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Speaker building with foam core board

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musiklava79

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Every newcomer who wants to own a good music set up at home faces a dilemma at some stage. What kind of music system should he own? What should he buy? If he has budget constraints then the decision becomes all the more critical. Again, branded or DIY?

Let's assume that he's decided on his music source and amplifier. That leaves the speakers. Once again, branded or DIY? The options are manifold and the selections are huge. Its all very confusing!

Suppose the person opts to take the DIY route then which driver(s)? What type of enclosure? What enclosure materials? Will he find a carpenter to make the enclosure for him? Doing the entire build by oneself has limited scope given the space constraints in urban living.

Building speaker enclosures out of Foam Core board offers a way out. Its light weight, cheap (if available locally) and does not involve the attendant problems like saw-dust and huge investment and availability of tools with the DIYer. What's important is that its entirely a self-involved project requiring just a minimum investment in tools. These are the basic requirements for making Foam Core board speaker enclosures

Foam Core Board, usually 5 mm thick
A good hobby knife
A cutting mat of appropriate size or a smooth board
A ruler
A straight edge (if available)
A glue gun and glue sticks
PVA glue like Fevicol SR or Fevicol MR

These speaker enclosures give one a good idea of the type of speaker that he intends to build and also the driver(s) performance in them.

Whats more it gives one the full bragging rights to say that he built the speakers all by himself from scratch!! :D

There are many projects that have been showcased in diyaudio where one can select and try out the various types of enclosures. All plans and building methods have been posted in detail so you wont have any problems.

Do give it a shot once. You wont regret it. :)
 

musiklava79

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The first recorded Foam Core build in HFV was the popular Cornu Spiral Horn speakers. That was built some two years ago by FM jetlag.

http://www.hifivision.com/diy/34145-cornu-spiral-clone.html

Theres been no follow-up thereafter from jetlag so we have no way of finding out the long term assessment of his Cornu speakers.

Ive been wanting to build my own Cornu speakers for long but Foam Core Board is not available locally where I live. It was only through the kindness and help of a friend that I got my hands on these sometime ago.

I started out by building a 21 x 21 size with 3 size spirals. Unfortunately I got stuck when I decided to use bamboo plywood for the baffles. The surface of bamboo plywood is quite uneven because of the plaited bamboo. I didnt want to abandon the baffles so I decided to build a small sized Cornu to find a solution to this problem.

Thus my first Cornu build was effectively a 14 x 14 size Cornu with 2 size spirals. Im using cheap computer 2 FR drivers which are rear-mounted on cannibalized front parts of a different cubic computer speaker box.

The inner side of the bamboo plywood baffle was line with 5 mm thick EPE foam lining. This method allowed me to experiment with the damping several times without having to seal the enclosure fully. The EPE foam formed a contour of the spirals that made a near perfect seal and enabled to change the stuffing at will.



EPE Foam Lining



Spirals with Dampening



Driver chamber close-up







View of semi completed Cornus





The Completed Cornus!

The sound? Wow!!

Loud with deep bass unlike anything Id heard before, at least from drivers this small, unlike what they sounded before in their original enclosures. Try it and see for yourselves.
 

musiklava79

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Here are some images of the larger 21 Cornu build. I keep forgetting to take snapshots of my builds while working to Ive missed out on a few steps. These enclosures were built for the Indian made Peerless 3 FR drivers and the damping was tuned for them.









Spiral building in larger Cornu speakers



Bamboo plywood baffles and Peerless (India) 3" FR drivers

The build is not completed yet. The enclosures are being used to temporarily house other 3 FR drivers for breaking-in to use in another build. Ive not yet sealed the baffles so this is what the bare-bones Cornu speakers look like presently.



Ill post my hearing impressions only after completing this build. Needless to say, these Cornu spiral horns have roused my curiosity to know what similar TL and horn speakers will sound like and Ive already started down that path. More later!
 

Sumanta

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I was quite interested in cornu spiral for all those reasons you mentioned.
Now I have someone to ask for detail incase I think of making one.

How about using it for two way. Let the woofer be in the centre and back loaded by cornu spirals and the tweeter be at aesthetically suitable place.

