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Any reason NOT to do a THT? - Page 7

post #181 of 211
Regardless of what causes the difference (be it turbulence, flow interruption, extra air in bends that don't have reflectors or rotational mass) the advanced centerline folding method makes the measurement of the end product agree with the simulation. Soho54 used to say all the time that when the measurements didn't match the sim, the person didn't build what he simulated. He went on to prove it by simulating the end product accurately (which included adjusting the length through the bends) and the measurement would match his sim.

If the measurement matches the sim then by definition the sim is accurate. And by extension, soho54's method is accurate, he proved it.

I really don't care what causes the discrepancy (although I would be interested to read about it in proper studies), all I care about is making accurate simulations that will match the measurements of the finished product. The centerline folding method won't get you there.
post #182 of 211
Since this is an interesting subject, here are a couple of quotes from soho54 from here: http://www.diyaudio.com/forums/subwoofers/175658-tham15-compact-15-tapped-horn.html
It's a long thread but highly recommended (even if you only read soho54's posts), it's jam packed with useful info on horn folding. (He also talks about the importance of placing the segment markers in exactly the right spot when simulating/folding in this thread, which can be a problem with Hornresp's limited number of available sections.)
(Bold added by me.)
Quote:
The bends are made out to be harder than they are. The quote you are talking about from Tom is where he is explaining how to convert a straight horn simulation into a folded horn, and how it can be messed up during the translation, IIRC. The idea is to carry the horn around the bend like you were just bending it around. You want to keep the volume, distance, and flare rate correct at every position around the bend. You are going to get a little extra volume around the corner if no filler is used, and it will be ok as long as it is kept to a minimum. Calculate the volume that was supposed to be in the straight horn section that is taken up with the bend, and then calculate the actual volume taken up. They should be pretty close. If not you will want to redo the bend, or come up with a new simulation. Any mess up will throw your sim out the window, as has happened here it seems.

I have a thread showing how I am tackling it right now, and it shows what I mean.
Horn Folding in Sketch-Up - AVS Forum

Most designs out there mess this portion up using cut and twist 90deg methods of bending. This normally results in a non-flared, overly flared, or pinch point in the bend.
Quote:
I came up with it (the advanced centerline folding method) through a lot of research, and trial and error. About two years ago I got feed up with the "common knowledge" surrounding horns, so I threw it all out and started over from scratch. I read everything I could by Keele, Edgar, Leach, and Danley looking for common threads. I have pages and pages of excel work exploring their different papers, and ideas from posts. I then went back to Rayleigh, found measured data on acoustic pressure around bends, and sourced fluid dynamic, FEA, and BEM simulations.

I then spent a lot of time trying different ideas out, coming from the view point of getting the simulation to match reality. I would work until I found something that worked for a certain folded horn, and then tried it on another. You can find different ways to sim a single horn, but most of them fail when you try it on another. I kept redoing things until I found a way that works on all the horns I have tried it on.

In truth, every method you have there along with the 45deg, and SQRT of the product of the inside and outside path lengths works well enough on smaller bends in horn with only one to three corners. It is when you start to add more corners, or larger flares that they start falling away. The .707 one is more of a mid horn up thing.

Up until ~6months ago I actually used different methods for different corner setups, but in the end after dozens of more tests I have found that using the single method produces the most consistent results no matter the corner number, or geometry.

The problem with most of them is that they are inflexible, don't scale well, and do not account for the extra volume in a non-squared corner that will add path length. The bass horn system I came up with does.

The Danley quote is actually a key piece to the puzzle. If the volume around the corner is exactly the same as the straight line distance, then the acoustic path will be shorter than the straight line distance. That means a corner should have slightly more volume than it's straight sectioned counterpart, and adding even more volume will increase it's acoustic length beyond the straight sections length. It also means that if you know the volume is the same, and you path length sims longer than the real deal, you haven't measured the path through the corner correctly.

The nice thing about this method I found is that you can take a measured horn, create a sim from the plans that is equivalent. Then use the simulation output to refold the horn, and the results will be within a tolerance of mm to the original horn. It works in reverse as well. The only trick is learning where/when reflectors are needed, but it isn't hard to figure that part out. It is just a continuation of the line of thought stemming from the quote, and applying the same solutions.

