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Fostex T50RP Incremental Mods and Measurements - Page 46

post #676 of 1477

Wanted to separate this second question.

 

I'm trying to understand your dampening decisions in the cup 'wells'. It seems you've experimented with Paxmate, Acoustipack, Dynamat and Silverstone for the left and right wells, and settled on felt for the center 'column'.

 

  • Firstly, why have you used multiple materials that seem designed for the same thing? Is it not possible to simplify and use only one of these, Paxmate for example?
  • Secondly, why have you used felt for the center column and not Paxmate contiguously? (Ventilation slots and symmetry?)
  • Thirdly, what is the purpose of the rungs? Is it scatter sound waves? Have you experimented with alternate shapes? Might have missed them but I don't see measurements anallysing the improvements the rungs make.
  • Fourthly, why are the rungs a different material to the wells? From DBV3 you seem to have settled on Acoustipack wells and Paxmate rungs. Why not use the same material for the rungs since they are similar?
  • Finally, why have you not uniformly covered the entire inner cup with dampening, instead of only the wells? (Not enough space? Surely if you have to sacrifice a material for the sake of space you should sacrifice cotton and rather damp away that shiny reflective plastic.)

 

Thanks for taking the time to answer some of my questions, I really appreciate and enjoy this thread.

post #677 of 1477
Thread Starter 
Quote:
Originally Posted by Modulus View Post

I have a question concerning weighting of the baffle.

 

Is it possible that the loading materials used; clay, modeling clay, blu-tack, are limiting the usefulness of this modification due to their relative lack of density?

 

Simply put, would a significantly denser (heavier) baffle improve sound quality? I'm talking about an increased density of between 6 to 8 times that of blu-tack Bringing baffle weight to near 100g). Would this conceivably improve sound, or does the weight of modeling clay/blu-tack already provide an optimal solution for the baffle weight design flaw?

 

Thank you for the very informative thread. 

 

Short answer: I don't know. Try it and draw your own conclusions. 

 

Long answer/best guess: I don't think mass loading offers much benefit (if any), If the 4 shock absorbers' rubber caps remain in place. The shock absorbers decouple the baffle/driver from the cup to minimize "sympathetic" mechanical vibration. The baffle partition "ribs" may offer enough stiffening to adequately control driver vibration, if actually present, obviating the need for mass loading with Blue Tak, plasticine, Newplast, etc.

 

I have a hunch that the driver does not produce enough vibration to matter one way or the other. Note that the driver frame is very rigid and securely attached to the baffle with 3 screws and 2 side snap tabs. There is a gasket between the baffle and the under-surface of the driver. The driver diaphragm is very light weight, its bipolar excursion is only a few millimeters, and the amount of air movement is miniscule so mechanical vibration is likely a non-issue. I suspect that acoustic resonance and standing waves are the most likely problems. These can be effectively managed by damping with foam, cotton, fiberglass, rock wool, felt, etc. for necessary acoustic absorption and dispersion of the bipolar back wave and its reflections. Pads play a significant role in sound quality and modification configurations are often pad-specific.

 

The stock T50RP and its siblings weigh 330 grams. Adding Newplast, which one source indicates its damping factor is superior to plasticine and both of these are far superior to Blue Tak, adds only 9 grams per baffle if filled flush to the top of the baffle partitions. Adding a more dense material that weighs significantly more may be over-kill, especially if not needed in the first place. Again, you'd have to try various materials and judge for yourself.

 

A case in point:  I have tried a variety of configurations using only Paxmate with either stiff felt on the back of the drivers OR a 1x5x5 cm block of Grodan Rock Wool OR cotton with good sonic results. I cut strips of Paxmate about 4 mm wide and placed them in the cups at either 45 degrees or 90 degrees, over 2x7 cm Paxmate in the side floor wells. Instead of Newplast, I custom-cut pieces of Paxmate for each of the baffle compartments and a "ring" of Paxmate around the ear side of the drivers, under Shure 840 pads.

 

Here are some photos of various mods I tried last year:

 

Noting in the baffles. Cross-hatch of Paxmate. Stiff felt.

 

Paxmate around ear side of drivers and GE Silicone II

around the rims.

Grodan Rock Wool over Paxmate in the cup floor wells.

