# Mounting drivers REALLY far away



## Patrick Bateman

For a few years I've had a suspicion that you could mount drivers VERY far away from the cabin if you built a proper waveguide.

Looks like this is true.

Danley discusses it in this thread, where he describes routing sound through three feet of tubing. This sounds a little ridiculous, but the reason that it works is that the wavelengths are shorter than what they're passing through, so they come out the other side intact.

*You could use this to do some bizarre things, like mounting your tweeters in the glove box.* Or putting a subwoofer under the hood of your car and routing the output into the cabin. Or put your midranges under the seat. All kinds of bizarre stuff. Just keep the duct acoustically small.

Very technical discussion here:

PSW Sound Reinforcement Forums: LAB: The Classic Live Audio Board => Mid cone driver slots and holes

_Think of a vented box and woofer, one has several things;
First, obviously you have a source that has two phases and one has a 2nd order acoustic low pass filter attached to the rear side of the radiator. 
That low pass filter is made from the air in the box, a compliance volume or acoustic spring force (which electrically appears as a series inductance) and the mass of the air in the port (which looks like a Capacitor to ground), hence a 2nd order system.
You can see that relationship if you imagine a ruler clamped to a table, you can see its resonant frequency goes down if you add mass (add a penny at the end / make a longer port or reduce its area) or make the spring weaker (make the ruler longer / or box larger).

When the radiators two opposite phases add, they cancel each other out as they are always 180 degrees apart and of equal magnitude.
The sealed box simply contains one half of the signal allowing the other half to radiate away unhindered.
The low pass filter in a vented box (the vent + box volume) is in the form of a Helmholtz resonator and “at resonance” is an inverter, in other words introduces a phase shift which makes the port radiation “in phase”, additive with the front radiation.
While one doesn’t normally think about this as a “low pass filter” it is. Progressively less comes out of the port as the frequency rises above resonance.

As one lowers the frequency from the resonance (normally the low corner in a vented box), one finds that the phase shift imposed by the L and C reduces towards zero and the sound coming out of the port reaches the same phase angle as the rear radiation.

At this point, this is the “pass” region and the rear radiation increasingly cancels out the front side as the frequency lowers and the vented box has twice the roll off compared to a sealed box.
At a point WAY below Fb, the cancellation is complete. 
Above resonance, the output from the port decreases, reverting to a sealed box, which contains the anti-phase rear radiation.

When one has a normal horn, one finds that the radiators rear volume is a sealed box.
At the high frequency corner, one finds that another acoustic “low pass filter” is present although potentially not as obvious.
Here, some portion of the air in the horn throat acts like a lump of mass like a port and some portion of the air between the radiator and throat acts like a compliance or spring, forming a low pass filter.
By sizing the L and C relative to the resistances, one can often extend the hf response by having a suitable low pass filter. As with the vented box, the ultimate roll off is steeper than an unaided alignment.
Here the only output is what comes out of the port (and drives the horn) so to speak.

In the Synergy and Unity horn boxes I designed, I use that “low pass” filter effect to attenuate the distortion products that all drivers produce. The distortion products are 2,3,4,5,6, ect times the fundamental frequency and so to the degree these fall on the rolled off part of the acoustic filter, they are attenuated. 
The filter here is made of the volume trapped under the cone and the mass of the air in the port and throat. I don’t use phase plugs here.

Also, when sound is introduced into the horn at some point forward of the apex (such as the cone drivers in our horns), one finds that the upper frequency limit is also set by an additional “low pass” filter effect caused by internal self cancellation. 
When the wavelength is short enough (frequency high enough) the sound that went to the pointy end, bounces back and arrives out of phase with the driver pressure.
One finds (as you raise the frequency) that you eventually have a BIG cancellation notch when that “driver to dead end” distance is about 1/4 wl. 
The two low pass filter effects strongly attenuate above band energy from the cone drivers and helps make the distortion especially low.
It was that notch, or pondering that notch that made me wonder about and then try what became the Tapped horn.
I thought what happens if I substitute a source of the opposite phase for that reflection? (a source which was present in the back side of the radiator), then they add instead of cancel. Some considerable fiddling in the computer eventually resulted in boxes that work better than similar sized normal bass horns using this new principal.

Anyway, up to now, the only function a phase plug has is to occupy an excess air volume that would have other wise made the acoustic “low pass filter” too low in frequency.

Once one is dealing with a radiator who’s dimensions are approaching the wavelength size, then the other function of a phase plug comes in handy.
The speed of sound governs how a pressure disturbance radiates away from its source.
If one has a radiator that is “large” acoustically and also has a single exit point, one finds that just like in the Synergy and Unity horns, one gets a deep cancellation notch when the difference in the two paths is 1 / 2 wl. The range of coherent summation is limited to the frequencies BELOW the region where cancellation begins.
This is like a pile of subwoofers, when the array is less than about 1/4 wl across, they all add together and feel “mutual radiation pressure” while a significantly larger spacing produces directivity and then lobes. 

Here, a phase plug can be shaped so that the acoustic passages all have the same length or have a length appropriate to the desired exit wave front shape.
One big difference in the sound of compression drivers (IMO) after being eq’d flat is that many have a phase plug that produces a converging wavefront at the summation, while what one needs at the throat of a horn is a diverging wavefront. That “clash” can cause diffraction or interference, which produces Higher Order Modes that Earl Geddes describes.

So far as the Paraline as used in the VTC array and GH-60, this is an acoustic device which can be shaped to provide an exit wavefront that can be flat, a line source or diverge or converge, an astigmatic point source with positive or negative focal point..
It works by allowing the sound to expand radially between two plate that are too close together to support any reflected modes between them so only radial expansion takes place.

A correction slot who’s shape defines the exit wave front shape and who’s dimensions are small enough to allow the sound to bend around the corners, is placed in the radial path. The sound passes through the slot and what emerges on the other side is a wave that travels to the center from each side, bends around a corner and exist at a center slot having entered at a center hole at the rear. The VTC site had a nice graphic of the one they are using.

It probably sounds weird to suggest that you can bend sound without ill effect but you can when the acoustic dimensions are small enough. The difference as it is in the examples above is that keeping the difference in path lengths less than about 1/4 wl at the highest frequency of interest..
I used to work with 21KHz levitation sound sources and needed to place a microphone in the levitation furnace to monitor the source sound level.
Well, very very few things are “happy” at 1500 degrees C but I found that a Zirconium / Alumina tube with a 1/16 inch bore passed 20KHz sound out of the furnace to an external microphone with no problem. 

Funny, the external microphone’s heatsink wasn’t large enough on the first one and the microphone melted.
Later fooling around (research) showed that a 3 foot long, 1/16 inch bore copper tube could be wound around a small coffee cup and not effect the sound passing to the microphone.

A constantly re-occurring theme in much of what I do is that many things depend on how large X is compared to the wavelength.
Anyway, I hope that makes some sense. _


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## schmiddr2

From your description it sounds ideal for the automotive world. What kind(s) of tubing?


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## asawendo

Interesting thread Patrick, subscribed. Thx


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## ErinH

I know of a few folks who have done this by putting drivers in the bottoms of the dash and routed the tubes up through the stock locations in the dash. I'm personally not sure how well it would work. 
The one thing I've wondered; if sound originates at the voice coil, is there any crazy benefit to PLD's?