I don't think it is the only way to do it, or even the best way. It just seems to work for me, and a few others.

Edited by diy speaker guy - 9/1/13 at 3:46pm
post #183 of 211
"I really don't care what causes the discrepancy (although I would be interested to read about it in proper studies), all I care about is making accurate simulations that will match the measurements of the finished product. The centerline folding method won't get you there."

the centerline method results in a longer horn which would give a lower corner than the advanced centerline method, so something is backwards.
post #184 of 211
Quote:
Originally Posted by LTD02 View Post


the centerline method results in a longer horn which would give a lower corner than the advanced centerline method, so something is backwards.

I agree with the part in bold, it's what I've been saying. The quotes from Danley, BFM and soho54 suggest that all 3 of them agree with both of us. So I'm not sure what you are referring to as being backwards.

Let me try to put this another way.

A random guy (let's call him Dave) makes a horn sim with Hornresp. Dave lays out his Hornresp horn sim into a folded horn plan using the centerline method. He doesn't use reflectors in any corners. He builds the horn and measures it. The LF corner of the physical horn measures a bit lower than the sim predicted.

Dave emails his Hornresp sim to Sam. Sam uses Dave's Hornresp sim to fold the horn using the advanced centerline method. Sam doesn't use any reflectors in the bends either. Sam builds this horn and measures it. The LF corner of the horn measures exactly the way the sim predicted.

This issue is as simple as that.
post #185 of 211
i see what you are saying. using the advanced centerline method actually results in a slightly longer horn than the centerline method, so it correlates more closely with the measurement.
post #186 of 211
Quote:
Originally Posted by diy speaker guy View Post

...The LF corner of the horn measures exactly the way the sim predicted...
I'd like to see this hypothetical as HR sims...
Would it be possible to work one up to see the effects of "Dave's deviation"?
post #187 of 211
I was thinking about it again today and it is still backwards.

using the centerline model in hornresp gives a horn of length X.

that horn in actuality measures with a slightly lower corner than the model, which means the model is too SHORT and the real horn is too LONG.

using the advanced centerline method, the horn would be even LONGER which means that the model would be even further off.

just say'n....

:-)
post #188 of 211
If the advanced centerline model results in a longer horn length, isn't this measuring the actual horn, which wouldn't make the horn longer, but would make the horn model longer? In other words, the physical folded horn doesn't change length, but the unfolded model of the horn would need to be longer to match the length given by the advanced centerline model?
post #189 of 211
These explanations need pictures lol..
post #190 of 211
Quote:
Originally Posted by diaz View Post

These explanations need pictures lol..

They need more than pictures, they need real proof. I'm thinking about a way that I can provide some real data.
Quote:
Originally Posted by LTD02 View Post

I was thinking about it again today and it is still backwards.

using the centerline model in hornresp gives a horn of length X.

that horn in actuality measures with a slightly lower corner than the model, which means the model is too SHORT and the real horn is too LONG.

Sorry for the delayed reply, I was away all day.

Yes, this is my current understanding of the centerline method.
Quote:
using the advanced centerline method, the horn would be even LONGER which means that the model would be even further off.

just say'n....

:-)

Thanks for pointing this out. This seems to make sense, I'm not sure why I was thinking otherwise.

If these last two quotes are true that means some of my comments about the advanced centerline method in the last few posts are wrong.

I've been thinking about the best way to test this and get some real data, I think I have some good ideas but I'd appreciate your input so I'll be sending you a PM soon, maybe tomorrow.

Anyway, thanks for making me take a critical look at this issue.

Now in the meantime, the good news is that this issue is not life or death important, it makes very little real world difference unless the horn has a lot of bends. And even then it usually only amounts to 1 or 2 hz difference in the low corner frequency.
post #191 of 211
Data FTW.

I have attached a blank sketchup layout of a tapped horn that I have built and measured. I've also included a front-loaded horn we're all familiar with.

