A sweep of DT770 Pro shows FLAT BASS RESPONSE - what's wrong?

[va3ttn]

Quote:

Originally Posted by Fitz /img/forum/go_quote.gif I'm not sure why you're so against measuring a full sweep of the frequency response?

At the moment I feel much more comfortable with wavelengths
measured in meters, rather than in millimeters

10 kHz measurements are 1000 times more difficult than 10 Hz measurements
because the wavelength is 1000 times shorter.

Everything is much simpler when the wavelength is much longer than earpad and ear dimensions.
There are no resonances due to reflections and the sound pressure
is much more uniform in space, making microphone placement much less critical.

As said above, I'd like to perfect low frequency measurements
before I even attempt higher frequencies.

 

[va3ttn]

Quote:

Originally Posted by Fitz /img/forum/go_quote.gif I just applied a high shelf eq to attenuate all frequencies above 1KHz

Do you know what was the the actual frequency response produced that way?

 

[Fitz]

Quote:

Originally Posted by va3ttn /img/forum/go_quote.gif Do you know what was the the actual frequency response produced that way?

Exactly the same as the normal frequency response, with everything above 1KHz lowered by the same amount of dB (I varied the attenuation amount several times so I don't remember where I had it last before turning it off). The attenuation rate was 12dB/octave past 1KHz, until it reached the set level.

 

[milkweg]

Quote:

Originally Posted by va3ttn /img/forum/go_quote.gif As explained in the picture, spikes at 50 Hz and 121 Hz are due to room noise, nothing to do with headphones.

Ah, didn't notice that before.

 

[Tiemen]

Quote:

Originally Posted by va3ttn /img/forum/go_quote.gif DT770-2006 response on HeadRoom site is fundamentally different from my sweep: They got a much more spectacular response with 8 dB notch on 45 Hz, where the wavelength is over 7 meters. Well, I couldn't imagine a way for such a simple oscillatory system to have a response as complex as having this narrow notch at 45 Hz, and my sweep shows nothing of a kind, just an ordinary well-behaved high pass response.

That graph is the DT770 Pro 250 ohm.....

 

[Alpha 1 Omega]

is it not the pro 80 that is known as the bass monster not the
pro 600??

 

[b0dhi]

Good stuff. It wouldnt surprise me if HeadRoom's graph were off. Ryumatsuba's graphs also disagree with HeaRoom's. Also remember that the graphs you see at HR are the "corrected" graphs, not the actual response measured.

I've just got a couple of questions:

-So the electret(s) were in your ear-canal and the headphones placed on your head as per usual?

-What FFT size and windowing type was used in the graph? It would be good if you could upload the data as a .wav file or similar, I'd like to have a play with it.

Quote:

Originally Posted by Alpha 1 Omega /img/forum/go_quote.gif is it not the pro 80 that is known as the bass monster not the pro 600??

The Pro-80 is the bass "light" one as far as I know. The 250 is the usual "bass-monster" version. Not sure about the 600 but it should be bassier or as bassy as the 250.

 

[ph0rk]

Quote:

Originally Posted by b0dhi /img/forum/go_quote.gif The Pro-80 is the bass "light" one as far as I know. The 250 is the usual "bass-monster" version. Not sure about the 600 but it should be bassier or as bassy as the 250.

If the pro-80 is bass-light I cannot fathom the pro-250 being useful for any purpose other than a head massage.

 

[b0dhi]

Quote:

Originally Posted by ph0rk /img/forum/go_quote.gif If the pro-80 is bass-light I cannot fathom the pro-250 being useful for any purpose other than a head massage.

Well it's all relative in the end. A year ago I used to find the GS1000+flats (they make the DT-770/250 seem like tweeters) bass level normal. Now, I mainly use the PK1 and they have much less bass than the GS1k setup, but in the past 9 months I've gotten accustomed to the light bass and find it enjoyable. Bass at the level of the GS1k setup I had previously now makes my head hurt.

