Simple Tapped Horn Tutorial using Hornresp - Page 2 - AVS Forum
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post #31 of 114 Old 01-13-2010, 11:01 AM
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You have to keep the cone and suspension compliance in mind as well.

Look at the real parameters BL, Re, Mmd, Sd, and Cms, not derived ones. Of course different parameters are needed for different horns (bandwidth, horn/driver size, compression,...)

Here is a link to the patent application with the supplemental images in a pdf link.

http://www.freepatentsonline.com/20090087008.pdf
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post #32 of 114 Old 01-13-2010, 04:23 PM
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I've got a question about these sims. Hornresp is assuming a conical expansion which means both the X and Y dimensions are growing as you go along the line. But it seems like people are folding these so only one dimension grows linearly along the line. The depth of the box stays constant and the internal baffles all expand about the same amount. Simple example measuring the area at equal 1/4 points along the line....

Code:
        Conical Folded
S1      100     100
S2      194     475
S3      475     850
S4      944     1225
S5      1600    1600
Now you could adjust the angles of the individual folds so it follows the conical expansion more accurately but it doesn't really look like that's what Danley is doing. Help.

Dennis H
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post #33 of 114 Old 01-13-2010, 04:56 PM
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catapult,

Something is off there. You seem to be comparing an exponential profile conical horn to a straight conical one with a single taper.

In order for the second column to match the first you would need multiple conical sections. It is the surface area change that counts, not the shape as much. You could build an exponential "T" horn out of square boxes if you wanted too.

Here is a link to a paper that talks about it, but the site isn't working right for me today. http://www.scribd.com/Loudspeaker-Ho...rt-1/d/9778607

EDIT: The link is working again.
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post #34 of 114 Old 01-13-2010, 05:03 PM
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catapult,
I see you changed your numbers.

To add to that last post, remember a TH doesn't need the mouth area of a regular horn. As a result you can get away with a less exponential profile. Hornresp will only simulate the horn profile you input. You can see it in the Schematic Diagram section. In order to simulate your "conical" example you would have to use multiple conical sections, or input it as an exponential horn.

Hornresp thinks of conical as a straight wall from throat to mouth section. The shape doesn't really matter, only the area. At sub frequencies it doesn't really mess anything up. At higher frequencies it messes up the directivity graphs.

I will add that they seem to do a little better with non-ideal drivers with two conical sections after the throat, with varying expansion rates.
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post #35 of 114 Old 01-13-2010, 05:11 PM - Thread Starter
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While we model a conic expansion (both x and y expand), we typically draw and build a parabolic expansion (either x or y expand), which is close enough for most, especially within the ranges of tapers we're usually dealing with. A sequence of varying prismatic sections can be used to approximate conic (or any other) flare rate, it just takes more math to fold things up.

There is a great series of posts explaining this here and I'd rather link to it than try and re-explain it.

A few posts later, here is the answer from Mr. McBean himself.
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post #36 of 114 Old 01-13-2010, 05:52 PM
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Soho, you're quick, yeah I changed the numbers when I goofed the math the first time.

Lilmike, thanks for the links. It sounds like adjusting the folds to more closely follow the conical flare works better although it's probably no big deal as they all say -- it just makes figuring the folds a little harder. Figure the length of each fold and what the area should be at that length. Doing that automatically does the slow-early, fast-later thing they are talking about if you look at a 2-D picture of the folds.

Dennis H
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post #37 of 114 Old 01-13-2010, 07:04 PM
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Quote:
Originally Posted by lilmike View Post

Some manufacturers present the ratio of Bl/sqrt(Re), which seems to have a good correlation with a driver's performance in a tapped horn.

Would you want Rv here instead?
Rv (virtual mechanical resistance)= Bl^2/Re
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post #38 of 114 Old 01-13-2010, 07:48 PM
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I'm going to go back, and highlight a few things in the Tom D. quote section.
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post #39 of 114 Old 01-14-2010, 08:14 AM
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Quote:
Originally Posted by soho54 View Post

Look at the real parameters BL, Re, Mmd, Sd, and Cms, not derived ones.]

This...
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post #40 of 114 Old 01-14-2010, 08:15 AM
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Quote:
Originally Posted by Rythmik View Post

First, very interesting thread. The correlation between excursion bump and valley and SPL output gives us clue on how to modify the BL value or Qts to get smoother output. For instance, at excursion peak, if the SPL output is too high, increasing BL value can reduce the SPL output at that frequency. On the other hand, at excursion valley, if the SPL output is too high, reducing BL value can reduce the SPL output. Overall, it is a process of how we can pick a BL value to get the smoothest output. Of course other factors such as fs and Mmd affects the general shelving direction.

Want to work on a servo controlled horn sub ?

How clean would that be.
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post #41 of 114 Old 01-14-2010, 10:34 AM
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Quote:
Originally Posted by Ricci View Post

Want to work on a servo controlled horn sub ?

How clean would that be.

Wouldn't that take away some of the impedance peaks that are needed for a good horn? Just asking cause I don't know much about servo controlled stuff. I still believe a standard horn within its limits should be cleaner sounding but I am just guessing on that.
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post #42 of 114 Old 01-17-2010, 09:10 PM - Thread Starter
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OK. After a little bit more refining of the model, I made some sawdust and took some measurements.

I'll cut right to it - how does 27-90 Hz. +/- 3 dB of 90 dB @ 2.83 volts sound?

After working out the impulse response and phase issues discussed earlier, the model was revised a bit more. Once I was happy with it, I made a sketchup diagram of a single-folded tapped horn that matched the model as closely as possible.



It's nothing special, it just allowed me to figure out the dimensions and cut-list. If anyone wants the actual file, PM me an email address.

Then - it was time to make some sawdust. Let's just say that it has been a little while since I built a sub - and it shows. It is certainly not a thing of beauty. Ultimately, in translating the model to MDF, I missed a few measurements slightly, and I also had to allow for an access hatch to install the drivers. I measured what I built, then revised the model to reflect the reality. I also broke in two new MCM 55-2421 drivers and measured the Thiele-Small parameters of the pair, as well as an older one that I had sitting around. All three measured very similarly. I averaged the parameters of the two I used and entered that into Hornresp.

Here is the final input screen:



Here is what I measured (2.83 V, 1 Meter, groundplane)



Here it is compared to the model:



Well, it appears that all the bumps are in all the right places, and are a little bit flatter than the model predicted, though the response is also down a few dB from the predicted SPL (which could be my meter or measurement technique, my mic and meter are not perfectly calibrated).

I also ran an impedance sweep with my Woofer Tester 2:



Looks like the resonances may have attenuated the high Q peaks. The slight shift in frequencies could be due to the straight line measurements I used when I calculated the path length.

Anyhow - in a nutshell, this little exercise completely met my expectations and nearly matched the predictions of the simulation. While the drivers may not be ideal for use in a tapped horn, they certainly perform as predicted.

I've not really had a chance for any sort of subjective listening yet, I barely got the basic measurements done and plotted up today.

Let the armchair quarterbacking begin.
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post #43 of 114 Old 01-17-2010, 09:31 PM
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It looks like you installed both drivers the same way. Drivers facing the throat, and sitting on the mouth side, correct?
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post #44 of 114 Old 01-17-2010, 09:34 PM - Thread Starter
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Yes, magnets are in the mouth, cones fire into the throat.

That is one of the drawbacks to using this particular driver, it likes a higher compression ratio, which makes the throats pretty small.
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post #45 of 114 Old 01-17-2010, 09:37 PM
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Yep, that will do it.

You need to add in the throat chamber that mounting that way creates.


EDIT: and account for cone dish cc's.

EDIT: You need to add a Vtc of 636, and Atc of 532. This will shift the FR down a few Hz to match the measured response.
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post #46 of 114 Old 01-17-2010, 09:43 PM - Thread Starter
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Pics or it didn't happen.....

Drivers installed:


Access cover on (and one MESSY shop....):


Somewhat less than ideal 2pi measurement (in the rain):
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post #47 of 114 Old 01-17-2010, 10:49 PM
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This is with no damping martial, correct?
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post #48 of 114 Old 01-17-2010, 10:58 PM - Thread Starter
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The test tapped horn was made of 1/2 inch MDF, held together with brad nails and PL Premium. No damping material was used. I did use bracing on both sides of the baffle, but I did not install any corner braces or reflectors.
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post #49 of 114 Old 01-18-2010, 05:49 AM
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Nice work! You get those dialed in and I can see some of those hidden in some drywall and spread around the room.


dbl

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post #50 of 114 Old 01-18-2010, 06:10 AM
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Very nice... I'm still struggling with mine a bit over at HTS, but right now it's a lot of me being nitpicky for not much benefit. My original design needs 4 sheets of plywood and I'm trying to get it down to 3 by making better use of the wood.
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post #51 of 114 Old 01-18-2010, 07:06 AM
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I really like seeing the hornresp values vs the actual values. I wish we could get some more graphs like that. What I would really like to see are more tests. What did you use to do your tests? I have a bunch of different subs and would like to some tests on hornresp vs actual. Also check the sealed box vs horn box in measurements vs projected.
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post #52 of 114 Old 01-18-2010, 07:57 AM
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Nice work Mike. Looks like it matched up quite well with the model other than the little dip at 72hz. There's not enough comparisons like this.
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post #53 of 114 Old 01-18-2010, 09:32 AM
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The little dip is an artifact caused by a folded path length standing wave.

With a length of around 2.2m, and the mid-40s temp the 1st harmonic should come in around the 76Hz area. This is not accounting for the pipes taper, or fold and mouth end corrections.

