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Old 9th February 2016, 03:27 PM   #1
vrfood is offline vrfood  Bulgaria
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Default 1 driver tapped horn / hornresp

Hey guys. I've got an 8 inch KEF sub driver just lying around and I decide I am gonna build a tapped horn with it. Since there's no description / model or anything, I measured it myself using ARTA/LIMP; here are the parameters:
Click the image to open in full size.

So, here's the deal.. I've played around with Hornresp before, but I've never actually built anything based on it. That's why I read and tried to follow Lilmike's excellent guide, but there are some thing that are unclear to me, mostly about the way Hornresp implements the data you feed into it.. let me post some screens from Hornresp:

Hornresp / driver parameters:
Click the image to open in full size.

Acoustical response without power / xmax input:
Click the image to open in full size.

Response with 60W / 4mm xmax input:
Click the image to open in full size.

Displacement at 1W vs 60W / 4 mm xmax
Click the image to open in full size.
So, there are a couple of things that I am worried about; first off, does everything look normal to you in the parameters and simulations?

Is it normal to have a much flatter response at 1W than it is with added power? Looks much too lumpy to me at 60W.. 11dB of difference between the highest and lowest spike.

And lastly, the displacement simulation at 60W looks awful, pretty sure something is wrong with it.

So, that's pretty much all I am concerned about; Hornresp is a beautiful piece of software and I do look forward to learning how to utilize it in the best way possible. I just want to have everything straight theory-wise, before I even start exploring ways to fold it so that there's still space for me in the room

Thanks in advance

Last edited by vrfood; 9th February 2016 at 03:30 PM.
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Old 9th February 2016, 03:38 PM   #2
sine143 is offline sine143  United States
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sim in 2 pi.
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Old 9th February 2016, 04:11 PM   #3
vrfood is offline vrfood  Bulgaria
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I did that as well. The displacement doesn't change a lot, which is my main concern right now, since it does not look right at all. Will post some screens in a minute or two.
EDIT: here it is, sim @ 2pi:
Click the image to open in full size.

btw, i am not sure about the Ap1 and Lp parameters; i blindly copied what Lilmike used in his tutorial; is that what i am supposed to do? :0

Last edited by vrfood; 9th February 2016 at 04:21 PM.
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Old 9th February 2016, 05:17 PM   #4
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Your sims are not showing frequency response at 1 watt or at 60 watts.
2.83V is only 1 watt if the driver is 8 ohms so your "1 watt" sim is actually more than 1 watt.
The max spl tool does not show the frequency response you will get at 60 watts, look at the instructions to see what the max spl tool is actually showing.
Adjust Eg to find how much power your design can actually take by looking at the displacement graph. You'll probably hit xmax with around 5 watts.

Use PAR segments, not CON.

Ap1 and Lp describe the dimensions of the throat adapter. You don't need a throat adapter. Use Vtc and Atc to account for the air in the driver cone and wood thickness it fires through if applicable.

A driver with only 4 mm xmax probably isn't the best choice for a tapped horn subwoofer.

Check your design against a ported box sim with the same driver. The tapped horn will be much larger so if you don't see substantial gains from the tapped horn design then the extra wood probably isn't worth it and you should probably stick with a ported design.
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Old 9th February 2016, 09:00 PM   #5
vrfood is offline vrfood  Bulgaria
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Quote:
Originally Posted by just a guy View Post
Your sims are not showing frequency response at 1 watt or at 60 watts.
2.83V is only 1 watt if the driver is 8 ohms so your "1 watt" sim is actually more than 1 watt.
The max spl tool does not show the frequency response you will get at 60 watts, look at the instructions to see what the max spl tool is actually showing.
Adjust Eg to find how much power your design can actually take by looking at the displacement graph. You'll probably hit xmax with around 5 watts.

Use PAR segments, not CON.

Ap1 and Lp describe the dimensions of the throat adapter. You don't need a throat adapter. Use Vtc and Atc to account for the air in the driver cone and wood thickness it fires through if applicable.

A driver with only 4 mm xmax probably isn't the best choice for a tapped horn subwoofer.

Check your design against a ported box sim with the same driver. The tapped horn will be much larger so if you don't see substantial gains from the tapped horn design then the extra wood probably isn't worth it and you should probably stick with a ported design.
Oh, yes, of course, how the hell did I miss that.. I just clicked on Eg and fixed it. Okay, now the displacement sim looks much better, thanks for the explanation. I used 80W / 3.6R and now everything looks much more manageable. TBH, I am not quite sure what the correct XMAX of the driver is. I know it is quite hard to measure this by yourself, but I've gotta read up a bit more on the topic.
-One question here; is the xmax (in mm) in Hornresp one way or both ways? If I see 10mm excursion in the sim, does that mean 5mm up and 5mm down, or 10mm up and 10mm down?

