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jazzfan

KLF20 cabinet damping

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Any thoughts on the best material for internal damping for a KLF20 woofer section. Ive recently upgraded the crossovers, tweeter and mid drivers. Added extra bracing and have them out as far as possible into the room. They sound great with the upgrades, however, Im getting more boomy bass than I remember. Should I add damping to the woofer area? Should I damp all four internal walls? What would work best for this? Thanks in advance.

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I don't know these speakers well, but what did Klipsch design them to have for damping? 

Did you change the inductor that is in series with the woofers? 

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Damping is only around the tweeter and mid drivers from the factory. I have installed new crossovers from Bob Crites, completely replacing the stock crossover.

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I'd take a look at Parts Express for damping material.

They have a good selection.

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28 minutes ago, jazzfan said:

Damping is only around the tweeter and mid drivers from the factory. I have installed new crossovers from Bob Crites, completely replacing the stock crossover.

Bob's crossover is the factory crossover same design and xo points only better parts/layout. You can stuff the top of the box with acousta-stuf and if you want you can line the bottom, side walls and back section with felt to catch top response of the woofers but the cavity between the woofers and the vents must stay open and free of any damping. That air must be able to resonate freely for the woofer to drive the vents into resonance. Time to experiment with re positioning your speakers.

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You can get rolled batting that is pretty cheap (used in quilts).  That way you can add a little at a time.  Too much wouldn't be good.  As stated, make sure the ports are clear.  Mostly just need a layer or two on the sides and bottom.  Another worthwhile tweak is to drill out the other 4 holes in the woofer frames so you can use all eight screws to hold in the woofers along with putting better seals between all the drivers and the cabinets.  Outside of that, positioning / amplification.

If you do the screws, drill from the back of the frames so you can use the holes in the frames (yes they are already there and you are shorted the extra stability of 8 screws) as guides.  Then drill the front holes (just to the frame) using the same size bit as the rest of the holes in the plastic face plate.  This gives the woofer a better seal and stability, being locked better to the cabinet.

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I used semi rigid fibreglass called Sound Screen in my KG 5.5's thats designed specifically for sound absorption. I've read it's the second best sound absorption material, but seeing as asbestos is somewhat hazardous, second best will do!

To me the damping made the speakers sound cleaner and perhaps less boxy if that makes any sense.

 

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Moray  James was a big help several years ago when we repaired a pair of KLF 20 that had loose motor boards and installed Bob Crites Ti diaphragms in the tweeters and had the X/O re-capped.  I would follow Moray's advice  on speaker placement as we never had a issue with the bass after we did the repair and Bob Crites mods. The brighter mids and tweeters made us increase the gain to the woofers until I found the best gain adjustment. 

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how did you brace them?  I may want to do that to mine as I also have to reglue the motor board.  If you doubled the walls then you may have reduced the innervolume, making them more peaky and raising the resonance frequency.   Adding dampening works to make the volume look larger to the woofer.   May work.  Dow Corning used to have this lovely white no itch glass unsulating bats.. sadly they dont make in anymore.     My KLFs seem to use foam? 

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9 hours ago, efzauner said:

 Adding dampening works to make the volume look larger to the woofer.   May work.  Dow Corning used to have this lovely white no itch glass unsulating bats.. sadly they dont make in anymore.     My KLFs seem to use foam? 

Not so much actually.  In KLFs it may deaden the sound also, particularly depending on the amplifier.  Some poly batting from a hobby store or a eggcrate mattress pad works well used judiciously. 

Easiest way to brace if you do not want to remove the motorboard and back is to glue several slats to the sides and back, then glue a brace going front to back/side to side to those slats to lock the movement (vibration) forward and sideways.  Use a glue that can work with the covering material around the edges of the back and front.

Don't do too much dampening or bracing since you don't want to affect the volume much.  The 2 10" woofers can actually use a little more air.

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I am working on my KLF20s right now. Starting with regluing the front and backs. Are yours still solid? have they been reglued already?

 

Mine  had 1 inch foam on the back and sides. I think it was stock. 

 

Can you do me a favor? Can you measure the port length from the outside surface of the back to the   inside end of the port? Someone modified mine with abs plumbing pipe and I want them back to stock.

 

Can you also let me know what cap values Crites is using for the tweeter circuit? My stock xover is 1.25uF but Sonicaps does not seem to have that value.  And for the woofer electrolitic. Stock is 8mF but again Sonicaps does not seem to have that value.    

 

I am also installing the Crites titantium tweeter domes. 