Since cornu spirals must to be suitable for certain T/S parameter limits, limited by physics of sound, I want to know what they are. So, is there any calculation available to decide dimensions, curves of cornu spirals based on T/S parameters of a driver?

Please share if you know anything on this.
 

musiklava79

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Hi Sumanta,

I'm happy to note that you are interested in building the Cornu speakers.

To reply to your queries -

1) As far as I can remember correctly, I have not read of anyone using woofers and tweeters in a two-way build for Cornu speakers in either of the two Cornu thread is diyaudio. However, I distictly remember reading one example of tweeters being used to enhance the HF in a Cornu build with FR drivers.
I think using FR drivers will suffice in these types of enclosures as they cover a wide frequency range. Of course, your choice of FR drivers (and size) will be a deciding factor here.

2) The first factor for determining the physical size of your Cornu enclosures will be the dimensions of the drivers. The driver cut-out diameter, magnet diameter and depth will have to be taken into account. If you study the close-up image of the driver chamber in my 2" Cornu build, you'll understand what I mean. There's not much space in the surrounding spiral walls for bigger drivers in this build. There's a scalable PDF plan for the Cornu speakers -

Foam Core Board Speaker Enclosures? - Page 23 - diyAudio

Go to Post #230 for the plans.

3) Once you've selected the enclosure size which is suitable for your driver, your next step will be to select the appropriate spiral height (or depth). As a thumb rule, 3" FR drivers can use 3" to 4" height for the ~ 20" x 20" build but once again, the driver depth will have to be accounted for. Some space should be left behind the magnet rear plate, too.

4) As you well know that the output frequency of a horn will be determined by the throat area, the line's length and the mouth area. In the Cornu, the median of the spiral is taken as the length.We are confined in the size of the mouth by the size of the enclosure. There are 4 spirals in the Cornu of which the two longer horns originate from the driver chamber while the other two are located further down the spiral.
So effectively, we have two different output frequencies. To find out the throat size we take the value of Sd from the driver T/S parameter and divide it by the height of the spiral wall. (If the Sd value is sq. cm then all other calculations will be in cm.s or as applicable). Divide the throat size by two as there are two spiral horns. This gives the actual throat size that one needs to set when building the Cornu.

An image of the throat -



5) About the other T/S parameters - the lower the Fs the better the bass. Qts above 0.50 also helps with the loudness of the speakers.

Let me point out at this stage that the Cornu's are definitely not audiophile grade speakers. Far from it. All I can add here is that should you decide to build them, you're in for a unique treat and listening experience. Otherwise this build would not have been so popular and praised by so many DIYers who built them. The Cornu thread(s) in diyaudio are a long way away from losing steam!

If you can build it correctly and get the tuning just right, you, as a musician, will be surprised by how realistic the tabla (bayan) and mridanga and other percussion instruments are capable of sounding! And Im only talking of the low frequencies here.
 
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Sumanta

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I think a simple, suitable capacitor put in parallel to a mid woofer of suitable Fs and Sd can accommodate a tweeter and overall the speaker will look good as well.
If you measure line length of the Cornu it might match Transmission line thumb rule table of MJC. Plus, we can increase size of speaker from 20" to somewhat bigger (if required).

Let me draw an artist's impression to demonstrate it to you.

If you see available Peerless wide band 3 or 4 inch drivers, only one of them remain in 90 SPL level at >10k Hz. I would rather prefer a driver having lower Fs and augmented with a tweeter.
Since the back loading is increasing it's mouth area at exit, it needs longer line length. If we can come out with a tapered line design and can somehow mass load it, we can have better bass!
Things are getting interesting? Let's go back to drawing board first.
Thanks again for initiating this topic.

Although I am not going to start another speaker build immediately but this Cornu design is a wonderful design for all that has limited floor space in their apartments. And so I am interested to make one for one of my friend.
 

musiklava79

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The actual line measurements in my larger Cornu build are 64" and 47" for the respective spirals. I used a flexible curve ruler to measure the lines and its fairly accurate. I did not measure the smaller Cornu spirals but going by the materials (Foam Core board) consumed it is ~ 34" and ~ 23" respectively.

