Cheap Acoustic Simulator (Crossfeed) for Headphones

Intro: Cheap Acoustic Simulator (Crossfeed) for Headphones

Hi! Welcome to my second instructable! Don't forget to rate and comment! :D

First off, what is an "acoustic simulator"?

It can be anything to simulate the effect of being in a room, creating an effect of open space, or even give the illusion of hearing sounds from different directions. This is usually achieved through software. Results vary, as there is coloration to the sound and the simulations can be very invasive to listening.

Unlike software implementations, what I will show here is a simple hardware solution to get rid of the "in-head" effect that headphones have. It is not designed to give the illusion that you're in an auditorium with reverb. Rather, it is designed to simulate the feeling of hearing audio in front of you. Its purpose is to improve the soundstage.

The main goal is to reduce fatigue and make headphone listening natural and pleasant.

In this instructable, I will show my build of a Linkwitz crossfeed. This particular design was modified by Chu Moy, the person responsible for the famous "cmoy" headphone amp design. I take no credit for this design, only my simple modifications.

STEP 1: What Is a Crossfeed? (Theory)

When you hear sounds panned hard right/left with headphones, you don't hear anything in your other ear. In real life, you always hear sound with both ears. A person speaks to the right of you. Do you only hear them with your right ear?

In reality, you're hearing with both. Your brain recieves signals from both ears and interprets the direction from which the sound is coming from. You may be hearing to the right of you, but your brain also interprets if the sound is close, far,  in front of, or behind you. When you listen to audio with headphones, this directional information is lost.

To remedy this, we welcome the crossfeed. A crossfeed circuit bleeds the left and right channels just a bit to give off  that lost sense of direction. While it does not give the illusion of surround sound, it does give you the feeling of listening to audio from speakers in front of you rather than through headphones on your ears.

Music from live performances and orchestras sound particularly good with a crossfeed. Mono recordings and music that generally sits "in the middle" will not benefit from a crossfeed much, or at all.

STEP 2: Tools & Components

Other than the cost of shipping, the components required to build this circuit are fairly cheap. If you cut the cost of enclosure, protoboard, and tools, you can probably build one with very little money. You may even have some of the parts lying around from other projects.

Because I was aiming to spend as little money as possible, I made some changes to the modified Linkwitz crossfeed that is presented by Chu Moy.

The original circuit had a switch for bypass and another to adjust the "perspective" of the crossfeed effect. I did not use these. A bypass would only be good if you wanted to compare before and after crossfeed. The other switch was not used, as I did not care to adjust the crossfeed from my final setup and wanted to save a little more money.

Test the circuit on a breadboard, if you have one. You may want to make changes as stated in the notes below.


Tools:
- soldering iron and solder
- small screwdriver
- scissors / wire cutter

Components:
- 2x 150 ohm resistor (R1)*
- 2x 100 ohm resistor (R2)
- 2x 910 ohm resistor (R3)
- 4x 330 ohm resistor (R4,R5)
- 2x 0.22 uF, 35V film capacitor (C1)
- 2x 1.20 uF, 35V film capacitor (C2)**

- 2x 3.5mm audio jack***
- 3.5mm male-male cable to connect to devices***

- jumper wire
- protoboard / cardboard(?)
- something to put it in


*You can experiment with the soundstage and 'open-ness' of the sound by using different values of R1. Lower values will make it feel as if you're hearing things farther away, while larger values will bring sounds closer towards the middle. The "perspective" switch in Chu Moy's original schematic switched between values of this resistor.

**Changing C2 will alter the threshold frequency and depth of the crossfeed. I used a 1.0 uF capacitor instead of 1.2 uF. More explanation on threshold frequency and how this works can be found here.

***Depending on the type of input you're using. You may want to use RCA or 1/4" jacks and cables.

STEP 3: Protoboard Substitution

I did not have time or money to go out and buy prototype boards, so I decided to improvise. As you can see by the image below, instead of protoboard, I decided to solder on top of cardboard. It is much like point-to-point soldering, only you have something to hold everything in place. I cut a piece from a box, as it has more than one layer and doesn't bend or fold easily.

The first thing you should do is figure out the layout. If you decide to follow my simple circuit, I have provided some images on what the layout should look like. While it isn't the most compact, it is very easy to follow.

Simply poke holes with your small screw driver to where the components will be placed.

STEP 4: Build

There are a few ways you can go about soldering the components to each other on the cardboard. I went ahead and placed all the components on the board and bent the leads, to prevent them from falling off of the board.

Make sure to bend the leads, that are to be soldered to each other, in the same direction and group them where applicable. You can do one entire channel first, and then the other. Depending on your soldering skill, you may or may not want to solder one component at a time. Soldering groups of leads seems to be much easier.

*Be careful when soldering R5, as the leads may touch. They are arguably the most important resistors, as they are the ones where the signals are being crossed into each other.

Forgive my drawings, they are not to scale.

The layout follows the modified schematic in the last image. Original can be found here.

STEP 5: Testing

Here comes the best part of DIY. Testing!

To test the crossfeed, all you need is some music to listen to.

If you want to see how much audio is bleeding into each channel, connect the crossfeed to your computer using a 3.5mm male-to-male extension cable and open up your favorite media player. Switch all output to either the left or right and see how it is. If all sound on one side seems louder than all sound on the other, you may have done something wrong. Check your connections!

Be aware that there will be a total volume drop due to the crossfeed. This is normal.

STEP 6: Enclosure

Once done, you need to put it in something.

