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Klipsch RF7 (old version) crossover modification


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Hi Alexander

It is interesting to see the original RF7 tweeter crossover response modeled. This is similar to the response of the RF3.

 

My theory is  that the Klipsch design engineers deliberately sloped the tweeter response to compensate for the extra energy produced by the woofer cone breakup around 3-5kHz. Once you remove this breakup with a notch filter i believe you need to level out the tweeter response.

 

I have attached modeling of the original RF3 tweeter response( which also has a rising response to higher frequency)  and my modified crossover which is 3rd order with a Zobel and an LCR to give a virtually flat impedance.

 

Original

post-54453-0-36880000-1428264060_thumb.g

 

New

post-54453-0-60320000-1428264089_thumb.g

 

Robert

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Agree with that.

The second problem of 3 kHz peaks is that they come from two point sources separated with the distance of 28 cm (two LF drivers). 28 cm is a wavelength at 1.2 kHz, while 3 kHz is already almost two wavelengths. So the vertical angle phase interference is very irregular, next plots show the sum of two woofers and the tweeter in Leap at 1 m distance, at the middle between the top woofer and the tweeter.

Original Klipsch crossover

post-61032-0-89880000-1428344878_thumb.ppost-61032-0-16200000-1428344890_thumb.p

These speakers are a lot of compromises :).

I expect that reducing this unwanted energy at 3 kHz from two woofers also improves the directivity patern.

Considering the design with 1 cap and main notch filter on the tweeter resonance one can also easily add the second cap after the notch. It would be already 3rd order of course, but with main notch filter outside of working region.

These is calculated for the tweeter without the mesh. It doesn't differ much from the "1 cap-version", but at low end the tweeter is filtered more.

post-61032-0-08640000-1428346000_thumb.ppost-61032-0-81920000-1428346010_thumb.ppost-61032-0-41320000-1428346020_thumb.p

At the moment I put stainless steel mesh with 1mm cell on the compression driver, think it sounds quite well with 1 cap cross, but haven't measured it yet.

Edited by Yasnyi Sokol
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It would be interesting with all your ability to measure things would be to see what a dense foam rubber such as a mouse pad cut to fit the inside of the woofer spokes and held there with tape or something would look like. It sure seemed to quell my woofers at a certain point. A point where they became laser like and slicing the ear drums.

Edited by cradeldorf
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I think that most unpleasant peak comes from the dust cap. Damping the basket wouldn't help it much. Some resonances across the woofer may go away, of course.

I think most people consider it dampening of the frame like the frame is making some kind of noise,  where I think it's stopping the sound wave coming off the cone from hitting the hard surface of the spoke and bouncing back at the cone and either creating a second sound in the cone or mucking up the waves coming off the cone. much like when you yell into a canyon and it hits a hard surface and comes back to you as an echo.

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That could make some possitive effect, thank You for the idea.

Meanwhile I am waiting for my best caps from Mundorf, let's play with enclosure of RF7.

Bass Reflex or Back Loaded Horn?

TypicalT/S parameters (they are published) are as follows:

Fs =31

Qes=0.22

Qms=11

https://community.klipsch.com/index.php?/topic/24048-diy-project-k-1089-av-rf-7-copper-woofer/

These make one think why they use bass reflex enclosure for the drivers? It looks like the drivers are more suitable for horn load.

I put parameters of bass drivers in 3D acoustical simulator (3D Acoustic Research project I take part in, the last version of software is not published yet).

The idea behind that program is to solve the wave equation in 3D domain for given electrical and mechanical parameters of the drivers. For simplicity I use single driver with same parameters (double Vas and Sd, half Re). For acceleration CUDA is used with powerful graphic card. The element size of numerical grid is 1 cm.

Equivalent parameters

Re =3.02 ohm

Sd =0.0720 sq.m

Fs=31

Vas=212 l

Qes=0.22

Qms=11

Here are some results. The BR is tuned to around 43-44 Hz similar to real speaker of Klipsch. Black point shows the mic position.

Open space

Here the baffle-step effect is presented, and also the enclosure is too big for given Qts.

post-61032-0-92200000-1428506616_thumb.p

post-61032-0-74720000-1428507905_thumb.p

post-61032-0-00240000-1428506635_thumb.p

post-61032-0-40120000-1428506649_thumb.p

post-61032-0-16840000-1428506658_thumb.ppost-61032-0-40520000-1428506666_thumb.ppost-61032-0-64200000-1428506674_thumb.ppost-61032-0-03160000-1428506685_thumb.ppost-61032-0-28240000-1428506694_thumb.ppost-61032-0-72360000-1428506701_thumb.ppost-61032-0-38280000-1428506719_thumb.g

This next plot is real impedance measument of two woofers in parallel (the simulation doesn't take into account the losses due to dampening material inside the volume, that's why impedance peaks are smaller). Also I have the second peak close to 60 Hz instead of 70 Hz (i didn't measure T/S parameters for my own drivers, just took the data above from the given link).

post-61032-0-02360000-1428520496_thumb.p

Half space (on the floor)

post-61032-0-34080000-1428506794_thumb.ppost-61032-0-73280000-1428506822_thumb.p

Floor and ceiling

post-61032-0-96400000-1428517071_thumb.ppost-61032-0-60000000-1428517084_thumb.p

Close to wall

post-61032-0-01800000-1428512368_thumb.ppost-61032-0-48960000-1428512395_thumb.p

A lot of bass. But ...do You like this?

