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Old 9th July 2010, 07:39 PM   #71
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The drivers are cheap, and an infra-sonic thingy wouldn't help. Apparently, it's 35Hz pulses. Still, in a sealed box with lots of Linkwitz gain, that's enough. They come out loud enough mind.
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Old 9th July 2010, 09:50 PM   #72
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May I please learn what is today's take on Doppler distortion (AKA as FM)... when a cone is moving very far for low notes while also playing higher notes?

Klipsch thought it was important and, of course (or "because"), TRUE horns have minimum cone displacement for a given loudness.
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Old 9th July 2010, 10:23 PM   #73
Mark Kravchenko --- www.kravchenko-audio.com
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Default Sealed box in back of driver?

Quote:
Esp. souls with enclosures that let go (all enclosures except for sealed ones or Klipschorn with sealed box in back of driver, eh).
You mean like this?

A rear chamber to anull the reactance that stops woofers from flapping wildly in the breeze below their pass band?

Never heard of it!

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Old 10th July 2010, 12:09 AM   #74
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Quote:
Originally Posted by mwmkravchenko View Post
You mean like this?

A rear chamber to anull the reactance that stops woofers from flapping wildly in the breeze below their pass band?

Never heard of it!

Mark
Mark - hard to tell from a picture, but I think yes. Is that a cross-section picture of a true horn?

By "never heard of it" do you mean "yes I've heard of it"?

Do I gather correctly you think control-of-flapping is a good idea?

And your opinion of Doppler, etc?
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Last edited by bentoronto; 10th July 2010 at 12:11 AM.
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Old 10th July 2010, 12:30 AM   #75
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Quote:
Originally Posted by bentoronto View Post
Don't you guys use sub-something filters?
Yep - 10Hz, fourth order high pass in the case of my 16Hz Tang Band tapped horn. I let it have a little bit below the corner, but by 10Hz it needs to be well controlled or the woofers would bottom out.

So far, I've had it working pretty hard with no signs of distress. I've seen up to 120dB at listening position during Flight of the Phoenix while testing. It's too loud for me to run it that hard all the time, so I still don't quite know where the bad noises point is yet. I didn't think it would get as loud as it does.
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Old 10th July 2010, 12:09 PM   #76
Mark Kravchenko --- www.kravchenko-audio.com
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Default A bit oh esplanation.

Hi Ben

That is the rear chamber of a true horn. A twenty three foot monster that I recently built. It's good down to 16 hz. With the proper volume of air behind the woofer you get a nice roll off below the woofers pass-band. Takes some calculation but it is not to hard to figure it out. When done right it acts like a shock absorber on a car. They are there to dampen spring oscillation in your vehicle. Without shock absorbers or strut assemblies that have an integrated shock the car bounces all over the place. When the shock absorbers are functioning correctly the springs in the suspension bounce and are dampened out almost immediately. Same goes for a properly sized rear chamber on a front loaded horn. Unwanted cone flap is dampened out very quickly.


For your distortion question I like calling it Frequency Modulation distortion. It describes it a bit more concisely. Yes it is a big problem in most systems that are using woofers to produce deep bass and low mid-range.

But is it really a problem in a sub-woofer where we are trying to produce two and a half octaves at most? Not usually. The distortion is most subs is due to driver nonliterary pushing them so hard that they are no longer in control of the motor structure design. The ways to get around that are rather simple. Use more drivers. But to have any appreciable difference we have to remember that to drop an octave in bass we need four times the volume of air moved to keep the SPL equal. You need quite a few woofers. The second solution is to provide a better acoustical match between the driver and the air in the room. This is the method that is being discussed in this thread. I don't recall seeing a figure of actual box gain over raw data from Patrick's posts. But in the horn I'm fooling with the gain is between 8 and 10 db over the raw driver. That is an increase of efficiency of just over and around four times that of a driver on it's own mounted in a conventional enclosure. So the driver in a horn has to move one quarter the amount of air to get the same sound pressure level of that same driver in a vented enclosure.


Gain? Well the distortion is cut down dramatically. More than the 1/4 you would think. If you use a driver that has a very linear motor structure like the XBL type in the TRIO12 you are getting great control of the driver over a far longer stroke. A stable BL is very important in keeping all forms of distortion low. The BL is the number of turns of wire in the voice coil that are saturated by the magnet and motor structure. It is the best measurement of how in control the cone remains at any position. It is also a curve that most manufacturers will not provide.


No matter how much power you throw at a driver it is only a repulsive force from the existing motor structure. So the inherent linearity of the driver itself is very important. The other very interesting thing about drivers and actual speaker boxes is that the more power we push into the driver the more they heat up. Then the voice coil parameters change drastically. If we can create an enclosure where the driver is better coupled to the room we are in the required power is greatly diminished and the resulting sound from the driver/enclosure system is cleaner. There is no warmed up voice coil that is now two to three tikes the resistance of one at room temperature. The amplifier does not have to try and push gobs of power into a voice coil that is literally compressing the power instead of tracking it. Nope we can get a driver that will track the music signal and produce what we are after. The idea that we can take a driver and push hundreds of watts into it and get a louder response is more a myth than reality.

Here is the power versus SPL progression

Base line 90 db one watt.

1-2-4-8-16-32-64-128-256-512-1024-2048 watts


90-93-96-99-102-105-108-111-114-117-120 in db

These are all increments which increase the sound level by 3 db.


