Scottmoose said:
You know, when I wrote that I knew I was using the wrong term. I didn't mean the expansion as much as I was talking of the tuning of the cabinet. The Imperial looks to be tuned around 25 Hz (does this sound correct?) And the AN12 has an FS of 36 Hz. Now, I may be very wrong but that would be akin (since we are talking about 1/16 scaling here) to sticking an FE126 in a 1/32 scale horn tuned at 40 Hz. Not particularly ideal. You will have dips in the 90-200 hz range that are pretty severe and the xmax for the lower notes will exceed spec. Does this sound right Scott? Sorry for the wrong terminology here.
Tom
Re: RE: The imperial with AN 12"
In what way would you want to scale the Model II? I will be happy to try if you give more information on what you have in mind. Thanks!
Tom
gurley123 said:Oh, I was just having dirty little thoughts of the Imp. with the AN 12" and a pro 18"To read Steve D's write up of them, you'd think anything would work in that guy. I have a soft spot for really big speakers(but no space to put them
)
Back on topic, Tom you have to stop putting these great cabs out where I can see them.
I do wonder how far does this approach scale down? Could a simplified model II be done? I've seen someone scale down the imperial for two 6.5" Fostexs.
Uh-Oh, used up my smiley quota on this one.
In what way would you want to scale the Model II? I will be happy to try if you give more information on what you have in mind. Thanks!
Tom
No worries Tom -I suspect that'd probably be what you meant, but I figured it'd be best to clarify.
Hmm. Be very careful with this scaling business guys. As a rule, you can't simply scale a horn cabinet design; it's a case of needing to do a whole new one from scratch. That said, when parallel walls are present (as they are in most BLHs) then volume / pathlength tends to dominate over perfection of flare constant, so YMMV.
The Imperial was indeed tuned to ~25Hz or so; but there were about 4 different versions so the exact tuning will depend on which you're going with. Good box; bit of a compromise, like all BLHs though -for LF duties I prefer 'proper' horns (i.e. front-loaded) though at least the Imperial had / has size on its size, so it's making the most of what it has. I'm not sure I'm following your scaling references though Tom (1/16th, 1/32) that you mention WRT driver Fs & tuning frequency etc? What am I comparing it to? Probably just me being dense -I'm tired tonight.
Within reason, Fs isn't that much of an issue to a fully sized horn. More so for a compromised one, though IMO the real trick with the latter is blending the different actions & attenuating midrange leakage without damaging anything else. The nulls in the FR caused by output from driver & terminus combing (& a couple of other reasons) will depend very much on the specific design as to exactly where & how severely they will occur. You can push excursion down compared to its IB performance with a BLH, though you need a front-horn with a sealed rear chamber (i.e. a compression chamber) to fully control it.
Hmm. Be very careful with this scaling business guys. As a rule, you can't simply scale a horn cabinet design; it's a case of needing to do a whole new one from scratch. That said, when parallel walls are present (as they are in most BLHs) then volume / pathlength tends to dominate over perfection of flare constant, so YMMV.
The Imperial was indeed tuned to ~25Hz or so; but there were about 4 different versions so the exact tuning will depend on which you're going with. Good box; bit of a compromise, like all BLHs though -for LF duties I prefer 'proper' horns (i.e. front-loaded) though at least the Imperial had / has size on its size, so it's making the most of what it has. I'm not sure I'm following your scaling references though Tom (1/16th, 1/32) that you mention WRT driver Fs & tuning frequency etc? What am I comparing it to? Probably just me being dense -I'm tired tonight.
Within reason, Fs isn't that much of an issue to a fully sized horn. More so for a compromised one, though IMO the real trick with the latter is blending the different actions & attenuating midrange leakage without damaging anything else. The nulls in the FR caused by output from driver & terminus combing (& a couple of other reasons) will depend very much on the specific design as to exactly where & how severely they will occur. You can push excursion down compared to its IB performance with a BLH, though you need a front-horn with a sealed rear chamber (i.e. a compression chamber) to fully control it.
I am not sure what Gurley meant by scaling but I know for sure that just scaling a horn is not even remotely an option. Quite a few other things need to be taken in to account such as (the obvious) rear chamber (which is not that hard to deal with) but the tuning of the horn will be altered drastically by scaling. As I have learned in my experiments with horn design, scaling has to be done very carefully. Exponential scaling is really the only way to accurately scale and be sure of where you are going. This leads me to what I was referring to with the 1/32 and 1/16 references. That and throat size will drastically effect a horn's performance.
