Damping The Rear Chamber Of My Compression Drivers ?

[ka7niq]

Work is slow right now, and I have some extra time on my hands.

So, I am going to take my horn drivers out of my speakers, and place some damping material behind the dome.

I have NO IDEA what, or how much to put behind the dome, but I plan to try cotton, felt, and maybe even a foam rubber plug.

The speakers are Klipsch CF 3's, but I have Cornwall's too.

IF it works, I may even try it on the Corns ?

I have done many Google searches for this, and can't seem to find anything about it, except that PWK supposedly did not like it, or something to that effect.

Well, PWK did not like the Tractrix flare either ~ ~ ~

I will of course be careful not to have the damping material actually touch the dome, etc.

I posted a similar thread, and didn't get many responses.

I can't see why it would not be a good thing ?

My "take" on the many Klipsch speakers I have heard and owned is that they place efficiency above ALL else.

Perhaps they were meant to be EQ'd, and a peak, dip, or resonance here and there was "overlooked" , all in the name of getting the MOST efficiency.

I guess this is ONE design approach .......

[Guest " "]

The k-55-v's has a small amount of felt material inside the octagon hole that passes thru the magnet....this hole is on the rear side of the diaphram....the amount of felt is about the size of a circle...half and inch, by one quarter inch....it plugs the hole up pretty good...not sure if adding anymore would add any value.

On some of the square magnet k-77's there is a small flat piece of felt about the size and thickness of a dime, behind the the diaphram...attached to the magnet....looks a lot like the adhesive door stops and sliders that home depot sells. I don't think increasing the thickness of this one...would add any value.

It would be pretty difficult to open up a k-77 driver to add this felt plug with out damaging the leads to the coil.

In the cas of the k-55-v's, disaasembly is pretty easy as long as you ensure that the 2 guide pins line up and are evenly spaced during re-assembly.

Overall, I would not expect much in return for any time you spend on this.

From left to right...a k-55-v with felt out of the center hole, a k-77-m with small piece of felt in center magnet area, a st-350 with a bare magnet, and a K-79 with a bare magnet.

[Guest " "]

If you are going to disassemble a tweeter to repair a voice coil, you can add a small cork pad like the photo shows, these are sold as door stops, but I would not disassemble one just to install a cork or felt spacer, odds are , your going to break off the leads to the voice coil in the process.

[ka7niq]

Thank You for sharing your experience and pictures.

The Klipsch CF 3 uses a different midrange driver.

It is from the Klipsch commercial line.

It is either a titanium or Aluminum dome compression driver, and has a Neo magnet.

I have had the compression driver domes apart before, and trhey use guide pins.

I feel totally comfortable taking them apart.

There is no tweeter in the Klipsch CF 3.

It is a two way.

I was thinking that all that undamped energy coming off the rear of the dome can't be a good thing ?

I mean, think about it ?

All that reflected sound is bouncing off the magnet, then back into the dome ?

I really wish I had SOME theory to go on, but all I have is my ears.

With all the tweaks people do to their horns, etc, I am really suprised there is so little info on doing this ?

I know if you really stuff say a conventional midrange driver's compartment, it sometimes reduces coloration, and can alter the Q of the driver, which MAY not be a bad thing ?

I am NOT here to bash Klipschm far from it!

But, I currently own 12 pairs of speakers, and I TRY and remain objective, and not get emotionally involved with any speaker I own.

But I have to say there is not a Klipsch speaker I have ever heard that was not in need of improvement.

I think the OLD Forte's were quite good, and I personally prefer them over the two pairs of Klipschorns I have owned, and the Cornwalls, except in the bass.

They are still voiced a LITTLE too "on the edge" for my long term listening satisfaction though.

I like the CF 3's and CF 4's, but they have their faults too, and I am trying to see if it is something in the compression driver itself that is at fault.

I also have a pair of 1978 Cornwalls I picked up, and the guy SAID he replaced the tweeter diapraghms, but they sound almos muted, unless pointed right at you.

The CF series speakers image very well, and are smooth.

But I hear some midrange problems, noticeable on some female voices.

I have a RANE active crossover, and I almost want to biamp them using the Rane and it's 24 db slopes.

I believe the compression driver/horn combo used in the CF series speaker has a peak in it's lower range.

It becomes clearly audible at higher levels, and I have a large room, and have never been known to be shy with a volume control.

Maybe adding damping material will lower the drivers Q, and/or raise the drivers resonance frequency, hence reducing it's output in this range I find offensive.

All that will be "lost" is some time.

