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Discussion Starter · #1 · (Edited)
OK, here it is.

I have a ton going on in addition to the sub builds right now, but I really wanted to get this posted up and let everyone know the results of what I have been working on.

I'll cut right to the chase.



Modeled is red. Actual is blue. I offset the data to match the curves at 30 Hz. Though the measuring equipment is essentially flat, this particular amp is NOT, it has a 12 dB/oct highpass filter that is essentially flat to 20 Hz. Looks like the length might be a touch short with this fold (first time folding a horn with Sketchup). The -3 dB point from the average SPL from 20-60 Hz is approximately 15 Hz, even with the highpass on the amp.

These are initial close-mic measurements only - no real numbers on the SPL graphs yet, other than that the divisions are dB. Not cause I can't, but rather because I have not measured things properly. This is what it looks like currently:



Pretty much every clamp I own on there right now. I did use weatherstripping on all the internals, and it all compressed with the clamping. I still have significant air leaks, so no high SPL testing yet. As you can see, this is still a work in progress, I am trying out placement and types of damping materials to tame the upper portions of the response plot. I have active EQ, so it is a non-issue for me, but I'd like to try to flatten things out as best I can as a bit of a science project. There is a significant 67 Hz spike, but it is less than Hornresp predicts. I have tried 3/4" fiberglass and some acoustic ceiling tile material so far, planning to try acoustic cotton and poly batting as well. If anyone else has ideas, chime in before I button it up, maybe we can all learn something.

Anyhow - plans and much more details to come.
 

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Discussion Starter · #2 · (Edited)
So - a little background. This design is as small as I can make it and still fit the Shiva X2 inside and manage a low corner in the teens. The criteria were that the enclosure needs to be as small as possible, preferably under 10 cubic feet. I could not do that and still manage 15 Hz. I could not manage 15 Hz and fit the driver in anything smaller - honest. There is less than 3/4" behind the driver, and I recessed it 1/4" into the baffle. It also needed to have a minimal footprint, and it needed to be something that can be built in a reasonably-well equipped shop. I used a circular saw, radial arm saw, router, belt sander, drill press, and a cordless drill for this build, but I could have gotten by without using the radial arm saw and drill press, I just used them because it was convenient.

OK, We'll start with the simulations. I used the supplied Thiele/Small Parameters for this project rather than measure them myself. Rather than throw a ton of screengrabs in here - I attached the hornresp record. Save this text file in your \\hornresp\import directory, then import it into hornresp, you'll have what I do.



If you want to do it the old way, have fun.

Anyhow - the simulations are the easy part, the true kung-fu is in the folding.
 

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Discussion Starter · #3 · (Edited)
Folding. It was a learning experience.

I do not want to tell you how many times I tried to fold this cabinet.

Ultimately, I used a method similar to what was described over here. When folding a tapped horn, things are considerably more complicated, you've got to fold it up, and you've got to get the front and the back of the driver lined up exactly. You've also got to maintain L12, L23, and L34.

Simple, right?

Here is what I wound up with:



External dimensions are 71" tall, 24.5" deep, 14.25" wide.

Sorry - no folding how-to here. I had to brute-force it, and I have not found an easy-button yet.

So - step one - cut the wood. We talked about that in another thread, but suffice to say - a good guide track makes a decent circular saw a phenomenal tool for cutting down sheet goods. I use the EZ Smart track system from Eurekazone, no affiliation other than they sell a great product.







Once the wood was cut, time for layout. I used an accurate framing square to locate the corners, then drew in the panels in with a strip of 3/4 wide aluminum. Of course, I screwed it up. Triple-check your work!!! At least I caught these mistakes before drilling or glue-up. Once I was satisfied with the layout, I marked 1 inch in from the end of each panel for drilling layout holes, then made sure I had the panels aligned right (good sides touching) and drilled 1/8" holes through both panels.



You can see the ruler, framing square, and aluminum templates I used in the photo above.
 

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Discussion Starter · #4 · (Edited)
Damping Discussions

Well, I tried.

Nothing had a significant effect on the 67 Hz spike in the response. Personally, I am not too fussed, as my room eats up 70 Hz like nobody's business, and I have active EQ if I need it. For other rooms, active EQ is probably going to be required.

I tried:

Nothing at all
3/4" fiberglass (multiple placements)
1.5" fiberglass (multiple placements)
Acoustic Ceiling Tile (several locations)
Bonded Acoustic Cotton (duct wrap)
32 oz fiber carpet cushion (throat-side only)

I even mixed things up a little bit, ceiling tile and fiberglass, ceiling tile and carpet cushion.

Nothing really helped.

I've probably got 50 sweeps of data I need to sort through, but when I overlay them, the only differences are above 120 Hz.

I'll post the plots when they are sorted.

Long story short - for this build, the work in adding damping material does not appear to be worth the extra effort.

The only reason the carpet cushion is still in the enclosure is because I did not want to try to remove it - I used lots of glue and staples and I would have had to pull the driver again.
 

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Discussion Starter · #5 · (Edited)
So - Sunday was a great day to measure subs, except everyone and their brother was riding their Harley, running their chainsaw, mowing their lawn, or tuning up the hot rod. Not me, nope, I'm out there testing a subwoofer...

Background noise was higher than usual, nearly 70 dB.

Measurements were collected with my WT2, and with REW and my measurement gear. I measured SPL with a drive of 2.00 V at 1 meter, groundplane.



Nothing within ~10 M.

Results (real in blue, modeled in red)



Hmmm - not so close, and the dip in the saddle is 2X what was predicted.

Impedance and phase:



Looks like the horn is a little bit short too.

Well, it is built, and all painted up nice, I might as well listen to it while I design its replacement. Here is a pic in room - this placement was better than the others, but still not great.



