Hey soundnovice,
When I was at stock builds of V1.2 and V 1.3 I started a project with some BPA-150s for the bottom of a bi-amped system. I still think it's a productive approach if one is using 4 ohm woofers, but I found the actual SPL to be about the same as the MyRef. One of the veteran MR builders, Tom E, has been perfecting a bi-amp - active crossover system for several months. You might get some good info with a PM and a search of his posts.
It should be noted that the addition of the Mundorf AG caps at C3 and C8, plus a larger transformer has given me all the deep, controlled and musical bottom end I can handle. With that combination the MyRefs do everything from shaking the house with pipe organ pedal notes to finely played bass lines in a jazz trio. The beauty of the MyRef approach, it's best feature is just letting what's being fed come through over the entire spectrum.
When I was at stock builds of V1.2 and V 1.3 I started a project with some BPA-150s for the bottom of a bi-amped system. I still think it's a productive approach if one is using 4 ohm woofers, but I found the actual SPL to be about the same as the MyRef. One of the veteran MR builders, Tom E, has been perfecting a bi-amp - active crossover system for several months. You might get some good info with a PM and a search of his posts.
It should be noted that the addition of the Mundorf AG caps at C3 and C8, plus a larger transformer has given me all the deep, controlled and musical bottom end I can handle. With that combination the MyRefs do everything from shaking the house with pipe organ pedal notes to finely played bass lines in a jazz trio. The beauty of the MyRef approach, it's best feature is just letting what's being fed come through over the entire spectrum.
It depends on how much voltage it will take to drive the woofer to max travel. You don't want the amp to max out before the driver. If you have an abundance of low frequency in music content, the summation can get pretty high.
The required drive voltage to the speaker is determined by the SPL and the speaker sensitivity.
Bigger speakers tend to have higher sensitivity (more SPL for the same drive voltage).
A driver that is big relative to the other drivers in the speaker is likely to require less drive voltage than the other drivers, not more !!!!!!
By way of example:
a normal 8ohm 2way speaker with 6.5" & 1" drive units that are both 88dB/W @ 1m when assembled into a passive cross-overed speaker may result in a speaker that is 87dB/W @ 1m.
If you replace the 6.5" driver with a 12" driver with a sensitivity of 88dB/W @ 1m then the drive voltage requirement has not changed and with a bit of correction to the passive crossover will reproduce the same SPL as the unmodified speaker.
However, if you chose a higher sensitivity 12" (or bigger) driver, maybe 92dB/W @ 1m then the new speaker will have a bass/mid response that is around 4dB higher than the treble. The speaker will sound as though it had very much reduced treble output.
The way to solve this is to send a lower drive voltage to the high sensitivity Bass/Mid driver.
Soongsc, this is the complete opposite to what your post implied.
Bigger speakers tend to have higher sensitivity (more SPL for the same drive voltage).
A driver that is big relative to the other drivers in the speaker is likely to require less drive voltage than the other drivers, not more !!!!!!
By way of example:
a normal 8ohm 2way speaker with 6.5" & 1" drive units that are both 88dB/W @ 1m when assembled into a passive cross-overed speaker may result in a speaker that is 87dB/W @ 1m.
If you replace the 6.5" driver with a 12" driver with a sensitivity of 88dB/W @ 1m then the drive voltage requirement has not changed and with a bit of correction to the passive crossover will reproduce the same SPL as the unmodified speaker.
However, if you chose a higher sensitivity 12" (or bigger) driver, maybe 92dB/W @ 1m then the new speaker will have a bass/mid response that is around 4dB higher than the treble. The speaker will sound as though it had very much reduced treble output.
The way to solve this is to send a lower drive voltage to the high sensitivity Bass/Mid driver.
Soongsc, this is the complete opposite to what your post implied.
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Not bad speed for quick head calcs, 
Those big numbers help keep the world economy running.
I guess all things are relative - Check out the middle of this page Teflon Film and Tin Foil audio capacitors by V-Cap
BTW, I got mine from Parts Conexxion in Canada.
Those big numbers help keep the world economy running. I guess all things are relative - Check out the middle of this page Teflon Film and Tin Foil audio capacitors by V-Cap
BTW, I got mine from Parts Conexxion in Canada.
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Having a higher sensitivity does not mean it has lots of headroom. Normally you also have to look at the BL curve. But you may be correct. There are drivers out there that max out at very low voltages even though they are large and sensitive drivers. In this case it makes no sense to have higher driving voltage or wattage amplifier. But the drivers I look at generally have increased maximum driving voltage capability with size. For drivers of the same size, higher sensitivity generally do have lower Xmax, in this case you need less driving voltage for it to reach max excursion. So I think we are looking at the issue from different points of views. I tend to look for drivers of similar sensitivity and a wider range of excursion. Maybe the Fostex drivers mentioned have higher sensitivity than I am used to. Selection of drivers is a more complicated process, not only simple sensitivity numbers. The maximum sound pressure level you wish for the target bandwidth is just as important. If you have an amplifier that is clipping before the driver maximum capability is reached, you are wasting the driver; if you have the driver maxing out before the amplifier limit is reached, you are wasting power capability.
Good luck with whatever you like to choose.
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i think 60w is enough to drive 8" to 12" woofers with sensitivity >=90dB (the woofers i have in my mind are all having more than 90dB sensitivity and are rated at 8 ohms). if not LM3886's in bridge mode can be used. the real question is 'is it worth to spend more on driving woofers using MyRef amps? as these woofers will only cover upto 250hz (max). or even less. in my case if FE126En(in bk-12m back loaded horn) are capable of reaching below 150hz, then i will cross the woofers at 150hz only. so considering the small freq.range that woofers will be operating on, will it make sense to use just normal LM3886 amps for woofers and MyRef amps for fullrangers?
(i am speaking this with the knowledge that significant music information lies between 300hz to 3000hz)
(i am speaking this with the knowledge that significant music information lies between 300hz to 3000hz)
Here is some damping characteristic measurement comparison. Green is a MyRef, Red is a 120W commercial amplifier. Both measurements had the same driver as a load.
Wattage is not everything. The MyRef has better bass than the 120W amp, and sounds MUCH better.
An externally hosted image should be here but it was not working when we last tested it.
Wattage is not everything. The MyRef has better bass than the 120W amp, and sounds MUCH better.
To give you an idea of what a MyRef can easily handle, these are the speakers I'm using.
https://sites.google.com/site/undefinition/diy-sunflowers
There is some good driver information on the page and at the corresponding links at Parts Express. My listening room is ~ 12X17 and just the MyRefs give all the full spectrum SPL for 90% of the music I play. I did asked Paul the designer, if he considered a 10 or 12 inch version. He said from what he hears and the response he gets from builder - there is no need for that at normal listening levels, though it would be fun. (BTW, he is just starting a new full range driver cabinet design)
I am in no way trying to discourage anyone from the adventure of bi-amping. Just want to offer some insight on some sort of baseline.
https://sites.google.com/site/undefinition/diy-sunflowers
There is some good driver information on the page and at the corresponding links at Parts Express. My listening room is ~ 12X17 and just the MyRefs give all the full spectrum SPL for 90% of the music I play. I did asked Paul the designer, if he considered a 10 or 12 inch version. He said from what he hears and the response he gets from builder - there is no need for that at normal listening levels, though it would be fun. (BTW, he is just starting a new full range driver cabinet design)
I am in no way trying to discourage anyone from the adventure of bi-amping. Just want to offer some insight on some sort of baseline.
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More difficult to get than I had thought. Look here:http://www.diyaudio.com/forums/chip...on-beta-build-fine-tuning-69.html#post3044116
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