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Beyerdynamic t70p vs t70

post #1 of 7
11/29/11 at 8:21am
Thread Starter 

Hi all, I'm new to everything on this forum and have been self educating for a little bit now. Everyone has to start somewhere right? Just looking for other's opinions and help here. I'm in the process of obtaining decent closed back cans for the holiday season. I'm looking at the t70p's but wanted to get a number of opinions on whether or not to get the t70's instead. Reason being is that I want to be able to listen to the cans on my ipod, but in the near future plan on updating my home stereo equipment. From what I understand the t70p's I can listen to without any extras immediately in junction with my ipod. I do however want the best quality from my ipod and have delve into the depths of portable headphone amps and line out add-on's to bypass the ipod's minimal amp. Therefore wondering if I should get the t70's because in the end after I do get the above mentioned, I will be able to enjoy better quality overall. Any thoughts on this? Any thoughts on an affordable starter portable amp that will drive the t70's 250 Ohms (possibly a cmoy on ebay)? And is the line-out necessary? I truly appreciate your responses. Regards, Ryan

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post #2 of 7
11/29/11 at 8:52am

If this is correct, then the T70 250 Ohm is actually not that hard to drive due to its high sensitivity, it is basically comparable to the 32 Ohm versions of the older DT770/880/990 series. But you can of course always buy a small portable amplifier after the headphone if you are not satisfied with it using the iPod.

 

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post #3 of 7
11/29/11 at 9:45am
Thread Starter 

stv014: From what I understood the ipod's amp can only drive somewhere around a 70 - 80 Ohms pair of cans. In understand that is in rare cases and that mainly a 32 Ohm pair is recommended. These are 250 Ohm cans....if you can elaborate about the sensitivity because I was under the impression that it was strictly about the watts and ohms?

 

If I were to try and pickup an amp, do you have any suggestions for ultra portable and yet affordable?

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post #4 of 7
11/29/11 at 10:31am

The sensitivity and impedance together determine how much voltage is required for a particular level of loudness. Using a high impedance headphone on an iPod or other portable device will not damage the player or the headphone, nor will it generally degrade the sound quality at the same volume setting, other than getting quieter. So, there is no single hard upper limit on impedance like "this device can handle 250 Ohms, but not 251". Of course, once the impedance is too high, you will not be able to get a sufficiently loud sound before the source starts clipping (distorting). However, what is "too high" impedance also depends - in addition to your preference of loudness level - on the efficiency of the headphone; at the same impedance, some will take more power than others to sound equally as loud. The difference can be significant, and can sometimes outweigh impedance differences of a factor of 10 or more (although this is not typical).

In practice, the T70's combination of high impedance and high sensitivity means that it will be usable without an amplifier, although obviously not as loud as something that has both low impedance and high sensitivity (e.g. ATH-M50). But it will be similar to 32 Ohm DTxx0 headphones, which have low sensitivity (96 dB/mW vs. 104 dB/mW).

Regarding portable amplifiers, the FiiO E5/E6/E7 are a popular cheap option, but there are probably better ones.

 

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post #5 of 7
11/29/11 at 10:33am

I just got a pair of T70, but it looks like a refurbished one, does any one know how to check whether it is genuine or brand-new or refurbished?

 

Thank you very much!!!

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post #6 of 7
11/29/11 at 12:37pm
Thread Starter 

Brilliant info..... Sorry to bombard you with questions that may seem common sense, but not being an engineer or having much prior knowledge to pull this stuff from, it's my only option. 

 

The link you first posted of innerfidelity, which of those represents the sensitivity that we are both referring to at this point. Specs on headphones say 250 ohms, but obviously the sensitivity is just as important. How do I figure that info on my own without having someone as kind as yourself dictate it for me? 

 

The other question is since a amp is measured in watts and a headphone is measured in ohms. What is the rule of thumb when pairing the two together? Typically with speakers there are watts, but with headphones that doesn't seem to be the case on the specs.

 

Truly thanks, you have been filling some blanks that different articles have been leaving due to their technical lingo I'm not familiar with. It takes teaching myself the techniques, but even within the technique are very intricate terms that I must learn as well. It gets quite confusing to figure what applies to me and what doesn't.

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post #7 of 7
11/29/11 at 2:52pm
Quote:

Originally Posted by heinsryan View Post

 

The link you first posted of innerfidelity, which of those represents the sensitivity that we are both referring to at this point.

 

It is in the table at the bottom right:

 

Volts RMS required to reach 90dB SPL:    0.099 Vrms
Impedance @ 1kHz:    313 Ohms
Power Needed for 90dB SPL    0.03 mW
Broadband Isolation in dB (100Hz to 10kHz):    -18 dBr

 

Perhaps the most relevant of these is the first one, because it takes into account both the impedance and the sensitivity. Basically, if this number is lower for a headphone, then it is expected to be louder when plugged into the same source at the same volume setting (assuming that the source has insignificant output impedance - otherwise the balance can be tilted somewhat in the favor of the high impedance headphone).

 

Quote:

Originally Posted by heinsryan View Post

 

The other question is since a amp is measured in watts and a headphone is measured in ohms. What is the rule of thumb when pairing the two together? Typically with speakers there are watts, but with headphones that doesn't seem to be the case on the specs.

 

The most useful basic information for a headphone amplifier is the maximum RMS output voltage without clipping, and the output impedance. Although for a more complete understanding of how it will behave with a particular load more parameters are needed, these are enough to have some quick estimates. Often the output power (in mW) is specified instead, at one or more load impedances. From multiple impedance/power pairs the output voltage and impedance can be estimated by solving some simple equations, but it is generally enough to know that if the impedance of the headphone is much higher than that of the amplifier, then doubling it will result in halving the power and reducing the sound pressure by 3 dB.

For a reasonably loud sound, you want a peak SPL of at least 100 dB, and 110 dB for really loud. Adding 20 dB to the SPL means multiplying the voltage by 10, and the power by 100 (it is a logarithmic scale). So, for 110 dB (= 90+20) peak SPL, about 1 Vrms is needed (that is about the most a good portable player can output, but it could be just a few tenths of a Volt), or 3 mW. If the source can output 30 mW to 32 Ohm, then it will be > 3 mW on 250-300 Ohm.

For completeness, the basic formulas for converting RMS voltage, power, and SPL are (ignoring reactance and the possibility of current limited sources for simplicity):

  - voltage on the headphone (Vrms): Vhp = Vout * Rhp / (Rhp + Rout)

  - power on the headphone (W): Php = Vhp ^ 2 / Rhp

  - SPL from "Power Needed for 90dB SPL": 10 * log10(Php * 1000 / P90dBmW) + 90

  - SPL from "Volts RMS required to reach 90dB SPL": 20 * log10(Vhp / V90dB) + 90

 

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