Dramatically improved characteristics on RF-7 iii

[Dan Masters]

We know speakers can sound different depending on placement, room dimensions, etc., etc.  Importantly, horns can sound very different depending on the space they radiate into.  For example, if you design a horn to produce low frequencies, and then slice it short at say 1/2 it's length, the lowest frequencies will be lost UNLESS it radiates into a more limited space, as it would if it were placed in a corner.  This is the principle behind Klipschorns.   

 

I truly love my RF-7s, but unlike some heritage lines, the high/mid horn radiates straight out into 3D space.  The more box-shaped speakers in the heritage line provide a "backboard" for the midrange horn because the mouth of the horn is set into the larger face of a box shaped speaker.  So, the waves exiting the mouth radiate into 1/2 of a sphere for just a bit.   Now, how big of a difference does this "backboard" really make?  Well, as an experiment, I made simple backboards (anyone could do it) for the top 1/3 of my RF-7s. I made them much larger than they probably need to be, 11" on either side and on the top.  Anyway, the results were truly, absolutely and measurably astounding.  

 

The backboard accomplishes two things.  First, it makes the mid/high horn more efficient only for the lowest frequencies it's designed to produce (For reasons stated above, I don't believe they have the same effect for higher frequencies, which would be unwanted). I think it's well known that the RF-7 is quieter in the mids.  I discovered quickly that the vocals in some of my favorite songs were put solidly into the background as a result.  These backboards absolutely corrected the issue.  Vocals now have that presence and ghostly realism that made my spine tingle when I owned Klipschorns.

 

The second thing the backboard accomplishes is to change the waveshape of these mid frequencies.  This is crucial.  It's well-known that to maximize the imaging from the RF-7, you must point them almost straight toward you.  This is because those mid waves exit the horn in elongated fashion, like a blimp leaving a hangar.  The tip of the blimp needs to be pointing almost at your ears or else it will seem like the sound is "moving past you" on the sides.   But the backboards make the waves more spherical, matching the geometry of the high frequency waveforms.  I can now point my speakers nearly straight ahead, yet both the imaging and the soundstage are very noticeably enhanced. 

 

The RF-7 is already a great value, sounding as good as many non-Klipsch speakers twice the price (in my opinion).  But this little "adjustment" absolutely propels them into another realm.

 

Now, I'm sharing this experience in the hopes that someone with RF-7's and more diagnostic equipment than me (and/or better ears than me) gives this a try.  I expect some will argue on principle that A), this "changes the design", or B.) "effectively changes the profile of the horn" or C) that, in theory, it will negatively impact the linearity of the frequency response.  My responses are:  A) The backboard is already a feature of several heritage lines and makes a valuable contribution, B.) The horn profile is not changed, just the space the horn is radiating into and C), as I said, the frequencies that are boosted are exactly the ones that would benefit the RF-7, by virtue of the shorter mid/high horn with smaller mouth.  The most worthwhile feedback will be from someone who gives this a try for themselves. 

 

So very interested to get your feedback!!   

[jjptkd]

 Interesting- I was researching this same thing only a week or so ago and there is definitely something to it. From what I gathered there were trade-offs, no free lunch kind of thing. Have you tried different size baffle extenders? I think you can go too far with it may be worth trying a few different sizes to get the best sound possible thanks for sharing!

[Dan Masters]

Jjptkd, thanks for those thoughts!  I'd be very interested if you learned of any acoustic-theoretical downsides to the baffles in your research. I personally can't detect any issues, but my listening skills are limited.  Overall, they just sound much better to me.  I agree with trying some different sizes.  If I can find info on the trade-offs, it would be interesting to change size/shape and try to find the "sweet spot".   Thanks again!!  Dan

[Iteachstem]

Interesting idea.  I'm always trying to make my speakers/systems sound better, so this is not such an odd idea.  However,may I add a 4th letter... D) It will look very awkward in a nice living room and only be allowed to exist in a single man's mancave. 

 

I have a set of RF-7II's that I could give this a try on... probably won't happen for a bit though.

[jjptkd]

Google "baffle step compensation" there is science behind it. One would have to think that the engineers at Klipsch would have accounted for this in the crossover design but no doubt expanding the width of the baffle can dramatically alter the sound. 

[Fish]

It may be good to have more input..but. If you like the set up is the most important. You shared your set up and opinion, that's what this forum about. If I had any issues with mine I'd give it try. Fortunately my placement and room work pretty well but it's great to see opinions.

