Acoustic delay effect (experimental)

[Dr.EM]

Hello all

I have had a strange idea for an audio delay effect. Most now use digital storage or tape delays, but I am keen to try a real acoustic delay. I am aware of the big limitation of a fixed delay period, but it's an experimental thing and I change the playback speed of my samples a lot anyhow.

My idea is to use a flexible hose, I have seen one 4mm internal, 6mm external. I will say around 150m will be used for a 437ms delay time, but certainly over 100m. I plan to "drive" the line with an inner ear/ear canal phone and recieve at the end with a small electret capsule (WM-61A or similar). Electronics to adjust feedback levels etc will be incorporated.

My concerns are firstly, can a small ear piece drive a 150m hose? How would you find out/work this out? It should act as a type of transmission line so I would expect it to be efficient?

Secondly, I do not want the sound to be a perfect replica at the other end (I'd use my existing digital delays for that!), but I also don't want it to be too seriously degraded. I'm expecting to experience a loss of treble, mabye some resonance effects and some reverb/ghosting from sound reaching the mic early through the hose walls etc. Any ideas how much treble loss I am likely to experience? How significantly will bending of the hose effect this?


I know this is pretty obscure but any insight is appreciated!

[Dr.EM]

I have mostly been trying to make progress on my main speaker project but am still interested in this idea! Any thoughts?

[scott wurcer]

Originally Posted by Dr.EM

I have mostly been trying to make progress on my main speaker project but am still interested in this idea! Any thoughts?

From my experience (limited) there would be severe attenuation and I don't see how you would get any drive into the lows with one of those. For an experiment I would couple a real speaker with a funnel or something and I'm sure you have an unused computer mic in the junk box that would yield a small capsule. Intuition says that no matter what there will be severe degradation.

[Dr.EM]

Thanks for replying!

The only test I've managed to set up is with about 1m of slightly larger hose (7mm internal mabye) and an earphone and electret mic. The sound recieved at the mic was perfectly clear, the only issue being that with a ~1m hose I got a large lift to the bass frequencies akin to loading a speaker in a transmission line (I presume).

This is clearly too short a length to judge with though, I can't imagine the results multiplied up by a factor of 100 or more. I didn't notice significant treble loss but possibly some, again multiplied by 100 it could be significant; an EQ to boost the earphone treble level could be employed up to a point. I need a longer hose to test with, around 10m should be enough to guage it.

Severe degredation sounds a bit drastic! I certainly want there to be some, but if the recieved sound is indistinguishable it won't be very satifactory. Ideally there will be some, which after several feedback repeates becomes very noticeable, to create an interesting effect

[PeteMcK]

I would think that a hose would act as a straight pipe, & you get resonance at 1/4 wavelength; but I wonder what effect coiling the hose would have on this???
Treble loss is part of the trad 'echo' effect anyway, because you'd be mixing the result back into the original signal as an effect I don't think it's too important; To be practical I think you'd need more input power than an earpice could provide; How about multiple paths - several different lengths of hose driven by a large driver???

[scott wurcer]

Been done US4701952. They needed a way to pipe music to patients during NMR with no metalics allowed. The patent uses a 4" speaker in a small box coupled to the tube. I don't know if it would reach 300' but they say "very" long tube. Google has it as a free download. Keep us informed, I wanted to do an "eternal" echo sound installation a few years ago but never tried it.

[Dr.EM]

A possible improvement a freind and I came up with. Gaining the advantages of using a more compact hose, variable delay time and presumably no issues driving the hose etc. Hopefully such a length provides enough "degredation", that's yet to be found out.

Unfortunately, I have no real idea about PICs, but if I can get enough help from some people I know it might be possible, mabye.

[neutron7]

Originally Posted by scott wurcer

Been done US4701952. They needed a way to pipe music to patients during NMR with no metalics allowed. The patent uses a 4" speaker in a small box coupled to the tube. I don't know if it would reach 300' but they say "very" long tube. Google has it as a free download. Keep us informed, I wanted to do an "eternal" echo sound installation a few years ago but never tried it.

ships have used "speaking tubes" for ages as well.

[neutron7]

Originally Posted by Dr.EM

A possible improvement a freind and I came up with. Gaining the advantages of using a more compact hose, variable delay time and presumably no issues driving the hose etc. Hopefully such a length provides enough "degredation", that's yet to be found out.

Unfortunately, I have no real idea about PICs, but if I can get enough help from some people I know it might be possible, mabye.

for the adjustable delay part you could just get one of these. the delay on the chip is not mixed with the original on the board, so you can mix it as you please.

i have a few on order to try out with a DIY synth i am building, and eventually hope to get the development board and make some effects and active crossovers with it.

[scott wurcer]

Originally Posted by neutron7

for the adjustable delay part you could just get one of these. the delay on the chip is not mixed with the original on the board, so you can mix it as you please.

i have a few on order to try out with a DIY synth i am building, and eventually hope to get the development board and make some effects and active crossovers with it.

The samples sound pretty good. Certainly a speaking tube works but I'll bet there is a lot of acoustic power at the input.