 

[va3ttn]

Quote:

Originally Posted by b0dhi /img/forum/go_quote.gif -So the electret(s) were in your ear-canal

The microphone was at the ear-canal opening,
where earbuds get placed usually.


Quote:

Originally Posted by b0dhi /img/forum/go_quote.gif the headphones placed on your head as per usual?

Exactly.
That was the only available head


Quote:

Originally Posted by b0dhi /img/forum/go_quote.gif -What FFT size and windowing type was used in the graph? It would be good if you could upload the data as a .wav file or similar, I'd like to have a play with it.

Recording was made using 6000 Hz sampling rate.
File size is 1172 KB, it's too big to be attached to this
message, but I can email it to you, just send me PM.

It was then downsampled to 500 Hz, and the spectrum
was computed using 1024-point FFT with Blackmann-Harris window,
giving bin size of 0.488 Hz.

The spectrum shown is the average of the sliding FFT, and it represents
frequency response well enough, given the linear sweep.
Averaging promoted noise at 50 Hz and 121 Hz.

The downsampled file is attached here.

 

[b0dhi]

AutoSignal corroborates the graph shown on the first page. It's +/- 2dB between 40Hz and 200Hz. Below 40Hz you're almost certainly seeing the electret's bass rolling off though. I'd wager the 770 are flat down to about 20hz.

It's worth noting that the graph HeadRoom has on the DT-770 is the 2006 version. The DT-770 Pro graph they had previously had a smooth response up to 200hz or so without any notches. The bass on that graph was quite a bit louder than the rest of the spectrum though, so I think it'd be worth measuring the whole spectrum when you're ready.

 

[catscratch]

Quote:

Originally Posted by va3ttn /img/forum/go_quote.gif 10 Hz to 1000 Hz is NOT a very limited range as far as the bass in concerned. Actually, it's more than we need to judge the presence or absence of bass-heaviness. In other words, whatever the response over 1 kHz, it cannot make the sound bass-heavy (or bass-light). This property is defined in concrete long before we reach 1 kHz.

Bass-heaviness depends on the rest of the frequency response. If the highs and upper mids are recessed compared to the bass, you will have perceived bass-heaviness and your hypothetical sweep to 1kHz won't show it worth a damn. Emphasized highs will have the reverse effect.

All you're doing is measuring bass linearity. Which is very useful in its own right.

I find the DT770/80 (older version) to have a linear bass that is overblown, but is of rather good quality. The problem is that the mids are recessed, and the highs are pretty rolled off in the upper treble, and tipped up in the lower treble.

The DT770 sounds like a good club system. Which, when you think about it, makes it really useful for a lot of things.

 

[Tiemen]

Quote:

Originally Posted by ph0rk /img/forum/go_quote.gif If the pro-80 is bass-light I cannot fathom the pro-250 being useful for any purpose other than a head massage.

X2. The pro-80 is bass heavy.
The one that is bass light, is the 2005 Premiumline consumer edition (250 ohm)

 

[Tiemen]

Quote:

Originally Posted by b0dhi /img/forum/go_quote.gif AutoSignal corroborates the graph shown on the first page. It's +/- 2dB between 40Hz and 200Hz. Below 40Hz you're almost certainly seeing the electret's bass rolling off though. I'd wager the 770 are flat down to about 20hz. It's worth noting that the graph HeadRoom has on the DT-770 is the 2006 version. The DT-770 Pro graph they had previously had a smooth response up to 200hz or so without any notches. The bass on that graph was quite a bit louder than the rest of the spectrum though, so I think it'd be worth measuring the whole spectrum when you're ready.

HeadRoom had a review of the DT 770 Pro 250 ohm, with the year 2006 as referral, prior to their review of the DT770 2005 conusmer edtition.
The graph of that Pro 250 ohm version is still on their website.
See archive.org to dig up the old reviews.