Trying to design first horn for Sundown X-8

BIGlep

Member
2016-05-28 8:05 pm
Hey everybody. Just joined the forum and was looking for advice/help on a subwoofer design. I recently came into possesion of a Sundown audio X-8. It's a really beefy 8" driver. I am looking to maximize this subs potential and try something new so I am looking to build a horn encosure.

The limitations of the design are that it must fit into my cars trunk which is no problem, and I want it to fire through the ski hole. The ski hole has measurements of 20cm by 30cm giving 600cm^2 of mouth area. The goals are response into the mid/high twenties with as much efficiency as possible.

Here are the TS parameters:

Specifications X 8"D2 X 8" D4
RE (ohms) 4.00 ohm 6.00 ohm
FS (Hz) 46.770 hz 48.506 hz
Vas (L) 4.190 3.933
Qes 0.544 0.533
Qms 4.432 5.542
Qts 0.485 0.486
Le (mH)
BL (NA) 18.508 23.218
Mms (Grams) 158.641 g 157.131 g
Cms (uM/N) 72.995 68.515
Sens (1w/1m) 80.8 db 81.1 db

Xmax: 19

I am approximating Le to be around 3-3.5 since it is a large voicecoil for an 8, but it has a great amount of engineered inductance reduction measures taken including a full sleeve of copper throughout the magnet inner diameter.

I have been messing around in hornresp with a front loaded offset horn and it took some weirdness to get it looking good but the response looks promising.

Screenshots:






Tell me what you think
 

BIGlep

Member
2016-05-28 8:05 pm
At 234 liters, you could fit a ported box for 15" subs in that space.

I know you are wanting to experiment with horns, but the X-8 is mostly intended to be a peaky SPL sub. Its suspension is so stiff its going to be hard to work with.

I know. I already have a 15" psi platform 2 on an aq2200d in my old car. I want to try something new is all. And I think horns are cool. It's mostly for experimentation since I can always just throw it in a proper 6th order through the ski hole
 
As you know your Sundown X8 is not a good candidate for a FLH, but its fun to learn about them by simulating. So, since you are willing to experiment, you may as well be starting off with a more workable sim for a horn design in Hornresp.

I am a rookie too, but some really smart and helpful guys here on this forum schooled me on the basics, so here are a few tips that may help you. The Hornresp Help file is pretty useful too. Also attached is a quick sim with estimated figures entered for an example.

1) You should measure the T/S params of your driver if you can, as they are rarely accurate matches to the manufacturers claims. The Sundown website is also missing the Sd and Le specs so those have to be estimated at this point. I get burned almost every time when guessing or making assumptions... hope your luck is better.

2) Its probably a best practice (in most cases) to define your horn path in an expanding manner all the way from the throat to the mouth. Your sim shows S2 at 50 sq cm and S3 at 27 sq cm, which doesn't allow the sound wave to expand as it traverses the path. There are exceptions made sometimes for various reasons, but most designs allow an expanding horn design for best results. The "Schematic" tool gives you a pretty good picture of what your unfolded, expanding path horn design looks like. Also, you can double click the "Manual" label above the S2 slider inside the Loudspeaker Wizard tool, changing that to "Auto" will automatically maintain a proper S2 as you move the sliders about for S1 and S3. This is important at folding time when you have to place the driver and chamber at the S2 location, as you'd like that area to be flat for easiest driver mounting.

3) You will need to define a chamber for the driver to fire into at the S1/S2 junction. This is done in the Vtc and Atc fields of your Hornresp inputs. You can measure your driver to get the necessary figures, and by double clicking inside the Vtc or Atc field a wizard pops up to help you calculate. Be sure to provide enough space in front of the cone/surround to allow for maximum excursion of the driver with no part of the surround ever able to protrude into the horn path. My example shows about 2 cm Ltc in the status bar when hovering the mouse, which may or may not be adequate with your high rolled surround. Note that the compression ratio (Driver Sd vs S2 volume) is indicated in the status bar (and shows in my example screenshot attached below) as you hover your mouse over the S2 entry field. Your Sundown X8 will probably need a fairly high compression ratio to obtain best looking response. A safe maximum is up to you to decide. :D

4) You'll need to change all your horn paths to "Par" type so you'll actually be able to fold your OD/FLH horn design into a cabinet when its ready for sawdust and glue. You can click in each of your "Exp" fields and press the "P" key on your keyboard to change them to Par. The help file explains this.