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## Svendingo

That's exactly what I was wondering; is the zero plane the voice coil or radiation point/mouth ? 



Sent from my Rezound using Tapatalk


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## Patrick Bateman

Svendingo said:


> That's exactly what I was wondering; is the zero plane the voice coil or radiation point/mouth ?
> 
> 
> 
> Sent from my Rezound using Tapatalk


When it comes to phase, I am a dope. So take this with a grain of salt. But here's how I *think* this works.









Picture a wave moving in a duct. The wave could be composed of *anything* - water, air, light, whatever. For me, water is the easiest to visualize because we can see waves in a pool.

As long as the duct is larger than the wavelength, *there are well defined peaks and troughs in the wave.*

But as the dimensions of the duct become smaller than the wave, *the peaks and troughs in the waves cease to exist.*

As Danley noted in his message, the wave comes out of the duct intact. Intuitively, it seems like the wave would be screwed up. I mean, the whole idea of running your loudspeaker through a duct seems a bit absurd. *But if you look at it from a theoretical standpoint, the wavelength should arrive intact, up until a certain frequency.* (Hang in here for a second and I'll post the math.)









I've built a few speakers like this, and it's always fun to stick your ear against the port end, like you're putting your ear up against a sea shell. If you have a speaker and some PVC at home, you can try this trick with about 30 minutes worth of work. When you listen to the port end, you'll notice that the entire frequency spectrum is present. There are highs, there is midrange, and there are lows. *But the lows are predominant.* The sound is also a bit strange, because the high frequencies sound like they're coming from far away, while the low frequencies sound like they're coming from the port's mouth.

Here's how this works*

The PVC is 7.5cm in diameter. When the dimensions of the duct are much smaller than the wave, peaks and troughs do not form. Smaller than one quarter wavelength, according to Danley's post. 7.5cm is one quarter wavelength of 1133hz, *so anything below 1133hz won't form waves.* The origin of the waves below 1133hz will seem to originate from the port.

Note that there's a delay introduced. For instance, if that PVC pipe was 340 meters long, and you hit "play", the sound coming out of the cone is still going to lead the sound coming out of the port by one second.

In summary -

*Can you run a soundwave through a duct, with impunity?* - YES, it looks like you can. To determine the maximum duct size, take the maximum frequency you want to reproduce, then divide it by four. For instance, Danley wanted to reproduce 21khz. 21khz is 1.6cm long. Therefore, he had to use a duct that was 0.4cm or smaller. He used a duct that was 0.0625" in diameter, or 0.15875cm.

*Where is the origin of the sound?* - The origin of the sound depends on the frequency. If the frequency is more than 4x the size of the duct, the origin will appear at the mouth of the duct. This is because the wave simply cannot form until the wave reaches a space that is large enough to contain it. For instance, with the 0.15875cm duct mentioned above, the wave expands when it reaches the mouth.** 

_* Please note that I'm still figuring a lot of this out. There are probably some mechanical engineers scoffing at this post. If so, please speak up  I've studied loudspeakers for almost twenty years, and the more that I do, the more I believe that timing information is incredibly critical, and that most of us spend far too much time obsessing about frequency response, when getting the timing right is more important. A speaker with poor timing can sound very good, but it still sounds like a loudspeaker. Our ears are very well tuned to detect timing problems.

** If you're one step ahead of me, you'll realize that in an expanding duct (aka a horn) the sound can originate from multiple points in the horn, depending on wavelength. Rather mind bending isn't it? The high frequencies can originate from the throat, or even the diaphragm of the compression driver, while the low frequencies appear further down the length of the horn.
_


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## Patrick Bateman

bikinpunk said:


> I know of a few folks who have done this by putting drivers in the bottoms of the dash and routed the tubes up through the stock locations in the dash. I'm personally not sure how well it would work.
> The one thing I've wondered; if sound originates at the voice coil, is there any crazy benefit to PLD's?


I believe the point of origin is frequency dependent. If the duct is smaller than the frequency, the wave cannot expand, and so it's origin will appear to be at the mouth. Conversely, if the duct is *larger* than the frequency, the wave will expand at a point further up the duct, and that portion of the spectrum will sound farther away.

If you put your ear up against an air condition duct in an office, you'll be able to perceive high frequency sounds, but they sound like they're coming from very far away. But the low frequencies will sound like a dull thud of indistinct origin, because the wave is expanding at the mouth, not further up.

I think


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## Mic10is

Elderidge did this in his 4runner as well as Matt Robert in his Truck


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## thehatedguy

Matt's truck wasn't like this.


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## Mic10is

thehatedguy said:


> Matt's truck wasn't like this.


ok, apparently I stand corrected, but Elderidge at least did something similar where the drivers were mounted near the headlights and sound funneled in through a wave guide


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## Genxx

Damn I wish I was not in Saudi Arabia I would grap the pics for what Mark did showing the detials. This is similiar to what Mark did. The drivers were mounted beyond the firewall but basically horn loaded back into the cab if I remember correctly. So this seems a little different if I am grasping the above concept.


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## thehatedguy

Yeah this is completely different than horn loading.

This is more like a bandpass and putting the port where ever you wanted. Not really bandpass, but an all pass...but it helps illustrate the point.


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## Patrick Bateman

Mic10is said:


> ok, apparently I stand corrected, but Elderidge at least did something similar where the drivers were mounted near the headlights and sound funneled in through a wave guide


The thing is, all of these devices are points on the same spectrum. A horn is a waveguide, and a horn can have some features of a waveguide. Even a straight piece of PVC pipe will have directivity at certain frequencies. Put your ear up against the port of a loudspeaker, and you'll hear some high frequencies coming out of it.

The 'trick' is maximizing or minimizing the directivity, depending on what you're trying to do.










For instance, if you have a waveguide under the dash, you probably want very wide vertical directivity, and very narrow horizontal directivity. For instance, the horn in the pic above has about 45 degrees of horizontal directivity.

But there are situation where you want NO DIRECTIVITY whatsoever. And it looks like you can do that, as long as you size the duct properly.

(The formula is earlier in this thread.)

If I understand how this works properly, the waveform will expand at the point where the duct becomes large enough. So the origin of the loudspeaker will 'appear' to be the point in the duct where it expands to a specific size.

Obivously, you could use this 'trick' to manipulate the apparent origin of the loudspeaker. This would likely be particularly effective below 2khz, because our perception of location is dictated by phase more than by amplitude as frequencies get lower and lower and lower. For instance, all the DSP in the world won't fool you into thinking a midrange that's in the center of the car is *outside* of the car. But if you can move the apparent source of that midrange somewhere else, the midrange enclosure could easily be behind the dash, or even behind the firewall.

Also, it's not obvious in the pic above, but that's exactly what Image Dynamics is doing with the vertical directivity of this horn. If ID wanted ninety degrees of coverage in the vertical plane, they'd need a VERY tall waveguide. For instance, to get down to 1khz, they'd need a waveguide that's 34cm in height! But by making the vertical height VERY small, the waveform doesn't expand vertically until it reaches the mouth of the waveguide. This is one of the reasons that the transition from the mouth of the waveguide to the dash is so critical. Screw up that transition and you screw up the wavefront.


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## sonikaccord

I've been looking at this thread and the creating a perfect soundstage thread and I got an idea about a unity horn design.

