Vertical center channel?

[yepimonfire]

Due to the poorer off axis response of a horizontally oriented MTM, I'm considering placing my Klipsch rp-250c sideways so the its oriented vertically. The horn is 90x90 and identical on both the top and bottom of the mouth, so I don't think this would change the dispersion. Originally I was just going to add another rp-150m as a center channel, but seeing as the rp-250c is about 4dB more sensitive, has a similar f3 (66 hz anechoic, 50hz in room), and has twice the driver area due to dual woofers, I figured it'd be better equipped to handle the demands placed on the center (about 60-80% of the entire soundtrack is anchored in the center channel).

Has anybody done this and had good results?

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[shadyJ]

I would predict that the overall behavior of the MTM will be better when vertically oriented, but I would just use another rp-150m. That would be the ideal. If you aren't running the speakers hard, the extra woofer of the center speaker won't really be an advantage. If you are running the speakers that hard, than it is time to switch to an entirely heavier-duty front stage speaker set anyway.

By the way, the dispersion will absolutely change vertically, and will probably change horizontally. You are likely looking at a different crossover design, and it will affect these behaviors. How much it will affect the dispersion is hard to say without measuring it.

 

[Hetfield]

I have a studio monitor as my center channel standing straight up the way it was intended and it sounds fantastic. I have Definitive Technology Studio monitor 65 mains and center channel, so the same speaker across the front sound stage and it's awesome. Dialog is clearer definitely. Also when I added an external amp, a very clean and powerful amp to drive all 5 channels I noticed the center channel dialog became even more clear and could great it better. Just my experience.

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[TheWarrior]

Centers started becoming horizontal due to demand from consumers placing them in cabinets/stands for TVs. 2-way MTM's by design cancel out a lot of midrange frequencies due to the distance between the two mid range drivers providing a very narrow listening window. When placed vertically, the cancellations are moved to the vertical plane so the speaker can be positioned to satisfy a couch of listeners, but would suffer the same problems if you had a riser and multiple rows of seating.

If seeking a horizontal center channel, look for a 3 way design with a midrange tucked right below the tweeter, flanked by woofers, or at least a 2.5 way MTM.

 

[Pogre]

Agree with the others about getting the same matching speaker for a center. I bought a matching bookshelf I'm using vertically as my center right now. It's timbre matched very nicely with my towers.

 

[yepimonfire]

Agree with the others about getting the same matching speaker for a center. I bought a matching bookshelf I'm using vertically as my center right now. It's timbre matched very nicely with my towers.

If only I could buy a single RP 150m. I'd hate to spend the extra money and have a single speaker just taking up closet space. Couldn't even use it for a rear surround either since Atmos receivers don't allow a 6.1.2 configuration.

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[yepimonfire]

Centers started becoming horizontal due to demand from consumers placing them in cabinets/stands for TVs. 2-way MTM's by design cancel out a lot of midrange frequencies due to the distance between the two mid range drivers providing a very narrow listening window. When placed vertically, the cancellations are moved to the vertical plane so the speaker can be positioned to satisfy a couch of listeners, but would suffer the same problems if you had a riser and multiple rows of seating.

If seeking a horizontal center channel, look for a 3 way design with a midrange tucked right below the tweeter, flanked by woofers, or at least a 2.5 way MTM.

The RP 450c uses a 2.5 way crossover at 500hz/1500hz in an mmtmm design, however, the center to center spacing of the innermost drivers is still longer than one wavelength, meaning it would have the same problem. Unfortunately, I can't just pick a three way center channel without replacing my entire setup because Klipsch doesn't make one. I don't have a riser, all seats are the same height.

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[yepimonfire]

@shadyJ, could you elaborate on the crossover design affecting the dispersion vertically? What I meant by the dispersion pattern not changing was in regards to the designed dispersion pattern of the horn, being that it has a 90° radiation pattern horizontally and vertically, unlike the old 60x90 horns, which had poorer response vertically.

