My Mind's Playing Tricks on Me - More Fun with Waveguides and Psychoacoustics

[Patrick Bateman]

While messing around with a center channel this week, I accidentally created the most realistic soundstage I've ever heard in a car. Considering that I've been studying this subject for the better part of twenty years, I thought some others might enjoy reading about what I did, and some further experiments to improve things.

A lot of my previous work on the subject is over on diymobileaudio.com. However, the more that I work with car stereo, the more I realize that the tricks we use in the car can be used at the home and office.

For instance, I sit in front of a computer for 8-12 hours every day, and the work day would be a lot more enjoyable with a high quality stereo. Many of the tricks featured in this thread will also work in very small rooms, for instance a home office or a computer gaming room.

What I am going to explore in this thread is using psychoacoustic tricks to fool the listener into believing that they hear speakers which aren't there.

We've all seen these HDTV soundbars, which attempt to recreate a five-channel experience using as many as a hundred speakers in a single enclosure. The way that the good ones work is that they create a beam of sound which is focused at specific locations in the room, creating reflections which fool the listener into believing there are speakers there (which don't exist.)

Here's the thing though - they suffer from distortion, due to the small size of the drivers, and their goals are quite ambitious - five channels from one enclosure.

What I am going to document in this thread is the use of a single enclosure to cover stereo high frequencies, using waveguides to control the beam, and compression drivers to lower distortion down to inaudible levels.

If my engineering goes according to plan, we'll have two virtual speakers which seem to emanate from the left and the right.

If you're interested in reading further, see these threads:

Creating a Soundstage with Waveguides and Psychoacoustics - diyAudio

Creating The Perfect Soundstage - DIY Mobile Audio

Anyone Tried Using One Tweeter? - Page 2 - DIY Mobile Audio

[makingmoney]

Anyone Tried Using One Tweeter? - Page 2 - DIY Mobile Audio
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OT: I used my ATC mids and one Stage Accompany ribbon tweeter as a sound bar under my 42" TV for a couple of months. Sounded good, but I prefer stereo, with 2 tweeters.

[judtoff]

Just read your other threads. Wow, great work.
I'm going to try out what you did with the 2" drivers mounted in the middle of the dash. Are these the drivers you used Parts-Express.com:*Peerless 830970 2" Full Range Driver 4 Ohm | Peerless P830983 2" Full Range Driver tymphany vifa danish speaker technology dst lat250 Symphony of Savings Peerless070109 npa00453? Either way I think that's what I'm going to use.

Keep up the great work!

[dantheman]

Patrick,

Have you ever tried just mono? I've been doing it for years and it's still my preferred method for listening to music. The sweet spot is everywhere you'll practically be and set up is like falling off a log.

Dan

[Patrick Bateman]

Originally Posted by judtoff

Just read your other threads. Wow, great work.
I'm going to try out what you did with the 2" drivers mounted in the middle of the dash. Are these the drivers you used Parts-Express.com:*Peerless 830970 2" Full Range Driver 4 Ohm | Peerless P830983 2" Full Range Driver tymphany vifa danish speaker technology dst lat250 Symphony of Savings Peerless070109 npa00453? Either way I think that's what I'm going to use.

Keep up the great work!

I am getting very good results with a Peerless 830970. I'm feeding it about four times as much power as it's supposed to get, and it's taking it like a champ. Then again, I have it crossed over at 3khz, so that helps

While it's marketed as a woofer, due to it's very small size, it's makes a compelling tweeter. It has a copper cap and an underhung motor. So if you use it down to 200hz, it's distortion performance is good considering it's size. But if you limit it to high frequencies only, you're basically looking at a tweeter that can run with the big boys that cost $50 and up.

As a bonus, it's smaller than 80% of the tweeters out there, and it has enough excursion to be used with very shallow slopes.

I am also using it dipole, as I've found that dipole tweeters sound very 'open'.

[CLS]

Mono, I've been thinking on and off over the years. Eventually I never do because it's hard to integrate with video section of the system

The height of (TV) screen is at eye-level, which is almost the same as ear-level the speaker(s) should be. And it's not so practical (for me) to use projector/screen all the time. So I've still not figure out how to put them together

Two separate systems? Good idea, but the space is not allowed

[ultrakaz]

Originally Posted by Patrick Bateman

If my engineering goes according to plan, we'll have two virtual speakers which seem to emanate from the left and the right.

Hello,

How big is this one enclosure going to be? And what would the maximun listening distance be?

Thanks.

[Elias]

Originally Posted by Patrick Bateman

What I am going to explore in this thread is using psychoacoustic tricks to fool the listener into believing that they hear speakers which aren't there.

Your goal is to make the listener to hear the speaker? I think what you like to do is to make a phantom image at the location where there is no speaker?
Some say a stereo setup can do this, but I'm not convinced

Originally Posted by Patrick Bateman

For instance, I sit in front of a computer for 8-12 hours every day, and the work day would be a lot more enjoyable with a high quality stereo.

For this, you might find Ambiophonics satisfying.

Originally Posted by Patrick Bateman

What I am going to document in this thread is the use of a single enclosure to cover stereo high frequencies, using waveguides to control the beam, and compression drivers to lower distortion down to inaudible levels.

Stereo from one speaker for home listening:
Stereolith Loudspeakers Question


- Elias

[Key]

Originally Posted by Elias

I think what you like to do is to make a phantom image at the location where there is no speaker?
Some say a stereo setup can do this, but I'm not convinced

You can do it with just traditional stereo. You can get phantom out of speaker localization up to about 90 degrees ime. BUT it is not as strong as just sticking a speaker in that location. It always seems to be bandwidth limited even if the source isn't. And on some speakers it can sound "phasey". I've never had much luck with the front speakers that bounce sounds of the side walls though. I have had success with rear Bipolars that are similar but I really don't think it has anything to do with the side wall as much as it is summing localization.

[Patrick Bateman]

Originally Posted by Elias

Your goal is to make the listener to hear the speaker? I think what you like to do is to make a phantom image at the location where there is no speaker?
Some say a stereo setup can do this, but I'm not convinced





For this, you might find Ambiophonics satisfying.





Stereo from one speaker for home listening:
Stereolith Loudspeakers Question


- Elias

I tried ambiophonics in the past, and found that the processing sounded unnatural and distracting. As you know, it's possible to do the same thing with a physical barrier.

In this thread I'll be doing something similar. But instead of a physical barrier, I will use a waveguide to narrow the response of the high frequency drivers.

Theoretically, this should give us the best of all worlds:

• Using a wall to eliminate crosstalk is effective, but it looks ridiculous
• Using DSP to eliminate crosstalk *should* work, but sounds unnatural to me. It also reduces dynamic range.
• A carefully designed waveguide can limit radiation even more effectively than a physical barrier.

Stay tuned...