If you can get a driver's origin to appear at the end of the pipe/tube, you can do a multiple midrange and compression driver set-up and route the tubing to a waveguide as long as the tubes for each driver and each side are the same length,correct? It sounds like it would be the best thing to do as far as efficiency, frequency and polar response.


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## quietfly

sub'd


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## req

simply put, put a 6" driver to mate with a tube, the tube should be smaller than 1/4 of the xover point, put the 6" driver in a suitable cabinet and cover the cone with the tube. if this works then wherever the end of the tube is it will sound like the driver is there. you could then mount a small tweeter on top of the tube and see if you can have the "footprint" somewhere other than the "sound radiation location "... is that the concept? sounds like only an hour or two of work to test that out...6" drivers in the pillars would be awesome... even ported enclosures could be possible this way...


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## The A Train

I see what youre saying req. Ive been following this to the best of my ability, but what you described sounded alot like a bandpass enclosure. If I am wrong though, the possibilities are endless with this idea. Especially with drivers that dont necessarily need a large enclosure (type r comes to mind). Some creativity would be needed to create an enclosure and route the pvc, or whatever medium tube to the dash or a-pillar. If it works, then I think car audio has just evolved.


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## nautic70

Mic10is said:


> Elderidge did this in his 4runner as well as Matt Robert in his Truck


I thought that's how Richard Clark horns were built. They went from the top of the dash all the way down through the bottom of the dash and out the horn lenses.


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## Patrick Bateman

ameuba10 said:


> I see what youre saying req. Ive been following this to the best of my ability, but what you described sounded alot like a bandpass enclosure. If I am wrong though, the possibilities are endless with this idea. Especially with drivers that dont necessarily need a large enclosure (type r comes to mind). Some creativity would be needed to create an enclosure and route the pvc, or whatever medium tube to the dash or a-pillar. If it works, then I think car audio has just evolved.


I took an hour or so and did a "brain dump" of what this is doing here:

Sound Where You Want It. - diyAudio

Some things I noticed, when I played with the 'ducted woofers' in Hornresp:


How high you want your woofer to play has a big influence on how big it can be. For instance, to get to 1500hz you need a duct that's less than 6cm in diameter. So you're not going to cram the output of a 30cm woofer through a 6cm duct.
Standing waves in the duct are the biggest challenge. The response is NOT flat. But you can flatten it out pretty easy, and getting a couple octaves out of this beast is easy. For instance, let's say you have a 2" dome that will play down to 700hz. You can 'duct in' a woofer and get an F3 of 100hz instead of 700.
By far the coolest thing is arraying these. If I had more time, I'd start figuring out how to 'duct in' a bunch of tiny speakers, like the 2.5" woofers that Dayton sells. Since the apparent source of the sound is the end of the duct, you can put the woofers *anywhere* within reason.

Of course, a miniDSP would be killer for this. Gives you the delay you need and some EQ and a crossover.

All of this scales to any frequency band; it's even easier to do this for midbasses or subs, but then the duct size starts getting out of hand.


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## req

i guess real life testing needs to be... tested lol.


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## ErinH

2nd picture:
http://trueaudio.com/st_diff1.htm

Sounds like what you guys are talking about and the issue you'll run in to.


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## thehatedguy

I don't see how that applies.


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## ErinH

Mounting a driver on a circular ring of sorts. 
Depends on the baffle size.


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## thehatedguy

But this is a port in front of the speaker.


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## ErinH

Well, then ... 

Lol.


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## The A Train

The 'port' is now the where the sound would originate from. I believe the whole point of this idea is to mount a driver in one location and have the sound come from another, just as if the driver was placed there. In that case, the opening of the 'port' is now acting as the driver, and if the port is standing alone (not flush mounted) it is now the baffle. So to bring back what erin was pointing out, there may be some unfriendly diffractions due to a cylindrical baffle. My remedy would to either flush mount it in the dash/a-pillar what-have-you, so the solid structure would then take over as the baffle, or I would like the opening to be flared.


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## sonikaccord

Couldn't you use multiple "small" ducts for larger speakers?

I would terminate the duct with a waveguide, and have its baffle blend into the windshield and dash.

Sent from my SCH-I500 using Tapatalk


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## The A Train

I dont see how multiple small ducts would work. The tuning of the ducts would be completely off.


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## req

this what im seeing, obviously putting the driver anywhere we need it to be compared to the listening space/position is the goal.










are we all clear?


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## ErinH

Seriously guys, grab a mic, put a driver in a tube, take it outside and rig up a way to hold if off the ground and away from reflecting surfaces and measure the response. 

Takes all of 20 minutes. 

Spend an hour or do trying different bends and lengths to see what happens.


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## ErinH

Also, try varying the nozzle; converging and diverging.


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## req

maybe ill give it a try with an idq8.


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## Patrick Bateman

I posted some info on how to model this in hornresp here:

Sound Where You Want It. - diyAudio

It's quite a bit easier than a horn, but the results can be a bit unexpected. This might be one of the reasons that the very small tube worked for Danley, whereas it seems like the larger ones are trickier.


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## Darth SQ

ameuba10 said:


> I dont see how multiple small ducts would work. The tuning of the ducts would be completely off.


Look, I'm no soundwave engineer and it's taking a lot of my attention to grasp the concept put forth in this interesting discussion, but here's my two cents worth regarding the above.

Are you sure?
Tuned headers operate under the same principle.
The only problem I can see is a loss of efficiency for the driver unless you use an equally sized collector to direct it into the muliple ports which is once again, a tuned header pipe only set up to work in reverse.

Taken a little farther, exhaust pulses when ran through a same length of tubes actually helps scavenging.
Can the same theory work with soundwaves?

Then there's the concept of back-pressure (size of the header tube and the exhaust system) which when applied correctly, can improve hp.
Can the same theory be applied based on the small tube vs. large tube problems mentioned above by Patrick?


FWIW.

Bret
PPI-ART COLLECTOR


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## Darth SQ

bikinpunk said:


> Seriously guys, grab a mic, put a driver in a tube, take it outside and rig up a way to hold if off the ground and away from reflecting surfaces and measure the response.
> 
> Takes all of 20 minutes.
> 
> Spend an hour or do trying different bends and lengths to see what happens.


Please post pics of the setup during testing. 

Bret
PPI-ART COLLECTOR


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## req

this got me thinking about my navy days. we had radar parts with transmission lines... not what youd think of in car audio world, but energy guides that would transfer electromagnetic or high radio waves (like microwaves) down a physical tube that terminates with an electrical sensor, or is propogated out of an antenna of some kind... thinking that those high energy waves could be shot out of the plane got me thinking that the radar transmitter was mounted far away from the antenna and those high energy waves traveled through tubes between each component, not wires. so a little reading material;

Waveguide - Wikipedia, the free encyclopedia

this is what the waveguide looked like;









so... more reading material;
Acoustic transmission line - Wikipedia, the free encyclopedia

if you skip down to the area about sound ducts, it says it in plain english that this should work. so we just need somone to try it. i nominate bikinpunk =)


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## jdsoldger

Now this is cool. You guys are basicly trying to make an acoustic version of single mode optical fiber (google, not going to explane it on a phone keyboard, sorry). The only issue I foresee is that you are going to excite the standing mode resonances of the pipe lengthwise. Not sure how that would be solveable, appart fromy raising the speed of sound in the tube so it resonates at a higher freqency. Maybe some dense gass inside and then put mebrains on either end?