1/32 and 1/16 clarification. The Imperial's mouth is approximately 1/16 the size of the ideal horn tuned at 25 Hz. And you know, I think I am wrong about that number. Let me go do some numbers.
Ok, I figured it out. A 25 Hz non-scaled horn's mouth is 14.89 Square meters. Now, lets say we are looking at the Imperial's "built in" plan. The mouth size is approximately .7567 sq meters. With that known, I surmised that the scaling on the horn is around 1/16 scale of a full size horn at 25 Hz. In actuality the scale is not that close to 1/16 but is 1/19.7 or whatever that equals in true fraction. Knowing (these days) that a horn needs to be scaled exponentially, this scale will give inferior performance as opposed to a horn that is scaled with exponentials in mind (1/2, 1/4, 1/8. 1/16. 1/32 etc.) So, I don't know where I am going with this but it makes be think of the Frugal Horn and simulations. The reason the Frugal horn was difficult to simulate was that none of the simulation programs on the market are capable of simming 1/64 or 1/128 horns (which I believe the Frugal was).
Ok, all that said, I hope I explained the idea of what I meant. I think I ran on and said more than was needed.
To respond to the next paragraph of what you said Scott. I am only going with what I have experienced with designing and building. In my experience in 1/16 and 1/32 scaled horns (which is what I am going with in most cases on my designs) will show distinctive peaks in the 80 to 200 Hz regions that I have to deal with through mouth sizing and for that matter horn diameter adjustments.
Oh, and the rest of the paragraph you wrote is just good information and I thank you for it!
Ugh, I have just run out of steam. Class today was incredibly tiring and I am now out of steam. My students, though wonderful minds are also quite taxing. I hope all is well for you and I will respond later to your reply.
Tom
1/32 and 1/16 clarification. The Imperial's mouth is approximately 1/16 the size of the ideal horn tuned at 25 Hz. And you know, I think I am wrong about that number. Let me go do some numbers.
Ok, I figured it out. A 25 Hz non-scaled horn's mouth is 14.89 Square meters. Now, lets say we are looking at the Imperial's "built in" plan. The mouth size is approximately .7567 sq meters. With that known, I surmised that the scaling on the horn is around 1/16 scale of a full size horn at 25 Hz. In actuality the scale is not that close to 1/16 but is 1/19.7 or whatever that equals in true fraction. Knowing (these days) that a horn needs to be scaled exponentially, this scale will give inferior performance as opposed to a horn that is scaled with exponentials in mind (1/2, 1/4, 1/8. 1/16. 1/32 etc.) So, I don't know where I am going with this but it makes be think of the Frugal Horn and simulations. The reason the Frugal horn was difficult to simulate was that none of the simulation programs on the market are capable of simming 1/64 or 1/128 horns (which I believe the Frugal was).
Ok, all that said, I hope I explained the idea of what I meant. I think I ran on and said more than was needed.
To respond to the next paragraph of what you said Scott. I am only going with what I have experienced with designing and building. In my experience in 1/16 and 1/32 scaled horns (which is what I am going with in most cases on my designs) will show distinctive peaks in the 80 to 200 Hz regions that I have to deal with through mouth sizing and for that matter horn diameter adjustments.
Oh, and the rest of the paragraph you wrote is just good information and I thank you for it!
Ugh, I have just run out of steam. Class today was incredibly tiring and I am now out of steam. My students, though wonderful minds are also quite taxing. I hope all is well for you and I will respond later to your reply.
Tom
Now it's my turn to use the wrong terminology. My reference to "scaling" was to the percieved concept of Tom's "EZ" style quasi-horns. I was really taken with the simplicity of the design. I was wondering if it could be appied to a smaller design like for the model II or for any smaller 4" drivers. Maybe get down to 60hz or so. Mostly I'm just thinking out loud and typing faster than I think.
Strangely, the more dumb questions I ask, the more I learn. Thanks Guys.
Kris.
Strangely, the more dumb questions I ask, the more I learn. Thanks Guys.
Kris.
Ah, I have you. Interesting take.
Hmm. Actually, if you want a horn tuned to 25Hz in practice, then you need a horn with a flare constant of roughly 17.75Hz (cut off being roughly 1.4 times flare frequency). So about 23.5m^2 is required with a minimum length of ~9.7m (why am I using metric? I hate metric.) dependant on the type of horn contour. For myself, I don't really think in those terms at all when designing, but whatever works for you. Keep in mind though that it can end up being a bit misleading because you have to take the type of horn & the room into consideration, along with other factors.
