I'm trying to decide on a subwoofer to complement my Theatre-3 for HT use. Space is tight, so it'll have to be sealed or BR. The Pi-3s alone go plenty low for most music, but they're missing the lowest rumble for HT. I think the Pi-3s are good down to mid-30's in my room, so I'm looking for something to fill in that last octave between 20 and 40.

Your Theatre-3 BR Sub, based on the LAB-12 seems like a logical choice. But I need help getting over its description as "designed for use in pro sound bass horn enclosures". Would this mean I'll be getting compromised performance if I use the LAB-12 in BR or sealed? I would love to hear from people who have used the LAB-12 in BR at home.

Also, what are the main difference between a pro-driver like the LAB-12 vs HT sub drivers like the Titanics or Peerless? I've been very happy in the past few years adapting pro-drivers for home-use in the form of Pi speakers and my JBL system. The advantages of these speakers over "normal home" speakers are apparent in higher sensitivity and power handling. However, the difference between the LAB-12 and "normal" HT sub drivers are not obvious to me.

thx,
Gar.

For home hifi, I prefer the direct radiator subwoofer over the horn. It's smaller and you can tune it lower as a result. A horn run below cutoff is basically an undersized sealed cabinet with a horn that amplifies harmonics. So unless you have a lot of real estate, I prefer the LAB12 in a vented or sealed box for home hifi.

As for comparison with other woofers, most of the really good parts have shorting rings and the LAB12 doesn't. But before writing it off, consider the fact that shoring rings don't really work below 100Hz. Theoretically, one could be made that reduced distortion at very low frequencies, but it's difficult. The ring has to be large, and that takes away from magnet space. From a practical design standpoint, it becomes prohibitively impractical to design a subwoofer with an effective shorting ring. That's why you see other technologies employed, things like differential voice coils and other forms of push-pull drive.

If you really want to make the best small subwoofer you can make, look at implementening a pair of LAB12 or HL10 woofers in push-pull, perhaps driving a bandpass box that attenuates higher frequencies. The push-pull drive will cancel second harmonics, the front chamber will reduce third harmonics and both the push-pull drive and front chamber will reduce fourth harmonics. Above that, the front chamber will remove the higher harmonics.

That's a very similar technique that I used in the 12π horn subwoofer. It uses push-pull drive to cancel second harmonics and the front chamber and horn folds reduce higher harmonics. It's probably too large for home use, and if pushed below cutoff then the horn would amplify harmonics in its passband. But as long as it is used above its 30Hz cutoff, it generates almost no distortion.

No matter what kind of system you run, if you push it below cutoff, distortion will rise. Excursion is lower in the passband than it is below cutoff. This applies to bass-reflex and bandpass systems as well as horns. So system tuning is very important. Don't tune the system for 30Hz cutoff and try and EQ down to 20Hz. If you want to run the subwoofer down to 20Hz, then tune it for 20Hz or below.

Thanks for the feedback. I've never considered a push-pull design because of driver cost. However, after stumbling on this driver on Partsexpress (see link below), it seems quite affordable. According to the specs, it looks like a light version of the Lab-12. It models almost exactly like a Lab-12. Probably made by Eminence. Wayne, any thoughts on this driver?

Also, can you provide me with more background on designing a push-pull sub, or point me to some links. Googling has turned up very little.

Would cabinet size be double that of a single driver box? If so, that would make the cabinet 6 to 7 cu ft, and far too big for most home use.

What about driver mounting? I don't think I want to see the back of a driver sticking out of the front baffle. Can drivers be mounted front baffle/ back baffle?

thx,
Gar.

• Lab-12 Lite?

As for information about push-pull drive, see the post called "Push-pull verses shorting rings". It has links to several posts, some containing links to outside information sources and test data as well.

gar.