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DIY bass horn build...Up next - Page 12

post #331 of 448
Not sure if that would work out too well. All the harmonics, albeit lower than usual on the LMS-U, will still be amplified by the horn loading up high. Can't really have it both ways, as much as I'd like it to work like that.
post #332 of 448
GOD ALMIGHTY!

i bet you one of those alone would literally rattle my small little family room apart....

Granted that isnt entirely bad as I do not like the built in entertainment center that was there when we bought it and my wife wont let me rip it out...so maybe I will let the "sonic forces" do the work for me....
post #333 of 448
I wonder if that Vas on the RCF LF21N451 would make it unsuitable for this horn?
http://www.parts-express.com/pe/show...number=294-895.
post #334 of 448
Quote:
Originally Posted by Scott Simonian View Post

Not sure if that would work out too well. All the harmonics, albeit lower than usual on the LMS-U, will still be amplified by the horn loading up high. Can't really have it both ways, as much as I'd like it to work like that.

I have seen a couple of builds recently that showed either ported Front loaded horns or EQing the sealed front loaded horn for a lower response.
post #335 of 448
Quote:
Originally Posted by Looneybomber View Post

I wonder if that Vas on the RCF LF21N451 would make it unsuitable for this horn?
http://www.parts-express.com/pe/show...number=294-895.

Interesting XMax and Xmech

"13.2 mm Xmax, 58 mm peak-to-peak Xmech"


Does that mean people can push them past Xmax without destroying them?
post #336 of 448
Thread Starter 
Quote:
Originally Posted by penngray View Post

Interesting XMax and Xmech

"13.2 mm Xmax, 58 mm peak-to-peak Xmech"


Does that mean people can push them past Xmax without destroying them?

Sure. The 21sw152 is 15mm xmax but rated at 30mm xmech. It doesn't start sounding bad until about 18-20mm. It would be very hard to bottom that driver. It just quits going any further at about 20mm. The rcf is probably similar.
post #337 of 448
Thanks Ricci, That is impressive to me.
post #338 of 448
RE: the throat distortion....

What SPL you calculating that at? Is it the same for both plots?

One thing to keep in mind is that it's calculated assuming the wavefront is travelling down the horn. You're side firing so there will be some diffraction as the sound bends direction. In that small of a space, I think you're also going to see pressure modulation as the cone moves back and forth. The bandwidth is small so I'm not sure where the IMD's would end up relative to a vented cabinet. Going to a more square throat would be a possible improvement for both.

But like you say, it's all about design tradeoffs. I'll be looking forward to tbe results.
post #339 of 448
Thread Starter 
Quote:
Originally Posted by MBentz View Post

RE: the throat distortion....

What SPL you calculating that at? Is it the same for both plots?

One thing to keep in mind is that it's calculated assuming the wavefront is travelling down the horn. You're side firing so there will be some diffraction as the sound bends direction. In that small of a space, I think you're also going to see pressure modulation as the cone moves back and forth. The bandwidth is small so I'm not sure where the IMD's would end up relative to a vented cabinet. Going to a more square throat would be a possible improvement for both.

But like you say, it's all about design tradeoffs. I'll be looking forward to tbe results.

Mike. Like I said throat distortion calculation isn't my forte. The first graph was due to a mathematical error in my excel calculator I made. It is simple. You export the acoustic power graph from Akabak at whatever drive level you wish to use as text and then open it in excel or open office and paste the data in. Then plug in the throat area and it calculates the distortion for every frequency exported from Akabak automatically. Then put that data back into text format and import into REW or similar to generate a graph. The second is what I believe to be correct. I will remove the first. Tom said that he doesn't consider this much of an issue for bass horns covering a relatively small bandwidth and Id take him at his word on that. The calculation seems to bear it out. This has about a 3.8 to 1 compression ratio and the throat air distortion seems to be well less than 1%. The graphs are labeled as 130v input. That corresponds to about 4500w into the minimum impedance and puts the driver a few mm away from xmech at peak excursion in the passband. The Spl level is everything she's got on short term peaks basically. I thought I explained most of this in the first post? The data for simulating it in HR or Akabak is on the last page. You could use it to check me on this if you want.

