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Lilmike's Cinema F-20 - Page 48

post #1411 of 1695
I have read the majority of this thread, but not all of it. So hopefully this wasn't asked already... Visualize if one were to take his/her f20, and line the front corners with weather stripping and shove it into a corner, with the horn facing the corner. My logic says that you could extend the horn another 5ft this way, kind of like how the old klipschorns work. Would it make much of a difference, or would you just get 1hz lower and not even notice?
post #1412 of 1695
Quote:
Originally Posted by beastaudio View Post

Now this...
This will possibly upset some folks. Haha, I am in the same camp however, the lady LOVES the theater.

I was standing the the same room and we were discussing what to do and he was minimizing his system and saying he does'nt really need a HT and then his wife gently touched his shoulder but what about Lord of the Rings and Iron man?
The whole thing brought a tear to my eye.
Myself I have more audio equipment packed up than in use. last renovations took the Omega hemps and subs out of the living room and the room was rearraged without them. My HT now consists of completely stock RCA speakers ( SMALL ) and Stock Sub. Even my simple basic ported 12"DVC was not allowed back in.

I had one audiophile system going and one HT, now I am down to a iphone.

Looks like I will be going to my sons house to watch movies wink.gif
post #1413 of 1695
Quote:
Originally Posted by doodoobutter View Post

My logic says that you could extend the horn another 5ft this way, kind of like how the old klipschorns work.

My own experience with horns is that this is not the case. You do benefit from eighth space boundary loading, but that's about it.
post #1414 of 1695
Quote:
Originally Posted by doodoobutter View Post

I have read the majority of this thread, but not all of it. So hopefully this wasn't asked already... Visualize if one were to take his/her f20, and line the front corners with weather stripping and shove it into a corner, with the horn facing the corner. My logic says that you could extend the horn another 5ft this way, kind of like how the old klipschorns work. Would it make much of a difference, or would you just get 1hz lower and not even notice?

From what I was reading extending the horn changes the parameters of the driver and depending on the driver it can be a problem. That said I like to try things and see how they work out. A more suitable driver will handle an extended horn and extend the bass. I would not mess with this design and think about another sub or design myslef.
I am still looking but I really like this design and the success it has shown.
I am hoping to take this design and use it in the front of the room and put the ported velodyne directly behind the sofa and possibly couple it to the sofa. with all the settings on the velodyne many things are possible. My other idea is to revisit the subwoofer that was used with the old Imperials and seeing if I can adapt that design for ultra lows. It has been awhile since I have seen it so I don't know if that will do my lows below 20hz or not.

He is still working on the room itself so we shall see where things go from here over the winter.

All the best.
Gexter

*EDIT* Correction on the Imperials the sub woofer used with the Imperials was the Jenson Transflex and it basically only picked up when the Imperial started dropping off below 60HZ .
the Transflex seems to drop off earlier than lilmike's F20 so its pretty much useless suplementing the F20.
Edited by gexter - 11/6/12 at 9:36am
post #1415 of 1695
Thread Starter 
Quote:
Originally Posted by doodoobutter View Post

I have read the majority of this thread, but not all of it. So hopefully this wasn't asked already... Visualize if one were to take his/her f20, and line the front corners with weather stripping and shove it into a corner, with the horn facing the corner. My logic says that you could extend the horn another 5ft this way, kind of like how the old klipschorns work. Would it make much of a difference, or would you just get 1hz lower and not even notice?

This horn was not exactly designed to work that way. K-horns require a corner to work properly, the F-20 does not, it performs as "advertised" in a groundplane setting.

Certainly, loading it into a corner will make an SPL difference due to the presence of the boundaries, but it will not play significantly lower.

The other thing to remember here is that the effective low corner is not just a result of the horn. I get to pick a low corner based on horn length, but it is important to remember that the driver also dictates how low a horn can play by virtue of its displacement limits. I am pushing the drivers I recommend in this design about as far as they can go and still maintain decent power handling and a reasonable margin of safety.
post #1416 of 1695
Thanks for the interesting responses. I was just curious really, because I'm using the dayton HF, and I believe it can play a little lower without too much distortion in a ported box, so I figured, why not try and extend the horn by shoving it up against a corner? It does make sense though when you say it works as is, because the k-horn wasn't meant to just be placed anywhere and work properly like the f20.
post #1417 of 1695
DVC 15s on sale FYI.


http://www.parts-express.com/pe/showdetl.cfm?partnumber=295-190

Cant get much more bass than that for $99.
post #1418 of 1695
that's not how to say it...try it like this:

!!!DVC 15s on sale for $99!!!

