"Minibox" upgrade

[redwood forest]

I am using K-horns on the sides with a LaScala in the center, and the same Mark Levinson amps for all speakers. While all speaker drivers and amps are identical, the sound was noticeably inferior in the center. It then dawned on me that the only difference between the center and the other speakers was the use of the minibox with it's three resistors to create the mono effect. Two 27K Ohm resistors go from left and right inputs to the center output, and a 27K Ohm resistor goes from the center output to ground. That's it! The other four resistors are not needed, because I'm using separate preamps to individually control the three channels. A "Y" spliter is then placed on the source of each channel with one lead going to the K-horn preamp, and the other going to the minibox input used by the LaScala. This allows the K-horns to bipass the minibox entirely.

To improve the minibox, I then replaced the standard $ .10 resistors in the minibox with $ 10.00 Vishay S102C bulk foil resistors, and instantly the center channel was as good as the others. While this seems like an expensive tweak, the difference was very rewarding. I would recommend this change in your minibox if you find that you are not satisfied with sound of your center speaker. Nothing will make your center speaker sound as good as the other speakers if the center speaker is not the same quality. However, it's amazing how by upgrading three resistors in the minibox will cause such a drastic improvement in the sound of center speaker.

[Daddy Dee]

Thanks, that's interesting. How far apart are your Khorns?

[redwood forest]

The K-horns are ten feet apart forming an equilateral triangle with the sweet spot. I was able to do this with false corners. The hole in the center is not as obvious as when the K-horns are in the corner, but the center speaker does make a difference in making the image lifelike across the entire wall. Before changing the minibox resistors, the center sound was raspy. Now it's perfect!

[mark1101]

My biggest issue with the minibox is that the timing is off. The center channel needs to be delayed. With the K's in the corner the seating position is actually closer to the center channel than the L/R. I am getting very similar sound from my center cornwall to the K's......but I still bet you are right about the better resistors. It's just that the timing issue is very evident to me. You wind up with with a compromise. You plug the hole in the middle, but get some mud added to the image. On certain music I don't use the center channel. My K's are 24' apart. Otherwise I love the minibox. It works great.

I remember a forum member discussed running the minibox output through a surround sound receiver rear channel so you could use the adjustable delays they typically have. Pretty smart. I never tried it because my HT amp is in use in another room.

Does anyone know of any other cost effective delay device?

[redwood forest]

Good point, Mark; however, what I do to avoid the time delay is to place all of the speakers in an arc so all of the speakers are the same distance from the sweet spot. You can do that by using false corners and bringing out the K-horns so they are closer to the sweet spot. I am surprised that it took 60 years for Klipsch to finally build false corners into the K-horns. However, after the 60th aniversary model was gone, so were the false corner additions. Oh well, back to the status quo.

[PrestonTom]

Mark,

You are absolutely correct about the timing differences!

Part of the problem is lessened since the center channel is typically decreased several dB in gain. The timing is still different, but there is less contribution.

A cheap method of delay would be a Behringer DCX or DEQ-2496, these are less than $300 and it can do other things as well. If the delay is exaggerated (so it actually arrives substantially later than the mains) this could help create an illusion of depth (probably requires some fiddling around ...). However, there may be some other consequences also. Personally I would only recommend the Behringer if you can feed it a digital signal and use pre-amp afterwards (this is to eliminate an extra conversion and it also maximizes the SNR).

Good Luck,

-Tom

[mark1101]

Tom, thanks for the info.

[redwood forest]

It's just that the timing issue is very evident to me. You wind up with with a compromise. You plug the hole in the middle, but get some mud added to the image. On certain music I don't use the center channel. My K's are 24' apart. Does anyone know of any other cost effective delay device?

What is the advantage of having the K-horns 24 feet apart? Unless you are using the short wall in a 24' x 36' room, the speaker to sweetspot angle is too extreme, probably 90 degrees. Perhaps you like listening from the conductors position, which is fine if that is what you want. With a 90 degree listening angle, Mary would sound like she is sitting at the front of the stage while Paul's voice would be from a distance aimed directly at your right ear, and Peter's voice would be aimed from a distance directly at your left ear. Sorry if I'm showing my age. Not only is there a sound delay problem, but an image positioning problem as well. I've been there and done all that while in my previous home. False corners will not only allow you to move the K-horns closer together, but move them outward into the room. While keeping the center speaker up against the wall and moving the K-horns outward, will create an arc that will keep all of your speakers equal distance from the sweetspot. This will eliminate the time delay problem. The false corners need only come to the front of the speakers so they won't be seen from the sweet spot. This will also solve the WAF problem. I hope this will take care of all of the foreseeable problems.

[mark1101]

My corners are 24" apart, and that's the long wall. The room is approx. 24x18. In that room I don't have any other options. The sound I'm getting is excellent though. I don't have any issues there. I just need to delay the center channel. I just may replace the resistors in the minibox as well for the fun of it.

As far as the false corners, that's just something I won't need to do. I'm sure they work as many others have done that with success. Sounds like it is working for you.

Thanks for the tip on the resistors.

