Sunfire subs

The Sunfire approach (small cabinet, big amp) is not for everyone. I can't speak to the specific model you're considering, but - in general - subs using this approach tend to produce a lot of THD at high SPL/low frequency (relative to larger cabinet subwoofers). Neither do they particularly distinguish themselves (as a group) on group delay - the test some folks to use as a proxy for "speed". So, for the quant types, these designs my not hold a ton of appeal.

To be clear, that's a general observation from reviewing test data across a lot of these types of subwoofers - not a specific comment on the TSEQ12.

One reason you see a lot of Rythmik (I use a pair of their 12" subs) and SVS recommendations is that both brands tend to perform unusually well on both tests (SVS better on clean output, Rythmik better on Group Delay). Another reason IME (for Rythmik, at least) is that they sound great.

Marty

I owned a TSEQ12. Before that I owned a cheap M&K sub. The Sunfire definately beat out the M&K. It was tighter and much louder. That said it leaves much to be desired compared to sota designs. IMO it is still muddy and bloated compared to the best. It has plenty of output though. The best I have heard was a REL Studio III. Cleaner and deeper bass.

My current speakers do not require a sub. If I had a bigger room and money burning a hole in my pocket I would get 2 Studio IIIs and call it good.

I am using a stereo pair of Sunfire Signatures subs with my Magnepan 20.1s with great success. I previously used them with 3.5 for many years.
Improperly set up Sunfire subs will demonstrate all of the negatives mentioned above. For best results:

1. Keep the subs away from room boundaries.

2. keep the volume as low as possible.

3. Use the lowest xover frequency of 30 hz when possible.

4. use minute adjustments in the volume and Phase to maximize clarity and minimize "muddiness" in the crossover region.

My subs are undectable in my system, blends seamlessly with my 20.1s, are tuneful and certainly not "boomy"

"wondering if there's something wrong with the Sunfires"

Seems like the higher up the x/o freq the worse they sound.

I thought the Sunfires were good enough with my 3.6's (back when) but not so much with my studio monitors.
A friend gave me an older Velodyne 12" (analog amp inside) and it works much better especially with the SM's.

The real overlooked sub is the Martin Logan. Sunfire subs are fine but all high power subs eventually break and repair pricing on the Sunfire's are very high. ML repairs are very reasonable having dealt with this recently. A friend recently trashed his Sunfire because it was worth less than the repair costs.

Look at the ML Grotto. Fantastic sub for the $$.