Ahuja 12FRX Open Baffle

[Subbu68]

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.

 

[Subbu68]

Use Basta to simulate according to the choice of baffle dimensions you can afford in your room size. It gives an excellent idea of low end roll off and over all linearity of midrange response. Off centre the driver so that it sees different distances from all the four edges. If the software simulates larger than desirable baffle, get that width by using L shape baffle.

Tolvan Data

Thank you for the heads-up. I did download Basta but found it a bit cumbersome to use. Will definitely try again

 

[Subbu68]

Pretty easy though not so user friendly but very useful for OB.

I was trying it now. the software does not open. It opened two days back though. After inputting the license number given in their website, it just runs through some windows and disappears!!

 

[Subbu68]

Is it incompatible with Win-11?

 

[Subbu68]

Strange ! I will try and update…

You need to right click Basta and Run as Administrator for it to work on Win 11

 

[Subbu68]

That must be the issue. I use it on Windows 8 ultimate 64bit

Thanks a lot. It worked and the response came out nearly the same as XBaffle output I posted.

Xbaffle is super easy to use and easier to compare the responses for various conditions as you can see the curves immediately though limited to 4 curves.

 

[Subbu68]

Thanks to @yogibear ran a simulation on Basta for various options of OB for the subject Speaker.

The legends are Baffle Width x Baffle Height, Mounting Height of Spkr from floor. The orange curve is the current cardboard one. It is 940mm x 1010mm and spkr at 240mm from floor. The rest are various options for a permanent baffle.

Felt higher the mounting a little better to smooth the dips in 500Hz - 1000Hz region. Lower end I have to blend in my KEF sub.

Favoring 700mm mounting height for spkr. No Tweeter, hence, this choice to bring to ear level with a little tilt.

Any other consideration to include? Please advise.

 

[Subbu68]

Looks good. Are you planning to top it off with a tweeter ?

A lot would depend on your amp driving these, your source and quality of recordings. OB is ruthlessly transparent. Do measure these nearfield and at your listening position, on axis, to compare with what Basta simulated.

Thank you

I think the stated 16kHz of 12FRX is good enough so would think of tweeter later. Will make a provision for it on the baffle. A simple helper tweeter.

Aging ears won't make out anything more than 10kHz. Even a rough test shows my ears are complying with this. Have a daughter who seems to detect ultrasonic. She is my measurement device for sibilance and all audio tuning . Ultra sensitive ears and musically more intelligent too. She'll come home from University coming weekend and would make her test the speakers.

Even the Klipsch Heresy are ruthless with poor recordings.

The amp is a SE valve running EL34 in ultra linear mode. Can take 6L6GC, KT88, 6CA7 too as it is auto bias. Have those valves too with me.

NAS>PC>DAC>AMP is the chain. Or CDP/tape> valve preamp > amp but rarely used

I think more than the FR curves, what is comfortable to ears is important.

I would try measurements albiet with my phone.

 

[Subbu68]

Is it necessary to flush mount the FR driver on the proposed OB?

Since the diffraction would kick-in for HF drivers the come / dome being close to baffle, I understand that they need to be flush mounted on the baffle. For a dual cone FR since the HF cone is about 15cm from the edge of the speaker frame would it matter much by surface mounting the speaker.

• Trying the first DIY speaker,
• leaving out the carpenter (virtually no one near my house to do it - all moved to industrial area some 30km away),
• my carpentry skills are school level,
• living in apartment so to keep the wood work to bare minimum,
• Dremel circle cutting tool has a maximum circle limit of 300mm while 12FRX has an overall dia of 310mm.
• Buying a router would be a good choice but my not have any use after this work.

 

[Subbu68]

Not needed…..

File manually to make the circle larger….

Thank you....

Dremel can cut the required cutout of 285mm to surface mount the driver. However, to flush mount it cannot do a 310mm dia recess. Else it would have been neat.

 

[grindstone]

Sometimes, people put a felt "ring" around the driver rim for these experiments or add a thin facing layer of wood to their baffle for these concerns. It saves counterboring/rebating to inset a driver frame (and sometimes baffles are thin-enough to cause concern.

Finding difficulty expressing how great it is that you are doing this and following your ears. It doesn't take a lot of money to learn vast amounts about one's preferences and gear and rooms using these sorts of microscopes. This is a really good "spirit" of diy-audio. Single-drivers are grand in many ways and especially when they are economical! Those kinds of things are hard to find in my region anymore. The market has learned and the word is out so everything became too expensive to cut-up and modify I cannot commend both of your efforts more strongly and thank you for posting.

 

[sdk]

Is it necessary to flush mount the FR driver on the proposed OB?

Since the diffraction would kick-in for HF drivers the come / dome being close to baffle, I understand that they need to be flush mounted on the baffle. For a dual cone FR since the HF cone is about 15cm from the edge of the speaker frame would it matter much by surface mounting the speaker.