:-)

actually that deserves its own post...i'll go set one up. nice find.
post #1419 of 1695
My dvc 15 just arrived yesterday! Id like to thank the gentleman that pointed out they were on sale. Going to get my mdf tomorrow probably. Or i might go back out tonight... this will be replacing a kicker L7 15 i have in a 5.5 cuft 25hz ported box in my theater. Im so excited after hearing sooo many rave reviews of this design.
post #1420 of 1695
I've been through most of this thread, and what a great one, but can't seem to find any discussion on altering the width of the f20 similarly to how the THT plans allow you to do. Is there discussion on this somewhere else? If not would making a f20 that is 24" wide and braced like a THT cause any ill effect?

The reason I ask is about a year ago I bought enough 1/2" arurco (6 4x8 panels) to build 2 THTs. I ripped 4 of them into just under 24" strips on my table saw so every panel I cut would be exactly the same width. I did this so at the end when you put the final side on everything lines up perfectly and flat.

I only built 1 THT (awesome dB/$ btw) so I have enough wood for a f20 and would now like to build on for comparison. So, do I need to rip down my ~24" strips to the f20 plan width or will I be fine making it wider? I'll be using the Dayton Hf driver.
post #1421 of 1695
Thread Starter 
Well, you can juggle the widths a bit. There are limits though. The driver loading varies with width, which messes with the response.

I have modeled narrower ones, but I am not sure I modeled wider ones. I could without too much trouble.

Biggest issue is that this plan is for 3/4" thick ply, and you have 1/2".

My experiences with large drivers and thin plywood (even fully braced) have taught me not to go there, so for me, drivers larger than 12" get 3/4" thick ply.
post #1422 of 1695
Could you please look at what a 24" width version of the F20 would look like? Can you show a comparison between a 24" width and the stock width?

I am willing to be the guinea pig as I plan on measuring the response of both horns outside, as well as the same driver in a sealed box. I can always make a 3/4" baffle and make the rest out of the 1/2" that I have if there is a driver mounting issue. I would like to start making dust ASAP.
post #1423 of 1695
looks like it works fine. the low corner moves up by a hz or two, but the spl also goes up by 2-3 db at the low corner. i don't want to post the frequency response because i didn't calculate it exactly. i just guesstimated the cross sectional area numbers by about a 1/3 larger and left the lengths the same. also increased the rear chamber by 1/3. you'll definitely want to brace that sucker up using 1/2" though.
Edited by LTD02 - 12/3/12 at 11:30am
post #1424 of 1695
Thread Starter 
The only 15-loaded tapped horn I designed with 1/2" material literally tore itself apart when run at war volume. It was built like all the others, cut to the same tolerances, and braced properly. It was a PA sub, not a home theater sub, and did not have to cope with nearly 2" peak to peak excursion. Still failed rather spectacularly.

I'll try to run a model for you tonight if I have the time. Files are all on the home PC.

If you're proficient with Hornresp, simply take each of the S-values (1, 2, 3, 4, and 5), divide them by 18.5 and multiply by 24 or whatever your baffle width is. Then - do the same for Vrc. That will get you in the ballpark

This approach to the model won't reflect the increase in area due to the thinner internal parts. Full bracing may offset some of that increase though.
post #1425 of 1695
Did you get a chance to compare the two widths lilmike? I am not proficient with Hornresp yet and figured you would give me a better comparison than I could get myself. If not no worries.

Is it possible a narrower width would give a flatter overall response? I am still trying to get my head around how these things work and am not sure I understand it well yet. For example, LTD, how would having a wider horn move the low corner up a few Hz? Could you please explain how the width of the horn drives the response?

Sorry for all of the questions. Thanks for the patience.
post #1426 of 1695
"For example, LTD, how would having a wider horn move the low corner up a few Hz? Could you please explain how the width of the horn drives the response?"

because you are moving more cross-sectional area of air relative to the length of the horn. that's nothing unique to an f20, that is the nature of horns.
post #1427 of 1695
Thread Starter 
Not yet.

Been busy trying to get my Jeep back on the road, sorry. Will try to run things ASAP.

Edit:

Took a peek. Looks like it will work, sort of. I am not a fan of the acoustic loading at 23.5" (stock THT width). I guess - the easiest way for me to put it is that I personally would not waste the time and plywood. LTD's comments were spot on.



Dark trace is the 23.5" width.

Honestly - you have the wrong thickness of ply for the F-20, but it is the proper thickness for the THT. The wood you have is already cut to an appropriate width for the THT. If it were me, I'd just build a second THT. The differences between the F-20 and THT are not that significant, and what you'd be building would not really be an F-20 anyhow, so it would not be a valid comparison at all, and your efforts would largely be wasted.
Edited by lilmike - 12/5/12 at 1:30pm
post #1428 of 1695
Do what mike says, build a second THT. I have two, and cancelling room modes is a nice thing, and you instantly get 6dB of headroom below the lowest modal frequency.

