Suitable midrange cone, for bandpass mid in Unity horn.

[Hrmmf]

There is something I just don't understand

No matter how small I make the entry holes (compression ratio 100:1) the port velocity does not exceed ~3 m/s. What am I missing? Should one multiply m/s by factor 10?

/Thomas

 

[tinitus]

looks like a normal 1" tweeter still needs to be pushed(crossed) below its optimal lower limit ?

 

[Hrmmf]

looks like a normal 1" tweeter still needs to be pushed(crossed) below its optimal lower limit ?

If it's post #785 you're refering to, please disregard the SPL chart, it's just a consequense of the very small port hole/s.

BTW - I'm planning on using the Beyma TPL 150 as tweet!

/Thomas

 

[kessito]

Regarding the velocity, I think hornresp shows the velocity in the throat of the horn, not in the holes. For this you need to use Akabak, which will certainly tell you the velocity will be too high.

 

[tinitus]

If it's post #785 you're refering to, please disregard the SPL chart, it's just a consequense of the very small port hole/s.

BTW - I'm planning on using the Beyma TPL 150 as tweet!

/Thomas

no, I was more interested in your chart from #784
but I guess ok if equalised linear down to around 115db
anyway, I thought a smaller port hole would push the rolloff upwards

 

[JLH]

Like what Kessito said, you need Akabak to view the port velocity. Horn Response can't show you the port velocity.

 

[Hrmmf]

Regarding the velocity, I think hornresp shows the velocity in the throat of the horn, not in the holes. For this you need to use Akabak, which will certainly tell you the velocity will be too high.

Thanks kessito and John!

Akabak it is then

 

[JLH]

no, I was more interested in your chart from #784
but I guess ok if equalised linear down to around 115db
anyway, I thought a smaller port hole would push the rolloff upwards

The port length and diameter does not control where the high frequency rolls off. The ports only affect the smoothness of the roll off (i.e. whether the roll off at the shoulder is rounded and smooth or peaking).

The high frequency roll off is controlled by the half wave cancellation distance from the acoustical center of the compression driver to the port and the cross sectional area the port taps into. With an area of 76.9cm^2 you will begin to get roll off at 1100Hz. If you want to reach 1500Hz, then you have to tap into the horn where the area is 41.5cm^2 or less. In addition, the distance from the acoustical center of the compression driver to the port has to be 11.4cm or shorter to reach 1500Hz.

 

[JLH]

Here is an Akabak script you can study. The model includes all the drivers and the crossover. Simulate the Acoustic Power Response.

System 'Tri_Unity'
Def_Driver 'CompDriver' | RCF ND350 compression driver
Sd=15.51cm2
Bl=7.5Tm
Cms=3.45E-05m/N
Rms=0.18Ns/m
Fs=785Hz
Le=0.10mH
Re=6.5ohm
ExpoLe=0.618

Def_Driver 'MidDriver' |Eminence LA6-CBMR 6" mid
Sd=133.1cm2
Bl=11.1Tm
Cms=1.58E-05m/N
Rms=7.00Ns/m
fs=460Hz
Le=0.33mH
Re=6.3ohm
ExpoLe=0.618

Def_Const | Unit is cm
{
FcMid_Len=0.65e-2; | Front Mid chamber length
FcMid_dD=13.018e-2; | Front Mid chamber diameter
FcPortMid_Len=0.6e-2; | Mid Enrty Port length
FcPortMid_dD=1.07e-2; | Mid Entry Port diameter

Rg=0.35; |Amplifier output impedance (ohms)

R1Comp = 47; |compression driver Crossover R1 Resistor (Ohms)
R2Comp = 12; |compression driver Crossover R2 Resistor (Ohms)
R3Comp = 2.0; |compression driver Crossover R3 Resistor (Ohms)
R4Comp = 10; | compression driver Crossover R4 Resistor (Ohms)
C1Comp = 7.5e-6; |compression driver Crossover C1 capacitor (Farads)
C2Comp = 3.3e-6; |compression driver Crossover C2 capacitor (Farads)
L1Comp = 0.51e-3; |compression driver Crossover L1 inductor (Henries)

