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How to dial in a center channel


bracurrie
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System Overview: 2 channel active crossover 2 way Jublilee clones with Eliptrac 400 horns and Faital HF200 drivers. Crossover and EQ as close to ideal as I have ever had them. Center channel is for now a Forte II elevated off the floor to mate the height of the HF drivers. Center is driven with a DBX Driverack PA+. I am using the LF section normally devoted to Subwoofers where the right and left channels are combined to a single output. I set the Xover points all the way out on the high frequency side and low frequency side to get a full range signal.

So I have the ability to adjust the gain and the delay of the signal. Plus I can also roll off the low end to clean up the bass which I have already played with and discovered that rolling off the bass of the center channel at 50Hz took alot of muddiness out of the sound.

So what I want to know is how should I go about dialing in the center channel? I can generate test tones and measure with REW or I have a test CD Point of Reference that has a number of usefull test tones like pink or while noise. I also have a RS db meter.

I have the DBX right next to my listening chair and I have been trying to just listen and tweak. I noticed that when I got to a certain delay that the center channel image faded or blended in better. But on further delay it reappeared then disappeared again.

If anyone has a procedure in mind or a link to a resource for one I would be much obliged.

Thanks

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Plus I can also roll off the low end to clean up the bass which I have already played with and discovered that rolling off the bass of the center channel at 50Hz took alot of muddiness out of the sound.

So what I want to know is how should I go about dialing in the center channel?

Go ahead and roll it all the way up to 80 Hz. The center is close enough to the mains to be interfering below that. [8]

That, and toe in the Eliptrac horns some.

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Brad,

This is just my take, you've got a fabulous system with your Jubes. IOW i don't think you will improve upon that, in your room, with a center channel.

I worked a long time to try to integrate a center channel into a system with Khorns in a room a bit larger than that. No sour grapes here, i just was not able to do anything that made the khorns sound better than they already did.

i think PWK's use of a center channel was to fill in a "hole" in the sound which occured in much larger room with Khorns spread to the corners.

center channel is not a bad thing at all. it's just very hard to improve on near perfection.

if you do get it dialed in so it sounds better to your ears, great. please post on the technical issues.

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i think PWK's use of a center channel was to fill in a "hole" in the sound which occured in much larger room with Khorns spread to the corners.

When I placed my Jub clones in the corner with the HF pointed in the same angle (I guess that would be 45 degrees) I experianced a hole in the middle of the sound stage. But I also experianced the enhanced bass presence that I really like alot with the bass bins in the corner. I had the equipment alrerady so I am out nothing but time and trouble.

Because I am using the tape outs to feed the DBX I cannot change the volume without adjusting the gain on the DBX as well. If this center channel thing works out I will have to come up with a solution that I can drive with the main outs of my preamp.

Further technical details:
Time delay settings for the HF horns 2.86 ms which equates to .984 meters.
The Forte II center channel drivers are roughly in line with the HF horns on the Jub clones. Time delay is currently 1.475 meters or 4 ms.

My geometry skills or more than rusty and I haven't measured the distance directly so I was hoping to discover a sonic way to dial in the delay.

Thanks for the reply.

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you've got a fabulous system with your Jubes

Indeed the Jub clones are great, but until I put them in the corner the bottom end wasn't as pronounced as it is now. But with them in the corner the sound image had a hole in the middle. Hence the center channel. The challenge is to take nothing away from the two channels and fill the hole. It has thus far been worth it, with more to come as improvements come with I hope a La Scala Bass bin coupled with the same horn tweeter I am using on the two channel.

if you do get it dialed in so it sounds better to your ears, great. please post on the technical issues.

So I took the suggestion to roll off the low end of the center channel at 80hz and yes it cleaned up the bass even more than rolling it off at 50hz. I tried going as high as 160hz but then center speaker disappeared too much and as I added gain the center speaker would go from gone to way too much out front all of a sudden. I am doing this all by ear using a pink noise signal because I know of no other way to go about it.

Time delay is also another interesting adjustment for the center channel. While the pink noise signal demonstrates little as far as time delay is concerned, music demonstrates an interesting effect. Once the center channel is in time alignment and as I increase delay the sound stage will widen and the center channel's presence diminishes. If I keep adding delay the sound stage narrows again. Then at some point as when I came from delay=0 to the first widening of the sound stage, the widening effect will not come back. So my question is what kind of source material should I use to tune the delay? Should I use the middle instance of sound stage widening, seems there are four or five of these in phase to out of phase transitions before additional delay no longer results in the widening sound stage effect.

I was listening to Patty Loveless - Mountain Soul and I am convinced that I could detect the three dimensional positioning of the band. Reminds me of the first time I heard a well setup system using early KEF speakers. As I recall it was KEF's calling card to design a speaker system where timing of the components was taken into consideration from attack through decay.

In my room, the center channel setup seems to work, but I want to see how much better it can be with a horn bass bin and matching HF.

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  • 2 weeks later...

I have fooled myself on several occasions when the center channel was off. The higher quality recordings do not seem to need the center channel as much as other lower quality recordings. Alison Krauss's recordings project such a solid image across the left and right speaker that I actually thought the center channel was on, but the speaker selector switch was off. Lower quality recordings seem to benefit much more from an active center channel, so I will probably keep it.

Has anyone else experienced such a solid center presence with a two channel corner placed speaker setup and what recordings did you experience it with?, it

It appears that with a great horn and driver that is properly delayed and where the first reflection point on the sides is mitigated then imaging in the center can actually occur with some recordings. To my surprise it is happening for me with the forte II stuck in the middle as a center channel not emitting.. Do I dare see what happens if I remove the Forte II?

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Brad,

This is just my take, you've got a fabulous system with your Jubes. IOW i don't think you will improve upon that, in your room, with a center channel.

I worked a long time to try to integrate a center channel into a system with Khorns in a room a bit larger than that. No sour grapes here, i just was not able to do anything that made the khorns sound better than they already did.

i think PWK's use of a center channel was to fill in a "hole" in the sound which occured in much larger room with Khorns spread to the corners.

center channel is not a bad thing at all. it's just very hard to improve on near perfection.

if you do get it dialed in so it sounds better to your ears, great. please post on the technical issues.

gotta agree with Dee, i tried everything between my k-horns ( 20x 27 room ) starting with a rc-3/heresy/academy/vertical cornwall/belle and finally a lascala, which sounded the best but never really perfect. even my dealer told me not to use one.

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Has anyone else experienced such a solid center presence with a two channel corner placed speaker setup and what recordings did you experience it with?

Yes: all the time--with all my 2-channel recordings, as long as my ears are pretty much on-axis within a foot or two of centerline between the speakers. In fact, I can hear the degree to which the recordings didn't put in enough stereo information to spread the sound out into the front sound stage, and the worse the recording is in this respect, the more monaural it sounds--which is also fairly boring.

This is actually the core subject of The Corner Horn Imaging FAQ. In particular, use of "zero reflection zone" near field sound absorbers in proximity to your midrange horns, on each side of the midrange horns and on the floor touching the front of the speaker, out to about 3 feet. Also place absorption on any sound reflective surfaces between the front speakers, and it will enable an amazing phantom center image to a degree that you might not believe is possible.

mikebse2a3 (i.e., Miketn) also proposes the use of diffusers in smaller rooms in order to avoid overdamping the diffractive field of the room.

Chris

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toe in the Eliptrac horns some

+1...in fact I'd recommend turning your bass bins until they are on centerline with your HF horns, i.e., no "twists".

So what I want to know is how should I go about dialing in the center channel?

I believe that it's 99% about "timbre matching" with your fronts. If you can't achieve a timbre match then I've found that most other adjustments are like arranging chairs on a sinking ship... [:o]. It took time alignment for me to achieve that with my setup, but it can also be achieved simply by using the same midrange/tweeter horns, drivers, and crossovers as the fronts.

Chris [:D]

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I noticed that when I got to a certain delay that the center channel image faded or blended in better. But on further delay it reappeared then disappeared again.

Congratulations! You have both discovered the secret to setting center (or any other delay) and have refined your listening skills to a very high level to be able to do this.

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Has anyone else experienced such a solid center presence with a two channel corner placed speaker setup and what recordings did you experience it with?, it

Yup. Music-wise, Bjork & Sinnead O'Connor come to mind right off the top of my head. There are others, but I'd have to thumb through the library. That and any of our movies with a 5.1 mix will do the same, like the "Hell Freezes Over" DVD for example.

IME, pretty much anything with a dry vocal mix and the system will plunk the voice down dead center.

To my surprise it is happening for me with the forte II stuck in the middle as a center channel not emitting.. Do I dare see what happens if I remove the Forte II?

This is actually one of Danley's favorite parlor tricks when showing off his Synergy horns. He'll have a center channel that's not playing anything, yet everyone will swear it's on. It's the result of proper setup more than anything, and a very good indicator that your system is positioned correctly in the room. [Y]

FYI - It could be easy to mistaken the filter frequency settings on an AVR as an option for band-passing a speaker because of it's ability (or inability) to play low frequencies. Although that can play a small factor in determining a set point, the over whelming auditory issue is to structure the speakers' low frequency behavior in order to keep the system from cancelling itself out (from other speakers or the room).

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As usual, Chris, you bring clarity to us "duffer wanna be audio experts". Thanks.

Has anyone else experienced such a solid center presence with a two channel corner placed speaker setup and what recordings did you experience it with?

