Finally tried the 25ohm resistor trick that Mr. Pass has mentioned before. The results with my phase plugged B20s on small OBs was noticeable but not dramatic. I was able to reduce my EQ significantly up top and slightly on the bottom and was able to get about 2Hz greater extension on the bottom. However, after extended listening, I determined they just weren't as pleasant sounding, maybe slightly gritty or veiled.
I was just using standard Dayton 25ohm resistors. What that not adequate, or are these results typical and explain why I haven't heard anyone else talking about doing this?
Kensai
I was just using standard Dayton 25ohm resistors. What that not adequate, or are these results typical and explain why I haven't heard anyone else talking about doing this?
Kensai
Jack from NHT was also nice enough to run an impedance plot of the B20FU driver. It is attached below.
He also ran an impedance plot of the Aiwa tweeters Nelson Pass was giving away, unfortunately I do not have a printout but they were smooth above 5-6k with a slight ripple around 3-4k. The ripple is apparently due to the damping of the ferofluid. Jack was impressed with how clean they were in the high end and recommended using them about 6k.
I also asked Nelson for his recommended tweeter setup with the Aiwas, he said to put two tweeters in parallel to match efficiency with the B20FU and to place a 1-2 uFd capacitor on the tweeters. And of course I can't find a link to the capacitor table at the moment, so I can't post what frequencies these values correlate to.
- Matt
He also ran an impedance plot of the Aiwa tweeters Nelson Pass was giving away, unfortunately I do not have a printout but they were smooth above 5-6k with a slight ripple around 3-4k. The ripple is apparently due to the damping of the ferofluid. Jack was impressed with how clean they were in the high end and recommended using them about 6k.
I also asked Nelson for his recommended tweeter setup with the Aiwas, he said to put two tweeters in parallel to match efficiency with the B20FU and to place a 1-2 uFd capacitor on the tweeters. And of course I can't find a link to the capacitor table at the moment, so I can't post what frequencies these values correlate to.
- Matt
Attachments
Ouch. 15wpc & that amount of series resistance doth not a good combination make. Your description of the sonics (gritty, veiled etc) tallies with the amp, particularly its power-supply, waving a white flag. It's probably crippling the dynamics too. Nelson suggests at least 100wpc for attempting this (see p.23 of his article 'Current Source Amplifiers and FR Drivers') with a voltage source & the B20.
Scottmoose said:
Yeah, haven't done the math in awhile, but seems like at least 400 W/ 8 ohms is required to make the B20 'sing' good enough in ~ quasi-current mode with wide dynamic range signals. For highly compressed R&R, etc., ~100 W should be fine. Back when I was running ~112 dB eff. mid-bass horns I was occasionally clipping a MC2300 (http://www.roger-russell.com/amplif2.htm#mc2300) on symphony transients, so when folks mention how 'dynamic' their system is with low power 'anything' I just have to shake my head in dismay.
That said, at some point the audible difference between truly dynamic (~'live') and perceived as dynamic is extremely subtle, with only a bit more 'space' between instruments and top end 'air' if the system goes up high enough ~flat (few do), so spending significantly more $$$ for components and/or increased listening room space just for that last few % is fine for those that can afford it, but not worth sacrificing for IMO.
GM
I keep wondering if the high power needed is related to class-AB amps and how they operate when a sudden requirement for high current is needed.
It seems like a smaller class-A amp would work great, especially since the B20 speaker is so efficient. Wouldn't a 15watt Aleph work great?
From my personal experience, I'm amazed how much less power is needed for a class-A amp over AB for a given application.
-David
It seems like a smaller class-A amp would work great, especially since the B20 speaker is so efficient. Wouldn't a 15watt Aleph work great?
From my personal experience, I'm amazed how much less power is needed for a class-A amp over AB for a given application.
-David
Maybe a bit less, but not that kind of less. 
I was discussing this elsewhere on the Thor thread. A pair of the Small Thor MLTLs were at the recent Burning Amp fest & powered by the 30wpc Aleph at moderate levels the amp was struggling, especially on LF transients. At home, with 250wpc, narry a problem. The Thors aren't the most efficient speaker on the planet, but a whole lot more than a B20 with 25ohms in series.