 

Thanks

 

 

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dynomat.  it serves 2 purposes.  it will sound dampen, but it will also absorb vibrations which will give you a more structurally sound cabinet.  it basically gives you the sound of very well braced cabinets. i have some aviation grade stuff in my 7's, but dynomat is pretty much the same thing.  go for the .5" stuff. you can even put the .25" stuff on your plastic speakers and it will make those plastic speakers sound like wooden speakers. do one side and A/B it!

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On 10/26/2017 at 8:37 AM, pzannucci said:

Not so much actually.  In KLFs it may deaden the sound also, particularly depending on the amplifier.  

 Really? I thought it was called "damping" from a sinusoidal driven harmonic oscillator.  The damping factor reduces the amplitude of the resonance as well as lowering the resonant frequency... This lowering of frequency is similar to making the system less stiff. ergo larger box..

 

 

https://en.wikipedia.org/wiki/Harmonic_oscillator#/media/File:Mplwp_resonance_zeta_envelope.svg

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16 hours ago, efzauner said:

 Really? I thought it was called "damping" from a sinusoidal driven harmonic oscillator.  The damping factor reduces the amplitude of the resonance as well as lowering the resonant frequency... This lowering of frequency is similar to making the system less stiff. ergo larger box..

 

 

https://en.wikipedia.org/wiki/Harmonic_oscillator#/media/File:Mplwp_resonance_zeta_envelope.svg

I'm not sure where damping factor came from when we are talking about damping/dampening material to damp the cabinet.  Too easy to use damping and dampening B)

Technically it is damping though I find both occur though are two totally different things.  The current available and high damping factor of the amp may reduce the impact on adding material to the cabinet (like putting a blanket over the woofers reducing dynamics or making the woofers sound sloppy).  

I find that making the most dense and strongest cabinet without putting too much material in it (just enough to stop stray mid frequencies from affecting the cone or coming through the port) is the best.  Trying to make the box bigger by adding material seems to work best when doing a closed box.

 

 

 

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8 hours ago, pzannucci said:

I'm not sure where damping factor came from when we are talking about damping/dampening material to damp the cabinet.  Too easy to use damping and dampening B)

Technically it is damping though I find both occur though are two totally different things.  The current available and high damping factor of the amp may reduce the impact on adding material to the cabinet (like putting a blanket over the woofers reducing dynamics or making the woofers sound sloppy).  

I find that making the most dense and strongest cabinet without putting too much material in it (just enough to stop stray mid frequencies from affecting the cone or coming through the port) is the best.  Trying to make the box bigger by adding material seems to work best when doing a closed box.

 

 

 

 

 

You seem to believe that damping material in speakers is to prevent the wood from vibrating.  Perhaps somewhat but I believe the main purpose is to increase the damping factor in the resonant system.. much like your shock absorber in a car.     Damping is the correct term in resonant systems.  We seem to also use the word dampening as well as it also means to reduce amplitude.  I don't believe that is the correct term to use but lets not get lost in semantics.   The material in speaker cabinets is to dampen the response of the woofer, not to reduce the vibrations of the cabinet. 

Wiki has  a good write-up on it.  Basic engineering and physics.  It would apply to vented cabinets also as the box acts as sealed above the resonant frequency.. 

Here is the complete link.   https://en.wikipedia.org/wiki/Harmonic_oscillator

 

there are other sources of good information 

http://www.data-bass.com/data?page=content&id=79

 

 

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On 10/31/2017 at 8:43 AM, InVeNtOr said:

dynomat.  it serves 2 purposes.  it will sound dampen, but it will also absorb vibrations which will give you a more structurally sound cabinet.  it basically gives you the sound of very well braced cabinets. i have some aviation grade stuff in my 7's, but dynomat is pretty much the same thing.  go for the .5" stuff. you can even put the .25" stuff on your plastic speakers and it will make those plastic speakers sound like wooden speakers. do one side and A/B it!

The dynomat will dampen higher frequency vibrations of the panels, but will not stiffen them to lower frequency flex.  Only a brace or thicker wood will do that.    I question its usefulness as I doubt the issue is high frequencies as the amplitude is to low.   Didn't Mr Klipsch do some audio testing of this anyway? Not noticing any audible quality difference with stiffer/thicker  wood?

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17 hours ago, efzauner said:

 

 

You seem to believe that damping material in speakers is to prevent the wood from vibrating.  Perhaps somewhat but I believe the main purpose is to increase the damping factor in the resonant system.. much like your shock absorber in a car.     Damping is the correct term in resonant systems.  We seem to also use the word dampening as well as it also means to reduce amplitude.  I don't believe that is the correct term to use but lets not get lost in semantics.   The material in speaker cabinets is to dampen the response of the woofer, not to reduce the vibrations of the cabinet. 

