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Eliptrac 240


Guest David H

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Guest David H

I was hoping someone else would jump on this one.

Dummy question? Please explain in detail what unloading is. I can't be the only non engineer to wonder.
Not a dumb question.

Driver unloading occurs when the energy applied to the drivers diaphram is lower then the horns cutoff frequency. What happens is the driver diaphram starts moving excessively causing intermod distortion.

Basically the only dampening the driver has below the horns cutoff is the diaphrams suspension and motor assy.

Best example I can think of is using a driver open air rather than in a box for loading. In this example the sealed box resistance is the load, in a ported box the port resistance is the load.

I am sure there are better explanations, and examples.

Dave

This artice has a lot of good info. http://www.volvotreter.de/downloads/Dinsdale_Horns_2.pdf

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I took a look at the plots on the D-405 phenolic, it looks about like the rest -10 to -15db at 300hz.

I did not do any distortion testing on these.

Fortunately there is not a real big need to crossover at 300hz anyway, and if there is there are still a few JBL 2482's around.

Dave

I'm getting response down to 300 Hz. from my Klipsch made K-1133 drivers, and they are Titanium! As I recall it's a mylar suspension and it uses a different phase plug from the K-1132 drivers, so they give up the high end and get lower. I'm thinking those would work well with your new horn and new super tweeter for those who can't afford the dollars of the cubic feet of a K-402. I think your are going the right direction with your latest mid horn. the bigger the better. So when you can get a Klipsch made driver that behaves like a relatively high mass phenolic with a low mass titanium diaphragm which is operated well BELOW it's diaphragm resonance point, which is up about 16 Khz. you have the best of both worlds. But it's gotta a be a 3-way in either case, especially with a JBL Phenolic.

Edited by ClaudeJ1
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I believe the half-octave rule has more to do with the horn's ability to accurately and adequately reproduce frequencies a half-octave above Fc, and not so much to do with protection of the driver.

I believe the main purpose of the half octave rule is to keep the crossover point high enough to keep the driver from unloading.

I have no desire however to debate this, it is just my understanding. Either way, It really doesnt matter, its a good rule to follow.

Dave

I'm using only first order (single cap value, 6 DB/octave electrical) on my K-1133 driver. I'm relying on the K-402's ACOUSTIC cutoff, which is 18 db/octave at 320 Hz. So it's effectibely 4th order at 320 Hz. in combination to match the active 4th order on the woofer section. The driver is made to handle lots of power and I'm typically only using 10 MILLIWATTS rms through it. I don't think it will ever see a 1W peak too often (+20 db up from nominal), which would be 105 db peak at my sweet spot from one channel only (3 db less......half of that with both channels drive, obviously).

Edited by ClaudeJ1
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I was hoping someone else would jump on this one.

Dummy question? Please explain in detail what unloading is. I can't be the only non engineer to wonder.
Not a dumb question.

Driver unloading occurs when the energy applied to the drivers diaphram is lower then the horns cutoff frequency. What happens is the driver diaphram starts moving excessively causing intermod distortion.

Basically the only dampening the driver has below the horns cutoff is the diaphrams suspension and motor assy.

Best example I can think of is using a driver open air rather than in a box for loading. In this example the sealed box resistance is the load, in a ported box the port resistance is the load.

I am sure there are better explanations, and examples.

Dave

This artice has a lot of good info. http://www.volvotreter.de/downloads/Dinsdale_Horns_2.pdf

I will defer to you Dave, but for a good example that we can all think of, it is like blowing into a straw vs the open air, you get a "backpressure" that loads the front of the driver.

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Guest David H
I will defer to you Dave, but for a good example that we can all think of, it is like blowing into a straw vs the open air, you get a "backpressure" that loads the front of the driver.

I can live with that.

Dave

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I was hoping someone else would jump on this one.

Dummy question? Please explain in detail what unloading is. I can't be the only non engineer to wonder.
Not a dumb question.

Driver unloading occurs when the energy applied to the drivers diaphram is lower then the horns cutoff frequency. What happens is the driver diaphram starts moving excessively causing intermod distortion.

Basically the only dampening the driver has below the horns cutoff is the diaphrams suspension and motor assy.

Best example I can think of is using a driver open air rather than in a box for loading. In this example the sealed box resistance is the load, in a ported box the port resistance is the load.

I am sure there are better explanations, and examples.

Dave

This artice has a lot of good info. http://www.volvotreter.de/downloads/Dinsdale_Horns_2.pdf

I’m not an engineer, but just a hobbyist that reads a lot and likes to experiment and apply what I’ve read, but I’ll try to add to Dave’s thoughts. It could either be mostly correct or it may be enough to drag out the true horn / compression driver engineers.

I think that another way to think about ‘unloading’ is to understand ‘loading’ and I believe that unloading occurs when a compression driver and horn combination are asked to do something in a horn system that they are not designed to do. However, I believe that more serious problems that damage compression drivers tend to occur at the low frequency extreme in high SPL situations.

