Ever think of building a Cornu Spiral horn? Now you can!

[Coen]

Hello there,

I've been lurking around the forum for a while and just keep getting back to this thread. So i decided to try and make a pair of cornu speakers for myself. Anyhow, now i find myself lost in a sea of full range drivers and cornu spiral horn speaker sizes. I would greatly appriciate if someone could help me out with the following:

I wanted to start out with something small, so from reading the posts i gather:

2 inch driver = 36 cm
3 inch driver = ?
4 inch driver = 50 cm
5 inch driver = 75 cm

Can someone tell me the depths to go with these? Or is there a formula to calculate the speaker size (including depth) to go with the driver?

Ok so i was either thinking to go with something really small like 2 inch, or would it be better to go with 50cm for a living room speaker?

I'm from the netherlands myself and i'm finding it hard to get drivers for a decent price, parts express get expensive quite fast because of the shipping. Drivers i could get here are:

Visaton FRS 5x (2inch, the cheapest i found, would these be worth getting? i read some bad things about visaton)
FRS 5 X - 8 Ohm

Peerless 830986
Peerless 830986 3" Full Range Woofer 264-1056

The wavecor FR070WA01 (these are actually more expensive then i'd planned..)
FR070WA01_02

Or if anyone knows a driver of one of those brands that would be better suited i'm open for suggestions

Last question is about which drawings to use, i found the ones in post #30, are these still the ones to use? i also saw some "rounder" designs in other posts.

Thanks!

 

[Cal Weldon]

Hi Coen,

I used a 4.5" driver (Fostex FF125WK) My box was 70 cm and the channel depth was 4.5" I used the first of the two drawings in post 30. I think we have agreed the more bends (elbows) there are, the better, as they filter out the mids from the horn.

As far as what size to use, that up to you, your environment and listening preferences. For myself, the 4.5" and the 3" are night and day apart.

 

[Zigis]

Hi Coen,
of course, Part express is for North Americans, try SpectrumAudio:
Breitbandlautsprecher und mehr - SpectrumAudio

there was few more speaker sellers in Germany and I saw in Netherlands too, just google.

 

[petervr]

I used a 4.5" driver (Fostex FF125WK) My box was 70 cm and the channel depth was 4.5" I used the first of the two drawings in post 30. I think we have agreed the more bends (elbows) there are, the better, as they filter out the mids from the horn.

As far as what size to use, that up to you, your environment and listening preferences. For myself, the 4.5" and the 3" are night and day apart.

Hi Cal,

Rather than trawling through hundreds of posts, can I ask you what the 3" driver was?

I have a a 50cm one with the Vifa (as per xrk971) and really like them, but wouldn't mind at some future stage trying a 4.5" one like yours. Your current opinion on the 70 cm with the FF125WK is still the same as per some of your previous posts?

Peter V

 

[xrk971]

I think it was either an Aura NS3xxx or some salvaged white cone LG drivers from the thrift store?

But I would imagine the bass from a FF125wk is going to be superior with longer channels.

 

[Cal Weldon]

I tried 6 different 3" drivers and it was a tie between a salvaged JVC and a salvaged LG. No comparison between the 3's and the 4.5. Go with the largest you can.

When it was placed outside recently, the bass made us all giggle like children.

 

[Don Hills]

...
When it was placed outside recently, the bass made us all giggle like children.

Whatever you were smoking out there, I want some.

 

[Coen]

Hi Coen,
of course, Part express is for North Americans, try SpectrumAudio:
Breitbandlautsprecher und mehr - SpectrumAudio

there was few more speaker sellers in Germany and I saw in Netherlands too, just google.

Thanks for the site, i did google for german shops to but didn't find this one yet, i'll email them for the shipping costs.

Hi Coen,

I used a 4.5" driver (Fostex FF125WK) My box was 70 cm and the channel depth was 4.5" I used the first of the two drawings in post 30. I think we have agreed the more bends (elbows) there are, the better, as they filter out the mids from the horn.

As far as what size to use, that up to you, your environment and listening preferences. For myself, the 4.5" and the 3" are night and day apart.

Well bigger might be better, but i guess my first pair will end up in my home office (2.5m x 3m) so 70x70 might be on the large side..

I did order some foamboard, might go for 50x50 or 40x40. What depth should i make those, 7cm for the 50 and 5cm for the 40 ?

 

[xrk971]

A rough way to estimate the depth of the Cornu is to set it so that the cross sectional area of the two throats leading from the driver chamber is equivalent to the Sd of the driver. However, you can be about 25% off and it will be fine. The deeper channel will allow more bass amplification and also more upper bass and mids to leak through, possibly necessitating use of more stuffing in the channels or even some light stuffing at the mouths. If you use a driver with a higher strength motor (high Bl and low Qts), you can make the throat on the smaller side to keep Vb down. Opposite is true of high Qts drivers. It is quite forgiving. If you have a driver you want to try get me the TS params and I can run a simulation for you.
X

 

[Coen]

A rough way to estimate the depth of the Cornu is to set it so that the cross sectional area of the two throats leading from the driver chamber is equivalent to the Sd of the driver. However, you can be about 25% off and it will be fine. The deeper channel will allow more bass amplification and also more upper bass and mids to leak through, possibly necessitating use of more stuffing in the channels or even some light stuffing at the mouths. If you use a driver with a higher strength motor (high Bl and low Qts), you can make the throat on the smaller side to keep Vb down. Opposite is true of high Qts drivers. It is quite forgiving. If you have a driver you want to try get me the TS params and I can run a simulation for you.
X

I've decided to go with the Fountek FE85

Fountek FE85 3" Full Range Driver 296-717

I read Switters already made a set with these so perhaps i should send him a message

 

[xrk971]

Fountek FE85 can probably work well with a 20 in Cornu, based on the Sd of 27 cm^2 the depth should by 2.7 in. So anything from 2.5 in to 3 in deep should work. Looks like a neat little driver that I would like to try one day. Good luck.

