Cornwall Port mod

[Klipschguy]

My Cornwalls have an annoying peak (according to my ear and meter) around 40Hz (yes, I think it is a room problem - the Cornwall is still a good design). It is just more boom than I want in my current listening room.

After reading a lively thread on ports, I am considering modifying my Cornwall ports to lower the tuning point. Tuning the box to about 36Hz sounds good to me. I know I could lengthen the port or narrow the existing one to decrease the tuning frequency.

Narrowing is certainly easier (vs. lengthening) and is "more reversible." But will I get noticable port noise?

Will this idea work? Any recommendations? Can I just stuff a 3"x7"x9" piece of foam rubber to one side of the port.

Thanks for your input,

Andy

[BiggerIsBetter]

It must be a room thing, and your lucky. Mine drop like a brick around 70 in my room. I would play around with room positioning first. A small move might make a big difference

[JJkizak]

I really think you should try different things than messing with a superbly

designed speaker. New Crossover?

JJK

[Daddy Dee]

Well, I certainly think that's a creative and easily reversible solution.

I hope you check it out and post on the results.

[Klipschguy]

I have had these Cornwalls in huge rooms and in smaller rooms (14x16). They sound better in the huge rooms, imho. Anyway, the mids project much better with the speakers in the corners (to my taste), but they boom distastefully. The bass sound better with the speakers pulled out of the corners, but the mids and highs suffer (the projection and tonality, not the imaging). Corner bass traps are unacceptable esthetically. If I can't get the bass right, I will banish these babies to the basement for storage - and they have been my mains for almost 15 years! Right now a small pair of two-ways I designed (plus a sub) are outperforming the corns due to the 40-45hz boom.

Andy

[DrWho]

Adjusting the port tuning in the stock cornwall cabinet is only going

to result in changes to the 60-100Hz region - so I don't think this is

the best approach to fixing your problem.

But if you wanted to change the tuning to 36Hz, then you need to shrink

the width of your port down to 13" wide, keeping the stock length and

height.

[D-MAN]

Why not tackle the real problem - the room. A bass trap or two would do ya.

As for making mods, DrWho is right, the volume of the cabinet determines its resonance, and you wouldn't be changing that by modifying the port area except you could move up or down a couple of Hz. Probably not enough to effect the room resonance...

DM

[Klipschguy]

Thanks guys. Why would lowering the tuning frequency affect the 100Hz region instead of the low 40's? The plot looks looks like it will reduce output around 40Hz to 50Hz. The reason I do not want bass traps is esthetic in nature.

Andy

[D-MAN]

I do not think that it would effect the 100Hz range at all. Perhaps he'll explain his thinking.

The enclosure volume is not changing MUCH * (nor does the driver in question), therefore, the enclosure resonant frequency does not change. Adjusting the port volume would effect the frequency it resonates at to a degree, but will be limited by available space constraints and the natural Fr of the enclosure (and driver) combination, but it is certainly acceptable that it could be altered as much as 10Hz by changing the port length (and overall volume) which alters the mass (air plug). Making it go lower would mean lengthening it or otherwise increasing its area/mass. Keep in mind that these are "subtle" changes to the length of the duct only.

The formula for a Helmholtz resonator (from Keele) is attached.

* the volume of the port is removed or added to or from the Fb, depending on whether one is shortening or lengthening the port "duct".

DM

[DrWho]

here's a rough model of a lot of different tuning points for the same enclosure:

(green = stock cornwall)

[DizRotus]

I have had these Cornwalls in huge rooms and in smaller rooms (14x16). They sound better in the huge rooms, imho. Anyway, the mids project much better with the speakers in the corners (to my taste), but they boom distastefully. The bass sound better with the speakers pulled out of the corners, but the mids and highs suffer (the projection and tonality, not the imaging). Corner bass traps are unacceptable esthetically. If I can't get the bass right, I will banish these babies to the basement for storage - and they have been my mains for almost 15 years! Right now a small pair of two-ways I designed (plus a sub) are outperforming the corns due to the 40-45hz boom.

Andy

You need some rear loaded RS 40-1197s.

[Klipschguy]

Well I would Neil, except I can't remeber what I did with my 4" full ranges. Can't seem to find 'em anywhere!....kidding of course, but I have been thinking about firing up the FE83 MKII Buschhorns lately. I 've been listening to (and playing) a lot of classical guitar lately and those backloaders do a great job reproducing the acoustic instrument - for real.

Seriously, I would like to get the mighty Cornwalls straightened out. I have lived in a number of houses; each listening room has had particular ideosyncrasies, but I have always been able to get the system right - until now. Maybe a parametric equalizer is the answer. I wish I could just stick a big piece of foam rubber in the sides of the ports and viola - fixed. From D-Man's and Doc's posts, my epiphany/idea is not as sweet as I hoped it might be.

You know, I seem to recall some article on extending the CW port length to tune the box to 25Hz. They had the port in an "L" shape. Seemed like it was in an old audio magazine.

It is truly incredible how much difference the room makes. We talk wires. What about the room!

You guys are great,

Andy

[DrWho]

It is truly incredible how much difference the

room makes. We talk wires. What about the room!

Makes you wonder what those wire people are hearing doesn't it? []

The cornwalls do have a bump in their response at 80Hz (even more than

the model shows)...the fact that it is a harmonic of 40Hz makes one

wonder if you weren't hearing an 80Hz problem (80Hz could definetly be

amplifying it).

