DIY Mini-Unity Horn. Am I crazy?

[AwesomeSauce2015]

Howdy everyone!
I am toying with the idea of a very compact unity horn (12"x12"x15" ideally).
The goal being to have point-source behavior as well as high output, but without the gigantic size and cost of comparable systems (ie: Danley SH50) or the downsides of pro audio coax drivers (rough FR).

I understand that without the large size, we lose pattern control at a higher frequency, but I still think that constant directivity from around 1khz up is still pretty nice.

So my question is this: Am I crazy? Could this possibly work? And if so, how would I go about simulating this?

I've looked on here and it seems like AKABAK is one place to start for simulating things, but is there anything else I should know about?

Thanks!

 

[Keened]

Are you going to create a cube for each frequency range and stack them on top of each other with offset to match the phase differential (???? like what perlstein does) between frequency ranges?

It would be a very modernist approach to speaker design, both in the historical art sense and the cultural turning point sense. We're seeing the death of the 'romantic period' in audiophile circles, the rise of 'modernism', and also the rise of 'neo-romantic' at the same time. I can't tell if it's at the same rate and just appears to be happening at the same time or the cultural evolutionary timeline is just sped up here (maybe because of technology's scaling, or just the general cultural turnover rate, etc); but I think if you made it out of very nicely veneered cubes you could manage to hit all three groups at once.

Or make it look like a child's wooden blocks if you wanted to be cheeky

 

[AwesomeSauce2015]

Not really. I mean, eventually I may have multiple boxes but the current design objective is to get point-source horn sound in as small a space as practical.

Basically what I'm envisioning is something like the Danley SH50, just scaled down to be usable as a big-bookshelf sized speaker with horn-controlled directivity down to about 1khz, without having to resort to large and expensive compression drivers that can actually play that low. Below 1khz I could feasibly transition to a separate cardioid bass setup, but if I am using woofers already in that range, they can probably handle down lower than the horn cutoff frequency.

If I take a B&C DE10 and pair it with 2 6.5" midbass drivers crossed at 2.5khz, then I would get a fairly high output system in a fairly small package.
Now, for large bass output below around 100hz, we will need larger drivers to keep up with the mids and CD tweeter, but that is easy to solve later, once I figure out how to model a synergy / unity / (whatever else its called) horn.

 

[voodooless]

If I take a B&C DE10 and pair it with 2 6.5" midbass drivers crossed at 2.5khz,

I doubt that would work. You’ll need to put the mids very close to the compression driver to make the 2.5 kHz. Usually crossover point of these things is around 1-1,5kHz due to physical size limitations.

Best bet might be a wideband driver with the midbasses. You can cross lower in that configuration.

 

[AwesomeSauce2015]

Just to verify my understanding is right: The injection port for the mids needs to be within 1/4 wavelength (at xo frequency) of the CD right?
I could build it with a lower X-over, and that would probably solve the issue of separation.- But that's mostly in the driver choice phase, right now I'm just trying to figure out if a bookshelf-sized synergy horn would work.

My real question is how I would go about modeling / simulating this kind of horn design.
I can do CAD quite easily, but am at a loss about how to simulate or predict the horn's effects.
Additionally: How do I determine where the directivity control will be lost for a (constant directivity type) horn of given dimensions? I read on wikipedia that it is a function of the mouth circumference, but real designs seem to differ.

 

[voodooless]

My real question is how I would go about modeling / simulating this kind of horn design.

Hornresp will do a fairly okay job at simulating the loading of the mid bass. There are a few examples to be found of this. It will show if the driver works well in the horn and how high it will play.

Additionally: How do I determine where the directivity control will be lost for a (constant directivity type) horn of given dimensions?

Size is indeed the determining factor for pattern control. 12” will get you to just over 1 kHz. Mileage may vary a bit depending on specific horn design.

 

[fluid]

My real question is how I would go about modeling / simulating this kind of horn design.
I can do CAD quite easily, but am at a loss about how to simulate or predict the horn's effects.
Additionally: How do I determine where the directivity control will be lost for a (constant directivity type) horn of given dimensions? I read on wikipedia that it is a function of the mouth circumference, but real designs seem to differ.

Hornresp is one way to evaluate drivers and get an idea of what you might get.

This thread might give you some inspiration
https://techtalk.parts-express.com/forum/tech-talk-forum/1331723-synergy-horn-build

I have attached the project pdf document

It is possible to use ABEC to simulate the ports as lumped element models

https://www.diyaudio.com/forums/mul...cone-bandpass-mid-unity-horn-post4152484.html

It is possible to model the whole port configuration but the results aren't accurate as all surfaces are modelled as reflective.

 

[gnarly]

Hi, I can't offer any useful advice about modeling or simulations, but i have built a number of synergy's/unity's...albeit they were all larger than what you are proposing.

For estimating pattern control, i use Keele's classic formula: freq = 1,000,000 / ( degrees x inches)
So for a 90 degree pattern, 12 inch wide horn, we get about 925 Hz. 60 degrees climbs to almost 1400 Hz, with the linear relationships in the formula.
Use same formula for vertical pattern and dimension.

As far as where you will need to xover from the CD to whatever cone drivers you are using, as others have said, 1/4 WL from injection ports to CD mounting flange needs to be held.
I think using a CD that can reach down to 1000Hz makes the most sense. Much above that gets oh so difficult unless using tiny cones.

A 100Hz CD gives 2 basic options imo:
Use small cones, like 4"s, can get the box to reach down to around 200Hz.
Or go with something a little bigger like the 6.5"s you mentioned, hoping to get closer to 100Hz (reaching 100 Hz is not easy!)

(I've used CD's that can reach down to 500Hz on 30-48" wide horns, with cones ranging from 8"s to 12", and 100Hz is still tough without any bass-reflex ports.)

If you use small cones, getting the ports within 1/4 WL at 1000Hz will be pretty easy, and the ports can be more under the cones centers, which help helps raise the cones upper end response.
If you use bigger cones, the ports obviously get tougher to fit within 1/4 WL, and will need to be close to, or even under the surround. This hurts the high end response some.

If i were going to build a small synergy like you propose, I guess the starting question to myself would be, how high a xover frequency am i willing use with a sub?

Hope this helped.

 

[hex168]

Example synergy design, simmed:

http://www.libinst.com/SynergyCalc/Synergy%20Calc%20V5.pdf

 

[AwesomeSauce2015]

Thanks for all the replies, I definitely have some reading to do.

I do agree that I need to target a CD/mid xover near 1khz, and that the injection ports need to be within 1/4wl of the CD @ x-over frequency.
My plan was to use dual 6.5" midbass drivers or 4 4" drivers.
I also get that I'm not going to be getting bass output anywhere near what the tweeter will do, but this design is sacrificing that for small size and high output capacity / efficiency. I can always add separate woofer boxes to increase bass output for larger spaces.

Also:

Example synergy design, simmed:
http://www.libinst.com/SynergyCalc/Synergy Calc V5.pdf

For whatever reason that website isn't loading for me... Could be campus internet being weird, but IDK.

-Thanks,
Me

 

[fluid]

For whatever reason that website isn't loading for me... Could be campus internet being weird, but IDK.

Try this

 

[AwesomeSauce2015]

The above worked, thanks.

Another question: I know that the injection ports should be within 1/4wl of the CD @ x-over frequency.
But could I make the distance longer if I use DSP to add delay to the woofers?
Or would that have an adverse effect on the off-axis response?

 

[voodooless]

But could I make the distance longer if I use DSP to add delay to the woofers?

No! The hole and horn form an acoustic bandpass, you cannot DSP that away.

 

[nc535]

Its the reflection of the mid's signal from the throat/CD's diaphragm that comes back to the mid out of phase and cancels resulting in a null at the frequency where the roundtrip delay is half the period that can't be filtered away. That is what limits how far from the throat the mid ports can be located.

 

[kipman725]

One method for small unity horns for getting the midrange taps very close to the throat is to use a pro audio coaxial driver at the apex with the cone portion of the driver connected to the bandpass ports and the compresion driver connected to the horn throat.