BTW: Bateman, I head those exact PVC speakers at AK fest (looks like that is where the picture is from, I see Raw W.'s Indignias under them). They sounded quite good.


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## jdsoldger

Did a bit more thinking on this, first of all, I think you could bump the diamiter up a bit without any isues. The walls of the pipe are either going to both be nodes or antinodes for any freqency to form a wave there, which dictates at least a half wavelength, so you should be able to get away with diameters more than 1/4 wavelength (maybe try 1/3rd?). For the standing waves along the length though/ I have an idea. Vary the diamiter of the pipe enough that you get parts acting as individual pipes, rather than one long one. Maybe have the smaller sections be half the diameter of the large ones, and keep each individual section less than a half wavelength of the highest freqency you want to runthrough it and you should be good. The only thing will be having to keep an eye on the air velocity at each transition so there is no chuffing.

What do you guys think? I would try it but with school on top of working 6 days a week, I have no time to do it.


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## The A Train

Im wondering if there is an audible difference in the different bend styles like right angle compared to a true curved bend. Im finishing some test enclosures and I hope to perform an experiment. I dont have any measurement equipment so, I wouldnt be able to provide any concrete evidence; just subjective opinions.


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## req

did anyone ever boot this up and give it a run?


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## richiec77

Would be interesting if a Microwave/MM waveguide would work to allow for more flexible installation methods.


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## Patrick Bateman

The A Train said:


> Im wondering if there is an audible difference in the different bend styles like right angle compared to a true curved bend. Im finishing some test enclosures and I hope to perform an experiment. I dont have any measurement equipment so, I wouldnt be able to provide any concrete evidence; just subjective opinions.


Yes, it makes a difference.

I have three or four threads on various forums covering this stuff, so it's a bummer that there isn't one place that's authoritative.

In a nutshell, it works like this:

If you're trying to move the apparent location of a speaker, you'd think that the most important thing would be to avoid sharp edges, and have a very smooth, slow rate of change.









The B&W Nautilus comes to mind.









Oddly enough, this is not the case. Sharp bends are fine, even 180 degrees *as long as the diameter of the duct is a small fraction of the wavelength.* Ideally, one quarter wavelength or less. For instance, if you're bending a wavelength that's 5khz, you'd want the diameter of the duct to be less than 1.7cm. (34000 centimeters per second / 5000 hz/ 4)



The thing that IS important - very very very important in fact - is that the pathlengths are equal.

This is the super-duper incredibly important part of this puzzle which I didn't realize when I first wrote this thread. *Even if you get the duct size correct, you can screw it up if the pathlengths aren't equalized. That's how the Paraline in the picture above works; it looks funky because the sound is bent a full 180 degrees, but the pathlengths are equal.

So that's why something like a B&W Nautilus or a snail shell seems like a good idea, but actually isn't.




If I were going to build a device to relocate the apparent location of a speaker, here are the steps I would take:

step 1 - figure out the highest frequency it's going to reproduce. For example, the Paraline above goes to 20khz. That upper frequency limit will dictate the ideal diameter of the duct. In the case of the Paraline, the 'ideal' duct diameter is 0.425cm. (Same equation as above.)

Though 0.425cm is ideal, the 'real' Paraline uses a larger duct. This is something you have to juggle, because you'll likely need to use a larger than ideal duct because very very small ducts will change the parameters of your loudspeaker. Note that it *won't* produce reflections, even though it seems like it would! The reason that reflections aren't a problem is that the duct is literally too small for the wave to even form. (Picture water in a pipe; if the pipe is smaller than the wave, the wave can't even form.)

Step 2 - figure out some way to keep the pathlengths equal.








In the Paraline, the pathlengths are kept equal because the wave expands radially.

Step 3 - figure out some way to couple your device to the air. In the Paraline, it's coupled to the air via a horn. You don't have to use a horn though; you just have to figure out some way to get it from your device into the room, without creating diffraction and reflections. Even something as basic as a roundover will do.



Once you start understanding how all of this works, you can create some truly bizarre devices, such as the DSL high frequency combiner. Danley started off combining three tweeters, and is now at the point where he can combine sixty four(!)









IIRC, there's something like three tweeters combined in this speaker. The one with sixty four is being premiered in Vegas later this month IIRC. No pictures have been published that I am aware of.




Anyways, this has been a long post, but I hope it's clear that you can *definitely* move the apparent source of sound. It just requires some careful attention to pathlength. The apparent source of sound will be the mouth of the device. (IE, if you want to make it sound like your midranges are ten feet outside of the car, then you'll have to put the mouth of the device ten feet outside of the car.)

But it definitely opens up some interesting options, such as making it sound like your midranges are in the corners of the dash, or even behind it. Or putting midrange under the seat, weird locations like that.*


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## req

so basically as long as the pipe is the same length on each side, you should be golden?


what about coupling this pipe to the loudspeaker? could you just make an enclosure to drop the speaker in, and then put another baffle (considering excursion and what not) that is as close to the speaker as possible for the pipe entrance point with roundovers and such?

so if i needed a midrange to play, say from 200hz to 5khz.

34000 centimeters per second / 5000 hz/ 4 = 1.7cm = .67 inches. so i would need about 1\2" pipe from the front of my midrange to the corner of the pillar and have proper crossover points?

i may just try this out in the car seeing as how im going to have to rip it all apart anyway!


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## raamaudio

Though quite a bit off from the theme of this thread I have a 1953 Studebaker body sitting next to a C5 Z06 chassis(once the body was off it became just another C5 in essence) where the dash in the Stude is little, high, tons of room for horns under it. 

The chassis was heavily modified as a race car in that the firewall and footwell plates between the tunnel and frame rails were removed and rebuilt offering a huge amount of space to easily fit 10" mids and big horn motors with custom huge waveguides, mids and waveguide motors mounted very far forward, really next to the rear of the engine sides.

That is a far as the project got, been playing with other cars since but if I pick up the build again I plan to play with a single driver element instead of mids and horn motors with huge waveguides, some sort of widerange driver, as well as other ideas I have in mind. 

The end goal is an absolute world class sounding, take your head off if you want(backed up by two 21" pro audio subs, IB mounted) in a car under 3k lbs, fully caged, upholstered in fire retardant materials(even bout the commercial sewing machine already), 13" wide rear, 12" wide front wheels, full race build but have AC, etc and actually drive the crap out of it, all over the country and on a ton of race tracks.

I just turned 60 and am slowing down, just building a 400HP, 2200lb BMW race car right now, shopping for a motor home, adding a low weight aluminum enclosure to the new open deck aluminum trailer I just bought, selling off my other trailers, trucks, Vette, etc....

Anyway, very cool thread, I have a ton of room in that car so can do most anything in it but will be looking into these ideas if I decide to continue with the project but the car is for sale if somebody comes along and wants it, I call it the Studevette.

-----------

I have added a center channel with small mids mounted into heavily deadened center vent ducting before, worked pretty well

-----------

Rick


----------



## Patrick Bateman

req said:


> so basically as long as the pipe is the same length on each side, you should be golden?
> 
> 
> what about coupling this pipe to the loudspeaker? could you just make an enclosure to drop the speaker in, and then put another baffle (considering excursion and what not) that is as close to the speaker as possible for the pipe entrance point with roundovers and such?
> 
> so if i needed a midrange to play, say from 200hz to 5khz.
> 
> 34000 centimeters per second / 5000 hz/ 4 = 1.7cm = .67 inches. so i would need about 1\2" pipe from the front of my midrange to the corner of the pillar and have proper crossover points?
> 
> i may just try this out in the car seeing as how im going to have to rip it all apart anyway!