I was discussing this elsewhere on the Thor thread. A pair of the Small Thor MLTLs were at the recent Burning Amp fest & powered by the 30wpc Aleph at moderate levels the amp was struggling, especially on LF transients. At home, with 250wpc, narry a problem. The Thors aren't the most efficient speaker on the planet, but a whole lot more than a B20 with 25ohms in series.
GM said:
Crickey, Greg! What were you trying to light up, the entire county?
I've run a system with 115dB mid bass horns on a 50W tube amp and never come close to clipping. But that was in a "reasonably sized" room. About 520 cubic meters, or 18,300 feet ^3.
Hmmmm.... It' s an interesting question, actually. See if this makes sense.
If your McIntosh amp was true to spec, you were clipping the peaks at about 70 volts.
To reach the same SPL my 115dB horns would need 1/2 the power, or about 50 volts.
But my 50 WPC tube amp could supply only about 28V peak. So I could never get close to the same SPL.
Yep, you were playing it mighty loud! (or you were outside)
Well, an amp change, especially to a beast of any sort, isn't exactly in the cards, at least for the time being. The resistors didn't even last a day in the system, but since I needed to order some parts from PE anyway, I figured an extra couple of bucks to try it out for myself was fine. The JVC really does sound good, you know, relative to what I've used previously (original T-Amp, Pioneer VSX-D411 receiver, Sanyo shelf system core).
Oh well, not much time to worry or bother right now . . . National Novel Writing Month starts Thursday, so its just gonna be me and the B20s, as is, for the next 50,000 words or so
Kensai
P.S. Been working with a pair of Pioneer A11 fullrangers (4.5") as a project for a friend. Got one in a variant of a floor loaded BiB so far, and while its bass performance is obviously better than the B20 on small OB (12"x18", hinge mounted to the open framework of my desk), even when EQed, it doesn't quite have the top range extension (only 14khz or so, to my ears, as opposed to the 16khz the B20s get, same method), though it seem like it has more treble. That must be the "shout" that folks using small Fostexes talk about (hot upper mids and lower treble, I'm guessing). Listening to the one BiB and the other A11 just propped up on desk at a similar level, I seem to be getting some pretty impressive sound staging (is that because the BiB's baffle is only about 7.25" wide?). I'm finding that I can easily hear the more "boxy" nature of the sound and that I can easily hear that the bass is coming from the bottom rear of the cabinet. Would a standard up firing BiB help with that? Not that I'm changing the project at this point. My buddy isn't very discerning. He'll think these are the greatest things he's ever heard.
Anyway, I'm finding that I may not ever be able to go back to a box, at all, and that I'm much more satisfied by the sound of the B20 (albeit phase plugged thanks to P10) than by its smaller cousin in a big cabinet. Now I just need to get a bit of bass reinforcement in here so I can dump the EQ . . .
Oh well, not much time to worry or bother right now . . . National Novel Writing Month starts Thursday, so its just gonna be me and the B20s, as is, for the next 50,000 words or so
Kensai
P.S. Been working with a pair of Pioneer A11 fullrangers (4.5") as a project for a friend. Got one in a variant of a floor loaded BiB so far, and while its bass performance is obviously better than the B20 on small OB (12"x18", hinge mounted to the open framework of my desk), even when EQed, it doesn't quite have the top range extension (only 14khz or so, to my ears, as opposed to the 16khz the B20s get, same method), though it seem like it has more treble. That must be the "shout" that folks using small Fostexes talk about (hot upper mids and lower treble, I'm guessing). Listening to the one BiB and the other A11 just propped up on desk at a similar level, I seem to be getting some pretty impressive sound staging (is that because the BiB's baffle is only about 7.25" wide?). I'm finding that I can easily hear the more "boxy" nature of the sound and that I can easily hear that the bass is coming from the bottom rear of the cabinet. Would a standard up firing BiB help with that? Not that I'm changing the project at this point. My buddy isn't very discerning. He'll think these are the greatest things he's ever heard.
Anyway, I'm finding that I may not ever be able to go back to a box, at all, and that I'm much more satisfied by the sound of the B20 (albeit phase plugged thanks to P10) than by its smaller cousin in a big cabinet. Now I just need to get a bit of bass reinforcement in here so I can dump the EQ . . .
Well, I have no skills or tools (not to mention time or money right at the moment), so it would have to be ridiculously simple. Got a link to a good place to start.