If making a small unity horn you also don't need to have all the sound coming from the horn, you can cross the horn with midrange and trebble drivers to a conventional direct radiatior.

3D printing is relativly low cost now so you can design your own horn with mounting points for midrange drivers and have it printed by somone like JL PCB.

Here are some small unity horn projects:

ExBushMe, Meister! 2-way speaker Synergy WAW / FAST

Hey DIYAudio! So I've read a few threads on Synergy concept and then got fascinated and sold on two fay Synergy FAST design that xrk and Bushmeister used in their speaker build. I decided that i need that thing! First, i started acquiring equipment. While there are plenty of speaker and horn...

www.diyaudio.com

A Bookshelf Multi-Way Point-Source Horn

This originally started in this thread which asks the question "why aren't we building a bookshelf synergy monitor" and answers it with "we are" or at least "let's try and see what we get." I got inspired back in the Trynergy thread to build a semi bookshelf point source horn The results with...

www.diyaudio.com

 

[AwesomeSauce2015]

I guess I might as well define why exactly I'm investigating this idea.
The reason is as follows, I want a speaker (or speaker system) that can fit these criteria, and I haven't found anything that does (yet).

1. Point source / coaxial design / good vertical directivity. Basically every 2-way speaker out there has beaming at the crossover frequency in the vertical region. I want a speaker that behaves well vertically, as it allows more usage flexibility.
2. High output. I personally define this as a single speaker that can hit 105+ db without excessive distortion at 10 ft listening distance. - This design will try to hit 105+ @ 10 ft from 400hz up, with bass drivers added externally to go down to 80hz for sub x-over.
3. Good frequency response. Standard goal, flat frequency response throughout the intended passband of the speaker.
4. Relatively compact size. I want a speaker that won't take up the entire room in a small room. (However, bass modules can be large if needed.

Hence my justification for a synergy / unity horn:
They are point source, with controlled directivity, which is good. Additionally, they avoid the nasty FR of typical pro-audio coax drivers.
Due to the way unity horns are packaged, I can (hopefully) fit the drivers into a smaller space than if I was to do a standard 2-way MTM design.
-- Basically, I'm going to want a horn anyways, so I might as well use it for everything than just the tweeter.
And lastly, compression drivers are far better at hitting high SPL. Basically every non-pro audio coax driver I've seen cannot hit 105+ db cleanly.

And to answer the inevitable question: Yes, this would be used in a home theater context. I want the ability to hit full reference level without large distortion, in a variety of spaces. Also, I have done some comparison testing, and speakers that can cleanly get loud (with all other variables the same), sound better to me even at reasonable volume levels.

-Me

 

[freddi]

Ha - even Mr. Flexy is thinking small Synergy/Unity. (I have some of Tom's original Unity prototypes where he experimented with the MISCO's entry point holes) Done right, its more coherent than most "fullrange". Frazier speakers made two ways with horn tweeters in front of a woofer which they claimed coherent.

I had CAT50's - very nice and can be found cheap sometimes.

http://www.frazierspeakers.com/download/coax.pdf

CAT 50

 

[AwesomeSauce2015]

Looks interesting...
----------------------------------------------------------------------
Out of curiosity, does anybody have any idea where one could find spec sheets for the JBL D2430k or 2408h-(1,2, or 3) or the 2409?
I've tried looking, but I couldn't find anything, especially for the D2430k.
And yes, I get that the D2430k would be completely and utterly overkill for this project.
I should add that the reason I'm looking at these drivers is because they seem to have clean HF response. If anyone has any other recommendations I should look into for CDs than I would be very appreciative .

 

[nc535]

If you are doing a Synergy, then you don't need a large format CD. You'll get a better quality high end from a 1" exit device. The trick is to find one that sounds good down to 1.2 khz or so. I used a BMS 4550 in mine crossed at 1050 Hz. There are likely better choices today - like the 1.4" exit HF1440 from Faital, which will play well below 1 khz allowing you to use larger mid woofers.

 

[abdo123]

Stupid (is it?) question: Why not just buy a couple of Uni-Q drivers from the KEF R-series and just attach enough bass drivers for your output needs?

This is like way cheaper and way easier and meets the goals.