What are head-fi members views on apt-x lossless codec (over bluetooth)?
May 2, 2015 at 8:10 AM

#### Giogio

##### Bluetooth Guru
Sensitivity determines how much voltage or power is required to drive the headphones to a particular loudness. Impedance determines the amount of current they will draw. A pure bluetooth headphone has everything built in, done correctly you are good to go, otherwise you have a turkey. When using a bluetooth adapter with an external headphone then all of this technical mumbo jumbo is important because the adapter must be able to drive your headphones and do so properly.

Very very interesting point...
So, the impedance is like the resistance?
Something like this?

For other electrical stuff I knew that it was the ampere to determine how much power does a device suck.
Not to abuse of you but, as I am sick in bed with nothing else to do but I have no energy to read tons of google results instead of two lines of you, could you also explain how the impedance relates to the amperes? Please?

May 2, 2015 at 8:21 AM

#### StanD

##### Headphoneus Supremus

Very very interesting point...
So, the impedance is like the resistance?
Something like this?

For other electrical stuff I knew that it was the ampere to determine how much power does a device suck.
Not to abuse of you but, as I am sick in bed with nothing else to do but I have no energy to read tons of google results instead of two lines of you, could you also explain how the impedance relates to the amperes? Please?

Impedance is the resistance at AC, not DC. It can vary with frequency. In simple terms, Impedance relates to Current (amperes) by Ohms law, just use the impedance value in place of resistance. Wnen a headphone has a flat impedance curve, like a planar, then it's very simple.
Get better.

May 2, 2015 at 6:33 PM

#### Giogio

##### Bluetooth Guru
Thanks. It's just a cold, but the throat is in fire. I take a local analgesic which made also my tongue sleep. I speak like Sylvester Cat right now.

So, I still did not understand how can the impedance be related to AC and not to DC if the Headphones work with DC.
Am I missing something?

May 2, 2015 at 6:49 PM

#### StanD

##### Headphoneus Supremus
Thanks. It's just a cold, but the throat is in fire. I take a local analgesic which made also my tongue sleep. I speak like Sylvester Cat right now.

So, I still did not understand how can the impedance be related to AC and not to DC if the Headphones work with DC.
Am I missing something?

Audio is an AC signal, not DC. DC is not good to put through a headphone as it displaces the diaphragm to a fixed offset position and can even damage it if the voltage is high enough.
Impedance is the resistance of a component at AC frequencies. Idealy a capacitor is an open circuit for DC, or infinite resistance at DC. It is a reactive component and exhibits an impedance that varies with frequency. The higher the frequency the lower the impedance (AC resistance).

May 2, 2015 at 8:27 PM

#### Giogio

##### Bluetooth Guru
And when choosing the right receiver, must it deliver exactly that the headphones specs are? Or more?
The problem is, many receivers do not report those kind of specs.

May 2, 2015 at 9:22 PM

#### StanD

##### Headphoneus Supremus
And when choosing the right receiver, must it deliver exactly that the headphones specs are? Or more?
The problem is, many receivers do not report those kind of specs.

Most receievers are light on power and driving voltage. Driving voltage is more importantfor high impedance headphones. I suspect that most are designed with reasonably sensitive IEMs in mind. I avoid audio products that have no specs.
Extra power above headroom is not used so not necessary. Since these receivers tend to be light on power I'd be more concerned about having enough power rather than having too much.

May 7, 2015 at 4:18 PM

#### Giogio

##### Bluetooth Guru
I will use it with my K553, so it will not have so much trouble to run these cans.

And the K553 are also the ones which gave you hiss with the Clipper?
So, you have no hiss with the AT?
Of course, not a fair comparison though

btw: as I wrote in my thread, the AKG K845BT ARE APTX.
I just had the confirmation from their support.
WHich, per se, would mean nothing to me, considering that (no offense meant) for what I see their Customer Care is a low level, low prepared, probably low paid call center based somewhere in Bosnia or similar places where people have surnames which end in isovic or ievik.
And Beats Support keep saying people that the Studio Wireless support Aptx, while they clearly DO NOT.

But in this case, I believe these guys, because the reason why i asked them is that I am (re)testing the K845 and I get the "connected with Aptx device" notification on both my pc and my phone. This can NOT happen, with a non aptx headphone.
They told me "we forgot to write it in the documentation, I have just informed the right department so that this information will be updated".

