hi.
I have 802 B&W driven by krell FPB 600. 600w rms each into 8 ohm. Now i have crossed over the mains with 2 paradigm 15 inch woofers below 40 hZ drivern by 600 W rms pro amplifier and Benringer FBD with room equalization
I have no electronic cross over in the cd-dac-pream-amp chain. The pre is KRC_HR krell and DAC is ACCUSTIC ARTS MK4 DAC2.
Problem: the 802 bottoms out at high volumes. Althought the mains go deep but they do bottom out particulary with HT. So what can i do to prevent bottoming oput i.e restricting output below port resonance without using any passive or electronic cross over.
Any ideas about sealing the port with cloth or something like that.
regards.
I have 802 B&W driven by krell FPB 600. 600w rms each into 8 ohm. Now i have crossed over the mains with 2 paradigm 15 inch woofers below 40 hZ drivern by 600 W rms pro amplifier and Benringer FBD with room equalization
I have no electronic cross over in the cd-dac-pream-amp chain. The pre is KRC_HR krell and DAC is ACCUSTIC ARTS MK4 DAC2.
Problem: the 802 bottoms out at high volumes. Althought the mains go deep but they do bottom out particulary with HT. So what can i do to prevent bottoming oput i.e restricting output below port resonance without using any passive or electronic cross over.
Any ideas about sealing the port with cloth or something like that.
regards.
I think the problems is that the room EQ is sending exceesive boost to your main speakers. Blocking the port may or may not help, try it and see. But the real answer is an electronic filter for your 802's.
no sir, nothing is in the signal path to the main speakers. the room equalization is for subwoofer below 40 Hz only to equalizle low rol off of dual sealed subs.
Here is the measurement i took from interner. Red is the woofer response .blue is port. it seems to be tuned to 26 Hz.
and we can see roll off below 40 Hz. i want to block all frequencies below 40 hz to limit the woofer excrusion, thermal heating and greater and cleaner power handling. below 40. the 15 inch dual paradigm can take over. regards
Suggest you contact B&W for advice.
My experience with them has been positive and helpful.
Patrick
My experience with them has been positive and helpful.
Patrick
Jamming rolled up socks in ports can effectively seal the cabinet, synthetic socks work best as they "breath " less.
Hard foam works well too, but requires careful shaping, a bread knife works well.
If your subs are sealed, covering the 802 ports probably will make the two different cabinets "play together" better, you may actually need less power to sound louder and cleaner.
I would not recommend covering the ports. Above the port tuning frequency, the displacement of the driver will be less with an open port rather than sealing it up.
What is the recommended power amp size for the 802's?
You probably need to either turn it down or decrease the bass going to the B&Ws.
What is the recommended power amp size for the 802's?
You probably need to either turn it down or decrease the bass going to the B&Ws.
Exactly, thats what i want to do. but i as i mentioned earlies i cannot/donot want to alter the signal path to reduce bass to maintin signal purity. a high end DAC-audiophile grade pre-amp-power amp. no bass/tone control so turning down or decreasing bass is not possible. the only way is to physically limit the bass respone of the B&W drivers to 40 Hz. any suggestions?
It may sound condescending but why not just turn down the volume until they stop bottoming out??
otherwise a passive high pass in the signal path to the 802s is possible but the values are very high and if you use electrolytics you may ( Possible ) here a little degradation in SQ.
Something around 400uF will limit excursion at the nominal 6dB per octave, setting the XO a little higher would probably work better in practice
otherwise a passive high pass in the signal path to the 802s is possible but the values are very high and if you use electrolytics you may ( Possible ) here a little degradation in SQ.
Something around 400uF will limit excursion at the nominal 6dB per octave, setting the XO a little higher would probably work better in practice
You can try modifying the port. Put longer cartoon tube in the port so it tunes enclosure lower and you may achieve "acoustical protection" for drivers.
Often you can measure the input resistance to your amp with a multimeter (Zin may be primarily resistive and therefore easy to work with) and use a single, small, very high quality capacitor at that point.