I wouldn't be surprised if it was the cause of the dip at 73 and bump at 78Hz.
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post #54 of 114 Old 01-18-2010, 09:41 AM - Thread Starter
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Testing Details:
Dell Laptop, Windows XP
Woofer Tester 2 (Impedance and Phase)
E-Mu 0202 USB External Sound Card
Radio Shack 33-2050 modified per Wallin, Panasonic WM61 Capsule on a remote wand for a Mic and Preamp
RoomEQ Wizard (SPL measurements)

Amplifier used was an Audiosource Amp100, which is flat in our area of interest.

The WooferTester 2 was calibrated and is accurate.

The SPL equipment is not absolutely calibrated, but reads within 1 dB at 100 Hz of a calibrated meter. No calibration files were used for the mic or sound card. Comparisons between my 3 meters were within 1 dB. The plots presented are the data as measured, no smoothing or correction factors were applied.

Due to the rain, I was a bit rushed, so the reference voltage was not as exact as I'd have liked. I think I ran the sweeps at 2.81 V rather than 2.83, I just wanted to get the box in out of the rain.

I think the dip at 72 Hz is the result of the fundamental resonance of the single fold. It is off a couple of Hz from what is predicted by the math, but that seems to be the easiest explanation. It may also have been a measurement artifact. It was not as evident in the close-mic response.

As soon as I can find a more capable amp (I have one, I just don't know where I put it...), I plan to put some power to it and see if I can hear the woofers complain during home theater use. There are a few scenes in Iron Man that have made nearly every sub that I have tested thus far complain (though the toys I play with are nothing like the equipment some of the folks here use). I also want to get an idea of how this tapped horn sounds with music.

I also have some other 8-inch woofers that I'd like to try out in the enclosure, a pair of Tang Band W8-740s and some old OEM drivers that I've had sitting around. While neither of these drivers is a good fit, I hopefully will be able to learn something from the effort.

Ultimately, the plan is to take what I have learned here and incorporate that into a more refined fully folded design, so this is by no means a final point in this project.
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post #55 of 114 Old 01-18-2010, 01:46 PM
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ra, ra, ra!

(that is me cheering you on )

Love the comparison graphs (projected vs. measured), I am subscribed and watching closely. Keep up the good work!

Chris

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--Despair, Inc. "Regret"

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post #56 of 114 Old 01-18-2010, 04:42 PM
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Quote:
Originally Posted by soho54 View Post

I wouldn't be surprised if it was the cause of the dip at 73 and bump at 78Hz.

I am going to take this back. This only explains the slight downward shift in Hz of an artifact that should be there. I believe what we are seeing here is the product of a darn good/top shelf measurement job.

I believe he has actually captured the phase summation product/effect of the anti-nodes and surrounding 1/4 wave tapered pipe resonate nodes. Notice that this dip and then small peak phenomenon is located at the corresponding center point of every valley in the sim. Especially when throat chamber volume is taken into account. The standing wave ~76Hz just seems to have pushed the effect downwards a small amount from the 80s. Phase differences between the horn resonances and the standing wave may account for this.

Very interesting graphs. I look forward to more measurements from you. Do you have the package that allows distortion component measurements? Does it allow acoustic phase sweeps?
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post #57 of 114 Old 01-18-2010, 08:18 PM - Thread Starter
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Quote:
Originally Posted by soho54 View Post

Very interesting graphs. I look forward to more measurements from you. Do you have the package that allows distortion component measurements? Does it allow acoustic phase sweeps?

Got any software suggestions? I am currently using REW, primarily because the capabilities are hard to beat for the price.

If you've got any more measurement suggestions, I'm all ears. I've got pretty good equipment and I am a bit of a measurement geek.

The phase plot is interesting. It compares, but not as well as the impedance and SPL. Will get that polished up and posted as soon as I can. Should I plot it with impedance?
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post #58 of 114 Old 01-18-2010, 08:24 PM
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ARTA

You can use the demo version free. Been trying to get acquainted with it myself. There's also HolmImpulse.
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post #59 of 114 Old 01-18-2010, 08:43 PM
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I was just interested in what you can do on hand now. I know there are different levels of WT2 capabilities. I guess you have the base(read "non-overly expensive") hardware/software package.

A manual graph with distortion levels from REW would be nice. Something like this:

Maybe just a table with levels at different drive or SPL levels.

I would like to see HD component levels, but I don't remember REW being able to do that. Speaker Workshop is pretty easy to get setup and going, but you will need a Wallin's jig. The Arta demo is good too, you can't save (directly) though. The REQ THD would be great by itself, though. Not trying to force you, or put you on the spot here.

You have an imp graph already, phase can stand alone.
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post #60 of 114 Old 01-18-2010, 09:04 PM
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I just got through with dusting off REW, it will give you the different component harmonics along with THD.

In the spectrum tab.
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