May 7, 2015 at 5:33 PM

#### Giogio

##### Bluetooth Guru
The Amp's mW and headphone's sensitivty determines how loud your headphones can get, consider that against one's average listening volume one can deterimine how much headroom they have. The headhone or IEM's sensitivity determines how the ambient noise level of your amp plays into what you can hear. The mroe sensitive, the more apparent the background noise of the amp becomes. So for 50mW to play loudly one needs sensitive headphones/IEMs. but that makes the amp's noise more apparent.

I have been thinking again to this fact also because of the conversation in my thread, where I have just named you.
So, to understand all well, I take the example of the K553.
I read the have:
Sensitivity: 114 dB SPL/V
Max. Input Power: 200 mW
Rated Impedance: 32 Ohms

So, how do we read these values? And what should we read on the specs of a BT receiver in order to chose the right one?
I am re-reading your answers, but you use terms I do not know.
Like when you say "they are 38 Ohms and their sensitivity 89  dbSPL at 1 mW which reaches 119 dbSPL at 1W RMS, which is good headroom" which is like hyerogliphics to me.
I have tried to document myself with http://en.wikipedia.org/wiki/Root_mean_square and with http://blog.prosig.com/2008/04/14/what-is-db-noise-floor-dynamic-range/ but they have the tendency to explain things like for who already knows them. So that, who does not know them, will never understand them.
Specially wiki, 2km of bla bla and they never explained what this rms really is, practically, in the daily life, for example, in your sentence above.
I have understood that "headroom" is the space between the max which the headphone can take without clipping and the max it can take without being damaged, or something like that.
But I am not sure of how I should use this in the practical way.
I understand that 1 mW is one micro Watt, and 1W is one Watt, but, what is 1 W RMS???

Now, Sensitivity, ok, 114 decibel sound pressur level. this /v means? On the second link I read "dBV Voltage measurement relative to 1V – regardless of impedance."
Cool. I have no idea of what that should mean.

Max imput power. What do they mean with max? That a higher one would kill the headphone? Or that it is just useless? Anyway, 200mW, so, we need a 100mW channel amp, right?

Impedence 32 Ohms. Ok, normal. Besides, if the Impedence is not important because the only important thing is the power of the amp, why do they even bother writing about the impedence.
What is the difference between two headphones, both with max imput power 200mW, but one 32 and one 600ohm?
Or should BoTh values be matched?
I mean, should we choose an amp which says 100mW channel und 16ohm channel?
Some of your answers confused me because you said the impedence is not important of whatever.

May 7, 2015 at 5:56 PM

#### StanD

##### Headphoneus Supremus

I have been thinking again to this fact also because of the conversation in my thread, where I have just named you.
So, to understand all well, I take the example of the K553.
I read the have:
Sensitivity: 114 dB SPL/V
Max. Input Power: 200 mW
Rated Impedance: 32 Ohms

So, how do we read these values? And what should we read on the specs of a BT receiver in order to chose the right one?
I am re-reading your answers, but you use terms I do not know.
Like when you say "they are 38 Ohms and their sensitivity 89  dbSPL at 1 mW which reaches 119 dbSPL at 1W RMS, which is good headroom" which is like hyerogliphics to me.
I have tried to document myself with http://en.wikipedia.org/wiki/Root_mean_square and with http://blog.prosig.com/2008/04/14/what-is-db-noise-floor-dynamic-range/ but they have the tendency to explain things like for who already knows them. So that, who does not know them, will never understand them.
Specially wiki, 2km of bla bla and they never explained what this rms really is, practically, in the daily life, for example, in your sentence above.
I have understood that "headroom" is the space between the max which the headphone can take without clipping and the max it can take without being damaged, or something like that.
But I am not sure of how I should use this in the practical way.
I understand that 1 mW is one micro Watt, and 1W is one Watt, but, what is 1 W RMS???

Now, Sensitivity, ok, 114 decibel sound pressur level. this /v means? On the second link I read "dBV Voltage measurement relative to 1V – regardless of impedance."
Cool. I have no idea of what that should mean.

Max imput power. What do they mean with max? That a higher one would kill the headphone? Or that it is just useless? Anyway, 200mW, so, we need a 100mW channel amp, right?

Impedence 32 Ohms. Ok, normal. Besides, if the Impedence is not important because the only important thing is the power of the amp, why do they even bother writing about the impedence.
What is the difference between two headphones, both with max imput power 200mW, but one 32 and one 600ohm?
Or should BoTh values be matched?
I mean, should we choose an amp which says 100mW channel und 16ohm channel?
Some of your answers confused me because you said the impedence is not important of whatever.

