Need midrange cabinet modeling tips, am I on the right track? [message #199569]
Tue, 27 March 2007 13:59
Stephen Kramer Messages: 100 Registered: January 2007 Location: Dayton, OH
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Hello,
I need some compact midrange cabinets for medium outdoor and larger indoor applications. I've found a good deal on the Peavey 1201-8 Lf 12" drivers, and would like to design around them. Here are some links to the Thiele-small parameters.
The spec on the horn flare shows a low range of 150 hz, I'm wondering, with proper cabinet design, if I can achieve a little lower. Trying to concentrate on the 100-1.5k range here.
These cabinets will be mid-bass only, the HF horns will stack on top. My hopes are that 4 of these boxes will give me enough coverage. Currently the 12" horn flares are in this design:
My thinking is to adjust the dimensions of these boxes for proper volume, and have some tuning ports in the area on top of the 12's where the HF horns currently are.
I use MacOSX, and have not yet found a speaker modeling program. Any help on cabinet volume and porting would be appreciated.
Mike {AB} Butler Messages: 2020 Registered: April 2004 Location: Lynchburg, VA
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Elliot Thompson wrote on Sat, 31 March 2007 07:39
If you vent the box (Horn/Reflex combo aka Altec 816/817) you will have no problem getting down to 100 Hertz.
Elliot,
True, but the OP did suggest he wanted to go with Pattern control down to 150:
Quote "Ideally, I would like each driver in an individual 60 degree enclosure with these horn flares".
Stephen,
Antone is correct, for direct radiating horns, you will want a mouth size that is ideally at MINIMUM 1/3 wavelength, so;
1100 / 150 = 7.33 ft; 7.33 * .3333 = 2.44 ft.
As I said, 1/3 wavelength is the MINIMUM size.. best is > 1/2 wavelength.THAT translates into a 3.5 ft sq.+ mouth size.. and the box you show sure doesn't look as such to me, but maybe I'm not cognizent of the true scale..
Regards,Mike Butler,
Principal, Technology and Operations,
Dascott Technologies, LLC
Ivan Beaver Messages: 8441 Registered: January 2005 Location: Atlanta Ga area
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The horn size pattern control also has to do with the pattern of the horn. Given the same freq cutoff you need a larger horn to control down to a particular freq with a narrower horn.
That is a 60° degree has to be larger than a 90° horn for the same cuttoff freq.
Given a 2'x2' mouth of the horn a 60° horn will have good pattern control down to 700Hz. While a 90° horn of the same size will have control down to around 460Hz.
There are other variables as well, do it does depend. But gives an idea of the actual sizes needed.
It appears he is going to need MUCH larger horns to get pattern control down to 150Hz.
For every complicated question-there is a simple- easy to understand WRONG answer.
Can I have some more talent in the monitors--PLEASE?
Ivan Beaver
dB Audio & Video Inc.
Danley Sound Labs
Stephen Kramer Messages: 100 Registered: January 2007 Location: Dayton, OH
Has No Life
Thanks people, lot's of great info,
Quote:
If you vent the box (Horn/Reflex combo aka Altec 816/817) you will have no problem getting down to 100 Hertz.
Thanks Eliot, that's what I was hoping, a combination of horn and vents.... I'm still having trouble finding Mac software to calculate ideal cabinet volume and vent size. Also very little information came up on my searches on how to actually check the tune of the cabinet. Can anyone point me to a good book or link?
Quote:
Antone is correct, for direct radiating horns, you will want a mouth size that is ideally at MINIMUM 1/3 wavelength, so;
1100 / 150 = 7.33 ft; 7.33 * .3333 = 2.44 ft.
As I said, 1/3 wavelength is the MINIMUM size.. best is > 1/2 wavelength.THAT translates into a 3.5 ft sq.+ mouth size.. and the box you show sure doesn't look as such to me, but maybe I'm not cognizent of the true scale..
Regards,
Thanks Mike, I measured approx 1.75 sq ft of horn opening... apparently much smaller than needed for good pattern control in the lower ranges. I still would like to build these cabinets to optimize the horns and 12" drivers... that is to get them tuned down low, despite the pattern issues.
Quote:
Given a 2'x2' mouth of the horn a 60° horn will have good pattern control down to 700Hz. While a 90° horn of the same size will have control down to around 460Hz.
There are other variables as well, do it does depend. But gives an idea of the actual sizes needed.
It appears he is going to need MUCH larger horns to get pattern control down to 150Hz.
Thanks Ivan, I believe these are 70 degree horns. The polar pattern on the DDS site appears to me like the 250 Hz range is still pretty usable, I guess it was just wishful thinking that these things could cover lower with the proper driver and cabinet design.
A larger horn isn't really an option right now, as my main goal is to keep things fairly compact. I really hoped I could run two of these per side on top of subs, but It looks like I may be adding bass cabinets to the design.
I appreciate all the tips, you guys are a big help!!!
