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Horn throat area reduces? (Read 8572 times)
johncc
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Horn throat area reduces?
07/23/08 at 08:02:47
 
I am contemplating making a scaled down WO (due to space limitations).

Looking at the sound paths, when the two join, it seems that the total area of the horn subsequently reduces.  On the surface of it, that doesn't seem like a good idea.  What is the science behind it please.

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musgofasa
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Re: Horn throat area reduces?
Reply #1 - 07/23/08 at 23:43:47
 
John,
I can't speak for Steve and I may even be incorret here, but I have built a LOT of WOs over the last 9 or 10 years. Looking at the drawings and looking at the way the plans lay out for a 36x36 WO I don't see how the area reduces at any point. I might have to draw one out on a peice of wood at different sizes to see if it happens when the length gets shortened.

Putting that aside as I don't "think" it is really applicable, I will give you my opinion. The WO is too short and to fast a flare to provide any real horn gain action. It really acts more like a 4th order band pass enclosure. In fact, you use the 4th order bandpass design calculators to determine where to place the baffles and if a woofer is useable in the WO. That being said, it is my belief that the flare from the opening to the mouth of the "horn" are intended to give the two separate enclosures a way to share the space and effectively combine two strong waves into one and give them a sizeable surface are from which to launch. The results are above average performance for a band pass enclosure in both SPL gain and in Frequency bandwidth. With the right drivers, the WO sounds terrific. With the right drivers it can produce huge amounts of SPL for it's size.

As with anything in audio it has it's compromises, but it is one terrific design albeit I don't think it is a "horn" in the classic sense.

So to answer your question, if it does reduce the area somewhat, it is still effective. I don't think it matters if it does, but from what I see and recall it didn't actually do that.

I don't know how you plan on scaling the design, but read through all the posts about it before you decide on what you are going to do there. Some have had success manipulating the design, but only a few. If you can build it by the plans and live with the size, you won't be dissapointed, That much I am certain of.

Take care,
Robert
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johncc
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Re: Horn throat area reduces?
Reply #2 - 07/24/08 at 02:49:07
 
Robert,

Thanks for the input.  I accept that the design does provide very good result as indicated in this forum.  My aim is to try and make the right decisions in the scaling down process.

Your reasoning about the "horn" side of things makes sense as the "horn", even in the 36x36 version, would not be regarded by horm purists as being large enough to deal with low bass, yet the design obviously does.

I am fairly sure that the area does decrease from the point of the triangle (off my printed diagram the width measures 0.45"+0.45"=0.9") to between the points of the airchambers (measures 0.6").

I'd be interested to hear more about the role of the horn/port section if anybody can help.

I do realise that a reduced size will compromise performance, but I really can't accommodate the fullsized design easily in my living room.  I just want to maximise bass output from the space available at this point.  If I'm not satisfied with the results, I may have to go full-sized later on.

John.
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Re: Horn throat area reduces?
Reply #3 - 07/24/08 at 15:13:26
 
Ahh
I see where you are talking about now. I was looking at a different point. I would assume that where the waves meet at the end of the triangle might be sort of a "loading" position where the wave can be restricted enough to help combine and the launch from the wide disperse opening.

Considering your design aims, what space do you have to work with? If the WO is going to be less than 36" wide, you might be better with a different design. Also what speakers are you mating the sub up to? I suppose I should ask all the normal questions like what sort of music, any idea on SPL levels, how big is the room etc.

Since you are looking at the WO, though, the size you need to scale to might be the most important factor. I have built 8" WO and 10" with success. I scaled down for the 8" and was happy, but don't think it would have been impressive in my current living room set up. Of course I needed a MUCH bigger sub for that space than I needed in the back of a 240sx hatch, lol.

Keep us posted!

Take care,
Robert
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gexter
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Re: Horn throat area reduces?
Reply #4 - 07/24/08 at 20:33:40
 
If I was to scale down after playing around with the design in the past. I would just lower the height to use a smaller driver.
I would not use less than an 8"
Robert pretty much says it all better than I can as far as how to look at the function of the box.
If you do not have the room you may just go to a sealed design with a low volume sub and more power.
I made a downsized scaled WO with 5 1/4 and it was really loud and peaky ( if thats a word) Mid bass was loud and annoying and I had to cross it over really low.
I also made a 6" WO32 that was just lower in height and it worked really well and would build another. But I did use the 24X32 design with internals modded slightly. (  1/2" smaller throat )
Use another design if its too big.
I am really picky about my bass so tits always an adventure.
Good luck
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johncc
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Re: Horn throat area reduces?
Reply #5 - 07/25/08 at 00:22:33
 
Thanks for the replies.

