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Old 31st January 2009, 02:02 PM   #1
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Thumbs up The Ultimate Remote Control Audio Project.. Please Help :)

Hi guys,

I'm new to this, but not to Remote Control in general.

To keep the story short, I'm interested in building a scale Warbird of around 100"+ wingspan.

In the old days, Gas was the only option, but with the advent of more powerful electric system, electric flight is the way to go these days IMHO. On top of that, there are folks making sound modules to fully replicate the actual warbird engines, so that we're not stuck with a weed wacker for engine sound.

http://www.aerosoundrc.com/

A great implementation of that design can be seen in this YouTube video.

http://www.youtube.com/watch?v=wdsu4...eature=related

The explanation of the system is here:
http://www.youtube.com/watch?v=0V_nS-iuWlA

The problem with the system as I see it is that it is TOO WEAK. While it sounds great on the ground, the sound nearly disappears in the sky. In the video, he's using 2 x 4-5" drivers with about 100 watts max output.

So I figure to get enough grunt, I'd probably need somewhere in the neighborhood of 500-1000 watts (or more maybe??) of power. When this aircraft takes to the sky, I want everyone around it to know that there is a plane in the sky. Maybe some spectators will even mistaken it for the real deal .


Design Parameter:
I'm planning on building a P-47 just like the video, but much bigger. It will be able to accomodate AT LEAST an 8" SUBWOOFER... maybe even 10" if you really twist my arm .

The whole components must be kept really light because they do have to fly after all, and too heavy of a component can kill the flight characteristics.

I can easily supply the amount of wattage and amperage from my lipo (lithium polymer) batteries. Just tell me the watts and amps, and I can come up with whatever combination you guys ask me to.

For this part, I'm going to need to find the lightest driver, mated to possibly the lightest amplifier, and enclosure.

When I do design the plane, it will be a kit built from scratch, so I can accommodate whatever design parameters you guys think would be best to get the max bang for the watts.

Budget (for the most part) is not an issue (within reason of course). My resources are not endless, but I don't want to have the initial planning stage be hampered by budget constraints. I'm thinking that I'd probably want a Neodymium speakers?

For the box, I was thinking of Balsa reinforced with fiberglass (or even carbon fiber if that's what I need). I figure balsa alone would totally suck, but with Fiberglass / CF reinforcement, it might be ok?? The box will be built into the airframe itself.

Again, I appreciate the help you guys give me. I may know my way around RC, but I'm a complete neophyte when it comes to audio.

Thanks

Josh "BoneDoc" Young

In case you guys are wondering what I do for fun, here's a little snippet
http://www.rcgroups.com/forums/member.php?u=42135
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Old 31st January 2009, 06:22 PM   #2
simon5 is offline simon5  Canada
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First, it would be good to know what's the frequency response needed to achieve a warbird sound.

I would effectively suggest a neodymium soeaker because of the smaller and lighter magnet. You should maybe look at pro drivers because they are sometimes lighter. I would take a very efficient driver, so you need a smaller amplifier. Something in the 95-100 dB range.

I'm not that much experienced with light and efficient pro drivers with neodymium magnets, maybe someone else will want to jump in.
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Old 1st February 2009, 01:19 AM   #3
jbell is offline jbell  United States
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sounds like an interesting challenge.. what 'exact' dimensions do you have to work with, and what weight limitations do you have?

A horn of some kind, with a neo driver and a class-d amp (tripath or other) is probably what you'll end up with to get the efficiency that's needed.

Can you post a wave file with the sound you are trying to reproduce so we know what bandwidth is needed?

Also, these are interesting... could make them flush with the fuselage.

http://www.nxtsound.com/index.php?id=415
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Old 1st February 2009, 03:50 AM   #4
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Thanks for the reply guys.

As for the sounds, they can be found here:

http://www.aerosoundrc.com/products.htm

Also that page contains some products that they sell (speakers, amplifiers, etc).

I'm guessing that the freq response is probably around 100-500 hz to get the drone of the engine. Some of the idling sounds might be lower, but most I guess will be in this range.

My questions are these:

1) Can several of the amplifiers sold on their site be combined in parallel to produce higher wattage if I choose a bigger speaker.

2) Is the 5" speakers enough to produce the frequency response I desire, or should I look into 8" speakers?

3)What are good brand names for pro speakers & drivers? I'm completely clueless with this regard .

As for design constrains, I have some flexibility since I'm building it from scratch (not pre-made).

Thanks again,

Josh
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Old 2nd February 2009, 01:29 AM   #5
Ron E is offline Ron E  United States
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Interesting application -

I just looked at a few recordings of warbirds and found that the sound goes from a couple Hz to ~5000-10000Hz, But you can make a reasonable facsimile of the sound bandpassing it from 200-5000Hz.

Look for the highest sensitivity fullrange Public address or guitar speaker of the size you can fit in you fuselage. 1000 watts is only 10dB louder than 100, just a perceived doubling in sound intensity. Not worth the extra trouble, IMO, and you are much more likely to burn out a driver.

