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Old 19th June 2010, 09:11 PM   #1
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Default Tapped Horn Feeding A Unity Horn

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Over on one of my other threads, someone posted an interesting new loudspeaker from Danley. It's named the SM-60M and the SM-60F. According the the brochure, "The loudspeaker shall utilize the synergy Horn/Tapped Horn patent-pending enclosure covering three pass bands.
The coverage pattern shall be 60 horizontal x 60 vertical. The loudspeaker shall have an operating rage of +/- 3 dB 270 Hz – 15 kHz. Sensitivity of 100 dBSPL @ 1m."


This is a really interesting device, so I thought I'd take a stab at guessing what's inside.

Click the image to open in full size.

Sorry about the crummy illustration. I'm away from home, and don't have access to my usual array of software

Anyways, in a unity horn, you have a compression driver at the apex, flanked by a pair of midranges. The compression driver is easy; the midranges are very tricky. By smooshing them up against the side of the horn, the air under the cone forms a low pass filter, and this chokes off your high frequencies. So you have to use midranges that have a very light cone, along with a powerful motor, to get them to play high.

The documentation on the new device has me thinking there's a tapped horn, and here's my "guess" on how it works. I'm guessing that there's a tapped horn that feeds the output from the back of the woofers cone to the front, just like in a tapped horn.

Click the image to open in full size.
Here's a pic of one of jbell's tapped horns. Imagine this, but shrunk down by 80%, and with the output feeding a Unity horn.

According to the literature, the SM-60M has a coverage angle of sixty degrees, and a 20" mouth. Based on that, the distance from the front to the back of the horn is about 32". (Each side of the triangle would be 20", and you lose about 25% because the output of the tapped horn is offset.)

So lets do the math!

Normally, when you build a horn, you pick a driver, and build a horn to fit it. In this case [b]we already know the horns dimensions[/i]. So instead of picking a horn to fit a driver, we need to pick a driver to fit the horn.

First, we need to figure out what 32 inches is. That's 422hz. (Speed of sound / 32 inches.)

But horns are tuned to a quarter wavelength - so that's 106hz.

Some people on the forums recommend tuning a tapped horn to 0.707 times the driver's free air resonance. I tend to agree with this - it's given me good results. So based on the dimensions of this horn, we'd want to feed it with a woofer that has an FS of 150hz. (150 * .707 = 106hz.)

Here's the specs of the woofer that's purportedly in there:

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  • Resonance frequency Fs Hz 138
  • DC resistance Re Ohm 12.2
  • Mechanical Q factor Qms 3.4
  • Electrical Q factor Qes 0.87
  • Total Quality factor Qts 0.69
  • Equivalent volume Vas L 1.03
  • BL factor BL Tesla m 10.7
  • Effective piston area Sd m2 0.0074
  • Max. linear excursion Xmax mm 3.5

If anyone has any comments on this, I'm all ears! I'm just guessing here. And the full-range version of this horn seems like a substantial upgrade over the Lambda Unity horns which were popular about ten years ago. This looks like an excellent hifi horn!

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Old 19th June 2010, 10:14 PM   #2
SunRa is offline SunRa  Romania
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There are still some issues with coax drivers. The transition between the cone and the tweeter horn is very steep, and then you will have another discontinuity between the cone and the cabinet (even if the angles match).

There is however Tannoy. Those are known to do coaxial the right way. An if you think to the largest cabinet they use, with a rather large front loaded horn, the concept is quite similar.

Click the image to open in full size.

edit: I took a closer look at your drawing. I see now that it's nothing like the westminster... Mhh.. Food for thought..

Last edited by SunRa; 19th June 2010 at 10:17 PM.
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Old 20th June 2010, 01:06 AM   #3
soho54 is offline soho54  United States
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Well, Ivan Beaver was the one who said it used the "BMS 5" cone coax," and "Fatial 8" over at PSW, so it is a pretty safe bet it is the BMS 5CN140.

Here is the patent app. See fig. 7 Sound reproduction with improved ... - Google Patent Search

Here is a CAD drawing of the SM-60F below:
Attached Images
File Type: jpg sm-60 prototype.jpg (16.4 KB, 262 views)

Last edited by soho54; 20th June 2010 at 01:25 AM.
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Old 20th June 2010, 01:19 AM   #4
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Curiosity got the best of me, and I threw together an Akabak model for a tapped horn feeding a Unity horn.

The script needs some work - for instance there's no duct to represent the transition from the tapped horn to the Unity horn. So the script exaggerates the size of the holes in the Unity's throat. (I'm assuming the throat is fed by holes, just like in a Unity horn. Without pics, who knows?!)