See - it is the only painted speaker I have....everything else is a prototype, honest. :D
 

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Discussion Starter · #6 · (Edited)
So - let the armchair quarterbacking begin. I'm thinking that the driver is too big for the horn I have it stuffed into.



Pretty snug. I measured an inch from the back panel flange to the magnet. You can also see the aluminum flanges I made. I figured I was going to be opening this one up more than once, so I used an aluminum flange. It is also a lot thinner than wood and does not block the horn. Too bad I went through all that work, since the driver is doing such a nice job of blocking the horn for me. A few quick calculations suggests that the driver is blocking about 60% of the area at S3, which may have raised my low corner a bit and definitely deepened the saddle by 3 dB.

Here is a little more detailed view of the aluminum access panel flange.



It really worked well, once I figured out how to locate the holes. I am a bit embarrassed to say that it took me three tries. Thread screws through the aluminum from the back side, hold the panel in place, and smack it with a rubber mallet. Hey, presto, all your screws are marked exactly.
 

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Lookin' good! Strange though, for my first Insub design, the peaks were shifted left from model to real, these peaks appear to be shifted a tad to the right....but still good correlation.

JSS
 

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Awesome work and great results. I only wish I had the space to build and use some too.

Nice correlation between the measured and Hornresp predictions. It will also be good to see some bettwe measurements (preferably a la Illka to give reference to his test results) but my gut says the differences won't be huge.
 

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Discussion Starter · #9 ·
Oh, rest assured, this will get better measurements. Just not quite there yet, need to sort out the damping material first.

I just wanted to show what I have done and that it appears to correlate well with what was predicted.
 

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Discussion Starter · #11 ·
Keep checking back - I am adding to the first few posts as I can.

External enclosure dimensions are: 71" by 24.5" by 14.25".

Full plans and drawings will be posted.
 

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Looking good so far - can't wait to see what effect the damping has on it, and what it looks like with a different amp attached.

After the SPL graph, I was ready to refold my own design just to get rid of the length errors in it, but then I realized something... it still needs to fit on three and a quarter sheets of stock, and won't if I try doing that. So, no refolding for me. I doubt I'll miss a few centimeters off of a 16Hz horn.
 

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Very nice...looks like the length came in a little short, but not enough to matter. I'd like to see a before and after of the damping used as well.
 

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Discussion Starter · #14 ·
The comparisons will be documented as best I can and presented. If anyone has suggestions as to additional materials I can test, please chime in.
 

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I agree... looks like it is a little shorter but not enough to cause any grief. Once you use one in both corners of a room.... the bottom will be more than sufficient. Of the two curves... I'd rather have the actual than the modeled response anyway! ;-)

It probably is most useful to do a final measurement with a 50Hz, 60Hz, 70Hz, 80Hz 2nd/4th order electrical LP. It won't be nice and perfectly smooth like a sealed box but that is just part and parcel of horns. You can probably kill some of the ugliness with fill and lose some SPL doing so and I can say that 99% of people who build something like this will have PEQ in the system so the little wobbles in the response are a non-issue other than the fact that they don't make good marketing curves.

I like the box though. That is of a size that can fit in a lot of applications for people building false walls, or for people who want to shoe-horn one in a crawlspace or attic with the exit into the room.

Nice job! Your effort is top-notch.

Kevin Haskins
Exodus Audio
 

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Thanks for the post Mike. So far all the measured vs actual graphs of horns that I have seen track pretty closely to the model.

Nice folding! I was puzzling over how to maintain a square box on the outside when you have lots of folds on the inside. I folded an Anarchy design that just happened to work out. Dumb luck really. Now I need to buy an amp so I can try the design out.

Is that peak at around 70 Hz because of internal resonances related to the 71" length?
 

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Discussion Starter · #17 · (Edited)
Thanks for the post Mike. So far all the measured vs actual graphs of horns that I have seen track pretty closely to the model.

Nice folding! I was puzzling over how to maintain a square box on the outside when you have lots of folds on the inside. I folded an Anarchy design that just happened to work out. Dumb luck really. Now I need to buy an amp so I can try the design out.

Is that peak at around 70 Hz because of internal resonances related to the 71" length?
The peak is present in the model (no folding), and corresponds to phase and group delay features on the respective charts. It is significantly attenuated from the modeled predictions in reality, and I may yet be able to attenuate it further. For those with active EQ (myself included) it is really a non-issue. Two or three cuts, and the response will be fairly flat from 15 to 80+. I'm sure my in-room response will be a LOT uglier and take a lot more work.
 

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I will have to start learning more about these horn designs.

I am confused on which to do though. Sealed horn like the THT or tapped horn like your build Mike.

Is there just alot of trial and error? I dont really have the wood to waste for that.

I think I will have to send alot of PM to others on here to try and see what I will need for my future application.

Awesome build I look forward to seeing more pics.
 

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The tapped horns are much smaller and reach deeper. They give up efficiency to do so and they are a better fit for a high-stroke driver like the Shiva-X.

lillemike has done an excellent job... on the simulations, the tutorial and the builds. Nice job!

Kevin Haskins
Exodus Audio
 

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I will have to start learning more about these horn designs.

I am confused on which to do though. Sealed horn like the THT or tapped horn like your build Mike.

Is there just alot of trial and error? I dont really have the wood to waste for that.

I think I will have to send alot of PM to others on here to try and see what I will need for my future application.

Awesome build I look forward to seeing more pics.
Kevin is absolutely right. For a given size, a tapped horn will go lower. But that comes at a price: they are harder to fold. If you have the patience, you can do it. A front-loaded horn is easier to fold, and has potentially less phase and excursion issues. In my experience, for the same volume box, you can get about 5-10Hz more extension with the same sensitivity with a tapped horn, if you play your cards right.

JSS
 
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