Surround Sound for car audio

[wuemura]

Hello guys!

I was wondering, if i build a "spatial stereo" with the Philips TDA3810 and using my car audio REAR output, could this make the effect of hearing  everyting but vocals and bass in the rear speakers of the car?

I think it would be a nice effect to let the front channel to be normal and the rear channels a bit different (spatial or wide stereo).

This Philips TDA3810 will do the effect or i'm in the wrong direction?

 

[audioguru2]

The discontinued TDA3810 does not make surround sound. It also doesn't make a "spatial-only output".
Instead it makes a stereo image wider by cancelling the lowest-level sound that is on both channels, and makes a "psuedo-stereo" from mono by feeding some frequencies to one channel and the remaining frequencies to the other channel.

Go to Google and look-up "Hafler Surround Sound" and you will see how to connect a speaker or two speakers to the "difference" signal in stereo to hear what you want. It has a small surround effect but there used to be (30 years ago?) a Motorola IC that applied variable Full-Logic gain to it and it sounded quite good. it was called "SQ Surround Sound" and some vinyl records were made for its effect. Ordinary stereo heard through it made weird sound cuts and enhancements.

 

[wuemura]

Thanks audioguru!!

 

[Sukhbinder]

U could use a NJM2702 3D surround audio processor from New Japan Radio Corporation (NJRC). however u'll need to connect the line out of ur car stereo to the surround processor input an u'll need to connect an amp to processor output to drive the rear speakers. so you need more hardware. u can use a TDA1555Q audio amplifier from philips. it's in a SIL package designed for car audio purposes with an output of 2x22W. its has a BTL output so take care not to connect the speaker negative to the car's ground. > u can check up the datasheets for more info.

NJM2702.pdf

TDA1557Q.pdf

 

[wuemura]

Hello Sukhbinder, thanks!

The effect that i want is the same as an Home Theater, do you know if this circuit will do the same efect? I'm working with the Hafler Surround Sound (waiting for the IC) now, tell me something, do you think that if i use a filter to make a voice attenuation i will get a better result?

Thanks!

 

[wuemura]

Oh... by the way...
I have all the power amps that i need in my car, you can see my car pictures at this address.

 

[audioguru2]

The Hafler opamp circuit should do what you want.
The New Japan Radio IC datasheet doesn't explain what it does. It has graphs showing bass-frequencies-only, some phase-shift amounts and its block diagram shows a subtraction circuit for both channels but doesn't show what is subtracted.

 

[Sukhbinder]

how about using some delay line circuits if u can handle them.  thers are some ICs like TDA1022,SAD512,SAD512D,MN3004,SAD1024A,TDA1097,MN3011 and SAD4096. u cn produce popular effects like echo, reverb, chorus ans phasing. these are CCD audio delay line circuits. u can try them out if u like.

 

[wuemura]

Thank for the reply.....

But, the main problem is how to power up the Hafler circuit, is opamp based and this kind of device need a +12vdc/-12vdc (symmetric) ???

 

[audioguru2]

the main problem is how to power up the Hafler circuit, is opamp based and this kind of device need a +12vdc/-12vdc (symmetric) ???

Opamps don't need a positive and negative supply. They just need their inputs biased at a voltage that is half-way on a single supply. Then they would need bias resistors and coupling capacitors. As the coupling capacitors charge when the power is turned on, the speakers would probably make a "pop" noise.View attachment 39128

 

[wuemura]

This could be a problem, the circuit ask for a +12v, -12v and GND, maybe i will have to work out an dc-dc converter for this circuit.... or not.

Maybe i could do something like this but the voltage will be too low (+- 6v), the second option i think it will not give the circuit enought power 40ma. Or maybe work out a way to convert the car 12vdc to something like +-15vac and use this circuit instead.

After a few tests maybe i will add a level control and a specific filters and maybe an active crossover control to the centre and subwoofer output.

View attachment 39131

 

[audioguru2]

This could be a problem, the circuit ask for a +12v, -12v and GND, maybe i will have to work out an dc-dc converter for this circuit.... or not.

The circuit can be modified simply to use a single supply as I showed before.
It doesn't need a total of 24V, the TL072 opamp works fine with as low as 7V.
The signal voltage is nowhere near as high as 24V.

After a few tests maybe i will add a level control and a specific filters and maybe an active crossover control to the centre and subwoofer output.

You missed joining some parts on your schematic. The center and sub-woofer are not the sum of both channels, they are just the right channel. Your center and sub-woofer level control doesn't work.
I corrected your schematic:
View attachment 39132

 

[wuemura]

Ok, fixed.
I will work on the values to work with simple supply. Tell me something, what about noise? What should i consider, killing?

View attachment 39133

 

[audioguru2]

Noise is easy to eliminate.
With a single supply, the half-the-supply-voltage reference needs filtering with a capacitor to ground as I showed. Then use shielded audio cables to connect everything together.

 

[wuemura]

I've been messing around a bit, but i need to build this to make further tests.

View attachment 39135

 

[audioguru2]

You had some missing parts. You also had some extra parts including parts for positive feedback! I fixed the schematic.

View attachment 39136

 

[wuemura]

Thanks audioguru.
One thing that mess my mind aroud was the fact that there the circuit is using L/E channel input in to +/- of the IC, but you solve it!

Now i have made two versions, one that you have fixed and another one based on your modification.

View attachment 39137

View attachment 39138

 

[audioguru2]

In your fix5 circuit, the DC voltage at the input (it could be 0V) determines the bias voltage of IC1B since there aren't input coupling capacitors. Also the input to IC1B is attenuated by the additional 100k resistor.

In your fix5-alt circuit, pin 5 of the IC1B opamp isn't at half the supply voltage so its output might clip unsymmetrically, especially when the pot is turned down.

 

[wuemura]

Ops, my mistake! Let me fix that.