For example, the difficulty in modelling the frugel-horn has nothing to do with x 'scale' horns -you use MathCAD yourself, so you know it couldn't care tuppence about the scale; it simply models what you put into it. The problem is that nothing out there at present accurately models the in-room response of corner horns. The Frugel-horn itself is not a complete horn; put it into an anechoic chamber & its response wouldn't be up to much, because it uses the room corners to complete the horn's expansion, and this isn't accounted for in a simulation of the box itself. Loaded in that way, the mouth is 8 times larger than that of the cabinet itself. And so on.
Hmm. Actually, if you want a horn tuned to 25Hz in practice, then you need a horn with a flare constant of roughly 17.75Hz (cut off being roughly 1.4 times flare frequency). So about 23.5m^2 is required with a minimum length of ~9.7m (why am I using metric? I hate metric.) dependant on the type of horn contour. For myself, I don't really think in those terms at all when designing, but whatever works for you. Keep in mind though that it can end up being a bit misleading because you have to take the type of horn & the room into consideration, along with other factors.
For example, the difficulty in modelling the frugel-horn has nothing to do with x 'scale' horns -you use MathCAD yourself, so you know it couldn't care tuppence about the scale; it simply models what you put into it. The problem is that nothing out there at present accurately models the in-room response of corner horns. The Frugel-horn itself is not a complete horn; put it into an anechoic chamber & its response wouldn't be up to much, because it uses the room corners to complete the horn's expansion, and this isn't accounted for in a simulation of the box itself. Loaded in that way, the mouth is 8 times larger than that of the cabinet itself. And so on.
Scottmoose said:
That is exactly what I was saying about the FH though. Though it is not a full horn, in theory it sort of is. The flare on it looks as though it is about 50 Hz right? Mix that with a corner and you get a horn that will hit that. If you were to scale the frugal up about 128 times you should have a full size horn that will reasonably cleanly hit 50 Hz in 2pi space. Now, I was generalizing about no sims being able to model corner horns and in theory that is true. However, if one were to measure a corner, and calculate the flare of the 90 degree angles being used as a horn mouth on said horn, one would be able to model it in a rudimentary fashion. This is where accuracy begins to fail, correct? I have a feeling we are saying the same thing but I tend to be long winded and always seem to approach things in a more complex manner than is required. Thanks Scott!
Tom
The FH in 1/8 space, as it's designed to be, will have a mouth of roughly 1276in^2, maintaining horn loading down to ~93Hz. As the corner expands of course this takes horn action lower, though QW behaviour dominates around Fc (BTW -MathCAD's first section assume 2pi, not full radiation space. & yes, you can fudge it by measuring up a corner).
What you're noting is mostly true, but remember if you're going to try to follow some system of scaling that as soon as it is compromised, the horn math starts to become less useful low down. Horn action increasingly will give way to TL behaviour, & it needs to be considered as such -Ron's A126, which is effectively flat to the low 40Hz regions, is probably the best example of blending the two actions.
What you're noting is mostly true, but remember if you're going to try to follow some system of scaling that as soon as it is compromised, the horn math starts to become less useful low down. Horn action increasingly will give way to TL behaviour, & it needs to be considered as such -Ron's A126, which is effectively flat to the low 40Hz regions, is probably the best example of blending the two actions.
Thanks Scott for the information. It is always a struggle to learn all these things and remember to take them in to account when designing.
So, the scaling is not as important as I originally thought? Hmm, well, that could do some interesting things to my designs. I have been sticking tightly within them as I thought it was supremely important. I need to learn more TL math so I can figure out the dos and don'ts of seamless integration. I am getting excellent results with what I am doing now but a lot of the TL stuff is just fudging until it looks right. Any suggestions on TL reading? I think I will go read MJK again. See what new, I can glean from it.
I really want to hear a pair of the a126s. I wish someone lived close to DC that has a set.
Tom
So, the scaling is not as important as I originally thought? Hmm, well, that could do some interesting things to my designs. I have been sticking tightly within them as I thought it was supremely important. I need to learn more TL math so I can figure out the dos and don'ts of seamless integration. I am getting excellent results with what I am doing now but a lot of the TL stuff is just fudging until it looks right. Any suggestions on TL reading? I think I will go read MJK again. See what new, I can glean from it.
I really want to hear a pair of the a126s. I wish someone lived close to DC that has a set.
Tom
It depends on your approach & what you're hoping to achieve with the design really -you might find you still prefer using that as a starting point. Your existing boxes are proof positive.