 

[Cal Weldon]

Whatever you were smoking out there, I want some.

hehe. That's years in the past my friend.
I can't blame you for thinking I'm exaggerating about the bass. I wouldn't believe me either.

Well bigger might be better, but i guess my first pair will end up in my home office (2.5m x 3m) so 70x70 might be on the large side..

You remember these are wall mounted and there's only about a 5" protrusion from the wall?

 

[Coen]

Well the drivers are here, now if only the foamboard would arrive. Anyhow gr8 reason to get the marantz down from the attic and try them out

An externally hosted image should be here but it was not working when we last tested it.

 

[Vix]

Coen, it would be nice if you could make and post photos of work-in-progress of this one.
Me, I don't need another set of speakers at this time, (no space) but this one may be hard to ignore. I was just staring at a blank wall in my bedroom and thought "why not...."

 

[Cal Weldon]

Do it Vix.

 

[Dave R]

Dave,
The 3 in Aura's as I recall work really well from what Cal and his BIL did. The TB 1772 is an 8 incher and that will be a HUGE Cornu - we are talking 15 to 17 square feet of baffle! You can make it smaller by designing your own custom channels, but if you simply scale the basic plan (which was designed for a 4.5 in driver) you will get a 50 inch x 50 inch or 17 square foot baffle Cornu! 48 in can probably work and that will fit exactly a front and back panel for a single sheet of plywood. Doesn't have to be thick plywood, probably 1/4 in is sufficient. Let me know if you are serious and I can run a sim with the venerable W8-1772 for you to fine tune the channel depth and throat openings.
Regards,
X

Hi xrk971,

If memory serves me, horn loading has been reported to work best for drivers with Qts ~ .30 or so. However, from what I gather here, this configuration is somewhat forgiving for a wide variety of Qts values.

With that in mind, I found another possibility in my stash. It's a 4" with a phase plug. Haven't had time to measure FR yet, but I do have T/S parameters. Could this driver with Qts = 1.02 still yield a reasonable response?

T/S for nominal 4"
------------------
Fs = 89.5 hz
SPL = 83.4 dB
Sd = 52 cm^2
Vas = 2.7 liters
Mms = 4.6 g
DCR = 6.7 ohm
Le = 1.14 mH (@ 1kHz)
BL = 3.62 T-m
Qes = 1.34
Qms = 4.30
Qts = 1.02
Xmax = 3 mm

I don't currently have T/S on the Aura 3" that I have, but the Qts was closer to 2.0, IIRC.

 

[xrk971]

Sim of Cornu with mystery 4 inch high Qts driver

Hi xrk971,
With that in mind, I found another possibility in my stash. It's a 4" with a phase plug. Haven't had time to measure FR yet, but I do have T/S parameters. Could this driver with Qts = 1.02 still yield a reasonable response?

DaveR,
You are lucky - this driver seems to work quite well in a Cornu. Below is a simulation for a 27 inch x 4.5 inch deep Cornu mounted at 45 in above the floor (centerline of driver). Use moderate stuffing in the driver chamber and the first 40% of the channel leading from the chamber to the channel split point. It has a very flat bass shelf with about 10 to12 dB of gain from the nominal 83 dB efficient driver. The bass extends down to 50 Hz which es excellent, and like all Cornu's suffers from a few peaks in the mids, particularly at 230 Hz. Adjusting the stuffing at the mouth to taste can balance the bass out to be more in line with the 80 dB output in the HF's. You really should use a much more efficient driver in order to get a good balance between the bass and highs.

I would go for it and build this! Good luck!

SPL vs Freq with no stuffing

SPL vs Freq with stuffing in chamber and first 40% of channel leading to split

Impedance

Cone Excursion

Impulse Response

 

[xrk971]

I tried 6 different 3" drivers and it was a tie between a salvaged JVC and a salvaged LG. No comparison between the 3's and the 4.5. Go with the largest you can.

When it was placed outside recently, the bass made us all giggle like children.

Here is what I think the bass might look like if placed near a wall. 27.5 x 5.5 inch Cornu with FF125WK.

 

[Dave R]

DaveR,
You are lucky - this driver seems to work quite well in a Cornu. Below is a simulation for a 27 inch x 4.5 inch deep Cornu mounted at 45 in above the floor (centerline of driver). Use moderate stuffing in the driver chamber and the first 40% of the channel leading from the chamber to the channel split point. It has a very flat bass shelf with about 10 to12 dB of gain from the nominal 83 dB efficient driver. The bass extends down to 50 Hz which es excellent, and like all Cornu's suffers from a few peaks in the mids, particularly at 230 Hz. Adjusting the stuffing at the mouth to taste can balance the bass out to be more in line with the 80 dB output in the HF's. You really should use a much more efficient driver in order to get a good balance between the bass and highs.

I would go for it and build this! Good luck!

[/IMG]

Wow! Wasn't expecting all of that. Much appreciated. Almost forgot that I had these. They are packaged with Tang Band, and "hand-marked" as W4-1806S (shielded). Got them from Bob at CSS a while back, and have been trying to find a good use for them. This sounds like a great fit.

Now it's back to Santa's workshop -- get those little elves busy! ;^)

 

[Cal Weldon]

Hey Dave, you big lug. So glad you're joining the foam gang.