Building a Cornwall-compatible Center Speaker

[Def Leper]

Hi folks. I'd like to integrate my Cornwalls into my home theater system and would appreciate your opinions on the following plan:

I have some 3/4" solid core furniture plywood left over from a home improvement project. I'm planning to make a center speaker that will match the sonics of my '84 Cornwalls. I plan to make a "low boy" bass cabinet with the same volume, venting and bass driver as the Cornwall, but in different proportions to fit under my TV. A Cornwall squaker and tweeter will be placed in a separate cabinet to go above the screen. I'd like to update my speakers with new crossovers and the center channel will get a matching new crossover as well. Does this plan make sense? Because it will be a center channel speaker, should I consider a midrange squaker with a lower crossover point?

[colterphoto1]

It makes a lot of sense, I might be following right along with you. I have all the components from a Cornwall (the K600 is the tough one to get- so making a Cornscala would be larger, but might sound better. ) and even got ahold of an empty CW box, yet due to architectural constraints, I might be in a very similar situation as you.

Perhaps DrWho or JWCullison can help us with the cabinet details. I know that you DON"T want to build anything resembling a cube, the dimensions should be varied, like the ideal room dimensions. The port must have the same VOLUME, not just area size.

See JTMalotky's posts for a view of his ceiling mounted wedge shaped 'LS top' he uses for his awesome HT, it uses a double Heresy bottom section, which might also work for you.

Michael

[Def Leper]

....The port must have the same VOLUME, not just area size.

By volume, do you mean the total of the hole sizes (widthXheight) multiplied by the board thickness? I've noticed that most of the ports I see seem to be a round hole with a tube that extends into the the box, which are certainly 3-D spaces with volume.

[DrWho]

Proper port dimensions are a function of mouth area and the length of

the tube....NOT volume. For example, in a 2 cubic foot cabinet you

could have a port tuned to 20Hz with a 0.5 inch diameter and 0.23

inch length, or a 4 inch diameter with 36 inch length. The two have

vastly different volumes, but have the same tuning points. Another way

to look at it: In a 2 cubic foot cabinet a port with a 4 inch diameter

and 36 inch length has a tuning point of 20Hz. However, a port with a 3

inch diamter and a 63 inch length has the same volume, but a tuning

point of 12Hz.

Btw, the ports in your cornwall are "slot type" and you will notice

that there is a big shelf that extends back about 9" or so just above

the ports.

If you stick with the same internal volume of the cornwall then you can

just take the exact same dimensions of the port and implement it into

your new design. Or if you want, we can provide you with other

alternatives that would fit better within the cabinet. In which case,

just give us the dimensions you're looking at building.

[PrestonTom]

Just a thought.

Why not use a Cornwall cabinet placed on its side. If you are more adeventurous, then replicate the Cornwall (and place it on the side), but realign the mid and high for a preferred orientation of the horns.

The advantage is that much of the tweaking has already been done for you, courtesy of klipsch. I would suggest using the same drivers, horns, damping material & crossovers. The voicing should be identical (perhaps differing slightly due to altered peaks & dips due to floor bounce & placement of the ports).

If you are trying to get something more akin to a subwoofer incorporated into this, then certainly ignore my comments.

Good luck,

-Tom

[tofu]

I know that you DON"T want to build anything resembling a cube

then why is it that so many subwoofers are built as cubes?

[DrWho]

I know that you DON"T want to build anything resembling a cube

then why is it that so many subwoofers are built as cubes?

easier to build and generally the frequencies being reproduced by the

driver are low enough such that no standing waves can occur anyway. The

cornwall woofer will be producing notable output well into the 1kHz

region, which can certainly have standing wave issues. A cube just

makes this problem 8x worse.

[colterphoto1]

Proper port dimensions are a function of mouth area and the length of the tube....NOT volume. For example, in a 2 cubic foot cabinet you could have a port tuned to 20Hz with a 0.5 inch diameter and 0.23 inch length, or a 4 inch diameter with 36 inch length. The two have vastly different volumes, but have the same tuning points. Another way to look at it: In a 2 cubic foot cabinet a port with a 4 inch diameter and 36 inch length has a tuning point of 20Hz. However, a port with a 3 inch diamter and a 63 inch length has the same volume, but a tuning point of 12Hz.

