DIY Open Baffle Experiment

[aashish351]

Hi Folks!

Getting intrigued by so many good things I have heard about Open Baffle, I though I'd try some for myself. I had 7 Focal Chorus IC 706v Ceiling speakers lying idle for a long time. 5 of them were mounted into custom made wall hanging 19mm plywood boxes. For surround sound application from which I don't expect much, it worked out pretty good...

For the remaining two, I though of trying a simple open baffle design not based on any proper calculations of compensations to start with. So I asked my carpenter to cut two 36" tall by 24" wide pieces of 19mm plywood board and attach triangular supports on both sides of each such that the front board is inclined backwards from the top. Mounted the ceiling speakers at 2/3rd height from the bottom and I was good to go.

I connected it with little expectation, but I was in for a pleasant surprise. The Focal IC 706v are rated at 89dB, 8 ohm, 25-125 w, 65Hz to 25 Khz. It is coaxial speaker with 6" mid-bass and a centrally mounted 1" inverted dome tweeter, so I was not expecting much in the bass.

The surprise was a very nice, fast, tight mid-bass. True, there was no bass below the rated frequency, but the drum kicks and bass guitar notes were beautifully produced. The highs were a little less refined, but that I know is the focal's inverted tweeter. The vocals were open and energetic. A little too energetic, as I found in some songs there was an extra "glaring" or "echo" in the vocals. I guess this was the negative effect of improper baffle calculations! Some of the vocal glaring is also due to my room, which I find a problem even with Dali Ikon 6 which too have energetic vocals. But overall, more than a successful first attempt. I am certainly not going to stop at this stage....

I can see a lot Open Baffle experiments in my near future!

Will post pictures soon... In the meantime, I would really appreciate suggestions from DIY and Open Baffle experts to shine some light on the Vocal glaring & echo reduction.

 

[denom]

Hi aashish351,

Good show! Waiting for the pics :licklips:

We have FM's Jaudere(who by the way is absent form the forum for quite some time) & more recently Sumanta for sharing their handy work w r t open baffle speakers.

Congrats to both of you as well, for creating the DIY interest in fellow FM's
Maybe some more will join in the fun soon???

 

[aashish351]

Thanks denom!

Here are the pictures. The baffles are still unfinished as I may need to make a few changes or additions depending on the suggestions and advice of experts...

Pardon the quality, took from Nexus S... will take SLR pictures when finished.

By aashish351 at 2012-05-15

By aashish351 at 2012-05-15

By aashish351 at 2012-05-15

By aashish351 at 2012-05-15

 

[Sumanta]

Dr. Jaudere is busy in cycling.
I had a small chat over SMS last week. It seems he is enjoying bike riding a lot.
I wanted to thank him for identifying Ahuja full ranger driver to me.

 

[aashish351]

I have decided to fine tune these first before replacing the ceiling speakers with Ahuja Full rangers... I know the bass is only about 70 Hz (I think, no measurement) but it is good enough for me at the moment...

maybe a dipole subwoofer in the future!

Anyway, to fine tune, Hari has suggested a combination of Inductor & Resistor as Baffle step compensation, which I am trying to procure (help in where to get from will be useful). Thanks to Hari for taking the time out from vacation to respond!

The other tweak I have thought of to tame the midrange glare is to cut the side supports to half from top and also remove the top horizontal 4" plate... I think the current back support dimensions are creating this horn-like midrange glare...

what say?

 

[jaudere]

Hi folks. Glad to know that you remember me. I had a freak cycling accident and fractured forearm bone near elbow. So I am under compulsory rest and that is how I am back on forum.

@Ashish: Those speakers look very well made. Would love to listen to them. Don't forget to polish the wood. I feel that the midrange boom is more likely to be due to driver characteristic than the problem of the OB design. You can choose the driver for your next experiment more carefully. Reducing the baffle width in any direction will affect lower frequencies rather than the midrange.

 

[aashish351]

@jaudere.. welcome back and hope you get well soon....

i have the same speaker installed in a 0.3 cu.ft. sealed box as satellites where the midrange boom is not so evident. anyway, I am not going to reduce the front baffle size in any way, but you see the back supports which are all around at the baffle edges. I am planning to cut the vertical back support to half the height and shift it a inside the edges by 2" from both sides. More like this...

By aashish351 at 2012-05-26

 

[jaudere]

The supports are adding to baffle width. So by cutting supports, you will reduce baffle width. That will further reduce lower frequency reproduction. I suspect that such a measure will in fact indirectly make the midrange more prominent. A selaed enclosre makes lowrr frequencies more prominent and thus reduce the emphasis on midrange. That is hwy you don't get the midrange bloat in sealed box. Do you have TS parameters and frequency response curve of your speakers. A speaker made for special purpose will give best result in that situation only. It will behave as a totally different animal in other kind of enclosre or on open baffle. There are some speakers meant to be used on opne baffle. The frequency response curve of your speaker is important. Please try to get it.

 

[aashish351]

Actually this is the focal jmlab chorus ic 706v in ceiling 2 way coaxial speaker. I have specs but not ts parameters. I thought being a ceiling speaker it should work in open baffle arrangement. But in the long run I too want put a suitable full ranger.

Sent from my Nexus S using Tapatalk 2

 

[jaudere]

Ok. Now I got what modification you are planning. The image was not opening before. The modification will not give desired effect. Are the supports parallel to each other and perpendicular to the front baffle?If yes, they may give rise to something called as standing waves(about which I am not very clear but I know that if affects the sound in bad sense due to waves getting reflected multiple times). Instead if possible, the supports should be at obtuse angle to the front baffle rather than at 90 degr and top plate can be made slanting down forward rather than being horizontal. My carpenter did it for me. Needs bit of skill. Try it and let us know the effect.