I happened to have an extra enclosure laying around and decided to use that. You can use anything you want. Much like the popular cmoy headphone amp, you can try putting it inside an altoids tin. To match the "protoboard", why not put it inside a small cardboard box? Use your imagination.

I really like these hammond cases. I tried putting a headphone amp in this particular model, but it came out very, very cramped. It seems fairly roomy for the crossfeed, and matches my amp perfectly.

STEP 7: Final Thoughts and Improvements

It takes some time to really notice the impact of this crossfeed circuit. At first, I barely noticed it and almost wrote off the whole idea to be nonsense. After a good hour or so of listening, I decided to not use it and immediately noticed the difference. Your mind needs a little bit of training to get used to the feel of listening, and is well worth the time.

Because of the volume drop, it is important to use good, clean amplification before or after the crossfeed circuit. It works great when paired with a cmoy headphone amplifier. While not having a good amplifier or sound source may discourage you from building this, it is still fun to try out and only requires a few components to build.

The crossfeed filter also works surprisingly well when coupled with my Playstation 3 and cmoy headphone amp. There was some benefit when playing first-person shooters online with headphones on. It was easier to determine where sounds were coming from in-game and it felt a lot more natural with the crossfeed on. If you didn't see it, check out my quick and dirty way to use headphones with a PS3.

In the future, I want to build an improved cmoy headphone amplifier with this particular circuit built in. Some simple improvements I plan are to shrink the size of my layout, use smaller sized capacitors to save space, and to possibly include a rotary switch to adjust the soundstage.

Well, those are all my thoughts for now. I hope you enjoyed reading my instructable. Don't forget to rate and comment! I appreciate any thoughts or criticisms. If you have any improvements or suggestions, give them! Thanks. :]

Comments

[DaveK183.]

As you were talking about the games, I think its important to set the settings to ''speakers'' as an audio output. Headphones setting actually tries to simulate this crossfeed.

[padbravo]

Wow!

I will try it... tks... also, the idea to build de amp+soundstage, its a good one...

(BTW: I did not get it... save some cents on components, but, U have a expensive (sort of) headphones...)

[wbwillie]

I went ahead and bought a pair of iFrogz Coda headphones, the ones with the removable cord... you can always use a 3.5mm to dual RCA cord on those and just plug right into the RCA jacks

[kweinberg]

This was awesome! My first real DIY soldering project and it works and sounds great with no troubleshooting! I had to use 1k instead of 910 resistors and electrolytic and mylar caps, but it doesn't seem to have messed anything up too bad. I'm looking forward to the day when I understand enough to start my own circuits like this. Thanks for the great instructable!

[faxwork]

Thanks!

You should be careful with electrolytic capacitors being in the audio path because they have a polarity associated with them. AC signals like audio are moving positive and then negative and then back. Over time, electrolytic capacitors "go bad" when the polarity is backwards. It might not be a problem now, but maybe in the future it will be.

Electrolytic capacitors are mostly used for power sections in a circuit that require filtering. An example is on a power supply to remove noise.

It's pretty awesome that it worked on the first try. That almost never happens. :D

Good luck on your future projects.

[lindenturn]

This is a really good project. You did a nice job putting it together. Just as a thought people might want to use one of the "bread boards" that has solder pads instead of the cardboard to make it a little more sturdy.

[faxwork]

Thanks for the nice words. So far, after extended use, none of the parts have become loose. Although this is the case, I would still suggest using some sort of board if it's available as my method is only good if you have little to nothing in the way of parts.

[nshabbir]

someone plz send me circuit diagram of this equipment

[faxwork]

You'll find a link to the original design and an image of my modified version in step four.

[faxwork]

I'm not sure if it's one of the best Instructables, but thanks for the comment. :)

Currently I'm trying to come up with another simple electronics project revolving around audio. If anybody stumbles across this comment, don't be afraid to give ideas. :)

[7wist]

Thanks a ton man, I just soldered this up my my dads Christmas present :)

[faxwork]

What a great gift idea! I hadn't thought of that.

Tell me if he likes it. :]

[killerjackalope]

Great build, I wonder it it's easier to have a physical crossfeed or not, with digital music being to ubiquitous. Though I suppose a couple of hours building this would be way faster than fiddling with every song...

[faxwork]

I've noticed that many software crossfeeds can be invasive and can color the sound a bit. I built mine in about an hour, not including time spent designing the layout. :D

If you want more options, consider looking in to switching between different R1 resistors. This will enable you to adjust the soundstage to your choosing on the fly.

Thanks for the comment. :)

[killerjackalope]

Good to know, I may well build one depending on my ever changing sound setup, really taken to using my little bluetooth speaker about the house and just bringing it with me but this would be great for the bus etc, using big cans seems to make the issue more apparent than leaky earbuds...

[faxwork]

It's really great to have on the go, but the only problem I have now is finding a short 3.5mm cable to use it with. Having a cable from my sound source, between the crossfeed and amp, and my headphones is a bit much. :/

[killerjackalope]

Might be better with a small cable soldered direct to the board rather than a jack.

You get short cables in audio shops, also handsfree kits etc often have odd length cables with them if it's any help...

[faxwork]

I'll consider the idea. I just hate that it feels so "permanent". :p

Maybe I'll replace my input with RCA jacks instead. I see RCA to 3.5mm adapters everyhere.

[killerjackalope]

How about wiring on a little cable but keeping the input too? Just a couple of inches of cable you could slide away when you're using the input...

[faxwork]

Sounds good, but I would still need to find a cable to tear apart. :|