Penal room (all reflecting walls except the rear to the listerner which is open, or in other words, perfect wave absorption behind the listerner. In this particular case it makes big reverberation time and low absorption in bass region as follows from the plot)

post-61032-0-72280000-1428506916_thumb.ppost-61032-0-42920000-1428506924_thumb.ppost-61032-0-86720000-1428506933_thumb.p

(in the last case the real energy level in bass region would be determined by the amount of energy absorption in real room)

One consideration from that is:

the driver placed too high above the floor generally lacks from the midbass region due to reflection from the floor. This effect is reduced when the mic is far to the speaker. Carpet is better than rigid floor surface.

The last picture shows the effect still remains in real room. Partially also due to low Qts of the driver. I guess that engineers of Klipsch tryed to get most possible low bass with the bigest possible volume of the enclosure.

Compare that with real measurements of RF7 which were published in my first posts.

The next consideration is to replace BR with BLH. Horn has big exit area along vertical, and reflection from the floor from numerious point sources at the exit is partially compensated. This improves midbass region. Floor acts as a part of the horn. On the other hand, bass horn is difficult to build, the exit area is always a compromise as it is less than the wavelength, and the reflection of back wave inside the horn produces ripples, which are reduced for half space radiation, quarter space etc. A lot of literature on that. BLH is also tricky as one should take into account both frontal radiation from the driver and from the horn with time delay.

Here is an example of BLH for RF7 drivers (two in one enclosure). Quite simple as it consists of almost plain elements.

Back loaded horn (width is about 45 cm, height 1 m, depth about 40cm) on the floor.

post-61032-0-13280000-1428507236_thumb.ppost-61032-0-86720000-1428507245_thumb.p

Lets "listen"

By this i mean that I can calculate FIR (finite impulse resosponse) at the mic position. I take a test wav file, split it into LF and HF parts (HF is original minus LF obtained with a digital filter, Hamming window function is used for filtering with -42 dB outside the main frequency region).

Then the LF part is convolved with FIR from 3D simulation.

The result is summed with original untouched HF part, taking into account the volume level of both. So, bass comes from the enclosure, while HF is "sonically ideal".

This can be considered as I "did nothing to real wood work but still is able to listen" to the result :)

The comparison is here (two WAV files). LF is filtered at 800Hz. TIme shift between LF and HF is zero. (When crossed at at 250-300 Hz the delay 3-5 ms for HF to compensate the group time delay of bass section sounds better).

http://mab.to/ZFvb7liIs

Forgive some sibilants (they come from numerical simulation).

Bass reflex has typical sound of bass reflex, the horn has typical "tabouret bass". . :)

Edited by Yasnyi Sokol
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I think that most unpleasant peak comes from the dust cap. Damping the basket wouldn't help it much. Some resonances across the woofer may go away, of course.

I think most people consider it dampening of the frame like the frame is making some kind of noise,  where I think it's stopping the sound wave coming off the cone from hitting the hard surface of the spoke and bouncing back at the cone and either creating a second sound in the cone or mucking up the waves coming off the cone. much like when you yell into a canyon and it hits a hard surface and comes back to you as an e

I like to address both issues I use Dynamat on the inside of the basket and I use F-11 Acoustical Felt to damp the area over the spider to catch spider talk and cone reflections in large drivers I also apply F-11 to the inside of the basket over the Dynamat. Best regards Moray James.

PS: I like the sound of the first sample above.

Edited by moray james
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Continue the story.

 

I compared two meshes on compression driver, #20 and #40 (the number of holes per inch), and found #20 sounds better for me.

 

Mundorf silver/gold/oil 2.2uf caps have arrived. At the moment the crossover is as follows. 2.4uf  cap is 2.2 uf mundorf silver/gold/oil  plus 0.22 uf tin foil multicap RTX.

 

All other caps are Mundorf supreme. All coils are Jantzen wax coils.All resistors are jantzen MOX super resolution.

 

post-61032-0-56960000-1429080503_thumb.p

Edited by Yasnyi Sokol
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Continue the story.

