How do horn subs sound indoors?

Yes it is. But there are free plans for single 18 BPH just like it, or close.

Maybe you should take a look at Cubo18 also. 

Has a nice thump to it and still goes fairly low. And compact box. 

Some years ago i used 8 Cubo15 for a hardstyle gig in a large club (up to 1100 guests). Center stacked them all and hammered them all night. A bit more LF response would have been great, but oh my they kicked alot and hard!

In my opinion, BR are just too slow sounding. They don't have that nice controlled thump you get from a horn. 

He ask for punisher so it’s a closed horn

Work and try. 

Edit. 

Cubo are tapped. I suggest to build tham15 instead of cubo15 because they sound tighter and more controlled. Great bin to small purpose but 4/6 of this have enough authority to fill a small club with smiles

1. How much money do you have?

2. Where you’ll use the subs?

3. Which are the tops?

4. How much space/people do you have to cover? Indoor/outdoor

5. How can you carry your sound system? 

6. How much people to move the sound system?

a modern 2x18” br (one with 3.5kw program strong motor high bl) will outperform the punisher with the right amp. 

2. Indoors including warehouses, bunkers, commercial buildings like office blocks and such. Also outdoors in fields / forests.

3. I was thinking of some Orbital 4s

4. Don’t know the space as each venue will change, but aim to cover 200 people with some naughty bass. 

5. Van, can tow a trailer as well. 

6. Not sure but at minimum 3. 

2x Orbit 4 neo 

2x Tham15 loaded with 15tbx100 

1 and 1 sound lovely, never tried 1 and 2 but for sure it will be better. 

You need at least 6 channel of amp. 

Don’t economize on amp choiche.