5) Someone will correct me if I'm wrong but I think its probably OK to sim your horn in 1xPi rather than 2xPi, since this design will be loading into the small cabin of your car. My example also shows Eg field with 1 watt into 6 ohms driver Re at 2.45 volts. You can double click the Eg field to have Hornresp calculate the voltages for you at each wattage level you sim for.

6) You should always simulate with a Highpass filter active (either from the Tools > Filter... menu or from the Tools > Filter Wizard menu when viewing Displacement screen) to help control excursion for max SPL. If you don't intend to use a highpass then you can skip it, but you'll be unable to push it much without one. Use the Bandpass filter option in the Filter Wizard to define both high and low pass filters at once.

7) You'll notice your biggest design limitation right away... and that is the very small mouth size you have to maintain to fit in your car. Most Front loaded horns that are designed and built are severely undersized and this one will be much smaller than most. My guess is that the response cannot be smoothed out much given the tiny mouth size and T/S params of your driver. But as I said, guessing usually gets me in trouble, so hopefully you can fix it up good.

attachment.php


Have fun with it!
 

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BIGlep

Member
2016-05-28 8:05 pm
As you know your Sundown X8 is not a good candidate for a FLH, but its fun to learn about them by simulating. So, since you are willing to experiment, you may as well be starting off with a more workable sim for a horn design in Hornresp.

I am a rookie too, but some really smart and helpful guys here on this forum schooled me on the basics, so here are a few tips that may help you. The Hornresp Help file is pretty useful too. Also attached is a quick sim with estimated figures entered for an example.

1) You should measure the T/S params of your driver if you can, as they are rarely accurate matches to the manufacturers claims. The Sundown website is also missing the Sd and Le specs so those have to be estimated at this point. I get burned almost every time when guessing or making assumptions... hope your luck is better.

2) Its probably a best practice (in most cases) to define your horn path in an expanding manner all the way from the throat to the mouth. Your sim shows S2 at 50 sq cm and S3 at 27 sq cm, which doesn't allow the sound wave to expand as it traverses the path. There are exceptions made sometimes for various reasons, but most designs allow an expanding horn design for best results. The "Schematic" tool gives you a pretty good picture of what your unfolded, expanding path horn design looks like. Also, you can double click the "Manual" label above the S2 slider inside the Loudspeaker Wizard tool, changing that to "Auto" will automatically maintain a proper S2 as you move the sliders about for S1 and S3. This is important at folding time when you have to place the driver and chamber at the S2 location, as you'd like that area to be flat for easiest driver mounting.

3) You will need to define a chamber for the driver to fire into at the S1/S2 junction. This is done in the Vtc and Atc fields of your Hornresp inputs. You can measure your driver to get the necessary figures, and by double clicking inside the Vtc or Atc field a wizard pops up to help you calculate. Be sure to provide enough space in front of the cone/surround to allow for maximum excursion of the driver with no part of the surround ever able to protrude into the horn path. My example shows about 2 cm Ltc in the status bar when hovering the mouse, which may or may not be adequate with your high rolled surround. Note that the compression ratio (Driver Sd vs S2 volume) is indicated in the status bar (and shows in my example screenshot attached below) as you hover your mouse over the S2 entry field. Your Sundown X8 will probably need a fairly high compression ratio to obtain best looking response. A safe maximum is up to you to decide. :D

4) You'll need to change all your horn paths to "Par" type so you'll actually be able to fold your OD/FLH horn design into a cabinet when its ready for sawdust and glue. You can click in each of your "Exp" fields and press the "P" key on your keyboard to change them to Par. The help file explains this.

5) Someone will correct me if I'm wrong but I think its probably OK to sim your horn in 1xPi rather than 2xPi, since this design will be loading into the small cabin of your car. My example also shows Eg field with 1 watt into 6 ohms driver Re at 2.45 volts. You can double click the Eg field to have Hornresp calculate the voltages for you at each wattage level you sim for.

6) You should always simulate with a Highpass filter active (either from the Tools > Filter... menu or from the Tools > Filter Wizard menu when viewing Displacement screen) to help control excursion for max SPL. If you don't intend to use a highpass then you can skip it, but you'll be unable to push it much without one. Use the Bandpass filter option in the Filter Wizard to define both high and low pass filters at once.