Just like that stupid rope caulk, it can easily be removed.

I say "stupid" because on my fiberglass Tractrix CF3 and CF 4 series Horns, it did not sound good.

On a metal horn, I bet it could work magic, although I think a mixture of Tar with sand added to it could be good too.

[DrWho]

For what it's worth, PWK was a fan of the tractrix - he only rejected it until the math made sense (as should be expected from any good critic).

The real question is what are you trying to achieve / "fix" ?

Adding foam to the rear chamber isn't like adding foam to the walls of your room. It behaves quite differently when so close to the diaphragm. Also, compression drivers wouldn't work if the rear wave didn't "interfere" with the diaphragm - that's the whole point of the design. Get rid of the compression and you're just back to a direc radiator.

Why not try measuring the output of your speakers and seeing what you can do from there?

[Duke Spinner]

wy do you think your smarter than PWK ...??

[ka7niq]

For what it's worth, PWK was a fan of the tractrix - he only rejected it until the math made sense (as should be expected from any good critic).

The real question is what are you trying to achieve / "fix" ?

Adding foam to the rear chamber isn't like adding foam to the walls of your room. It behaves quite differently when so close to the diaphragm. Also, compression drivers wouldn't work if the rear wave didn't "interfere" with the diaphragm - that's the whole point of the design. Get rid of the compression and you're just back to a direc radiator.

Why not try measuring the output of your speakers and seeing what you can do from there?

I am FAR from an expert on Horn speakers, but it is my understanding that the compression you speak of occurs in the mouth of the horn and the front of the driver.

And, adding foam or damping material like fiberglass, etc, can make it appear to the driver that there is actually a larger amount of air space.

I THINK it may be a good thing in slowing down the rear radiation of the back of the diapraghm.

Think about it for a minute ?

The rearward sound is ping ponging around, hitting the magnet, then the rear of the diapraghm, mixing with the intended frontal radiation.

I would think this powerful rearward radiation can modulate the dome, and do not understand, nor can I find any reason why some attempt should not be made to do something about it, except to save money, ease manufacturing, or prevent possible warranty claims when and if it comes loose ?

I'm gonna try it, cant hurt anything, and will give me soething to do.

[ka7niq]

wy do you think your smarter than PWK ...??

I actually met PWK for the first time at Cobo Hall, in Detroit.

I was 16 at the time, 52 years old now.

I remember seeing these people in an Elevator with big buttons on their jackets saying "Bull Shit"

I followed them back to their room, and heard Klipsch speakers for the very first time.

Paul was very kind to me, and my young friends.

But, with all due respect to what I consider a truly great man, he did NOT design my speakers!

The CF 4's and CF 3's are Roy Delgado's design, not Paul's.

I am simply trying to make a speaker I like very much, possibly better.

I think any wooden speaker needs to have it;s insides coated with a Tar/Sand mixture, to deaden the cabinet walls.

This would hardly be practical in production, but it don't mean it isn't better ?.

From the limited time I spoke with him, I think he would encourage an audiophile to experiment ?

I told him, at the Cobo Hall Audio Show, in Detroit that my Grandpa was a Ham, and that someday, I was gonna be one too.

I told him of helping my Grandpa make antennas out of aluminum, and wire, and how i climbed trees for my blind Grandfather, to put his antenna's up.

Grandpa went blind from Diabetes

Paul knew exactly what a Ham was, and I told him of Grandpa's Bozak and old Fisher Stereo.

BTW, I took home Klipsch literature from that show, read it, and told grandpa all about meeting PWK.

To my surprise, Grandpa knew exactly who he was, and said he wanted to someday own Klipschorns.

Grandpa made good on his dream, sold the Bozak Concert Grands, and bought 2 Klipschorns for the basement.

He kept the Fisher tube stuff.

My Mom And Dad moved us kids to Florida, and finally the Diabetes killed Grandpa.

My Aunt gave me all Grandpa's Ham stuff, but knew the value of the old Klipschorn and Fisher stuff.

I made my case that I was the only Audiophile/Ham in the family, and that Grandpa would want me to have his electronic stuff.

But my Aunt Theresa prevailed, and I got "stuck" with only Grandpa's Collins S Line Ham Equipment.

I still have it Duke, and sometimes, in a darkened room, I swear I can go back to to being a young boy at my Grandparents home, as I watch the glow of the tubes.

A mint, complete Collins S Line is worth big bucks, but I wouldn't sell it for the world.

Some may call it a "boat anchor", and so be it.

