Reviews, MB Quart QP55x/45x (very very poorman's DT990 & K701 ?) - Page 9

Somebody has to be held accountable for this purchase!

Thanks for the info; I'll pop down to Goodwill tomorrow to see what I can find.

Oh man! If it's as bad as it's stated, someone is going to get strung up and whipped!

j/k of course. Mine are due Friday, but I won't post any impressions until I exceed about 200 hours of usage...which may be a while.

Hmm all of this makes me want to hear my set even more! too bad they will get here on the 6th then require burn in after that

It's weird that they are so hard to drive, electrically it doesn't really seem to make sense that they would be, being 100 ohms, maybe it's because they have been sitting for so long? I wonder if after a lot of HARD burn in they will loosen up a lot..

Just a reminder: impedance and efficiency are two entirely separate and independent things. You can have 2000 ohm phones that are very efficient and 16 ohm 'phones that suck all the juice out of an amp and go blatttt when you turn up the volume.

Impedance is also more than just a number. Much more. Read about PF, Power Factor, as it relates to lighting and electric motors, and why it's a problem for electric utilities. That'll give you an idea of what "hard to drive" should really mean beyond "not loud enough".

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Thanks for the link. These phones must be ridiculously inefficient huh?

Interesting, it sounds like the problem with the 45x is that there aren't many amps with enough current to play the bass.

Who is gonna hook them up to speaker outputs first? lol

I think so. I'll find out just how inefficient in a few days. One good engineering reason for inefficiency is extended response. It's a very common tradeoff in speakers and headphones. You make the voice coil very small with few turns so highs don't suffer due to the inductance of the coil, but if the coil is small, efficiency goes down. Maybe you make the cone stiffer so it doesn't break up at high volume,and the extra mass also pushes the primary resonant frequency lower for better bass, but that added mass also eats efficiency. Fiinally, you go cheap on the magnet because you want to market the 'phone at a particular price point... zingo, you now have an inexpensive 'phone that has a good frequency response and good sound but miserable efficiency. No problem back in the day of big receivers, but a whole different ballgame in the ibrave inew iworld of iportable igear and low-power tube amps.

I'm not an engineer, and these are simply my guesses based on what I know of transducer design in speakers, headphones and microphones and life in the business world. Everything's a zero-sum tradeoff, and the size of the pie is determined by the selling price, so you try to make the right decisions that don't come back to bite you in the butt. It used to be that trading off efficiency was a smart move, because nobody in the target market paid any attention to efficiency, and once upon a time it was even true that efficiency itself was suspect.

An interesting speaker company that made efficiency its byword:

http://www.cerwin-vega.com/history.php

Hee hee. Now I feel like a real estate investor.

I have no idea what to expect with these 'phones except that they're German and are likely to have the stereotypical shelved-up treble that German speakers and phones used to favor. That's not my kind of sound, but ya never know. I'll feed 'em some low bass to flex the "suspension" and see what eventuates. If after all that they sound meh, I'll gut 'em and stick various things in their apertures, because that's the kind of evil guy I am.

[David Warner voice] So I'll give 'em a chance, let them hope for awhile, then blow them away.

By thermo burn in you mean..?

Whoa! Thanks for the update on dimensions and assembly details!

You're right, it'll be much harder to resist trying to cram this craggy but otherwise working set of HP-1 drivers into that headset. I'll get out my cheap rotary tool and have at the baffle like a mad dentist.

Are you going to send it to a remote mountain top to train with the master?

I'm gonna try burning in with a 60Hz test tone at 120V to greatly accelerate the process.