I have no guarantee that these will hold together at war volumes. That is a lot of stroke and force in the cabinet. Perhaps the driver will grenade or fold the cone up that is what a lot of people more versed in horns seem to believe. I won't know until I have tested it. Kyle seems to think that the cones will handle it . Tom does not think that amount of compression is too much or even out of the ordinary for a bass horn from comments he has made. After all this isn't some thin, paper coned pro driver, like a 2242h or something. I've got faith that the IMD wont be too bad and the drivers will hold up. If they don't blow during outdoor testing then they will be fine.
post #340 of 448
Quote:
Originally Posted by penngray View Post

I have seen a couple of builds recently that showed either ported Front loaded horns or EQing the sealed front loaded horn for a lower response.

Oh yeah? I'd like to see that if you happen to remember where you saw that but I remember some discussion about a similar (identical?) topic and the idea was shot down. At least, that's what I remember.

Also, I don't think it would really work with Ricci's horn. Looks like a tapped horn so... gotta highpass. Would definitely need to be a FLH such as the THT or Lilmike's F-20. You know that though.


Ricci - are you going to test the new horn with your older 5400 with the titanium cone or the newer LMS-U with an aluminum cone?
post #341 of 448
Thread Starter 
Quote:
Originally Posted by notnyt View Post

very impressive. you have 1w1m model with 5400?

Here is a 1w (1.97v) 2.0pi 1meter graph comparing the horn to a 120L sealed and a 250L vented/PR alignment.





Here is the same comparison with the power input actually limited to 1w. Actual 1W efficiency. This gives some indication of how heavy of a load each will be to an amplifier.








This shows the excursion of a 120L sealed enclosure versus the horn at the same voltage drive level.

post #342 of 448
Quote:
Originally Posted by Ricci View Post

I thought I explained most of this in the first post? The data for simulating it in HR or Akabak is on the last page. You could use it to check me on this if you want.

Ya, I was just confused why you left both plots up (like maybe they were at different SPL's or something). 0.4% seems a bit on the low side, but isn't that crazy considering the bandwidth you're operating over. I'll wager you end up closer to 2%, but that's just a gut feel.

Btw, I agree that a 4:1 compression ratio isn't that crazy.

One thing that I think would be interesting would be to compare the predicted maxSPL for your vented cabinet versus the tapped horn. I know one of the things that always comes up is the supposed 10dB boost that a tapped horn should give relative to a vented enclosure, but if you look at your 2V input plots, the low frequency corners aren't the same for the TH and the vent....and if you moved the vent (and changed the driver), you should be able to slide up that LF knee to match output at 20Hz....and then you'll also be a lot more similar on the true efficiency plot. The area I'm not confident in is how to change the driver for a tapped horn to maximize its performance.

Do you have a good feel for your way around in Akabak? I haven't been able to figure out how to get reliable results in the program, or even how to model things that break standard paradigms (which it seems capable of doing). I always have to do my calculations by hand...
post #343 of 448
Thread Starter 
I have enough of a grasp of Akabak to do some things, but it is still daunting in other aspects. I can whip up most of your basic enclosure types with no problem. I wouldn't say I have grasped it totally yet. It really is all about understanding the scripting and how that operates. There are other deeper aspects of the program that I have not attempted to learn yet. Like anything else the best way to learn is to use it. HR will export basic scripts for Akabak. That is how I started because it is easy to understand what is going on with those exported scripts and the flow of the text formatting. Then that can be used as a jumping off point to get into more complicated simulations. I think of what some of Tom's scripts for the biggest synergy horns must look like...

You mention the efficiency difference between the TH and vented alignment. A couple of things that I have noticed are that a TH has the final minimum excursion notch quite a bit below the knee usually such that if you match up the apparent acoustic knee of a vented sub and a TH the TH which actually be able to extend with real output quite a bit lower. For example this horn looks for all the world like a 20hz cut off from looking at the response shape but the minimum excursion notch is at 17hz and full program power input is available till below 15hz without risk of damage . This is not what you would expect from looking at the response shape. If you match the roll off and knee with the vented sub it will end up tuned more to 20-22hz and will not have the same real world extension and headroom below 20hz even though just looking at the response shape would make you believe that it would. That is why I match up the actual minimum excursion notches to compare the 2 so that they have comparable power handling and extension. I am building a set of test cabs to try drivers in and the large PR enclosure is what is represented in the simulation. I will be testing that too in addition to this horn and also the sealed cab as well.