The original drivers I used were the Peerless 3" FRs and these could go down to about 60 Hz or lower by reckoning. I'll measure actual frequency responses once I've re-mounted the Peerless drivers and completed the build.

Cornu speakers perform best when mounted on walls. Perhaps the wall at the back of the speakers act as an extension and enhance the bass to unbelievable levels.

I'm sure you've already read the following article but nevertheless I'm adding the link here so that anyone else who might be interested can have a read.

6moons audioreviews: Cornu Compact Spiral
 

yogibear

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Kudos to you Man ! Excellent Experiment ! I will try this out with some great FL 3 inch drivers I have acquired. Thanks for sharing.
 
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musiklava79

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.....I will try this out with some great FL 3 inch drivers I have acquired.....
Thanks, yogibear. It would be a great experience if you make one. I'm sure you can easily build one. Have a shot at it! :)
 
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Sumanta

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The actual line measurements in my larger Cornu build are 64" and 47" for the respective spirals. I used a flexible curve ruler to measure the lines and its fairly accurate. I did not measure the smaller Cornu spirals but going by the materials (Foam Core board) consumed it is ~ 34" and ~ 23" respectively.

The original drivers I used were the Peerless 3" FRs and these could go down to about 60 Hz or lower by reckoning. I'll measure actual frequency responses once I've re-mounted the Peerless drivers and completed the build.

Cornu speakers perform best when mounted on walls. Perhaps the wall at the back of the speakers act as an extension and enhance the bass to unbelievable levels.

I'm sure you've already read the following article but nevertheless I'm adding the link here so that anyone else who might be interested can have a read.

6moons audioreviews: Cornu Compact Spiral
Thank you for dimensions.
Yes.
Yes.
Yes, yesterday again at sprinting speed.
 

ememm

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Thanks musiclava for starting the thread.

I'm also seriously(for quite some time now) thinking of building a pair. I want to use my 2.5 inch FR speakers pulled from my Yamaha HT. But I don't have the TS parameter or the FR chart for it, so currently looking for a way to setup a cheap measurement system(which, hopefully,I can use later for more HiFi speakers).

Anyways, just to add to this thread, I found the following diyAudio posts very informative:
Ever think of building a Cornu Spiral horn? Now you can! - Page 193 - diyAudio
Ever think of building a Cornu Spiral horn? Now you can! - Page 11 - diyAudio
Ever think of building a Cornu Spiral horn? Now you can! - Page 12 - diyAudio

I admit I haven't gotten my head around all that, but it is good to know that the science behind it is understood and documented.

As the OP mentioned, getting foam core board seems to be a problem. Someone on this forum has suggested that it is available as "Depron" in RC plane building hobby shops, but I am yet to visit any and see if it is useful.

So if anyone can share any information on availability of foam core board (esp in bangalore), it would be great.
 

linuxguru

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How about using it for two way. Let the woofer be in the centre and back loaded by cornu spirals and the tweeter be at aesthetically suitable place.
If you have a good FR driver with decent treble extension, the tweeter should be unnecessary. However, you can always add one anywhere on the front baffle of the Cornu, maybe just adjacent to the FR driver. A small silk or mylar dome tweeter should be adequate.

BTW, there are some 2" Cambridge Soundworks HT satellite drivers that may be suitable for a mini- or micro-Cornu:




They're both 4-ohms, though.
 

ememm

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linuxguru, what about the Tymphany ones you have proposed for groupbuy?

I thought of jumping in and getting a pair, but then decided to put the unused Yamaha to some use. And learn some DiY on the way.
 

Sumanta

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Just one point to note from my side. I am playing on wide bander 3 inch through pipe. It plays quite wide a spectrum quite flat (by my ear). But a small driver does not play sound as realistically as a 12 inch one.

