Weak bass in DIY headphones?

[anyar]

Ok, so I had a pair of 3M hearing protectors and a pair of broken Sony MDR-NC6's lying around, and I decided to combine the two. Everything came together nicely, despite my horrible soldering and the 99% Sn Walmart solder I used (nothing else was open today and I didn't feel like waiting), but the bass is very weak. I'm guessing that this is because of the sound-absorbing foam inside the hearing protectors, but I saw this, and thought maybe drilling some holes in the cups would help? I'd like to hear from someone that knows more than I do before I go drilling holes and reducing the isolating qualities of what I have.

 

[anyar]

Pics:
http://i58.tinypic.com/op9pae.jpg
http://i61.tinypic.com/11lluro.jpg

 

[billybob_jcv]

Oh boy - I think I would spend A LOT of time reading in the DIY forum before you start drilling holes. It might not look like it, but the cups of quality headphones are actually carefully designed, as is the way the drivers are mounted, and the baffle between the cup and the driver face. Drilling a hole in the back of the cup is not the same thing as having a port from the cup behind the driver through to the driver facing your ear. Small changes in these air channels can have significant effects. I'm not a headphone designer, but I know enough to know that it's not as easy as it looks - at least not if you actually want the headphones to sound good...

 

[anyar]

Oh boy - I think I would spend A LOT of time reading in the DIY forum before you start drilling holes. It might not look like it, but the cups of quality headphones are actually carefully designed, as is the way the drivers are mounted, and the baffle between the cup and the driver face. Drilling a hole in the back of the cup is not the same thing as having a port from the cup behind the driver through to the driver facing your ear. Small changes in these air channels can have significant effects. I'm not a headphone designer, but I know enough to know that it's not as easy as it looks - at least not if you actually want the headphones to sound good...

Well, these are not the cups of quality headphones I'm talking about drilling; they're the cups of some 3M hearing protectors (the pics I was going to post are pending approval I guess??). I desoldered the drivers from the donor pair, snipped the wire off a pair of earbuds that had gone bad, drilled a hole and put in a female 3.5mm jack off of another failed speaker, then soldered everything together within the hearing protecors.

 

[billybob_jcv]

That's my point. Look at this exploded diagram. The driver sits on a baffle plate that separate the volume into two parts. There is space in front of the driver from the baffle to the ear that is sealed by the ear pads. then there is a separate volume behind the driver from the back of the baffle to the rear of the cup. Do you have that separation into two volumes?

 

[anyar]

There is space in front of the driver, but behind it is filled with foam. From what you're saying, I should make sure there's space behind the driver? I could probably take out the foam and rig up some kind of mount for the driver.

 

[billybob_jcv]

You need to separate the front side of the driver from the rear. Think about a speaker box. The front of the driver is isolated from the volume behind the driver by the front baffle of the enclosure. Then, if the speaker is a bass-reflex design, they put a specific size port in the box to increase the bass. But in order for that port to be effective, the volume behind the driver must otherwise be sealed off from the front of the driver. Take any speaker driver out of the enclosure, and when the front and back are in the same air, you lose all the bass. There actually are "open baffle" speaker designs, but these still require a that the driver be mounted to a baffle board.

 

[ProtegeManiac]

  I could probably take out the foam and rig up some kind of mount for the driver.

 

Your problem then will be resonance as the soundwaves bouncing off the rear side of the drivers hit the surface of the ear muffs. You can potentially lose more bass response due to that. That's like people blowing hundreds of dollars on new car speakers, then just mounting them without so much as laying down some Dynamat on the outer skin of their car doors, which a midwoofer with a strong upper bass response will just cause to rattle (ie it's not that the bass isn't "there," but the end listener hears the rattles and cancellation more), as opposed to those who will make a baffle and a second layer of Dynamat to isolate one side from the other. The usual sequel to that is getting angry at everyone who recommended said speakers while continuing to ignore the posts about how to mount them properly.

 

Really it would be best to go over to the DIY section. Still, why transplant those drivers into those earmuffs anyway? The headband on the Sonys are better designed with joints and other parts to compensate for irregularities of a human head and maintain a good angle for the drivers, as opposed to a chassis that's designed to just close off the ears.

 

[anyar]

Thanks for all the info guys, you've given me a good idea of what the problem actually is, and I'm going to think about how to best implement something that will work. I wish I had a CNC router, it would make life so easy!

 

 

Really it would be best to go over to the DIY section. Still, why transplant those drivers into those earmuffs anyway? The headband on the Sonys are better designed with joints and other parts to compensate for irregularities of a human head and maintain a good angle for the drivers, as opposed to a chassis that's designed to just close off the ears.

 
Ah, well the Sony's were quite old and the padding covering the ear parts had fallen off and the wire was broken. The "noise canceling" really sucked too, it just added an audible hiss and didn't block much at all. I use the earmuffs every day at my job, running earbuds underneath to listen to music, and I thought it would be fun to convert them into headphones. They actually sound pretty good, the bass is just weaker than I'd like.

EDIT: Cut 2 strips out of a toilet paper tube, made a recessed cut in the foam behind the drivers, used the cardboard for the walls and cut a circle for the back for a ghetto speakerbox, and there's a noticeable increase in bass. Thanks for the help guys!