Tracy - Vintage nut Posted August 12, 2014 Share Posted August 12, 2014 I am almost finished reworking my KLF-30's and noticed the foam configuration was quite different between the four I have. Would it be good to line all the sides plus the top and bottom with egg crate mattress foam or what do you think? Your input would be greatly appreciated Quote Link to comment Share on other sites More sharing options...
cradeldorf Posted August 13, 2014 Share Posted August 13, 2014 (edited) anything will work but I got the best sound from what I did in my KLF 30 mods post. Less is more. https://community.klipsch.com/index.php?/topic/150640-klf-30-mods/ Edited August 13, 2014 by cradeldorf Quote Link to comment Share on other sites More sharing options...
moray james Posted August 13, 2014 Share Posted August 13, 2014 (edited) both reflex and passive radiator (they work the exact same way) need to have a resonant volume of air in order to work. It is the driver which excites the air inside of the vent or passive by first setting the air inside of the cabinet to resonate at the chosen tuning frequency of the reflex device. The volume of air resonating (in the cabinet) is what acoustically couples the speaker to the vent or passive. What this means is that you must have a volume of air around the vent/passive and the woofer which is free to resonate in other words that volume of air should not have any damping in it if you want the vent/passive to have maximum control. You can add damping to the top two thirds of the cabinet and if you choose the right material and install it in the optimum way you can even cause the speaker to act as if it were in a physically larger cabinet. This means that you could then re tune the cabinet vents or the passive to a lower frequency. Of course the driver response will determine how much lower that you will be able to tune as would the passive itself but it is fairly safe to say you can almost always squeeze out 3 - 4Hz more bass extension from most systems which will make for a very nice difference in the sound quality and balance of the speaker. Remember that with production reflex and or passive designs that the damping that you find inside of the cabinet is almost always just enough to damp out internal mid frequency resonances. The internal damping has or should have nothing to do with damping the fundamental cabinet resonance as that is what the vent or passive takes care of. So a very good general rule of thumb is not to place any damping material in close proximity to the vent(s) or the passive. I fully realize that this is very often seen (damping around vents)but that just means that a lot of vents and passive radiators are not operating at optimum capacity. Hope this helps. In your case the factory foam is best placed on the top of the cabinet and on the sides or back from the top down toward the middle of the cabinet. The back side of vents should be left unobstructed by any material such as damping and brace work. Remember that the air in a vent which is in full resonance will move fully in and out of the vent length about 1.5 times the actual vent length and any obstruction will have an impact on the optimum operation of the vent. Easy to see then that most vents are compromised from the start by designers who have little cabinet space to begin with and too many concerns other than audio performance to take into account. Passive radiators move the air in a cabinet is a very different way than a vent does. You can have a passive firing into a cabinet with brace work and so long as you provide some breathing space of 3 -5 inches the passive will function as desired. Vents present a rather unique situation as they concentrate the action of the air that they are moving much more so than with a passive where the air motion is spread over the full surface area of the passive as well as its suspension. Damping near vents such as on the bottom of the cabinet in a KLF20 or a KLF30 will generate turbulence in the air moving in and out of the vents. It is best to keep hard surfaces around the vents and where the air from the vents flows. I hope that this gives readers a good overview as to the general workings of vents and passive radiators. Best regards Moray James. Edited August 13, 2014 by moray james Quote Link to comment Share on other sites More sharing options...
cradeldorf Posted August 13, 2014 Share Posted August 13, 2014 Excellent description Moray. And I totally agree to the vent compromises that designers are up against. With that said in the case of the KLF series the ports being very near the inside corners really compromises the sound IMHO and having vent tubes protruding into the corners only made it worse IMHO. Thats why I stuck the foam the way I did on the bottom of my cabs right up against the bottom of the port outlets and eliminated the port tubes,To eliminate the sound of multiple waves following all the surfaces and colliding in the corner. Just my .02. Quote Link to comment Share on other sites More sharing options...
moray james Posted August 13, 2014 Share Posted August 13, 2014 nothing to stop you from you having the vents extent out of the cabinet rather than into the cabinet. Of course many will not like the esthetic of reflex tubes protruding from the cabinet but if you don't mind and you don't see them in your set up it is a very simple fix. Still best not to have damping in close proximity to reflex vents. The top is a great location for vents so long as you don't have kids or people at home who like to drop things into your speakers. Best regards Moray James. 1 Quote Link to comment Share on other sites More sharing options...
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