I am looking at 30x18 and using 8" isobaric drivers to reduce to chamber volumes and hopefully keep the horn section closer to full size.

The application is basically home theatre (enhancing low freq. effects)  and classic rock music.  I like the sound of the reviews of the WO and I think that it's a case of trying a smaller one and if I'm not satisfied with the results, fitting in the full sized one somehow.

Can you please give details of your 8" versions.  (or link to a thread if it's in the forum)

Thank you,

John.

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mwsartain
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Re: Horn throat area reduces?
Reply #6 - 07/25/08 at 19:23:25
 
I am restricted on space also. I have 36" to work with on width but I only have 20" in depth.
The 10" woofers that I will be using will tune nicely in a .5 cu.ft. sealed, that being said, can I just shorten the whole encousure on the horn mouth side by 4"s?
Will I lose much efficiency by doing so?

Thanks for the help guys! Smiley
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musgofasa
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Re: Horn throat area reduces?
Reply #7 - 07/25/08 at 20:45:18
 
A lot of factors come into play when you reduce the width on these enclosures. (or widen them for that matter).

I am guessing (Note GUESSING) that the original angle was arrived at with careful consideration. I think this because of the method used for building the enclosure. IE: Measuring 2 inches from corners and drawing lines so that they cross at specific points. The only recommendation I can make for scaling is to model the driver of choice in a 4th order bandpass design with the ported chamber volume and port size and try to make that equal to the port volume you have with the space between the slot and the combination of the 2 waves. In other words, not with a 1/2 slot port, but rather a port equivalent in volume to the area at the back of the box. This will likely give you good results.

The one thing it doesn't take into account is the angle at which the 2 waves combine coming out of the enclosure. I have built many boxes with woofers firing into an angle. Some worked very well and others flopped big time. My guess has been that the angle caused reflection issues at certain frequencies. That's an awfully vague assumption for something so complex, but it's the best I can offer.

For the sake of being simple, I might suggest using a death box in the smaller space you have available. Honestly, I like the sound of the DB better than the WO. 2 DBs will be as loud as a single WO as well. Of course, 2 boxes is not smaller so there is a trade off.

Take care,
Robert
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Re: Horn throat area reduces?
Reply #8 - 07/26/08 at 00:13:28
 
The area of the horn does indeed reduce at a certain plane after the two throats come together. I can remember that Steve addressed this question once in the past, but I am not sure how to find it. It was a couple of years ago, at least, and on the old forum.

I can also remember him saying that it was purposeful and it had to do with the combining of two throats and increasing efficiency of the mouth.

Don't change it. It's right the way it is.

After saying that, I will admit to altering the design a couple of times, but the stock WO kicks ass the was it is. I have built several and used several different drivers and they all were really powerful.

As far as scaling, it has been done by a few, but the results vary widely.

I have built two that were not to spec and one (beefed up for fifteens) worked after some additional tweaking.

The other one I'm not sure I want to talk about, because I broke all the rules and it worked out great. I needed a small subwoofer for the bedroom, but I had no place to put one without creating a domestic territorial dispute. I got to thinking that using multiples of my smallest drivers and making a squatty one to fit under the bed might work, after removing some forgotten shoes. I ended up making it 36"x48"x6" and I used eight four inch pro-audio midrange drivers (four in line on each side, which I already had and still have more), which have decent X-max. The baffle is angled a bit. I am crossing them over a full octave below the free air resonance of the drivers, boosting the lowest octave a bit, but they really do pound in a modified WO and no one knows there is a Pseudo-sub under the bed.

So, I scaled in two dimensions and it worked fine once, but not as well the other time, some have scaled in three dimensions and run into trouble.

The WO plans call for scaling in only one dimension when switching to a twelve inch driver.

