February 29, 2012
February 28, 2012
Akabak vs Hornresp vs Real measurements
Here is a chart that shows the results from Hornresp vs Akabak when compared to the measurements of the actual real thing:
Black is the measured response of the 4" closed back midrange on S1. Red is Hornresp, green is Akabak.
S1 is a 60 x 60 point source horn:
Note: Pyle drivers shown are not what is being investigated here.
Here are the Hornresp parameters:
Included at the end of this post is the script for Akabak. I exported the script from Hornresp, so it was automatically generated.
You will notice an offet of the ports larger than built - 9.2cm was entered as it matches the first dip. The ports were located 8.6cm from the throat - a 7% difference. This could be related to the compression driver exit tube coming into play, or it could be related also to atmospheric conditions and the speed of sound which is used to determine the port offset.
In this example it's interesting to see that Hornresp is actually more accurate where it matters most. In particular I'm interested in the top and bottom end roll off behaviour as it assists in choosing the parameters. Hornresp is closer with both. It estimates the first dip well enough to guide design decisions and then becomes very inaccurate at higher frequencies where the crossover takes over. In the bottom end, both fail to predict the peak and dip.
Akabak script generated by Hornresp:
|DATA EXPORTED FROM HORNRESP - RESONANCES NOT MASKED
|COMMENT: Celestion 4" single on 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 = 2.83V 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:
S1 = 4.90e-4; |Horn segment 1 throat area (sq cm)
S2 = 100.00e-4; |Horn segment 1 mouth area and horn segment 2 throat area (sq cm)
S3 = 2500.00e-4; |Horn segment 2 mouth area (sq cm)
L12 = 9.20e-2; |Horn segment 1 axial length (cm)
L23 = 33.00e-2; |Horn segment 2 axial length (cm)
Ap = 2.50e-4; |Chamber port cross-sectional area (sq cm)
Lpt = 1.80e-2; |Chamber port tube length (cm)
Vtc = 34.00e-6; |Throat chamber volume (cc)
Atc = 55.00e-4; |Throat chamber cross-sectional area (sq cm)
|Parameter Conversions:
Sd = 60.00e-4; |Diaphragm area (sq cm)
Ltc = Vtc / Atc;
}
|========================================================================================================
|Network node numbers for this offset driver horn system:
| 0-Voltage-1
| |
|Radiator(1)-5-Driver-6-Chamber-7-Port-
| |
| 8-Segment-9-Segment-10-Radiator(2)
|========================================================================================================
Def_Driver 'Driver'
Sd=60.00cm2
Bl=6.49Tm
Cms=3.01E-05m/N
Rms=0.98Ns/m
fs=444.4946Hz |Mmd = 4.00g not recognised by AkAbak, fs calculated and used instead
Le=0.60mH
Re=5.69ohm
ExpoLe=1
System 'System'
Driver Def='Driver''Driver'
Node=1=0=5=6
Radiator 'Diaphragm'
Node=5
SD={Sd}
Label=1
Duct 'Throat chamber'
Node=6=7
SD={Atc}
Len={Ltc}
Visc=0
Duct 'Port'
Node=7=9
SD={Ap}
Len={Lpt}
Visc=0
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
Radiator 'Horn mouth'
Node=10
SD={S3}
Label=2
Black is the measured response of the 4" closed back midrange on S1. Red is Hornresp, green is Akabak.
S1 is a 60 x 60 point source horn:
Note: Pyle drivers shown are not what is being investigated here.
Here are the Hornresp parameters:
Included at the end of this post is the script for Akabak. I exported the script from Hornresp, so it was automatically generated.
You will notice an offet of the ports larger than built - 9.2cm was entered as it matches the first dip. The ports were located 8.6cm from the throat - a 7% difference. This could be related to the compression driver exit tube coming into play, or it could be related also to atmospheric conditions and the speed of sound which is used to determine the port offset.
In this example it's interesting to see that Hornresp is actually more accurate where it matters most. In particular I'm interested in the top and bottom end roll off behaviour as it assists in choosing the parameters. Hornresp is closer with both. It estimates the first dip well enough to guide design decisions and then becomes very inaccurate at higher frequencies where the crossover takes over. In the bottom end, both fail to predict the peak and dip.