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[shadyJ]

@shadyJ, could you elaborate on the crossover design affecting the dispersion vertically? What I meant by the dispersion pattern not changing was in regards to the designed dispersion pattern of the horn, being that it has a 90° radiation pattern horizontally and vertically, unlike the old 60x90 horns, which had poorer response vertically.

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Different frequencies are going to react differently in the horn. Assuming that the center speaker is using a different crossover point than the bookshelf speaker, that will change the dispersion pattern.

 

[TheWarrior]

The RP 450c uses a 2.5 way crossover at 500hz/1500hz in an mmtmm design, however, the center to center spacing of the innermost drivers is still longer than one wavelength, meaning it would have the same problem. Unfortunately, I can't just pick a three way center channel without replacing my entire setup because Klipsch doesn't make one. I don't have a riser, all seats are the same height.

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1500 hz = 9 inches
500 hz = 2.26 feet

Are you sure that the 'left bank' of drivers are not two mids, and 'right bank' are two woofers? Can't tell by their vague data sheet. If you can confirm that, you'll be fine. But if it's just an WMTMW (yes I know they call them all woofers, but operational bandwidth is as written) then yeah that would not be a wise purchase.

The JBL 235C has a similar dome tweeter with wave guide arrangement in a 2.5 way, might be a pretty close timbre match?

 

[TheWarrior]

@shadyJ, could you elaborate on the crossover design affecting the dispersion vertically? What I meant by the dispersion pattern not changing was in regards to the designed dispersion pattern of the horn, being that it has a 90° radiation pattern horizontally and vertically, unlike the old 60x90 horns, which had poorer response vertically.

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Crossover design is almost as much art as it is science. The selected crossover frequency and rate of roll off are not arbitrarily chosen, all of the drivers have to work as a collective. And that includes accounting for 2pi and 4pi loading depending on where the speakers are to be placed. Armed with the correct acoustic measurements and complete t/s parameters you can select ideal crossover frequencies that limit/expand mainly vertical but some horizontal dispersion characteristics of cone/dome drivers. Speakers radiate energy 360deg on both planes, so it would be important to have measurements to verify this '90deg dispersion pattern' and compare it to a dome without a wave guide. If your spec is +/- 3db 45deg off axis vertical and horizontal, you might be quite surprised to find many dome tweeters doing that unassisted.

Passive crossover topology choices are ideally made free from budget constraints, but that seldom happens in the big box retail space. Thats why guys like Dennis Murphy can build complex crossovers that would be crippling to a large production. He can individually test each driver and make individual adjustments to maintain his design spec. That reproducibility is incredibly expensive in mass production. Those AA monitors he makes started before as a crossover redesign of a popular Pioneer speaker line. Same drivers, just a better crossover yielded a completely different and very satisfying system.

 

[lovinthehd]

Those AA monitors he makes started before as a crossover redesign of a popular Pioneer speaker line. Same drivers, just a better crossover yielded a completely different and very satisfying system.

FWIW the current AA pair is based on the Dayton BR-1 speaker kit, the previous AAs on the Pioneers. The center is still based on the Pioneer, tho.

 

[yepimonfire]

Crossover design is almost as much art as it is science. The selected crossover frequency and rate of roll off are not arbitrarily chosen, all of the drivers have to work as a collective. And that includes accounting for 2pi and 4pi loading depending on where the speakers are to be placed. Armed with the correct acoustic measurements and complete t/s parameters you can select ideal crossover frequencies that limit/expand mainly vertical but some horizontal dispersion characteristics of cone/dome drivers. Speakers radiate energy 360deg on both planes, so it would be important to have measurements to verify this '90deg dispersion pattern' and compare it to a dome without a wave guide. If your spec is +/- 3db 45deg off axis vertical and horizontal, you might be quite surprised to find many dome tweeters doing that unassisted.