Tell me what your goals are - basically where you want to fool the listeners into thinking the sound is emanating from.

If you can give me that info, I might be able to come up with something that works.

The think that's difficult with pipes is that the pathlengths tend to get screwed up. For instance, if you take a 10cm woofer and couple it to a 10cm pipe, *the pathlengths from one edge of the cone will not be in phase with the other edge of the cone.*

That's why the crazy pancake-shaped radiation of the paraline works. The sound radiates radially, but there's so little height in the thing (something like 2cm), the pathlengths stay equal.

A paraline isn't the *only* thing that works, it's just clever.

Also, the pathlength problem gets worse and worse as you get higher in frequency. For instance, if you want to play to 2000hz, to keep the pathlengths in phase, you basically need the pathlengths to be within 4.25cm of each other. (about 1.5")

When you use plain ol' pipes, it's pretty easy to violate this rule, because even radiation from one edge of the cone will be out of phase with the other. This isn't a huge problem on a flat baffle because the sound radiates in 180 degrees; you don't have all the energy focused into a narrow duct, like you do in a pipe.

You can likely experiment with this on a plain ol' table top. Just take a small woofer, put it in a baffle with a sealed back. Now push the woofer closer and closer to a flat table top. As it gets closer and closer, the high frequencies will change a bit, but the sound should still be intelligible (since the sound continues to radiate radially.)

All of this works better with smaller drivers; as the driver gets larger and larger it starts to interfere with itself. The diaphragm of the driver in the Paraline is about 1.5" IIRC


----------



## Patrick Bateman

raamaudio said:


> Though quite a bit off from the theme of this thread I have a 1953 Studebaker body sitting next to a C5 Z06 chassis(once the body was off it became just another C5 in essence) where the dash in the Stude is little, high, tons of room for horns under it.
> 
> The chassis was heavily modified as a race car in that the firewall and footwell plates between the tunnel and frame rails were removed and rebuilt offering a huge amount of space to easily fit 10" mids and big horn motors with custom huge waveguides, mids and waveguide motors mounted very far forward, really next to the rear of the engine sides.
> 
> That is a far as the project got, been playing with other cars since but if I pick up the build again I plan to play with a single driver element instead of mids and horn motors with huge waveguides, some sort of widerange driver, as well as other ideas I have in mind.
> 
> The end goal is an absolute world class sounding, take your head off if you want(backed up by two 21" pro audio subs, IB mounted) in a car under 3k lbs, fully caged, upholstered in fire retardant materials(even bout the commercial sewing machine already), 13" wide rear, 12" wide front wheels, full race build but have AC, etc and actually drive the crap out of it, all over the country and on a ton of race tracks.
> 
> I just turned 60 and am slowing down, just building a 400HP, 2200lb BMW race car right now, shopping for a motor home, adding a low weight aluminum enclosure to the new open deck aluminum trailer I just bought, selling off my other trailers, trucks, Vette, etc....
> 
> Anyway, very cool thread, I have a ton of room in that car so can do most anything in it but will be looking into these ideas if I decide to continue with the project but the car is for sale if somebody comes along and wants it, I call it the Studevette.
> 
> -----------
> 
> I have added a center channel with small mids mounted into heavily deadened center vent ducting before, worked pretty well
> 
> -----------
> 
> Rick


Even if you have a ton of space to work with, I find that diffraction and reflection off of objects that are near the waveguide or horn becomes a problem. For instance, my Gedlee Summas have a waveguide that's just about ideal, and it's 38cm in diameter. But if I place *anything* near the waveguide, it's audible.

It's kinda eerie to hear. For instance, if I'm working on the computer and someone walks by the speaker, I can hear the sound change, simply from reflection and diffraction off the person walking by. (IE, I don't even have to 'look up' to tell that they're there.)

If I were going to make a speaker for the car, designed to fool people into thinking it's further away than it really is, I'd probably make a nearly ideal waveguide *and then I'd place it somewhere that there's a straight unobstructed line from the diaphragm all the way to my ears.*

That's one of the reasons I put the waveguides on my dash for my Unity projects. On the dash, there's nothing between the diaphragm and the ears for the most part. Also, Unity and Synergy horns do some things that are really important for the illusion of depth. (They get the phase response right. Phase response makes a big difference to soundstaging.)

Having said that, I found that 80% of what I listen to has basically no soundstage, so screwing up the cosmetics of my car to have a great soundstage had limited value. Personally, I find that movies have much better soundstaging than music. Music is mostly fake stereo.


----------



## goodstuff

req said:


> did anyone ever boot this up and give it a run?


I missed this. And it's hot. Otherwise I would do it.


----------



## Nismo

Would flexible PVC work for transmission? Theoretically, you could build a lower console for under the dash to hold a pair of drivers, then you could do a flexible 2, 3, or 4" flexible PVC run around to the kick panel.

This is semi-OT, but related. I want to put bass in a compact space. Can I put a pair of 8" subwoofers in my rear deck, use a 4" flex PVC pipe to go from the back of the woofer's [partial] enclosure to the other part in my trunk, and then use a 3" flex to run a port back up to the rear deck?

Eric


----------



## The Baron Groog

Patrick Bateman said:


> For instance, if I'm working on the computer and someone walks by the speaker, I can hear the sound change, simply from reflection and diffraction off the person walking by. (IE, I don't even have to 'look up' to tell that they're there.)


You need to change your name and avatar:









Back OT-another very interesting find Patrck, look forward to some more reading

Re port resonances-would it be possible to do a hemholtz resonator out of phase with the resonace to cancel it?


----------



## pocket5s

So I read through this a couple times and the actually the pic of the 3" driver in the PVC pipe helped quite a bit.

most of the conversation so far seems directed and remote mounting low end frequency drivers (i.e. subs or midbass) and directing that output. But what about the other way around? Say I wanted to take that 3" full range and play as low as possible and have the point source further away, to equalize PLD?

If I read correctly and did the math right, I get this for max lower frequency (each approximate) to NOT originate at the port mouth:

3" tube = 1075hz 
4" tube = 807hz
5" tube = 645hz

So in theory, if I wanted my 3" full ranges and wanted to put them into the engine bay I could play them down to the above frequencies with no issues with the appropriate size tube. Assuming I could route such tubes into the dash and all that. Anything below those frequencies would originate at the port mouth due to the wave length.

That all sound correct?


----------



## The Baron Groog

pocket5s said:


> So I read through this a couple times and the actually the pic of the 3" driver in the PVC pipe helped quite a bit.
> 
> most of the conversation so far seems directed and remote mounting low end frequency drivers (i.e. subs or midbass) and directing that output. But what about the other way around? Say I wanted to take that 3" full range and play as low as possible and have the point source further away, to equalize PLD?
> 
> If I read correctly and did the math right, I get this for max lower frequency (each approximate) to NOT originate at the port mouth:
> 
> 3" tube = 1075hz
> 4" tube = 807hz
> 5" tube = 645hz
> 
> So in theory, if I wanted my 3" full ranges and wanted to put them into the engine bay I could play them down to the above frequencies with no issues with the appropriate size tube. Assuming I could route such tubes into the dash and all that. Anything below those frequencies would originate at the port mouth due to the wave length.
> 
> That all sound correct?


