Collaborative Tapped horn project - Page 30 - diyAudio
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Old 30th April 2007, 06:51 PM   #291
freddi is offline freddi  United States
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was high H2 from Kove driver? (I've lost track of which horn had which driver) could nearfield somethow make H2 appear high?

which drivers give clean result in tapped horn such as Cowan's layout?

Freddy
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Old 30th April 2007, 07:02 PM   #292
MaVo is offline MaVo  Germany
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"would the waveguide model work for these mutual load cases?"

Sure. Check the AbAbak manual on page 65 and following. There is a great example how to simulate a bandpass box. You can see how to translate a box into akabak models. Your pictures contain some ducts for the rear volume, an accoustic mass for the 90 degree bend, waveguides for the expanding structure and a radiator.

Cowans 30hz horn with the 830500 driver:

http://img260.imageshack.us/img260/7550/830500ft6.jpg

What do you think about the accuracy?
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Old 30th April 2007, 07:14 PM   #293
freddi is offline freddi  United States
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830500 looks almost dead-on - do you get same accuracy when 830515 is dropped into the script?

what about the simplified model with only a few lines of script?

Freddy
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Old 30th April 2007, 10:08 PM   #294
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G'day MaVo

You've done a great job with your tapped horn model in AkAbak. The results appear to be close to my measurements, which were done with the mic in the center of the mouth. The Mathcad model was difficult to use and didn't offer anything that your model doesn't. The ability to include path length between the driver and mouth is very useful and should be included in your model. It is one of the variables one can use to fine tune a tapped horn.

I am starting to doubt the 830515 measurements I made. They were made quickly one evening and never repeated. I always thought the 830515 should work better in a 30Hz tapped horn than a 830500. I was very surprised when my measurements showed me this was not the case. Your model shows the 830515 to be a better performer and that matches my gut instinct a bit better.

Keep up the good work.

William Cowan
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Old 1st May 2007, 12:00 AM   #295
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Hey Freddi,

I just revisited my THD sweeps and I'm actually Better than 30-40dB down for the 2nd Harmonic (measured at mouth unclear what power level is I didn't check) I would like to take more accurate measures outdoors soon.

I'm around 70dB down for 3rd Harmonic distortion which is RETARDED LOW !!!!!

I will have to post my dimensions so we can try and see if response I got can on my proto type final can be recreated in aKaBak.

Antone-
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Old 1st May 2007, 02:00 AM   #296
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Quote:
Originally posted by MaVo
A different simulation. This time using a single waveguide as the main part. The driver is connected via ducts to it and the radiator. Perhaps this one is easier to understand then the last one i made. Better to play around with at least. It does modell slightly different then my other script (in the range of a few decibels here and there).

<snip>

Waveguide 'W1' Node=102=103 WTh={Xwidth} HTh={Xthroat} WMo={Xwidth} HMo={Xmouth}
Vf=50mm3 Len={Lhorn-Ldriver-Ldriver} Conical
Radiator 'Rad1' Node=105 Def='Df2' WD={Xwidth} HD={Xmouth}
Using your model, here's the response of Cowan's 30hz tapped horn with an MCM 55-2421 woofer. The sensitivity is poor, but for $25, the response goes VERY low.

I'm going to reduce the size and see if I can bump the efficiency.

http://www.spicealley.net/~johnv/tra...-30hz-horn.jpg
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Old 1st May 2007, 02:06 AM   #297
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Patrick, you may want to re evaluate your driver sensitivity, you didn't adjust your input voltage.

.707 Volts is not 1 watt unless your runing some really funny low impedance. And change the view window.

Its about 2.8V for 1W @ 8Ohms and about 2V for 1 Watt at 4Ohms.

But also you need to take a look at your Xmax numbers, around rated power.

Antone-
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Old 1st May 2007, 07:17 AM   #298
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Default Tapped Horn For Dummies (part 1 of 3)

I have an idea -

What if I post a "tapped horn for dummies?"

This would be a tapped horn that ANYONE with a $40 circular saw can build... In fact you could probably build it with a handsaw!

In order to make it super-simple to build, I'm going to make it out of sonotube. Sonotube is cheap, easy to work with, and rigid. To make it dead-simple to build, I'm NOT going to taper the horn. So it's going to be a simple resonant pipe. Picture a sonotube with a divider down the center, and you have the general idea.

In order to make it accessible, I'm going to use my favorite cheap sub driver, the MCM 55-2421. For $25, there's no better sub driver.

First things first though...

Tom Danley often uses two subwoofers in his designs, and models them as a SINGLE sub. For example, the lab sub uses two twelve inch woofers. I'm going to do the same with my "tapped horn for dummies." I am going to use a PAIR of eight inch woofers.

Why two you ask?

By using two woofers, we double our power handling, and halve xmax for the same volume as a single eight. Can't beat that right?

But we have to figure out the parameters for a pair of drivers, instead of one.

Luckily I have a spreadsheet that does this. This spreadsheet allows you to model one, two, even four woofers as a single unit. It takes care of all the parameters for you (BL, VAS, SD, etc...)

Here it is:

www.spicealley.net/~johnv/diyaudio/050107/ts.xls
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Old 1st May 2007, 08:50 AM   #299
MaVo is offline MaVo  Germany
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"what about the simplified model with only a few lines of script?