 

I compared two meshes on compression driver, #20 and #40 (the number of holes per inch), and found #20 sounds better for me.

 

Mundorf silver/gold/oil 2.2uf caps have arrived. At the moment the crossover is as follows. 2.4uf  cap is 2.2 uf mundorf silver/gold/oil  plus 0.22 uf tin foil multicap RTX.

 

All other caps are Mundorf supreme. All coils are Jantzen wax coils.All resistors are jantzen MOX super resolution.

 

attachicon.gifs1.PNG

all these capacitors are very expensive and high end - you sure know your stuff - how much did you spend so far on caps alone -

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Stick around Yasnyl - we've lost many of our most technical folks.

I never would have thought the screen would have had that profound of an effect.

As for the experiments and modifications - very interesting stuff, and I can certainly appreciate the use of well constructed higher performing passive components.

Why'd most of them leave? I've seen a few people say that. That's unfortunate. :(

 

We actually killed them and buried them in the Klipsch graveyard.  :ph34r:

 

We have our fair share of technical folks wondering the halls still. I have said it before and I will likely say it again and again. There is not a better online community than this one. These folks are family. There is not a single doubt about it in my mind. I rekon that's why we can get away with murdering people who are smarter than us, or who don't pay their taxes by the 15th or April.  :lol:

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That could make some possitive effect, thank You for the idea.

Meanwhile I am waiting for my best caps from Mundorf, let's play with enclosure of RF7.

Bass Reflex or Back Loaded Horn?

TypicalT/S parameters (they are published) are as follows:

Fs =31

Qes=0.22

Qms=11

https://community.klipsch.com/index.php?/topic/24048-diy-project-k-1089-av-rf-7-copper-woofer/

These make one think why they use bass reflex enclosure for the drivers? It looks like the drivers are more suitable for horn load.

I put parameters of bass drivers in 3D acoustical simulator (3D Acoustic Research project I take part in, the last version of software is not published yet).

The idea behind that program is to solve the wave equation in 3D domain for given electrical and mechanical parameters of the drivers. For simplicity I use single driver with same parameters (double Vas and Sd, half Re). For acceleration CUDA is used with powerful graphic card. The element size of numerical grid is 1 cm.

Equivalent parameters

Re =3.02 ohm

Sd =0.0720 sq.m

Fs=31

Vas=212 l

Qes=0.22

Qms=11

Here are some results. The BR is tuned to around 43-44 Hz similar to real speaker of Klipsch. Black point shows the mic position.

Open space

Here the baffle-step effect is presented, and also the enclosure is too big for given Qts.

 

images deleted

This next plot is real impedance measument of two woofers in parallel (the simulation doesn't take into account the losses due to dampening material inside the volume, that's why impedance peaks are smaller). Also I have the second peak close to 60 Hz instead of 70 Hz (i didn't measure T/S parameters for my own drivers, just took the data above from the given link).

 

image deleted

 

Half space (on the floor)

 

images deleted

Floor and ceiling

 

images deleted

Close to wall

 

images deleted

A lot of bass. But ...do You like this?

Penal room (all reflecting walls except the rear to the listerner which is open, or in other words, perfect wave absorption behind the listerner. In this particular case it makes big reverberation time and low absorption in bass region as follows from the plot)

 

images deleted

(in the last case the real energy level in bass region would be determined by the amount of energy absorption in real room)

One consideration from that is:

the driver placed too high above the floor generally lacks from the midbass region due to reflection from the floor. This effect is reduced when the mic is far to the speaker. Carpet is better than rigid floor surface.

The last picture shows the effect still remains in real room. Partially also due to low Qts of the driver. I guess that engineers of Klipsch tryed to get most possible low bass with the bigest possible volume of the enclosure.

Compare that with real measurements of RF7 which were published in my first posts.

The next consideration is to replace BR with BLH. Horn has big exit area along vertical, and reflection from the floor from numerious point sources at the exit is partially compensated. This improves midbass region. Floor acts as a part of the horn. On the other hand, bass horn is difficult to build, the exit area is always a compromise as it is less than the wavelength, and the reflection of back wave inside the horn produces ripples, which are reduced for half space radiation, quarter space etc. A lot of literature on that. BLH is also tricky as one should take into account both frontal radiation from the driver and from the horn with time delay.

Here is an example of BLH for RF7 drivers (two in one enclosure). Quite simple as it consists of almost plain elements.

Back loaded horn (width is about 45 cm, height 1 m, depth about 40cm) on the floor.

 

images deleted

Lets "listen"

By this i mean that I can calculate FIR (finite impulse resosponse) at the mic position. I take a test wav file, split it into LF and HF parts (HF is original minus LF obtained with a digital filter, Hamming window function is used for filtering with -42 dB outside the main frequency region).

Then the LF part is convolved with FIR from 3D simulation.