JSS
post #1429 of 1695
Thanks for looking into it for me, good luck with the jeep. After looking at the response comparison can someone tell me why i wouldn't want the darker trace? It looks like there is more output everywhere i would want it. Sorry if I am missing something, I just want to know why the grey trace would be better than the black one.

I get that i have the wrong wood for the F20, but if i kept the stock width and use what i have with braces, will that really effect the responce? I have beat on my THT for long periods of time like no other and the cabinet is rock solid. For example with the 30hz high pass turned on on a ep4000, the THT will take almost everything one channel of the ep can give. With the filter off it will still take quite a bit of power before it will complain. Because of this i am confident that a properly braced cab with 1/2" material will live a long happy life.

Also, would corner reflectors in a F20 be of any value?
post #1430 of 1695
"i am confident that a properly braced cab with 1/2" material will live a long happy life."

that is the question. the lilmike f20 is a design. changing it up means changing it up, which means another design. the next question that you are going to ask is how to properly brace an f20 for use with 1/2" wood. that's just not a quick and simple answer, hence the recommendation to just double down on what you have.
post #1431 of 1695
Thread Starter 
Quote:
Originally Posted by boostick4 View Post

Thanks for looking into it for me, good luck with the jeep.

Thanks. Looks like the hard work is done. I am driving it again for the first time in a month plus.
Quote:
Originally Posted by boostick4 View Post

After looking at the response comparison can someone tell me why i wouldn't want the darker trace? It looks like there is more output everywhere i would want it. Sorry if I am missing something, I just want to know why the grey trace would be better than the black one.

There is a LOT more to a horn design than the frequency response. I am not happy with the acoustic loading of the F-20 at 23.5" internally.
Quote:
Originally Posted by boostick4 View Post

Because of this i am confident that a properly braced cab with 1/2" material will live a long happy life.

My direct experience says otherwise.
Quote:
Originally Posted by boostick4 View Post

Also, would corner reflectors in a F20 be of any value?

No.

Best of luck with whatever you choose to build. If it is not an F-20 as I presented in the plans I prepared, please don't call it one.
post #1432 of 1695
Quote:
Originally Posted by LTD02 View Post

that's just not a quick and simple answer, hence the recommendation to just double down on what you have.

This. Just build a second THT.

No point trying to re-invent the wheel unless you're willing to put the time in and learn how to use Hornresp.

I personally haven't bothered with 1/2" ply on any of my horn builds. There are reasons for that. I did use some 5/8" stuff on the first one, but only as bracing.
post #1433 of 1695
I've built several of BFM's designs and feel that the 1/2" wood is plenty strong when properly braced. Even the baffle where the driver mounts in his designs are reinforced although I could see the concern with mounting heavy drivers to 1/2" wood. Having said that I've mounted pretty beefy drivers such as the Alpine SWR-1243's and Definimax 4012's to them before with no issues even after war volume and in use for years.
A properly reinforced box with 1/2" will be stronger than an unreinforced box using 3/4" wood. There is no denying that.
post #1434 of 1695
Thread Starter 
To be fair - the design I am referring to that failed was mine, no one else's. I'm not bashing the THT or any of Mr. Fitzmaurice's designs at all, and recommended that the poster build one rather than the F-20 because he had the proper material for the THT.

Mr. Fitzmaurice's designs are his to worry about, not mine. He specifies 1/2" material for his own reasons, and lots of people have great results with them.

I'm not second-guessing that. I just shared that I have seen fully braced cabinets constructed with 1/2" material fail when loaded with a modest 15. In my design's case, the failure resulted from the baffle separating from the side of the cabinet. Fully bracing the internal structure to itself was not effective in preventing this. Bracing the sides (as the mouth of the THT is, at least in the plans I bought a LONG time ago) may have been helpful, but might not have prevented the failure, and would have precluded installing the driver.

Keep in mind, this happened with a relatively modest driver, with an xmax of 5 mm, that has a relatively low mms (at least as far as a 15"), that was loaded in a cabinet tuned in the mid 30s. The forces at work with larger-throw drivers that have higher mms values increase a LOT. I will not design a cabinet for a 12 or 15 that is made of 1/2" material, which is consistent with the vast majority of commercial horn and tapped horn subwoofer cabinets out there. I have no problem constructing smaller cabinets out of lighter material for use with a smaller driver, I just don't like the idea of using lighter material with a heavier driver, even when fully braced.

All I am trying to do is share my experiences, and the rationale behind the choices I made when I came up with this design and recommendations I make. Though feelings should not be ignored, at least in my book, "experience" trumps "feeling" any day, which is why I felt obligated to share mine. I've also "disassembled" quite a few unbraced and fully braced cabinets, the braced ones were not that much more difficult to flatten for hauling to the recycler, though to be honest - neither style was easy to flatten.

