Risers vs. tilt-back for Cornwall IIIs

[Boomzilla]

All comments in this thread by me are specific to the Cornwall III speakers.

To understand the behavior of the Cornwall IIIs the 15" woofers need to be evaluated in two different ways - as bass transducers and as midrange transducers. The behavior in these two modes is different.

FOR BASS:

The Cornwall's woofers radiate almost omnidirectionally at lower frequencies. As designed by Mr. Delgado of Klipsch, the near-field presence of the floor barrier both increases the effective bass level and confuses the bass launch due to reflections. Tilting back the speakers does nothing to change these effects. The woofer is still the same distance from the floor.

Greater distance between the woofer and the floor clarifies the bass but reduces the level. This is what happens when the Cornwalls are placed on stands. If you like the bass presentation of the Cornwall IIIs as shipped from the factory, then by all means, leave them on the floor. In my room, however, the Cornwalls sounded boomy and had excessive bass when left on the floor.

FOR MIDRANGE:

The Cornwall's woofers are 15 inches in diameter. At the 800 Hz crossover frequency to the midrange horn, the effective wavelength is 1.4 feet - very close to the woofer's diameter. This means that at the crossover frequency, the woofers dispersion narrows significantly. For discussion of this effect, see the following Wikipedia discussion:

http://en.wikipedia.org/wiki/Loudspeaker#Directivity

Klipsch recognized with the new, higher crossover frequency (800 Hz. vs. 600 Hz. on the original Cornwall) that dispersion would be a factor. For this reason, the woofer was moved to a higher location on the motorboard than in the previous Cornwall models. Unfortunately, the change is not sufficient. The woofer does beam and the axis of the woofer is still significantly below the plane of the listeners' ears. The woofer to midrange horn discontinuity is very obvious with my speakers on their factory risers.

Two options are available to the listener: Tilt the cabinets back to put the listener's ear on the axis of the woofer or raise the cabinets about 12 to 14 inches.

Although either of the options will make the woofer-to-midrange transition smoother, only the risers will provide the additional benefit of smoothing and clarifying the bass response.

For this reason, I have used risers below my Cornwall 3 speakers. I find the effects to be significant, easily audible, and repeatable in back and forth testing.

Cordially - Boomzilla (Moniker NOT indicative of listening preferences).

[Chris A]

Although either of the options will make the woofer-to-midrange transition smoother, only the risers will provide the additional benefit of smoothing and clarifying the bass response.

Are your risers solid or of an open design? See the fourth page of this article, under the heading called "Cavities".

If they are of an open design, you might be surprised to see FR suckouts apprearing around 200-300 Hz due to cavities under your CW box.

Chris

[Boomzilla]

Hi Chris -

My risers are currently open plastic shelves. I plan to build some, however, which will present a "flat plate" toward the radiating side of the speaker.

May I also point out that if one is using a room correction software such as Audissey, that the bass equalization will be adjusted by the microphone feedback regardless of whether the speakers are on the floor or on risers. That correction, however, will do nothing to correct the beaming of the woofer at the crossover point.

Given a choice between accurate midrange and accurate bass, I find it easier to live with comb-effects in the bass than in the midrange.

Also, as I said in the original post, my Cornwalls sounded VERY bass-heavy and boomy on the floor. This may be a room-dependent artifact, but the stands have certainly made a HUGE improvement in the bass as well as the midrange. I don't have a room evaluation software package, so I can't say what the "in room" response is of the Cornwalls on stands. I can say that my ear can easily tell the difference and that for both smoothness in the bass and smoothness at the crossover, the stands are preferable.

I might also mention that I tried tilting back the Cornwalls before trying the stands. The results were unsatisfactory,

Cordially - Boomzilla

[Chris A]

May I also point out that if one is using a room correction software such as Audyssey, that the bass equalization will be adjusted by the microphone feedback regardless of whether the speakers are on the floor or on risers.

I've found that you cannot boost suck out frequencies due to cavities underneath your speakers--all you do is push the lobes around and create other issues, especially off-axis issues. I do recommend solid boxes for risers.

I use two CW IIs for surrounds, and have them on solid boxes currently. I expect to find some better looking wood boxes in the near future. It helps to have the surrounds at or slight above ear level with our high-back chairs.

Chris

[Boomzilla]

Hi Chris -

Thank you for the information. I can just as easily build solid boxes as open stands for the Cornwalls. In fact, the boxes may be the easier of the two. Do all sides of the box need to be solid? I'd certainly assume so since the bass output, being essentially omnidirectional at those frequencies would "wrap around" any partial cavity.

Cordially - Boomzilla

[Chris A]

Do all sides of the box need to be solid? I'd certainly assume so since the bass output, being essentially omnidirectional at those frequencies would "wrap around" any partial cavity.

I think you answered your own question --yes. The issue is due to reflected acoustic energy underneath the speakers, and solid boxes preclude this. Open boxes, however, do not.

Good to hear that you're finding improvements using your CWIIIs. I've found that room acoustics themselves together comprise the second most important factor is achieving a good listening experience.

Chris

[Boomzilla]

...I've found that room acoustics themselves together comprise the second most important factor is achieving a good listening experience.

Chris

Hi again, Chris -

Once again, we're in agreement. My room was highly reflective with significant slap echo. I treated it using some ATS absorber pads on the wall and it now sounds great.

Cordially - Boomzilla

[derrickdj1]

I am not an expert on Heritage speakers, but an open riser can be design/made with with 1 or 2 in. of acoustic foam on the bottom side of the riser. This has been used for subwoofer risers. For the height of the Cornwall riser dense fiber glass(Owing Corning) or mineral wood insulation can be used to fill the open space under the riser. These products need to be wrapped with outdoor carpet. This will act as a bass trap. Very effective for the lower frequencies, under 300 Hz.