You probably can get 10db of extra voltage sensitivity out of a TH over the vented cab, but not in this particular case with the cabinet size I limited myself to. That's the great thing about horns is that you can easily get more output and efficiency by just making the cabinet larger and it affects the entire range for the most part. A vented cab will only increase around the vent tune and a sealed or IB will not gain much at all. The cabinet size here limits the amount of gain to roughly 6db over most of the intended range.
post #344 of 448
Thread Starter 
Quote:
Originally Posted by Scott Simonian View Post

Ricci - are you going to test the new horn with your older 5400 with the titanium cone or the newer LMS-U with an aluminum cone?

Sold the old 5400 to Penn actually last year. Bought 2 of the current model in February. Those are what I will be testing with.
post #345 of 448
Aaahhhh. Okay, very good. Just curious cuz you mentioned the possibility of a cone failure. Oh! I sure hope that doesn't happen to you.
post #346 of 448
Quote:
Originally Posted by Ricci View Post

The cabinet size here limits the amount of gain to roughly 6db over most of the intended range.

Isn't the 6dB coming from the 4:1 compression ratio?
post #347 of 448
Thread Starter 
Quote:
Originally Posted by MBentz View Post

Isn't the 6dB coming from the 4:1 compression ratio?


If you take a horn and chop all of it off except for the throat area how much gain will you be seeing? If you take a horn and increase the compression ratio in the throat from 4:1 to 2:1 how much average efficiency across the intended range of bandwidth will you pick up? Now you take the same horn as before but leave the compression ratio and throat as is but increase the horn volume by 500% while maintaining the same knee. Will this provide some extra efficiency? The throat has a large effect but the acoustic efficiency gain comes from expansion in the horn volume itself.
post #348 of 448
I see you forged ahead with the build. Looks like a new AkAbak script as well.

I am very interested in how this one turns out after testing. If the bends don't treat it to badly it opens up a few more possibilities for other horns in my mind.

Is that the only sub coming out of the shop? I've been away awhile, and might have missed it.
post #349 of 448
"If the bends don't treat it to badly"

i was kind of wondering about that too.

"Bought 2 of the current model in February. Those are what I will be testing with."

so this horn is for the lms driver not the b&c?

i look forward to hearing what you think about this one vs. your ported b&c cabs. i know the latter are tuned a little higher, but both are very roughly in the same price/size category, so it'll be interesting to hear your opinion.

as you also have dts10 experience, i see that you chose to more or less split the tuning difference between that one and the th50.
post #350 of 448
Thread Starter 
Quote:
Originally Posted by soho54 View Post

I see you forged ahead with the build. Looks like a new AkAbak script as well.

I am very interested in how this one turns out after testing. If the bends don't treat it to badly it opens up a few more possibilities for other horns in my mind.

Is that the only sub coming out of the shop? I've been away awhile, and might have missed it.

Ho there stranger! Haven't seen you around lately.

Yes I too am concerned about the center section of the horn. We will see won't we?

You didn't miss the "other" horn. It is next in the pipeline.
post #351 of 448
Thread Starter 
Quote:
Originally Posted by LTD02 View Post

"If the bends don't treat it to badly"

i was kind of wondering about that too.

"Bought 2 of the current model in February. Those are what I will be testing with."

so this horn is for the lms driver not the b&c?

i look forward to hearing what you think about this one vs. your ported b&c cabs. i know the latter are tuned a little higher, but both are very roughly in the same price/size category, so it'll be interesting to hear your opinion.

as you also have dts10 experience, i see that you chose to more or less split the tuning difference between that one and the th50.

