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For various reasons, I settled on the following for my latest OB experiment:One Alpha 15AOne Dayton AMTPRO-4Baffles are ~ 20" wide, 42 inches tall. They are tapered so they are ~12 inches wide at the top of the panel.Currently using a simple coil/cap arrangement with the drivers rolling in/out around 4-5 KHz. With this arrangement, I guess I just got lucky with the efficiency/xover points/slopes and the drivers match well with no need for padding down the AMT. I can post pix if anyone is interested but so far, I am very impressed with how good these sound. I am still using a sealed ML sub for < 50 Hz. Setting up a local listening panel soon to A/B these with Maggies, Logans, and a few other single driver setups. You really need to discount the pride factor when you build your own. But right now I would say that these are Maggie killers. All of the open and boxless sound of Maggies with much more bass, efficiency, depth, dynamics, and better and more extended highs.I have also been trying to determine if the AMTPRO driver is as good as the great Heil AMT. I'm still not sure, but it is close.
Guy,Thanks for the question. I used to use either a modified Bottlehead Stereomour 2A3 amp (3.5 watts) or modified Bottlehead Paramount 300B mono blocks (8 watts) when I had it "not" MTM (just MT) but after making the move to MTM, I find I have a difficult load...the efficiency is still nearly 100 dB but the load is complex. So I have Quicksilver Silver 88 mono blocks and a Pass Labs XA-30.5 amp. Both are excellent but I find the Pass Labs XA-30.5 is in the rig nearly all the time these days. John
By far the perceptually most uniform response in the range below 200 Hz is obtained with an open-baffle, dipole or figure-of-eight radiating source. Because of its directionality, the dipole excites far fewer room resonances than an omni-directional source. The measured room response is not necessarily any smoother than that for an omni-directional source. But the perceived difference in bass reproduction is startling at first, because we are so used to hearing the irregular and booming bass of the typical box speaker in acoustically small rooms. Quickly one learns to recognize the distortion of this combination and it becomes intolerable.
Thanks for the info. The Hawthorne thread is interesting with an Alpha 15 crossed to the AMT at 5K. I already own a pair of AMTs and a pair of Ed's horns. Its a great match but I miss the OB sound of my old Emerald Physics clones. Those had an OB pair of Alphas with a compression driver crossed at 1K. I have heard the Alpha's crossed at 1 K and never had a problem with them. My current AMT/horns use Ed's series xover and are roughly crossed around 1K too. I'm very tempted to just try 2 15-inch Alphas on a simple OB and electronically crossed to the AMT around 1 K. I don't think you get the magic of the AMT if crossed at 5KHz. Very helpful responses.
After researching and working on a set of OB speakers myself, I would say that your set up would work nicely. I am using a ribbon tweeter (G1 Aurum Cantus) crossed at 2000hz, with a 10" Morel woofer. Those Morels (made in Israel.) are the same model that www.pureaudioproject.com uses, and they are hard working and very nice. I use one amp for the G1/Morel and I have another amp driving an Eminence Delta 15FLA woofer to support the low end. (The 15FLA has a low pass filter of 180hz.) My system isn't exactly like yours, but you get the idea. I experimented with a x-over at 1600hz, because the Morel has a bit of a spike at that frequency, but it just worked/sounded better at 2khz. Both drivers, G1/Morel have very accurate specs available, unlike some manufacturers. Did you end up trying two woofers or did you stay with one ?V....