R1Mid = 4.7; |Mid Crossover R1 Resistor (Ohms)
R2Mid = 25; |Mid Crossover R2 Resistor (Ohms)
R3Mid = 0.47; |Mid Crossover R3 Resistor (Ohms)
C1Mid = 36e-6; |Mid Crossover C1 capacitor (Farads)
C2Mid = 18e-6; | Mid Crossover C2 capacitor (Farads)
L1Mid = 1.5e-3; |Mid Crossover L1 inductor (Henries)
L2Mid = 0.22e-3; |Mid Crossover L2 inductor (Henries)

S1 = 1.5518e-4; |WG1 throat area & Comp phase plug (sq cm)
S2 = 5.07e-4; |WG2 mouth area & horn segment 2 throat area & compression driver exit (sq cm)
S3 = 33.6e-4; |WG3 mouth area & horn segment 3 throat area & Mid tap point (sq cm)
S4 = 219.6e-4; |WG4 mouth area & horn segment 4 throat area (sq cm)
S5 = 675.07e-4; |WG5 mouth area & horn segment 5 throat area (sq cm)
S6 = 1636.24e-4; |WG6 mouth area & horn segment 6 area (sq cm)
S7 = 3061.06e-4; |mouth flare out

L12 = 2.75e-2; |WG1 axial length(cm)
L23 = 4.5e-2; |WG2 axial length(cm)
L34 = 9.85e-2; |WG3 axial length(cm)
L45 = 12.3e-2; |WG4 axial length(cm)
L56 = 15.87e-2; |WG5 axial length(cm)
L67 = 6.0e-2; |mouth flare

VrcComp = 0.08e-3; |compression driver Rear chamber volume (litres)
LrcComp = 0.84e-2; |compression driver Rear chamber average length (cm)
VtcComp = 0.75e-6; |compression driver Throat chamber volume (cc)
AtcComp = 15.520e-4; |compression driver Throat chamber cross-sectional area (sq cm)

ArcComp = VrcComp / LrcComp; |Conversions for CompDriver
LtcComp = VtcComp / AtcComp;
Sd=133.1E-02;
}
Duct 'CompRearChamber' Node=30=31

SD={ArcComp} Len={LrcComp} Visc=0

Driver 'D1' Def='CompDriver' Node=12=0=31=32

Duct 'CompFrontChamber' Node=32=140

SD={AtcComp} Len={LtcComp} Visc=0

Radiator 'Diaphragm1' Node=100 SD={Sd} Label=1
Radiator 'Diaphragm2' Node=101 SD={Sd} Label=2

Driver 'D2' Def='MidDriver' Node=41=42=100=120
Driver 'D3' Def='MidDriver' Node=41=42=101=121

Duct 'DuMid_Fc1' Node=120=130 dD={FcMid_dD} Len={FcMid_Len}
Duct 'DuMid_Fc2' Node=121=131 dD={FcMid_dD} Len={FcMid_Len}

Duct 'DuMid_BP1a' Node=130=160 dD={FcPortMid_dD} Len={FcPortMid_Len}
Duct 'DuMid_BP2a' Node=131=160 dD={FcPortMid_dD} Len={FcPortMid_Len}
Duct 'DuMid_BP1b' Node=130=160 dD={FcPortMid_dD} Len={FcPortMid_Len}
Duct 'DuMid_BP2b' Node=131=160 dD={FcPortMid_dD} Len={FcPortMid_Len}

