Jim's post seems to have garnered scant attention, but is exactly on track.
Second point is that some folks just don't like the sound of the Alpha. I've not heard them, but know a few very good speaker builders who have used them and not liked them. A matter of taste, perhaps. Some folks love them.
Bada-Bing! OB crossovers are counter intuitive to those of us used to box crossovers. You have to fight the rising response that a woofer will have on an open baffle. That often means a much lower electrical crossover point than the acoustical point. Most OB builders simply don't understand this.
Second point is that some folks just don't like the sound of the Alpha. I've not heard them, but know a few very good speaker builders who have used them and not liked them. A matter of taste, perhaps. Some folks love them.
A bit OT but Pano was it you that went to an audio show with a set of OB's using 4 18'' Goldwoods and an Altec 604 per side, and some there thought it was the best bass they had ever heard etc? I remember reading that somewhere and it helped me to reassure what I was already hearing with my H-Frame GW's via MJK's spec, but crossed at aprrox 70hz etc..
Cheers
Cheers
>>> You have to fight the rising response that a woofer will have on an open baffle. That often means a much lower electrical crossover point than the acoustical point. Most OB builders simply don't understand this.
The dial on my plate amp indicates around 80hz crossover when the Alpha's sound their best in my room. My Beta 12lta begin rolling off at around 200hz. You gotta use your ears when designing these things.
The dial on my plate amp indicates around 80hz crossover when the Alpha's sound their best in my room. My Beta 12lta begin rolling off at around 200hz. You gotta use your ears when designing these things.
Including me. Can someone explain this electrical/mechanical thing? I have crossed the alphas at 500hz and the 207s at 250hz and it's not sounding bad at all. If I bring xo down on the alphas I don't get enough detail. If I move 207's up to not overlap alphas they sound too thin. Does this sound technically wrong? (not that it matters much) Whats up with Neodymium magnets? as apposed to ferrites? The Deltalite has a puny 7oz mag, and the Beta 15a has a 34oz magnet I would have thought the 34oz would be the way to go. Anyone heard of Technical Pro zxp-15? That has a 200oz magnet but I can't find any TS info on it.
If your woofer has a rising response from LF to, say, 200Hz, you could set a plate amp's crossover to 70Hz, which would counteract the rising response (giving a ~flat response) to 200Hz. At which point, the woofer itself becomes more or less flat, but the crossover is still being applied by the amplifier, so it will roll off (acoustically - what actually comes out) at 200Hz, but electrically (what's being fed into the speaker), the crossover will be 70Hz.
Nd magnets are by far more powerful (mass for mass) than ferrite, allowing the use of tiny magnets, thus saving a shed load of weight - important for travelling musicians, etc.
Chris
Nd magnets are by far more powerful (mass for mass) than ferrite, allowing the use of tiny magnets, thus saving a shed load of weight - important for travelling musicians, etc.
Chris
The Alphas are slow. In my experience, if you cross them any higher than 120-150 Hz, it sounds really sluggish. Your crossover also seems to be off. As the others have explained, to get proper overlap on an OB, the alphas need to be crossed somewhat lower than where the full range starts to roll off. So, if your 207s are rolling off at 250 Hz, the alphas could be crossed at 100 Hz. The exact frequency and slope will depend on your baffle size and driver locations on the baffle.
Use EDGE, the baffle diffraction simulator to visualize what your baffle is doing to the response. An even better way to design the crossover is to actually measure the response.
Use EDGE, the baffle diffraction simulator to visualize what your baffle is doing to the response. An even better way to design the crossover is to actually measure the response.
Fast means low distortion, low distortion means high BL high xmax high quality driver in an appropriate box with a high power amplifer. I use 400Wrms just for the midrange drivers in my current project. I say for what your using with what I'm guessing is high effciency drivers 250Wrms per driver is a must.
Ha! No, not me - but I was there. That was my buddy John who taught me most of what I know about OB. For the record that was 2x18" GW per side with a 10" mid + tweeter. The year before he had the Altec 604 with an 18" Eminence woofer. John knows how to do OB right, that's for sure.
4 15 inchers sound slow, as they should
Guys,
as a proponent of OB speakers I do have a little insight.