[parlophone1]

Any photos of that setup?

 

[Dan Masters]

Great comments!   Iteachstem, So true!!  My wife walked into the family room and said "Why are your speakers wearing funny hats and when are they coming off"?   Jjptkd, Thanks for pointing me to that research...exactly what I was hoping for.  I think Klipsch really made the most of the high/mid horn given constraints of a tower speaker.  But the quieter mid frequencies indicate that the size of the horn's mouth is a bit small, causing the lowest mid frequencies to reflect back into the horn a bit...it's physics!  The "baffle" allows those mids to escape the mouth.  Parlophone1, I might post photos, but these are just banged-together prototypes and quite unattractive.  If I make nicer ones, I'll definitely post.  But they are just like basket ball backboards surrounding the upper 1/3 of the speakers. 

 

Fish, again, I love my RF-7's, funny hats or not. I fear that the "blimp out of a hangar" metaphor sounded disparaging, but that elongated wave shape is typical for most speakers.  It's like blowing a bubble...it's quite elongated until you stop blowing, after which it becomes more spherical.  The backboard helps the "bubble" to stay more spherical as its forced out of the horn.  This is all theory and I'm not an expert, however several friends with good ears agreed that these backboards had exactly the effects I had predicted, as described in my first post. 

 

Now, my room dimensions require that I sit pretty close to my speakers, so I really need to point my speakers inward to get that effect of the vocalist standing right in front of me.  I have very accurate components, so the imaging is amazing.  Friends always comment on my great center speaker...but I have no center speaker!!!  Anyway, because I'm close to the speakers, the "shape-changing" effect of the backboards was dramatic and obvious.  Now I can turn my speakers forward, but the imaging is still perfect...I think even better than without backboards, although more testing is warranted.  

 

Most speakers have strong and weak points. Many folks, including me, are happy with the RF-7's mildly U-shaped frequency response.  Many prefer it!   But the quieter mids are noticeable when you watch side-by-side comparisons on Youtube with other higher-end towers or various heritage lines.  Listening to those videos on midrangey laptop or tv speakers, you hear the obvious drop in volume when they switch to RF-7s.  And folks comparing various heritage-line speakers with RF-7s often comment on the greater liveness and realism of heritages. 

 

I wanted to see if I could get the same "live" experience from the RF-7s.  Adding the backboards created a whole new world.  Voices, pianos, brass all sound more real and alive.  I'm going out on a limb and say maybe better than forte's because they sound at least as good as I remember my Klipschorns to be.   Note that, unlike the narrow horns on Heritage-line speakers and other similarly priced horn speakers, the RF-7 horns are more square shaped.  Sound waves perform better when the horn mouth is closer to circular.  Those narrow shapes are chosen specifically to keep the waves moving laterally toward the listener, but are in other ways a compromise.  That's why many narrow horns include those square shaped bifurcations inside, to minimize those drawbacks.  Anyway, I think it's that square shape of the RF-7 horns that make them benefit so profoundly from these baffles/backboards. 

   

 

 

 

[SWL]

This is interesting. What materials did you use for this? Posting some pics of this would be cool. I'm always up for trying a cheap tweak.

[Dan Masters]

SWL and Parlophone1 -- OK, this is embarrassing, but I'm posting photos in the interest of science.  PLEASE NOTE!!  Like I said, these quickly banged-together protype backboards are grossly oversized.  I used old pine planks that happened to be handy.  Plywood cutouts would have been better.  Sitting on top of terrycloth towels to protect the speaker finish and to "pinch" them into place on the sides.  But a positive point is that these work VERY WELL sonically even though the construction is totally abysmal.    

 

[Southern]

@Dan Masters You have nothing to be embarrased about, that is a very cleaver way to test your theory.

 

I have RF-7 HT setup along with a Forte 2 channel setup in the same room. 

 

I prefer the Forte's in 2 channel mode but the RF-7/RC-7/RS-7 really shine in home theater which I mainly listen to SACD's or Blu-ray concerts.

 

I'm not sure if it's the center channel RC-7 that contributes to this but it sounds like I am sitting in the concert venue or in the case of SACD inside the recording studio.

 

I have my RF-7's slightly towed in similar to yours but the Forte's are facing straight forward which I obtain better imaging.

[parlophone1]

Same as above - nothing embarrassing in trying to experiment, does not have too look nice and trying to save money.