Resistor 'Amplifier Rg' |Amplifier output impedance
Node=1=2
R={Rg}

Resistor 'R1Comp'
Node=2=10
R={R1Comp}

Resistor 'R2Comp'
Node=10=12
R={R2Comp}

Resistor 'R3Comp'
Node=11=12
R={R3Comp}

Resistor 'R4Comp'
Node=12=0
R={R4Comp}

Capacitor 'C1Comp'
Node=2=10
C={C1Comp}

Capacitor 'C2Comp'
Node=10=11
C={C2Comp}

Coil 'L1Comp'
Node=10=0
L={L1Comp}

Resistor 'R1Mid'
Node=0=42
R={R1Mid}

Resistor 'R2Mid'
Node=41=42
R={R2Mid}

Resistor 'R3Mid'
Node=41=43
R={R3Mid}

Capacitor 'C1Mid'
Node=40=41
C={C1Mid}

Capacitor 'C2Mid'
Node=43=44
C={C2Mid}

Coil 'L1Mid'
Node=2=40
L={L1Mid}

Coil 'L2Mid'
Node=44=42
L={L2Mid}

Waveguide 'WG1'
Node=140=150
STh={S1}
SMo={S2}
Len={L12}
Conical

Waveguide 'WG2'
Node=150=160
STh={S2}
SMo={S3}
Len={L23}
T=1

Waveguide 'WG3'
Node=160=170
STh={S3}
SMo={S4}
Len={L34}
Conical

Waveguide 'WG4'
Node=170=180
STh={S4}
SMo={S5}
Len={L45}
Conical

Waveguide 'WG5'
Node=180=190
STh={S5}
SMo={S6}
Len={L56}
Conical

Waveguide 'WG6'
Node=190=195
STh={S6}
SMo={S7}
Len={L67}
Conical

Radiator 'Horn mouth'
Node=195
SD={S7}
x=0
y=0
z=0
HAngle=0
VAngle=0

 

[JLH]

BTW - I'm planning on using the Beyma TPL 150 as tweet!

/Thomas

That's not going to work. The throat area will be too large to allow a crossover point (mid driver tap in point) within the TPL-150 recommended operational range. Use a 1", or 1.4" compression driver.

 

[JLH]

That's not going to work. The throat area will be too large to allow a crossover point (mid driver tap in point) within the TPL-150 recommended operational range. Use a 1", or 1.4" compression driver.

I take this back. I just sat down and ran the numbers for the TPL-150 mounted to a 60 X 40 conical horn. If you can get the mids to tap into the horn within the first 3.5cm to 4cm you can just get a 1KHz crossover point. This is cutting it very close, but it appears it might be possible. It will not be easy getting the mids that close to the throat. I also don't know how difficult the crossover will be due to the half wave cancellation notch being much higher in frequency than the acoustical roll off point for the mids.

 

[tinitus]

thank you

 

[Hrmmf]

I take this back. I just sat down and ran the numbers for the TPL-150 mounted to a 60 X 40 conical horn. If you can get the mids to tap into the horn within the first 3.5cm to 4cm you can just get a 1KHz crossover point. This is cutting it very close, but it appears it might be possible. It will not be easy getting the mids that close to the throat. I also don't know how difficult the crossover will be due to the half wave cancellation notch being much higher in frequency than the acoustical roll off point for the mids.

Thanks for the Akabak script, John.

Revisiting something I wrote a few pages back:

Due to the geometry of the Beyma’s faceplate I’m able to get the midrange holes very close to the throat (~2cm distance in a 60x30 horn). The area of the AMT diaphram, which is also the area at the throat is 31.25cm^2. This translates to a circumference of 19.8cm = ~1740Hz.
The area where the midrange/s tap into the horn is 67.5cm^2 = 29.1cm = ~1180Hz. This calls for a fairly low x-over point to the Beyma.

I'm modelling a 60x30 horn due to the narrow vertical dispertion characteristics of the Beyma TPL.

Measurements on a trial horn indicates that ~1200Hz (pushing it: 1100Hz) is the lower limit.

/Thomas

 

[JLH]

I take this back. I just sat down and ran the numbers for the TPL-150 mounted to a 60 X 40 conical horn. If you can get the mids to tap into the horn within the first 3.5cm to 4cm you can just get a 1KHz crossover point. This is cutting it very close, but it appears it might be possible. It will not be easy getting the mids that close to the throat. I also don't know how difficult the crossover will be due to the half wave cancellation notch being much higher in frequency than the acoustical roll off point for the mids.