If you port the cab for lower tunning you will not have a very linear bandpass. Their will be much more gain where the driver is effectivley loaded by the horn. Then a dip in response below horn loading. Which is what a lot of Old School Horn/Reflex cabs did. I don't see how getting flat response out of that sort of configuration would be easy, if possible. There is a reason why people like JBL don't make cabinets like that anymore.
Great thread, lot's of stuff I didn't consider (or know about) when arraying cabinets.... if I'm understanding correctly, it may be better to stack and splay my 2 midrange boxes in one column, and my high's next to it? You've definitely given me something new to think about, thanks, I'll have to read on.
Stephen Kramer Messages: 100 Registered: January 2007 Location: Dayton, OH
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Thanks Antone,
Quote:
If you port the cab for lower tunning you will not have a very linear bandpass. Their will be much more gain where the driver is effectivley loaded by the horn. Then a dip in response below horn loading. Which is what a lot of Old School Horn/Reflex cabs did. I don't see how getting flat response out of that sort of configuration would be easy, if possible. There is a reason why people like JBL don't make cabinets like that anymore.
Antone-
I guess I was hoping to port the cabinet to the frequency right where the horn loading starts to drop off... to fill the void in that 150-250hz area. Then I was gonna cross my subs a little high, with hopes that it would all blend together ok (with a fair amount of processing of course).
So are you suggesting I shouldn't port the cabs at all, and just work with what the horn was designed to do?
Well I think that DDS Horn is intended to be used in just that way. I think they may also have a larger model. But Again, depending on the in band horn gain You could have around a 6 or 10dB sensitivity difference between Reflex box output (Below Horn Loading) and Horn Output.
Someone else here would be more qualified to comment on the merits of this approach. I have seen some of the Old JBL Single 15 boxes that are Horn Loaded and ported with a Constant Directivity Radial Horn HF affair Going on. But never actually heard or used them.
I don't think anybody but DDS is making anything intended to be used with that design approach these days, as it is a bit dated. Perhaps there is a good way to integrate them smoothly with a subwoofer. I'm sure Ivan B. Has worked with this type of cabinet before? I know he had quite an impressive array of Karlson Coupler copies!!!
My only thoughts about using such a vented horn, arrangement are this. Added pasband directivity aside, you will either have to EQ out the horn passbands added sensitivity, or boost the Reflex ranges sensitivity to match the horn passband.
Or if you want to sacrifice directivity just do the whole thing in a vented cab with no horn, less EQ necessary.
Or design a much larger horn that will go as low as you need pattern control. The only commercial midbass horn that comes to mind is the one that Community made, for Colosseum type installs. Giant fiberglass affair.
From what few attempts at playing with a midbass horn in Horn Resp I've found its hard to design one that goes from 80-Hz much beyond 300Hz (At least modeled response). And Directivity starts getting crazy beamy up around the upper range until you start playing with some sort of Phase plug or diffraction slot (At least for Exponential/hyperbolic type horns).
Elliot Thompson Messages: 1545 Registered: April 2004 Location: New York
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Stephen Kramer wrote on Sat, 31 March 2007 20:35
Thanks people, lot's of great info,
Quote:
If you vent the box (Horn/Reflex combo aka Altec 816/817) you will have no problem getting down to 100 Hertz.
Thanks Eliot, that's what I was hoping, a combination of horn and vents.... I'm still having trouble finding Mac software to calculate ideal cabinet volume and vent size. Also very little information came up on my searches on how to actually check the tune of the cabinet. Can anyone point me to a good book or link?
Steve Kramer
Hey Steve.
If you want to go that route, you basically scale the internal chamber the woofer is sitting in and, tune the box accordingly.
A lot of "Horn Purist" don't like going that route for they feel its cheating. Personally, if the box can't deliver what I want it's pretty much useless for the job.
Your designs are extremly small, and venting the box is the alternative under those conditions.
You'll need to focus on low QTS (0.2 - 0.3) woofers in order to get the most extension using such a small internal chamber.
The picture below is a 15 inch woofer (0.26 Qts) sitting in a 1 cubic foot internal chamber. Notice the response between the sealed (Yellow) and vented (Red) version. Where the horn cuts off the vented cabinet comes in. That's the same concept found in the Altec 816/817 models.
Most (If not all) "Home Made" straight horn designs will sound best with a Parametric to flatten out (or tune to taste) the annoying (or increase the tonal)frequencies that are all so common with small straight horns.
Unless you have the space to make a 100 Hertz horn (In depth) in addition, to creating the proper mouth size when using multiple boxes, the vented route is the better than keeping the internal chamber sealed.
Mike {AB} Butler Messages: 2020 Registered: April 2004 Location: Lynchburg, VA
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Ivan Beaver wrote on Sat, 31 March 2007 12:11
The horn size pattern control also has to do with the pattern of the horn. Given the same freq cutoff you need a larger horn to control down to a particular freq with a narrower horn.
That is a 60° degree has to be larger than a 90° horn for the same cuttoff freq.