... and the popular addendum when talking audio ... YMMV.
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« Last Edit: 07/26/08 at 00:17:22 by Dirty_Dawg »  

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Re: Horn throat area reduces?
Reply #9 - 07/26/08 at 06:05:50
 
Thanks for the replies guy's!

I'll keep the width the same, but I need to reduce the front to rear size to 20". I'm thinking that maybe I should just scale it down. Is this the right enclousure choice?

This is a wierd application and this design may not be the best choice. I have built my offroad vehicle as my Kenwood Excelon demo vehicle. So, far it has worked great! It seems to appeal to the right demographics (17-30 yr old). I currently have a transmission line box in it with a 12" woofer and it works well. It just looks like a$$. In these pics I have a 4th order bandpass, it worked well also.

I know that this seems goofy, but it really sounds good. The amps are high quality D-class and sound very good, $599 each. The head unit has 24 bit D to A converters at a low impedence output and the sound quality is remarkable accurate.

I don't expect it to sound great while the engine is running, but when I'm hooked to the power supply, it does actually does very well.

Here are some pics;






I appreciate your advice.

Thanks, Mark.
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johncc
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Re: Horn throat area reduces?
Reply #10 - 07/26/08 at 12:15:05
 
Readers of this thread may be interested in the following quotes from Steve from the old forum in 1999/2000...

Quote:

If you took a traditional horn flare and a traditional port... and they had sex, the wicked one would be the result.

Think of the horn flares of the wicked one, as an esoteric variable port.

The dual design yeilds more complexity, as the last order of the horn flare is shared by both sides. At this point the pressure doubles, and the wavefronts from each side are combined in phase.


Quote:
In a ported enclosure the port which is really a piston of air, reasonates at one frequency in phase with the woofer. When this happens the dampening action on the woofer increases causing it to move less. (Interesting to note that at this point where the woofer's excursion is the least, the output of the cabinet/speaker combo is at it's loudest.) So we can see that a port increases power handling at a given frequency. This damping action reduces as you get farther away from the tuning frequency of the box. Basically, you have damping across about a 1 octave range.

In a horn, the flare itself creates an impedance against the woofer, and effects it similarly to a port. The main difference is that unlike the port which works at one frequency, the flare of the horn acts like a variable length port. By this I mean it dampens the woofer at every frequency. For this reason, power handling and effeciency is increased over a ported box design, and because the woofer moves less, accuracy goes way up, and distortion goes way down.

As for calculating the wicked one's response on a computer program, it can't be done. There are some horn flare calculators available in the shareware archives on madisound's bbs, but in designs like the wicked one, velocity, phase, capacitance, and complimentary resonances are also factored in.

That should be a good start.

Steve Deckert


Doesn't help my understanding of the WO.  Interesting though.
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« Last Edit: 07/27/08 at 02:41:31 by johncc »  
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mwsartain
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Re: Horn throat area reduces?
Reply #11 - 07/26/08 at 21:03:25
 
Very interesting. So, do you think that changing the length of the horn will change the tuning? Or maybe just lose some efficiency?

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johncc
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Re: Horn throat area reduces?
Reply #12 - 07/27/08 at 01:56:41
 
Quote:
Very interesting. So, do you think that changing the length of the horn will change the tuning? Or maybe just lose some efficiency?


I'm no expert, but I think that because it changes the mouth area it changes the cut-off fequency.
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« Last Edit: 07/27/08 at 02:42:16 by johncc »  
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Re: Horn throat area reduces?
Reply #13 - 07/28/08 at 17:45:22
 
That's pretty close to what happens. This enclosure doesn't exactly have horn effect. Steve says it is more like a variable length port. The way a port works is similar to a passive radiator. The slug of air in the port has a specific amount of weight and requires a specific force to move. If the port were to change lengths on the fly, that amount of force would change. This is why a solid port is tuned at one frequency and horns are said to affect efficiency across a band of frequencies. In either case, we are talking about lower frequencies.