This is a power output progression showing the power required to raise a signal 33 db. So from about 90db to about 120 db.


The greatest magic in getting things louder happens below 128 watts. Between 128 watts and 2048 watts there is a 12 db rise in sound pressure level. A little over twice as loud acoustically.

From 1 to 128 watts there is a 21 db increase from a 1 watt level in sound pressure.


If your bass line power is say 96 db then you get this funky thing happening

96-99-102-105-108-111-114-117-120 in db
1 - 2 - 4 - 8 - 16 - 32 - 64 - 128 in watts to get to that level of db.

You get very loud with not so much power when you drive a woofer in a horn. The not so much power enables greater ability to generate peaks without there being compression electrically in the driver itself or mechanically from there being no more stroke for the cone.

Trade off?

Big box. The one in the picture is the 23 foot horn it is 16.5 " x 32" x 92". Only addicts may apply! But once you hear one of these brutes all other sub-woofers sound.....neutered is the best term.

Mark
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Old 10th July 2010, 09:03 PM   #77
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As a Klipschorn guy, couldn't agree with you more about horns (esp. an all-out unit like yours) and for all your good reasons. Still, the flapping control is not an inherent or necessary horn aspect but a sealed enclosure issue.

The comparison to shock absorbers is interesting and you said nothing in error. But it is instructive to compare a modern shock absorber to the "thing" behind woofers or one sort of another.

First, shocks are inherently resistive although (1) they vary with frequency and (2) direction (compression vs. rebound). Not a very pure resistor! Today, some are no longer mechanical marvels, but are computer driven.

Could somebody create an "enclosure" which is driven by computation, not physical design?

One of my pet hobbies was "motional feedback" which is similar.
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Old 10th July 2010, 09:47 PM   #78
Mark Kravchenko --- www.kravchenko-audio.com
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Hi Ben thanks for your kind words. I've been designing and building horns from when I had to calculate every inch of the horn progression with a calculatior to the first basic programs I had to type into my 486 run by two hamsters and a guinea pig on a little wheel. At least it seemed like it when it was crunching out the numbers! Still better than a calculator. I don't think I have been doing it as long as you ( 16 years for me ) but it is encouraging to have a vote of confidence from someone who has been at this hobby as long as you have.

Quote:
Still, the flapping control is not an inherent or necessary horn aspect but a sealed enclosure issue.
Your right in the statement above. But as a question.

The combination of the reactance anulling chamber on the rear of the woofer and the comparatively small volume directly infront of the woofer cone in the throat of the horn are two sides of what is ideally a linear air resistor. Linear in that the two when balanced out will present the woofer cone on the front and the back with a more or less equal acoustcal impedance. That is the aim for a properly designed horn loaded woofer design. The front of the cone sees a blend of the air from the beginning of the throat well into the horn expansion. It is only through David McBeans program that you can easily adjust parameters to create this desired effect. Even with having many horns under my belt I find this one of the most challenging parts of proper horn design.

When that goal is achieved you get a second order roll off below the woofers designed pass-band and little to no cone flap. It unloads gracefully and does not shred cones as easily.

I'm quite familair with the Klipsch K-Horn copy. Below about 42 to 44 hz there is a wild amount of cone flap. Those boxes really require a high-pass filter to protect them.

I tried to design a no holds barred sub that would survive as much abuse as was possible. The shape is large but the form factor allows it to be stood in a corner laid down on either side tall or narrow. And almost all the ways to situate it will give optimal mouth coupling to the room. That is with the mouth on the bottom of the long narrow side.

Mark
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Last edited by mwmkravchenko; 10th July 2010 at 09:57 PM.
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Old 10th July 2010, 10:27 PM   #79
micb is offline micb  United Kingdom
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That is one mean looking TH Patrick.

Have you got any in room plots?
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Old 11th July 2010, 12:09 AM   #80
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Mark - one need not be falsely modest about old age and experience fooling around since it I didn't "make" myself old and so can take no credit for it. But I am certain you know more about these things and I labour to follow the tech depth of your post (... maybe I know more about shock absorbers).

I have impression was that once the sealed chamber behind a horn "grabs hold" of the motion, there's no flapping at any frequency lower (quite different than vented or TH boxes, eh). Odd that you see you saw it? Maybe the horn rear box is too large or the cone too heavy and so the "grab" frequency is below where the horn radiation resistance no longer weighs down on the cone.

The size of the sealed box in a true horn is pretty small since the radiation resistance FACING a cone in a horn (esp. with a little entry mouth, like Klipsch did) is way larger than the meager radiation resistance felt by ordinary hunks of cardboard flapping in boxes with large vents, or THs, where the radiation resistance is barely there at all.

Without the sealed box, you have loose flapping when any electrical stimulus appears although I don't think that is quite as serious as the lower-resonance peak of a bass-reflex, which is a resonance and gets triggered far more easily and disastrously.

Even with a horn, I don't think a Rice-Kellogg hunk of cardboard (AKA cone-type driver) is anywhere near the proper impedance match or anywhere near what the match an ESL has. Matching the impedance is only one factor leading to proper sound output, but still flapping big chunks of cardboard, even in a horn, is a dumb way to make sound. THERE, I said it and I'm proud I did.

The right way to make sound is with direct gas motion. But a horn tries to act as a radiation resistance matching transformer.
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