Eminent Technology 8b Speakers - Amp/wattage Recommendations

VERY interesting. Thanks @jwr159.

I don’t yet know anything about the new ET woofer system for the LFT-8, but unless it’s a dipole design I can’t see how it will be as good a mate as is any dipole sub (including the Rythmik Audio/GR research OB).

Magnepan is working on a "concept" model which will include dynamic (cone) woofers of OB/dipole design to augment their well-known magnetic-planar midrange/ribbon tweeter panels. Their MG30.7 model uses very large panels to reproduce bass frequencies, those panels sharing with OB/Dipole subs the same acoustic properties.

I own a pair of the Magneplanar Tympani T-IVa loudspeakers, which is basically a 30-year old version of the MG30.7. The Rythmik Audio/GR Research OB/Dipole Sub comes closest to equaling the outstanding sound of the T-IVa bass panels as I have yet to hear. Remember when Harry Pearson created his own "Super Speaker" by using the Tympani bass panels with the midrange/tweeter panels of Infinity?

OB/dipole woofers share with dipole planar loudspeakers the same drop off in SPL output as speaker-to-listening position distance changes. Omnipole subs (sealed and ported boxes) do NOT, so the sub/speaker balance is "correct" at only one speaker-to-listening position distance. That is imo a major flaw, one inherent in the mating of dipole loudspeakers with omnipole subs. Dipole subs also load the room the same way dipole loudspeakers do, very differently than boxed loudspeakers and subs. Mating omnipole subs with dipole loudspeakers is doomed to failure: it can’t be done, at least not to perfectionist standards.

There is a new listing on USAM for a Music Reference RM-200 MK.2, asking price $3,000. The amp has been Michael Fremer's "reasonably-priced" reference tube amp for about 20 years. Roger Modjeski's engineering brilliance allowed him to produce 100 watts out of a pair of KT88 tubes, and without sacrificing tube life. The amp has Classic written all over it. 

@jrw159: One thing to know about open baffle woofers is that because of their inherent dipole cancellation characteristic (the front and rear waves meeting on either side of the open baffle frame, the opposite polarity waves causing a drop off in the very low frequencies), a dipole cancellation compensation network is necessary. Brian Ding installs just such a circuit into the A370 plate amp that is included in the Rythmik Audio OB/Dipole Subwoofer kit.

@jwr159: I’ve been away from home for a coupla weeks, and have been playing catch-up, just now seeing your thread. First, congratulations on your new speakers! And on your good taste ;-) . The ET LFT-8b is an outrageous bargain, imo one of the best in all of current hi-fi. Why most audiophiles continue to ignore it is a complete mystery.

Here are some facts that may help with your amp considerations:

- The 8b run full range is a pretty even 8 ohm load. However, the magnetic-planar panel itself---when used in a bi-amp manner---presents the amplifier with an almost purely resistive 11 ohm load, great for tube amps. Whereas Magneplanars (a pair of which in addition to the 8b I also own) present the amp with a 3-4 ohm load and therefore benefit from a solid state amp, the ET loves tubes. I’ll bet the Atma-Sphere M60 would sound great with the 8b (I sold mine before I got the ET’s), and I can also recommend both the Music Reference 100 watts amps: the RM-200 Mk.2 (which uses a pair of KT-88’s per channel, a real engineering feat to create 100 watts!) and the RM-9 Mk.2 (a quartet of EL34’s per channel). You can then use a solid state amp to drive the sealed woofer. As you must know by now (but some posters on this thread may not), the magnetic-planar panels and the dynamic woofer each have their own bindings posts, simplifying bi-amping.

- If you are going to not only bi-amp, but use your own subs in place of the 8b’s woofer (in pojnt number 3 in your above post you refer to "my subs") , know that the crossover between the woofer and the m-p drivers is at 180Hz, a simple 1st-order (6dB/octave) symmetrical filter. Very few subwoofers will play up to 180Hz (and above: remember, the x/o is 1st order), so don’t expect to be able to use any ol’ sub. Bruce Thigpen worked very hard to come up with a woofer that blends well with his LFT driver. As with all dipole loudspeakers, the ultimate woofer to use with the 8b is an open baffle design (why that is so requires more explanation than may be appropriate in this thread). If employing outboard woofers, you may simply leave the binding posts on the 8b woofer enclosure disconnected.