In some cases you can block your ports and then solid fill some of the rear chamber to create a smaller closed system. You'd want to measure Vas and Qt.
I would have to suggest putting aside purist OCD tendencies and designing a practical high-quality filter at the power amp input. You might not even need any additional buffer stages if you never change what's before and after the filter. One high-quality capacitor and one high-quality inductor would give you a very effective high-pass filter with overly complicating the signal path. You might even be able to modify the amp without additional parts, just changing values. See if you can just limit the amp's bandwidth without doing much harm (phase shift) in the rest of the audible range. Done right, limiting the amp's bandwidth might even reduce some forms of distortion (like IM). Or get 808's. Stuffing the ports would really change the spakers' response and adding EQ could be worse than adding a high-pass.
Or build yourself a hefty passive high-pass at the amp's outputs, but that will require enormous expensive high-power caps and enormous expensive high-power inductors. Much cheaper before the amp, and the filter works better because of consistent impedances (compared to speakers).
Or build yourself a hefty passive high-pass at the amp's outputs, but that will require enormous expensive high-power caps and enormous expensive high-power inductors. Much cheaper before the amp, and the filter works better because of consistent impedances (compared to speakers).
I'd suggest a series cap, afaik, plugging the port, while having the effect of reducing the amount of audible bass, will load the cone and it will move more. If your problem is with the drivers' former bottoming against the back plate "loud ra ta ta ta" sounds, plugging the port will probably make it worse.
You can try it by playing some music at a reasonable volume and put your hand over the port while watching the cone.
I'd probably just put about 400mfd of capacitance in line along the positive terminal going to the 802, as cycle suggested, but I disagree that it would be expensive. Depending on the grade of capacitors you use, it'd probably be less than a hundred bucks, or it could be a couple hundred if you get good poly caps, like here:
Solen 200 mfd Fast Cap 400V: Madisound Speaker Store
4 of those (2 twisted in parallel for each speaker on the positive terminal) would probably do the trick.
You can try it by playing some music at a reasonable volume and put your hand over the port while watching the cone.
I'd probably just put about 400mfd of capacitance in line along the positive terminal going to the 802, as cycle suggested, but I disagree that it would be expensive. Depending on the grade of capacitors you use, it'd probably be less than a hundred bucks, or it could be a couple hundred if you get good poly caps, like here:
Solen 200 mfd Fast Cap 400V: Madisound Speaker Store
4 of those (2 twisted in parallel for each speaker on the positive terminal) would probably do the trick.
Hi,
By far the simplest option is to reduce the, or apply an, input capacitor
to the amplifiers powering the 802's to reduce LF excursion if needed.
Solder it into the input plug if you don't want to open up the amps.
rgds, sreten.
By far the simplest option is to reduce the, or apply an, input capacitor
to the amplifiers powering the 802's to reduce LF excursion if needed.
Solder it into the input plug if you don't want to open up the amps.
rgds, sreten.
I had to go back and read the first post, I missed the part about bi-amping.
Yes, in your case, if the Krell is only powering the B&W speakers, this is the easiest method. After looking online, I've found the input impedance of the FPB 600 to be 85k ohms, so (correct my math if I'm wrong) you need a pair of capacitors about this size:
Kimber Kap 0.047uF 600V Capacitor 027-818
You could probably make your own rca cable that goes from the pre-amp to the amp which has one of these caps in each left and right.
Dude...you are using one of the most under rated amps ever built, as quoted from StereoPhile mag-
""Driven on a toneburst equivalent to peak program duty at 8 ohms, it reached to touch the 1kW line, while at 4 ohms it attained 1.85kW, and for 2 ohms 3.53kW. And for 1 ohm—wait for it—an amazing 6kW! These are single-channel results, but, measured as short-term ratings, they should be available from both channels simultaneously."" -Quote
LOL, you got a underrated $12,000 amp driving $8,000 worth of overrated tower speakers....TURN IT DOWN....geez. If you had any sense you would know you are drastically exceeding the speakers mechanical limits when you hear clatter from those tiny voice coils trying to jump out of their cones.