[redwood forest]

Glad I could help. Vishay plays hard to get when it come to giving out distributers for their products. Guy Hammel, the owner of Placette Audio uses nothing except Vishay S102C resistors and one of his sources has the following email address: haim.shmutz@vishay.com . It doesn't matter If you use the 3 resistor or 7 resistor minibox, because all resistors used will be 27K Ohm. Good luck.

[Klewless]

I think there is more at issue than simple delay for the derived center channel  (sum).  I believe that the Center should only receive the delayed L+R sum as suggested AND the Sum should be removed from the L and R channels also.

I am using a Rotel HT receiver in 3-channel operation.  I mean by that I set the receiver up for 5-channel mode, fail to connect any rear speakers (which prevents the decoders from sending rear info up front because it thinks there are some speakers hooked up back there), and appropriately delay the Center.

I also believe that in some of the decoders the Center info is also deleted from the L/R channels and only the Sum gets to the center.  When I play a mono source, ONLY the Center is operating.  L and R are dead silent as well they should be.

I am very happy with the  resulting sound.

[redwood forest]

Klewless, this is an interesting concept of making the center channel mono without any left or right information. Wouldn't this have some negative effect on the total wall to wall image? With my mono channel including all of the left and right information, the overall image has equal loudness from wall to wall, and the location of every instrument is well defined and focused. I would think that with only mono sound from the left and right channels, the amount of information fed to the center speaker would be very restricted. What effect does this technique have on the total wall to wall image?

[PrestonTom]

I think there is more at issue than simple delay for the derived center channel (sum). I believe that the Center should only receive the delayed L+R sum as suggested AND the Sum should be removed from the L and R channels also.

I am using a Rotel HT receiver in 3-channel operation. I mean by that I set the receiver up for 5-channel mode, fail to connect any rear speakers (which prevents the decoders from sending rear info up front because it thinks there are some speakers hooked up back there), and appropriately delay the Center.

I also believe that in some of the decoders the Center info is also deleted from the L/R channels and only the Sum gets to the center. When I play a mono source, ONLY the Center is operating. L and R are dead silent as well they should be.

I am very happy with the resulting sound.

With all due respect, I thinks this advice needs to be carefully re-considered. It is going to lead to a number of problems.

The center channel as PWK envisioned it, was only meant to fill in the "hole in the middle" It is not meant to reproduce that much material. Much of a stereophonic recording is common (or mostly common) to the both the L & R channels. This is typically the vocalist and percussion etc. The center channel itself should not even have much relative gain.

I would not deviate too far from the original recommendation.

Good Luck,

-Tom

[Klewless]

You are absolutely correct.  Consequently I do not listen to that mode (Neo6) for mono sources.  I discovered this effect when I scanned through an FM station which was mono because of poor (weak) signal.  I was surprised and went to all three speakers to verify that what I heard was really happening.  I thought I had lost my L/R mains.

I only mentioned it to illustrate that HT decoders are available which can separate channels.  Stereo is decoded as true stereo without shrinking the image width.  The resulting sound is a lot like listening to one of my 3-channel sources from the 50's, which I have on an SACD.  No matter where I go in the room the center channel sounds like it is where it belongs.

I also realize that in the real world there will be sounds from all channels in all channels.  However these signals are properly delayed by the physical distance between performers.  I also realize that the sound path from performers to playback systems is far more complex than I understand.

Learning from people's comments on this forum is one of my greatest pleasures.  I have been interested in stereo ever since my hero, Mr. Paul Klipsch, answered a letter from a clewless teen.  Now I own Khorns, LaScalas, Cornwalls, and Heresys.

[mark1101]

Klewless,

It sounds like your HT receiver is creating fine ambience in your room. However, you are probably not producing the same center channel signal that PWK created with his minibox. There is obviously no center channel information in a stereo signal. It is simply derived via L+R in the minibox.

I'm guessing now.....but in my HT receiver (Denon) it is not simply adding L+R....it is first looking for a specific center channel signal (I.E. 5.1, etc.), then if it doesn't find one.....it "simulates" one with some digital enhancements. There are specifc modes to create a "ghost" center channel on most HT receivers.

When folks on this forum talk about the so called "center" channel and PWK minibox, they are specifically looking for the simple L+R signal. All it does is fill in the center of the room with = information from each speaker (L/R). As you move from the center of the room to either the right or left you get the correct increase / reduction of each channel. It's use is solely to fill in between 2 speakers that are too far apart. It adds no processing or special effects.

What PWK minibox folks are specifically not looking for is some sort of simulated, or enhanced "ghost" center channel.

[redwood forest]

Mark,

I agree with your view that the image created from the minibox should not be changed. The image is natural and smooth from wall to wall with no abrupt emphasis at the center. What is really nice about the untampered minibox is that by making the center louder, you can actually make the image narrower for those that have K-horns that are too far apart. This also works with trios having two on the far sides and one in the middle. As I increase the volume of the center channel, I can actually "see" the left and right side sources gradually move toward the center. All that I've heard so far from this forum is the use of the center speaker to fill in the center hole by having the center channel volume slightly less than the sides. Even with this narrow image, the spectrum across the wall is still smooth and even, though not as much as if all the speakers had the same volume. Perhaps with the center speaker being louder, the time delay between the K-horns and the LaScala in the center won't be as obvious. How's that for a partial solution?