The result is summed with original untouched HF part, taking into account the volume level of both. So, bass comes from the enclosure, while HF is "sonically ideal".

This can be considered as I "did nothing to real wood work but still is able to listen" to the result :)

The comparison is here (two WAV files). LF is filtered at 800Hz. TIme shift between LF and HF is zero. (When crossed at at 250-300 Hz the delay 3-5 ms for HF to compensate the group time delay of bass section sounds better).

http://mab.to/ZFvb7liIs

Forgive some sibilants (they come from numerical simulation).

Bass reflex has typical sound of bass reflex, the horn has typical "tabouret bass". . :)

I like the bass response of the back loaded design here. You mention that the floor becomes part of the horn, which gives it different gain characteristics in a room. I have seen the setups of most people who have the RF7, and they are usually very close to a wall, and in many cases in corners.  That being said, the gain for a BLH from those surfaces would boost the low frequencies nicely, and maintain a flat bass response.

 

The question is, who is willing to build a pair of these and take some real measurements? Frankly, I could see this as a line in the Klipsch arsenal. They are the horn people, after all. :)

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Placing the horn close to wall could unbalance the responce. Only bass notes will be amplified by "big horn".

 

Look at that:

 

post-61032-0-85120000-1429107627_thumb.p post-61032-0-13920000-1429107643_thumb.ppost-61032-0-20120000-1429107653_thumb.p

 

The same applies to Jensen corner horn with Altec 416 driver:

post-61032-0-85800000-1429107886_thumb.ppost-61032-0-37240000-1429107897_thumb.p

post-61032-0-46560000-1429107907_thumb.ppost-61032-0-75840000-1429107919_thumb.p

 

My friend has built the last one and here are his measuments in real room (which is also quite small). His room has more complex wall behind the speakers than one used in the simulation, which might be also the reason why the plots differ.

 

http://photo.qip.ru/users/yras/4142238/101865539/#mainImageLink

 

post-61032-0-98720000-1429108556_thumb.j

 

http://photo.qip.ru/users/yras/4142238/100875270/#mainImageLink

post-61032-0-43840000-1429108821_thumb.j

Edited by Yasnyi Sokol
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  • 1 month later...
  • 4 months later...

Hi, all,

Some recent updates.

I stay with this crossover for a long time already and want to say i like it. But if someone decide to repeat my modification I would strongly recommend Mundorf silver oil caps on the high pass of the scheme (8.2 and 15 uf). I have compared both and found SIO much and much better. These are really true high end caps and i could not expect how much they outperform regular Mundorf Supremes!! Regular supremes are the waste of money compared to SIO. Less resolution, less dynamic. Yes, they are detailed, but that is not that details which come from the real resolution. Also regular supremes add some touch i felt always with them.

SIO must be trained for about 200 hours to break in. I used a simple scheme with amplifier and load resistor to cook them.

I also compared SiO s to not known widely Rike Audio S-caps. These caps are very open and transperant. Very impressive, too. Even more dynamic than Mundorf silver oils. But they add some coloration. Overall, Mundorf SIO give more balanced and deep presentation, so i left SIO caps.

Probably, Rikes could be used for bass or mids very well.

Edited by Yasnyi Sokol
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  • 2 weeks later...

i did a complete mod on my 7's back in 2010.  i wonder how they would test....based on what you found, just looking at mine, what do you think the results would be....

https://community.klipsch.com/index.php?/topic/119273-rf-7-rc-7-cabinet-mod/?hl=%2Brf-7+%2Bcabinet

https://community.klipsch.com/index.php?/topic/119525-upgraded-rc-7-crossover-wpics/

https://community.klipsch.com/index.php?/topic/119526-upgraded-rs-42-crossover-wpics/

https://community.klipsch.com/index.php?/topic/119183-rf-7-and-rc-7-horn-mod/

 

i'll need to find someone who has the same equipement so i can test them out....

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  • 1 month later...

Hi, all,

InVeNtOr, thank You for the information. Actually I saw Your upgrage before i started, also there must be a video somewhere on Youtube about plastic horn modification. My friend used to do that and he thinks this is a must be for RF7 plastic horn.

As for myself i am so happy with the result that don't want to change anything already. I guess one can make better speakers, but that will be another story.

We tryed these speakers with rather good equipment: i.e. Lavry gold Dac. My interest is now digital source, and i replaced my old Weiss Minerva 1394 board based dac (updated with 1853 chip, blackgate caps etc) with simple TDA NOS 14 bit 1540 selfmade dac and like it very much. Will play soon around 1541 just to compare with 1540. These black caps on the photo are all BG FK type and that really makes sense to the sound.

Good luck to everybody, hope someone would follow my modification to RF7 some day!

post-61032-0-04740000-1449862831_thumb.j

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