The crossover is going to be a mess. With the half wave cancellation notch up around 3.9KHz you will have a terrible time trying to get the mid to "turn off" at 1KHz. That cancellation notch is a very important tool because it cuts out the midrange's high frequency output acoustically. Without the notch, you will get a ton of interference with the high frequency driver.

It is also important to understand that since the compression driver and mids are half a wavelength apart at the crossover point, they are 180 degrees out of phase. This is why you want to use a 3rd order highpass on the high frequency driver, and a first order on the mids. It puts the two drivers in phase at the crossover point. This is why the phase behavior of the Unity and Synergy are so good.

About the only way you are going to get close is use DSP and very steep electrical crossovers. I don’t know what that would sound like. However, I can’t imagine it would be better than a horn that followed all the rules of how a Unity or Synergy horn is supposed to work. Using the TPL-150 puts you well outside of how these horns are supposed to work.

 

[JLH]

Thanks for the Akabak script, John.

Revisiting something I wrote a few pages back:

Due to the geometry of the Beyma’s faceplate I’m able to get the midrange holes very close to the throat (~2cm distance in a 60x30 horn). The area of the AMT diaphram, which is also the area at the throat is 31.25cm^2. This translates to a circumference of 19.8cm = ~1740Hz.
The area where the midrange/s tap into the horn is 67.5cm^2 = 29.1cm = ~1180Hz. This calls for a fairly low x-over point to the Beyma.

I'm modelling a 60x30 horn due to the narrow vertical dispertion characteristics of the Beyma TPL.

Measurements on a trial horn indicates that ~1200Hz (pushing it: 1100Hz) is the lower limit.

/Thomas

You do realize that a 60 X 30 horn on the TPL-150 flips its geometry at around a distance of 16.5cm? (You were positioning the TPL-150’s throat in the vertical plane?) What I mean is it goes from being tall and narrow at the throat to being wide and short at the mouth. You might be better off turning the TPL-150 on its side so you don't get this geometry flip.

The other issue is the local area of expansion where you purpose your midrange tap in point has a flare rate of only 527Hz. This means your mids will only be covering from about 520Hz to 1100Hz. That’s basically an octave. Kind of seems like a waste.

 

[nc535]

JLH:
Your 2nd paragraph in post 798 confirms a guess/inference I had made lurking in these forums. Thanks for making it crystal clear.

Re' "With the half wave cancellation notch up around 3.9KHz" are you saying that the cancellation notch needs to be much lower in frequency, e.g. just above the xover frequency? In my naive HornResp simulations, I've seen its possible to get a steep cutoff just above a 1 Khz anticipated crossover frequency. Is that what I should be aiming for.

 

[JLH]

JLH:
Your 2nd paragraph in post 798 confirms a guess/inference I had made lurking in these forums. Thanks for making it crystal clear.

Re' "With the half wave cancellation notch up around 3.9KHz" are you saying that the cancellation notch needs to be much lower in frequency, e.g. just above the xover frequency? In my naive HornResp simulations, I've seen its possible to get a steep cutoff just above a 1 Khz anticipated crossover frequency. Is that what I should be aiming for.

What I aim for is having the cancellation notch slightly lower in frequency than my crossover point for the mid. (e.g. Crossover is 1st order lowpass at 1300Hz, notch at around 1200Hz to 1250Hz.) You want the acoustical cancellation notch doing most of the filtering work. If you place your crossover point too close to the notch, you end up with a peak in response once it sums with the compression driver and its crossover. The 1st order lowpass on the mid is there for phase shifting, and to filter out the mids high frequencies once it rebounds from the notch an octave above.

 

[nc535]

re' "what I aim for..."

thanks! exactly what I hoped you would say. The fact that you've said it gives me confidence to move ahead!

 

[tinitus]

how can you get yourself to put that nice 'ribbon' into such a ugly horn

 

[nc535]

Me. ribbons ???? I'm going to use BMS4550s in these horns and hide them in the front corners. I agree aesthetics is an issue but the sound is the primary concern.