Orthodynamic Roundup - Page 1376

Physical vs. digital modding (convolution) again.

 

Yamaha HP-50S. Measurements are raw; compare only to each other and not to measurements outside this post.

 

Right channel, stock foam (but without the white paper disc):

 

Left channel, modded (two nylon discs):

 

Right channel, stock foam + a convolution filter applied to the test tone:

 

The convolution filter was aimed at turning the stock right channel response to a response identical to that of the modded left channel. Which it did. The two responses are identical, given some variation in positioning, except for the increased peak around 15 kHz or so. I listened to the phones with the left side modded and the right side convolved - they sounded more or less the same.

 

No artificial ear was used in the above measurements. Below are measurements with an artificial ear to test whether the convolution filter was ear shape-dependent or not. The filter was lowpassed at 12 kHz for experimental reasons.

 

Left, convolved:

 

Left, modded (no convolution):

 

Given some variation in ear placement (more than previously), the graphs remain similar. Based on this one test, the filter seems to have but a weak dependence on ear anatomy at worst (which is good).

 

I also noticed that there are a few small ridges - around 5 and 6 kHz - that occur in the same place in all of the measurements. This often means it's an ear-independent feature and thus something that's easy to fix with EQ. To that end, I made a crude convolution filter based on the earless measurements from above aimed at eliminating the two small peaks in those areas of ringing, then applied that filter to the impulse response from the modded left channel (which was measured with an ear):

 

The two spots of ringing are gone. Since the filter was created from earless measurements and nonetheless worked for an eared measurement as well, there's a good chance that it's not dependent on the ear's anatomy, and would thus work for my own ears too. (This was somewhat of a theoretical test since I filtered an already measured impulse response rather than filtering the test tone and measuring the result off the phones themselves - but usually the end result from these two actions seems much the same.)

Edited by vid - 10/22/12 at 4:01pm

Finally made new pads for my Headphone People HP-2!
I initially wished to recreate my original pads (stacked Headphone People pad on top of HP-2 pad) so made a design of a wider opening on the bottom, smaller opening on the top, and a foldable inner layer.

End result? Forgot to consider the inner tubing layer will take up space, so both top and bottom openings are smaller than on the original. The top opening should have been about 3mm smaller in diameter than the bottom, and my new ones are only about 1mm smaller.

I'm actually slightly surprised by the way the different fill material will alter the sound. I tried memory foam, memory foam + open cell foam, original pads, original pads + open cell foam, original pads + memory foam... it seems that unless the pads are rigid enough (by placing the original pads inside) the sound changes ever more.

In the end I've achieved larger bass quantity without much quality loss, and more (it used to not be) linearity up till 2kHz but... I lost most of my 2kHz to 6kHz range. Aw well :S Might redo the project when I get more time. But at the moment I can only say that memory foam really is hard to work with... with compression it goes back to nothing in terms of thickness. How would you guys stuff memory foam? Would the volume of the earpad = compressed or uncompressed memory foam?

hey those look great now that I see how you did them I may do similar ones for a project.

 Got no experience with memory foam myself but sounds like a pain. Maybe you could do simply a top layer of it and regular foam for the bottom half to avoid the crazy compression?

 

I hope those aren't the calculations there on the paper for the pads, or I'll never be able to do it. I forget all that stuff.

 Hmm square root for the diameter of the waxed thread times the friction loss over distance during sewing and increased foam stuffing with %30 factored compression , need to calculate for the inverted surface areas of the leather torus ... aaaahhhhhhhhhhh (runs screaming from the room )

 

try out the stacked foams with the memory stuff on top, for some reason i think someone else did that in here to great effect.

Heh, calculations? Those I *am* good at. 

Oh no that was just part of an example on view factors I took down in class! Has nothing to do with the pads, whose calculations were only adding a few extra mm to the diameter so I can sow on the next piece, etc.