For example, a horn used with a compression driver should be one wave-length long at the lowest sound frequency of intended use (i.e. possibly the approximate half octave above cut-off frequency that was discussed). The horn should not be shorter (I know there are exceptions on size of mouth and length of horn when using a direct radiator driver in our folded horns as a direct radiator does not have the hard limitations of a compression driver and horn placement is a consideration 1/8th space vs. ½ space, etc.). In addition, if you try to run longer wave-lengths through the horn than the horn is designed to handle (i.e. running a 300Hz signal through a horn with a 400Hz cut-off), this will cause the diaphragm in the compression driver to move excessively (I believe that the diaphragm movement increases four times for each unloaded octave decrease ran through the driver). Considering that the diaphragm cannot flex for very long with excessive movement without hitting the phase plug, it will break easily once high power is applied for SPL. In a horn-loaded compression driver and horn combination, the diaphragm movement is designed to be extremely small and provide a constant exertion over a frequency range.

I believe that the limits of the compression driver can be explained with the electrical and mechanical parameters outlined in the Thiele-Small-parameters (TSP). If you look at page 3 of the JBL technical note, I believe it gives a decent description and calculation of a flat horn loading range by using the TSP data.

http://www.jblpro.com/pub/technote/tn_v1n24.pdf

In designing a compression driver for a specific application with certain TSP, considerations are typically made regarding the diaphragm material, the surround design, diaphragm size. The rated power handling essentially relates to how much ‘xmax’ or excursion before the diaphragm hits the phase plug.

If you think about the JBL 2482 compression driver mentioned by a few posters above (I have a pair of these drivers that I use on occasion with my Khorns), the 2482 uses the same driver body as the JBL 2440 and JBL 2441 drivers with the main difference being a different diaphragm that uses a larger mounting ring. The 2482 has a heavy phenolic diaphragm with a large half roll surround to allow for more xmax and is rated down to 300Hz, as discussed above, at full power. But running at high power at 300Hz through a horn with a 400Hz or 500Hz cut-off frequency is only asking for problems due to unloading and high diaphragm excursion.

What does “loading” the horn accomplish? I think about it this way. The loading essentially eliminates the impedance mismatch between a driver and the air it is trying to move as the weight of the diaphragm (or cone in a direct radiation driver) is much heavier than the air. If you think about a direct radiator, it is very difficult to transfer energy (move air) and this is why efficiency is often around 1 percent with the more efficient direct radiators being around 2 percent to 3 percent.

If we ‘couple’ the driver to a horn with the horn mouth much larger than the horn throat and use the appropriate horn length and flare rate, now the driver has the contained volume of air in the horn to push against, which in turn creates the sound energy more efficiently. The small area of the horn throat restricts the passage of air and shows high acoustic impedance to the compression driver allowing the compression driver to develop the high pressure with reduced diaphragm excursion. The sound waves at the throat are high pressure/low area displacement and the flare of the horn allows the sound waves to decompress and increase in area displacement until they reach the mouth where they are of a low pressure/large area displacement.

I believe that the compression driver was specifically designed to take advantage of the benefits of horn loading. This is why the compression driver must be a good match for the horn being used and appropriate cross-over points must be considered. You have the large mouth area of the horn (of a certain length) and curved with a certain flare rate down to the throat end of the horn. The throat is very small in relation to the mouth. Most compression drivers have internal components to continue the reduction of the horn to the very small slits in the phase plug (although there are compression drivers where the phase plug is practically at the throat of the horn).

Instead of a cone, the compression driver uses a formed metal or composite diaphragm that is extremely light and thin; in addition, the shape is usually intended for the greatest rigidity. The concave side (some think of it as the reverse side) of the diaphragm dome faces the compression chamber and phase plug. Sound generated from the diaphragm movement passes through the slots in the phase plug. Essentially, the slots in the phase plug direct the sound emanating from the diaphragm dome to the throat of the horn, which creates the ‘coupling’ to the horn.

The machining of the phase plug is done to tight tolerances as it comes very close to the diaphragm dome. The slots in the phase plug should provide acoustical path lengths from any place on the entire diaphragm dome surface to the throat of the horn that are identical.

The surface of the diaphragm dome is a lot larger than the area of the phase plug slits (I believe around ten times or so) and must move air in and out of the slits. Compared to the cone movement in a direct radiation driver moving air directly, the pressure created by the movement of the diaphragm moving air in and out of the slits will be much greater when moving air through the horn. The “radiation resistance” or “loading” from the entire mass of air in the horn against the pressure created by the compression driver is what creates the “efficiency” of greater sound power output compared to the electrical power input (increases the maximum output capability and decreases the power input for a given volume level).

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Guest David H

Klipschorn owners, I need the dimentions for the wood panel on the top hat located just aft of the grill frame.

A photo of the mounting would be helpful as well.

Dave

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Guest David H

I also added an additional motor mount support for those crazy heavy drivers, and of course UPS drivers.

Dave

Would the Eliptrac 400 model need this bracing if one has used a Great Plains 399 8A mid drivers ?

FR

No, just place a support under the driver.

Dave

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Guest David H
You're amazing Dave. Seriously. I'm proud to know you both as friend and peer.

Wow Dean, quite the compliment coming from someone as creatively artistic and meticulous as you are.

Dave.

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