Paxmate instead of Newplast in the baffle compartments.

 

Corner snipped from Grodan Rock Wool to expose more

of the internal cup vents for more bass.

 

Grodan Rock Wool 1x5x5 cm.

 

700

Paxmate cross-hatch in cups and Custom-cut Paxmate

in the baffles instead of Newplast.

 

 

Fostex BMF Lite Lattice Felt.jpg

A variation with Paxmate cross-hatch set at 90 degrees and

100% wool "window frame" over back of driver. Nothing

in the baffle compartments.

 

Mod 2 pix 3 ear side of baffle.jpg

 

 

 

Here's a more recent trial with sound equivalent to DBV #3:

 

 

 

Cross-hatch of Paxmate strips at 45 degrees over 2x7 cm

Paxmate in the cup floor wells. Paxmate in the baffle 

compartments instead of Newplast, 18 mm treble reflector.

 

Grodan Rock Wool 1x5x5 cm over Paxmate cross-hatch set

at 45 degrees, and Paxmate in the baffles.

 

1x5x5 cm Grodan Rock Wool. Paxmate in cup floor wells

and strips of Paxmate set at 45 degrees to acomodate

the rock wool. Not shown: Paxmate around ear side

of the drivers, under the 840 pads.

 

 

DIY Experimentation:  "There are many paths leading to the same destination."

 

______________________________________________________________

 

 

FYI/FWIW:

 

http://qualia.webs.com/newdampingfactors.htm

 

damping factors   n [eta]

....re-assessed the results of the damping factors already given, and by adjusting calculations and changing bandwidths on some of the tested higher valued materials, I have found that some materials have higher values than previously given. Those below 0.2 are unchanged, those above 0.2 have been re-assessed.

 

Here are the revised data. Any new values have the centre of the bandpass region quoted, all attenuation out of band at 24dB/oct, as before, at a Q of 0.7071.

 

 

visco elastics and soft foams

 

 

material

frequency

damping factor

 

 

 

blutack (white)

15

0.166

closed pore foam

 

0.151

expanded polyethylene

 

0.167

foam for glass bricks

 

0.288

foam board (paper)

94

0.030

polyurethane foam

120

0.054

polyurethane foam block

141

0.109

above, reconstituted

82

0.149

Plasticine'

77

0.304

'Newplast'

160

0.635

rho C' [polyurethane]

 

0.287

smart putty'

 

0.134

sorbothane

 

0.197

tungsten loaded putty

80

0.725

Wickes' 'lead' flashing

 

0.161

 

 


Edited by bluemonkeyflyer - 8/18/13 at 5:18am
post #678 of 1477
Thread Starter 
Quote:
Originally Posted by Modulus View Post

Wanted to separate this second question.

 

I'm trying to understand your dampening decisions in the cup 'wells'. It seems you've experimented with Paxmate, Acoustipack, Dynamat and Silverstone for the left and right wells, and settled on felt for the center 'column'.

 

  • Firstly, why have you used multiple materials that seem designed for the same thing? Is it not possible to simplify and use only one of these, Paxmate for example?
  • Secondly, why have you used felt for the center column and not Paxmate contiguously? (Ventilation slots and symmetry?)
  • Thirdly, what is the purpose of the rungs? Is it scatter sound waves? Have you experimented with alternate shapes? Might have missed them but I don't see measurements anallysing the improvements the rungs make.
  • Fourthly, why are the rungs a different material to the wells? From DBV3 you seem to have settled on Acoustipack wells and Paxmate rungs. Why not use the same material for the rungs since they are similar?
  • Finally, why have you not uniformly covered the entire inner cup with dampening, instead of only the wells? (Not enough space? Surely if you have to sacrifice a material for the sake of space you should sacrifice cotton and rather damp away that shiny reflective plastic.)

 

Thanks for taking the time to answer some of my questions, I really appreciate and enjoy this thread.

 

My damping decisions and configurations are based upon ongoing experiments and what sounds good to me. Successful modification configurations may be simple or complex. What works and sounds good to me may not sound good to others; and vice versa. 

 

Best wishes and please post the results of your mods.

