This tweeter is super!

[Ajani]

My Zu's were exceptional speakers but I could not justify ownership when these OB's IMO are clearly better in every respect.

Ajani,

If you bi-amp that combo and use active crossovers you will not want for a better system.

I'm thinking of buying this stand alone bass amp with built in active crossovers to power the Alpha 15A's while it's on sale.

Dayton Audio SA230 230W Subwoofer Amplifier 300-813

This project looks like a great way to use the Emotiva XPA-2 I have lying around - that 300 watt beast should be an ideal bass amp for the Alpha 15A's...

+

I've been undecided on whether to buy towers (which I prefer) or monitors (since I've tended to change country every few years and portability is key). The advantage of this build is that I could just take the drivers and dump the plywood if I move. So I'd get towers that are portable...

I'll definitely get the Fostex to try out and if I see some promise in the results, I'll go through with the whole build...

[Poultrygeist]

The Emo will do the but you will need a Behringer active or a two 80hz low pass XO for the Alpha's. Even though the low pass XO's for the Alpha's would be passive they will have no effect on the other drivers as they are driven separately.

Choose a Fostex with a high Qts. ( .5 or higher is desirable for optimum OB sound )

[Ajani]

I plan to get the Behringer DCX2496 Ultradrive Pro Digital Crossover. And my choices for Fostex are either the really cheap (and disposable) FE103En 4" Full Range (used in MJK's original design) or the FE108EZ 4" Full Range Sigma Series (MJK's current favourite for this design)...

I think my only concern right now is whether this system will have sufficient bass... I would love to see some designs with dual Alpha 15s, as the height of the speaker would not even need to be altered to accommodate the additional driver...

[Ajani]

Did a search for OB with dual Alpha 15's and found that the Emerald Physics CS2.3 (speaker I got the inspiration for the Behringer Crossover from) uses twin Alpha 15's. It has the following spec:

Frequency Response: 20Hz - 22kHz -3dB (with DSP correction)

CS2.3 Specs

So it seems really good bass is possible with dual Alpha 15's in an OB...

Also I would be using the same dual bass drivers and active crossover as in a $5K pair of speakers (I see why DIY folks get so excited about cost savings)... Of course the big difference in my build and their design is that I'd use a fullrange 4" Fostex while they use a Eminence Beta-12CX 12" Coaxial Driver with a Selenium D220Ti 1" Titanium Horn Driver.... + their Baffle is not made (exclusively anyway) of the kind of cheapy plywood I'd be using....

6moons audio reviews: Spatial/Emerald Physics System Review

[Poultrygeist]

With two 15 inch full range bass drivers of 98db sensitivity you will have high quality and plentiful bass. And unlike most subs the Alpha's bass is very musical. Although I now have four Alpha's I haven't felt the need to try them all in the same system. But for kicks and giggles I may.

[Ajani]

Of interest is that I added up the total cost of drivers and active crossover (assuming dual Alpha 15's) and it is only $30 less than the cost of drivers and active crossover for the Emerald Physics CS2.3 (I mentioned earlier)... So in theory I could build my own version of the CS2.3... Though I'd rather stick with MJK design...

[Ajani]

With two 15 inch full range bass drivers of 98db sensitivity you will have high quality and plentiful bass. And unlike most subs the Alpha's bass is very musical. Although I now have four Alpha's I haven't felt the need to try them all in the same system. But for kicks and giggles I may.

Let me know how it turns out and whether it sounds better or worse than just using a pair of Alpha 15's...

[Poultrygeist]

I have no doubt my home spun OB's would go toe to toe with those Emerald Physics. My main drivers are better and the Alpha's are equal. They bi-amp that design while I quad-amp mine. Anyone who would pay that much for the Emeralds would probably need the four Alpha's for their banquet hall.

[Ajani]

I have no doubt my home spun OB's would go toe to toe with those Emerald Physics. My main drivers are better and the Alpha's are equal. They bi-amp that design while I quad-amp mine. Anyone who would pay that much for the Emeralds would probably need the four Alpha's for their banquet hall.

How is the bass on yours? I'm getting confused because some persons claim to have experienced very little bass response using the Alpha 15's in OB... Though I think most (if not all) of those persons used tube amps to drive the Alpha's, while SS is recommended by MJK...

If the bass is good with a single pair of 15's, I probably wouldn't bother with the dual pair (I like bass but I'm not obsessed with it and don't need to fill a huge room with sound)...

[Poultrygeist]

In one set up I drive two Alphas with solid state mono blocks of 150 wpc and I'm only using slightly over a quarter volume at normal listening levels

In the other set up I power two Alphas with a JVC RX-D205 AVR digital amp in two channel mode which makes 110 wpc and I can't go above half volume comfortably. I tried selling the JVC on CL for $75 but thank goodness no one was interested. It now has a useful purpose in life! Older AVRs are a good and cheap choice to drive the Alphas as their internal DAC allows use of the optical connection from a CD player while the analog outputs from the same CD player can be fed to the tube preamp or integrated amp.

The Alphas would sound anemic with my tube amps but tubes are divine for the main FR drivers. In my home office which is about 13 ft X 15 ft I could get by with only one Alpha.