Freddy"

i made the sim with the following script. I figured the variables out of William Cowans schematic of the 30hz horn. When calculating the length of the horn, only take into account the straight parts without the bend, since the acoustic mass i used in the script should handle it. Thats why the length is 330cm.
I included the parameters for one of the "tapped horn for dummies" drivers for Patrick Bateman. It shouldnt be too complicated to simulate the horn with two drivers. For this i can again point to the manual on page 65 and following where a box with two drivers is simulated, taking into account the physical distance between the drivers, which could be more accurate than changing the TS parameters and handle it as a single one.

Def_Driver '830500'
dD=26cm |Piston
fs=18.1Hz Mms=166.3g Qms=3.7
Bl=17.6Tm Re=3.5ohm Le=4.2mH ExpoLe=0.618

Def_Driver '55-2421'
dD=26cm |Piston
fs=29.1Hz Mms=59.78g Qms=14
Bl=12.99Tm Re=3.4ohm Le=2.47mH ExpoLe=0.618

Def_Const | all sizes in centimeters
{
| Input Data
DriverSize = 26e-2; | The outer driver diameter
Hornlength = 330e-2; | The length of the horn including the ducts around the driver - not including the length of the 180 degree bend.
Box_z = 32e-2; | The depth of the box (z is constant - x & y get bigger from throat to mouth)
Throat_x = 10e-2; | Throat Area = Box_z * Throat_x
Mouth_x = 30e-2; | Mouth Area = Box_z * Mouth_x ... The area radiating into the listening room
| Experimental Data
Mass = 1.85/(Throat_x+((Mouth_x-Throat_x)/2));
Mass2 = 1.85/Box_z; | I dont know which dimension fits the accoustic mass of the bend. One can try both, "Mass" will be used in the calculation, "Mass2" will be ignored.
}
| Horn Modell
System 'Tapped Horn'
Driver 'D' Node=2=0=100=105 Def='830500' | Write the name of the driver which should be simulated here
Duct 'D1' Node=100 WD={Throat_x} HD={Box_z} Len={Driversize/2}
Duct 'D2' Node=100=101 WD={Throat_x} HD={Box_z} Len={Driversize/2}
Waveguide 'W1' Node=101=102 WTh={Throat_x} HTh={Box_z} WMo={Throat_x+((Mouth_x-Throat_x)/2)} HMo={Box_z}
Len={(Hornlength/2)-DriverSize} Conical
AcouMass 'Bend1' Node=102=103 Ma={Mass}
AcouMass 'Bend2' Node=103=104 Ma={Mass}
Waveguide 'W2' Node=104=105 WTh={Throat_x+((Mouth_x-Throat_x)/2)} HTh={Box_z} WMo={Mouth_x} HMo={Box_z}
Len={(Hornlength/2)-DriverSize} Conical
Duct 'D3' Node=105=106 WD={Mouth_x} HD={Box_z} Len={DriverSize}
Radiator 'Rad1' Node=106 WD={Mouth_x} HD={Box_z}
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Old 1st May 2007, 09:05 AM   #300
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I don't have to change the "mass" parameter do I???

Here's what I used, but it's different than what you posted. The drivers are in series, which raises the BL. It's also a different enclosure - it's basically a seventy two inch long sonotube divided in half.

If you ask me the response is pretty darn good. And anyone could build this in under two hours!

Click the image to open in full size.

###########################################

Def_Driver '55-2421x2'
dD=24.4cm |Piston
fs=30.95Hz Mms=119.58g Qms=12.29
Bl=25.08Tm Re=6.8ohm Le=4.84mH ExpoLe=0.618

Def_Const | all sizes in centimeters
{
| Input Data
DriverSize = 25.4e-2; | The outer driver diameter
Hornlength = 335e-2; | The overall length of the horn including the ducts around the driver
Box_z = 12.7e-2; | The depth of the box (z is constant - x & y get bigger from throat to mouth)
Throat_x = 12.65e-2; | Throat Area = Box_z * Throat_x
Mouth_x =12.75e-2; | Mouth Area = Box_z * Mouth_x
| Experimental Data
Mass = 1.85/(Throat_x+((Mouth_x-Throat_x)/2));
Mass2 = 1.85/Box_z; | I dont know which dimension fits the accoustic mass of the bend. One can try both, "Mass" will be used in the calculation, "Mass2" will be ignored.
}
| Horn Modell
System 'Tapped Horn'
Driver 'D' Node=2=0=100=105 Def='55-2421x2'
Duct 'D1' Node=100 WD={Throat_x} HD={Box_z} Len={Driversize/2}
Duct 'D2' Node=100=101 WD={Throat_x} HD={Box_z} Len={Driversize/2}
Waveguide 'W1' Node=101=102 WTh={Throat_x} HTh={Box_z} WMo={Throat_x+((Mouth_x-Throat_x)/2)} HMo={Box_z} Len={(Hornlength/2)-DriverSize} Conical
AcouMass 'Bend1' Node=102=103 Ma={Mass}
AcouMass 'Bend2' Node=103=104 Ma={Mass}
Waveguide 'W2' Node=104=105 WTh={Throat_x+((Mouth_x-Throat_x)/2)} HTh={Box_z} WMo={Mouth_x} HMo={Box_z} Len={(Hornlength/2)-DriverSize} Conical
Duct 'D3' Node=105=106 WD={Mouth_x} HD={Box_z} Len={DriverSize}
Radiator 'Rad1' Node=106 WD={Mouth_x} HD={Box_z}
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