 

beerchug.gif

post #679 of 1477
Thanks for the response. Those are pretty interesting data from qualia. What caught my eye was that it contains the 'secret ingredient' that I had discovered after searching for massive putties. Tungsten putty. I found a Chinese supplier, but it doesn't come cheap. What I find interesting is that it also has the best dampening rating while being almost 10 times as dense as the others. I was considering that or lead tape cut to size.

So in your estimation mass loading has a rather negligible effect? Is that what you're saying? Have you experimented by taking DBV3 and replacing new last with paxmate only, to isolate the effect of mass loading?
Quote:
Originally Posted by bluemonkeyflyer View Post

My damping decisions and configurations are based upon ongoing experiments and what sounds good to me. Successful modification configurations may be simple or complex. What works and sounds good to me may not sound good to others; and vice versa. 

So you discern a clear audible difference using a single damping mat material versus using two different ones in the cups?

I appreciate what you're saying about experimentation and I will do some of that when my 'test subject' arrives. I may still experiment with the tungsten if I'm feeling rich.
post #680 of 1477
Thread Starter 
Quote:
Originally Posted by Modulus View Post

Thanks for the response. Those are pretty interesting data from qualia. What caught my eye was that it contains the 'secret ingredient' that I had discovered after searching for massive putties. Tungsten putty. I found a Chinese supplier, but it doesn't come cheap. What I find interesting is that it also has the best dampening rating while being almost 10 times as dense as the others. I was considering that or lead tape cut to size.

So in your estimation mass loading has a rather negligible effect? Is that what you're saying? Have you experimented by taking DBV3 and replacing new last with paxmate only, to isolate the effect of mass loading?
So you discern a clear audible difference using a single damping mat material versus using two different ones in the cups?

I appreciate what you're saying about experimentation and I will do some of that when my 'test subject' arrives. I may still experiment with the tungsten if I'm feeling rich.

Tungsten Putty: I bought some and it was too dense to install and very expensive for a small amount. There's a photo in Post 1 of this thread, toward the end.  It's probably possible to custom-cut pieces to fit the baffle compartments, but it would take about 6 squares; I think I paid something like $15.00 for just 1 square.   I bought some golfer's tungsten powder, talc, petroleum jelly, and plasticine and made my own....labor-intensive and very messy. I cannot hear a benefit over Newplast which is ready-made and easier to install/remove than plasticine and my DIY tungsten putty.

 

Removing Newplast from DBV #3: Yes, I think mass loading the baffles has a negligible SQ effect. I tried Paxmate Plus instead of Newplast in the baffles. I cannot tell a difference but you/others may. Paxmate offers added absorption and it's lighter than Newplast. 

 

One vs Three materials: I have "opted out" of using Acoustipack Lite and Newplast in favor of Paxmate Plus, alone, when making an initial build of DBV #3....cheaper and easier with 2 fewer components. Although I don't hear a difference, others may and I won't argue with my measurements of my modified DBV #2 and how the config variations sound to me.

post #681 of 1477

Has anybody come up with an adjustable bass port? I keep going back and forth between two different sized bass ports. It's like one week i'll want more bass out of them, and then the next I'll want less. Lately I've been using a larger bass port and last night the bass/lower mids actually got tiring and I had to take them off and stop listening for the night. Just a few minutes ago I put them on and felt the same as last night. So I made my external bass port smaller again. I've never actually moved my final bass port mod to the inside because I keep changing my mind on how much bass I want out of them, so instead I just keep using masking tape over the 4 slots and poke whatever size hole I want through the tape. I'd kind of like to finalize my mods, but I really want an adjustable bass port. So, again, has anybody came up with anything, besides Mr. Speakers with his 3D cups?

post #682 of 1477
Quote:
Originally Posted by jasonb View Post

Has anybody come up with an adjustable bass port?

 

sort of...

post #683 of 1477

I have thought about an external bass port for a while, but in order to have it implemented without the custom cups ala AlphaDogs, a way to do it is to have a sliding mechanism on the vents.  There will have to be a certain level of taping to make the vents relatively air tight.

 

Alternatively, you can try sticking a syringe like apparatus on top of the bass vent, punch little holes on the body of the syringe, and then adjust the syringe to open/close the number of holes.  This will make the headphones horribly ugly though.

post #684 of 1477
Thread Starter 
Quote:
Originally Posted by ambchang View Post

I have thought about an external bass port for a while, but in order to have it implemented without the custom cups ala AlphaDogs, a way to do it is to have a sliding mechanism on the vents.  There will have to be a certain level of taping to make the vents relatively air tight.

