Building a fullrange horn - any advice for a newbie?

[lineweight]

Hello everyone, a bit of a search around the internet has suggested this is the place to find out about building my own speakers!

I've always had a bit of a fascination with horn speakers (and have been impressed with the few that I've actually heard) and also with the concept of the fullrange driver.

After many years living in rented rooms I now have the opportunity to build something, because I'm in the process of renovating a flat I'm going to move into, and I'm thinking it would be fun to build some big(ish) horns - probably built into a wall of storage etc. I've attached a diagram showing the basic dimensions of the room they will live in.

I currently own a pair of Lowther PM6C drivers...acquired a while ago in anticipation of building my own speakers at some point but as yet unused. So I'd like to use these, but if it turns out they aren't appropriate, I can sell them and get something else instead.

Potentially each speaker could occupy a space of approx. 600mm wide by 2000mm high by 700mm deep.

There are lots of designs on the internet...but it's difficult to know where to start. I'm hoping some of you might be able to point me in the right direction at this stage.

As for my listening preferences... I'd like to build something with a fairly low reach. I don't want bass at the expense of everything else but I would definitely like it to be present. I've considered horns + subwoofer but I really like the idea of the simplicity of just two drivers and would like to stick to that if possible. At the high end... I like it to be there and sharp but it's not my no. 1 priority. I would like to make sure if possible to avoid excessive brightness or harshness in the upper midrange/top end.

Like I say, any suggestions at this point would be much appreciated.

I will post photos here if and when I start the project!

[Ty_Bower]

Originally Posted by lineweight

Potentially each speaker could occupy a space of approx. 600mm wide by 2000mm high by 700mm deep.

My goodness, that's a lot of working space. Quite a bit bigger than a Sachiko (340x1830x460), and they're pretty hefty cabinets. I wonder if your PM6C would be compatible...

The Spawn Family of Double Horns

edit: Hmm... the construction plans specifically mention the PM6C. I'd say go for it.

[hm]

Hello,

may be a solution would be:
TUBA, BASSTUBA,

[lineweight]

Originally Posted by Ty_Bower

My goodness, that's a lot of working space. Quite a bit bigger than a Sachiko (340x1830x460), and they're pretty hefty cabinets. I wonder if your PM6C would be compatible...

The Spawn Family of Double Horns

edit: Hmm... the construction plans specifically mention the PM6C. I'd say go for it.

Thanks very much for the link - lots of designs to look at there. Did you mean the Sachiko plans mention the PM6C - I couldn't find any mention on them...?

[lineweight]

Originally Posted by hm

Hello,

may be a solution would be:
TUBA, BASSTUBA,

Thanks - where would I be able to find details for these?

[lineweight]

A couple of general questions:

1. Am I right in thinking that generally, bigger is better (especially if I want a good low frequency response)? Or are there problems that begin to appear beyond a certain size?

2. Should the size and shape of my room have any particular bearing on the design of speaker I choose?

3. I will probably end up building them from plywood, as per most designs but I also have this idea that I'd like to try and cast something from concrete... this may be wildly over-ambitious but is this something that other folk have tried / succeeded with? I'm thinking that I'd be able to make the formwork from something like dense polystyrene which would allow smooth curves and also possibly a horn that is circular in cross-section along its length. I'd probably make it in two halves that would be bolted together. Is this a completely crazy idea?

[jrenkin]

Originally Posted by lineweight

A couple of general questions:


3. I will probably end up building them from plywood, as per most designs but I also have this idea that I'd like to try and cast something from concrete... this may be wildly over-ambitious but is this something that other folk have tried / succeeded with? I'm thinking that I'd be able to make the formwork from something like dense polystyrene which would allow smooth curves and also possibly a horn that is circular in cross-section along its length. I'd probably make it in two halves that would be bolted together. Is this a completely crazy idea?

Being only one and a half sets of speakers from being a newbie myself, I suggest you go with an established design out of plywood.

If you do something complex, immovable and not at all adjustable out of concrete, you have to get everything just right the first time and re-dos are a PITA.

Besides, the first time(s), it won't be perfect, so give yourself a break and start simple, established and enjoy the process of learning enough so that you can safely pour concrete in the future.

A good simple start could be a BIB. you could pick your driver based on the space available. I did a BIB with the Fostex 208EZ and it is big and sounds great. Easy first build with excellent results and with the right driver, enough bass, which is important, a room the shape of yours may eat some lower frequencies.

[Ty_Bower]

Originally Posted by lineweight

Did you mean the Sachiko plans mention the PM6C - I couldn't find any mention on them...?

How curious. Version 1v0 (dated 23-03-07?) of the drawings had a note near the bottom of page two. The current package 1v01 (dated 22-03-09?) has some changes, and the mention of Lowthers is no longer there. I think that part of the drawing got snipped because it contained some response plots that tended to cause more confusion than clarity. Regardless, I suspect the design is still valid for the Lowthers. Perhaps Scott Lindgren can chime in.

If you are to build them, definitely use the newer drawing package. I seem to recall there are some important corrections in it, especially with regards to the wedge deflector.

Originally Posted by lineweight

I also have this idea that I'd like to try and cast something from concrete... this may be wildly over-ambitious but is this something that other folk have tried / succeeded with? I'm thinking that I'd be able to make the formwork from something like dense polystyrene which would allow smooth curves and also possibly a horn that is circular in cross-section along its length. I'd probably make it in two halves that would be bolted together. Is this a completely crazy idea?

It's been done here before. Search long and hard, and you should find the thread. The builder used some kind of styrofoam for the casting, poured the cement, then used a solvent to remove the foam. I'm sure it was messy and most likely bad for the environment. He managed to build one but never completed a pair. I'd stick with wood. If you pour a solid block of concrete to the dimensions you've described earlier, you're dealing with over 2.2 tons per cabinet. Even recognizing that some fraction is going to be empty space (60%?) it's still going to be incredibly heavy.

edit: Here's the thread with the concrete horn -
TQWT Concrete cabinet attempt, building thread.

[hm]

Here you get feedback, plan, measurement, may be take goo.. translate if you need:
tuba
tubamess
tubaFB
tubaplan
basstuba
basstubamess
basstubaFB
basstubaplan

[Scottmoose]

1. Am I right in thinking that generally, bigger is better (especially if I want a good low frequency response)? Or are there problems that begin to appear beyond a certain size?

To an extent, yes, providing it's correctly designed, bigger is better. However, as horn length increases, so does group delay, thus the acoustic XO frequency from horn to direct radiation will need to drop to render it ~inaudible and / or you will need some form of digital delay on everything above that point. If this XO occurs significantly below the driver's mass corner, you will then need a short front-horn to 'fill in' the resultant dip in the response.

2. Should the size and shape of my room have any particular bearing on the design of speaker I choose?

The room dominates low down, so unless it's of ideal acoustic proportions & you've lots of treatment, then yes, you want to think about it. A lot of it is common sense though; if you want to fill a concert hall, you don't pick an LS3/5a.

3. I will probably end up building them from plywood, as per most designs but I also have this idea that I'd like to try and cast something from concrete... this may be wildly over-ambitious but is this something that other folk have tried / succeeded with? I'm thinking that I'd be able to make the formwork from something like dense polystyrene which would allow smooth curves and also possibly a horn that is circular in cross-section along its length. I'd probably make it in two halves that would be bolted together. Is this a completely crazy idea?

It's been done, but it's not especially easy. I wouldn't discourage you from it, but I'd probably consider something in wood initially, as it's quicker & simpler to ascertain whether you like the results or not. If you do, & you're feeling ambitious, you could always consider the cast concrete at a later date.