Hi Art,
How rigid was the FLH cabinet - if you put a hand on a side wall, could you feel it vibrating?
Panel losses can be significant at low frequencies.
The results of the following investigation by Brian Steele are quite interesting:
The Subwoofer DIY Page v1.1 - Projects : Using Impedance Graphs
Kind regards,
David
Thanks just a guy for those detailed posts. That was some very helpful information. I don't think I am actually as dumb as I appear in some of my posts - it is just that I was getting a bit overwhelmed. This is not over yet - I'll be baaaaaaaaack!
David,
Brian's results show a reduction in the midrange of the passband impedance peak, and an increase in the upper peak with increased bracing.
Floppy sidewalls usually result in more of an upper pass band loss than low frequencies, unless flopping panels are rather huge.
Were his impedance graphs accompanied by any frequency response charts to show the effect of the bracing?
The FLH ended up being a DFLH (ducted front loaded horn):
http://www.diyaudio.com/forums/subwoofers/217929-lab-12-domino-dflh.html
it has small, well braced panels, about the size of DHAA's design.
I have never experienced any cabinets which I could not feel panel vibrations at high drive levels, but this FLH/DFLH has less vibration than most.
This DFLH is unusual in that the duct goes from the horn throat to a latter portion of the horn, still using a sealed compression chamber.
I don't think Hornresp can model that type of enclosure 😉.
Art
In that particular case the Hornresp sim was a four segment sim and the Akabak sim was a ~40 segment sim to see if I could get a more accurate result with more segments (which allows more detail of the bends, etc). So the graphs wouldn't match regardless of whether I showed the Akabak results as Acoustic Pressure or Acoustic Power. But having said that ...
I always use Acoustic Pressure in Akabak. I don't have any instructions for Akabak (other than Soho54's Akabak tutorial) and the Help file is close to useless, so if I don't intuitively understand something in Akabak I usually just don't use it. The Acoustic Pressure dialog box is very straightforward and simple.
On the other hand, the Acoustic Power dialog box doesn't make any sense to me. You have to choose 2 or 4 pi-sr and then enter between 3 and 30 degrees into the two "Steps for integration" boxes. I'm not at all sure what any of that means (although the 2 pi-sr denotes infinite baffle if I'm not mistaken). And then the resulting Acoustic Power graph is ugly, with two lines on one graph, the response and the Directivity Factor Q, which is the difference between the on axis and power response. I can't see any way to remove the Directivity Factor Q from the graph and I really don't need that info.
So the Acoustic Pressure graph works for me. If you would like to discuss, or have a link to some info about the Acoustic Power graph (or general Akabak instructions or manuals) I'd love to learn more. But for now I'm not comfortable with it.
You definitely don't appear dumb, you are picking this stuff up pretty quickly. But I think what you were trying to do (and I think tb46 noticed as well) is choose a box size (17 x 17 x 48) and repeatedly trying to fold your sim into that space. You can't do that, it won't work, you have to let the dimensions of the box be what they need to be so the simulated horn fits inside it. (Unless of course you pick your dimensions first and change the sim to fit the dimensions you've chosen. This is a much easier way to do it but it's a completely different way to approach a fold, it's actually designing and folding at the same time, and it's one of the tricks that allows me to be able to design and fold a horn in about an hour if I want to rush the process.)
One more note about this - I think Akabak actively encourages the use of Acoustic Pressure. In the toolbar there are buttons for the most commonly used features, like excursion, impedance and Acoustic Pressure. But not Acoustic Power.
Hi Art,
Not that I am aware of. It would certainly have been interesting to see, though.
Kind regards,
David
Hi just a guy,
If in doubt just use the default settings given in the Hornresp exported script file.
Differences between Hornresp and AkAbak results can be misleading unless like is compared with like.
