hifi column bass speaker

toastyghost wrote: snowflake wrote: @Pasi, what software would you recommend for producing plots like those? I've always used Hornresp and Akabak to design my other projects but they aren't going to be much help on this one. That’s just side view of EASE Focus with a generic source. It’s free, but it doesn’t do boundaries. You won’t get much of anything that does boundaries for sub-100Hz I’m afraid.

FrederikMA wrote: I dont see any kind of usefull directivity in those simulations. Without any boundaries, the little cancellation/lobing indicate absolutely nothing about real bahaviour.  1.5 meters of relative delay is quite insignificant at those wavelengths. Even a dipole, which has 180 degrees of delay duo to the opposite polarity, acts like a monopoly at those wavelengths, since they virtually in-phase.  If you separate the rear chamber and invert the polarity of one driver, you have yourself a something like a simple cardioid to play with.  Directivity below 100 hz is a non-issue really. In the modal region (approx below Schroeder fs), our hearing can only detect steady-state, that is we can only analyse a signal after multiple wave cycles, and at that point the signal has reflected so many times, that it is basicly just bass-soup.  In fact, monopoles and the many modes they excite are quite desirable in achieving flat bassresponse. Above the modal region it is a different game entirely, and cardioid can be quite useful.

"if you are always stood in the main horizontal lobe then the directivity is significant."

With bounderies and your ears integration/processing time, there is no such thing as lobes at those frequencies.
"1.5 metres is significant. it's half a wavelenth at 110Hz"

It is also likely to be more than the distance to any nearby boundery, thus making any anachoic situation a purely academic matter.

"for a cardoid to be useful I would have to point the tube horizontally rather than vertically which isn't going to fit in my living room"

My bad, this was inaccurate. I used the word "cardioid" duo to its more commonly known understanding as an intentionally directional source.

"things do become problematic below the Schroeder frequency but that doesn't mean that nothing at all can be done."

I agree, but to me, directivity, in the traditional sence, is not the solution to those problems. Modal smoothing by the use of multiple sources is.

EDIT: quotation failed, so put in quotation marks


Edited by FrederikMA - 17 January 2019 at 4:06pm

No not on a LONG pipe, and not for the purpose of directivity. for the other reasons mentioned in my earlier post. search "diyaudio + sonotube".

Def_Const
{
tubelen = 2;
floor = 25e-2;
L23 = 5e-2;
L78 = 15e-2;
diff = 15e-2;
dia = 29.5e-2;
L45 = ((tubelen-L23-L78)/2)+diff;
L56 = ((tubelen-L23-L78)/2)-diff;
section = 3.1412*dia*dia/4;
top = tubelen+floor;
}

|              0-Voltage-1                                  1
|                        |                    |
|RadiatorA-2-ChamberB-3-DriverC-4-ChamberD-11  12-ChamberE-6-DriverF-7-ChamberG-8-RadiatorH

Def_Driver 'Driver'

  Sd=380.00cm2
  Bl=17.00Tm
  Cms=2.41E-04m/N
  Rms=2.10Ns/m
  fs=45.00Hz  |Mmd = 47.64g not recognised by AkAbak, fs calculated and used instead
  Le=0.60mH
  Re=6.20ohm
  ExpoLe=1
 
Def_Reflector    Wall=0.1cm
Hangle=0 Vangle=-90
absorbcoeff=0.1

Def_Listeningpoint
    x=0m y=1.3m z=6m

System 'System'

  Driver Def='Driver''Driver top'
    Node=1=0=3=4
  Driver Def='Driver''Driver bot'
    Node=1=0=7=6

  Duct 'Rear chamber D'
    Node=4=11
    SD={section}
    Len={L45}
    Visc=0
    QD/fo=0.1
    
  Duct 'Rear chamber E'
    Node=6=12
    SD={section}
    Len={L56}
    Visc=0
    QD/fo=0.1

  Duct 'Horn segment B'
    Node=3=2
    SD={section}
    Len={L23}
    Visc=0
    
  Duct 'Horn segment G'
    Node=7=8
    SD={section}
    Len={L78}
    Visc=0

  Radiator 'Horn mouth A top'
    Node=2
    SD={section}
    x=0
    y={top}
    z=0
    Vangle=90
    Reflection dEdge=30cm
      
  Radiator 'Horn mouth H bot'
    Node=8
    SD={section}
    x=0
    y={floor}
    z=0
    Vangle=-90
    Reflection dEdge=30cm