The internal panel width of the tapped horn panels is 22.5", the front loaded OD is 18.5"

So, since I have accurate (enough) SPL and impedance data for both of these horns, go ahead and draw things up for both pathlines, then let's calculate up some sims and compare them to the measured reality.

I've got pretty good kung-fu when it comes to graphing data (I do a lot of it at my real job), so I'd be happy to generate the plots, as well as plot my measurements alongside.

I know how I drew things, and I know how I modeled things. I also know that the models are not quite exact.

Pathlines.zip 10k .zip file
post #192 of 211
Yeah, this will work. It's not at all what I had in mind but it will save me the time and effort of designing a test protocol and actually building and measuring something myself.

It's going to take a bit of time to learn Sketchup. Let's see how long it takes me. tongue.gif

I'm going to do the F20. Normally I'd use Akabak to reverse engineer something with this many segments but maybe if I'm using Sketchup anyway I can use it to find out where S3 and S4 should go so Hornresp should work fine. (Obviously there's no choice where S1, S2 and S5 will have to be.) I'll show my work as much as possible.
post #193 of 211
Quote:
Originally Posted by diy speaker guy View Post

Yeah, this will work. It's not at all what I had in mind but it will save me the time and effort of designing a test protocol and actually building and measuring something myself.

It's going to take a bit of time to learn Sketchup. Let's see how long it takes me. tongue.gif

I'm going to do the F20. Normally I'd use Akabak to reverse engineer something with this many segments but maybe if I'm using Sketchup anyway I can use it to find out where S3 and S4 should go so Hornresp should work fine. (Obviously there's no choice where S1, S2 and S5 will have to be.) I'll show my work as much as possible.

Great, we can compare notes when we're done.

The F-20 fold is pretty simple, only 3 flare rates.
post #194 of 211
I did a small study on the centerline vs advanced centerline issue, so for those that wanted more info on the subject here it is.

http://www.avsforum.com/t/1489784/horn-folding-a-brief-study-of-the-centerline-vs-advanced-centerline-method
post #195 of 211
Thread Starter 
Hey!

I finally got this thing fired up yesterday and despite all of the negativity on this thread, I love it! I haven't really had a chance to put it through its paces yet but man is it loud! I DO realize it's limitations in the ultra low end, and it is a great bang for the buck solution! I think the highest I saw the Volts read was 14... And that was about ready to break the windows!

Next on the list is to make sure this thing is properly set up. I have a denon 1713 and have run odyssey but would like to do some frequency response testing. I have a rat Shack meter and a test tones dvd so I can go the old school route of just graphing at different frequencies or I can try to use REW with the meter as a microphone. I would like to get the THT dialed in and then see if there is any way I can introduce the SVS into the mix... I hate to see it just sit there... And advice/suggestions? Thanks in advance guys... And thanks Bill for a great design!!
post #196 of 211
Thread Starter 
Also, I have the sub in the front left corner along the back wall with the mouth facing the corner about 18 inches away from the corner. I could technically put it in the other corner as well, but it is definitely best to have it in its current spot...
post #197 of 211
Good to hear it's up and running and you like it! smile.gif

I'm not sure the SVS will be able to keep up lol I don't think you'd be able to EQ them as the SVS would be maxing out and straining while the THT would be cruising along not being made full use of, I reckon!
post #198 of 211
i would NOT try and integrate the SVS. getting horn based subs and sealed/ported subs timed just right and working together is pretty insanely hard to do. it CAN be done, but there's very little benefit.
post #199 of 211
Quote:
Originally Posted by jkkwaz View Post

Hey!

I finally got this thing fired up yesterday and despite all of the negativity on this thread, I love it!!

I think you misread the intentions. What you call negativity I call a study on the physics of the design and horns in general. No one ever said the tht was a bad design, the only issue was the claims that are made about it (including the no hpf required and boosting below tuning among other things).

My exact quote on the topic of your probable first impressions was this:
Quote:
To put it simply, depending on what you are used to, you very likely will not be disappointed. In fact you will probably be really impressed, horns are fun. But that does not mean the tht design with a cheap driver and no hpf is particularly impressive when compared to other designs in a similar price range.

