My Bass Horn Project (Input Welcomed:) )

[bigmike216]

I'm taking a shot at my own horn. Driver will be a single Eminence LAB12 per cabinet. This if my first time using Hornresp, so any input would be greatly appreciated. If you see something horribly wrong, please tell me, I will have a 35 Hz High pass on theese, as they will be used in PA applications. Will be running 2 per side, or 4 in the center. They will be low passed at 80Hz, as that's about where my midbass picks up. Having ISP problems right now, so images are going to have to put hosted on geocities. If the links don't work, copy and paste them into a new window.

Response in eigth space:

http://geocities.com/michaelmacwillie/response.jpg

My Input into Hornresp:

http://geocities.com/michaelmacwillie/input.jpg

All input is welcome If it looks good to you guys, I'll go ahead and do up a CAD drawing.

 

[Centauri]

Mmmm...... files not available for viewing. To have these files on Geocities, you may have to create an index.html file as per their terms of use.

Sort that out and we can take a look at the design.

Cheers

 

[bigmike216]

Hmm, wierd, works fine from here if I copy and paste it I'll make up a quick html file.

 

[bigmike216]

Here we go. Hopwfully this works.

http://www.geocities.com/michaelmacwillie/

 

[Centauri]

Yep, that worked!

Doesn't look too bad. Value of Vtc is a bit low, but this only effects top end response anyway. Quite a long path length, but this smooths the large ripples that show in the LabSub response - the Lab12 really likes to be in a 15Hz horn....

I would be inclined to increase Vrc a little just to get rid of that peak at 35Hz and smooth the rolloff.

Procede with the Cad! (BTW which cad will you be using?) and make sawdust!

PS: Check the diaphram displacement graph with different input levels to determine the power which will hit Xmax, then don't run too much more power than that into them - a few have been shredding cones in the LabSub lately by pushing them too hard.

Cheers

 

[paulspencer]

Mike,

I saw a website where a Lab12 was done in a modified version for a church. It was simplified by stretching it out into a long horn, not folded. I believe this gives a smoother response. If it can be done practically for your application then perhaps it's worth considering. I imagine it might be easier to construct.

 

[bigmike216]

Thanks for your suggestions! I will give that a go with increasing the Vrc to smooth out that ripple at 35Hz, and i'll post back in a few I am aware of thoose shredded LAB's, I read about it on the PSW forums. (I'm Michael M there.)

Paulspencer:

I have also seen that LAB12 stretchet out horn. Quite impressive! Unfortunately, it wouldnt be practical for my application, as mine need to be portable.

Mike.

 

[bigmike216]

I tried palying around with Vrc and Vtc. While i got the responce a bit flatter, I also lost a ton of power handling. that low peak is actually at 33Hz, which is below my HPF frequency (24db/oct) SHouldnt my High pass also help to bring this peak down a bit?

 

[Centauri]

With the steep hi-pass at 35Hz, combined with not a lot of signal this low anyway, then it maybe best to leave the peak if it gives you greater power handling - as usual, all these things are a matter of finding the right compromises.

I am currently working on single Beyma 12LX60 subs, slightly shorter path length, but still good to 35Hz.

Cheers

 

[bigmike216]

Cool, I'll have to keep an eye out for a thread about them



I started laying out this horn.. and I think i'm going to have to go back to the drawing board. Physical size will be huge I knew it would be big, but laying it out really put it into perspective.

 

[Centauri]

What method and cad are you using ?

I use a spreadsheet to calculate the required profile for a given width, and it chops this into 50 segments and generates an AutoCad script file. I AutoCad, I then keep the centre point of each segment joined and curve around to try and fit into a given space. Even this requires a bit of time and patience!

Cheers

 

[bigmike216]

I also use autocad. I'll give it another go.

 

[John Sheerin]

Woah - you might want to think about your front chamber for another minute... If you have a front chamber with 506cm^2 area and the chamber has a volume of 50cm^3, that gives you a length of 1mm. So.... think the cone might hit something? ;>

Okay, so seriously, Vd of the woofer is 506cm^2*1.3cm=658cm^3, so that is the absolute minimum your front chamber can be if you want to use the driver up to it's rated xmax. Now consider that if you made the front chamber just big enough, if you push the driver to xmax you will vary the acoustic capacitance of the front chamber by a huge amount. As the driver's cone moves from +Xmax to -Xmax, you will alternately reduce your front chamber to nothing and then double it. That will give you a wee bit of distortion. I would go at least 4x 660cm^3 for a good starting point (considering you might end up pushing the driver past xmax like everyone on the Lab board who reports blown drivers has done).

 

[mikee12345]

horns are all about compromise

Decide on your upper size limit.

Consider that the labhorn is ~750Litres and reaches ~30hz

You wont reach 30hz while keeping everything else constant with a smaller box

So you must decide what your limitation will be

consider a higher F3( i find an F3 near 40hz to be quite okay)
consider a smaller mouth for less efficiency(up to a point!!)
consider just building a labhorn (or similar horn that is easier to make by expanding in 1 dimension only)

Cheers

 

[paulspencer]

I thought that with a horn, a limit was placed on cone movement such that a driver would typically be cooked thermally before it reached xmax! I'm no horn expert, but I did a few simulations with hornresp and found that it didn't seem to get to xmax easily, yet output was extreme and the driver was at the limits of its thermal power. I tried a few drivers. With my sub (AV12) I found it went nowhere near xmax, to the point that it seemed there was no output advantage of a very high xmax over a sub with half the xmax.

I'm guessing those guys on the other board who blew up the Lab12 weren't doing it in a home environment!

I'm not sure which would be damaged first - the subwoofer ... or the house!

 

[bigmike216]

No, it was not done in a home eenvoronment. PA use. most people run their lab horns at around 2400 watts a cabinet. My original reason for not building the lab horns was not being able to afford 4. But, not i'm just cinsidering saving for a bit

 

[paulspencer]

Whoa! That is a lot of power! I think the power rating is something like 600 watts per driver, so I would have expected 1.2 kw to be more like it! Still, I'd think it would cook rather than break the cone due to excursion related damage .... how did they fail? Did they look at the drivers?

 

[bigmike216]

Nope, they didn't cook. They're rated at 400RMS per driver.. but that is a pretty conservative rating. The link below is the thread at the PSW forums with the failed drivers. Theese were reportedly running 1200 watts.

http://srforums.prosoundweb.com/index.php/t/1396/3313/?SQ=8b5f2ca988aae84159226f8eda383206

 

[GM]

Music isn't steady state as sim programs assume, it's dynamic, with high Q peaks that requires huge amounts of power in bursts too short to thermally overload the driver(s), hence excursion is the limiting factor. Also, sim programs assumes a perfectly rigid piston and if the compression ratio is so high it can't reach Xmax, then in music playback the driver will self destruct from non-linear movement due to suspension and/or diaphragm deformation long before it thermally overloads, and why point source driven horns should be limited to a ~3:1 compression ratio for most apps.

That said, in my early experiments I built a ~15:1 CR 150Hz horn (IIRC) loaded with a wide BW driver from a console and it self destructed from thermal overload during initial steady state sinewave testing.

GM