Given a 2'x2' mouth of the horn a 60° horn will have good pattern control down to 700Hz. While a 90° horn of the same size will have control down to around 460Hz.
There are other variables as well, do it does depend. But gives an idea of the actual sizes needed.
It appears he is going to need MUCH larger horns to get pattern control down to 150Hz.
Oops, thanks for the corrections, Ivan, I was thinking 90 degree boxes when I did that.
Also, he will need a deeper horn as well.. the expansion rate will have to slow down a bit.. in order to get 60 deg. dispersion.
(warning.. thread hijack coming..)
BTW, I'm still struggling with the mouth issue on the newer generation of horn loaded subs. I was taught 30 some odd years ago that the mouth issue is what drives the lowest Fc a horn will reproduce and operate at.. before the horn no longer has an effect.. and the driver becomes a direct radiator. How in the world is everyone bypassing that? They can't be! The response charts I read seem to indicate they aren't.. really. Lots of output up at 100.. and then it seems to drop off quite a bit. Can you say.. direct radiator? Someone gave the rationale that we are now PRESSURIZING the driver through a "forced" path.. but I'm not ready to buy that.
Thoughts? Mike Butler,
Principal, Technology and Operations,
Dascott Technologies, LLC
Ivan Beaver Messages: 8441 Registered: January 2005 Location: Atlanta Ga area
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Back in the 'ol days, what we did when we had seperate lows, mids, highs was to stack them up and splay them for coverage. You end up with the same "kinda" effect with a line array, except the splaying which they don't do.
When you stack them you get better/more predictable coverage maps. This may or may not be practicle in all applications.For every complicated question-there is a simple- easy to understand WRONG answer.
Can I have some more talent in the monitors--PLEASE?
Ivan Beaver
dB Audio & Video Inc.
Danley Sound Labs
Ivan Beaver Messages: 8441 Registered: January 2005 Location: Atlanta Ga area
Has No Life
I used lots of these type (4560-A7) boxes back in the day. The real problems is that back then I did not understand things as much as I do now and did not have anything other than an octave RTA to measure with. I never actually measured any cabinets and like many others simply "believed" what was happening. I just got the job done.
A lot of those cabinets (JBL 4560-which I had lots of) were designed to just be 2 way boxes with a high freq horn added. Porting added some extra bass response. It was larger companies that just used them as mid range cabinets with large horns and large bass cabinets. Back some 30 years ago sound systems sounded very different than they do today. There was a lot less bass, and the designs reflected this. It wasn't untill the 80's that needs for real bass started coming into play. Heck, a lot of bands did not even use monitors in the 60's and 70's. How did they live without them-because they played as a group and not a bunch of different ego driven individuals-but I am not going to get started on that one
Wavelength/ horn size/ combfiltering/ phase simply did not exist in my world, so therefore they were not a problem.
Freq response (+- how many db???) and sensitivity (not important how it was measured or at what freq ) and power handling were all that I was interested in. There were no computer models, no internet etc. so real data/understanding was hard to come by, and only if you knew where to look-I didn't.
Anyway here is my thought on a horn with a reflex ported cabinet. When used singly, yes the reflex part will be lower in level than the horn output. But when you use them in mulitples (lets assume the horns are positioned properly in regards to coverage patterns) the horns will cover just a particular part of the audience. Below the horns pattern control cutoff (assuming it being decently low) the output from the different cabinets will add together (assuming they are within 1/4 wl or so) and will sum together, adding to the output at the lower freq.
This will help to even out the output levels in regards from the mids to the lower freq. Of course this will vary with the size of the horn and the particular freq involved.
This is part of the problem we ran into in the developement of hte SH50. The origional version had a higher sensitivity than the current ones do. This is because Tom Danley had planned for them to be used in pairs and below the point where the horn has control the outputs of 2 cabinets have summed. together making the response of a pair of cabinets flat. The crossover design reflected this.
The problem with this is in the way people look at response graphs and their basic lack of understanding of the issues involved (a lot of people would look at the response and see that it is not flat and think poorly of the cabinet-not understanding it's intended useage), and not everybody would be using the cabients in pairs. How many response graphs of a single line array cabinet have you seen? Same idea. So I convinced Tom to redo the crossover and basically tame the mids and high outputs down to make a single cabinet have a flat response. This is the current version. You can argue both sides of which is better, they each have their own merits.
So right now when you put two SH50's together you have to pull out the freq below 300Hz or so where the cabinets have lost pattern control and start summing together in order to have a flat response. Some people do not do this and just let it build up, they like "the sound" better. Everybody has different things they are looking for a sound system to do.
As with all things audio, it is a matter of compromise.For every complicated question-there is a simple- easy to understand WRONG answer.
Can I have some more talent in the monitors--PLEASE?
Ivan Beaver
dB Audio & Video Inc.
Danley Sound Labs
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) and power handling were all that I was interested in. There were no computer models, no internet etc. so real data/understanding was hard to come by, and only if you knew where to look-I didn't.