There's a lot to be confused about if you haven't worked with this stuff, so don't take it to heart. TO correct one thing you just wrote 1 mW is not 1 micro Watt, it is a milli-Watt or 1 X 10-3 Watts.
Impedance is important, more so for high impedance headphones because an amp has to have a larger voltage swing to accomodate this. Also if the impedance of the headphones is too low then the amp may not be able to drive the headphone well as to provide electrical damping. A rule of thumb is that the amp should have an output impedance at least 1/8 or lower of the headphone's impedance. This ratio is less important for Magnetic Planar headphones.
If they don't spec that max is 200 mW per channel or in total, you can't be sure, but I believe it is usually spec'd as per channel.
Now 114 dBSPL at 1V is pretty sensitive. At 32 Ohms impedance this is 99 dbSPL/mW. So 15 mW should ring in at almost 111 dBSPL and 20 mW just over 112 dBSPL.  125 mW should take you just over 120 dBSPL which many consider to be the threshold of pain and sufficient headroom for most listeners. 200 mw should take you to just over 122 dbSPL. Notice that this is not linear. It takes 10 Db to double the loudness and 8 times the power only brings you to 9 dB, not quite doubling the loudness. I hope I haven't added to the confusion.

May 7, 2015 at 8:22 PM

#### cityle

##### 100+ Head-Fier
And the K553 are also the ones which gave you hiss with the Clipper?
So, you have no hiss with the AT?
Of course, not a fair comparison though

btw: as I wrote in my thread, the AKG K845BT ARE APTX.
I just had the confirmation from their support.
WHich, per se, would mean nothing to me, considering that (no offense meant) for what I see their Customer Care is a low level, low prepared, probably low paid call center based somewhere in Bosnia or similar places where people have surnames which end in isovic or ievik.
And Beats Support keep saying people that the Studio Wireless support Aptx, while they clearly DO NOT.

But in this case, I believe these guys, because the reason why i asked them is that I am (re)testing the K845 and I get the "connected with Aptx device" notification on both my pc and my phone. This can NOT happen, with a non aptx headphone.
They told me "we forgot to write it in the documentation, I have just informed the right department so that this information will be updated".

Yes, the hisses were with the K553 and the Clipper. Don't know with the AT though because I still don't have them. (the first deal was a fake one, got a refund but I wait a little before buying again). And too late for the AKG K845BT as I already modded my K553 and hopefully will get a good bt receiver.

May 7, 2015 at 8:40 PM

#### Giogio

##### Bluetooth Guru

Yes, the hisses were with the K553 and the Clipper. Don't know with the AT though because I still don't have them. (the first deal was a fake one, got a refund but I wait a little before buying again). And too late for the AKG K845BT as I already modded my K553 and hopefully will get a good bt receiver.

Why modded? Modded how? Why do you need to mod them if you just have to plug them into the receiver?
Anyway, you could write to Avantree, they are really incredible in this, really open and craving for these feedbacks, I am totally impressed by their attitude, never seen anything like that before.
Tell them about the problem you had with the Clipper, tell them about your needs of a good, powerful receiver with a good quality dac and enough power to drive that kind of headphone.

I gave them an idea which I think could be extremely cool.
Let me explain it and tell me what do you think: you know the clipper, ok? A thing with a 3.5 hole, for headphones with a fixed (not detachable) wire.
Then you may know the kickstarter project btunes, a thing with a 3.5 jack which you plug into the hole of a headphones with detachable cable. It also comes in 2.5 version. If you have many headphones, some 2.5, some 3.5, you need to buy two of this thing.
Now, imagine comething which is smaller and sexier than both these, with a form and dimensions and look which people would not feel like idiot plugging it in their headphones (I really do not like the btunes), with a good dac, and enough power for reasonably normal dimensions headphones, like yours.
It would be, basically, a better Clipper actually, with these improved quality/dimensionss/form/look. Something with a 3.5 hole, but with two male to male adapters, 3.5/3.5, and 3.5/2.5
This way you could use it to plug your wired headphone IN it, or plug it IN your (de)wired headphone, 3.5 or 2.5
It would be also Low Latency Aptx, so that you can play games or watch videos with your headphones.
So, there is already this btunes, yes, and the miccus is similar and it is low latency. But this would be the only one able to do all this.