Yeah, I tried the two different foam idea from bruma. I need to cut thicker layers of the foam to better try it. At the moment the two layers adds up as the volume of the pads uncompressed. But since I made the outer lateral side extra large and haven't quite closed them up yet, the whole thing sags quite a bit. If I need to restart I may as well close them up!

And the memory foam I got (the yellowish stuff in picture) is perhaps not dense enough. It came from a pillow that I shaved off 11mm roughly. Press it down and there is 1mm left!
The darker gray ones should be much better (or too stiff).

I should also mention that there is a considerable amount of reflection in that new earpad. Tunnel effect :S
Edited by kalbee - 10/23/12 at 9:47am

The quality of the foam makes all the difference - you need a very dense memory foam (that looks quite different from your sample in the picture) at least from the "tempur" quality. the relation of the thickness was good with 1 part memory foam  to 2 parts polyurethane foam in my thicker earpads. the positive effect of the memory foam stays also intact under tension if you round the edges of the polyurethane foam and leave the ring of memory foam intact. tip: look at the shape of the pu foam alone under the tension of the "finished pad" and cut it into this shape - beause memory foam can only follow the shape of the basis and looses some effects, if it is forced out of this form.

for thinner pads i cut small radial rims in the pu foam (like you see it in a mattress) - this has more cushioning effect in a smaller space.

Edited by bruma - 10/23/12 at 12:19pm

Yeah, the memory foam I have is very light and possibly more air than foam in volume. I'll have to find higher density ones. I did get the pillow for about $1.50 (garage sale type of source) so quality is definitely not up there.

Thanks for the tips! Though one question is the radial rims in the pu foam (the last part in your post)... I didn't fully understand it. Do you mean to put rings of pu foam and memory foam where ever takes the most pressure?

The white paper disc on the HP-50S smooths out the bass hump by 5 dB (says the freq resp measurement) and blu-tacking the driver onto the baffle causes ringing in the treble and worsens the decay at around 500 Hz (at least so with stock foam, didn't measure with mods). These were the two findings from today's evening of modding by measurement.

Edited by vid - 10/23/12 at 5:23pm

 

Do you mean just mass loading the rear of the baffle? or covering the driver?...

Sorry, by that I meant applying a small amount of blu-tack onto the rim of the driver where it attaches to the baffle.

It's strange that it would worsen decay.

Blu-tack:

 

No blu-tack:

 

First vertical line at the back of the graph is 100 Hz, then 1 kHz, 5 kHz, 10 kHz and 20 kHz.

Interesting... didn't think blue tack would worsen decay either. Basically this is from using blue tack to seal the driver to the baffle, correct?
If the change in height of the driver with respect to the baffle is large enough, then it could be a foreseeable problem. Otherwise... :S


On another note. The cups on the Headphone People have cracked >_<<br /> I just never noticed it too much. Guess I abused (like side sleeping w/ them on) it too much; the headband really did give the impression that they extremely rugged. Forgot the cups are a plastic net.
Looks like I'll have to make a replacement somehow in case. They're still holding up but probably not for long. Removed a layer of arctic bamboo to lessen the stress on the plastic (overstuffed state).

Also started experimenting turning it into a closed back headphone. Managed to cut out some plastic sheets to size and put them inside. Looks like the whole damping system inside had to be removed and replaced with simpler settings for it to sound better. Will have to try putting acoustic foam and increase the weight of the plastic.
Edited by kalbee - 10/23/12 at 8:14pm

 

Yep, blu-tack around the edge of the niche on the inside of the baffle the where you plop down the driver (and where the stock white paper disc is). I only had a thin strip of blu-tack there, but I don't really know how much others are putting on theirs, so maybe I was overdoing it anyway.

 

Not sure if RD blu-tacked the driver to the baffle on the HP-50S that Purrin measured in July, but you can see the same ~5 kHz ringing in those graphs as you can in my graph with blu-tack and which is missing in the 'tackless graph. Could be coincidence too, of course.

Edited by vid - 10/24/12 at 1:23pm