This cab actually seems to work ok for a few different drivers. It was designed on the LMS from the get go though. Being that this one is used down below 20hz I went for sheer displacement. The ported B&C's are a little bit of an apple to this orange though. I have other plans for the B&C's. I hope to sell those ported cabs eventually, empty that is.
post #352 of 448
Quote:
Originally Posted by Ricci View Post

If you take a horn and chop all of it off except for the throat area how much gain will you be seeing? If you take a horn and increase the compression ratio in the throat from 4:1 to 2:1 how much average efficiency across the intended range of bandwidth will you pick up? Now you take the same horn as before but leave the compression ratio and throat as is but increase the horn volume by 500% while maintaining the same knee. Will this provide some extra efficiency? The throat has a large effect but the acoustic efficiency gain comes from expansion in the horn volume itself.

How about looking at it from the other perspective....let's say the horn is designed to not be undersized - I was under the impression that the gains would be a combination of the compression ratio and whatever DI you get.

The horn itself should be providing the acoustic impedance match. As the horn is made smaller, the impedance match gets worse and starts to introduce ripple (if you keep the flare rate constant), and/or reduction in output (raising the flare).
post #353 of 448
Quote:
Originally Posted by Ricci View Post

Ho there stranger! Haven't seen you around lately.

Yes I too am concerned about the center section of the horn. We will see won't we?

You didn't miss the "other" horn. It is next in the pipeline.

Yeah, I've been pulled in other directions the last few months.

I know we have talked about it in emails, but for everyone else I'm not really worried about how it will work at "normal" levels. 105db-120dB peaks a couple of meters back in a median room. It is at war levels that I am interested in seeing how it works out. In high voltage PA applications, or the way some of the people around here abuse these things.

Glad to know I didn't miss anything else.
post #354 of 448
Thread Starter 
These cabs should be in tomorrow.

I will be getting a quote on the Otherhorn soon. Im just going to call it that. That one is for the 21sw152 and it is in a 24x36x36 cab. Its a TH and the cut off is 25hz. The response knee is at about 30hz. It is more of a typical pro sound type deal with about 10hz extra extension.

Mike,
Yes the horn provides the impedance matching with the air. That is where the lion's share of the potential efficiency gains come from. The throat is very important as well obviously. If your throat configuration is jacked up the horn is no better than scrap, but once you get the throat close to the range where it seems to bring the total response together all of the further tweaking in the world is not going to drag an extra 4db broad band sensitivity out of it. This cab or any other. I spent a LOT of time designing this thing. The horn is simply to small to to realize a 10db broad gain over the vented alignment I used for comparison. 6db average is what I could get. If you give me a cab 400% bigger than the vented then it is possible. In a cab of the same size as the vented I don't think you would get much more than 3db extra. Twice the cab seems to give maybe 6 db. Maybe its possible but I definitely don't see a 10db gain unless looking at specific frequencies in isolation. Certainly not at the vented enclosure tuning. If anybody has a simulation that pulls that off I would love to see it. I am by no means an expert on this stuff.
post #355 of 448
i suspected that you had an 'otherhorn' brewing somewhere in the background. you had a flurry of designs and then all went quiet. ;-) it is kind of funny, but you will be well positioned to have your own shootouts!

btw, and just out of curiousity, what does 'gjallerhorn' mean? any relation to this: http://www.youtube.com/watch?v=vllx1fAIaVc or this http://www.youtube.com/watch?v=EYwzy...eature=related (neither of which aren't too bad btw).
post #356 of 448
Thread Starter 
It is from Norse mythology. The horn that is associated with the deity Heimdallr and Ragnarock. The horn that awakens the gods or does some other craziness depending on the translation.
post #357 of 448
nice...
post #358 of 448
just to hit an earlier point, the rcf 21lfn451 has a compliance that is about twice the b&c, so it is a little bit of a different animal.
post #359 of 448
Thread Starter 
Just a small update. The cabs have been coated with duratex. 3 gallons for the 2 cabs. Hopefully I can get a driver loaded and get some preliminary measurements in the next couple of days. A close mic FR check should tell me a lot about how close these will be to the goal.





post #360 of 448
Quote:
Originally Posted by LTD02 View Post

just to hit an earlier point, the rcf 21lfn451 has a compliance that is about twice the b&c, so it is a little bit of a different animal.

I didn't see that. The biggest TSP difference I noticed was the Vas.
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