I think a couple of drivers like these:
http://www.fullcompass.com/product/264817.html
might also be an option. Connect in series.
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Old 2nd February 2009, 01:50 AM   #6
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Interesting, you realise of course that realistic volume level will not be possible, I've been next to one of the old Mustang at an airshow and those engines are loud.
Maybe ( conjecture on my part ) you can use the shell of the fuselage as a Tapped horn to squeeze out a little extra noise.
Just for interest is it going to be a scale replica using original blue prints or a look-a-like.
If you are using 100 inch wing span what is the fuselage length??

Why not use petrol engine and add the correct mixture of sound to get the effect you want??


I would like to see a 1/10th scale RR Griffon V-12, it would have what?? 1200 CC of displacement, that would be some serious horsepower given the strength of todays metallurgy
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Old 2nd February 2009, 02:21 AM   #7
Ron E is offline Ron E  United States
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I believe that a perfect 1/10 scale engine has 1/1000th the displacement, so instead of 36.7 liters, it would be 36.7 cubic centimeters. About the displacement of a chainsaw (or weed wacker) motor.

I agree that realistic SPL is unrealistic (hah!). I wonder if a tuned gas engine could simulate the sound with less weight and more volume. A friend had a gas RC car with a 0.21 cubic inch engine that could damage your hearing 100 feet away. It was all high frequency though, perhaps with a resonant tube attached????
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Old 2nd February 2009, 02:45 AM   #8
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OK, you are correct, I make that mistake from time to time, resonance tube might do it.

There are some very high temperature materials out that have light weight, what does a resonance tube for those frequencies and SPL need in terms of length diameter and flare??

We had a race car once ( I got to polish the wheels ) the tuned exhaust on the 6 cylinder engine was folded to fit under the floor pan but if straight would have been over 29 ft long ( 9metres ) it gave a very deep and satifying rumble under idle but OMG when the go pedal was pushed all the way down, actually sounded deeper than the V-8s.
Does the same principle apply here
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Old 2nd February 2009, 11:18 AM   #9
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I realize that I'm not trying to make it as loud as the real thing. That would be impossible.

What I'm trying to achieve is that when the plane is flying about 100' away, people will have to look twice over to convince themselves that it is not the real deal flying.

How much wattage do I need for that effect?
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Old 2nd February 2009, 07:31 PM   #10
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Sounds like a very interesting project. As you say, it's going to be impossible to generate anything remotely like full scale, but in a nutshell here's what you need to know:

For every doubling of the number of speaker drivers and amplifier power you will gain approximately 3dB SPL (sound pressure level), as is shown on Aerosounds' web site comparison of a single 8 oz speaker versus a dual 16 oz speaker. For every doubling of the distance, you will lose a minimum of 3dB, and maybe as much as 6dB or more, depending upon your specific configuration, environmental conditions, the plane's attitude, etc. This means that to get 90 dB at around 200 feet, you will need to generate about 110 dB at one meter. (One meter is the standard distance at which loudspeaker efficiency is rated.) The rest is simple math.

To generate this kind of level in the 200-5000 Hz range is definitely possible, and will probably sound pretty good. Attempting to do full range will end up in frustration, disappointment, and a lot of burned up equipment. To do just midrange, cone type speakers will work fine. Horns, reflex cabinets, or other such efficiency increasing techniques will not produce enough of an improvement to justify the effort, and if you're not very experienced in audio will probably just make things worse instead of better.

The one exception might be the new LAT subwoofer design: http://www.tymphany.com/files/produc...LAT500-001.pdf (Avaliable from Madisound.com)
I do not have any experience with this unit, but it looks very interesting, and could probably be built into a fuselage very easily.

For this type of application, efficiency and ruggedness are the most important criteria for the drivers. "Professional" products, such as JBL or Electro Voice, will provide improvements here, but at a greatly increased cost and weight. Since you are not too concerned about cost, I would suggest purchasing a few different speakers and trying them out in a mock-up of the enclosure/amplifier/generator that you will be using. This is really the only way to know what you can expect, and will be a great learning experience. Look at sources such as PartsExpress.com or Madisound.com for speaker alternatives.

As far as the enclosure, fibreglas'ed balsa should work very well. I have actually built commercial speaker cabinets out of just fiberglas with some wood ribs to prevent flexing. Preventing flexing or any other vibration of the enclosure is the key. Any mechanical vibration will drastically reduce the volume and clarity of the sound from the speakers. Also, keep the enclosure airtight. This will give you more efficiency and extend the life of the speakers.

One big problem you will have to solve is that all of the speakers you will be using will have to fire out of the airframe somewhere. That is a lot of big holes to deal with, both structurally and visually. Another is you will be adding a LOT of extra weight, which must be distributed so as not to destroy the flight characteristics of the plane.

Good luck. Keep us posted of your progress.
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