Click the image to open in full size.
Published response of the SM 60M. I'm guessing the midrange cone is in a tapped horn, crossed over to the compression driver somewhere around 1200hz. This is complete conjecture, of course. Just basing this on what I see on the spec sheet.

Click the image to open in full size.
Here's the predicted response of a tapped horn feeding a unity horn. This one uses four of the W2 852SH woofers from Tang Band, the same ones I used in my Unity in the car. They have a nice set of params for a unity horn, an underhung motor that reduces distortion, and thanks to their small size, it's easy to get them close to the throat.

This thing has a very VERY small footprint, much MUCH smaller than the SM 60M. Less than a quarter of a cubic foot. The mouth measures just 5" x 5".

You get the general idea: higher efficiency than you'd get from a sealed box, along with some directivity control.


System 'S1'

|================================================= ================================================== =====
|REQUIRED AKABAK SETTINGS:
|File > Preferences > Physical system constants:
|Sound velocity c = 344m/s
|Medium density rho = 1.205kg/m3
|Sum > Acoustic power:
|Frequency range = 10Hz to 20kHz
|Points = 533
|Input voltage = 31.62V rms
|Integration = 2Pi-sr
|Integration steps = 1 degree ... 1 degree
|Integration method = Cross
|================================================= ================================================== =====

Def_Const |Hornresp Input Parameter Values

{
|Length, area and volume values converted to metres, square metres and cubic metres:
Rg = 0.01e-0; |Amplifier output resistance (ohms)
S1 = 6.15e-4; |Horn segment 1 throat area (sq cm)
S2 = 7.69e-4; |Horn segment 1 mouth area and horn segment 2 throat area (sq cm)
S3 = 9.60e-4; |Horn segment 2 mouth area and horn segment 3 throat area (sq cm)
S4 = 12.01e-4; |Horn segment 3 mouth area and horn segment 4 throat area (sq cm)
S5 = 15.02e-4; |Horn segment 4 mouth area and horn segment 5 throat area (sq cm)
S6 = 18.78e-4; |Horn segment 5 mouth area and horn segment 6 throat area (sq cm)
S7 = 23.47e-4; |Horn segment 5 mouth area and horn segment 6 throat area (sq cm)
S8 = 29.34e-4; |Horn segment 5 mouth area and horn segment 6 throat area (sq cm)
S9 = 36.68e-4; |Horn segment 5 mouth area and horn segment 6 throat area (sq cm)
S10 = 45.85e-4; |Horn segment 5 mouth area and horn segment 6 throat area (sq cm)
S11 = 154.80e-4; |Horn segment 6 mouth area (sq cm)

L12 = 2.54e-2; |Horn segment 1 axial length (cm)
| driver 100 here
L23 = 5.08e-2; |Horn segment 2 axial length (cm)
| driver 101 here
L34 = 5.08e-2; |Horn segment 3 axial length (cm)
| driver 102 here
L45 = 5.08e-2; |Horn segment 4 axial length (cm)
| driver 103 here
L56 = 20.40e-2; |Horn segment 5 axial length (cm)
L67 = 20.40e-2; |Horn segment 6 axial length (cm)
| driver 103 here
L78 = 5.08e-2; |Horn segment 6 axial length (cm)
| driver 102 here
L89 = 5.08e-2; |Horn segment 6 axial length (cm)
| driver 101 here
L910 = 5.08e-2; |Horn segment 6 axial length (cm)
| driver 100 here
L1011 = 15.20e-2; |Horn segment 6 axial length (cm)




|Parameter Conversions:

Sd = 52.00e-4; |Total diaphragm area for 2 parallel drivers (sq cm)

}

|================================================= ================================================== =====

|Network node numbers for this tapped horn system:

|0-Voltage-1-Resistance-2----------
| x x
| --Driver1------ ---------------------------
| x -Driver2-------------- x
| x x x x
| 8-Segment-9-Segment-10-Segment-11-Segment-12-Segment-13-Segment-14-Radiator
|================================================= ================================================== =====


Def_Driver 'TangBand W2-852'

Sd=13.00cm2
Bl=2.31Tm
Cms=1.04E-03m/N
Rms=0.19Ns/m
fs=195.0000Hz |Mmd = 73.86g not recognised by AkAbak, fs calculated and used instead
Le=0.03mH
Re=3.60ohm
ExpoLe=1

System 'System'

Resistor 'Amplifier Rg'
Node=1=2
R={Rg}

Driver Def='TangBand W2-852' 'Driver 100'
Node=2=101=9=17
Driver Def='TangBand W2-852' 'Driver 101'
Node=101=0=10=16
Driver Def='TangBand W2-852' 'Driver 102'
Node=2=103=11=15
Driver Def='TangBand W2-852' 'Driver 103'
Node=103=0=12=14