You already know my views on specifying ~40 segments in a folded bass horn simulation... 🙂.
|~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|REQUIRED AKABAK SETTINGS:
|File > Preferences > Physical system constants:
|Sound velocity c = 344m/s
|Medium density rho = 1.205kg/m3
|Sum > Acoustic power:
|Frequency range = 10Hz to 20kHz
|Points = 533
|Input voltage = 2.83V rms
|Integration = 2Pi-sr
|Integration steps = 1 degree ... 1 degree
|Integration method = Cross
|~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Kind regards,
David
If in doubt just use the default settings given in the Hornresp exported script file.
Differences between Hornresp and AkAbak results can be misleading unless like is compared with like.
You already know my views on specifying ~40 segments in a folded bass horn simulation... 🙂.
|~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|REQUIRED AKABAK SETTINGS:
|File > Preferences > Physical system constants:
|Sound velocity c = 344m/s
|Medium density rho = 1.205kg/m3
|Sum > Acoustic power:
|Frequency range = 10Hz to 20kHz
|Points = 533
|Input voltage = 2.83V rms
|Integration = 2Pi-sr
|Integration steps = 1 degree ... 1 degree
|Integration method = Cross
|~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Kind regards,
David
Huh. I never really even noticed that, I never paid much attention to any parts of the script behind the "|" character. But it appears you included all the info and instructions on the export file to actually run the sim. I probably should have connected those dots on my own. I still don't know why you chose those settings but at least I know how to duplicate your results now. If I could figure out how to stop it from displaying the Directivity Factor Q then I would be all set.
True, and that's why I usually put this disclaimer on posts where I show sims done with two or more different programs. But sometimes I forget and sometimes I just don't bother.
Yes, I know. But if you look close and compare to the measurement, the ~40 segment Akabak sim was just a bit more accurate in predicting the low frequency knee than the 4 segment Hornresp sim.
Last edited:
Next time 🙂. In any case, the impedance curves suggests a change in impedance at lower frequencies as well (the height of the lowest peak, the shape of the curve between the lowest peak and the lowest minima), suggesting that there were response changes at the lower end of the spectrum as well. That's all happening below the TH's effective passband however, so I'm not sure how much audible impact it would really have had.
Question of the Day - Ideal Driver for a Tapped Horn
Hey, I am still alive - the past two weeks have just been brutal though. First my snowblower got frisky on me and took me down, and then a few days later I had a slip and fall on the ice - so my old bones have taken a beating. Plus, I am actually having to do real work at my place of employment, so my time has been severely limited.
I am trying to get my mojo fired up to start a new design. I want to pick a driver that no one has used before to eliminate the temptation just to paraphrase someone else's work. I am not sure where I got this information form, but in my notebook I have written:
"I think it is very suitable for tapped horns with high BL, high fs, low Qts and fairly long excursion."
That seems to be pretty good advice - would anyone care to add anything else to it. Thanks.
Hey, I am still alive - the past two weeks have just been brutal though. First my snowblower got frisky on me and took me down, and then a few days later I had a slip and fall on the ice - so my old bones have taken a beating. Plus, I am actually having to do real work at my place of employment, so my time has been severely limited.
I am trying to get my mojo fired up to start a new design. I want to pick a driver that no one has used before to eliminate the temptation just to paraphrase someone else's work. I am not sure where I got this information form, but in my notebook I have written:
"I think it is very suitable for tapped horns with high BL, high fs, low Qts and fairly long excursion."
That seems to be pretty good advice - would anyone care to add anything else to it. Thanks.
Don't worry about that, just don't look at anyone else's work until you finish your own.
As both GM and I have pointed out a few times already, pick a driver that works in the bandwidth you want to use it in. Few people bother to do that.
And remember that everything is relative. For example, high fs by itself means nothing, you want high fs relative to your tuning frequency. (About .5 - 1 octave higher than you want your horn tuned.)
Or you could just try this little guy.