Yup, sounds correct


----------



## mwatson185

pocket5s said:


> So I read through this a couple times and the actually the pic of the 3" driver in the PVC pipe helped quite a bit.
> 
> most of the conversation so far seems directed and remote mounting low end frequency drivers (i.e. subs or midbass) and directing that output. But what about the other way around? Say I wanted to take that 3" full range and play as low as possible and have the point source further away, to equalize PLD?
> 
> If I read correctly and did the math right, I get this for max lower frequency (each approximate) to NOT originate at the port mouth:
> 
> 3" tube = 1075hz
> 4" tube = 807hz
> 5" tube = 645hz
> 
> So in theory, if I wanted my 3" full ranges and wanted to put them into the engine bay I could play them down to the above frequencies with no issues with the appropriate size tube. Assuming I could route such tubes into the dash and all that. Anything below those frequencies would originate at the port mouth due to the wave length.
> 
> That all sound correct?


You could play them UP to those frequencies without degradation, not down.

I would like to revisit the multiple small pipes for one driver question. If a driver is divided into two (or more) pipes that have an equal length and diameter, yet have mouths that are located in two different areas equidistant from the listerner, would there be a phantom image of a driver between these two mouths?


----------



## The Baron Groog

mwatson185 said:


> You could play them UP to those frequencies without degradation, not down.
> 
> I would like to revisit the multiple small pipes for one driver question. If a driver is divided into two (or more) pipes that have an equal length and diameter, yet have mouths that are located in two different areas equidistant from the listerner, would there be a phantom image of a driver between these two mouths?


I think he wants to simulate a longer path length, so below those freqs the sound would eminate from the port exit and above those freqs it would sound like it had come from the port "entrance"- if I read it right!


----------



## pocket5s

hmm. Very interesting. 

I have a truck, so the dash is close and the vehicle is wide, making the closest PLD I could measure in the 16" range. Which is horrible.

So in thinking out loud here, most commercial car audio HLCD setups play in the ~1200hz-1500hz and up range, so I could simulate that range using a conventional 3" fullrange and a 3" plastic tube sticking through my firewall in the attempts to get the PLD down for a two-seat setup. I could make said tube as long as needed to the PLD where I wanted it (more or less...) for a two seat setup.

Then the question becomes, would this even be worthwhile as the midbass are still stuck in the kick panels. I got a little lost in all the other threads on what frequency range imaging cues really start to form. In other words, what frequency range is the PLD the most important. If it is below the range above, then it is kind of pointless as not matter how equal the PLD is between these two drivers, the PLD difference in the midbasses (8" drivers) will screw it all up anyway. In which case I'd leave the drivers where they are and keep the TA turned on


----------



## pocket5s

The Baron Groog said:


> I think he wants to simulate a longer path length, so below those freqs the sound would eminate from the port exit and above those freqs it would sound like it had come from the port "entrance"- if I read it right!


That is correct. Sorry I was working on my post right above this one and didn't see these two responses. The idea being to keep the wideband aspect as much as possible from my 3" speaker and play it as low as possible. Currently it goes down to 250hz, but that equates to like a 13" diameter tube 

however I could play it lower with the smaller tube IF the originating source wasn't as crucial in those frequencies. For example, say I kept the current 250hz HP crossover. from 250hz up to 1000hz (assuming 3" tube) would sound like it originates from the tube mouth and everything else from where ever the driver was actually located. The question being, is that noticeable. I have a feeling it is, but not totally sure.


----------



## req

the idea is not to make the PLD longer in respect to the physical interior of the car, but to put the larger format (and lower frequency) drivers in another location, but have the sound come from another spot that the larger speaker can not physically fit for better PLD's.

for instance. install a sealed 8" speaker under the dash on either side and a tube that goes up into the pillar to send the sound out above the dash to mesh with maybe a small midrange and tweeter for equal PLD's of all speakers. that kind of thing.


i have this sweet tube here at work. its for a solder gas vaccum. basically its a base with a vaccum that sucks the solder 'smoke' away from the work area for worker safety. basically it comes off with a hose clamp. if i go to the pawn shop and get one of those cheap speakers in a box i could use this to do some A\B comparo's.

basically im only looking to do like 50hz~500hz, maybe even 1khz. i found that 1\4 wavelength for a 3" diameter tube will play up to 1130hz, thats perfect for me. does that work out correctly patrick?


----------



## Patrick Bateman

The thing that's tricky about tubes is that the pathlength on the inside and the outside of the tube is different. For instance, if you place a 3" woofer on a 3" pipe, the pathlength will be significantly different as soon as you put a bend in the pipe.










I'm really fascinated by these Paralines; hopefully I'll have one of these built this month.

http://mediamilitia.com/wp-content/uploads/2010/01/radial-600-15.jpg[img]
Basically the sound expands radially, and the height of the device is so short (1/4") that no waves form below 18000hz.

[/font]


----------



## trojan fan

req said:


> the idea is not to make the PLD longer in respect to the physical interior of the car, but to put the larger format (and lower frequency) drivers in another location, but have the sound come from another spot that the larger speaker can not physically fit for better PLD's.
> 
> for instance. install a sealed 8" speaker under the dash on either side and a tube that goes up into the pillar to send the sound out above the dash to mesh with maybe a small midrange and tweeter for equal PLD's of all speakers. that kind of thing.
> 
> 
> i have this sweet tube here at work. its for a solder gas vaccum. basically its a base with a vaccum that sucks the solder 'smoke' away from the work area for worker safety. basically it comes off with a hose clamp. if i go to the pawn shop and get one of those cheap speakers in a box i could use this to do some A\B comparo's.
> 
> basically im only looking to do like 50hz~500hz, maybe even 1khz. i found that 1\4 wavelength for a 3" diameter tube will play up to 1130hz, thats perfect for me. does that work out correctly patrick?


"Horton hears a who".....


----------



## req

Pat, I was thinking about a larger driver than 3" like a 6" driver. And what do you mean the driver pld is on the outside and Inside? I was under the assumption that using a tube under a certain diameter would limit the propagation of waves until the end of the tube?


----------



## Patrick Bateman

req said:


> Pat, I was thinking about a larger driver than 3" like a 6" driver. And what do you mean the driver pld is on the outside and Inside? I was under the assumption that using a tube under a certain diameter would limit the propagation of waves until the end of the tube?


Exactly that.

I am still wrapping my head around how all of this works, but I've realized a few things while pondering all of this:


You're going to get comb filtering when two wavelengths are separated by as little as 1/4 wavelength.* For instance, if you want a midrange to play to 2000hz and you want to use one of these devices, then you'll need to keep your pathlengths within approximately 4.25cm. (1.69")
Intuitively, it would seem that pipes would work well in this application, but they do not. This is because the distance from the inside of the pipe doesn't equal the distance from the outside of the pipe *if there's a bend in there.*
Intuitively, it would seem that firing a driver into a flat surface would create a monster of a reflection, but it actually doesn't *as long as the distance to the reflector is less than one quarter wavelength.* Basically, the thing you would think would work well *doesn't.* (a pipe.) And the thing you'd expect to be an acoustic mess (a mirror) works fine *as long as you satisfy one condition. (Keep the distance between the radiator and the mirror below one quarter wavelength.)
*
*

The size of the radiator makes a big difference. As you'll notice from the equations, the sheer distance from one side of a cone to the other can be large enough to make the device useless.