• Trying the first DIY speaker,
• leaving out the carpenter (virtually no one near my house to do it - all moved to industrial area some 30km away),
• my carpentry skills are school level,
• living in apartment so to keep the wood work to bare minimum,
• Dremel circle cutting tool has a maximum circle limit of 300mm while 12FRX has an overall dia of 310mm.
• Buying a router would be a good choice but my not have any use after this work.

If you plan to file the hole to final size then ask for a rapid cutting wood file called as Marfa in half round

And a half round medium file for finishing

Alternatively you could buy a jigsaw and cut inside the line and finish with a file
Or with these. Universal BUYER5pcs/set High Speed Steel Burr Drill Bit Set Wood Carving Rasps for Dremel Shank Burs Tools Cutting Tool Black Rotary Bit Set https://www.amazon.in/dp/B09B49N6Y2/ref=cm_sw_r_cp_apan_glt_i_49RP9GE07R0VMNCP7XK3

 

[Subbu68]

Still thinking of the baffle design. For WAF acrylic seems to be good. She is particularly keen that acrylic does not stand out in the room.

Now acrylic has to be very thick to avoid the vibrations due to the excitations the driver can induce on it.

What if I mount the driver on a frame and add a acrylic baffle on top of it without any contact with it - a kind of floating baffle? Baffle could be pretty thin like 3mm.

Thinking of a wooden frame or out of slotted c-channel 21mm x 41mm (Unistrut as we call in electrical industry). A single center pole with a base is my idea. Mount a couple of spacers on it equal to the depth of the driver and mount the baffle on it without touching the driver. My idea in a sketch



How do people mount the driver on single pole structures?

Thanks in advance

 

[sdk]

Still thinking of the baffle design. For WAF acrylic seems to be good. She is particularly keen that acrylic does not stand out in the room.

Now acrylic has to be very thick to avoid the vibrations due to the excitations the driver can induce on it.

What if I mount the driver on a frame and add a acrylic baffle on top of it without any contact with it - a kind of floating baffle? Baffle could be pretty thin like 3mm.

Thinking of a wooden frame or out of slotted c-channel 21mm x 41mm (Unistrut as we call in electrical industry). A single center pole with a base is my idea. Mount a couple of spacers on it equal to the depth of the driver and mount the baffle on it without touching the driver. My idea in a sketch

View attachment 68462

How do people mount the driver on single pole structures?

Thanks in advance

This reminds me of the air circulation fans at wedding venues. Maybe you can contact a local fan manufacturer and buy a pair of bases and mount the driver on them

 

[Subbu68]

This reminds me of the air circulation fans at wedding venues. Maybe you can contact a local fan manufacturer and buy a pair of bases and mount the driver on them

Do you mean those fans called "man coolers"? They'd be pretty heavy and aesthetics would be vetoed by wife.

And fans etc. are not manufactured here in UAE. Everything imported.

Have to make them as sleek as possible? Those Unistruts I mentioned are pretty slim but strong enough to take even heavy cables etc. These are easy to assemble with standard fittings available like L clamps, bases etc.

 

[aeroash]

What if I mount the driver on a frame and add a acrylic baffle on top of it without any contact with it

Purely from an aesthetics point of view, this design herebelow would be the simplest and the cleanest. It will have to be a 10mm acylic at least, Of course, thicker the better. Is tempered glass a possibility? It'll be cheaper and stiffer than acrylic for the same thickness.

 

[aeroash]

I'm sure you would've come across this, here's a suspension system.

https://www.linkwitzlab.com/Links/Baffle Vibrations in Open Baffle Dipole Loudspeakers Kopie.pdf

 

[Subbu68]

Purely from an aesthetics point of view, this design herebelow would be the simplest and the cleanest. It will have to be a 10mm acylic at least, Of course, thicker the better. Is tempered glass a possibility? It'll be cheaper and stiffer than acrylic for the same thickness.

View attachment 68482

This is the one that caught my wife's eyes.

10mm thick acrylic seems very expensive. I am trying to come up with a design using Aluminum profiles, pipe clamps to hold the driver and a thinner acrylic baffle
.

 

[Subbu68]

I'm sure you would've come across this, here's a suspension system.

https://www.linkwitzlab.com/Links/Baffle Vibrations in Open Baffle Dipole Loudspeakers Kopie.pdf

That article has some good solutions. Would think on that lines too.

similar to the leaf spring was thinking of using a 24 inch projector mount, mounted vertically on a base and turned 90 degree. Attach the speakers with long threaded rods and nuts with some nylon or neoprene bushes.

 

[Vineethkumar01]

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:

Here are the directivity charts and in-room performance sims with floor bounce activated (accounting for a single reflection from the floor):

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