I was thinking of DIY a compression driver.
What accounts for the low Fs of the 375 driver compared to a modern low cost ones where Fs is above 1Khz?
What accounts for the low Fs of the 375 driver compared to a modern low cost ones where Fs is above 1Khz?
The JBL 375 (same as the JBL 2440 other than color) uses a 4" diaphragm and a large back chamber.
It was designed in the days when two way usually meant 500 Hz crossovers.
Many current drivers are designed for use with crossovers one or two octaves higher, but there are still many compression drivers made that can be used to 500 Hz or lower.
Phenolic diaphragm PA type 1" exit drivers like the Selenium D250X can work for such low crossovers.
The Selenium D250X is for midrange use and not the highest in fidelity whereas the old Altecs and JBL's did 500Hz and up. Do you have another suggestion not Altec or JBL?
If I was looking for 500 Hz response up from a compression driver, I'd use a 1.5" exit 3" diaphragm, not a 1.75" diaphragm.
I use the EVDH1AMT, there may be other new drivers that sound better, I wish I had the budget to do comparisons with current drivers.
I still prefer the sound of small cone midrange to the DH1AMT below 1000 Hz.
I'd like a car that can do zero to sixty in under four seconds, preferably lower cost
and
I'd like to data a woman who looks like Kim Kardashian, but enjoys listening to me blather on about loudspeakers
While you're working on those two, I'll find you an inexpensive compression driver that fits your requirements 😉
(hint : none of the above exists)
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Totes. It's the whole reason I was trying to figure out the Thiele Small of my DE25.
DIY compression drivers are very much do-able, particularly thanks to the hard work of David McBean
Maybe the B&C DE250 is better than the 802 after all.
I want to use it with a 811B, it might work well above 1kHz.
I want to use it with a 811B, it might work well above 1kHz.
very unexpected imp. graph without back chamber!
did you fixed the diaphragm during measurement? in what way? i have similar china 3"..
have been playing round with this script to try and fit it to the published impedance curve. have not changed Re or Le or any of the dimensions of the front chambers on the driver. have changed the other driver parameters slightly, the Qb factors of the front chamber and duct, and the back volume to get close to the published curve. ended up with Vb a lot smaller at 5cm3. HF response isn't great but at least the impedance and response are vaguely right in the crossover area.
if anyone has any parameters OR akabak script for a BMS 4550 please post them.
| AkAbak script - DE250 Compression driver
| Parameters preceeded by ...... need to be defined
Def_Const
{
Ree=6.3; |Voice coil resistance [ohm] ......(Re)
Le=0.11e-3; |Voice coil inductance [H] ......(Le)
Bl=9.3; |Motor conversion factor F=Bl*i [Tm]......(BL)
Mms=1.4e-3; |Mechanical mass [kg] ......(Mms)
Rms=.5; |Mechanical resistance [Ns/m] ......(Rms)
Cms=30e-6; |Mechanical compliance [m/N] ......(Cms)
dDi=40e-3; |Diameter centre diaphragm [m] ......(Diam of inner magnet)
dDa=47e-3; |Diameter outer diaphragm [m] ......(Diam of outer chamber)
Hi=1.0e-3; |Eff. height of outer chamber under the ring ......(gap between diaphragm and phase plug)
Ha=4.5e-3; |Eff height of outer chamber under the ring ......(Averaged height of annular chamber)
ds=0.20e-3; |Slit between voice coil and magnet ........(Annular gap between magnet and voice coil former)
ls=11e-3; |Length of voice coil path .......(Length of annular gap)
}
System 'DE250'
|Voice coil (frequency-non-linear resistance and reactance)
Impedance 'Ze'
Node=1=502
Z={ Ree*(1 + f/25e3) + j*(w*Le)^0.5; }
|.......(f/? , w*Le^?)
|Motor
Gyrator 'Gy1'
Node=502=0=503=504
Bl={Bl}
|Reverse side with enclosure
Coupler Node=504=0=100
dD={dDa}
Enclosure 'Eb' Node=100
Vb=5cm3
Qb/fo=0.0008 | .......(Vb , Qb/fo)
|Mechanical part (Mms frequency depending, cut-off at ? kHz)
Impedance 'Zms' Node=503=505
Z={ wo=2*pi*15000;
Zms=Rms + j*(w*Mms/(1 + w/wo) - 1/(w*Cms)) } | ......(2*pi*?)
|Outer diaphragm (ring) with cavity
Coupler
Node=505=506=200
SD={ pi*(sqr(dDa/2)-sqr(dDi/2)) }
Enclosure 'Efo'
Node=200
Vb={ Ha*pi*(sqr(dDa/2)-sqr(dDi/2))}
|Centre diaphragm with compression chamber
Coupler Node=506=0=300
dD={dDi}
Enclosure 'Efi'
Node=300
Vb={ SD=pi*sqr(dDi/2);
Vb=SD*Hi }
|Voice coil tunnel between outer ring cavity and compression chamber
Duct 'Dvp'
Node=200=300
SD={ U=pi*dDi;
SD=U*ds }
Len={ ls }
QD/fo=0.003 | .......(QD/fo)
|Horn inside compression driver
Waveguide 'Wpp'
Node=300=400
dTh=2.32cm
dMo=1in
Len=3.0cm
Conical
|......dTh, dMo, Len
Horn 'H1'
Node=400
dTh=2.54cm
dMo=19.1cm
Len=12.4cm
T=1
|ME45 equiv
The above is quoted from Audio Psychosis • View topic - Simulating a B&C DE25
There are only two things I don't agree with in Patrick Bateman's (John) DE25 parameters. I've actually measured the Sd of a DE25 diapgragm and know it is 18.09557cm^2. The second thing is there is no way BL can be 18 T*m. It has to be somewhere between 7 T*m and 9 T*m. I do agree that Patrick's numbers for Fs, Qes, and Mmd are probably better than mine - Hey this was early on and we've learned so much since then. 🙂
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