Passive crossover topology choices are ideally made free from budget constraints, but that seldom happens in the big box retail space. Thats why guys like Dennis Murphy can build complex crossovers that would be crippling to a large production. He can individually test each driver and make individual adjustments to maintain his design spec. That reproducibility is incredibly expensive in mass production. Those AA monitors he makes started before as a crossover redesign of a popular Pioneer speaker line. Same drivers, just a better crossover yielded a completely different and very satisfying system.

It's an identical response to on axis measurements from 1.8khz-14khz +-90°. The difference between a dome and the horn is the coverage and directivity is constant throughout the frequency range, whereas domes I've measured have increasingly steeper rolloff as the frequency gets higher. 16khz starts taking a nosedive past 45° since the horn doesn't really "grab" and disperse the very top end as well.

The MTM center doesn't do this like the bookshelves, the response off axis horizontally is pretty lousy in comparison.

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[everettT]

It's an identical response to on axis measurements from 1.8khz-14khz +-90°. The difference between a dome and the horn is the coverage and directivity is constant throughout the frequency range, whereas domes I've measured have increasingly steeper rolloff as the frequency gets higher. 16khz starts taking a nosedive past 45° since the horn doesn't really "grab" and disperse the very top end as well.

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What domes have you measured? Were they crossover implemented or Raw drivers? I've seen a lot of measurements but haven't seen ones from a driver that measure identical across that large of a frequency band .

 

[shadyJ]

What domes have you measured? Were they crossover implemented or Raw drivers? I've seen a lot of measurements but haven't seen ones from a driver that measure identical across that large of a frequency band .

Agreed, especially from a horn-loaded tweeter. Perhaps later on in the summer I can measure one of the Klipsch RP speakers if I can borrow one from someone.

 

[yepimonfire]

What domes have you measured? Were they crossover implemented or Raw drivers? I've seen a lot of measurements but haven't seen ones from a driver that measure identical across that large of a frequency band .

Several Polk audio speakers, which supposedly scored well in Floyd toole's listening tests for off axis response. Plenty of speakers without waveguides or intentionally designed constant directivity have beaming issues with high frequencies, for example, here is the response off axis of a b&w 703

As you can see, after around 5k the response starts dropping, ending up 6dB down at 10khz, and 12dB down at ~14khz.

Any driver will narrow its dispersion pattern as the wavelength gets closer to or smaller than the drivers diameter, that's just physics. The only way to prevent that is either coaxial drivers, waveguides, four way designed speakers with xover frequency matched diameter drivers, or constant directivity horns.



Like you said, most domes will not hold an identical FR curve across a large range, wave guided speakers and horn loaded speakers (when designed for constant coverage/directivity) do. It makes a huge difference whether or not the sound that bounces off the first reflection points is similar in timbre to the direct sound. Floyd Toole has spoken a lot about this. Its also nice to be able to sit off axis and still get a similar response. This is even more important in my room since there are more seats off axis than on. Its just my center falls short of that same off axis response of the bookshelves.

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[yepimonfire]

Agreed, especially from a horn-loaded tweeter. Perhaps later on in the summer I can measure one of the Klipsch RP speakers if I can borrow one from someone.

Well, the whole idea of a horn besides increasing efficiency is pattern control, which is why they're used for sound reinforcement and cinema's. You want the sound directed at the audience, not sprayed all over the walls and ceiling with varying polar patterns, and you want everybody to hear the same sound regardless of where they're sitting, in cinemas you have multiple rows if seating, often elevated, a 90x60 horn gives a coverage of 60° vertically, so those sitting in the fist row 45° below the center speaker can still hear clear dialogue. Properly calibrated cinemas aim all speakers towards the center seat 2/3rds back into the cinema. Controlled directivity ensures every seat gets equal coverage at relatively the same response. Have you ever been to a cinema and noticed poor timbre when sitting in the front or back row, to the left or right side? I haven't.