You could further flatten the response of the cornwall by changing it

to an 8 cubic foot cabinet....keeping the port exactly the same results

in a 39Hz tuning with the new volume. The rear panel is removable so I

can't imagine it being too hard to build yourself a new rear panel that

adds 2 extra cubic feet of space....perhaps do it in a triangle shape

so that it tucks into the corner real nice.

Just for kicks, try walking around the room as you listen and notice

how different the bass response is at different positions. You might be

able to move your listening position and get away from the annoying

resonance (and shift it to a new frequency) []

You really should look into room treatment...and it really doesn't have

to be ugly either - though it's hard to suggest ideas without seeing

your room and knowing what you find aestehtically pleasing.

[DizRotus]

Well I would Neil, except I can't remeber what I did with my 4" full ranges. Can't seem to find 'em anywhere!....kidding of course, but I have been thinking about firing up the FE83 MKII Buschhorns lately. I 've been listening to (and playing) a lot of classical guitar lately and those backloaders do a great job reproducing the acoustic instrument - for real.

Andy

Andy,

You prompted me to listen to some acoustic guitar from your/my RS 40-1197s in rear loaded horns. As I type, Earl Klugh is sounding pretty good.

I'll follow your Cornwall taming efforts closely. When I have the time and money I plan to build a Cornscala type enclosure, but for the now the speakers made with the drivers that you gave me serve nicely. Thanks again.

[hwatkins]

D-Man's answer has my vote on what to try. If it is a hump, you may get enough effect to make a difference (although I wonder if you can).

Who's comment on the 80hz possible problem really makes some sense to me as well - the longer it sits in my head the more sense it makes. It would be a pretty good thing to check out. I am thinking that a noticable hump at 40hz on a Cornwall would be pretty hard to make happen.

Good luck and let us know.

[DrWho]

I am thinking that a noticable hump at 40hz on a Cornwall would be pretty hard to make happen.

Exactly what I was thinking...especially in the "undersized" cabinet.

[colterphoto1]

Perhaps this is just the stuff of Legend, but Klipsch is a LEGEND IN SOUND.

It is my understanding that the Cornwall was tuned using only the ears of the engineers at the time, using a sliding door type mechanism over the port. Also that later when the Thiele-Small parameters were published (with PWK adding to the wealth of knowledge) that the CW's volume and port dimensions were within 3% or so of being the 'ideal' for the K33 driver. Perhaps that is why is has such smooth bass and is such a universally-liked cabinet design.

I'd fix the room, not the speaker. Just my .02

Michael

[Klipschguy]

Okay I got the meter and test CD out yesterday and as I suspected, The Cornwalls were +10dB to 12dB (relative to 1000Hz) at 40Hz and 50Hz . Corns were also 6dB down from 60Hz to 80Hz. Falling fast below 40 and about +6dB @ 100Hz. It is a room problem. The room is 16'x18' with the Cornwalls on the long wall. NO subwoofer in effect here, these are the Cornwalls singing solo.

I tried blocking off 1/2 the ports. The meter said: "little if any difference." Scratch that idea.

I tried moving the speakers all around. The meter said: "a little difference, but you still got a problem." Okay I'll take any little improvement and move on to something else.

Then I turned the sub on and used the phase control to create destructive interference. This worked well. I could actually use the phase control to null the peak below reference level. Of course I adjusted it to match the level of the 1000Hz tone. Using the sub as an active bass trap is a good idea. Please note the CW's fall like a rock below 40HZ, so the subwoofer's bass was back on line below 40Hz to actually give me +2dB @ 30Hz (down 3dB @ 25Hz, down about 7dB @ 20Hz).

I couldn't touch the 100Hz peak with the phasing trick. I might have to do a little eq.

Conclusion: Although much improved, a speaker that once sounded glorious in a 22'x30' room are now suffering from claustrophobia and have a decent chance of being replaced by a small pair of two ways that currently still sound better. Believe me, I want the Klipsch to win!

Andy

[colterphoto1]

Where are the CW's located on the long wall? I'd suggest moving them well in from the corners, perhaps as much as 3-4 feet if you can do that, then angle them in toward the sweet spot, which might help somewhat.

How much upholstered furniture is in the room? My guess is that it's pretty spartan?

If you do have to go with Lernd-style foam corners, there are interesting architectural ways to disguise them. Keep on trying and experimenting.

[Klipschguy]

Spartan? Two couches, two large arm chairs, large coffee table , end table , big fake tree in the corner, huge Credenza, two Cornwalls, subwoofer, huge persian rug, classical guitar on a stand...

Pulling the CW's out from the corners helps in some ways, hurts in others, but it still does not solve the fundemental problem. Trust me, I've been messing with this thing for a while before asking you guys for suggestions (which certainly are appreciated).

I have set up a lot of systems in rooms over the years and have fully come to the realization that the system must fit the room. Imagine sticking a pair of Khorns in your bathroom and then striving for sonic bliss. Some small bookshelf speakers would sound much better in that environment.

I may try a parametric equalizer. Do they make one that looks like a home component that is not to expensive? Also, I'm currently using 16ga speaker wire, do you think larger cables might do the trick (sorry, I couldn't help myself - the laughter made me feel good).

I appeciate your help. Sorry about the frustrated nature of my posts, but I know how good these speakers can sound in the right room. Defying physics is an uphill battle.

Andy