Wiki has  a good write-up on it.  Basic engineering and physics.  It would apply to vented cabinets also as the box acts as sealed above the resonant frequency.. 

Here is the complete link.   https://en.wikipedia.org/wiki/Harmonic_oscillator

 

there are other sources of good information 

http://www.data-bass.com/data?page=content&id=79

 

 

No, I don't believe damping material in speakers prevents the wood from vibrating but certain types and implementations, applied appropriately, will change the frequency of the vibration.  

 

So in fact the material used in a cabinet can both reduce the cabinet resonance (introduced by vibrations) and have an effect on the workings of the woofer within the cavity of the cabinet.  All of the implementations are to varying degrees and when applied, the theory works to varying degrees.

 

Thank you for the pointers.  

 

I have been reading books on this since I have been 10 yrs old (very long time ago), a heavy internet user (unfortunately), and as an old man growing up in a time when you could buy lots parts, have done my share of speaker  building. 

 

efzauner, Have you built many speakers?  As you will find out there is an art and there is a science.  What material used by preferred by one person and applied in a certain manner will not work for another person and is possibly ear and hardware/amp dependent.

 

By the way, since most of our usage is in speakers with woofers that go up into the lower mids, you do need to also account for clarity and response variations in that area when sizing and adding material to the cabinet.  The information on subwoofers does not account for that.

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9 hours ago, pzannucci said:

 

 

I have been reading books on this since I have been 10 yrs old (very long time ago), a heavy internet user (unfortunately), and as an old man growing up in a time when you could buy lots parts, have done my share of speaker  building. 

 

 

 

 

You had speaker design books? Well young man.. let me tell you how us real old timers made speakers...back in the day when we had to wind our own voice coils and mash paper pulp with our feet to mold cones...  ;)    

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14 hours ago, efzauner said:

 

 

You had speaker design books? Well young man.. let me tell you how us real old timers made speakers...back in the day when we had to wind our own voice coils and mash paper pulp with our feet to mold cones...  ;)    

Thanks for the young man compliment :D

Yes, books.  I know those things don't exist much anymore.  Now just information overload of the internet.

 

Let us know what you do with the 20's.  I am always interested in different materials / methods that I don't want to have to try myself.  Experiences are great to share and learn from.

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1 hour ago, pzannucci said:

Thanks for the young man compliment :D

Yes, books.  I know those things don't exist much anymore.  Now just information overload of the internet.

 

Let us know what you do with the 20's.  I am always interested in different materials / methods that I don't want to have to try myself.  Experiences are great to share and learn from.

 

To be honest, my first HiFi system was taking the woofer and tweeter out of an old RCA tube console, and making a box for my bedroom,  and making a wood case for the electronics. maybe 12yrs? ... then I got a Heathkit WM5 system with a Lenco and a huge gorgeous Goodmans corner speaker from my neighbour. maybe 14-15? I still have the HK and Lenco..  on the list to restore.  I then purchased a new system.. New Advent speakers, Pioneer SA7500II and Dual/Sure TT.  Still have those too and being used.   I then found the original Philips speaker book.. made a small set for my car with a home built amp and inverting power supply to drive it..  Then got married and stopped listening to music on account of WAF... until I build the HT room last year.  Then not much till last few years when I made a couple of HT subs using winISDPro.  sweet sound but way to big physically for the room. got rid of those for a RSW15.    So you do surely have more speaker design experience and do appreciate your input even if you are 5 years my junior!   I am an engineer so I tend to seek formal technical explanations to wrap my mind around.  Forgive me for being a bit cool on the touchy feely explanations!

 

RIght now the second KLF20 is on the repair bench. Again both front and back boards almost completely detached.  The rear on this had been reglued but without any effort to remove the old glue.. sadly.      I did install a center brace between the 2 woofers.   Not adding too much extra damping material.  I also added some plywood blocks for the screws.  I'd add some T-Nuts and allen head machine screws but having trouble finding some with heads under 7mm in diameter... otherwise they wont fit in the plastic cosmetic ring.    I may add some additional side bracing.. but as you know.. diminishing returns...   I have experience with various "dynamat" material from car audio use but I am weary to put these on wood. They tend to try out over time and loose adhesion unless they are on non-porous surface. And a pita to remove.   Picking up new caps at Solen this afternoon...

 

A cloud with a silver lining.. Since I hooked up the older Heresy's I have  been able to enjoy music like I used to..   The KLFs where horrendous in comparison, not in terms of frequency response but in terms of imaging, listening fatigue and overall enjoyment... yep all those touchy feely things engineers cringe at! :)  

KLF20 Brace.jpg

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