They are thinking about it.
If you like the idea and you want to see it done, write them
You can name me.

In any case, even just telling them of your experience with the clipper would help them improving it.

May 7, 2015 at 8:55 PM

#### Giogio

##### Bluetooth Guru
There's a lot to be confused about if you haven't worked with this stuff, so don't take it to heart. TO correct one thing you just wrote 1 mW is not 1 micro Watt, it is a milli-Watt or 1 X 10-3 Watts.
Impedance is important, more so for high impedance headphones because an amp has to have a larger voltage swing to accomodate this. Also if the impedance of the headphones is too low then the amp may not be able to drive the headphone well as to provide electrical damping. A rule of thumb is that the amp should have an output impedance at least 1/8 or lower of the headphone's impedance. This ratio is less important for Magnetic Planar headphones.
If they don't spec that max is 200 mW per channel or in total, you can't be sure, but I believe it is usually spec'd as per channel.
Now 114 dBSPL at 1V is pretty sensitive. At 32 Ohms impedance this is 99 dbSPL/mW. So 15 mW should ring in at almost 111 dBSPL and 20 mW just over 112 dBSPL.  125 mW should take you just over 120 dBSPL which many consider to be the threshold of pain and sufficient headroom for most listeners. 200 mw should take you to just over 122 dbSPL. Notice that this is not linear. It takes 10 Db to double the loudness and 8 times the power only brings you to 9 dB, not quite doubling the loudness. I hope I haven't added to the confusion.

Let's say that I do not give up.
For sure, you're better than wiki
I will number my questions so you can answer them easily.
So, I understood that dbsplW is dbsplmW + 30.
But,
1) how you go from 114 dbsplV to 99 mW?
I understood that 8 times the power is +9db, but,
2) is this proportional? is 4 times the power +4.5db?
"It takes 10 Db to double the loudness" I did not understand this.
3) You mean that 120db is perceived as twice as loud as 110???
But more importantly I did not understand why you did all these calculations. It looked like if you were choosin your options, trying to customize the desired final desired loudness, and chosing the power of the receiver according to how loud you want the final result to be.
Which is cool, but I had understood that we were somehow limited in our choise at first by the fact of the hiss and headroom and noise floor and that we HAD TO choose an amp with AT LEAST as much output power as the max imput power of the headphone. so, in this case 200 or 2x200 in case that the specs are referring to one channel only (I do not think so anway).
4) or not?
Btw
5) what do they mean with max imput power? I was expecting max out power and/or min imput power, not max imput power...
What would then be a min imput power?
6) so, the amp must match the impedance of the headphone, right? how? </= or >/=? I mean, must the amp have "same or inferiot to" impendance than the headphone, or "same or superior"?
Or do amp have no impedence? It is still not clear to me how shoule I use the impedence value of the headphone when choosing the right receiver.

I would have another question but I think you may answer it with these six. If not, I ask it later

May 7, 2015 at 9:10 PM

#### cityle

##### 100+ Head-Fier

Why modded? Modded how? Why do you need to mod them if you just have to plug them into the receiver?
Anyway, you could write to Avantree, they are really incredible in this, really open and craving for these feedbacks, I am totally impressed by their attitude, never seen anything like that before.
Tell them about the problem you had with the Clipper, tell them about your needs of a good, powerful receiver with a good quality dac and enough power to drive that kind of headphone.

I gave them an idea which I think could be extremely cool.
Let me explain it and tell me what do you think: you know the clipper, ok? A thing with a 3.5 hole, for headphones with a fixed (not detachable) wire.
Then you may know the kickstarter project btunes, a thing with a 3.5 jack which you plug into the hole of a headphones with detachable cable. It also comes in 2.5 version. If you have many headphones, some 2.5, some 3.5, you need to buy two of this thing.
Now, imagine comething which is smaller and sexier than both these, with a form and dimensions and look which people would not feel like idiot plugging it in their headphones (I really do not like the btunes), with a good dac, and enough power for reasonably normal dimensions headphones, like yours.
It would be, basically, a better Clipper actually, with these improved quality/dimensionss/form/look. Something with a 3.5 hole, but with two male to male adapters, 3.5/3.5, and 3.5/2.5
This way you could use it to plug your wired headphone IN it, or plug it IN your (de)wired headphone, 3.5 or 2.5
It would be also Low Latency Aptx, so that you can play games or watch videos with your headphones.
So, there is already this btunes, yes, and the miccus is similar and it is low latency. But this would be the only one able to do all this.