Firstly, the amount of power required to move a single 15" driver is substantial. Something on the order of at least 10:1 compared to a mid-bass driver. Dave likes a bigger ratio, but I have used single 12" fullrangers with a 1" soft dome tweeter passively crossed. 10 Watts/channel is loud enough (in a 13' X 8' X 25') to force me out of the room. I think the choice of drivers is critical. The mass and impedance must be considered, as well as anty baffle losses, etc. More drivers are just more drivers, not better.
In my mind, the simpler the better. If driving higher Qts drivers, that are relatively heavy, I agree with all the comments regarding large power amps. However that should be qualified: The amps should also be high damping (100+) per channel, and proper amps used per driver.
That's the crux. The cost of good quality appropriate amplifiers and electronic cross-overs can be a little high. And good fullrangers can cost as well. These are not really budget builds at all (I never said OBs were cheap, and I don't think anyone here has suggested that either).
I do like the idea of smaller fullrangers (10" or 8") as they seem more responsive (or "faster").
Guys,
as a proponent of OB speakers I do have a little insight.
Firstly, the amount of power required to move a single 15" driver is substantial. Something on the order of at least 10:1 compared to a mid-bass driver. Dave likes a bigger ratio, but I have used single 12" fullrangers with a 1" soft dome tweeter passively crossed. 10 Watts/channel is loud enough (in a 13' X 8' X 25') to force me out of the room. I think the choice of drivers is critical. The mass and impedance must be considered, as well as anty baffle losses, etc. More drivers are just more drivers, not better.
In my mind, the simpler the better. If driving higher Qts drivers, that are relatively heavy, I agree with all the comments regarding large power amps. However that should be qualified: The amps should also be high damping (100+) per channel, and proper amps used per driver.
That's the crux. The cost of good quality appropriate amplifiers and electronic cross-overs can be a little high. And good fullrangers can cost as well. These are not really budget builds at all (I never said OBs were cheap, and I don't think anyone here has suggested that either).
I do like the idea of smaller fullrangers (10" or 8") as they seem more responsive (or "faster").
hmm, I would rather call it definition, or lack of
lack of integration appears to cause 'too fast' as well as 'to slow' bass
music sounds stressed
and you could even get stressed by just listening
proper integration through crossover appears to result in deeper bass, as a result of better definition
and its quite easy to hear when this happens
and you get very relaxed when listening to music, as a direct result
but I think that multiple woofers will always make it more difficult
I see it more like a 'brute force' approach
lack of integration appears to cause 'too fast' as well as 'to slow' bass
music sounds stressed
and you could even get stressed by just listening
proper integration through crossover appears to result in deeper bass, as a result of better definition
and its quite easy to hear when this happens
and you get very relaxed when listening to music, as a direct result
but I think that multiple woofers will always make it more difficult
I see it more like a 'brute force' approach
Hi, could you expand a little?
I don't see how one can draw such a conclusion, when surely moving a diaphram of any diamater any distance is rather dependent on the compliance of the suspension.
Perhaps I haven't understood.
Nelson Pass has posted on his preference for the Beta15's in OB's
"IMHO the Betas sounded better, specifically tighter and a little more punchy. They also have more bass down around 30 Hz. The Alphas had more mid bass by virtue of their higher
Qts, and it could simply be a matter of taste." from this thread http://www.diyaudio.com/forums/full-range/176792-ob-lowther-pm6a-2.html#post2361790
I know its a pain but you may find more joy selling/swapping your Alpha's for single pair of Beta15's. I know its a different kettle of fish but I used mine in a sealed box
and they were tight as a drum - real snappy bass letting you hear the twang of double bass strings and the strike of large drums as well as the resulting bass note
"IMHO the Betas sounded better, specifically tighter and a little more punchy. They also have more bass down around 30 Hz. The Alphas had more mid bass by virtue of their higher
Qts, and it could simply be a matter of taste." from this thread http://www.diyaudio.com/forums/full-range/176792-ob-lowther-pm6a-2.html#post2361790
I know its a pain but you may find more joy selling/swapping your Alpha's for single pair of Beta15's. I know its a different kettle of fish but I used mine in a sealed box
and they were tight as a drum - real snappy bass letting you hear the twang of double bass strings and the strike of large drums as well as the resulting bass note
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