Akabak script generated by Hornresp:
|DATA EXPORTED FROM HORNRESP - RESONANCES NOT MASKED
|COMMENT: Celestion 4" single on 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 = 2.83V 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:
S1 = 4.90e-4; |Horn segment 1 throat area (sq cm)
S2 = 100.00e-4; |Horn segment 1 mouth area and horn segment 2 throat area (sq cm)
S3 = 2500.00e-4; |Horn segment 2 mouth area (sq cm)
L12 = 9.20e-2; |Horn segment 1 axial length (cm)
L23 = 33.00e-2; |Horn segment 2 axial length (cm)
Ap = 2.50e-4; |Chamber port cross-sectional area (sq cm)
Lpt = 1.80e-2; |Chamber port tube length (cm)
Vtc = 34.00e-6; |Throat chamber volume (cc)
Atc = 55.00e-4; |Throat chamber cross-sectional area (sq cm)
|Parameter Conversions:
Sd = 60.00e-4; |Diaphragm area (sq cm)
Ltc = Vtc / Atc;
}
|========================================================================================================
|Network node numbers for this offset driver horn system:
| 0-Voltage-1
| |
|Radiator(1)-5-Driver-6-Chamber-7-Port-
| |
| 8-Segment-9-Segment-10-Radiator(2)
|========================================================================================================
Def_Driver 'Driver'
Sd=60.00cm2
Bl=6.49Tm
Cms=3.01E-05m/N
Rms=0.98Ns/m
fs=444.4946Hz |Mmd = 4.00g not recognised by AkAbak, fs calculated and used instead
Le=0.60mH
Re=5.69ohm
ExpoLe=1
System 'System'
Driver Def='Driver''Driver'
Node=1=0=5=6
Radiator 'Diaphragm'
Node=5
SD={Sd}
Label=1
Duct 'Throat chamber'
Node=6=7
SD={Atc}
Len={Ltc}
Visc=0
Duct 'Port'
Node=7=9
SD={Ap}
Len={Lpt}
Visc=0
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
Radiator 'Horn mouth'
Node=10
SD={S3}
Label=2
February 27, 2012
February 23, 2012
Saturday is badass bass day!
This Saturday I'm hosting a badass bass day. Included will be:
T20
F20
TD18H boxes (they have progressed further than shown)
Eminence boxes
The Maelstrom will go in a prototype box I have lying around.
- F20 - a 20 Hz front loaded horn with dual Acoustic Elegance PB10 10" woofers, 95 dB sensitivity down to 20 Hz
- T20 - a 20 Hz tapped horn with dual Rythmik 12" servo subs, 93 dB sensitivity, 120 dB max SPL
- Maelstrom X2 18" in a 120L aperiodic box
- 2 x AE TD18H 18" pro woofers in 100L sealed boxes
- 2 x Eminence Magnum 18LF 18" pro woofers in 60L sealed boxes
T20
F20
TD18H boxes (they have progressed further than shown)
Eminence boxes
The Maelstrom will go in a prototype box I have lying around.
How does the sensitivity of tapped horns compare?
Here is a simulation to illustrate. This is based on a Hornresp simulation that has been exported into REW for comparison:
In light blue you can see dual Rythmik 12" servo subs in a sealed box with 1w input. Around 88 dB nominal sensitivity which drops to 80 dB at 20 Hz. The black line shows T20, a 20 Hz tapped horn with around 500L volume. The nominal sensitivity at 100 Hz can't be compared, however it is 89 dB at 20 Hz.
The dark blue line shows the excursion limited maximum output. Around 370w shared between the two drivers has the driver reach excursion limits. 106 dB max SPL at 20 Hz. The tapped horn increases sensitivity and controls excursion more so that the full 740w can be used and excursion limits are reached around that point. The output is 118 dB, which is a 12 dB increase in output.
So the result is that two 12" drivers with 370 watts each can achieve the same output as eight with twice as much power. Since drivers and amps are much more expensive than a few sheets of cheap ply, this works out as a cost effective choice.
February 19, 2012
February 12, 2012
February 11, 2012
T20 Rythmik dual opposed tapped horns - construction
Construction of T20 has now begun.
I've paid extra attention to the area where the drivers are mounted. There are two main issues with a sub. One is dealing with vibration from the drivers, the other is dealing with acoustic pressure. The area where drivers are mounted are given extra attention because that is where mechanical vibration is transmitted. Dual opposed design reduces this a great deal. You can't see it here, but the driver baffles sit into a groove in the end to firmly hold them in place. At this point they are attached with polyurethane glue which is very strong. Dual baffles and as much bracing as possible.
Drivers will be installed via external hatches.
Progress has been slower than with F20 and the bass bins because a little more care has been taken over certain details, some of them now shown. Driver cut outs were cut all the way through with the router.
This is intended for a permanent installation under the floor. If I'm happy with the result then it will stay for quite some time.
February 8, 2012
February 7, 2012
February 4, 2012
More progress - AE TD18 bass bins and F20 bass horn
Two bass bins now assembled sans outer baffle.
Internal bracing:
I wasn't quite careful enough drilling into the ply, so it split apart. I used polyurethane glue to repair it. In the past I've used PVA but it's difficult to get the glue in. With PU glue it expands to fill the void, so that it pushes the glue both into the void and out. The glue seen on the outside is there only due to the expansion. This glue is four times stronger than PVA.
F20 part-assembled:
Driver cut-outs were done with a router jig: