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Introducing the Cinema BassHorn... - Page 3

post #61 of 232
Thread Starter 
Quote:
Originally Posted by MBentz View Post

Is there any reason you're not considering a tapped horn for this build? I only ask because it seems like your dimension limitations lends itself better to the tapped horn topology.

Have you looked into doing some of your horn expansion in the vertical dimension? I wonder how a bifurcated throat firing to the right in your graph would come out.

In the past, I've found that having such a narrow throat like you've drawn creates some extra distortion in the system. I'm not sure if it's throat overload or just the driver diaphragm flexing. That's a real tight space to be moving a lot of air in.

Compression ratio is 3.78:1. I thought about this, and also have a 3.45:1 compression ratio design with the same response, but 20L larger. Do you think it would be worth it to explore the lower compression ratio (even though it is only a 0.33 difference)?

The reason I am going FLH is that they offer slightly better phase/impulse/group delay (whether it's noticeable, I have no idea). Also, I need something that will go to the low 100s Hz-wise, as that's where I cross my mains. THs ROCK if you have a narrow bandwidth you need to reproduce, but 15Hz to 120-150Hz is a pretty big passband. I also am not as good at playing with THs as FLHs...

Please show me a drawing of this: Have you looked into doing some of your horn expansion in the vertical dimension? I wonder how a bifurcated throat firing to the right in your graph would come out.

I'm having trouble picturing this in my head....

Oh, and for everyone contemplating building one of these, please note that I designed it with the fact in mind that there would be two of them used in room to cancel room modes. I sacrificed overall output to keep the size down to the 26 cu ft seen here....Only 8 more cu ft than THT, and a smaller footprint....but THT wins hands down in the 25-40Hz department in a one on one comparo, but this guy beats THT below 20Hz...use two, and you beat a single THT throughout, with ~11dB more output at 10Hz, and ~15dB more output at 15Hz...with 6mm left before Xmax...

So, if you have the room, and want more extension, two of these will do the trick (you could get by with one, seriously). If you don't need the extension, THT is for you.

JSS
post #62 of 232
WRT to the tapped horn design, maxmercy and I are both working with the same individual, trying to figure out options for his room (i.e. the most bass out of the space he has available). This is not a competition or an ego contest or anything like that. It is simply friendly collaboration, as you can see, we're posting in each other's threads, and have corresponded quite a bit off-forum. I'm working on the tapped horn version (which will be a completely separate thread if it ever comes to pass), but since I have not even selected drivers yet, the CinemaHorn has a HUGE head start.

Given the inherent compromises maxmercy stated above, a tapped horn is a difficult fit without EQ, as the response tends to get pretty ragged above 80 Hz when they are designed to dig down into the deeper octaves. A flat 2-octave tapped horn is an achievement in and of itself, we're looking for three. Additionally, the explosion in driver excursion in a tapped horn below cutoff can be a killer. All it takes is one good LF thump and coils can leave gaps, then all the magic smoke comes out (ask me how I learned this one...).

All that being said, the inherent form factor of a typical tapped horn fold makes it an excellent fit for the space available, and EQ is cheap.

Performance-wise, the CinemaHorn is ahead - for now.....
post #63 of 232
Thread Starter 
Hey mike,

Will be very interested to see what you brew up TH-wise....

But, screwing around for 20 mins this AM got me this:

Same 15Hz 'mini' Cinema Horn, but maybe more friendly form-factor:

18" x 36" footprint, 5'8" tall. Could be made to look like a closed china cabinet or something if aesthetics are important:



Took my cue from the DTS-10's slim profile...

The AV15-H driver just fits... and, no 180 deg folds... Only 7 folds total. The fact that some of the segments are longer than 4 feet make me start to wonder about losses due to resonances in the passband, though...

JSS
post #64 of 232
Quote:
Originally Posted by maxmercy View Post


Please show me a drawing of this: Have you looked into doing some of your horn expansion in the vertical dimension? I wonder how a bifurcated throat firing to the right in your graph would come out.

I'm having trouble picturing this in my head....

JSS

A pair of C-shapes - one inside the other, maintaining a constant conic expansion. Easier to draw than describe. Something like this:



The circle is the driver, you'd only cut out the area inside the smaller "C". Walls are whatever height needed to get the areas you need. A more square section in the throat of a horn is a good thing.
post #65 of 232
Quote:
Originally Posted by maxmercy View Post

Hey mike,

Will be very interested to see what you brew up TH-wise....

But, screwing around for 20 mins this AM got me this:

Same 15Hz 'mini' Cinema Horn, but maybe more friendly form-factor:

18" x 36" footprint, 5'8" tall. Could be made to look like a closed china cabinet or something if aesthetics are important:



Took my cue from the DTS-10's slim profile...

The AV15-H driver just fits... and, no 180 deg folds... Only 7 folds total. The fact that some of the segments are longer than 4 feet make me start to wonder about losses due to resonances in the passband, though...

JSS

Nice!

The tapped horn is interesting - the more I learn, the more I find that there is to figure out.....

Driver choices are killing me now. I am trying to find a way to quickly weed out 90% of the drivers out there so that I can concentrate on the ones that matter. I've got a few ideas that I am working with.

For me at least, simulations are great, but I'd never bet the farm on one. I do computer simulations as part of my day job, and there is simply no way I'd ever take one as representing the truth without some sort of real-world calibration points.

Hornresp modeling is much the same way. I trust the measurements, math, and physics behind the models implicitly, but there are assumptions made. These assumptions are the wildcards, I need to know they affect reality before I blindly trust any results of simulations.

I guess I just need some more calibration points, I'm working towards that currently. (see my last post in the tutorial thread).

But - as it stands now - the best option looks like a pair of 12's in each of a pair of 22 cubic-foot tapped horns. When placed in corners, over 110 dB @ 15 Hz is achievable (and over 20 dB of headroom is available before reaching the driver excursion limits).

I feel sorry for the house.
post #66 of 232
Quote:
Originally Posted by maxmercy View Post

Compression ratio is 3.78:1. I thought about this, and also have a 3.45:1 compression ratio design with the same response, but 20L larger. Do you think it would be worth it to explore the lower compression ratio (even though it is only a 0.33 difference)?

It's not so much the compression ratio as it is the shape of the throat. When one of the dimensions gets narrow, it's my understanding that the air velocity shoots up quite dramatically, creating distortion. I believe it should start introducing a different impedance on the driver too, although at the frequencies we're looking at it probably doesn't matter too much.

All I really know is like what lilmike said...a more circular or square-ish cross-sectional area is advantageous to getting the wave to propagate as predicted.

Quote:
Originally Posted by maxmercy View Post

Please show me a drawing of this: Have you looked into doing some of your horn expansion in the vertical dimension? I wonder how a bifurcated throat firing to the right in your graph would come out.

I'm having trouble picturing this in my head....

Looks like lilmike beat me to the punch. I must confess I was doing a bit of armchair engineering trying to encourage you to also consider expansion in the vertical dimension.

Btw, I think the bifurcation would work better if you tried to combine the two subs into one big one, and then just have dual mouth exits on opposite sides...kinda like the Klipsch Khorn if you've ever seen one of those. Each mouth acts like its own acoustic source, so you might be able to get whatever room mode advantages you were aiming for that way...
post #67 of 232
Quote:
Originally Posted by MBentz View Post

When one of the dimensions gets narrow, it's my understanding that the air velocity shoots up quite dramatically, creating distortion. I believe it should start introducing a different impedance on the driver too, although at the frequencies we're looking at it probably doesn't matter too much.

THis was covered by Tom D. in post 27. Along with a link to the math to calculate it.

Non-issue for all but the baddest bass horns. I would be worried about the cone flexing, or the surround ripping from the compression way before you reach the throat limits. Hmm... thermal load might be a problem before it too.
post #68 of 232
Thread Starter 
Quote:
Originally Posted by MBentz View Post

It's not so much the compression ratio as it is the shape of the throat. When one of the dimensions gets narrow, it's my understanding that the air velocity shoots up quite dramatically, creating distortion. I believe it should start introducing a different impedance on the driver too, although at the frequencies we're looking at it probably doesn't matter too much.

All I really know is like what lilmike said...a more circular or square-ish cross-sectional area is advantageous to getting the wave to propagate as predicted.



Looks like lilmike beat me to the punch. I must confess I was doing a bit of armchair engineering trying to encourage you to also consider expansion in the vertical dimension.

Btw, I think the bifurcation would work better if you tried to combine the two subs into one big one, and then just have dual mouth exits on opposite sides...kinda like the Klipsch Khorn if you've ever seen one of those. Each mouth acts like its own acoustic source, so you might be able to get whatever room mode advantages you were aiming for that way...

Wow, that would be one big sub....both together, drivers together, like a giant W-horn....

The spiral fold above has a better, more square throat....but then you have the long path sections....

trade-offs, trade-offs....

JSS
post #69 of 232
Quote:
Originally Posted by soho54 View Post

THis was covered by Tom D. in post 27. Along with a link to the math to calculate it.

Non-issue for all but the baddest bass horns. I would be worried about the cone flexing, or the surround ripping from the compression way before you reach the throat limits. Hmm... thermal load might be a problem before it too.