Hi,
Like all vented boxes, if you want to explore maximum bass SPLs then you need
low pass fiters below the vent tuning frequency, its a given. The B&Ws are tuned
to 26Hz, (with a bessel roll-off alignment) so ideally something like a Q=2 high
pass filter at ~ 20Hz is what you need to boost bass and control overexcursion.
Why you'd need to add further 15" subs for them is beyond me, unless you want
to get down to 16Hz or so, and then you'd need something like the Contrabass :
http://forums.klipsch.com/forums/storage/8/363024/ContraBass.pdf
http://www.hometheater.com/content/way-down-deep-ii-servodrive-contrabass
rgds, sreten.
Like all vented boxes, if you want to explore maximum bass SPLs then you need
low pass fiters below the vent tuning frequency, its a given. The B&Ws are tuned
to 26Hz, (with a bessel roll-off alignment) so ideally something like a Q=2 high
pass filter at ~ 20Hz is what you need to boost bass and control overexcursion.
Why you'd need to add further 15" subs for them is beyond me, unless you want
to get down to 16Hz or so, and then you'd need something like the Contrabass :
http://forums.klipsch.com/forums/storage/8/363024/ContraBass.pdf
http://www.hometheater.com/content/way-down-deep-ii-servodrive-contrabass
rgds, sreten.
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Sreten, he may want to have bass match the volume of the mid & treble of the 802, which just isn't an 808. The Krell might be better used in the frequency range where the speakers work; system probably gets a lot louder across the band with the subs if he can control the 802s.
Like sreten says, all good pro vented boxes specify a high-pass filter. Well, he said low-pass but I assume he meant a low-frequency high-pass. B&W just didn't expect them to be played very loud. But adding the correct filter makes for a better speaker regardless of the subs IMHO. It's just the right thing to do to complete the design, unless you're using some super-clean 6 watt amp.
For this guy, the question is just whether to put the filter before, in, or after the amp.
If you don't want to limit bandwidth in the feedback loop or something like that, then just start like Dr. Dyna suggests, with a cap soldered across the input plug. 85K input impedance sounds like of high, but I would not know that amp. Or like Dr. Dyna suggests, spend some big (but relatively small) bucks on the speaker-level caps. If the hinge frequency is good but you need steeper cutoff, you can add the inductor later to make it twice as steep.
What were you using as the line-level active low-pass crossover for the subs? You just didn't want to add the buffer stages and filter? Those low-level sections are usually relativley clean anyway IMHO, as long as you get the levels matched right.
Good luck whatever you end up doing...I feel for 'ya...as I'm doing something similar. Bolted boards across the holes left from the ports of my Newform cabinets with loaded scan-speaks, but still had to go to active tri-amp and subs. There's just no point in trying to get a speaker to do what it just can't.
Like sreten says, all good pro vented boxes specify a high-pass filter. Well, he said low-pass but I assume he meant a low-frequency high-pass. B&W just didn't expect them to be played very loud. But adding the correct filter makes for a better speaker regardless of the subs IMHO. It's just the right thing to do to complete the design, unless you're using some super-clean 6 watt amp.
For this guy, the question is just whether to put the filter before, in, or after the amp.
If you don't want to limit bandwidth in the feedback loop or something like that, then just start like Dr. Dyna suggests, with a cap soldered across the input plug. 85K input impedance sounds like of high, but I would not know that amp. Or like Dr. Dyna suggests, spend some big (but relatively small) bucks on the speaker-level caps. If the hinge frequency is good but you need steeper cutoff, you can add the inductor later to make it twice as steep.
What were you using as the line-level active low-pass crossover for the subs? You just didn't want to add the buffer stages and filter? Those low-level sections are usually relativley clean anyway IMHO, as long as you get the levels matched right.
Good luck whatever you end up doing...I feel for 'ya...as I'm doing something similar. Bolted boards across the holes left from the ports of my Newform cabinets with loaded scan-speaks, but still had to go to active tri-amp and subs. There's just no point in trying to get a speaker to do what it just can't.
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