Congratulations on your first horn. I suspect it won't be your last. Horns are fun.
post #200 of 211
Thread Starter 
Sorry, maybe negativity was a harsh word... I really appreciate all the info. I definitely understand the that's limitations and also its strengths!! And I'll take the advice about not integrating the SVS. Sounds like a lot of work for not much payoff. The THT definitely has the SVS beat in terms of output.

So, can I ask some advice that I could probably find in the audyssey thread but haven't gotten far enough into reading it? I have run the calibration at 5-6 position, but am wondering if any of you use the dynamic volume. I am finding that I use it even when I don't have to keep things quiet because it brings the center channel vocals to a place where they are loud enough. Is it better to disable dynamic volume and raise center channel levels a bit? I also have dynamic EQ enabled as I don't normally listen very loud or at reference level, not that my system could quite achieve that anyway smile.gif My speakers are not very efficient at all and are being run off of receiver power.
post #201 of 211
Dynamic volume is kind of misleading in that it is not dynamic at all. It squashes the dynamics of the soundtrack. It is a type of compression, though, a complicated form of it. Dynamic volume makes a movie sound less dynamic.

I don't use it because I don't want to lose the dynamics of the soundtrack. My preference is that the soundtrack sounds better without it, even if I'm listening at more casual volume.

If you are having to raise the volume of the center higher than where it is set by audyssey you may have other acoustical issues that are making dialogue difficult to hear. Treating the first reflection points in my room made a difference for me.

Of course, if you are listening at very low volumes, like below -30db ref, the dialogue becomes difficult to hear while the sound effects are loud due to the relative difference in volume above the noise floor. This is the case where you may need to use dynamic volume to compress the peaks so that you can listen at very low volumes and still hear dialogue.
post #202 of 211
Thread Starter 
Wow, thanks... Awesome post. I think that is the issue I'm running into... I didn't think about the noise floor and it's effect when watching at low volumes like that. And I'm already in the process of doing some DIY acoustic panels to help with reflections. Thanks again.
post #203 of 211
Thread Starter 
Hey guys, sorry to bring this thread up again. Just a couple quick questions. Working with REW and taking some FR measurements, but Iam wondering what the most cost effective way is to accomplish a couple goals. First, iI would like to add a HPF so I am not working about abusing the driver in the THT if I am playing <20 Hz material at high levels. Also, I am thinking of TRYING to integrate my SVS PB2+ as a near field sub. I known many people here with much more experience have advised against this, but I do have a perfect spot right behind the couch that I could put this just to give it a try. However, I would need to implement some serious time delay here, right? Since this will be very close and audyssey reads the THT as being like 28 ft away. I'd also like to HP the SVS a little too, maybe like as a more of a mid bass Nearfield type sub? Am I crazy? What do need? A behringer dcx2496? Minidsp? Thanks!
post #204 of 211
what amp are you running on the tht again? is it a plate amp?
post #205 of 211
Thread Starter 
Yep, the BASH 300w
post #206 of 211
"However, I would need to implement some serious time delay here, right?"

that would be a good place to start, but who knows what kinds of interaction effects you are going to run into with this plan.

"I'd also like to HP the SVS a little too, maybe like as a more of a mid bass Nearfield type sub? Am I crazy?"

I don't really understand this part, but the easiest way to give it a higher roll-off point would be to plug the ports. you are saying that you want to use your low sensitivity sub for near field midbass (but still cross over at 80hz?) while you have a high sensitivity horn already covering the upper bass?
post #207 of 211
the 300 watt bash has a built in high pass filter. 18hz or so 2nd order high pass iirc (17.7hz q=1.0, just checked).
post #208 of 211
Thread Starter 
Excellent, so I guess that would mean about a 3db decrease at about 15hz? And a boost from 20-30...So I guess that is sufficient. Do i need to add anything online to the SVS to control delay if it will be near field do you think?
post #209 of 211

The highpass is adjustable so I don't know what Bill F. recommends for the THT, probably best to ask on his forums. The minidsp can set a delay but it seems like the highest you can set it is 7.5ms which isn't much.

post #210 of 211
Thread Starter 
Hey sorry, LTD02, totally missed your last post... Dieregard my last question
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