Martin's site's a great start, but remember that at present it only goes so far, so wider sourcing will help -he limits his own studies to the exponential contour for e.g. (not a favourite of mine) & to that you have to add further things -1 dimensional wave equation, which is fine, but not the whole story; parallel walls & the increasing dominance of volume / pathlength the further you compromise the horn & rely on QW loading. All good fun.
Martin's site's a great start, but remember that at present it only goes so far, so wider sourcing will help -he limits his own studies to the exponential contour for e.g. (not a favourite of mine) & to that you have to add further things -1 dimensional wave equation, which is fine, but not the whole story; parallel walls & the increasing dominance of volume / pathlength the further you compromise the horn & rely on QW loading. All good fun.
Well, I had some time this morning and decided to finish up the plans for the EZ10. They look good and as always, I am excited to see this one get built! Enjoy all. Oh, and I will have a site up soon that will host all of my designs. I will keep everyone posted on that.
S.P.Q.R. EZ10 final plans with cutsheet and all. http://www.box.net/shared/fbnx0ij28k
Tom
S.P.Q.R. EZ10 final plans with cutsheet and all. http://www.box.net/shared/fbnx0ij28k
Tom
If I'm following ya'll, then this 'handing off' (as RonC calls it) from TL to horn loading is simple enough to follow since horns are 1/2 WL resonators with a 1/4 WL fundamental, ergo once the horn is acoustically 1/2 WL long at the highest frequency of its passband (regardless of whether the mouth is large enough) all the BW below it is TL action, ergo as the horn's path-length increases the 'handing off' begins at a lower frequency. While you need to use the wave equation to calc this point accurately, as a general rule-of-thumb for typical compression horns it begins when the horn is a ~1.0 WL long and for conical, ~1/2 WL.
To get an approximation for corner loading, then any horn program that allows you to design it in sections can do it up to the second corner since a trihedral corner expands at a rate equal to a square conical horn with an included angle between opposite walls of 73 degrees up to the closest ceiling point where it slowly transitions towards parabolic to the next closest corner and finally to full parabolic at the last corner where the room gain curve kicks in to mass load it in a big way. Some folks claim Akabak can even do the latter, but I've yet to commit to what will be for me a huge chunk of what little quality time I have left to learn all its capabilities, so as always YMMV.
Note that while theory allows a horn to be foreshortened to 1/8 WL with corner loading, the longer the horn's path-length before it exhausts into the corner the smoother its response due to its rapid expansion.
GM
To get an approximation for corner loading, then any horn program that allows you to design it in sections can do it up to the second corner since a trihedral corner expands at a rate equal to a square conical horn with an included angle between opposite walls of 73 degrees up to the closest ceiling point where it slowly transitions towards parabolic to the next closest corner and finally to full parabolic at the last corner where the room gain curve kicks in to mass load it in a big way. Some folks claim Akabak can even do the latter, but I've yet to commit to what will be for me a huge chunk of what little quality time I have left to learn all its capabilities, so as always YMMV.
Note that while theory allows a horn to be foreshortened to 1/8 WL with corner loading, the longer the horn's path-length before it exhausts into the corner the smoother its response due to its rapid expansion.
GM
maxlorenz said:Hi guys,
What happens past 1000Hz? ...and past 10000Hz?
Regards,
M
In theory, if the horn is designed right, the driver is doing all the work right out the front. The horn in the case of a BLH is only reinforcement for the lower registers from around 15-200 down. Everything above is up to the driver itself.
Tom
GM said:
Good to hear from you Greg! Ok, let me see if I read you right. From what you say, I can accurately trick MJK's sheets into simming a corner since the expansion in a corner is similar to a conical or square expansion? I suspected that it could be done but I didn't think accurately. What you say makes sense though and if that is the case, then that is fantastic news! Akabak? I just went and installed it in the middle of writing this. This looks exciting! Hmm, this will take a while to learn me thinks. Thanks for the fantastic input. I appreciate it.
On another note, all apologies if you and I had harsh words in the past. I subscribe to the water under the bridge theorem so it was what it was.
Tom
SPQR Website
Well, I have set up a blog with all the plans. It is a bit sparse at the moment but it will grow. Enjoy all! And check in regularly, you never know if I will have something there that isn't posted here. http://spqracoustics.wordpress.com/
Tom
Well, I have set up a blog with all the plans. It is a bit sparse at the moment but it will grow. Enjoy all! And check in regularly, you never know if I will have something there that isn't posted here. http://spqracoustics.wordpress.com/
Tom
Alright, I had to do it. I bought a domain for the blog. The address is www.spqracoustics.com Thanks guys!
Tom
Tom
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