[ericj]

Mine is supposed to show up tomorrow.

 

[smeggy]

Oooh my word, those are pretty little things.

I'm feeling an itch......

 

[ericj]

Well, last i heard, there was one NOS pair left in north america, possibly in the world.

 

[facelvega]

Quote:

Originally Posted by Faust2D /img/forum/go_quote.gif Did more listing with QP85 and now I am curious can I somehow modify them to boost the bass without ruining the soundstage?

As ericj said, this is exactly the problematic tradeoff. There's a great deal of bass in there, just tape over the baffle grille around the driver and you'll hear it-- and also hear the soundstage ruined. I'm now toying with some thinnish felt to see if I can get back some bass without too much soundstage loss. It's a question of reaching a happy medium, I hope.

 

[facelvega]

Okay, after mentioning it yesterday, I finally sat down with some thick felt (thin won't do it, I think, though perhaps layers of thin will be easier to adjust and work with than the thick stuff) and blocked over the open parts of the baffle on my PMB100, which being planar has the bass backwave problem even worse than my QP85. For testing purposes, I blocked it from the outer, ear side, a trick I've seen used to produce bass boost in certain old Senns. I used pretty much the same shape as the yellow tape I used a while ago in the Orthodynamic Roundup thread, from which experiment I already knew that it was a backwave problem and not a lack of bass from the driver. Initial observations are very promising indeed. The bass is back, it's controllable and goes reasonably deep though it is not overwhelming, and though there has been some soundstage loss, it's not as dramatic as I'd feared. With a little tweaking, I think a satisfactory solution can indeed be reached.

Please try this out if you're so inclined and report back how it works with the QP85. Just pop off the lids, set aside the foam sheet, cut out a couple of pieces of felt to cover the baffle around the driver, and get them to hold themselves down with some speaker fabric, or string, or maybe the foam again if it can cover the added thickness. Easily done mod, easily reversible. Good luck!

 

[Faust2D]

Sounds interesting, I will try this when I have some free time (not any time soon

).

 

[wualta]

FV, very glad to hear the humble felt pad is working for you. Next time you see a flock of sheeps and rayons frolicking and gamboling on a hillside, silently thank them.

The trick with headphones that embody a philosophy is to keep the bass backwave distracted and busy as it exits the driver while the midrange and treble parts of the backwave work their soundstage-widening psychoacoustic magic. Midrange backwave is your friend. All you have to do is figure a way to separate it from the bad crowd it insists on hanging out with.

I think a damping layer on the back of the driver itself would accomplish something similar, but from what I understand of the construction of the PMB 100, it would have to be glued on. I know this goes against the Presutti/Jecklin dicta. Sometimes you have no choice but sacrilege if you want to breathe free.

.

 

[facelvega]

Quote:

Originally Posted by wualta /img/forum/go_quote.gif I think a damping layer on the back of the driver itself would accomplish something similar, but from what I understand of the construction of the PMB100, it would have to be glued on. I know this goes against the Presutti/Jecklin dicta. Sometimes you have no choice but sacrilege if you want to breathe free.

It would require serious and possibly damaging work to get a pad up against the driver in a PMB100, though it wouldn't have to be glued thanks to a cross-brace that crosses the back of the driver at a slight distance. It might help flatten out the lower-mid hump, though. Damping the baffle plate was the easier option to prove that treatment might work, and has the advantage of not requiring invasive surgery. I wouldn't say that it's a permanently satisfying solution yet, but I'll try a few permutations by and by.

I suppose I might also try it on my QP85, which might be more helpful since at least other people reading head-fi also own them now. But I get the feeling ericj and philodox will beat me to any damping breakthroughs apart from the "hey, damping gets some bass back" eureka.

 

[ericj]

Quote:

Originally Posted by wualta /img/forum/go_quote.gif FV, very glad to hear the humble felt pad is working for you. Next time you see a flock of sheeps and rayons frolicking and gamboling on a hillside, silently thank them.

I know some of my favorite creatures are rayons. It's a real shame about the naugas, though. Everybody kept saying that there were plenty of naugas and now where are we?

Got my quarts today. These things are so old they say "Made in W. Germany"! - so do the QP55x for that matter. The original seal on the box was very yellow, but intact.

My QP85's were a store demo pair, and are plenty clean, in good shape. Wearing them now, so I guess I've joined Team Sturzhelm.

 

[Faust2D]

It is great that you got them. Can’t wait to read your impression of this well…Sturzhelm.

 

[ericj]

Well so far I like 'em. I also think they enhance the aesthetics of my otherwise boring mug - or maybe they just distract from it.

Some of the ear-side foam is decomposing. It's holding up but only just. Anybody know where i can get 1/8" acoustically transparent foam sheets?

Also, so far, I don't feel like these are really bass-anemic, but I'm not a basshead either, and it's not like I've gone looking for the bass yet.

 

[wualta]

Quote:

Originally Posted by facelvega It would require serious and possibly damaging work to get a pad up against the driver in a PMB100...

Woof. Too big a risk, then.


Quote:

Originally Posted by facelvega I wouldn't say that it's a permanently satisfying solution yet, but I'll try a few permutations by and by.

Oh, if you found the answer this soon, it wouldn't be satisfying dramatically. Boy meets headstage, boy loses headstage but meets bass, boy has a bit of a think, boy gets bass and headstage but then takes up golf.

Quote:

Originally Posted by facelvega But I get the feeling ericj and philodox will beat me to any damping breakthroughs apart from the "hey, damping gets some bass back" eureka.

I don't know about that. As it was with FL Wright, once you get intuitive hold of the fundamental generative principle...

I would like to see the damping idea grow beyond the iso/ortho realm. There's still too much bouncy-bouncy going on out there.

 

[ericj]

Well, I think my QP85 has plenty of most of the audible bass, but does roll off severely as things get really low.

Speaking of damping outside the realm of the isodynamic, you'd like the damping sandwich in the QP55x. Two layers of half-inch bright red foam rubber, with a smaller stiff disc of something fiberous between them. I should take pictures. It's exactly the foam i wish i had in my K145, but more for aesthetic reasons.

Unlike most voicecoil designs, this damping sandwich gets right up against the driver, though an iso driver might need some more foam in the stack to get a piece of felt all the way to full contact.

 

[Faust2D]

So I did some tooooob rolling on my amp and played with the source and DAC and managed to put a combo together that pulled that bass right up on QP85. No need for EQ or modding for now. My A900 sounds like a bass monster out of my new rig, scary thing what some valve swapping can do.

 

[Faust2D]

Ok, so I still like QP85; I know that it’s an unusual MB model, but I still decided to get QP70 just to see what that closed comfortable MB headphones are all about. As soon as I listen to them I will post my impression and pics here.