Experiences have also taught me (subsequent to this design) that proper and complete bracing is simply not optional in a sub horn. These cabinets simply can not be built rigidly enough without it, even if I used steel plate.

We all live and learn I guess.

Not trying to ruffle feathers or anything, just sharing what I have learned through some "educational" experiences I've had along the way.

Would I design/build the F-20 or T-6 with bracing today? Yes.
post #1435 of 1695
I remember thinking the proto F20 could use some bracing when I saw it......it was fun putting that one through its paces. Wow, was that almost 2 years ago?

JSS
post #1436 of 1695
Everyone please take a step back smile.gif I am just looking for good feedback on the questions I am asking so I can try to better understand the process of horn design, and why certain things are done the way they are done. I am not saying anything is better than anything else. If I should start my own thread please tell me to do so. I just had a few questions that I thought fit here, but if not then I will start a new thread.
Quote:
Best of luck with whatever you choose to build. If it is not an F-20 as I presented in the plans I prepared, please don't call it one.
No worries, I won't. I am simply asking questions to try to further understand horns and how they should be built. My current real world frame of reference is the one THT I built so that is really my only real horn experience. I used to have 4 sealed 15" subs and like the sealed array sound down low. But, now that I have heard a horn sub there is definitely something I like about that too. In the end I will most likely have 4 THT / F20 type horns from 65 to 25Hz, then 8 sealed 18s from 25 on down. I am in the process of finding what I like, and in my mind, I can only do that through testing. Both analytically and just what sounds good at the end of the day.
Quote:
Do what mike says, build a second THT. I have two, and cancelling room modes is a nice thing, and you instantly get 6dB of headroom below the lowest modal frequency.

JSS
If I wanted to simply get more headroom I would have built a second one a long time ago. I am wanting to see what else is out there and find what best will suit my needs and my needs only. I am more of a build it and test kind of guy. I know I am lacking on the simulation side and just thought I could knock out another horn to test and compare to with what I have. No matter what simulation and calculations go on, in the end you still have to test the real world results. Since lilmike has a lot more experience in the simulation and building, that’s why I asked the questions I did. I am just trying to learn, that’s all.
Quote:
There is a LOT more to a horn design than the frequency response. I am not happy with the acoustic loading of the F-20 at 23.5" internally.
I completely agree there is more to it than the frequency response. Could you please tell me what else I should be looking at? Could you please tell me why you do not like the acoustic loading in the wider horn? What specifically is good / bad? If this is better in a PM then please do.
Quote:
Wow, was that almost 2 years ago?
Quote:
All I am trying to do is share my experiences, and the rationale behind the choices I made when I came up with this design and recommendations I make. Though feelings should not be ignored, at least in my book, "experience" trumps "feeling" any day, which is why I felt obligated to share mine.
I, and I know I am not alone on this, SINCERELY appreciate your contribution to the DIY community! People like you are what make this hobby so much fun to me, and provide such a great learning experience. I am trying to chip away at learning hornresp when I can. Free time is pretty lean right now however.

Again, I really appreciate all of the feedback, please keep it coming.

Are there any plans for a front loaded horn larger / lower than the F20?


JSS
Time really flies huh!
post #1437 of 1695
I just thought I would share an upodate of our winery's dinner theater, which incorporates the use of four F20s. For a visual reference, my 8 year old son has posed with the picture...flanked by a 12' Christmas tree. Can you spot the F20s? :-) I am going to purchase the projector tomorrow, and look forward to finally calibrating the whole sound system!

post #1438 of 1695
Very nice dutch, where abouts In Iowa are you located I would like to hear that system. What are you using for your L/C/R, I was thinking that room would be perfect for some Klipsch Jubilees, or Jubscala.
post #1439 of 1695
Quote:
Originally Posted by duder1982 View Post

Very nice dutch, where abouts In Iowa are you located I would like to hear that system. What are you using for your L/C/R, I was thinking that room would be perfect for some Klipsch Jubilees, or Jubscala.

Sully, IA...about 30 minutes East of the Des Moines Metro. For the LCRs I built Wayne Parham's 4pis with all the upgrades. I also built his 1pi for the 12 surrounds in this 7.2 system. :-)
post #1440 of 1695
lilmike, have you ever played with making one or more sections of the horn moveable/tunable? I'm sure you can do this "virtually" with software but still it would be fun to do it the old-school way. Like with the F20 you could move #8 in and out of the box. Could make that section wider than 18.5" and miter it in, them just need some type of oring or seal on the end of the cabinet.
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