Another big horn dream... comments and concerns?

just a guy

Member
2006-05-12 6:59 pm
[IMGDEAD]http://i30.tinypic.com/kd0h2r.jpg[/IMGDEAD]

This is a pic I drew up a few days ago and it's just so pretty I can't stop thinking about it. It's definitely not on the to do list, but it would be easier to make than floor to ceiling stacks of labhorns, so I might do it one day. A side benefit is that it turns the whole front wall into a poly cylindrical diffusor. I would expect to design this to cover somewhere around 10 - 40 hz or so.

The red outline is a massive floor to ceiling sealed box. The walls and the box form a dual waveguide with a rapid expansion that grows to the cross sectional area of the room at the mouth. So technically it's not really a horn. This would use as many highish vas 15 or 18 inch woofers (like the new tempestx) as it takes to maintain a decent system q and provide adequate spl, hopefully with loads of extra headroom.

I would use this in a small room so the dimensions and amount of drivers don't get out of hand. The walls of the room would need to be made of concrete or metal, in which case there should be lots of room gain (and lots of room treatments). A 10x7.5 foot front wall would amount to a mouth size of 75 square feet.

1. How do you model something like this? Since the mouth is the entire cross sectional area of the room, it's not 1/8th space, more like 1/16 or maybe even 1/32 space, I would think. ???

2. Should there be a front chamber? A front chamber would probably net some more spl potential, especially down low, but is that a good trade when spl levels should be more than enough anyway?

3. Would it be better to just do floor to ceiling stacks of labhorns in the front corners?

It's pointless to even try to model it without knowing it's context in relation to the room, so I haven't even tried yet.
 

MaVo

Member
2006-01-07 12:40 pm
1) easy approach:
one approach may be to model only the horn to the mouth and take everything that follows due to the room being smaller than 1/8 space as added bonus. another one may be to use hornresp and simulate part of the room as a part of the horn. both together could lead at least lead to a rough impression of what the room will do to the sound.

room influence:
i would think that the room wont act as a part of the horn, since its area doesnt change anymore, after your horn extension is finished. it will act more likely as an more or less sealed chamber, providing room gain below its fundamental and resonances above.

best approach:
best results will be achieved by using Akabak and modelling the whole system of horn and room as a whole. but i was too lazy to script something like that until now. maybe if i finally get to build a real subwoofer some day.

2) can only be answered by simulating the horn

3) labhorns are very efficient above 30hz, below they act more and more as a sealed box. if you want this, go with it. but you could build a horn with a behaviour, that matches your needs better, as the compromises of the lab were geared towards prosound and not home installation. for example a lower cutoff could be achieved.
 

tinitus

diyAudio Moderator R.I.P.
2005-11-24 1:47 am
Looks like a Lansing model just bigger, cant remember the name

Appears to be a good project with huge mouth area, so it doesnt matter that I think the mouth will only be reduced by floor and sidewalls, which means 1/4...unless you plan to make it all the way from floor to ceiling :hot:

But I suppose you will need a smaller chamber at the back of driver(s), thus it will leave you with a lot of wasted space in the middle...maybe you could just use some hinged "wings" or "loose" baffles to support mouth transistion

As suggested the Labhorn might be better fore you, and the easy way out...maybe with additional wings
 

just a guy

Member
2006-05-12 6:59 pm
Thanks guys.

Looks like a Lansing model just bigger, cant remember the name

I haven't seen anything like this before but there's nothing new under the sun (except tapped horns) so this shape has probably been seen in a few different designs in decades past.

unless you plan to make it all the way from floor to ceiling

Floor to ceiling is the plan, making it any shorter would drastically reduce it's performance, I think.

But I suppose you will need a smaller chamber at the back of driver(s),

Since it's not to scale and there's no way to accurately guess without at least trying to model it, off the top of my head I'm going to say the sealed box part contains about 100 cubic feet of air (based on a small room size with a front wall 7.5x10 feet and lots of internal bracing). Highish vas woofers like to be in a big sealed box. The tempestx looks like it needs about 13.5 cubic feet of sealed box to hit a .7 q. This amounts to about 8 drivers, which is actually pretty reasonable when you consider what goes into dual floor to ceiling stacks of labhorns, so I don't think I need to make the box smaller. Besides, making it significantly smaller would mess up the shape of the waveguide.

one approach may be to model only the horn to the mouth and take everything that follows due to the room being smaller than 1/8 space as added bonus. another one may be to use hornresp and simulate part of the room as a part of the horn.

The first idea may lead to a whole lot of eq to flatten out the end result, since it's only a guess. WRT hornresp... I would think you are right about akabak being the best tool for this job, since the room is a big part of this equation, but I have no idea how to use it. Even if I did, I would not know if I was doing an accurate model, since I would have no idea what results to expect.

3) labhorns are very efficient above 30hz, below they act more and more as a sealed box. if you want this, go with it. but you could build a horn with a behaviour, that matches your needs better, as the compromises of the lab were geared towards prosound and not home installation. for example a lower cutoff could be achieved.

I know a bit about the labhorn, and there are other horns out there with a 30 hz low end, not much below that. There's two ways to get lower response afaik, either make a larger single horn or stack the smaller horns to sum the mouths. A floor to ceiling stack of labhorns or similar could probably easily be flat to 20 hz, which is higher than I was hoping for and probably provide 30 db of extra unused dynamic potential. I was hoping to be able to trade that type of response for (much) lower tuning at the cost of peak spl with a single large "horn", hopefully with little or no eq.
 

MaVo

Member
2006-01-07 12:40 pm
Flat to 20hz may be a bit optimistic, since only the mouth area grows and the horn length stays the same (ignoring the fact, that the bigger mouth may lead to a slightly longer "virtual" horn). this should rather flatten the response. But since a stack of maybe 4 labs will be 8 12inch drivers, those alone will provide deep bass, even without horn loading.

