Wow, monitors for a Baldwin church organ are a tall order! Does your organ already have built-in speakers and an amplifier to drive them?
I'd forget Martin Logan speakers. In the price range you have mentioned ~$1500 per pair, ML speakers are only OK. You'd have to go much higher, to roughly $10,000 per pair to get really good MLs
. I am assuming that as a musician, you are interested in good sound and accurate frequency response across the entire music range, not just in the bass frequencies.
To get speakers that perform well in the octave below 50 Hz, you will probably need floor standing speakers. You can get very good floor standers for under roughly $3,000 a pair that deliver an honest 33 Hz at loud levels, but as you get down to 25 or 20 Hz, it will cost a lot more money. Speakers that produce sound below that are probably best used for movie sound effects, and not music.
For example,
Salk Song3 speakers, a 3-way floor stander sells for $3,000 per pair. They can produce sound with a flat frequency response (±3 dB) as low as 33 Hz to 40,000 Hz (well beyond what is audible). You can see the dimensions and weight on the web link. To get down to an honest 25 Hz, there is the Philharmonic 3, selling for $3,500-3,700 per pair (depending on cabinet & finish). At even higher prices is the
Song3 Encore, a beefed up version of the Song3, with a larger and more potent woofer and more robust mid range and tweeter, selling for $5,900 per pair. You can see where this is going.
The only bookshelf speaker I can think of that might do the job for you is the
BMR Philharmonitor. It claims it goes down to 30 Hz, and sells for as low as $1,350 per pair (depending on cabinet and finish).
All four of these speakers are designed by a concert musician, Dennis Murphy (violin, viola, piano), who also knows a thing or two about building speakers. You should definitely
contact him by email to get his thoughts on using any of these speakers as organ monitors. All these speakers were meant for listening to recorded music, not as musical instrument monitors. Also be sure to ask him about speakers with
transmission line cabinets, as this is important for good bass response.
You may have noticed how I repeatedly used the word
honest to describe low bass response in speakers. Many of the most widely marketed commercial loudspeakers report exaggerated low bass frequency response as well as exaggerated overall loudness levels (speaker sensitivity) because they know many buyers are swayed by such numbers. The Philharmonic Audio and Salk speakers are known for honest, even conservative ratings.
You should also be aware that both makers sell by Internet Direct sales only. There are no distributors, retail stores, or other middle men that elevate the price.
There are other good speakers available, but I am most familiar with these.
All these speakers require a good amplifier, capable of delivering at least 50-100 watts per channel. Wait on choosing an amp until you know what speakers you are getting.