Surround speakers and HRTF

[Paul W]

Looking for your thoughts on HRTF, as it relates to surround speakers. In this case, the application calls for a diffuse soundfield but, by nature, (all?) dipole surrounds suffer from ragged polar response. So, the search for a different solution.

For clarity, let’s assume a single side channel and ear/brain response rather than a microphone. “What if” we space two identical side surround speakers +/- 20 degrees fore and aft of the listeners head and feed them an in-phase mono signal. Will the different HRTFs decorrelate the two acoustic sources?

Would pink noise be the best test signal?

[Dennis H]

Define surround speaker. Do you want to be able to point to discrete sounds coming from beside/behind you (motorcycle, guitar, whatever)? My sense is that's the way to go with today's music/movie tracks. If the sound mixer wants it diffuse, he'll mix it that way. Those dipole thingies are so 90s when the surround channel was in mono and you needed to 'decorrelate' it. Now we've got 7.1 baby!

[Paul W]

Hey Dennis,
Your point about about directors intent is clearly valid but, for music, I simply don't care for ping-pong surround. It's fine for movies, and some well recorded multi-channel music (like the AIX audience perspective) but, for me, it can be extremely distracting/irritating with more aggressive music mixes.

This AV room will be too dead for stereo and I'm willing to sacrifice a motorcycle or two for a more ambient approach to music. So, in this case, surround means envelopment rather than laser targeting listeners ears. Yup, I'm stuck in the 90's, or maybe the 70's :W.

I think you've studied this stuff more than most, so your thoughts on the HRTF question? If it will work there should also be more uniform audience coverage with 8 surround speakers rather than 4.
Paul

[Brian Bunge]

Maybe I'm stupid (watch it!) but I have no clue what HRTF is. Can you enlighten us?

[---k---]

Brian,
I googled it yesterday. http://en.wikipedia.org/wiki/Head-re...nsfer_function
It sounded way to complex. I'm waiting for the experts here to explain it all.

Though, I tend to agree with Dennis. I've never been bothered by my surrounds. They can be quite diffused when intended and very precise at other times.

[Paul W]

In a nutshell, Head Related Transfer Functions provide our directional clues through through interaction of sound with the head, torso, and the various parts of the ears. Differences in level, time arrival, and relative frequency response between the two ears provide clues to the brain resulting in localization of the source.

That's my 2c version. Books on acoustics like Everest's "Master Handbook of Acoustics" go into far more detail. (BTW, that book is a fantastic source of information on hundreds of subjects of interest to speaker builders.)
Paul

[Brian Bunge]

Cool! I've got that book and resently found it again while going through boxes that hadn't been cleared out since we moved in 2 years ago. I'll have to check it out again.

[ThomasW]

Your point about about directors intent is clearly valid but, for music, I simply don't care for ping-pong surround. It's fine for movies, and some well recorded multi-channel music (like the AIX audience perspective) but, for me, it can be extremely distracting/irritating with more aggressive music mixes.

This creates a paradox....what you want to hear vs how the mix was made.

The obvious solution is of course......headphones... :B

Or changing the soundfield settings in the prepro to whatever option most closely approximates DynaQuad.

As the number of discrete channels goes up, I prefer monopole effects speakers. This avoids the smearing I associate with dipole effects

[Dennis H]

Paul, movie theaters have always used multiple surrounds so that should work fine for what you want. The dipole surrounds were just a way for THX to try to get the same sound from a single speaker.

If the drivers are relatively inexpensive, you could go with more than 2 for each channel. Maybe some fullranges and use however many you need for the bass response. TB W4-1337 maybe? I doubt you'd need tweeters in that application.

[Paul W]

Thomas,
Funny you should mention headphones since that is the only sound system I have at the moment. Everything else is in boxes for another month!

Dennis,
I've listened to theater surrounds with this in mind and it does seem to work quite well, though the angles and distances are different than I have in mind. I'm just wondering if anyone here has been down this path before and can offer pointers on proper tests, what to listen for, and ideas to try...like the multiple full rangers + bass. This is "bench racing" until some realistic tests can be set up, and I'm anxious to start!
Paul