Ahuja 12FRX Open Baffle

[Subbu68]

Hi,

Don't know of you have already finalized the configuration (dimensions) of the baffle.
I did a VituixCAD simulation of the open baffle concept you described in previous posts with baffle dimensions (Width = 940mm, Height = 1010mm) and driver center mounted 700mm above floor, on the baffle. Here is the diffraction response I got:
View attachment 68505
Here are the directivity charts and in-room performance sims with floor bounce activated (accounting for a single reflection from the floor):
View attachment 68506
All response data above assumes an ideal 12inch driver. Real drivers have their own bumps and peaks in response. But still this kind of study may be helpful for finding good locations/configuration of baffle and location of driver.
In the above charts, the orange curve on the middle plot in column-1 shows the in room response. If you want to explore more, front wall, left wall, ceiling reflections etc can be studied with VituixCAD by activating the corresponding functionality as seen in left side pic of above plot.
The bottom two plots in above plot shows the directivity (figure-8 radiation pattern) that open baffles are famous for. This can be understood by the nulls in the response around 90 degree off axis compared to much higher intensities as we move on axis of the driver, indicated by the strong intensity red colored regions.

Overall the response looks nice till about 500 Hz. After that above 1kHz, the driver starts to beam. In room response considering floor reflection along is a bit bumpy. Offcourse this will change one the baffle dimensions/location of driver changes But the whizzer cone may help compensate some loss in response off axis from 3-6kHz. But I must confess that I don't know much about the functioning of whizzer cones and how they spread the response better to off axis angles.

VituixCAD is free for use and can be downloaded from here:

VituixCAD features

I highly recommend playing around with this software to understand more, if you are interested.
Off course, nothing beats listening to prototypes and evaluating like you have been doing already..
Wishing all the best..

Regards
Vineeth

Wow Vineeth ...

Thank you for the time taken to do the analysis. The drivers are still on the cardboard baffles.

It's all Greek and Latin for me but something new to explore. I will surely learn something more from this than listening to music and soldering.

I have enrolled for a course on Speaker Design in Coursera (through my employer ) but never took off seeing all the math there. Will have to now try to start that course.

 

[Vineethkumar01]

Wow Vineeth ...

Thank you for the time taken to do the analysis. The drivers are still on the cardboard baffles.

It's all Greek and Latin for me but something new to explore. I will surely learn something more from this than listening to music and soldering.

I have enrolled for a course on Speaker Design in Coursera (through my employer ) but never took off seeing all the math there. Will have to now try to start that course.

Thank you.

I guess the speaker design course that you referred to on coursera is this one:

Fundamentals of Audio and Music Engineering: Part 1 Musical Sound & Electronics

Offered by University of Rochester. In this course students learn the basic concepts of acoustics and electronics and how they can applied ... Enroll for free.

www.coursera.org

If this is the one, I agree that they take a more theory-based route, at least in the beginning.
If you are not interested in the math and still want to know useful information about how to design closed box and bass reflex speakers using free software, I can suggest these courses:

https://www.udemy.com/user/marius-tanasescu-2/

The above ones just cost around Rs 500/- per course when udemy offers discounts (which happens almost on biweekly or monthly basis). The lessons are short, to the point, and conveys a lot of useful information in the short time those courses are designed for.
The above courses are limited to making the on-axis response flat kind of design philosophy and doesn't go into bit more advanced details like directivity matching of drivers and overall acoustic construct etc. Directivity considerations and driver selection, dynamics, nonlinear distortion, and time domain performance considerations are important to get the best 'measurably good' and 'subjectively good' speakers as per the current understanding.
Anyway, have fun with this project. Since you have already found the sound good to your liking, it is all good even if you proceed without any measurements..
All the best..

 

[Subbu68]

Thank you.

