EP21 - Single Stereo Loudspeakers

[KLBIrd]

In the late 1950s, when stereo burst forth there were a number of schemes derived to "fill in the center hole" of stereo systems. The first consumer systems were housed in coffin like consoles with the left and right speakers at each end. Stereo affect was limited and the word imaging was not used in audio. Paul Klipsch did a number of papers on how to derive the "third channel", both pre and post amplifier'n and a number of systems were sold using a third channel speaker. You might want to look up some of his work.

I like the idea, and in this era, when most everyone gets their music through ear buds the single speaker concept could find a market. Have you tried isolating the three drivers to prevent modulation artifacts? Also co-ax speakers might get you better highs and 4 ohm auto speakers would give 8 ohms impedance instead of the 16 ohms sum your design would produce per channel. I'm going to build a system using some old auto speakers I have in the collection, along with 10" DVC woofer.

[Elias]

Originally Posted by KLBIrd

In the late 1950s

Three speaker with linear stereo matrix is the system I'm using at the moment.

As pictured in post #4, the single speaker stereo is a simulation of the three speaker concept.

Originally Posted by KLBIrd

Have you tried isolating the three drivers to prevent modulation artifacts?
Also co-ax speakers might get you better highs and 4 ohm auto speakers would give 8 ohms impedance instead of the 16 ohms sum your design would produce per channel. I'm going to build a system using some old auto speakers I have in the collection, along with 10" DVC woofer.

Since the driver signals are on linear dependency through the matrix there is no 'modulation artefacts' ?

Sure coaxial elements might also perform well.

Check again the impedance math, total is not 16 ohms what the amplifier sees but 12 ohms. In practice it is a bit lower due to the psychoacoustic filter.


- Elias

[KLBIrd]

Thanks for the reply Elias, and you are right on the impedance due to two the speakers in parallel seen as 4 ohms. I was looking at each independent leg. 4 ohm drivers would be seen as 6 ohms, a closer match to most modern amps. What typical values have you used in your filters with the drivers shown?

[Elias]

For 8 ohm drivers good values for psychoacoustic filter as a starting point for experimentation can be found here:


It depends on the side wall reflectivity, room width and the specific drivers used, among others. So this is a guideline only


- Elias

[KLBIrd]

Thanks for the reply. I did some experimentation and in my application I liked the sound with out the filter. One could build a system with various values selected by rotary switch for differing locations.

[gainphile]

Originally Posted by graaf

months have passed so ...how's the EP21?

I've been really busy of late with work/family !

I already have all the stuff needed, drivers, terminals, even cables !

Only need the box.... Hope to kickstart this project again really soon

[Elias]

Originally Posted by gainphile

Only need the box....

I agree, the box is usually the hardest part You could even try cardboard box to get first feelings like I did

[KLBIrd]

Here is my version of the single stereo system. Three four inch mids with Piezos in a separate chamber with a sealed ten inch DVC with the crossover at 400HZ. OK, the color is strange but I had the paint left over and what else to you do with MDF?

It needs a narrow room ten feet of less to give stereo, however place it in a corner and you get some good imaging and of course more bass than you need.
The Piezos are attenuated 6dB to match the mids and the center channel is down 3dB. An interesting experiment that saves you some wood and work but it was tried in fifties and sixties but never caught on.

[KLBIrd]

Photo did not transfer so we try again.

[gainphile]

Very nice !

It will be a long weekend ... To build hopefully !