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Discussion Starter · #1 · (Edited)
Dual Tang Band W8Q-1071F Tapped Horn (completed)

Greetings, fellow audio nuts. Some of you will already know about this little project of mine thanks to my thread over at AVS, but I thought it would be good to share it here as well; if only to get a few more opinions on this little endeavor before I have the wood out on the deck ready for cutting.

This whole thing started with the advent of the Danley DTS-10, and my complete inability to afford such an awesome subwoofer. Given that I have been planning the installation of a projector here at Crazy Wolf Central, I wanted to build something up that would a) fit behind the screen, b) produce more output than my IXL 18.2.2 LLT ever could, c) teach me about horn design, and d) not cost a pile of bucks.

The gist of it is, I'm building myself a tapped horn with two Tang Band W8Q-1071F drivers. These are 8x12" woofers with 12.5mm Xmax. I found that while there is a rather impressive number of TB drivers that model well in tapped horn configs, these 8x12's are about the only ones that meet all my criteria - they're cheap, they have a good bit of cone area, they can be found for buying in Canada (well, they could... I just bought Solen out of these), and they will allow me to blow away the LLT and still have some headroom.

Before I post the Hornresp screenshots, here is my list of demands for this project:

-subwoofer can have a bandwidth of 16-80Hz, as my room is no good for anything lower than 16 and my mains are fine above 50Hz
-must be no deeper than 20"
-will be corner firing, because that's the only placement that works in this room
-has to be capable of above Dolby reference in eighth space for headroom's sake

The final design ended up being about 16.5" deep x 74" wide x 42" tall. I'm satisfied with this as is, but I would like to hear some opinions on a couple things. First, I've had some assurance that the original version's 3.12:1 compression ratio is ok... I'd like to hear some more feedback on that because in the final design it's now up to 3.35:1. I'd rather tweak it now if I have to than find out I need to buy more wood later. Am I being too paranoid about it?

The second thing I'd like to hear feedback on is whether or not y'all suggest the use of reflectors. I'm almost convinced it won't matter much to not have them in there, but there's still enough doubt in my mind to seek some more opinions on it as the design does have that one 73" stretch between folds.

Ok, screenshot time. These are all in half space. Corner loading looks to get me a good 10dB over reference, so I think I'm ok there. Attaching the Hornresp file so y'all can take a peek and play around with it as you like.

Hornresp parameters:



Schematic:



Diaphragm displacement at 36V:



Impulse response:



Phase response:



Half space SPL:



And finally, my scaled down folding diagram, done to scale in PSP:



Spot any errors? Let me know. The drivers have been ordered, will start with the actual pictures when they get here. The build will likely take place in March, weather permitting. Wood will be purchased from Windsor Plywood sometime in Feb, and will be 3/4" C2 grade void free shop birch.

And yes, there is a Wolfhorn I and even a Wolfhorn III. Wolfhorn I got left on the drawing board because II blows it away. III is still in development, and might stay there due to compression ratio worries - I found out the IXL 18.2.2 models well in a TH. Don't want to take chances with that woofer.
 

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Howdy

You don't need the reflectors for the pass band you are planning.

Mark
 

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Discussion Starter · #3 ·
Thanks - the majority of opinions seem to agree with you, so I'll put that one to bed now. No reflectors. I'm sure my not so good wood cutting skills won't miss them.
 

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Sorry I can't help with the math stuff being "challenged" on the subject, however I am rooting for you on this project because Yes I too have a pair of these drivers laying around. I just wonder how you will place them in the cabinet because mine measure abt 175 mm deep top to magnet bump out. Are you going to place them face to face or just next to each other? Anyway lets see how these drivers do, kinda a "super " KEF B 109 unit, good luck on the project!
 

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Discussion Starter · #5 ·
You have these 8x12's? Cool - I can't wait to see mine. How do you like them?

On my diagram up there, there is a green line. That's the midpoint of where the woofers will be. One will be in front of the line, the other behind the line. They will be firing downwards in my diagram with the magnets hanging down (or in this case sticking up) into the mouth area of the horn. The mouth is about 420mm x 380mm - that should be enough space.
 