HiVi SP10 10" Subwoofer | 297-460
Not many people use it, actually I've never seen anyone use it. It's expensive but it hits way above it's weight class in horns. It's probably going to be most happy with a lower tuning than your previous examples that you've posted here though.
Last edited:
Thanks, Mr. 143. I have never paid attention to that specification before. That would likely have an effect on the compression ratio you could use, or am I thinking about that wrong?
Last edited:
Thanks just a guy, I will keep that in mind.
I will play around with that one if I get some time this evening. Thanks for the suggestion.
Yes, though it also is an indicator of how much distortion the driver will have when close to Xmax.
Lightweight cones are more sensitive, but don't cut it at high drive levels in TH, too much shape shifting 😉.
yessir, and Art is spot on as always.
Its pretty easy to get a "sensitive" design using drivers with low MMD (like the 3015lf and its paper cone etc), however since most tapped horns are excursion hungry in the middle of their passband, these cones tend to "sound distressed" and or turn taco on you
reference (http://www.diyaudio.com/forums/subw...using-18-15-12-inch-speakers.html#post2512872).
Ditto high BL, low Qts. I never cease to be amazed at some of the drivers chosen for an offset driver TH since at least from a Prof. Leach compression horn design POV the driver physically won't fit in the calculated L1 distance, so I use to have to add series resistance to lower BL, raise Qts to make it fit and finally quit bothering to sim them when it became obvious that this detail was being ignored.
GM
Thanks Art, Sine143 and GM for your comments, they were all very helpful. Another layer of confusion has been stripped away.
I went through all my Hornresp files last night (about 60 now) paying close attention to the MMD specification. When I first started playing with Hornresp, I would just take a proven design and substitute a different driver to see what would happen. Well, there were certain drivers that seemed like they should have worked, but had failed. I now can see that the low MMD specification may have been the cause of that problem.
Additionally, I had also tried substituting some auto sound subwoofers into PA type tapped horn cabinets. Although I wasn't real pleased with the flatness of the frequency response, these drivers seem to perform well in all other areas. Now, looking at those drivers MMD specifications, I see they all had fairly high levels.
Art, I went back and read post #1 of you Keystone build, as Mr. 143 had suggested. I have read that many times in the past year, but I think I am finally truly understanding your comments. I really like how you took the time to compare those different drivers and the experimentation you did. I hope to do something similar to that this spring/summer.
GM, you have mentioned Prof. Leach many times, but I am not come across much information on him in my studies. Is there one particularly well written summary of his thoughts you could recommend? Thanks.
I went through all my Hornresp files last night (about 60 now) paying close attention to the MMD specification. When I first started playing with Hornresp, I would just take a proven design and substitute a different driver to see what would happen. Well, there were certain drivers that seemed like they should have worked, but had failed. I now can see that the low MMD specification may have been the cause of that problem.
Additionally, I had also tried substituting some auto sound subwoofers into PA type tapped horn cabinets. Although I wasn't real pleased with the flatness of the frequency response, these drivers seem to perform well in all other areas. Now, looking at those drivers MMD specifications, I see they all had fairly high levels.
Art, I went back and read post #1 of you Keystone build, as Mr. 143 had suggested. I have read that many times in the past year, but I think I am finally truly understanding your comments. I really like how you took the time to compare those different drivers and the experimentation you did. I hope to do something similar to that this spring/summer.
GM, you have mentioned Prof. Leach many times, but I am not come across much information on him in my studies. Is there one particularly well written summary of his thoughts you could recommend? Thanks.
Last edited:
Hi DHAA,
Look here:
http://users.ece.gatech.edu/mleach/papers/HornPaper/HornPaper.pdf
http://users.ece.gatech.edu/mleach/papers/hornmod.pdf
Regards,
Look here:
http://users.ece.gatech.edu/mleach/papers/HornPaper/HornPaper.pdf
http://users.ece.gatech.edu/mleach/papers/hornmod.pdf
Regards,
Last edited:
- Status
- Not open for further replies.