I guess the speaker design course that you referred to on coursera is this one:

Fundamentals of Audio and Music Engineering: Part 1 Musical Sound & Electronics

Offered by University of Rochester. In this course students learn the basic concepts of acoustics and electronics and how they can applied ... Enroll for free.

www.coursera.org

If this is the one, I agree that they take a more theory-based route, at least in the beginning.
If you are not interested in the math and still want to know useful information about how to design closed box and bass reflex speakers using free software, I can suggest these courses:

https://www.udemy.com/user/marius-tanasescu-2/

The above ones just cost around Rs 500/- per course when udemy offers discounts (which happens almost on biweekly or monthly basis). The lessons are short, to the point, and conveys a lot of useful information in the short time those courses are designed for.
The above courses are limited to making the on-axis response flat kind of design philosophy and doesn't go into bit more advanced details like directivity matching of drivers and overall acoustic construct etc. Directivity considerations and driver selection, dynamics, nonlinear distortion, and time domain performance considerations are important to get the best 'measurably good' and 'subjectively good' speakers as per the current understanding.
Anyway, have fun with this project. Since you have already found the sound good to your liking, it is all good even if you proceed without any measurements..
All the best..

Yes, that's the one on Coursera. It is free and sponsored by Abu Dhabi Govt. for us employees. It is not that math is intimidating but I am dated (32 yrs since graduation) .Will have to brush up the basics like complex numbers, Calculus etc before venturing into it.

I tried installing the VituixCAD but Norton and Windows Defender (Win 11) blocked it.

I switched off the sub last night and listened to the same track on those Ahujas. Intriguing... With sub ON of course it is full.

Maybe my wife will force axing my Klipsch (to get space in the room). Resisting it.

 

[Subbu68]

Has anyone tried to replace the dust cap of 12FRX with a phase plug to improve the HF dispersion?

Is there any complex math to decide the dimensions of a phase plug?

 

[grindstone]

Perhaps compare what people have done with the Eminence Beta 12LTA. Much experimentation was done on these by enthusiasts in the past. Many people just bought various "nose cones" from model rocketry suppliers and tried things

Possibly start at this page (specifically the internally-linked diyA page which has some dimensions). Elsewhere on diyA there are further experiments (and data) on whizzers as well.

If you have drivers you can sacrifice (or get more readily) and have the intent to experiment, much can be done with whizzer-cone drivers but opinions vary on utility.

 

[Indronil]

In my intro I had written that I got hooked to this forum through the thread on Ahuja 12FRX. Got a pair of Ahuja 12FRX with the intention of replacing the K-28 woofer of my Klipsch Heresy III with this full ranger, remove the mid and tweeters (horns), blank out the holes or leave the tweeter with a simple capacitor around 1.5 - 2 mfd. HIIIs cost me INR 2lac in UAE in 2016, is a special edition in California Black Walnut and lambswool grill - expensive and too pretty to be cannibalized.

Then seeing the designs (discussions) with Ahuja 12FRX of some of the members here @Sumanta, @Hari Iyer and on the net @Sumanta OB idea has taken over. Made a cardboard baffle nearly 95cm x 95cm (it was 45cm x 45cm earlier) to try out the speaker. Currently they are perched on a stool with center of the speakers at 700mm from floor, angled to point at my ears some 3m away. OB has smitten me.

Embarked on some research and stumbled upon a worksheet Xbaffle and playing with it got a few options as below. Results are below. Found that wider the baffle the first dip moves 100Hz.

Any further considerations to be given?

Sorry if I bored you with my rant.View attachment 68117

Are you listening vinyl with Ahuja speakers ?

 

[Subbu68]

Are you listening vinyl with Ahuja speakers ?

I don't use vinyl... Don't want the headache

 

[vdevgon]

In my intro I had written that I got hooked to this forum through the thread on Ahuja 12FRX. Got a pair of Ahuja 12FRX with the intention of replacing the K-28 woofer of my Klipsch Heresy III with this full ranger, remove the mid and tweeters (horns), blank out the holes or leave the tweeter with a simple capacitor around 1.5 - 2 mfd. HIIIs cost me INR 2lac in UAE in 2016, is a special edition in California Black Walnut and lambswool grill - expensive and too pretty to be cannibalized.

