um, no, this guy specifically stated he would not consider altering the the signal, actively nor passively. His specific question was how to muffle the ports on his B&W 802's with quote ""cloth or something like that""
Our,er my question is...what are the port diminsions? We really need to focus on whether Cotton would suffice or do we need to seek more exotic materials for this purpose? As one observant poster stated earlier..would a synthetic nylon sock be suitable?.one per port, or two folded together, inside out? How about color matching??..come on peeps..ok, I guess the only real plausible solution is to cut a peice of cardboard the size of the port (snug fitting). Slide the cardboard in the port creating a wall. Try to leave 3" of port open and fill er up with 3M expanding foam..might do 1/2, let er expand some, the fill er on up..let it swell nice and fat like out the port, then let it set overnight and cut off the excess and paint to match....Git er Done!
I take it back. There's really two possibilities:
He can stuff the ports and might be really happy. A lot depends on where his subs cross and how high the 802's start to roll off when closed up, and perhaps his source material (is it really bottom-heavy). The 802's will roll off a lot higher, losing all the port output, but they will roll off gradually and without EQ (which would be obviously against his ethic) the excursion will probably not increase as someone else stated...unless the port kicked in near the direct output resonance, or if you add power to EQ the sealed system to near flat again (which he wouldn't to). Multi-source bass and a shallow bass rolloff is not nearly so offensive low as at higher frequencies. Multi-source bass activates the room modes more randomly and gives a more uniform bass "coverage" as you move around. So a lot depends on how high those little woofers in the 802 roll off sealed up. The cabinet is still pretty big, so the Q might still be OK. Somebody should attempt to calcualte the Q for the sealed box. If the subs kick in high enough he might be very happy despite losing the flat low end of the 802's.
But if 2 small 802 woofers a side still get excursion-limited even with the box closed, or there's a low-mid dip in response as the sealed 802s roll off before the subs take over, then I would really encourage him to open the ports back up and limit the lows to the Krell instead. The system might well end up with more SPL capability everywhere and less distortion due to reduced IM and reduced excursion for the 802's, the 802's will run flat lower as designed to using their ports. All amps have some form of bandwidth-limiting in tuning for stability with various loads. The best thing for him to do within his aesthetic is to customize his Krell to suit his B&Ws, possibly without adding any parts. But reluctant to modify a classic, I would still try to convince hiim to install a good 2nd-order filter. He's got a dilemma...reflex really requires that filter, but sealing up a reflex doesn't usually do the trick without EQ, unless he's really lucky and the subs match the sealed 802's really well.
He can stuff the ports and might be really happy. A lot depends on where his subs cross and how high the 802's start to roll off when closed up, and perhaps his source material (is it really bottom-heavy). The 802's will roll off a lot higher, losing all the port output, but they will roll off gradually and without EQ (which would be obviously against his ethic) the excursion will probably not increase as someone else stated...unless the port kicked in near the direct output resonance, or if you add power to EQ the sealed system to near flat again (which he wouldn't to). Multi-source bass and a shallow bass rolloff is not nearly so offensive low as at higher frequencies. Multi-source bass activates the room modes more randomly and gives a more uniform bass "coverage" as you move around. So a lot depends on how high those little woofers in the 802 roll off sealed up. The cabinet is still pretty big, so the Q might still be OK. Somebody should attempt to calcualte the Q for the sealed box. If the subs kick in high enough he might be very happy despite losing the flat low end of the 802's.
But if 2 small 802 woofers a side still get excursion-limited even with the box closed, or there's a low-mid dip in response as the sealed 802s roll off before the subs take over, then I would really encourage him to open the ports back up and limit the lows to the Krell instead. The system might well end up with more SPL capability everywhere and less distortion due to reduced IM and reduced excursion for the 802's, the 802's will run flat lower as designed to using their ports. All amps have some form of bandwidth-limiting in tuning for stability with various loads. The best thing for him to do within his aesthetic is to customize his Krell to suit his B&Ws, possibly without adding any parts. But reluctant to modify a classic, I would still try to convince hiim to install a good 2nd-order filter. He's got a dilemma...reflex really requires that filter, but sealing up a reflex doesn't usually do the trick without EQ, unless he's really lucky and the subs match the sealed 802's really well.
I totally agree with you, cyclecamper. If it were me, I would be shopping for some new tops. I do not question the 802's renowned abilities. With 8 in drivers backed up with a pair of 15's, cut em off. The 802's are rated for 500 watts...that amp can hit 950 watts at 8 ohm transients (or possibly much more if there is a imp dip down low)...that thing is a bad a** beast!
Krell Full Power Balanced 600 power amplifier Measurements | Stereophile.com
Krell Full Power Balanced 600 power amplifier Measurements | Stereophile.com
Yeah, the big Krell is a monster. The problem is stuffing the port isn't going to stop the woofers from bottoming out, and in fact might make it worse...assuming that the drivers haven't been damaged yet. Try it yourself by plugging a port with your hand while watching the movement of your drivers.
If he wants to prevent shredding the drivers, there's going to have to be some kind of signal adjustment, either with self control or capacitors. Chances are, if the driver bottoms, it's probably exceeded it's maximum power handing anyway.
I'd imagine welding the voice coil of an 802 (or potentially destroying the amplifier that's now driving an open / shorted load at damn near full volume) would probably prove more costly than a few caps.
Am I the only one thinking that this thread sounds a little like we're trying to explain to a Ferrari owner why he shouldn't try to tow a motorhome with it?
If he wants to prevent shredding the drivers, there's going to have to be some kind of signal adjustment, either with self control or capacitors. Chances are, if the driver bottoms, it's probably exceeded it's maximum power handing anyway.
I'd imagine welding the voice coil of an 802 (or potentially destroying the amplifier that's now driving an open / shorted load at damn near full volume) would probably prove more costly than a few caps.
Am I the only one thinking that this thread sounds a little like we're trying to explain to a Ferrari owner why he shouldn't try to tow a motorhome with it?
""This amplifier obviously needs to be used with some caution. While it is well known that loudspeakers are more readily destroyed by smaller amplifiers when overdriven, the fact is that the FPB 600 sounds very clean when run loud—it's all too easy to reach life-threatening levels for your speakers! Further, while I found the plastic-shrouded binding posts a nuisance, I'm well aware of the relatively high voltages this amplifier can provide. In clip, the AC level on the output terminals was 86.4V RMS. Some thought should be given to the other end of the speaker cable; perhaps it should be shrouded in insulation, except at the point of contact to the speaker terminal.
The FPB 600 can vaporize some of the smaller speaker cables if inadvertently short-circuited at the speaker end. I measured a huge peak current of >115A into 1 ohm and stopped there, though more might well be available. If you give up listening, you could always use the amplifier for welding!""
....sorry, I could'nt resist quoting the article I posted earlier.
The FPB 600 can vaporize some of the smaller speaker cables if inadvertently short-circuited at the speaker end. I measured a huge peak current of >115A into 1 ohm and stopped there, though more might well be available. If you give up listening, you could always use the amplifier for welding!""
....sorry, I could'nt resist quoting the article I posted earlier.
Yeah, I've wanted a big Krell amp for years now, but I've never been able to afford one, and hearing about it being used to bottom out drivers is kinda like watching someone key a Bentley, lol.
Ah well.
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