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NO SMOOTHING is applied to the shown plots. Most measurement sites have some smoothing applied which ‘irons flat’ sharp peaks and ‘wiggles’. I do not use smoothing because some info about sound quality is lost when plots are smoothed.

Aside from a small correction of the microphone itself also some correction in the lowest frequencies is applied to the plots to compensate for the perceived loss of bass when using headphones. This is described HERE in more detail.
A ‘horizontal‘ frequency response curve on the shown frequency response plots on this website thus indicates a perceived ‘flat’ tonal signature.

ALL measurements are made with a good SEAL on a flatbed measurement rig.
The
shape of your head, bone structure, pad size, pad ‘softness,  (compliance), hair or no hair and or wearing glasses may (drastically) change the frequency response of some headphones, so… your personal experience may differ substantially from these plots.

post separation
t.bone HD 990 D

DSCN0147

One may wonder what the t.bone HD 990 D (Thomann) headphone does on this website amidst hi-fi headphones. The reason is it is a headphone and had a chance to measure it.
The t.bone brand fishes in the same pond as Superlux. They make/sell affordable gear for home recording and small studios of decent quality but with a high price performance ratio.

The t.bone HD 990 D is a cheap (27 €) headphone intended for drummers. It is intended for monitoring in loud environments and thus has a very high attenuation from outside noises (quoted at 22dBA attenuation) . It basically is an ear protector with small headphone drivers inside. It’s primary goal is to attenuate sounds from the drumkit itself and be able to listen to the recording as it is being made.

Comfort is low but doesn’t need to be high anyway. It is only intended to be used during recordings. It looks and feels like any other cheap hearing protector. Thin plastic (vinyl) replaceable earpads that can easily be cleaned. The headphone can be adjusted in height etc and will easily fit most heads. The whole assembly feels a bit flimsy but will probably be able to take some beating.
The whole assembly is squeeky when adjusting it on your head but once on, you won’t hear that anymore.

Specs.

  • Impedance: 35 Ω
  • Attenuation: 22 dBA
  • SPL: 105 dB (nowhere is it mentioned though whether this is at 1mW or at 1V)
  • Frequency response: 10-20.000 Hz  (as always a meaningless specification as cut-off points aren’t mentioned)
  • Cable length: 1-4m coiled with angled jack plug 3,5mm with 6.3 mm screwable jack plug adapter.
  • Weight: 358g with cable, 258g without cable

The impedance is low and efficiency is high so not much power is needed to make it play loud.
The clamping force is uncomfortably high but essential to get a good attenuation from outside noises. The thin plastic pads quickly get sweaty but are easily cleaned (wiped off).
The weight is decent but the coiled cable is a bit heavy and takes some strenght to stretch fully.

How does it sound… well .. not hi-fi for sure but then again it shouldn’t either. These things must play loud and not pierce ears with lots of treble/upper mids. Bass should be well extended because one needs to hear the essentials of the instruments while recording.
So everything from 100Hz to 3kHz should be audible and free of distortion. Above 1kHz it is preferable to be attenuate the signal so shrillness etc isn’t distracting from the essentials.
That’s indeed what it sounds like…. You can hear the essentials of the music played but sounds subdued in clarity/presence and highs.

Below the frequency response of the HD 990 D, left and right channel

FR HD990D

Surprisingly there is some channel imbalance below 600Hz reaching almost 5dB. Doesn’t appear to have been a measurement error but during the (very brief) listening it wasn’t really obvious. Bass extends well down to 10Hz. A slight mids accentuation which is a good thing for monitoring. Above 2kHz the sigal takes a nose dive so clarity isn’t there at all nor is it desirable when playing at high SPL. The upper mids and treble are about 12B lower in amplitude and lack any form of sound quality. Extension is good though and 20kHz is reached.
The frequency response from 10Hz to 20kHz is reached but at -10dB cutoff points and not counting dips of -20dB in the upper mids/lower treble area.

The distortion plot below actually isn’t that bad. At 95dB SPL the distortion never exceeds 0.5% (-45dB). For a cheap headphone this is quite good. This is a good thing, keeps the sound ‘clean’ at higher SPL. (Right channel only)

DIST R

The CSD below shows some resonances just above 1kHz and at 5.5kHz. Not something audiophiles will like but musicians couldn’t care less during a recording. Their focus lies on totally different things. Not on sound quality at all. , left and right channel superimposed.

CSD t.bone HD990D

For completeness also the spectrum plot from 100Hz to 30kHz. (Right channel only)

SPECT R

It shows some resonances at a a few frequencies and aside from the area around 1kHz isn’t really that bad nor problematic.

The step response plot below shows what’s heard. Attack is a bit slow and the sound is mids oriented with a good low frequency extension. Nothing hi-fi about this.

step L

This is not a hi-fi headphone BUT is well suited for its designed task. This task is to attenuate outside sounds and be able to hear what the rest of the band is doing without the headphone becoming harsh. Considering the price this may be a very welcome attribute in small (home) recording studios for recording the drumkit at full strength.

 

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