 

[Hari Iyer]

The supports are adding to baffle width. So by cutting supports, you will reduce baffle width. That will further reduce lower frequency reproduction. I suspect that such a measure will in fact indirectly make the midrange more prominent. A selaed enclosre makes lowrr frequencies more prominent and thus reduce the emphasis on midrange. That is hwy you don't get the midrange bloat in sealed box. Do you have TS parameters and frequency response curve of your speakers. A speaker made for special purpose will give best result in that situation only. It will behave as a totally different animal in other kind of enclosre or on open baffle. There are some speakers meant to be used on opne baffle. The frequency response curve of your speaker is important. Please try to get it.

I agree with Jaudere that the modification will reduce the low frequency even further as there is more chance for the front and back waves to intersect and cancel each other. The obtuse angle will be a better idea as it will be even more difficult for the front and rear waves to meet each other. Also a non-parallel sides will prevent any standing waves (if any). Keep the obtuse angle around 15 deg which are the standards for studio speakers placement.

 

[aashish351]

Thanks guys..

I will keep the baffle unchanged and work on finding a flat response full ranger. Also I will try the baffle step compensation first in this driver.

Sending the baffle for duco. Will post pictures when finished.

Sent from my Nexus S using Tapatalk 2

 

[aashish351]

Ok. Now I got what modification you are planning. The image was not opening before. The modification will not give desired effect. Are the supports parallel to each other and perpendicular to the front baffle?If yes, they may give rise to something called as standing waves(about which I am not very clear but I know that if affects the sound in bad sense due to waves getting reflected multiple times). Instead if possible, the supports should be at obtuse angle to the front baffle rather than at 90 degr and top plate can be made slanting down forward rather than being horizontal. My carpenter did it for me. Needs bit of skill. Try it and let us know the effect.

Yes the support are parallel to the main baffle. I will try and get the support angled as suggested by you and also get the top plate slanted before painting.

Sent from my Nexus S using Tapatalk 2

 

[Rajiv]

Hi,

I will keep the baffle unchanged and work on finding a flat response full ranger.

The LCao drivers seem to be getting a lot of praise. Nelson Pass thinks highly of them.

L CAO in OB W/ Eminence Woofer - diyAudio

New 8" full range speaker from L CAO - diyAudio

L.Cao full range speakers

L. Cao 8 inch Alnico Fullrange Speaker Matched Pair items in Vintage Audio Lab store on eBay!

The Alnico magnet version is around $350 for a pair. The ceramic version should be less expensive.


Regards
Rajiv

 

[aashish351]

got an idea from wildburrowaudio.com. I will use the hinges as mentioned here Wild Burro Audio Labs - Fullrange Speaker Projects - Basic Open Baffle Design and make the side support angles flexible!

Shoud work in finding the optimum balance between midrange control and bass by changing the angle of supports gradually!

What do you guys think?

 

[jaudere]

I would still say that since you know speaker model, try to get frequency response curve first. Should be there on net. Secondly, you will need very good hinges. Otherwise the hinges themselves will vibrate. In addition, you need to take care that there is no air leak between the front baffle and wings. With movable wings, such a gap is likely, although it can be sealed. Thirdly, changing the angle of wing will not change lower frequency response as such (as long as it is more than 90 degr). It will improve midrange provided that the problem is due to standing waves. I have played with the idea in past with simple hinges but I didn't like the result. Of course the experiment was very basic and non scientific. By the way, mounting driver offcentre also imrpoves sound. I forgot the logic behind it but it is easy to implement. Keep the width of the wings different. This way the driver is automatically eccentrically mounted and at the same time looks to be in centre when viewed from front ( which I like aesthetically )

 

[Sumanta]

Off centre driver location helps reducing peaks and dips in SPL for a particular frequency as distance of baffle edges varies instead of an uniform one.

I think having wider wings at the side wall side and narrower one at the centre side helps in getting lower frequencies.

 

[aashish351]

I would still say that since you know speaker model, try to get frequency response curve first. Should be there on net. Secondly, you will need very good hinges. Otherwise the hinges themselves will vibrate. In addition, you need to take care that there is no air leak between the front baffle and wings. With movable wings, such a gap is likely, although it can be sealed. Thirdly, changing the angle of wing will not change lower frequency response as such (as long as it is more than 90 degr). It will improve midrange provided that the problem is due to standing waves. I have played with the idea in past with simple hinges but I didn't like the result. Of course the experiment was very basic and non scientific. By the way, mounting driver offcentre also imrpoves sound. I forgot the logic behind it but it is easy to implement. Keep the width of the wings different. This way the driver is automatically eccentrically mounted and at the same time looks to be in centre when viewed from front ( which I like aesthetically )

How about unmounting the speaker from the baffle and measuring the SPL of the driver by playing the sine wave sweep using Room EQ wizard with nearfield mic? will that be helpful?

 

[jaudere]

I am not sure. May be Hary/ t Antony can help you here but it seems to be a good idea. If you have equipment, try to get the graph of the whole speaker without dismantling the driver. You will at least know where the thing is going wrong. But can you create sounds of frequencies (in increaments of 10 upto 100hz, in increaments of 100 upto 1000hz and in increaments of 1000 upto 20khz). At least that is how the curve is usually given. Have tried the manufacturer's web site?

 

[aashish351]

Graph of the whole speaker can also be done. The Software makes the graph excatly in the logarithmic scale as required. I think, the sine wave sweep is meant for that only. Here is an example of the curve of my laptop speaker through my laptop mic.

By aashish351 at 2012-05-28
Here is the link of the manufacturer's website. only commerical information as you can see.
Focal Chorus IC 706 V, In-ceiling loudpseakers