7) You'll notice your biggest design limitation right away... and that is the very small mouth size you have to maintain to fit in your car. Most Front loaded horns that are designed and built are severely undersized and this one will be much smaller than most. My guess is that the response cannot be smoothed out much given the tiny mouth size and T/S params of your driver. But as I said, guessing usually gets me in trouble, so hopefully you can fix it up good.

attachment.php


Have fun with it!

Thanks for the advice. And good point on the parabolic. Do they increase in area linearly is that why?

And I read about the measuring drivers ts params. I've seen a lot of different methods is there one you recommend that is fairly accurate but not too expensive? I'm on a college kid budget.

The reason why I ended up with the decreasing area of the throat was because it smoothed out the response A LOT. I think it acts as some type of pseudo compression chamber or something. Also, the reason why the mouth shrinks at end is a wierd one. I noticed that if I added a 4th horn length I could use the third to expand the mouth area all the way up to 1200cm^2 and then in narrowing through the last the response actually improved. I think what's happening is that the sounds waves are expanding trough the third section, and then the fourth is "coupling" them to the environment or something idk. I'm going to try to find a good medium where it is more of a traditional "horny" design. Pun not intended.

I also simmed a tapped horn but it required a 6:1+ compression ratio. This driver does have a very strong cone, but that seemed extreme to me but idrk.

It actually models well ported because of the incredibly strong motor, but the horn design gives me a minimum 10-15 db boost in efficiency. Plus points for wierdness.

Thanks for the advice thus far guys
 
Par segments can have a rectangular cross section with a static width dimension so they can be folded into a square or rectangular shaped wooden cabinet. Con and Exp segments require bending wood in each direction, so very difficult (or impossible) to accomplish using plywood/MDF/OSB sheeting for cabinet construction.

The TSP measuring stuff is pretty cheap as I found out when putting my rig together. Following the advice of a great guy who helped me an awful lot in my first thread on these forums, I ordered a cheap chinese made USB sound card off fleebay from a California seller for $11.74 and soldered together an easy Impedance jig that meets requirements for LIMP, (part of the ALTA software). LIMP can be used without purchasing the license, as the registration cost only adds the ability to save and load overlays and other files. LIMP is not limited in any way that prevents you from using it for free and the help file is excellent.

I experimented with my jig and sound card, eventually finding a good, cheap, non-inductance, 2.5 watt 100 ohm resistor made by Vishay-Dale on the Mouser website for my jig that measures very flat. I increased the coupling capacitors in the cheap USB sound card (6 of them I think?) from 100uf to 1000uF caps (must be less than 12 mm tall electrolytics and 6 volts or higher rated) to help correct the early low frequency rolloff the 2 ohm impedance headphone output was afflicted with. My shorted jig now measures flat from just under 20 hz to 20000 hz in LIMP and that correction sweep (saved as a file) is subtracted from each Sine sweep during all driver measurements now. I decided that purchasing ALTA is worth it for the ability to load my jig correction sweep, so thats what I ended up doing after refining my setup and seeing how consistent it is in action. If you decide to make your own impedance rig on the cheap, let me know and I'll link the Mouser stuff you'll need to help save you some time.

For some excellent advice in horn design and using Hornresp from a few of the great minds on this forum, check out my first DIYaudio thread HERE. There is a LOT of knowledge shared in that thread and if it weren't for all the help I received there so far, I'd have failed long ago on my own. The cheap LIMP setup is covered in that thread too.

It actually models well ported because of the incredibly strong motor, but the horn design gives me a minimum 10-15 db boost in efficiency. Plus points for wierdness.
Yeah, I can relate to that! The boost in sensitivity you can get from an FLH is outstanding. The larger you can make the mouth, the greater the output. I like weirdness too if it helps to solve a problem. Breaking rules are sometimes the best option, but generally speaking the experts are usually right about what you can or cannot get away with. Somewhere in that thread I linked above, just a guy showed how he experimented with a constriction at the horn mouth to flatten response in a horn, similar to what you have done in your sim. Check it out it works! You may get away with a high compression ratio too since your 8 inch driver has a small Sd and strong cone. I've heard of 8-10 to 1 (and higher!) compression being tried in a horn with a small Sd driver like yours.

Have fun with it....
 

BIGlep

Member
2016-05-28 8:05 pm
Par segments can have a rectangular cross section with a static width dimension so they can be folded into a square or rectangular shaped wooden cabinet. Con and Exp segments require bending wood in each direction, so very difficult (or impossible) to accomplish using plywood/MDF/OSB sheeting for cabinet construction.