I might try that with my RF42 II, just for fun 😂

[Paducah Home Theater]

On 3/13/2024 at 8:05 PM, jjptkd said:

Google "baffle step compensation" there is science behind it. One would have to think that the engineers at Klipsch would have accounted for this in the crossover design but no doubt expanding the width of the baffle can dramatically alter the sound. 

 

I mean, the baffle situation is real, however, it's not the tweeter that is affected.  it's all based on the wavelength of what is being reproduced.  Having a horn loaded tweeter / compression driver sitting in an 11.5" wide cabinet that's 4' tall... it's going to be crossed over higher than the frequency of where the response starts to flatten out.  

 

What happens is that with lower frequencies, the longer wavelength allows frequencies to wrap around and go behind the cabinet, so you get some loss.  Manufacturers account for this by having the natural output of the woofers higher.  By extending the baffle, or adding a full baffle wall like in higher end home theater applications, you get a bump in the bass / midbass / lower midrange because that loss isn't the same. Your response ends up being totally different.  

All this is very well known and nothing new.  However doing this while specifically concentrating on the tweeter is backwards.  

[YK Thom]

Very interesting thread. I'm not well versed enough in the physics but these two opposites are different designs people swear by. Many high end speakers are narrow and get rave reviews, at the same time there are many wide baffle speakers that get equally great reviews. All the Heritage line are wide baffle, as are Harbeths, Warfdales, Tannoy and Devores. Others like Focal, Sonus Faber, Paradigm and the unfortunately discontinued Palladium line go the other way.

[Dan Masters]

Awesome feedback, folks!  Responding first to Jjpdk: Totally agree, but my backboards/baffles surround the horn specifically, not the woofers -- and what a "baffle" does for a horn is VERY different than what a baffle does for woofers!  Specifically, the lowest frequency a horn can produce is strongly limited by the mouth area (square inches) and axis length.  Frequencies below the horn's physical limitations get reflected right back into the horn. Now, it's very clearly evident that the crossovers on the RF-7 are -- as a totally intelligent design compromise for a narrow tower speaker -- sending frequencies to the horn that are a bit lower than it can produce LINEARLY.  Hence, the well-known U-shape frequency response of the RF-7s. (Jason demonstrated this in his RF-7/forte side by side comparison video.  You can hear the mids get much quieter when he switches to the RF-7). But here's the point: A shorter horn with a smaller mouth CAN produce somewhat lower frequencies if the horn radiates into a smaller space, such as the corner of a room, as Paul Klipsch understood and capitalized upon (i.e. Klipschorns).  My backboard cuts the space in half.   It therefore physically helps frequencies at the horn's lower limit to escape the horn, instead of reflecting back into the horn.  Completely different concept from simply directing certain frequencies forward, as a baffle does. 

 

If I remember correctly, there's a mid and high horn AND a baffle under the front grill of the Klipschorn.  I won't go down the rabbit hole, but the baffle does much more for the mid horn than just add linearity (i.e. wave geometry).  I've owned Cornwalls, first gen RF-7s, and Klipschorns before the RF-7 iii's, and many other speakers.  The Klipschorns were the only speakers that actually gave me involuntary shivers and goosebumps when listening to great female vocalists.............until now. 

 

If you would like to test this out, just as a learning exercise, I'd gladly ship you my prototypes because I'd really love to hear your professional thoughts.  But for me, this is all just idle fun...I understand you guys need to run a business. 

 

 

 

 

 

[Dan Masters]

Oops, the above response was actually for Paducah, not jjpdk...unless the pdk in jjdpk means you're the same folks?   Southern, Parlophone and YK Thom, it's late here, but I'd like to respond to your great comments tomorrow. 

[winglet]

10 hours ago, Dan Masters said:

 

 

If I remember correctly, there's a mid and high horn AND a baffle under the front grill of the Klipschorn.  I won't go down the rabbit hole, but the baffle does much more for the mid horn than just add linearity (i.e. wave geometry).  I've owned Cornwalls, first gen RF-7s, and Klipschorns before the RF-7 iii's, and many other speakers.  The Klipschorns were the only speakers that actually gave me involuntary shivers and goosebumps when listening to great female vocalists.............until now. 

 

Here is PWK's paper from 1963 on the development of the k-400 horn and the effect of a baffle or flange on the low end extension of the horn..

 

 

K-400 Article.pdf

[Dan Masters]

Perfect!!! Great find! PWK found improved response at low end from baffle as I've claimed.  But much more to dive into in this paper, Thanks!