This is something I'm very interested in as well. I wonder what the practical limits are? At some point there have to be compression and perhaps even turbulence effects that set in right? When a driver starts getting into higher excursion levels in a high compression design this could actually end up reducing, or increasing the throat volume quite a bit too could it not? Assuming that the driver survives.
post #70 of 232
Quote:
Originally Posted by maxmercy View Post

The fact that some of the segments are longer than 4 feet make me start to wonder about losses due to resonances in the passband, though...

I have been reading this thread along with the tutorials, but must have missed something. Can you be a bit more specific about the issue you are concerned with here?
post #71 of 232
Quote:
Originally Posted by BeerParty View Post

I have been reading this thread along with the tutorials, but must have missed something. Can you be a bit more specific about the issue you are concerned with here?

I'm not MM, but...

I believe he is talking about the standing waves that will form in each folded (at both ends) section. The longer the sections the lower in frequency the standing waves will occur.

I believe you would consider this an open-end air column, so it would go like this:
1st Harmonic,
Frequency = Speed of Sound / ((2/1)*section length)

2nd Harmonic,
Frequency = Speed of Sound / ((2/2)*section length)
and so on...

Whatever frequencies the standing waves are at they will absorb some of the SPL from the output FR of the horn.
post #72 of 232
Quote:
Originally Posted by Ricci View Post

This is something I'm very interested in as well. I wonder what the practical limits are? At some point there have to be compression and perhaps even turbulence effects that set in right? When a driver starts getting into higher excursion levels in a high compression design this could actually end up reducing, or increasing the throat volume quite a bit too could it not? Assuming that the driver survives.

I have been looking for a link to post all day, but I don't have one. I must have read it in a physical book or paper around here.

If I remember all this correctly, the stuff you know about slot ports, and ports in general do not apply because at the throat area sound waves are high pressure and low displacement. As such you should be able to keep the velocity down to below 10m/s at full xmax, and under 5m/s at normal SPL levels in most any horn. You could also view the horn as one long flair, if that helps anyone out.

As SPL/pressure builds the things Tom talked about come into play, and the other stuff I have read has implied to stay under 150dB and not worry about it.

As you increase the compression velocity increases, but it is not by a lot. The horn I am using in AkAbak jumped 1m/s, from 3 to 4m/s, when going from 1.8:1 to 2.9:1.

It seems you don't have to worry about it, until the amount of compression begins to impede the drivers motion. At this point lots of other really bad things can happen.

I have given some thought to what you said about the throat area changing with high xmax. I can see it doing this in my head, but I don't think it works that way. The cone movement is coupled to the throat space, and should be viewed as a neutral wall.

That said... If you throw a throat chamber onto a TH with an Atc equal to the total Sd, and Vtc of say 50. Then sim it and change the Vtc to 3000. When you compare the two there really isn't much change in the subs passband at moderate compression. It does start to really show above it though. If you raise the compression and run it again, the effects are a little more apparent. In the passband it seems to mainly effect the dips, and only by a small amount. I don't think it would be enough to worry about, but it could be there.
post #73 of 232
Thread Starter 
Soho is correct. The great 'highpass' ability folded horns have to is due to this. For the spiral fold, I wouldn't use it above 100Hz or so...where most subs operate anyway....but for me, I cross to my mains at 120Hz, so it may not be the best folding choice...

JSS
post #74 of 232
Does it matter how fast the folds progressively get bigger?
post #75 of 232
Thread Starter 
I'm not really sure, that's a question for the experts...

JSS
post #76 of 232
That would be flare rate, and as long as you get the response from the horn you want it can be as large as you want.

There is a point where the flare rate is so large it stops acting like a horn, but the response graphs will let you know when you went to far.
post #77 of 232
Quote:
Originally Posted by soho54 View Post

I'm not MM, but...

I believe he is talking about the standing waves that will form in each folded (at both ends) section. The longer the sections the lower in frequency the standing waves will occur.

I believe you would consider this an open-end air column, so it would go like this:
1st Harmonic,
Frequency = Speed of Sound / ((2/1)*section length)

2nd Harmonic,
Frequency = Speed of Sound / ((2/2)*section length)
and so on...

Whatever frequencies the standing waves are at they will absorb some of the SPL from the output FR of the horn.

This can be seen in the response plots for the example tapped horn here.

It is a single-fold design, so it is long (7'3", or 2.21 meters). If I did the math close to right, the second harmonic is at ~155 Hz, though there is no dip evident. The first harmonic would be about 77 Hz, and you can see a dip of 3 or 4 dB at about 73 Hz in the response chart.

I used no batting or reflectors in the example build.
post #78 of 232
You have the first and second harmonics labeled wrong. Getting tired?

Temp and other nonsense affects the speed of sound. It looked muggy in those pics, I bet the SoS was bummed out and slowed down that day.
post #79 of 232
Quote:
Originally Posted by soho54 View Post

You have the first and second harmonics labeled wrong. Getting tired?

