[mayhem13]

Some of you may have seen my posts using the NHT surplus 10" subs in different configurations...for fun and education. First an overview


Ported Table-165 Liters tuned to 23Hz/500w Oaudio amp

Excellent 25-35hz. Smoothe and LOUD. Couldn't get the amp high pass to keep the drivers from bottoming below tune. Blew 2 drivers. Since replaced drivers with same( bought enough to go round)tweaked LP and Q and turned gain down a little. Still in service


Sealed Push Pull-Same Oaudio amp 70 Liters. Nice and clean output but early rolloff... ended in retirement.


Dipole H Frame 2x2 drivers each Stereo...Dayton Sa240 amp with boost x2. Excellent for music, maybe the best i've heard but still needed another sub for 45Hz on down. Used these under ported high end DIY 2ways and thought i could use them for HT....NOT....Also ended in retirement.


Dual sealed Horizontal/60 Liters/Oaudio 500w/x2-Built for MBMs in the theater with a single sealed 15 and Dual sealed 18 end tables. Currently reside in a friends system. Very loud and clean 40-100hz. He's happy so i'm happy.


So on to the last alignment with the remaining 2 drivers. Moved the 2ways ( Zaph SR71s) to nearfield computer use with a newly aquired and cheap Onkyo M-282 Amp ($149.00!!! and sounds unbelievable). As i'm sitting here typing i realized that i was nearing an excellent 2.0 music system that could really use .1 and the cleanest .1 i can give it. But it's gotta be small....really small like 1cuft small...you get the idea. The Re of the NHT drivers is too high for efficiency with 1 driver. So how do use 2 in 1cuft??

Well i figure i'll give the compound alignment a try but i have a few questions.


If the inside driver faces the rear of the outside driver, How close should they be?


Are there 2 sealed airspaces inside one box and should they be the same volume?


Should i stuff the volume between the two drivers, just the rear driver, or neither?


Like to work on this tomorrow and wrap up on Sunday without finish work to see if it can hang with the SQ of the SR71s.


Forgot to mention 300w plate amp @4ohms...probobly about [email protected] give or take. Won't be playing this al that loud in the Nearfield, but nice to have some headroom.

Here's a Unibox sim with 110watts each driver in 20L.

Attachment 129201

 

[michael hurd]

You will take a -6 db sensivity hit in an isobaric. The chamber between the drivers must be sealed in some way, but there is no magic volume. As long as one does not hit the magnet of the other at full excursion, you are fine.

 

[TheEAR]

In a Isobaric sub the drivers should be as close as possible(with no obstruction at full excursion). The air in the chamber separating the drivers presenting as stiff an air piston as possible.




Mike,


Get a pair of Klipsch RF7's to keep up with TheBEAST. At least keep up longer,to where yur ears will wave white flags.

 

[mayhem13]

Any thoughts on SQ? I thought Iso was the drivers facing eachother???

 

[fhlh]



Quote:
Originally Posted by mayhem13 /forum/post/15520937


Any thoughts on SQ? I thought Iso was the drivers facing eachother???

 

[TheEAR]

Front to front is a great solution to get the smallest volume of air in the AIR PISTON chamber.That is the route I would go when building this type of sub. Not ideal for looks as you see the back side of the driver.

 

[fhlh]

This is why you buy a real purty driver

 

[Warpdrv]

+1.... that is one of the reasons the TC/Audioplulse drivers were so attractive...


I always loved something like the Revo's - they were/are dang sexy IMO....

 

[mayhem13]



Quote:
Originally Posted by TheEAR /forum/post/15527478


Front to front is a great solution to get the smallest volume of air in the AIR PISTON chamber.That is the route I would go when building this type of sub. Not ideal for looks as you see the back side of the driver.

In the case of front to front, one woofer is in the enclosure and the other's back radiates into the room? If that's the case, i could do that in a up down firing config and build a box grill for the outside woofer AKA Ohm Walsh style. The modeled box volume should be the volume of the box and the volume between the 2 cones??

 

[unhappy_mage]



Quote:
Originally Posted by TheEAR /forum/post/15527478


Front to front is a great solution to get the smallest volume of air in the AIR PISTON chamber.That is the route I would go when building this type of sub. Not ideal for looks as you see the back side of the driver.

This may be a silly question, so be forewarned.


With such a small air volume, don't you get some nonlinearity in the motion of the drivers? If they're moving toward and away from each other, the air in the middle will be fairly well compressed, and push back harder on the drivers than it did when the drivers were at rest. So if you fed a sine wave in, you'd get a flattened sine wave out as the air tries to keep the speaker cones in the middle where the pressure is equalized.


Or are the two drivers wired out of phase so they're moving in the same direction? If so, why does the air volume matter?

 

[LHD21]



Quote:
Originally Posted by unhappy_mage /forum/post/15530069


This may be a silly question, so be forewarned.


With such a small air volume, don't you get some nonlinearity in the motion of the drivers? If they're moving toward and away from each other, the air in the middle will be fairly well compressed, and push back harder on the drivers than it did when the drivers were at rest. So if you fed a sine wave in, you'd get a flattened sine wave out as the air tries to keep the speaker cones in the middle where the pressure is equalized.


Or are the two drivers wired out of phase so they're moving in the same direction? If so, why does the air volume matter?

The two drivers are phased so they're moving the same direction. In the front to front or back to back one driver has the phase swapped. In the front to back they're wired normally.