I'd hypothesize that the reason you don't see the same comb filtering on a flat baffle is because the sound expands in 180 degrees. But in one of these devices the sound is restricted to a very small duct, so avoiding comb filtering becomes the challenge in such a restricted duct.

*


----------



## req

Patrick Bateman said:


> This is because the distance from the inside of the pipe doesn't equal the distance from the outside of the pipe




I guess that's the part I don't really understand... The driver will be in a sealed enclosure for the back wave and I suspension dampening, and the front wave will be in the tube band passed with a crossover to limit high frequencies depending on the size of the tube. What does a bend have to do with Anything?


----------



## sinister-kustoms




----------



## sinister-kustoms

Slightly different kettle of fish, but the principle is the same


----------



## The Baron Groog

req said:


> I guess that's the part I don't really understand... The driver will be in a sealed enclosure for the back wave and I suspension dampening, and the front wave will be in the tube band passed with a crossover to limit high frequencies depending on the size of the tube. What does a bend have to do with Anything?


The length on the inside edge of the bend is shorter than the outside, so the waves travelling down the inside have a shorter distance to travel.

If the tube works in the same way as fibre optics for light then I cannot see this as an issue.

If it doesn't then surely you could just put two bends in, the 2nd going the opposite way, so the total distance down the inside and outside are the same.


----------



## The Baron Groog

sinister-kustoms said:


>





sinister-kustoms said:


> Slightly different kettle of fish, but the principle is the same


No sound for me at work, but a cool way to explain a little physics to people


----------



## subwoofery

The Baron Groog said:


> The length on the inside edge of the bend is shorter than the outside, so the waves travelling down the inside have a shorter distance to travel.
> 
> If the tube works in the same way as fibre optics for light then I cannot see this as an issue.
> 
> *If it doesn't then surely you could just put two bends in, the 2nd going the opposite way, so the total distance down the inside and outside are the same.*


Really like the way you think :thumbsup: 

Kelvin


----------



## Patrick Bateman

The Baron Groog said:


> The length on the inside edge of the bend is shorter than the outside, so the waves travelling down the inside have a shorter distance to travel.
> 
> If the tube works in the same way as fibre optics for light then I cannot see this as an issue.
> 
> If it doesn't then surely you could just put two bends in, the 2nd going the opposite way, so the total distance down the inside and outside are the same.


It would be great if it were like fiber optics, but it's not because fiber optics are transmitting a narrow bandwidth centered on a single frequency, and we're trying to propagate a wider bandwidth. 

But in all other points, you're correct. The problem with pipes is the distance from the inside to the outside of the pipe.










Let's break it down to three dimensions. The first dimension would be "X". Let's say we want to transmit sound from point A to point B, and we don't want the wave to expand. To do that, *we'd eliminate wavefront expansion by restricting the diameter of the duct to a point where the wave can't expand.* In the pic above, I'm using a drinking straw to demonstrate how that would work. Put the drinking straw in front of your driver, and you can move the sound as far as you'd like *in one dimensions.*

Now the drinking straw isn't much of a solution, because it's pretty difficult to couple a drinking straw to a loudspeaker. I guess it would work find if you have a driver that's 1/4" in diameter. But if it's much larger than that you're going to have problems.









The 'pancake' type of duct is two dimensional. The sound is expanding in the X and the Y dimension, *but not in the Z.*

That's the critical piece, and it's what allows us to relocate the apparent source of the sound. Waves simply cannot form if the duct isn't large enough.

Actually, the animated GIF above is misleading, because it shows waves. I just wanted to illustrate how the sound is expanding radially. The actual waves won't form until they reach a point that's larger than 1/4". (The height of the 'pancake' is 1/4")

All of this gets really fun when you realize you can fold the pancake, or even manipulate the shape of the exit wave by tailoring the shape of the exit.









Kind of like water in a dam. If the dam wasn't there, the wavefront would be completely different. The channels in the dam can control both the exit location of the water, when the water is released, and where.


----------



## bigbubba

Mic10is said:


> Elderidge did this in his 4runner as well as Matt Robert in his Truck


I took these pictures at a 2003 IASCA contest in Memphis. Are the objects running down the sides of the engine compartment Mark's waveguides?


----------



## req

so this would be what you mean?


----------



## req

bigbubba said:


> waveguides?


we need to remember, what we are talking about, and what the HLCD concept is are totally different. in my eyes there several forms of sound wave control, here are a few;

waveguide
diffraction lens
horn

obviously, one can combine these three to make something a little different, but a waveguide is such that;

Waveguide - Wikipedia, the free encyclopedia



> A waveguide is a structure which guides waves, such as electromagnetic waves or sound waves. There are different types of waveguides for each type of wave. The original and most common[1] meaning is a hollow conductive metal pipe used to carry high frequency radio waves, particularly microwaves.
> 
> Waveguides differ in their geometry which can confine energy in one dimension such as in slab waveguides or two dimensions as in fiber or channel waveguides. In addition, different waveguides are needed to guide different frequencies: an optical fiber guiding light (high frequency) will not guide microwaves (which have a much lower frequency). As a rule of thumb, the width of a waveguide needs to be of the same order of magnitude as the wavelength of the guided wave.


obviously you can say that an audio HLCD is a waveguide because the sound starts at point A and comes out of point B - but that is not the purpose of them, the purpose of them is to control directivity and power dispersion. the purpose of a waveguide is just to take a wave from one spot and bring it to another.

a difraction lens is just there to allow the front wave to 'diffract' to the objet the speaker is mounted to really. 

what he was mark eldridge using in his car are HLCD's.

Horn loudspeaker - Wikipedia, the free encyclopedia

the thing about them is, the bigger they are, the lower they can extend frequency wise. think of a french horn versus a tuba. all he did was build huge horn lenses into the chassis of his car and put covers over them so people could not peek 

not the same idea as we are trying to come up with.



*pat, do you think that the bends in the tube would make such a huge problem that it would not be able to overcome it with DSP and tuning? *


----------



## thehatedguy

Maybe Mark had HLCDs then...maybe not. I've heard a million stories.

The ONLY difference between a waveguide and a horn is that a horn adds acoustical gain to the output. Both are used to control the wavefront of the speaker...they are the same basic thing.

You couldn't fix something like that with DSP or tuning...you can't fix beaming of a speaker with those methods.


----------



## bigbubba

I'm from the south so I'm not too up on the technical terminology. I like things simple. I call it a waveguide because I see it as an object used to guide the sound in a particular direction. When I saw those in the engine compartment, from headlight to firewall, I never would have guessed they had anything to do with the audio system. I was just curious as to what they were. 

Sorry for taking the thread off it's intended course. Carry on!


----------



## req

but we are using bandwitdth limitation to limit beaming right? and also isnt it useful when we beam to help with reflections in some cases?

*le sigh


----------



## Patrick Bateman

thehatedguy said:


> Maybe Mark had HLCDs then...maybe not. I've heard a million stories.
> 
> The ONLY difference between a waveguide and a horn is that a horn adds acoustical gain to the output. Both are used to control the wavefront of the speaker...they are the same basic thing.
> 
> You couldn't fix something like that with DSP or tuning...you can't fix beaming of a speaker with those methods.


These Paraline devices that I'm kinda fixated on lately are definitely horns and waveguides.