But to me, it's a Collins, made by Americans when American Quality meant exactly that.

My kid likes audio, thank God, but no way is he ever gonna be a Ham like me.

But .... Maybe someday he will "get busy" and make me a Grandchild to "carry on" our family's electronic and audio interests ?

The old Collins S Line, and all my audio stuff will then be heading his, or her way.

[DrWho]

How then can you have a compression driver with no horn? [] The compression of the air in the rear chamber is a major part of the compliance of the suspension. The compliance of the system is a variable chosen ahead of time to achieve a certain bandwidth for a given motor strength and diaphragm size. It is not something to be arbitrarily changed. To put it another way, the ping-ponging is part of the intentional design (though in reality it's probably not best described as a ping pong effect or anything similar)

The notion that damping material increases the effective volume is really a bit of a misnomer. It most certainly isn't the case at the higher frequencies where the wavelengths are on the same order of magnitude in size. That said, if increasing the rear volume was advantageous, don't you think the manufacturer would have done so? Blaiming it on cost and manufacturing decisions is a bit extreme considering that a driver even twice as large would certainly not be too big - not to mention extremely inexpensive to implement (especially on large scales).

[ka7niq]

How then can you have a compression driver with no horn? [] The compression of the air in the rear chamber is a major part of the compliance of the suspension. The compliance of the system is a variable chosen ahead of time to achieve a certain bandwidth for a given motor strength and diaphragm size. It is not something to be arbitrarily changed. To put it another way, the ping-ponging is part of the intentional design (though in reality it's probably not best described as a ping pong effect or anything similar)

Exactly, and since the volume of air effects the compliance, it should change things, for better, or worse ?

Remember, we are talking about a CF series speaker, the CF 3.

It's driver is from Klipsch Pro Line, and maybe it was not really intended specifically for this particular Horn ?

I hear a resonance peak in it, especially at higher levels.

I am HOPING to "push" this peak up higher in frequency, or subdue it.

Hey, if it don't work, nothing lost but some enjoyable time, right ?

[Duke Spinner]

Mmmmmnnnnn.....

Collins ......[]

I got ... Drake ....

copper chassis ..

lotsa ..... Tubes ....

[TBrennan]

According to horn historian Steve Schell some of the early Western Electric compression drivers had the back of the aluminum dome open to the air and covered by a protective screen. Below is a quote from Schell, a fella who by the way MAKES compression drivers including a bass compression driver.

"Some people think that the volume of air trapped by the back cover is a designed part of the driver, like the sealed rear chamber used for reactance annulling in a bass horn. I don't think this is the case in most drivers though. Early examples of the Western Electric 555W vented the rear of the diaphragm through a mesh screen, and Wente's patent on the original compression driver with circumferential phasing plug, as used in the Fletcher System, indicated screened vents in the rear cover. Lansing's first compression drivers for the Shearer Horn System were based on Wente's experimental driver, and his rear covers had a series of vent holes around the perimeter. My guess is that the pioneers eventually found that sealing the rear covers eliminated a source of contamination to the driver and made no difference in the response curves. Still, I have found many times that removing the cover eliminates a subtle layer of sonic hash from the driver's sound. YMMV of course."

I've run compression drivers sans rear covers but heard no difference.

[Guest " "]

"The rearward sound is ping ponging around, hitting the magnet, then the rear of the diapraghm, mixing with the intended frontal radiation."

I posted some pictures of magnets that had "a method", either felt or cork, installed. Newer K-77-M's is one example. So there are folks out there doing this.

The k-77-M is considered to be brighter than the alinco version of the k-77.

[ka7niq]

"The rearward sound is ping ponging around, hitting the magnet, then the rear of the diapraghm, mixing with the intended frontal radiation."

I posted some pictures of magnets that had "a method", either felt or cork, installed. Newer K-77-M's is one example. So there are folks out there doing this.

The k-77-M is considered to be brighter than the alinco version of the k-77.

I am sorry Fritz!

My K 77 is a neo magnet version, and I am sorry I did not recognize the picture right away, nor read very good either!

Well, that gives me another "Mod Path" to perhaps someday find an Alinco K 77 to replace the Neo K 77 ?

I find it "interesting: that the Alinco had the felt, yet the Neo K 77 don't ?

Maybe Klipsch "felt" the more powerful Neo motor would better make the K 77 diapraghm behave ?

Hey, what is the sonic reputation of the K 77 driver, overall ?

[ka7niq]

According to horn historian Steve Schell some of the early Western Electric compression drivers had the back of the aluminum dome open to the air and covered by a protective screen. Below is a quote from Schell, a fella who by the way MAKES compression drivers including a bass compression driver.