In relation to the WO, the expanding vent or "mouth" acts like a variable length port. If you shorten the port, or change it's width and or height, you change the band of frequencies affected by that slug of air by changing the effective weight of that same air. This can be tricky. In a 36x36 WO you have an effective damping I would guess to be somewhere between 35 and 70 hz. That is the one octave Steve refers to. By changing the shape and size of this vent, you change not only the low cutoff, but the bandwidth of the damping. It may be that the octave affected is higher or lower or it may be that you lose some of the bandwidth and it affects less than an octave. It is even possible that you lose some efficiency at the cost of gaining some bandwidth. The tradeoffs can probably be mapped using software somehow, but I wouldn't want to guess at how to calculate the port sizes for the given enclosure and then try to adjust them according to the new size of the enclosure. Having seen some success and some failure with changing the design, it is hard to say if it is a good idea or not. You may change it, love and leave it alone, or you may not like it at all.

To be honest, in the application in question, I would suggest a 4th order bandpass or maybe even a 6th order like the housewrecker. If you want lots of SPL, 4th order similar to the wedge might be a good idea. If you want smooth response and decent SPL, look at the housewrecker or similar designs. I just can't make any promises about the WO. If it were mine, I would build the WO and see if it worked. If it doesn't work very well, you have only gained experience and something to share with us as to a good or bad result of changing the design paramaters.

Hope that helps,

Take care,
Robert
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johncc
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Re: Horn throat area reduces?
Reply #14 - 07/29/08 at 02:38:45
 
musgofasa,

Thanks again.  I think that I will give it a go.  It is frustrating though not knowing the rationale or principles behind the design.  Your explanantion does seem plausible.  The fact that it does produce a good result can't really be attributed to horn-loading because it doesn't  conform.

What I am hoping is that by using pairs of face-to-face drivers and consequently halving the required chamber volumes, I will be able to come close to duplicating the original port/horn configuration.

Will let you know how I get on.


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Re: Horn throat area reduces?
Reply #15 - 07/29/08 at 03:24:35
 
Keep us posted Johncc ! I'm curious of your results.



Oh, and good luck!
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Re: Horn throat area reduces?
Reply #16 - 07/29/08 at 15:07:48
 
I had a thought this morning. Have you ever heard of a "quasi port" band pass design? Back in the early nineties, it was a popular design. Basically it was a 4th order box with one woofer in a sealed chamber on either side of a shared chamber that contained 4 ports, each tuned to a different frequency. I think the WO probably performs closest to this in function. Admittedly, I believe it is more efficient and has a smoother response, but I think this might be the closest resemblance to the design I can think of.

Good luck to both of you you guys.

Keep us posted!
Robert
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Re: Horn throat area reduces?
Reply #17 - 07/30/08 at 00:05:35
 
If you haven't built the cabinet yet, here are some thoughts, if you have, I apologize.

The box can be scaled up or down, but the proportions must remain the same.

Scaling the box down will raise the cut off frequency causing you to compensate with more power or EQ boosting the low bass.  That in turn will will create a clipping condition in the amplifier which will fry the voice coil.

Since your vehicle will have no cabin gain, this problem is multiplied by a factor of at least 3.

Best box, most possible bass for that vehicle is a DBK10, deathbox.

Steve
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« Last Edit: 07/30/08 at 00:06:08 by Steve Deckert »  
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johncc
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Re: Horn throat area reduces?
Reply #18 - 07/30/08 at 01:59:31
 
Steve,

Can you comment on my thought that I try to retain the size of  the port/horn section in the scaling down process?

Thank you.
John.
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Re: Horn throat area reduces?
Reply #19 - 07/30/08 at 02:40:59
 
musgofasa,

Thanks for the suggestion.  Looks like quasi port is a fairly complicated design process though.

John.
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Re: Horn throat area reduces?
Reply #20 - 08/01/08 at 00:52:38
 
On further research and because my space constraints make the scaling of the WO design iffy, I have decided not to proceed.  (I will go with a conventional ported enclosure.)  Thanks to those who have provided input and good luck with your own projects.

John.
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« Last Edit: 08/01/08 at 00:56:03 by johncc »  
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Re: Horn throat area reduces?
Reply #21 - 09/19/08 at 00:49:12
 
I'm new to Hornresp but if Hornresp can model a front loading horn than I believe the WO can be modeled in the program.

I read an article that explained the very close similarities between a front loaded horn and a bandpass enclosure.

I'll try to dig it up
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