They are thinking about it.
If you like the idea and you want to see it done, write them
You can name me.

In any case, even just telling them of your experience with the clipper would help them improving it.

I've done a detachable cable mod. They are so much agreeable to use now ^^ But I returned the Clipper long time ago to amazon for refund and lazy to write to them.

May 8, 2015 at 8:14 AM

#### StanD

##### Headphoneus Supremus
Let's say that I do not give up.
For sure, you're better than wiki
I will number my questions so you can answer them easily.
So, I understood that dbsplW is dbsplmW + 30.
But,
1) how you go from 114 dbsplV to 99 mW?
I understood that 8 times the power is +9db, but,
2) is this proportional? is 4 times the power +4.5db?
"It takes 10 Db to double the loudness" I did not understand this.
3) You mean that 120db is perceived as twice as loud as 110???
But more importantly I did not understand why you did all these calculations. It looked like if you were choosin your options, trying to customize the desired final desired loudness, and chosing the power of the receiver according to how loud you want the final result to be.
Which is cool, but I had understood that we were somehow limited in our choise at first by the fact of the hiss and headroom and noise floor and that we HAD TO choose an amp with AT LEAST as much output power as the max imput power of the headphone. so, in this case 200 or 2x200 in case that the specs are referring to one channel only (I do not think so anway).
4) or not?
Btw
5) what do they mean with max imput power? I was expecting max out power and/or min imput power, not max imput power...
What would then be a min imput power?
6) so, the amp must match the impedance of the headphone, right? how? </= or >/=? I mean, must the amp have "same or inferiot to" impendance than the headphone, or "same or superior"?
Or do amp have no impedence? It is still not clear to me how shoule I use the impedence value of the headphone when choosing the right receiver.

I would have another question but I think you may answer it with these six. If not, I ask it later

1) The amount of power for 1 V at 32 Ohms (using the equations previously given) amounts to 31.25 mW. Using the below equation the difference  in power to 1W is -15.1 dB, thus at 1 mW it's 98.9 dB SPL.
dB = 10 * Log (Pout / Pin)
2) 4 times the power is +6 dB. It is not linear thus not proportional. See the above formula in #1.
3) Yes 10 dB is percieved by humans as twice as loud. I picked a few power levels to give you an idea of what happens. One does not need to get to the maximum power level that headphones can handle, one needs to get to a level that does not cause harm to one's hearing, Keeping this in mind the consideration of how much power is required vs. S/N ratio and DR is not all that simple. The DR of recordings is a factor, however, since there is an undetermined amount of volume compression in recordings it's not cut and dry. Genreatlly one would be optimal to be able to reach a peak of 115 to 120 dB SPL, however, many people are very satisfied with lower numbers, especially with highly compressed rock/pop/hip hop, etc.
4) Answered in #3
5) The maximum sustained power that when exceeded will damage your headphones.
6) The Amp's output impedance required to drive a pair of headphones is determind by the attenuation (loss of volume) formed by the voltage divider of the Amp's output impedance and the Headphone's impedance. When using a headphone with a flat impedance curve (the impedance doesn't change much with frequency) the FR remains constant and one only needs to consider the possible dB loss by attenuation. As stated previously Magnetic Planar headphones are considered to be resistive and thus have a flat impedance curve. Many dynamic headphones have varying impedance curve and so the ratio of the amp's constant output impedance and headphone's varying impedance changes the attenuation with frequency thus makes the FR vary. That is why it is important to use an amp with an ouput impedance that is much lower than the headphone's impedance. Plus there is the Damping Ratio to consider.

May 8, 2015 at 3:01 PM

#### zzffnn

##### Headphoneus Supremus
Can we please get back to the original topic of AptX? Members view this thread because of its topic -AptX.

Headphone impedance/sensitivity/amp power is a different topic, which has been discussed elsewhere. Maybe take it to PM or open a new thread please. Thank you.

StanD is generally correct and clear. Also note that in 99% of CDs, dynamic peaks do not go over 35 db higher than RMS (~average) volume. So if you listen at 75-80 db on average like most people do, you may happy enough with 110-115 db peaks (and the amount of amp power to reach 110-115 db). For example, if I calculated it correctly, Creative E5 AptX amp can drive my Audeze LCD-2 headphones to over 110 db, which is good enough for my music listening volume (average 75 db).