We are using a bass reflex box with roughly the following specifications as given below
Since the box is no more having rectangular cross section along all dimensions, we are thinking the box mode distribution due to axial modes might see some attenuation along the breadth dimension. However the axial modes along the height dimension might still be strong and some damping might have to be put in place to try and tame it.
There is also a port pipe resonsance shown by the pink curve around 900 Hz (though it is hopefully outside the passband of the bass driver)
Native response curves with above tuning
With a bit of DSP assist and high pass filtering at the low end, the graphs look like this
Filter specs
Corresponding response curves
STATISTICS
f3 43 Hz
f6 37.8 Hz
f10 33.2 Hz
Zmin 5.2 Ohm @ 359.2 Hz
Zmax 63.4 Ohm @ 21.8 Hz
GDmax 20.8 ms @ 29.1 Hz
XmaxC 5.5 mm @ 26.3 Hz
VmaxR 9.9 m/s @ 38.3 Hz
Pmax 43.6 VA @ 42.4 Hz
-------------------------------------------------------------
DRIVER: FaitalPRO 15PR400, 1 pcs in series
n0 2.73 % Reference efficiency
SPL 96.5 dB/W Sensitivity
USPL 98.4 dB/2.83 Sensitivity
EBP 102.9 Efficiency bandwidth product
Dd 32.0 cm Effective diameter of driver
Vd 462.9 cm^3 Maximum linear volume of displacement
Cas 1.56E-6 m^5/N Acoustic equivalent of Cms
Mas 1.31E1 kg/m^4 Acoustic equivalent of Mms+Mme
Ras 4.8E2 Ns/m^5 Acoustic equivalent of Rms
Rae 8.44E3 Ns/m^5 Acoustic equivalent of Re+Rg
-------------------------------------------------------------
BOX REAR 1: Vb=110.0 l, Ql=15.0
Fb 45.0 Hz System resonance frequency
Cab 7.79E-7 m^5/N Acoustic compliance of air in enclosure
Rab 6.49E2 Ns/m^5 Acoustic resistance due to absorption
Ral 6.81E4 Ns/m^5 Acoustic resistance due to leakage
-------------------------------------------------------------
VENT REAR 1: Dv=10.4 cm, Lv=14.0 cm
Sp 84.9 cm^2 Effective area of port
Map 1.61E1 kg/m^4 Acoustic mass of air in port
Rap 4.54E1 Ns/m^5 Acoustic resistance of port losses
We probably need to take some impedance measurements with driver in the cabinet and see if there are other issues that can be solved with some damping material.
Regards
Vineeth
Since the box is no more having rectangular cross section along all dimensions, we are thinking the box mode distribution due to axial modes might see some attenuation along the breadth dimension. However the axial modes along the height dimension might still be strong and some damping might have to be put in place to try and tame it.
There is also a port pipe resonsance shown by the pink curve around 900 Hz (though it is hopefully outside the passband of the bass driver)
Native response curves with above tuning
With a bit of DSP assist and high pass filtering at the low end, the graphs look like this
Filter specs
Corresponding response curves
STATISTICS
f3 43 Hz
f6 37.8 Hz
f10 33.2 Hz
Zmin 5.2 Ohm @ 359.2 Hz
Zmax 63.4 Ohm @ 21.8 Hz
GDmax 20.8 ms @ 29.1 Hz
XmaxC 5.5 mm @ 26.3 Hz
VmaxR 9.9 m/s @ 38.3 Hz
Pmax 43.6 VA @ 42.4 Hz
-------------------------------------------------------------
DRIVER: FaitalPRO 15PR400, 1 pcs in series
n0 2.73 % Reference efficiency
SPL 96.5 dB/W Sensitivity
USPL 98.4 dB/2.83 Sensitivity
EBP 102.9 Efficiency bandwidth product
Dd 32.0 cm Effective diameter of driver
Vd 462.9 cm^3 Maximum linear volume of displacement
Cas 1.56E-6 m^5/N Acoustic equivalent of Cms
Mas 1.31E1 kg/m^4 Acoustic equivalent of Mms+Mme
Ras 4.8E2 Ns/m^5 Acoustic equivalent of Rms
Rae 8.44E3 Ns/m^5 Acoustic equivalent of Re+Rg
-------------------------------------------------------------
BOX REAR 1: Vb=110.0 l, Ql=15.0
Fb 45.0 Hz System resonance frequency
Cab 7.79E-7 m^5/N Acoustic compliance of air in enclosure
Rab 6.49E2 Ns/m^5 Acoustic resistance due to absorption
Ral 6.81E4 Ns/m^5 Acoustic resistance due to leakage
-------------------------------------------------------------
VENT REAR 1: Dv=10.4 cm, Lv=14.0 cm
Sp 84.9 cm^2 Effective area of port
Map 1.61E1 kg/m^4 Acoustic mass of air in port
Rap 4.54E1 Ns/m^5 Acoustic resistance of port losses
We probably need to take some impedance measurements with driver in the cabinet and see if there are other issues that can be solved with some damping material.