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Ok Wolfy

Here is something a bit different. A front loaded horn. Much better SPL / watt. Actually when I crunch the numbers on your Tang Band you have a bit of wrong data in the input screen you posted. Tang Band's numbers are more than a bit off when you use the Hornresp reality checker. There is a built-in program to compute the real Thiele Small parameters for the driver. That is of course unless you have actually measured what you have posted. But as far as I have crunched the numbers the dual 8 x 12 design is hardly anymore efficient than a competitive sealed box.

The SPL is 200watts in 2 Pi space. If you corner load it you will get at least 6 db better. With ideal corner loading you will get 12 db better.

Mark
 

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Discussion Starter · #7 · (Edited)
Hmm, interesting. That makes it look a lot different, that's for sure. Will have to think about this some.

Edit - not sure I follow this. Can't really find anything in there to compute the specs. I do know I had to get some of them by letting Hornresp calculate them, but I'm not sure how you got those numbers for the woofers.

Found a decent tapped horn alignment that works on the new numbers but there's a problem... it drops SPL almost too far and I don't know how to fold the thing when L34 is greater than L12. I don't know that I want to really try a folded horn... kind of had my heart set on the tapped horn idea.
 

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Hey Jeremy,

Can you post the 1w spl graph into full space (4x pi)? Is the SPL graph showing a 36v input (18v per drive)?
 

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Discussion Starter · #9 · (Edited)
Here you go - 1W into full space:



Not sure about the coil config on these woofers - this is 2V in, 1V per woofer.

This is with the original Tang Band numbers, with Rms and Cms being the two calculated specs. Yeah, my original SPL graph was at 36V - the most it would take before passing Xmax.

I'm kind of glad I went and ordered the woofers before the specs came into question, otherwise I might have decided not to go ahead with this at all.

Edit - it was Rms that was the calculated one, not Re. Getting to be late for me.
 

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Don't worry too much. I believe we have had a conversation about the parameter numbers used before.

Using the TB spec sheet from Parts Express you get: SD 460, Cms 2.33E-04, Mmd 143.44, Re 3.20, Bl 15.00, Rms 5.50, and for Le they give "Levc" 0.85. The Le is almost certainly higher, but it only really effects the high end roll-off so it doesn't really matter too much here.

Now most of the time the manufacturers numbers are off, this is why when going off their supplied numbers it is best to not over scrutinize the design. If you have the ability to measure the drivers yourself, that is another story.
 

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Discussion Starter · #12 · (Edited)
soho54 said:
I believe we have had a conversation about the parameter numbers used before.
Did we? Can't remember anymore. I think my brain is totally shot now. Of course, that could be a side effect from trying to make sense of Lady in the Water earlier this evening.

In the event the new parameters are more correct than the old ones (I just can't figure out where that 450 cm squared Sd comes from instead of 460), I did some more fiddling in both Hornresp and PSP on the folding diagram. I came up with a way to turn the original design into a 13.5Hz monster by merely adding one more fold to the box with no flare. I don't think it would outperform the LLT that way, but it should match it and it wouldn't be too awfully hard to tack that extra section onto the box. Downside is, the box turns into a seven footer that way, so it'll be longer than me by six inches. But it will still fit the room that way.

Edit - 16:1? :eek:

Yeah, I think I'll have to pass on that one.
 

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I would stay away from any bass horn with over 16:1 compression.
Wow...Yeah.:blink: Just saw that.

BTW thanks Jeremy. Almost 89db with 1w in at 20hz anechoic is actually not bad all. Plus you get up into the 95db area in the normal kick drum range.
 

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Discussion Starter · #14 · (Edited)
You're most welcome :)

After you hinted at that MTX 15" being good for tapped horns I went ahead and modeled it. What a monster that would be... wish I could afford one of those. The IXL 18 came close, but with the size of that driver plus the compression ratios needed (not to mention the box size) I don't think I want to try it with something I just paid $275 for only last year. I should email Mach 5 and see what he thinks about the idea.

Meantime, I'm going to model the two MCM 55-700's I have collecting dust on a shelf and see if I can do something useful with them at long last.

Edit - so much for that. The 55-700 is lacking just about all essential specs for horn modeling, either online or in my old MCM catalogs. Probably for the best - they don't have a whole lot of cone travel to them.
 