Btw, the ports in your cornwall are "slot type" and you will notice that there is a big shelf that extends back about 9" or so just above the ports.

If you stick with the same internal volume of the cornwall then you can just take the exact same dimensions of the port and implement it into your new design. Or if you want, we can provide you with other alternatives that would fit better within the cabinet. In which case, just give us the dimensions you're looking at building.

Who- mouth area x length of the tube = VOLUME of the tube. I checked your figures. the area of the tubular examples above is .5 dia x 1/2 = .25 radius, squared x 3.14159 x .23 " = .72 inch volume port

4 inch x 1/2 = 2" radius, squared x 3.14159 x .36" = .72 inch volume port

looks like the same by my math.

[Def Leper]

Tom, I had thought of that (getting a vertical cornwall) but the squawker/tweeter ends up being too low if it is below the TV screen. Frankly, my big feet when I prop myself up in my recliner would be in the way, hence the desire to move the squawker/tweeter to a position above the screen. Your idea would work fine, though, if I was using a front projector, which would place the screen higher up.

[DrWho]

Who- mouth area x length of the tube =

VOLUME of the tube. I checked your figures. the area of

the tubular examples above is .5 dia x 1/2 = .25 radius,

squared x 3.14159 x .23 " = .72 inch volume port

4 inch x 1/2 = 2" radius, squared x 3.14159 x .36" = .72 inch volume port

looks like the same by my math.

Ummm, for 2 ports with the same tuning point I get pi * (0.25) ^

2 * 0.23 = 0.05 cubic inches for the first port I mentioned and then pi

* (2) ^ 2 * 36 = 452 cubic inches. Last time I checked 452 cubic

inchses was waaaaay bigger than .05 cubic inches, yet they have the

same 20Hz tuning point []

(Ok, I just figured out your math error: It is 36.0 inches, not 0.36 inches for the length of the 4" port.)

The second pair of ports I listed use the same volume, but have different tuning points: 20Hz versus 11Hz (and they are both 452 cubic inches)

[colterphoto1]

sorry, I thought it was a typo on YOUR part.

452 in3 vs .05 in3 is the SAME TUNING?? There's no possible way, please check YOUR math.

Are you really trying to say that a port tube 1/2" x 1/4" long yields the same result as one 4" around and thirty-six inches long. That has got to be incorrect.

Please recheck, this just doesn't look right.

Michael

[DrWho]

I am 100% certain it is correct...I picked such crazy numbers just to

portray the point. The tuning point of a port has nothing to do with

the volume of it, but rather has to do with the ports resistivity to

air flow. Think of it another way....it is really hard to blow through

a long narrow straw, but it is easy to blow through a fat short straw,

even if both are the same volume. It is this resistance that causes the

air to compress and act like a spring.

Then of course the volume of the cabinet changes the tuning too, but

this is where it gets way more complicated because you basically have

two springs. But this turns out to be beneficial and is why the tuning

point of a port isn't a single narrow Q resonance, but rather a much

wider Q resonance.

Since this will probably come up...."why don't we just use the small

ports then instead of taking up so much space with the larger ones?" -

because the air velocity in that tiny port is going to be way faster

than the velocity through that big port - and less air velocity means

less chuffing noises from the port getting overloaded. So the goal is

to simply make the ports as small as possible while also keeping the

air velocity under 20m/s at full volume (20m/s is just a target number

that tends to result in noise 20dB quieter than the signal itself,

though other factors can affect this).

[colterphoto1]

ok, I just thought it bizarre that I got the same number if I just swapped that decimal in there.

Nevermind.

[jwc]

Hi folks. I'd like to integrate my Cornwalls into my home theater system and would appreciate your opinions on the following plan:

I have some 3/4" solid core furniture plywood left over from a home improvement project. I'm planning to make a center speaker that will match the sonics of my '84 Cornwalls. I plan to make a "low boy" bass cabinet with the same volume, venting and bass driver as the Cornwall, but in different proportions to fit under my TV. A Cornwall squaker and tweeter will be placed in a separate cabinet to go above the screen. I'd like to update my speakers with new crossovers and the center channel will get a matching new crossover as well. Does this plan make sense? Because it will be a center channel speaker, should I consider a midrange squaker with a lower crossover point?

