hi all just wondering how to calculate the vas from the qts,qes,qms and fs, Here are the specs i have found
cheers james
FULL RANGE SPEAKER
INPUT POWER 40 W MAX.
* Manufacturer: CORAL
* Model: 4A - 70
* f(s)= 121.10 Hz
* R(e)= 6.90 Ohms
* Z(max)= 27.10 Ohms
* Q(ms)= 2.455
* Q(es)= 0.838
* Q(ts)= 0.625
* L(e)= 0.19 mH
cheers james
FULL RANGE SPEAKER
INPUT POWER 40 W MAX.
* Manufacturer: CORAL
* Model: 4A - 70
* f(s)= 121.10 Hz
* R(e)= 6.90 Ohms
* Z(max)= 27.10 Ohms
* Q(ms)= 2.455
* Q(es)= 0.838
* Q(ts)= 0.625
* L(e)= 0.19 mH
Greets!
Need to know at least its ‘Sd’ or effective piston diameter to calculate it, though ideally its measured ‘BL’, ‘Mms’ and ‘po’, ‘c’ the machine used to measure with also if the person that measured them bothered to save these. Makes me wonder if his were dried out from age.
FWIW, some seriously different/better Fs, Qts specs published here: Vintage SpectrumAudio
GM
Need to know at least its ‘Sd’ or effective piston diameter to calculate it, though ideally its measured ‘BL’, ‘Mms’ and ‘po’, ‘c’ the machine used to measure with also if the person that measured them bothered to save these. Makes me wonder if his were dried out from age.
FWIW, some seriously different/better Fs, Qts specs published here: Vintage SpectrumAudio
GM
Hi GM thanks for the reply tried to find the piston size but was unable this is all the dimensions i could find. I might have to do it the old way by building a box and putting the signal generator on it and working it out that way but i have already built boxes for the corals here is the pic's with the box dimensions Picasa Web Albums - arustyrednail - coral 4A-70 p... but i wanted to try a back loaded horn design but don't know how to design one of them yet 
Greets!
You’re welcome!
OK, not that big a deal, you can measure [Dd] close enough by measuring the diameter across the diaphragm where it meets the surround [d1] and the diameter across the surround’s outer limit [d2], then [d1*d2]^0.5 = [Dd] and of course effective piston area [Sd] = Dd^2*pi/4.
WRT the speed of sound value [c] and air mass [po], I’ll use an average of the default values of some popular design programs.
Been there, done that many times and I date back to when the typical DIYer ‘designed’ based on a formula that only used Dd, Fs to generate a net box volume [Vb] and since this was back when amps typically had a very high output impedance and drivers had a huge Vas spec to keep efficiency high, the cabs were huge by today’s standards.
GM
You’re welcome!
OK, not that big a deal, you can measure [Dd] close enough by measuring the diameter across the diaphragm where it meets the surround [d1] and the diameter across the surround’s outer limit [d2], then [d1*d2]^0.5 = [Dd] and of course effective piston area [Sd] = Dd^2*pi/4.
WRT the speed of sound value [c] and air mass [po], I’ll use an average of the default values of some popular design programs.
Been there, done that many times and I date back to when the typical DIYer ‘designed’ based on a formula that only used Dd, Fs to generate a net box volume [Vb] and since this was back when amps typically had a very high output impedance and drivers had a huge Vas spec to keep efficiency high, the cabs were huge by today’s standards.
GM
True, but this assumes a maximally flat response which will tend to sound [very] 'boomy'/'one note' in-room, so better to make it around its ~110 L Vas spec and tune it to Fs if driven with a high output impedance, otherwise down around 30-32 Hz and use internal damping to quell any perceived 'ringing' it may have due to it being technically a somewhat under-damped alignment.
GM
GM
Last edited:
i just finished my design on sketch up thought you would like to have a look, I made the volume to 146 litres for the woofer to use the space behind the midrange because of the 15 litres that is only required for the midrange
Equipment:
Coral 4a-70
Coral 12L-25B
Vifa BC25SC55-04
james
Equipment:
Coral 4a-70
Coral 12L-25B
Vifa BC25SC55-04
james
Attachments
Last edited:
Well, it's what I would try first since a point source driver wants to 'feel' a matching acoustical impedance on both sides of it. At a glance, it looks like a ~7.88" wide baffle should suffice, so matching the wider width required for the 12L will be even better and if you don’t like it and/or want a lower XO point you can always box it in sealed [or even try vented] later plus the separate box will allow you to physically time align it instead of trying to work it out in the XO, just add some damping to any exposed cap top to quell early reflections.
Dimensionally, what do you have in mind? I mean I like such designs to have the ‘FR’ driver at ~ear height which dictates a tall cab with the woofer usually at the extreme top and any venting somewhere further down, i.e. MLTL layout.
GM
Dimensionally, what do you have in mind? I mean I like such designs to have the ‘FR’ driver at ~ear height which dictates a tall cab with the woofer usually at the extreme top and any venting somewhere further down, i.e. MLTL layout.
GM
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.