 

Alternatively, you can try sticking a syringe like apparatus on top of the bass vent, punch little holes on the body of the syringe, and then adjust the syringe to open/close the number of holes.  This will make the headphones horribly ugly though.

I've toyed with the idea of applying velcro around the outer perimeter of the cup vents and making rectangles of thin plastic with the opposing velcro applied around the under surface to align with the cup vent velcro. Cut a small hole in the plastic rectangle, say 4 mm wide, that aligns with one of the 4 cup vent slots. By making several plastic rectangles with different size bass ports, it would be easy to switch them out to tune the bass.

 

Another idea that I like better is to use thin, flat rubberized magnets instead of velcro. I think magnets would work better than velcro by ensuring a tight seal and should last longer than velcro.

 

Here's what I ordered from Amazon to try:

 

1" flexible magnetic squares (24 to a package for less than $5.00. These are only 1/16" thick. I think I will try a 5 mm "picture frame" attached to the outside of the cup vents with rubber cement. Next, I will cut a rectangle 23 x 17 mm from another magnetic square and cut, or punch, my 4 mm bass port that will be aligned with the bottom cup vent slot. The magnets will attract one another and will hopefully seal against one another. The top magnet with the bass port will only stick up about 1/32" above the edge of the top cup vent. It may be possible to shave off that upper portion of the bass port magnet, using a razor, so it will sit flush with the cup housing. I'll make additional top magnets with 2, 3, 5, and 6 mm bass ports for comparison.


Edited by bluemonkeyflyer - 8/20/13 at 4:23pm
post #685 of 1477
I do it ghetto style and just change the amount of blue tack over the vents, sometimes covering 3, other times 3 1/2, works great.
post #686 of 1477

I'm using masking tape over all 4 vents slots and simply poking a tiny needle sized hole, or a hole the size of the tip of a ballpoint pen. With my configuration, just a needle sized hole is enough to relieve enough internal pressure to increase bass response, especially sub bass response. It's pretty much the same concept as tuning a bass reflex port on a speaker enclosure except for the fact that all the venting is doing here is relieving pressure in the housing. 

 

When I increase the size from the needle sized hole to a hole the size of a ballpoint pen tip, what I notice most is more upper bass quantity. Sometimes it's enough where it actually bleeds into the mids and can get fatiguing. So, I guess the answer is to just get used to the sound with the needle sized vent. 

 

I eventually kind of see myself with the Mr. Speakers Alpha Dogs though. 

post #687 of 1477

Has anyone tried to control the depth of the baffle hole and/or cup vents? You look at the bass ports on speakers and there's often a tube inside since the resonant frequency is dependent on the mass of air in the neck.

 

The baffle hole has some depth since it flows through a corner of the driver assembly. The cup vents have hardly any depth (in which case the "depth" is actually a function of the equivalent radius). Then again, this is all assuming that those ports/vents are acting in some sort of helmholtz configwhatchamacallit. 

post #688 of 1477
I could be wrong, but I'm not sure a "tube" is really going to make any difference like it would on a speaker enclosure. In the case of headphones it's simply to reduce pressure inside the cup.
post #689 of 1477
Quote:
Originally Posted by Armaegis View Post

Has anyone tried to control the depth of the baffle hole and/or cup vents? You look at the bass ports on speakers and there's often a tube inside since the resonant frequency is dependent on the mass of air in the neck.

 

The baffle hole has some depth since it flows through a corner of the driver assembly. The cup vents have hardly any depth (in which case the "depth" is actually a function of the equivalent radius). Then again, this is all assuming that those ports/vents are acting in some sort of helmholtz configwhatchamacallit. 

I can see someone making a bass port similar to that on the Alpha Dogs using the baffle vent. Since it does have a certain length, and that length could be adjusted with a set screw (or something), it may work well, who knows?

post #690 of 1477

I've asked this before, and I guess I have to ask it again, does anybody know of anyway to tune these so there in less output in the 250-500hz range? Mine still sound a bit honky and sound a lot better when I EQ out 3db at both 250 and 500hz. I'd rather not have to resort to EQ, any ideas?

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