Make a search over at http://www.prosoundweb.com/forums/ since Tom has covered this subject there allready. i think search subject "10hz" could be usefull.
 
Hi,
Mavo's right. The expansion rate (flare) in the Labhorn is designed to perform down to 27Hz.
If the full mouth area matches the space loading this is achieved.
Using fewer boxes than required by the loading is equivalent to truncating the horn and leads to ripples in the response.

Increasing the area does not improve the horn. It does provide better coupling for the sealed bass unit that result below the effective horn frequency. I suspect there will be a step in the frequency response as the horn hands over to sealed box.
 

lousymusician

Member
Paid Member
2005-11-24 4:10 am
NorCal
tinitus said:
Looks like a Lansing model just bigger, cant remember the name


Paragon?

JBL-01.JPG
 

tinitus

diyAudio Moderator R.I.P.
2005-11-24 1:47 am
Not an expert but common sense tells me that waht you want is impossible...your horn would need to be much bigger, a big mouth is not all there is to it :D

Why not build something with multiple sub drivers in BIG fronthorn, floor to ceiling and a bit of EQ
 
Yeah, the brown dot is whoever is stupid enough to step into my room.

WRT the labhorn conversation, we've proven that I'm not very bright, especially before I've had my coffee. I have no real desire to build stacks of labhorns, much less to eq them down to 10 hz.

Below are a couple of pics, this is my first ever attempt at playing with hornresp, so may not be even close to accurate. Additionally, I just fudged the numbers to get kinda close to what I imagine it might look like. Not sure how to approach S1 with the drivers firing into a throat that tapers to nothing, so I just guessed at S1. This uses 8 tempestx 15 inch drivers. The length from the throat to each corner is 1 meter, at which point the combined cross sectional area of the dual "horns" is 8 square meters. This first section is conical. The second section grows to a cross sectional mouth area of 16 sqare meters, it's exponential and it's another meter in length. (At least I think that's what the inputs mean)

This sim is done with drivers in parallel for something like 30 ohms resistance and this is with 1000 watts, which only amounts to about 11 mil excursion, so the tempestx can handle well over 2x that much excursion. This response was modelled using 0 x pi space (infinite horn). It's probably a bit too bottom heavy, considering better than average room gain from stiff walls.

I realize what I simmed is not what I drew in the picture, but it leads me to believe that this might be a lot easier than I thought.

[IMGDEAD]http://i29.tinypic.com/27y3ntt.jpg[/IMGDEAD]

[IMGDEAD]http://i27.tinypic.com/wvtvrb.jpg[/IMGDEAD]
 
Not an expert but common sense tells me that waht you want is impossible...your horn would need to be much bigger, a big mouth is not all there is to it

I'm obviously no expert either, but my guess is that if this was a horn, you would be absolutely correct. My guess is that this is just a sealed box with a massive waveguide, and as such does not need to have the length of a true horn. Very similar to big vent reflex boxes, except this is big vent sealed.

As usual, I'm probably wrong, but the results of my quick and dirty modelling makes me think this might be worth persuing in detail.
 
[IMGDEAD]http://i31.tinypic.com/25zjdsj.jpg[/IMGDEAD]

The only change here is that the pathlength is now 2 meters instead of 20. Stupid mistake on my part, thanks for pointing that out.

If I change it to .5 x pi space then it drops like a rock below 40 hz. Is this design really .5 x pi? Maybe not 0 x pi, but somewhere in between? This is what I mean, modelling is almost pointless unless you know the space context.
 
One more try. I started from scratch. Still 8 tempestx woofers, in parallel this time. This is in 0.5 x pi space. It represents the picture I drew a bit better, but not perfectly. I'm still guessing at S1 at 1000 sq cm, and it conically expands to 5000 sq cm at the first bend, and up then exponentially up to 15000 sq cm at the mouth. Total horn length is 2 meters.

In this first graph, the black line is the Hornresp max spl feature (not sure if I used it right, I specified 27 mil xmax and 1200 max watts as per a single tempestx, but there are 8 in there, not sure if I was supposed to specify 8x more power), the blue line is the 2.83V input.

[IMGDEAD]http://i30.tinypic.com/5vyfi8.jpg[/IMGDEAD]

In this second picture you can see that this drawing does not have a similar expansion rate for the final flare as in my drawing. I can't figure out how to change the flare rate in hornresp, so this sim does not flare as much as mine near the end.

[IMGDEAD]http://i29.tinypic.com/28lctp5.jpg[/IMGDEAD]

And finally, the new input screen. I think it's trying to tell me the mouth is a bit too big. And now is a good time to note that playing with the throat area (S1) seems to allow me to tailor gain vs lower bandwidth. Am I using hornresp correctly?

[IMGDEAD]http://i25.tinypic.com/ix9vud.jpg[/IMGDEAD]
 
Hey, thanks again. I read the help file but must have missed how to switch to other than conical or expo flare.

What I would really like to know is what you think the throat (S1) would be according to the pic I drew in post 1, and assuming the drivers are all shoved as close to the throat point in the center as possible. The throat area (S1) seems to make huge differences in the final outcome, whereas other factors like the volume of the sealed box make very little difference.
 

MaVo

Member
2006-01-07 12:40 pm
hard to tell after seeing that picture, since it is really unprecise. You should model a throat that gives the best results and then build the box according to that. a compression factor between 1 and 4 seems to be normal.

by the way... have you ever thought about a tapped horn? can be made smaller than a real horn and gives really good results as a subwoofer.

besides, i doubt the current horn does much for the lowest bass, as it is just so short. compare it to a horn with length 1cm, to see the driver response. i bet there are not much differences below 50hz.