Yes: all the time--with all my 2-channel recordings, as long as my ears are pretty much on-axis within a foot or two of centerline between the speakers. In fact, I can hear the degree to which the recordings didn't put in enough stereo information to spread the sound out into the front sound stage, and the worse the recording is in this respect, the more monaural it sounds--which is also fairly boring.

What i am observing is that some recordings do in fact have a wide sound stage but have a hole in the middle.

This is actually the core subject of The Corner Horn Imaging FAQ.

I had read your excellent Corner Horn Imaging FAQ and its what led me to try the center channel as I just couldn't get the hole in the middle to disappear. The one thing that changed was I tried, after installing the center channel, was toeing the HF horns more on axis with my listening position. What baffles me is how the presence of the Forte II (not playing) seems to not hurt the effect. I will next take it out and see what happens.

I just noticed that my photo of the speaker system doesn't show the acousitic panels that absorb the first reflections from the HF horns. I know this helps because I tried it without the panels and the imaging wasn't there.

BTW I work at a desk on the other end of the room from the speakers which is a good 5 to 6 feet past my listening position and the center presence is obvious there too.

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It took time alignment for me to achieve that with my setup, but it can also be achieved simply by using the same midrange/tweeter horns, drivers, and crossovers as the fronts.

Does this comment apply to a HT 5.1 or similar setup?

1...in fact I'd recommend turning your bass bins until they are on centerline with your HF horns, i.e., no "twists".

I just tried removing the twist and the imaging disappeared.

Now I need to resit the temptation to try K402s.[:P]

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I've had a center channel (Belle) between two Khorns for a few decades. Until I acquired a McIntosh preamp/processor that had a center channel output I used the Klipsch phantom center channel circuit described in the Klipsch Dope From Hope newsletter. I used a high resolution pot to adjust the gain. With the McIntosh I had to use the volume control on the center channel amplifier to adjust the gain. More recently I acquired a Behringer DEQ2496 and also adjusted the delay by simply measuring the distance difference from the midrange voice coils (all three speaker used the same driver) and dialing that into the DEQ2496.

In general I think you'll find that you need to lower the center channel gain about -3dB to -6db. However this is highly dependent on the recording as well as the type of source (both recording and playback device). Analog tends to have more crosstalk and therefore more center channel bass than digital sources or recordings (summing the bass signal tends to create more apparent bass ~ try it if you have a stereo/mono switch).

Adding a center channel, like everything else, has its own benefits and caveats. If your speakers are 27' apart like mine were then the benefits probably out weigh the detriments. On the other hand, if the L+R speakers are large and less than 15' apart the benfits are minimal, possibly detrimental for stereo reproduction. HT OTOH is a different animal since all channels are discrete.

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I've had a center channel (Belle) between two Khorns for a few decades.

Thanks for chiming in. I don't have all the same drivers so I am guestimating the delay. Since the speaker in the middle is driven by a single amp using my DBX driverack PA+ I am adjusting the gain by ear. My 2 channel speakers are just at 15 feet apart and with most good recordings the center channel isn't needed to have a full image without a hole in the middle. I have the bass on the center speaker rolled off sharply at 80Hz, after a forum member suggested it, as the low end seemed to suffer with the direct radiator of the Forte II mixed in with the Jube clone horn.

One thing that I have failed to mention is how with the center channel on the stereo image is more apparent in more of the room, even playing back material that doesn't need the center channel when seated in my listening chair.

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I've had a center channel (Belle) between two Khorns for a few decades.

I have the bass on the center speaker rolled off sharply at 80Hz, after a forum member suggested it, as the low end seemed to suffer with the direct radiator of the Forte II mixed in with the Jube clone horn.

One thing that I have failed to mention is how with the center channel on the stereo image is more apparent in more of the room, even playing back material that doesn't need the center channel when seated in my listening chair.

You can trust Tom's (Quiet Hollow) advice. He has some pretty good and practical engineering background unlike some other wannbe engineers around here.

One thing you have to keep in mind is that the Forte uses a direct radiator for the bass and has higher throughput distortion. Klipsch has always (since the LaScala and Belle at least) recommended a fully horn-loaded center channel speaker when the flanking systems are fully horn-loaded. There's just to much difference in voicing between the two (direct radiator and horn) that makes integrating them much more difficult. Don't forget, the first 4 to 5 octaves of music, about half of the musical frequency range is in the bass range.

With Klipsch I've always found the center speaker beneficial to "improved" imaging across a larger area in the room. With other speakers, especially point source phase coherent speakers (the Danley SH50 and some electrostatics comes to mind) this is not necessarily the case and can even be detrimental to the overall sound stage and imaging.

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  • 3 weeks later...

do you think I should aim them directly at me?

That'd be a step in the right direction, but ideally they would be pointing at opposite ends of the listening postion to minimize any wash from the side walls.
I treated the side walls to minimize reflections and I have now abandoned the center channel. Simply not needed. Less distortion. Thanks again for the thoughts.
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