Def Leper

If you are still deabating on what you should do, I can give you my two cents.

I went through your situation a few months ago. I also considered the split speaker with the mid and tweets on the top of the TV. I had a few concerns with this but I don't know whether they would be a real problem or not. If the networks are 1st order like most of the Cornwalls out there, the midhorn and the woofer are duplicating the some of the same frequencies albeit at a lower dB. Wondering if this will be a problem with "voicing" at the center or with any music in general when the two drivers are seperated like that.

How large is your TV and how far back are you sitting. In my situation, I didn't think I was sitting far enough back to allow a seperated speaker to integrate well.

Will you be using this center mainly for movies or for surround music. If it is only for movies, I wouldn't be too concerned about having a bunch of low end. This could be completely oversight on my part...not sure. I also didn't want some hard hittin bass that close to my TV. My center channel is used solely for movies. Although I have played some surround DVD-A through it and it was nice.

If you want specs on a bass bin that will be like a Cornwall..port and such...I can send you some info on the measurements. Easy to find flaws on paper with the current K33 and the cornwall port. However, there is much confidence in it's sound that way because of the ton of Cornwalls out there with a stern following.

You question of the midhorn. I would go for the K600 or K601 if you've got the parts. The K600 is hard to find and can be sold pricey. The K401 is better and cheaper but not the PERFECT match. Although I would say it's better.

With the above, I ended up choosing a K55/K401, K77, K22 all in one enclosure. Have the speaker set as "small" in the HT setup. However, I am matching some Cornscalas with the same mid horn and driver. The cabinet is smaller and went under my TV.

Hope this helps some.

jc

[formica]

I had a few concerns with

this but I don't know whether they would be a real problem or

not. If the networks are 1st order like most of the Cornwalls out

there, the midhorn and the woofer are duplicating the some of the same

frequencies albeit at a lower dB. Wondering if this will be a

problem with "voicing" at the center or with any music in general when

the two drivers are seperated like that.

I'd also be concerned with separate bass and mid cabinets if you are

sitting relatively close to them. Although I haven't tried it, it

seems like they would appear as two separate audio sources given x-over

points involved, as well as the risks of cancellations at those

frequencies.

Have you considered installing the whole speaker above the TV...

Sounds huge, but you could be surprised if you vary the proportions...

ROb

[DrWho]

I would favor installing the whole thing above the screen too...you can get clever and inset parts of the cabinet up into the cieling or wall between the joists. I bet you could hide at least half the cabinet this way.

[Def Leper]

Puting the system above the screen isn't going to be possible at this point. My spouse is forebearing of my TV room because she enjoys using it too, but I some of the pictures I've seen of forum member's systems would put me right in the doghouse. I have a remodeling project coming down the pike in a few years that will move the TV and sound system into a "great room" with a false wall, and having the center speaker above the TV will work in that scenario. However, I plan on switching to front projection, which will likely place the screen too high. OTOH, it might be high enough to allow placement below the screen and still keep the higher frequency components above "foot level."

Would it make sense to check out some of the current Klipsch center channel speakers? My current center channel is JBL. It's OK, but simply lacks the presence of the Cornwalls. Perhaps a newer Klipsch center channel speaker will work until I get moved into the new room?

[DrWho]

You might try an academy.

It will have a pretty good resale value too.

[colterphoto1]

Who, no offense, but now yer back to square one.

I think he was trying to do something inventive that would be an exact match to the CW, we've gone from modifying the box shape and possibly splitting the components, to hanging the whole thing, to sodding the entire project and purchasing an Academy?

I'm going to make my center CW, it'll be a perfect match. Anyone care to join me?

Michael

[DrWho]

I totally agree, but an academy will still be a huge step up from his

current JBL center. Since he's for sure going to be moving to a new

house with a dedicated room, then I would save the custom built center

for that time so that he doesn't have to predict his exact situation in

the future. With a projection system he will for sure be able to fit a

veritical cornwall on its side. Why make comprimises on a custom center now that won't need to have been made in the future?