Quote Originally Posted by toddalin View Post
Never heard of a 251J and don't see specs on it anywhere though the cooling fins look to be substantially longer than the 2251J.

The 2251J is a nice match for the Heil and while an MTM would be cool, it is really not necessary. Run at its own impediance level (~3.3-3.7 ohms), the Heil will be a bit loud for one 2251J if it is not padded down a bit. It may be be just about perfect for an MTM arrangement without padding. BTW, the Heils really like/need a high current solid state amp.

Crossing the Heil over at 1kHz is a mistake. It's just too low and my Heil would "complain" where it interfaces with the 2251 at less than ~1,500 Hz. I bring it in at 2,150 hz and it really likes that. Keep it over 2kHz unless you use a steep slope on the crossover.

The 2251J has a natural rolloff below 300 Hz. Just forget about it going down to meet a subwoofer. Ain't gonna happen. Maybe this is where the 251J accels.

But, will the 251J run up high enough to meet the Heil at >2khz? The 2251J goes well over 4kHz and actually gets louder in this range so the 2,150 Hz crossover is no problem, and this is actually where the volume would normally be increasing. Still, there are those that would say that this is too high a frequency for a ~10" speaker based on the wavelength.

I subscribe to the theory that I always sit in the sweet spot and that crossing over @>2kHz keeps all of the fundementals in the 2251J adding a sense of coherency, soundstage, and imaging.

I like the 2241H for the bass because the accordion edge and relatively light cone give the woofer "speed" thereby letting the texture of bass instruments come through. The 2241H is actually rated from 30 Hz - 3kHz and I cross it over at 300 Hz. I run these as 2.5 ways and let the 2251 naturally roll off on the low end. I don't put the 2251 through a cap.

If you want to do this passively, this schematic will get you there. BTW, I typically run the L-pads at their max settings for the flattest response unless the music has lots of HF noise in which case I may turn down the Heil a bit.








This shows the nearfield spectrum for the 2251J. The dip at ~800 Hz is from a cabinet resonance/reflection, and I think a bit more insulation will take it out. It was much worse, with a subsequent peak, before I insulated the interior back of the cabinet, and I will try to do the sides in the near future to remove the remainder.

Typical 30 dB span:

Thank you for showing me all of your work so far. Saves me a good deal of time. I’ve collected together my drivers. I have the 2242Hs (curious how they’d compare to your 2241s) and I’m really wanting to try the 251Js, I have all 6 on hand, I’m really hoping to use 2 per speaker. I’ll have to measure them, but it’s nice to see that the specs were posted. They seem to be a very nice driver. I should be able to cross them lower to the 2242 and they should hopefully still play cleanly up high.

Only reason I suggested the 1000hz crossover point to the Heil was because that is the crossover point it’s used in the AMT-1B. I’m not sure if the 251J could go to 2250hz. Really dig your setup!

Dan