And not meaning to hijack the thread . . . I've got a note to folks who say that the B20 isn't the last word in resolution (including myself). I've got over 8000 tracks in my library which I have ripped losslessly to my harddrive, so I don't hear most of them very often . . . I had a couple tracks that I didn't even remember I owned come up on random last night, and I was hearing all sorts of things in the background that I wasn't aware were there. That's of course, coming from having last heard those tracks on lesser equipment, but I feel that the B20s are more than just "listenable at the least cost".
Kensai
And not meaning to hijack the thread . . . I've got a note to folks who say that the B20 isn't the last word in resolution (including myself). I've got over 8000 tracks in my library which I have ripped losslessly to my harddrive, so I don't hear most of them very often . . . I had a couple tracks that I didn't even remember I owned come up on random last night, and I was hearing all sorts of things in the background that I wasn't aware were there. That's of course, coming from having last heard those tracks on lesser equipment, but I feel that the B20s are more than just "listenable at the least cost".
Kensai
panomaniac said:
Crickey, Greg! What were you trying to light up, the entire county?
If your McIntosh amp was true to spec, you were clipping the peaks at about 70 volts.
To reach the same SPL my 115dB horns would need 1/2 the power, or about 50 volts.
But my 50 WPC tube amp could supply only about 28V peak. So I could never get close to the same SPL.
Yep, you were playing it mighty loud! (or you were outside)
Greets!
No, not really, just ~live, front row center, my preferred virtual listening spot in-room. The Mac has a high output impedance and combined with the speaker's passive components the speakers had no where near 300 W worth of voltage gain plus clipping occurred only when playing minimally compressed music.
Hmm, how did you arrive at the 70 and 50 V values? I get ~49 V and ~34.6 V. Anyway, the point was that it takes a lot of power even with an HE system to ensure no clipping of the amp on wide dynamic range music. For comparison, loud, highly compressed pop/rock music through this system only needed ~9 W for 'Headbanger Ball' SPL levels at neighborhood outdoor 'block' parties, so for a typical 90 dB efficient system this equates to ~1587 W, well beyond its power handling capability.
GM
GM said:
Peak values, since you said you were clipping. I assumed the amp to be rated for RMS power. 69-70 volts should be the peak voltage of an amp that can do 300W RMS into 8 ohms. It may be able to do higher peaks on music. A full power sine wave puts a mighty heavy load on a power supply.
So same numbers - I'm just using peak values where the clipping is likely to be.
I do agree it can take a whopping amount of power (voltage) to get clean peaks on classical stuff. The average level is often mastered 20 or 22 dB down from full scale (0dBFS.)
How loud do you think the peaks were a your listening postion? Must have been pretty hot. And what do you think you average spl was?
One word... wow!
Thanks to the generosity of Nelson Pass a pair of BOFUs followed me home from burningamp. Tonight I got around to hooking them up for an initial listen. I have them setup in my top secret UMOBD (ultra-minimalist open baffle dipole) enclosures, which are so minimal that they almost look like the drivers are just sitting on the floor.
I've played Jazz at the Pawnshop and an L.A. 4 album through them so far, and I'm very surprised and pleased with the sound they are putting out. There is very little bass because of limitations with the UMOBD enclosure design, such as the fact that the rear wave can immediately cancel out the front wave, but the there is something a bit magical happening in the midrange. The sax, guitar, and tom-toms on the L.A. 4 album are sounding particularly great.
The big question in my mind is what enclosure to put these in. I'm considering the BIB, a Chang variant, or possibly an open baffle design. Right now the UMOBD enclosures are making a solid argument for some sort of open baffle.
- Matt
Thanks to the generosity of Nelson Pass a pair of BOFUs followed me home from burningamp. Tonight I got around to hooking them up for an initial listen. I have them setup in my top secret UMOBD (ultra-minimalist open baffle dipole) enclosures, which are so minimal that they almost look like the drivers are just sitting on the floor.
I've played Jazz at the Pawnshop and an L.A. 4 album through them so far, and I'm very surprised and pleased with the sound they are putting out. There is very little bass because of limitations with the UMOBD enclosure design, such as the fact that the rear wave can immediately cancel out the front wave, but the there is something a bit magical happening in the midrange. The sax, guitar, and tom-toms on the L.A. 4 album are sounding particularly great.
The big question in my mind is what enclosure to put these in. I'm considering the BIB, a Chang variant, or possibly an open baffle design. Right now the UMOBD enclosures are making a solid argument for some sort of open baffle.
- Matt
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