO of course... But if people want it, why not make it and sell it? - Eric

I'm inclined to suspect the same thing, but like you I also haven't made a balanced listening test with a true balanced amp, so I won't know until I do. What I'm having trouble parsing is whether people think the balanced drive actually changes the quality and character of the audio signal (people talk about better bass, more separation between notes, better soundstaging, etc., etc.) or whether it's all 100% a function of reducing noise in the signal (cross-talk and RFI). If it's just about reducing noise, I can understand the value proposition, but it seems like it wouldn't have the monstrous impact most adherents claim it does. Confusing.

 

[slwiser]

eweitzman

[size=x-large] Good Stuff
[/size]
[size=xx-small]I have attempted to communicate some of this myself with failure.

Your doing a much better job of it than I ever did.[/size]

 

[Dreadhead]

Eric,

I checked your numbers and they are right. What I would like to further point out though is that if you take the currents calculated with the ideal amplifier and then calculate the sensitivities of the phones (dB/mw) at the various frequencies you used (using the data from Headroom and the fact they use 90dB at 1kHz as '0'db. I get the following bumps dB changes:

Freq, Db Change from ideal (0 dB SPL at 1kHZ)
20-10
802
6001
10000
6000-2
2000-2

As you can see this is well within the usual variation of these headphones over the audible range (Just look at the response curve) (Who can hear 20kHZ and 20 Hz?). So even though your numbers are correct they really don't change the actual sound output of the headphones that much. So maybe the added power etc is outweighing this.

Just my two cents,
Chris

 

[schaqfu]

Quote:

Originally Posted by Dreadhead /img/forum/go_quote.gif Balanced Headphones have both pluses and minuses Chris

Say, I'm just curious from your signature line -- what are the minuses of balanced headphones?