Waveguide 'Horn segment 1'
Node=8=9
STh={S1}
SMo={S2}
Len={L12}
Conical

Waveguide 'Horn segment 2'
Node=9=10
STh={S2}
SMo={S3}
Len={L23}
Conical

Waveguide 'Horn segment 3'
Node=10=11
STh={S3}
SMo={S4}
Len={L34}
Conical

Waveguide 'Horn segment 4'
Node=11=12
STh={S4}
SMo={S5}
Len={L45}
Conical

Waveguide 'Horn segment 5'
Node=12=13
STh={S5}
SMo={S6}
Len={L56}
Conical

Waveguide 'Horn segment 6'
Node=13=14
STh={S6}
SMo={S7}
Len={L67}
Conical

Waveguide 'Horn segment 7'
Node=14=15
STh={S7}
SMo={S8}
Len={L78}
Conical

Waveguide 'Horn segment 8'
Node=15=16
STh={S8}
SMo={S9}
Len={L89}
Conical

Waveguide 'Horn segment 9'
Node=16=17
STh={S9}
SMo={S10}
Len={L910}
Conical

Waveguide 'Horn segment 10'
Node=17=18
STh={S10}
SMo={S11}
Len={L1011}
Conical

Radiator 'Horn mouth'
Node=18
SD={S11}
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Old 20th June 2010, 01:47 AM   #5
soho54 is offline soho54  United States
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I should add this from Tom Danley when he posted the CAD drawing with it, "You can see there are two types of LF drivers shown (the two types that are used in the different versions). The outermost holes / duct are the outlets for a Tapped horn section used in one model. At the rear is the hf and mid source"
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Old 20th June 2010, 02:05 AM   #6
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Quote:
Originally Posted by soho54 View Post
I should add this from Tom Danley when he posted the CAD drawing with it, "You can see there are two types of LF drivers shown (the two types that are used in the different versions). The outermost holes / duct are the outlets for a Tapped horn section used in one model. At the rear is the hf and mid source"
Aha! You've explained it then.

So there's a coupling chamber in front of the *coaxial*, but the midrange cone of the coaxial is NOT loaded by a tapped horn.

The cone of the woofers ARE loaded by a tapped horn, and the holes near the mouth are the exit points.

This also explains why Danley couldn't build this Synergy Horn until recently. (According to the thread on prosoundweb, this is an old idea he had, but there hasn't been a driver available which was suitable until now.)

If Danley had used something like an eight inch coaxial, a notch would appear in the response because of the distance from the edge of the woofer's cone to the apex. For instance, with an eight inch driver a notch would appear somewhere around 844hz. (Speed of sound / 4" / 4 /) It's 4" and not 8" because you measure the distance from the edge to the center.

But with a 5" cone the notch moves up to 1350hz.

So that's the key. Even a 6.5" cone is a little bit too big. The cone *really* has to be small for the coax to work at the apex.

Very clever!

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Old 20th June 2010, 02:41 AM   #7
soho54 is offline soho54  United States
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Yeah, that's about the gist of it.

An evolution of the SH-50. Woofer taps plus the mid repositioning. Now to get a working model, with EQ.
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Old 20th June 2010, 02:46 AM   #8
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Quote:
Originally Posted by soho54 View Post
Yeah, that's about the gist of it.

An evolution of the SH-50. Woofer taps plus the mid repositioning. Now to get a working model, with EQ.
I just tried a sim using a Fountek FR88, to see if it would be possible to try the same trick with a full range. No dice! Looks like you need that coax.

Sounds like I'm going to be calling Assistance Audio on Monday
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Old 20th June 2010, 03:06 AM   #9
soho54 is offline soho54  United States
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It would be nice to know a non-2007 price on it. I don't think there will be any way around it.

The woofers could be another story. It would be nice to bump the horn and woofer size up a little to push the lowend a tiny bit further down.

Last edited by soho54; 20th June 2010 at 03:09 AM.
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Old 20th June 2010, 09:13 PM   #10
soho54 is offline soho54  United States
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OK, I'm getting something like this,

0 Voltage 1 Resistance 2

2 EQ
_ Comp Rear _ Comp Driver _ Comp Chamber _ WG1 _ WG2 _ WG3 _ WG4 _ Radiator (Mouth)

2 EQ
_ Mid Encl. _ Mid Driver _ Mid Chamber _ Mid Port X(x4)

2 EQ
_ Low Encl. _ Low Driver(x2) _ Low Chamber(X2) _ Low Port(x2) X(x2-4 total)

_ Low Tap X(x4)

With the colors indicating node linking, and "_" indication an un-numbered node.

Last edited by soho54; 20th June 2010 at 09:18 PM.
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