Then seeing the designs (discussions) with Ahuja 12FRX of some of the members here @Sumanta, @Hari Iyer and on the net @Sumanta OB idea has taken over. Made a cardboard baffle nearly 95cm x 95cm (it was 45cm x 45cm earlier) to try out the speaker. Currently they are perched on a stool with center of the speakers at 700mm from floor, angled to point at my ears some 3m away. OB has smitten me.

Embarked on some research and stumbled upon a worksheet Xbaffle and playing with it got a few options as below. Results are below. Found that wider the baffle the first dip moves 100Hz.

Any further considerations to be given?

Sorry if I bored you with my rant.View attachment 68117

Sir I am very much interested in using ahuja 12frx as a full range driver with my class a. Pls share the frequency response from your experience and your OB design if possible. Thanks a lot.

 

[Subbu68]

Sir I am very much interested in using ahuja 12frx as a full range driver with my class a. Pls share the frequency response from your experience and your OB design if possible. Thanks a lot.

I did not measure any FR as I don't have the right equipment to do it. For me 12FRX sounded a little bright but very clear. However, Lii Audio F6 came and it took the place. 12FRX is pretty cheap to experiment with.

 

[matgeo]

I did not measure any FR as I don't have the right equipment to do it. For me 12FRX sounded a little bright but very clear. However, Lii Audio F6 came and it took the place. 12FRX is pretty cheap to experiment with.

And ....

 

[Sumanta]

Wow, a lot has happened here. Thanks @Subbu68 for continuing work on this driver. Here are my inputs from my experience. Hope they help you and/or others.

1) I found out DX12-F200 is a better performer than SK12-FRX. The DX one has higher BL and Xmax as well. So, you can try below mentioned DIYs on the SK now and once happy, you can finally make your OB with DX ones.

2) Phase plug - You can cut off the dust cap, but be careful a LOT. I had used half of a shaving blade. But later, I realized I should have marked a suitable circle first on the cap and then use fine needle to poke on that marking through the circumference. Once done, then we can use that half blade to have a nicer cut.
Then you can simply buy a pipe piece with a little bigger dia than the magnet hole. Length of each pipe piece can be measured from magnet end till whizzer cone end. I had filled the pipe with metal cap at magnet end and wood dust or a bunch of toothpick or modelling clay (it was handy as my daughter had a lot of them then.
Do not worry of heat problem as we are blocking the passage on the magnet, OB has its back open.
Please peal off the paper stuck on the back of the magnet and expose the hole in the magnet.

3) I found that adding a compression driver for the HFs are like having your ears opened post a ear block from cough and cold or air pressure drop. so, you can add it this way - I have used CDH-50S with a simple 2.5mfd oil filled capacitor in parallel with the DX12. The capacitor to be connected on the positive plug before the current reaches the CDH. the CDH will be put in the back of the magnet, having their axis same. Their magnetic forces are enough to attach them and keep them in the place, I still suggest to have some other mechanism to hold the CDH strongly with the magnet of the FRX or DX12.
Once you are done with actions in 2, you can try action 3 by taking the plug out. since the pipe plug is to be attached by magnetic force alone, taking it out is easy. Once done, you can then add a horn on the front of DX/FRX through the cut out of dust cap. I had used various options, from plastic adopter to connect plastic pipe to a metal water tap to a plastic horn that comes with children's plastic flutes. All worked at various ways. This is the fun part of DIY.

4) If you want to keep the plug yet want to add a tweeter, I found out having a upward directed tweeter works very well with OB. I had additionally kept a reflector on top of the tweeter to have dipole sound. I think I have images of my speakers in my speaker blog which might help you.

Well, this is what I can write out of my experiences. I do not go by measurements from machines, rather use my ears (and my wife and daughters too like @Subbu68 ) as we are the actual user of the system.

Sometime back I had posted my recent designed OBs in DIY section. I need to find them again if required, as they didn't got much interest here so far.


Hope this long post helps you @Subbu68 and others too.