Temp and other nonsense affects the speed of sound. It looked muggy in those pics, I bet the SoS was bummed out and slowed down that day.

Yeah - a bit. Should be fixed now.

It was in the mid 40's and raining when I measured, typical of January in the Pacific Northwest. Everything gets depressed this time of year, even the speed of sound....
post #80 of 232
To any of the experts:

Would it be possible to mount the Cinema Basshorn in my attic?

I'm thinking it could be done, but it's an old house and the mouth would have to be extended to port it into the room (the closet actually). Would that present a big problem?

Also what about heat in the summer? Would the summer heat hurt the driver?
post #81 of 232
Thread Starter 
That is a good question, I have thought of this many times....but the temp extremes in typical attics have made me think twice...if your attic is insulated, it should be no prob....the horn 'extension' could be easily modeled to see what it would do, though....

JSS
post #82 of 232
Quote:
Originally Posted by mobius View Post

Would it be possible to mount the Cinema Basshorn in my attic?

...what about heat in the summer? Would the summer heat hurt the driver?

The IB guys might be able to answer this one.
Penngray might have some insight here.
post #83 of 232
I live in Florida so my attic is probably above 140degrees in the summer. I have never had issue or even read about issues from others with IBs either.


The amount of energy build up in a sealed box creates heat also and I suspect the internal temp of most sealed subs is fairly high when you consider they have a plate amp attached to them that runs pretty hot too.

In the end the heat in an attic isnt meaningful in my books.
post #84 of 232
Thread Starter 
I was thinking cold would be more of a problem, stiffening spiders and suspensions...but either extreme could present problems...

JSS
post #85 of 232
Quote:
Originally Posted by mobius View Post

To any of the experts:

Would it be possible to mount the Cinema Basshorn in my attic?

I'm thinking it could be done, but it's an old house and the mouth would have to be extended to port it into the room (the closet actually). Would that present a big problem?

Also what about heat in the summer? Would the summer heat hurt the driver?

I'm no expert, but if you install it in the attic I would suggest that you remove the insulation between the sub and the ceiling and add a bunch of insulation around the sub so that it thermally becomes part of the room instead of the attic. Otherwise the sub would create a "hole" in your ceiling insulation.
post #86 of 232
Quote:
Originally Posted by BeerParty View Post

I'm no expert, but if you install it in the attic I would suggest that you remove the insulation between the sub and the ceiling and add a bunch of insulation around the sub so that it thermally becomes part of the room instead of the attic. Otherwise the sub would create a "hole" in your ceiling insulation.

The BassHorn couldnt fit between trusses so he would have to extended the mouth down between them. I assume that is going to change the design a little bit since the mouth is being extended 6 to 8".
post #87 of 232
Quote:
Originally Posted by penngray View Post

The BassHorn couldnt fit between trusses so he would have to extended the mouth down between them. I assume that is going to change the design a little bit since the mouth is being extended 6 to 8".


Thanks for the input on the temperature issue. Yeah, the mouth would have to be extended between the trusses. What's more, the closet that I would vent it into has a drop ceiling (of sorts). I'll take pics to show what I mean and post them later.

My room isn't ideal for placing a sub this big. so I'd really like to do this if possible. I need to get acquainted with Hornresp and try to model this out. If it doesn't work, I may do a smaller version (like 18") of the TubaHT to place in room.
post #88 of 232
Thread Starter 
How long would the extension be, and what size? It would be easy to model as another 'segment' of the horn...

JSS
post #89 of 232
Quote:
Originally Posted by BeerParty View Post

I'm no expert, but if you install it in the attic I would suggest that you remove the insulation between the sub and the ceiling and add a bunch of insulation around the sub so that it thermally becomes part of the room instead of the attic. Otherwise the sub would create a "hole" in your ceiling insulation.

Quote:
Originally Posted by penngray View Post

The BassHorn couldn't fit between trusses so he would have to extended the mouth down between them. I assume that is going to change the design a little bit since the mouth is being extended 6 to 8".

I know it couldn't fit between the trusses (he said so), but he still needs to add the extra insulation around the box. He will have to remove a large chunk of insulation to extend the mouth into the room (I'll let other people more knowledgeable in HornResp help him with the modeling) so he will need to "plug that hole". My point was that he didn't need to worry about the temps in the attic. If he installs it correctly the horn would be on the room side of the insulation, not the attic side, and thus in the temperature controlled space.
post #90 of 232
Thread Starter 
One more iteration of a huge horn....

The driver: Maelstrom 18". The need: bass for parties and HT, and it has to be LOUD. The size: 32"x40"x64".

Two of them, 50V into each, just under Xmax so no need to highpass, corner loaded, prior to room gain:



Highpass, and more dBs are available. Excursion maximum is at 14Hz.

The basic layout:



They will also be an attic install....

JSS
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