The TSP measuring stuff is pretty cheap as I found out when putting my rig together. Following the advice of a great guy who helped me an awful lot in my first thread on these forums, I ordered a cheap chinese made USB sound card off fleebay from a California seller for $11.74 and soldered together an easy Impedance jig that meets requirements for LIMP, (part of the ALTA software). LIMP can be used without purchasing the license, as the registration cost only adds the ability to save and load overlays and other files. LIMP is not limited in any way that prevents you from using it for free and the help file is excellent.

I experimented with my jig and sound card, eventually finding a good, cheap, non-inductance, 2.5 watt 100 ohm resistor made by Vishay-Dale on the Mouser website for my jig that measures very flat. I increased the coupling capacitors in the cheap USB sound card (6 of them I think?) from 100uf to 1000uF caps (must be less than 12 mm tall electrolytics and 6 volts or higher rated) to help correct the early low frequency rolloff the 2 ohm impedance headphone output was afflicted with. My shorted jig now measures flat from just under 20 hz to 20000 hz in LIMP and that correction sweep (saved as a file) is subtracted from each Sine sweep during all driver measurements now. I decided that purchasing ALTA is worth it for the ability to load my jig correction sweep, so thats what I ended up doing after refining my setup and seeing how consistent it is in action. If you decide to make your own impedance rig on the cheap, let me know and I'll link the Mouser stuff you'll need to help save you some time.

For some excellent advice in horn design and using Hornresp from a few of the great minds on this forum, check out my first DIYaudio thread HERE. There is a LOT of knowledge shared in that thread and if it weren't for all the help I received there so far, I'd have failed long ago on my own. The cheap LIMP setup is covered in that thread too.

Yeah, I can relate to that! The boost in sensitivity you can get from an FLH is outstanding. The larger you can make the mouth, the greater the output. I like weirdness too if it helps to solve a problem. Breaking rules are sometimes the best option, but generally speaking the experts are usually right about what you can or cannot get away with. Somewhere in that thread I linked above, just a guy showed how he experimented with a constriction at the horn mouth to flatten response in a horn, similar to what you have done in your sim. Check it out it works! You may get away with a high compression ratio too since your 8 inch driver has a small Sd and strong cone. I've heard of 8-10 to 1 (and higher!) compression being tried in a horn with a small Sd driver like yours.

Have fun with it....

Thanks a ton man. I actually used your inputs but modeified s3 and with a 24db/oct lowpass at 70hz I have +-3db from 26hz to 80. I think it might be perfect.
 
Those inputs I provided were for example figures for the throat chamber (sometimes referred to as the filter chamber) and whatever else was missing in your sim. They were estimates... don't correlate to anything, so you should probably measure and correct or optimize any of those figures I supplied. You can play with the closed rear chamber volume and compression ratio as well for fine tuning a couple liters in or out of the final horn size. But, +-3Db across the band isn't too shabby for that driver regardless... Gonna be folding it soon?
 
If I'm not mistaken, I've published more car horns than just about anyone, except for Bill Fitzmaurice.

Here's some random things I've learned doing this:

1) The car itself acts like a quarter wave resonator. Due to this, if you want sheer output, it's pretty difficult to beat a sealed or ported box with a big amplifier. Basically the gains that you get with a big horn can be found with a plain ol' sealed or ported box, carefully placed in the car. Position make a big difference.

2) Having said that, I am running a horn sub in my car. Why? Because they have really nice phase response and they sound 'tight.'


When building a horn for a car, I think there's a tendency to use small drivers, to keep the horn size down. I made this mistake myself, when I built an autotuba clone, and when I built a tapped horn with eights. The problem with using small drivers in a horn for a car is that all of your gain is up high in the passband, where you don't need it. For instance, the Fitzmaurice Autotuba is something like 95dB efficient at 150hz, but at 30hz it's only 85dB efficient.

Due to that issue, I'm a fan of using drivers with a low FS and just making the enclosure too small. Making the horn too small will make it 'peaky', but you'll have a lot of gain down low, where you want it.


In a nutshell, if you use an 8" woofer with an FS of 40hz and put it in a front loaded horn, there's going to be virtually no gain at 40hz, and tons and tons of gain at 150hz, where you don't need it.

For my horn, I am using an Alpine SWS-15D4 in a tapped horn.

If you want to see my car horns, check out my threads at stevemeaddesigns and diymobileaudio