"Some people think that the volume of air trapped by the back cover is a designed part of the driver, like the sealed rear chamber used for reactance annulling in a bass horn. I don't think this is the case in most drivers though. Early examples of the Western Electric 555W vented the rear of the diaphragm through a mesh screen, and Wente's patent on the original compression driver with circumferential phasing plug, as used in the Fletcher System, indicated screened vents in the rear cover. Lansing's first compression drivers for the Shearer Horn System were based on Wente's experimental driver, and his rear covers had a series of vent holes around the perimeter. My guess is that the pioneers eventually found that sealing the rear covers eliminated a source of contamination to the driver and made no difference in the response curves. Still, I have found many times that removing the cover eliminates a subtle layer of sonic hash from the driver's sound. YMMV of course."

I've run compression drivers sans rear covers but heard no difference.

Thanks Tom, and btw, congratus on finding the Model 19's!

What's with this Lexington KY stuff ?

I thought you were in Chicago ?

I know you retired, and I remember you driving to go "rescue" the Model 19's.

I also saw your old VOTT's on AGon.

They sold right away!

[ka7niq]

"The rearward sound is ping ponging around, hitting the magnet, then the rear of the diapraghm, mixing with the intended frontal radiation."

I posted some pictures of magnets that had "a method", either felt or cork, installed. Newer K-77-M's is one example. So there are folks out there doing this.

The k-77-M is considered to be brighter than the alinco version of the k-77.

OOPS, The CF 4 and CF 3's have the K 63 KN aluminum driver, with NEO magnet, not the K 77

My Cornwalls of course have the K 77

[ka7niq]

Mmmmmnnnnn.....

Collins ......[]

I got ... Drake ....

copper chassis ..

lotsa ..... Tubes ....

You a Ham too Duke ?

I had a Drake C Link, and an old TR 4 CW, great stuff, American Made too!

Miamisburg, Ohio is where Drake was made.

BTW Duke, the CF 3 uses the K 63 KN driver

[TBrennan]

KA7---I moved from Chicago to Lexington in April.

The fella who bought my A7s (on AudioKarma) backed out and they're for sale again. $500, cheap. They were a gift from Rich Drysdale of Cogent and all I want for them is what they cost to ship to Lexington from Anaheim.

I'm also gonna sell my 605As in Barzilay cabinets.

[Guest " "]

"I find it "interesting: that the Alinco had the felt, yet the Neo K 77 don't ?"

Maybe i confused this some how......

I provided some examples only for the sake of "concept".....at one point you said or asked if this was every done before...answer is yes..by who ever makes the ceramic k-77-m and the alinco k-55-v.

The Alinco k-55-v has felt stuffed inside the octagon hole. If you look at the k-55-v in my photo, the felt was pulled out of the hole and I sat it on the top side at about the 3 o' clock position.

The ceramic k-77-m has a flat round material , maybe cork, or hard rubber

Not sure about the alinco k-77

The ev ST-350 has no material...I just added the photo to show how easy it would be to add one

The K-79 has no material....i also just provided the photo to show where one can be placed.

None of the above is to say any particular non heritage line of speakers has any of the above componets.....the photos were provided in response to the question if the use of dampening material was ever done before on a horn driver.

[ka7niq]

"I find it "interesting: that the Alinco had the felt, yet the Neo K 77 don't ?"

Maybe i confused this some how......

I provided some examples only for the sake of "concept".....at one point you said or asked if this was every done before...answer is yes..by who ever makes the ceramic k-77-m and the alinco k-55-v.

The Alinco k-55-v has felt stuffed inside the octagon hole. If you look at the k-55-v in my photo, the felt was pulled out of the hole and I sat it on the top side at about the 3 o' clock position.

The ceramic k-77-m has a flat round material , maybe cork, or hard rubber

Not sure about the alinco k-77

The ev ST-350 has no material...I just added the photo to show how easy it would be to add one

The K-79 has no material....i also just provided the photo to show where one can be placed.

None of the above is to say any particular non heritage line of speakers has any of the above components.....the photos were provided in response to the question if the use of dampening material was ever done before on a horn driver.

I thank You Fritz for the pictures!

My CF series driver is a bit different, but this gives me hope!

I see what i am contemplating has been done before.

Like I said, i am gonna do it, and see how it sounds.

If it does not improve the sound, I will remove it, just like I removed the Rope Caulk from my fiberglass Tractrix CF series horns.