It could be understood more if you listen a song first through a laptop or mobile speakers and then through a small home theatre speaker (or PC based 5.1 speakers).
I mean listening through small drivers is a compromise (consider it as my impression only as I do not want to hit honeybee's nest). Listen to a 8 inch or 12 inch drive for its mid. T/S parameters are not all.
 

musiklava79

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Hi ememm,

I'm also seriously(for quite some time now) thinking of building a pair. I want to use my 2.5 inch FR speakers pulled from my Yamaha HT. But I don't have the TS parameter or the FR chart for it, so currently looking for a way to setup a cheap measurement system(which, hopefully,I can use later for more HiFi speakers).
Good to hear that you're planning to build your own Cornu speakers. You don't really need the T/S parameters for the micro Cornu (size 14" x 14"). Just make sure that the driver cut out diameter and the magnet size are less than 2". Also check the depth if you are planning to cut the spiral width at 2". Make the throat size ~ 0.4". Else you can increase the spiral width to suit the depth of the driver. But don't forget to alter the throat size!
When I built my micro Cornu speakers, all the specifications I had to go on were 4 ohms impedance and 3 Watts output!

I admit I haven't gotten my head around all that, but it is good to know that the science behind it is understood and documented.
Don't worry too much about the technical aspects of building the Cornu's. It's a fun build and that's what you should treat it as. Just follow the instructions and there you have it.

As the OP mentioned, getting foam core board seems to be a problem. Someone on this forum has suggested that it is available as "Depron" in RC plane building hobby shops, but I am yet to visit any and see if it is useful.
That was yours truly in the Tymphany group buy thread. :eek:hyeah:
I had posted this information there.
Depron is a brand name for Foam Core Board. Its a paper laminated moulded Styrofoam sheet of various thicknesses. Its also called biofoam in different cities in India.

So if anyone can share any information on availability of foam core board (esp in bangalore), it would be great.
You can buy foam core board from RCbazaar in Bangalore. They sell it as Depron. I checked their website today and it seems they have none in stock. Just visit their website and take their phone number and call them to enquire about when they will receive fresh stocks. Theres another seller in Bangalore -

Depron Foam Sheet Bangalore - Buy Depron Foam Sheet Online - Kwality Products

His prices are outrageous! I got my foam core board sheets from the Pune branch of RCbazaar with the help of a friend, who took the trouble of going all the way to their store (it's 80 km.s to and fro his home), buying the stuff, cutting it in the shop because it did not fit into his car, then packing and shipping it to me.

You can try and contact members of aero modelling clubs. I believe foam boards are also used by aquarium fish enthusiasts.....
 

linuxguru

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Just a caveat that Bio-foam and Depron seem to differ in quality - some of the RC plane forums have postings that seem to imply that imported Depron is superior for RC models because it is stiffer, lighter and easier to cut.

However, the differences may or may not be relevant for speaker builds - these aren't going to be flying through the air at any rate, so weight may not be an issue.
 

musiklava79

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Why should linuxguru alone have all the fun with his Tabaq Box based folded MLTL? :eek:hyeah:

So I thought, why not join his company by making a Tabaq-like folded MLTL out of foam core board? So here's something that I'd completed around the time I completed my Tabaqs but didn't find the time to post......
 

musiklava79

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THE TABAQUBE
FOLDED MLTL SPEAKERS

Credit goes to xrk971 who built the original Tabaqubes. The details and plans can be found here -

TABAQ TL for Tang Band - Page 45 - diyAudio

Post #450

TABAQ TL for Tang Band - Page 53 - diyAudio

Post #530

I altered the quadrant dimensions to 2.25", increasing them so that I could accomodate 2" FR drivers. The TL line was retained at 36". The vent area was kept at 1 x Sd. This was easy since the driver T/S parameters were known. The intention was that if needed I could always add a cut piece of FC board to make the vent narrower to check the difference in SQ. FC board thickness was also factored in. This was not there in the original plans.

I used a pair of Visaton 2" FRWS5 FR drivers for the Tabaqubes. I changed the construction method slightly to suit me as I am not that skilled or fast with a glue gun like some folks over at diyaudio. I used a combination glueing method of PVA glue and hot melt glue, holding down the portions where I used mostly PVA glue with masking tape, to bind them together. Masking tape is easy to remove if one is careful. I used ~ 10 gm. of polyfill as damping initially. I'm still playing around with the damping as I've not yet sealed the top cover. I'm using a layer of closed cell HDPE to act as a seal during trials plus a weight on top of the cover.

Here are some snapshots showing some construction steps -













 
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