Best regards,
Mattias

They both use a B&C Neo 12 - don't remember #, but could get if its important.

Why two?

One is for the 25-50 Hz that the Summa cabinet size does not allow. This is a bandpass tuned to about 32 Hz covering about the octave mentioned. It has a very long port on a tall cabinet and thus has its output about five feet in the air - intentional to get it away from the floor. Takes a lot of power to drive - very inefficient, but adds a notible effect at VLF.

The second sub design, of which I have two, is also bandpass, same driver, but completely different design. This one is designed to cover a, 35Hz - 120Hz and is put into the LFE channel. It too is ver low efficiency - no tube amps here! These subs are located around the room. In my system, even in stereo, the LF are routed to the LFE channel, so in essence I have two speakers 50Hz and up (monopoles), two 35 - 120 Hz. and one 25-50 Hz. they were balance by measurements and tweeked by ear.

This seems to work in my small room, but does not seem to be required in my very large room. In the large room the single VLF sub with ported speakers works great.

The small room needs a different solution with subs placed around the room and a very well damped low end. This would be true of all small rooms.

Global solutions for frequencies above about 200 Hz. are possible, but below this the solution has to be matched to the room, and try as I do, I cannot find rules of thumb that work. Although bigger is always better - of that there is no doubt. But my home theater is small because of the sound proofing. I can use it anythime. The big hoowm upstairs is a 'cooperate with the family" issue. When I am home alone I always listen in the bigger room.

Isn't fs of B&C speakers too high to be used as subwoofers? How come you're not using for example Peerless XLS12, Eminence LAB12 or NHT1259?

/Mattias

Well, I have had avery good experiences with the B&C products and some not so good ones with most others. You can count on their data sheets being correct. With most companies data sheets are targets, which are only sometimes hit with any accuracy. I also buy enough that I get a good deal on them and they are already a good deal.

But remember that I am using bandpass designs. The bandpass design is ideal for subs because the fs of the driver (in its rear box) is at the center of the passband - not at the lower edge. Thus the fs of the driver is not a big issue, but box size can be. Hence the big box for my 25 - 50 Hz. sub.

I can't figure out why so few subs are bandpass - it seems ideal to me and the ones that I have made work very well when compared to the ones that I purchased - which were not bandpass.

I think that you also asked about the lever.

Think of it as a passive radiator with gain. The gain is the ratio of radiating to driven areas. Two to one is typical, resulting in about 6 dB of increased output from a given driver.

Wish someone actually made levels as I'd certainly use those if they were available.

I'm bookmarking that post.

Cheers,

Duke

I tweak, we all tweak in that I do use tone controls - typicaly -1 dB trebble and + 1 or 2 dB bass. The tweeaking that I was refereing to above was in setting the LFE channel level since this is hard to measure.

Wouldn't it be possible to build the lever with 3 passive radiators (two at the second stage)? What's the problem with using a large ratio of the radiating areas?

Also, I wonder about multiple subs. I think I've read somewhere that the more subs you scatter around the room, the flatter bass you'll get. Is this true?

/Mattias

The lever can theoretically go to any ratio, but beyong 2:1 we found that the parasitics were eating up the advantages. The mechanical parameters on the radiating side are mutiplied by the ratio squared. So acoustic mass load soon gets to be a problem, etc. Beyond 2:1 and we could not get the lever to survive very long. They get beat pretty hard. You don't have to use just one lever there can be more than one - if thats what you mean. We used two levers one driver.

You understand the lever function well enough. It can be used wherever a passive radiator is used.