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Jessie, 45Hz horn with 6”-7” throat around AK151 driver is from my perspective is the best thing might be theoretically built around a cone driver. I really envy of you and if I had room I would unquestionably go for it; this is why I keep a pair of AK151 and pair 15/40 in my storage.

Regarding the crossovers. You “might” need to cut off the LF that doing into the horn. Consider ~20Hez high pass, preferably line level. As far as low pass – it is very complicated subject. Of course everyone would like to get more LF out of LF horn and they drive it as low as the horn’s mouth allows. However, it is not necessarily good thing to do. You see, what I learned that all drives with back chambers (cone, compression… you name it) when they go down near their resonance frequency they become “congested” and not as relaxed and free as I would like them to be. I good solution is to let electrical filter to kill Sound before the diaphragm before stresses. Think this: a diaphragm dumping is good thing for mechanical calculation of suspension but a damped diaphragm is not a good transducer. Try to play any string instrument when you do not push a string strong enough to the deck – the string sound dull and subdued – exactly how most of the upper bass horns sound at thier lower knee. So, you would need to make your own conclusions where to cut it and how to use it. Do not forget that in your case many other variables will be playing: the boundaries gain, the room mode and so on…

Regarding the back chamber. When you lower back chamber it rises resonance frequency. Some people try to drive resonance frequency to the horn rate; some would like to be having the resonance frequency below the horn rate. I do not think that any rules might be in there. You have to listen how your given horn will behave and sound in your room. I can assure you that the level of freeness of the cone of this driver will be very-very much describing the sound you will be getting out of this horn. It will take for you a few weeks to play with it when you will be done. It is very interesting to change slightly the depth of the hermetic-ness of the back chamber and to see how sound from the horn will change HUGELY. I would say that a good staring point would be look what Vitavox did for their System 191:

http://website.lineone.net/~empson/Sys191.html

Find plans and see how they use the AK151 (chamber), then compare with your circulations… I would go for 1.2-1.4 times larger chamber to have some spare space. It is always possible to patch it with none-elastic foam and to make the chamber smaller…

Also, Jessie, there is another very important point. A construction of your systems should not be a pure DIY efforts or it will be just another stupid DIY project. Your should have none-DIY objectives and use those horns to resolve those none-audio objectives. You need to clearly visualize the result, to breed the result within yourself. Try to listen and to understand Sound that your horn does without even connecting the horn… The moronic DIY people always miss it and end up with garbage result but the problem is that they do not know where they are doing.  Good result come to people who are ready to recognize good results and you have to train and evolve own perception and understudying of Sound in order to be able to acknowledge and discriminate the result when and if you get it from this big new horn.  Without an evolvement of own awareness any DIY project is juts a pile of stupid activity resulting with typical nothingness… Try to develop some “leading” interests in  music and build this big horn to fulfill this “leading interest”…

Rgs,
Romy The caT

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