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Hello Jeremy

The design I posted is of course only an example. It is not optimised for your drivers and is a preliminary design I did for other drivers with your Tang Bands plunked in only. Feel free to mess with it and see what you get for results. I only posted it to get you thinking a bit. It is but an example of what can be squeezed out of drivers if you put your head to it.

What you have posted is basically a tapered quarter wavelength resonator. Not a true tapped horn. I have posted below the same drivers in an optimal vented enclosure. I know the response looks ragged but we are talking less then 3 db rise and fall. You would be so happy to get in room response like that!

To get hornresp to help you calculate a parameter double click on the box and a little pop up will guide you through.

I attach the input screen and 1 watt 2 Pi results for a vented version of your box. This is again just for comparison. I did this by getting an optimal box in WinISD and plunking in the numbers into Hornresp to do a fair head to head comparison. It to is quite interesting.

Every time I don't know how to do something in Hornresp I go to the manual. I have learned quite a bit over the years from it. Never hurts to read it.

By the way I'm not trying to say anything you have posted is wrong or bad. Just before you go and commit wood to the project it is good to get as accurate of a result through simulation that you can. I have simulated quite a few horns of various styles and sizes and sometimes they are not anymore efficient than a vented enclosure using the same drivers. I do the vented comparison as a reality check.

Mark
 

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Discussion Starter · #16 ·
To get hornresp to help you calculate a parameter double click on the box and a little pop up will guide you through.
That's how I got Rms and Cms. Still not sure where your conflicting Sd figure (450 vs. 460) comes from, as I cannot find anything in Hornresp to calculate it. I do know about the manual ;)

Did the cut sheet calculating today - the design needs four 4x8' sheets, along with my existing leftover wood for bracing.
 

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Sd is me being to blind to see the right number!

Calculating into 4 Pi is an interesting concept. Who of us listens 30 feet off the ground outside to a subwoofer 30 feet off the ground?

2 Pi is the most general free field SPL calculation.

Your woofers will sun to almost an 8 Ω load so you can do it as 2.83 volts into 8 ohms and be very close.

Four sheets! Heavy stuff!

I hope you get what you are looking for. I know you will get some deep bass no matter what.

Mark
 

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Discussion Starter · #18 · (Edited)
There are three panels that come out just a bit too long, or I could get away with three sheets. Debating doing one of two things - 1/2" thick stuff for the interior folds, or just shortening the horn a bit. Maybe I could get the fourth sheet cut at the store... not sure I can get four full size sheets home in a short wheelbase 2003 Caravan. I suppose I could enlarge the mouth a bit and get the most out of those four sheets too.

The whole aim of this project is to replace the IXL LLT in a package that will hide behind the projector screen and give a little more output at the expense of the subsonic extension my room doesn't allow anyway. The LLT is a 450L design tuned to 11Hz... it's just barely enough at my normal listening levels, but my problem with it is that there's not much headroom. Reference level with it makes me worry about the driver if I should dare to watch a movie mixed too hot.
 

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Discussion Starter · #20 ·
After debating some more, I think I might try to draw up a revision 6 tomorrow with the mouth size increased to between 1800-2500, the horn the same length, and the placement of the horn tap a little different so as to allow a front firing exit right in the corner of the box. It's showing enough improvement in the SPL sims to consider it.

Even if I don't do it that way, I might still move the tap - found a placement that seems to sim a bit better, and I think my brain is finally remembering enough high school geo-trig to let me fold it that way. May also go down to half inch stock on all four panels and just brace it well. The wallet's worried about four 3/4" thick panels as well, even though Windsor's C2 isn't too expensive.

About the graphing - just wanted to add a reminder that I'm designing this thing for eighth space placement. It will not be used any other way. The plan with the current revision was to park it with the mouth pointing right at the corner from about 15" away... concrete floor, and wood paneled concrete walls. If I point the LLT's woofer at that corner, the Pioneer's MCACC sets the LFE 6dB cooler than when front firing it. But that's the problem... with the screen installed, I can't do that anymore. Now, it's under the screen pointing at the wall, and I've lost some output.

I expect that even though the LLT and Wolfhorn II model pretty similarly in terms of SPL in half space (with a slight edge to the horn), the horn will wipe the floor with the LLT once I get it into the room and hit the magic corner with it.

Hmm... I better get the horn stuff out of my brain for today so I can go watch 24 in a bit :D
 
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