This is the first time I've attempted to build a FAST and I am wondering if there are any hard and fast rules? For instance how does one determine the placement of the drivers on the baffle, is it similar to mounting a mid-bass and tweeter? The FAST builds I have looked at seem to be crossed over in the 200 to 500hz region so any help with the crossover point and other parameters would be much appreciated. I will be using a MiniDSP 2x4HD for crossover and tuning and I have a UMIK1 for measurement.
This project is an evolution of the Nautilus tapered transmission line for full range driver idea I had. The drivers are a Wavecor FR090WA02 3-1/2" Aluminum Cone Full-Range 8 Ohm: Wavecor FR090WA02 3-1/2" Aluminum Cone Full-Range 8 Ohm and a Scanspeak Discovery 18W/4434G-00, 7" Midwoofer, 4 ohm: Scanspeak Discovery 18W/4434G-00, 7" Midwoofer, 4 ohm
Thanks for any replies.
This project is an evolution of the Nautilus tapered transmission line for full range driver idea I had. The drivers are a Wavecor FR090WA02 3-1/2" Aluminum Cone Full-Range 8 Ohm: Wavecor FR090WA02 3-1/2" Aluminum Cone Full-Range 8 Ohm and a Scanspeak Discovery 18W/4434G-00, 7" Midwoofer, 4 ohm: Scanspeak Discovery 18W/4434G-00, 7" Midwoofer, 4 ohm
Thanks for any replies.
They're just 2-way speakers, for all the acronyms that get bandied around. So once you eject those and look at them in that light, you see that for optimum results you approach them like any other multiway: measure the on & off axis FR curves, impedances, and design your filter based on that data, based on whatever frequency you may wish to cross at.
Being wideband drivers, you have the option in many cases of crossing lower than you can do with a regular dome tweeter, and there is typically less offset on the Z-axis so (especially if you cross relatively low) there is often less need for asymmetric slopes or physical offsets, which can make life easier. Otherwise it's just straightforward engineering / design process.
Being wideband drivers, you have the option in many cases of crossing lower than you can do with a regular dome tweeter, and there is typically less offset on the Z-axis so (especially if you cross relatively low) there is often less need for asymmetric slopes or physical offsets, which can make life easier. Otherwise it's just straightforward engineering / design process.
As Scott & waxx have already said.
A 2-way with a very low XO.
One does have to look at a WAW with a bit different perspective. The wavelengths at the XO frequency are much longer and ideally one wants to take advantage of that.
First of is that you now have the possibility of getting the drivers close enuff that the centre-to-centre is less than the quarter-wavelength.
As well one needs to also consider that this frequency is also in the same range as the transition from 2∏ to 4” space, so one gets the opportunity of placing the XO where it can be used to deal with this transition as well simply by having a more sensitive woofer.
As well it is often quite possible to choose drivers and design boxes that allow as little as a 1st order XO.
The bass is designed the same way one would use that midbass but without the worry of how they do at the top end of theire bandwidth — it is nice to have a midbass with an extended and well behaved roll-off at top.
The midTweeter enclosure follows the same route as a midrange, it is just extended enuf fthat one can ditch the XO.
The miniDSP will give you lots of verstaility in terms of quickly playing with XO options, and then if you find the ADC/DAC limitinf you can look at converting the scheme sorted out with the miniDSP into analog form. If you have found a 1st order XO that works this can often be implemented as a PLLXO with only 3 small passive parts per channel in the “XO”.
dave
A 2-way with a very low XO.
One does have to look at a WAW with a bit different perspective. The wavelengths at the XO frequency are much longer and ideally one wants to take advantage of that.
First of is that you now have the possibility of getting the drivers close enuff that the centre-to-centre is less than the quarter-wavelength.
As well one needs to also consider that this frequency is also in the same range as the transition from 2∏ to 4” space, so one gets the opportunity of placing the XO where it can be used to deal with this transition as well simply by having a more sensitive woofer.
As well it is often quite possible to choose drivers and design boxes that allow as little as a 1st order XO.
The bass is designed the same way one would use that midbass but without the worry of how they do at the top end of theire bandwidth — it is nice to have a midbass with an extended and well behaved roll-off at top.
The midTweeter enclosure follows the same route as a midrange, it is just extended enuf fthat one can ditch the XO.
The miniDSP will give you lots of verstaility in terms of quickly playing with XO options, and then if you find the ADC/DAC limitinf you can look at converting the scheme sorted out with the miniDSP into analog form. If you have found a 1st order XO that works this can often be implemented as a PLLXO with only 3 small passive parts per channel in the “XO”.
dave
I had a quick look at your choice of drivers. I have one comment on the choice of discovery as the bass driver. By utilizing something that goes down to such low frequency, you can have more freedom in bass driver now that it doesn't have to do any mid work.
The discovery has a Fs of 47 Hz, I think you can find many drivers to will have Fs cliser to 30 Hz, this will give you lower bass.
Oon
The discovery has a Fs of 47 Hz, I think you can find many drivers to will have Fs cliser to 30 Hz, this will give you lower bass.
Oon
"The discovery has a Fs of 47 Hz, I think you can find many drivers to will have Fs cliser to 30 Hz, this will give you lower bass."
Right, but I am now living in a townhouse with neighbours on one side who will appreciate my choice of F3 and I have the 18W/4434G-00 in hand. This will also allow me to keep the enclosure at a reasonable size which will keep my wife happy so all in all I think I'm on the correct path for my needs.
Thanks for the thoughtful and relevant input though.
Right, but I am now living in a townhouse with neighbours on one side who will appreciate my choice of F3 and I have the 18W/4434G-00 in hand. This will also allow me to keep the enclosure at a reasonable size which will keep my wife happy so all in all I think I'm on the correct path for my needs.
Thanks for the thoughtful and relevant input though.
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