Danley's invention is simply a really peculiar way to fold a waveguide.










For instance, you can use a horn for anything. Doesn't have to be sub. (And of course, 99% of you guys know this, I'm just mentioning this for some of the readers who may not be aware that you can horn load a subwoofer, a midrange, a tweeter, whatever.)

So the Paraline is a funky way to fold a horn, and is particularly suitable for drivers that don't need a lot of airspace. (Like a tweeter or a midrange.)


----------



## thehatedguy

I just mentioned beaming as it is a physical problem that needs a physical solution to be dealt with...much like the bends in the tubes would need a physical solution.

My off the cuff gut feeling is that bends in the tubes like a bend in a horn would be ok provided you have a properly placed reflector...but you would want to either have the tube be as straight as possible or a right angle bend close to the source considering the size of the speaker, tubes, and frequencies involved.

Here is an article from Dr. Edgar about bending horns and wavefront realignment:
http://volvotreter.de/downloads/Edgar-Monolith-Horn.pdf


----------



## jpeezy

On marks 4runner that was the horn bodies outside the truck,the mouths of the horns went from edge to edge of dash,(we all know the dimensions of ID horns just image making them that large at the mouth,how deep they would need to be.i also got to see some pics of the many different self made horns he built and tried in that truck, I remember him saying something to the effect that any partially sane man wouldn't have spent that much time or money building horns for one truck,an old one at that).what a beautiful job he did on that dash!


----------



## req

as far as this whole thing goes - i am particularly interested in medium sized woofers playing from 50hz up to a place to mate with a small midrange or tweeter. between 1khz and 3khz really. we all know fitting a 6" woofer on axis in the A pillar is nothing easy - and usually not pretty to look at - but if we can duct the wave front into the pillar with a 3" tube then we have something to work towards and thats what i am trying to pull out of this discussion.

(speed of sound in inches per second)13512in\s ÷ 1100hz lowpass crossover ÷ 4 (1\4 wavelength) = 3.07 inches for a 1\4 wave and the desired diameter of a waveguide from 1100hz and below

if my math is correct, i should be able to cross a driver (lets say a 6" speaker) with a lowpass filter @ 1100hz with a 3" duct.

how does this math work with the slots you are talking about pat?

do you REALLY think that bending the tube would cause that much of an audible problem? i need to get to the pawn shop and buy a cheap enclosure to test this out - but i dont have a out of car testing rig


----------



## Patrick Bateman

req said:


> as far as this whole thing goes - i am particularly interested in medium sized woofers playing from 50hz up to a place to mate with a small midrange or tweeter. between 1khz and 3khz really. we all know fitting a 6" woofer on axis in the A pillar is nothing easy - and usually not pretty to look at - but if we can duct the wave front into the pillar with a 3" tube then we have something to work towards and thats what i am trying to pull out of this discussion.
> 
> (speed of sound in inches per second)13512in\s ÷ 1100hz lowpass crossover ÷ 4 (1\4 wavelength) = 3.07 inches for a 1\4 wave and the desired diameter of a waveguide from 1100hz and below
> 
> if my math is correct, i should be able to cross a driver (lets say a 6" speaker) with a lowpass filter @ 1100hz with a 3" duct.
> 
> how does this math work with the slots you are talking about pat?
> 
> do you REALLY think that bending the tube would cause that much of an audible problem? i need to get to the pawn shop and buy a cheap enclosure to test this out - but i dont have a out of car testing rig


Why not just use a Paraline? They're easy to build.

One neat thing about the Paraline is that you can actually bend the wave. For instance, you can mount the driver ninety degrees off-axis, then bend the wave 45 degrees. Weird stuff.


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## req

i guess i am not completly sure what a paraline physically is, and on top of that - how one goes about designing one.

just looking at the pictures you posted of the paraline above is really confusing to look at. i understand the purpose is to re-direct the wave front and make sure its all in phase or whatever.

i guess the main thing was to drop off the wave in the corner of the dash at the base of the a pillar, and have a larger format (6 inch or so) speaker in another location.

oh well


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## The Baron Groog

.:: VTC Pro Audio - Paraline Element ::.


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## 94VG30DE

Tagging this so that I can go back later and re-read the whole thread (for a third time I think). I too am looking for ways to get increased output using stashed "larger" midrange drivers and tubing the audio output up into the pillar, probably terminated by a shallow waveguide of some sort. Need to re-read the paraline thread as well (square peg round hole)


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## dragonbat13

I have been watching this thread some.. I dont know if any of this is in the right direction or not. But I have observations and an experiment to do. 

I think the OP wants to place a speaker in an ideal mounting location, and route the sound to another location. First off, as long as the baffle or tube or whatever is totally sealed, to the front of the speaker, AND the rear of the speaker is totally sealed, the source of the sound will be wherever the last reflection off of the tubes inside for a given frequency with no restriction between that last reflection surface and the listeners ears will be the source. Also some frequencies are going to bounce out of phase and cancel out. 

As far as the latter, think about talking through a four inch foot long cardboard tube. Doesnt the highest pitches of your voice go away? Now this could be from the cancelling mentioned, or it could be because only certiant frequencies are amplified compared to the sound directly out your mouth.

Here is the bottom line, you could analyze this till your blue in the face, and honestly it wont be answered without being a killer physics dude, or actually doing it. SOOOO....

I got a pair of rotopod USD wave guides that I am going to look into detaching the driver from one and blowing it down some PVC with bends and see what it sounds like. 
Ill do it asap and see what happens and report.


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## dragonbat13

here, just to show i aint foolin


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## req

Im watching


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## thehatedguy

What you want to do isn't going to work how you think it is going to.


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## schmiddr2

Wouldn't the tube/pipe need to be perfectly round?


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## HulkSmash

First thing I thought of was rear mounting midbass (8" or 10") in a small box mounted low behind each front seat and piping the midbass to the front of the vehicle. Brings up another question. What happens if you put a T in the line? Single midbass piped in equidistant lines to both sides... I think I just made my nose start bleeding.


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## bigbubba

thehatedguy said:


> *What you want to do isn't going to work how you think it is going to*.


I don't know why but I think that is funny as hell. :laugh:

I need to go to bed.


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## Patrick Bateman

Brock_Landers said:


> That's incredible news. I'm going to mount my drivers in my garage and just use a bunch of extendable dryer vents trailing behind my car. Delay shouldn't be an issue.


All kidding aside, YES, these devices will introduce a delay.
That could be a defect or a feature, depending on how you look at it.



Brock_Landers said:


> Seriously though, I doubt using elbows or T junctions helps at all. I wouldn't expect the sound to stay linear, rather the junctions would create turbulence/diffraction and result in "port" noise. At low spls this may not present a significant problem, but at higher spls it could be highly noticeable. I would suspect that the tube would have to be straight to avoid diffraction. This sort of defeats the intended purpose.
> 
> Discuss.


In order for these devices to work, the duct MUST be a fraction of the wavelength. Ideally it should be less than 1/3rd or even 1/4 of the wavelength.

Once you satisfy that requirement, diffraction isn't an issue, as the waveform can't even fit into the duct. (You can't get diffraction unless the wave can form.)

As for port noise, sure, that would be a problem if you were moving a lot of air. But these devices are only practical for fairly high frequencies, where you're not moving a lot of air.

Hornresp can be very helpful for determining the limits here.


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## req

so no midbass then... once i buy a house i will do some experiments


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