Is the 8X rule correct ? Audio interfaces headphone output resistance 'Ohm' and Different impedance headphones.

[DoDo]

Is the 8x rule correct ? For example i have audent evo 4. Audient evo 4 has 22 ohm headphone output resistance. So 22*8=176 ohm
Can't I use the Dt 770 80 ohm with this audio interface? Does the frequency response of the audio interface deteriorate ?
For example there is m50x (38ohm) using with Evo 4 together

 

[dfuller]

The rule for impedance is generally 8-10x load impedance vs source impedance for minimal frequency response changes. You can use the 80 ohm DT770s, but the frequency response may be affected slightly, same with the ATH-M50X.

The reason for frequency response changes is that impedance is frequency dependent. any sort of traditional dynamic driver (be that a speaker or headphone) has a resonant frequency, at which impedance rises dramatically.
Take this impedance plot that Amir did for the Sennheiser HD650. The nominal (labeled) impedance is 300 ohms, but it spikes to nearly 500 ohms at the driver's resonant frequency around 110hz.

Remember our last discussion on this - higher impedance means less current, but more voltage swing. So, an amp with high enough output impedance (remember, high output impedance means it's not good at supplying current) can have its frequency response affected by the impedance curve of the headphones.

I'll also tag in @solderdude here, as he's actually done the comparisons.

 

[andreasmaaan]

I took NWAguy's measurements of the 80 Ohm version's impedance:

And modelled the effects on the amplitude response of using a source with an output resistance of 22 Ohm:

This gives approx. +/- 0.5dB, with the main impact being slightly elevated midbass.

Ofc, this assumes that the amp's output impedance is a constant 22 Ohm throughout the audio band. Real-life results may differ somewhat, but probably not by too much, at least not until the very high frequencies.

 

[solderdude]

The problem with NwAvGuys impedance measurement is that we don't know how he took it.
It looks like he had the DT770-80 lying on his workbench. Because of this the resonance frequency may be lower and the peak may be higher.
When on the head there is more damping so the frequency rises and the peak becomes lower.

 

[andreasmaaan]

The problem with NwAvGuys impedance measurement is that we don't know how he took it.
It looks like he had the DT770-80 lying on his workbench. Because of this the resonance frequency may be lower and the peak may be higher.
When on the head there is more damping so the frequency rises and the peak becomes lower.

Good point, I had not realised he doesn't measure on a HATS.

Still, you would not expect the deviation to become more pronounced when placed on a head, i.e. the modelled deviation is likely a worst-case scenario.

 

[solderdude]

I used the impedance measurement from RAA site (DT770-80) and calculated 0.3dB more bass on 22 Ohm output R.
That one is certainly taken on a rig when measured.

On RAA site you can even see the difference in tonality with various output R's

While the by the OP mentioned M50x has an even lower impedance it has a much 'flatter' impedance.
Because of this the M50x hardly changes tonality on higher output R amplifiers.

On 20 Ohm amp the bass boost is much less than that of the 80 Ohm DT770.

 

[DoDo]

[QUOTE = "andreasmaaan, gönderi: 658120, üye: 2367"] NWAguy'un 80 Ohm versiyonunun empedans ölçümlerini aldım:

View attachment 109888

Ve 22 Ohm çıkış direncine sahip bir kaynak kullanmanın genlik yanıtı üzerindeki etkilerini modelledi:

View attachment 109889

Bu yaklaşık verir. +/- 0.5dB, ana etki hafif yükseltilmiş orta basma.

Ofc, bu, amplifikatörün çıkış empedansının ses bandı boyunca sabit bir 22 Ohm olduğunu varsayar. Gerçek hayattaki sonuçlar biraz farklılık gösterebilir, ancak muhtemelen çok fazla değil, en azından çok yüksek frekanslara kadar. [/ QUOTE]
thanks

 

[DoDo]

The rule for impedance is generally 8-10x load impedance vs source impedance for minimal frequency response changes. You can use the 80 ohm DT770s, but the frequency response may be affected slightly, same with the ATH-M50X.

The reason for frequency response changes is that impedance is frequency dependent. any sort of traditional dynamic driver (be that a speaker or headphone) has a resonant frequency, at which impedance rises dramatically.
Take this impedance plot that Amir did for the Sennheiser HD650. The nominal (labeled) impedance is 300 ohms, but it spikes to nearly 500 ohms at the driver's resonant frequency around 110hz.

Remember our last discussion on this - higher impedance means less current, but more voltage swing. So, an amp with high enough output impedance (remember, high output impedance means it's not good at supplying current) can have its frequency response affected by the impedance curve of the headphones.

View attachment 109881

I'll also tag in @solderdude here, as he's actually done the comparisons.

t

I used the impedance measurement from RAA site (DT770-80) and calculated 0.3dB more bass on 22 Ohm output R.
That one is certainly taken on a rig when measured.

On RAA site you can even see the difference in tonality with various output R's View attachment 109903

While the by the OP mentioned M50x has an even lower impedance it has a much 'flatter' impedance.
Because of this the M50x hardly changes tonality on higher output R amplifiers.
View attachment 109909
On 20 Ohm amp the bass boost is much less than that of the 80 Ohm DT770.

Thank u. How u know m50x has more flatter impadence ?

 

[solderdude]

How u know m50x has more flatter impadence ?

Because the plots clearly show this.

 

[RHO]

Does all this also have an effect on the total Q of the system?
I've build some DIY subwoofers and there you would like not the have an overly damped system (or under damped).
How does impedance matching influence the bass performance (not just amplitude) with headphones? (if at all)