You might be thinking of exponential horns, which used to be used in older klipsch models and other horn speakers for home usage, those are very beamy, with worse and worse pattern control as the frequency increases. It might be 90x60 at 1khz, but at 8khz, it could be 40x20. There is a reason cinema and PA speakers don't use exponential horns. Klipsch no longer uses exponential horns, the modified tractrix horn was designed to be a constant directivity design. Its not a true tractrix.

Ever paid attention to how the highest frequencies are lost when you stand up and are 45° above the speaker? That doesn't happen with the speakers I've got now. It sounds the same, even the couch along the side wall, which is about 60° off axis gets equal coverage, and outside of crappy imaging, it still sounds good.

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[TheWarrior]

FWIW the current AA pair is based on the Dayton BR-1 speaker kit, the previous AAs on the Pioneers. The center is still based on the Pioneer, tho.

Yeah there were a couple of iterations until he got to the Dayton kit. KEW still has one that are surprisingly good, but terribly thin cabinets that are too big to be a bookshelf, and too short to be free standing. lol

 

[everettT]

It seems by your account that any driver loaded into a horn or wave guide will overcome the limitations of said driver, which isn't true. I completely understand where your thoughts are but it's not universal in theory. I can reference several domes, plannars and ribbons that can be well implemented via crossover that have nice vertical dispersion and good off axis response. The "horn" doesn't make the design, but the designer.

Several Polk audio speakers, which supposedly scored well in Floyd toole's listening tests for off axis response. Plenty of speakers without waveguides or intentionally designed constant directivity have beaming issues with high frequencies, for example, here is the response off axis of a b&w 703

As you can see, after around 5k the response starts dropping, ending up 6dB down at 10khz, and 12dB down at ~14khz.

Any driver will narrow its dispersion pattern as the wavelength gets closer to or smaller than the drivers diameter, that's just physics. The only way to prevent that is either coaxial drivers, waveguides, four way designed speakers with xover frequency matched diameter drivers, or constant directivity horns.



Like you said, most domes will not hold an identical FR curve across a large range, wave guided speakers and horn loaded speakers (when designed for constant coverage/directivity) do. It makes a huge difference whether or not the sound that bounces off the first reflection points is similar in timbre to the direct sound. Floyd Toole has spoken a lot about this. Its also nice to be able to sit off axis and still get a similar response. This is even more important in my room since there are more seats off axis than on. Its just my center falls short of that same off axis response of the bookshelves.

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[TheWarrior]

The difference between a dome and the horn is the coverage and directivity is constant throughout the frequency range, whereas domes I've measured have increasingly steeper rolloff as the frequency gets higher.

This is the 'spinorama'; Data extracted from measuring according to CTA 2034. My purpose in showing this to you is for you to better understand directivity. As frequency increases, wavelength decreases. All speakers become forward biased as frequency increases due to the millimeter sized wavelengths. What is constant directivity? Constantly increasing? Yup!

The Sound Power Directivity Index is a weighted sum of all sound radiated from all directions by the speaker in an anechoic chamber, with the First Reflections DI narrowing the focus, and more accurately representing what is heard in room. Bass is omni directional up to the transition frequency of the room where sound progressively gains forward bias as frequency increases. No speaker has 'constant directivity'. That is literally a marketing term from decades ago. Horn loading (with a compression driver) ensures those high frequencies lose less energy over distance which is why they are most commonly seen in Public Address and large commercial venues. In the form of a dome tweeter and waveguide, which includes your speakers, it serves to better limit the directivity increase between the crossover gap woofer/mid to tweeter, but does not keep directivity constant.

"Any driver will narrow its dispersion pattern as the wavelength gets closer to or smaller than the drivers diameter, that's just physics. The only way to prevent that is either coaxial drivers, waveguides, four way designed speakers with xover frequency matched diameter drivers, or constant directivity horns."

The wavelengths of the audible frequency range go from 56.5 feet down to 0.056 feet. At no time does wavelength correspond to driver diameter, example: 2000 hz (average tweeter crossover) is still about 6 inches compared to a 1 inch tweeter.