Regards
Vineeth
Attachments
It may be hard to predict the amount of damping material required in advance. Usually the box is baseline tested (nearfield acoustic and impedance) and compared to the damped box. The damping material is usually transparent to the low tuning freq, as long as the port is not blocked and the cone is not touched. Damping reduces rear wall reflections and standing waves that are seen thought the cone or port. A BEM sim would be required to predict the internal modes because its not a regular "cube" and it has a short horn. My preference is "just sufficient" internal damping and it's placed away from the walls (particle velocity is ~zero near a wall) to be most effective. Sometime the internal bracing can be used to "contain the material".
@docali @DonVK, we plan to add suitable damping once we obtain measurements. The driver must be mounted from inside, so the box has ample interior access, from beneath.
Do I fill in the space between the baffle and the surface of the horn with rockwool?
Installing the dual ports (104 mm x 140 mm), and finishing the skeleton for the bass horn. Next would be to assemble the horn skin, plane the edges, putty and sand down the box to a smoother finish.
Do I fill in the space between the baffle and the surface of the horn with rockwool?
Installing the dual ports (104 mm x 140 mm), and finishing the skeleton for the bass horn. Next would be to assemble the horn skin, plane the edges, putty and sand down the box to a smoother finish.
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That's a good idea. You could moderately pack those baffle-horn cavities with some porous material like RockWool. It would help damp mechanical vibrations and acoustic transfer to the horn surface.
The rear chamber acoustic damping can be placed in a fine mesh bag or mesh panels to center it and keep it in place. The damping material should be something safe, as the fibers could be ejected from the tuning ports.
While the bass bins were puttied and left to dry I snuck in and finished the new exponential adaptor. The inner shell is printed in resin and enveloped in mahogany. Ideally, I would've loved to have the entire adaptor milled in hardwood, but my fabricator expressed limitations. Nothing changes functionality-wise, it should do for now.
Maybe it is not possible with his equipment including the adapter plates? Maybe you could use a base block for the inner profile for cnc and attach the adapter plates later like the first picture in this post:
https://www.diyaudio.com/community/...rns-picture-heavy-thread.402587/#post-7435408
https://www.diyaudio.com/community/...rns-picture-heavy-thread.402587/#post-7435408
So @WetFartz took some measurements of the Bass horn (still in the construction stage) & wooden mk3b2 today 
Bass horn raw polar measurements (5ms gated measurements from 1.5m away from 0 degrees to 90 degrees taken in 10 degree steps)
Faital pro HF146 on Mk3b2 raw polar measurements (5ms gated measurements from 1.5m away from 0 degrees to 90 degrees taken in 10 degree steps)
Reference axis taken as 20degrees off axis response
A quick & dirty crossover using the above two
Bass horn raw polar measurements (5ms gated measurements from 1.5m away from 0 degrees to 90 degrees taken in 10 degree steps)
Faital pro HF146 on Mk3b2 raw polar measurements (5ms gated measurements from 1.5m away from 0 degrees to 90 degrees taken in 10 degree steps)
Reference axis taken as 20degrees off axis response
A quick & dirty crossover using the above two
Wow! A great speaker system in a unique listening roomSo @WetFartz took some measurements of the Bass horn (still in the construction stage) & wooden mk3b2 today
View attachment 1216621
Bass horn raw polar measurements (5ms gated measurements from 1.5m away from 0 degrees to 90 degrees taken in 10 degree steps)
View attachment 1216623
Faital pro HF146 on Mk3b2 raw polar measurements (5ms gated measurements from 1.5m away from 0 degrees to 90 degrees taken in 10 degree steps)
Reference axis taken as 20degrees off axis response
View attachment 1216624
A quick & dirty crossover using the above two
View attachment 1216627
View attachment 1216629
An updated crossover. However there could be a mistake in this one in the sense that I have done mild baffle step compensation on the nearfield response just based on the cabinet dimensions and not considering the effect of bass horn. Will have to confirm validity using full speaker measurements once. But for now here is how it looks.
Maybe redundant, but here is a reverse null test
By the way the final listening room of this speaker setup maybe this one (at @WetFartz's home)
Maybe redundant, but here is a reverse null test
By the way the final listening room of this speaker setup maybe this one (at @WetFartz's home)