As for the PAR / CON segments, I followed Lilmike's guide, as I was unsure exactly how to model the tapped horn. He specifically mentions to use 3 x CON segments, but I will gladly try PAR segments as well. Same goes for Vtc and Atc- guide says use zero; matter of fact, I am gonna leave all 6 fields at 0 for now.

Thanks for the comprehensive answer.
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Old 9th February 2016, 09:10 PM   #6
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Quote:
Originally Posted by vrfood View Post
Oh, yes, of course, how the hell did I miss that.. I just clicked on Eg and fixed it. Okay, now the displacement sim looks much better, thanks for the explanation. I used 80W / 3.6R and now everything looks much more manageable. TBH, I am not quite sure what the correct XMAX of the driver is. I know it is quite hard to measure this by yourself, but I've gotta read up a bit more on the topic.
-One question here; is the xmax (in mm) in Hornresp one way or both ways? If I see 10mm excursion in the sim, does that mean 5mm up and 5mm down, or 10mm up and 10mm down?

As for the PAR / CON segments, I followed Lilmike's guide, as I was unsure exactly how to model the tapped horn. He specifically mentions to use 3 x CON segments, but I will gladly try PAR segments as well. Same goes for Vtc and Atc- guide says use zero; matter of fact, I am gonna leave all 6 fields at 0 for now.

Thanks for the comprehensive answer.
You are going to be way past 4 mm with 80 watts, like I said, probably 5 watts will get you to 4 mm based on your excursion at 2.83V.

Hornresp is 1 way excursion just like most driver data sheets. If you are seeing 4 mm excursion it's 8 mm peak to peak.

Xmax is usually measured by coil/gap measurements (so if you have a data sheet with these measurements you can figure it out) or by Klippel. You can't measure xmax without these things.

Lilmike's tutorial might have been written before Hornresp could do PAR segments. If you are going to build with flat sheet goods and two walls are going to be parallel you want to use PAR, not CON.

You can leave all 6 fields at the bottom blank (Vrc and Lrc will always be blank for a tapped horn anyway) but if you want a more accurate sim you should fill in Vtc and Atc. It won't make a large difference but it will make a difference, especially if the cone holds a large volume of air and the driver is mounted such that it fires through the baffle cutout, which is the volume of the thickness of the wood x radius squared x pi.

You can use more than 3 segments, and you can make L12 a different distance than the last segment length too. Also you sim has no expansion in the last segment, this could be hard to fold depending on how you plan to fold it.

Last edited by just a guy; 9th February 2016 at 09:21 PM.
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Old 9th February 2016, 10:20 PM   #7
vrfood is offline vrfood  Bulgaria
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Okay, I made some small changes following your advice and ended up with a much more manageable excursion, that I think the driver would be able to take. I sacrificed the lower end a bit, but it looks like that's the only way. My former attempt went to levels of 8mm excursion at 60W, which would probably have been bad for the driver. Here are some screens:
Click the image to open in full size.

What do you think about these new sims? I really want to build a tapped horn with this driver just for the sake of it, hell, I am prepared to sacrifice it in the process. Worst case scenario, I am gonna get a much more suitable driver for a TH, in case this one fails.
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Old 9th February 2016, 10:32 PM   #8
GM is offline GM  United States
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FWIW, tuned to Fs, so a little higher cutoff, consequently a bit smaller with more power handling in the ~32-50 Hz BW. Download to the IMPORT Folder then load it to view/change [if desired]:

GM
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File Type: txt KEF_8'_TH_vrfood.txt (955 Bytes, 12 views)
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Old 9th February 2016, 10:34 PM   #9
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The big spike at 150 hz is just outside the passband and it's huge, it may be very hard to control unless you have parametric eq dsp. (Talking about your sim, not GM's)

Usually L12 is short, yours is pretty long. This may or may not be best.

In your previous sim you had no expansion in the last segment, now you've got a huge expansion in the last segment. This may or may not be the best way to do it.

There are several factors to play around with, just play some more until it looks good and it's something that can actually be folded. If there's an flare rate change where the first and second segments meet (or where the last and second last segments meet) it might be difficult to fold.
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Old 9th February 2016, 10:37 PM   #10
vrfood is offline vrfood  Bulgaria
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Quote:
Originally Posted by GM View Post
FWIW, tuned to Fs, so a little higher cutoff, consequently a bit smaller with more power handling in the ~32-50 Hz BW. Download to the IMPORT Folder then load it to view/change [if desired]:

GM
Thanks a lot. Really interesting, it looks pretty nice at only 76 liters of volume. I might just use that.
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