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description: Audio advice and discussions with audiophiles and professionals. Free discussion forums, open to all and frequented by industry experts. Ask questions and get advice on stereos, speakers, hi-end amplifiers, pre-amps, home theater, tube hi-fi, turntables, vinyl, tweaks, music, films, video, DVDs and more.
items: Subwoofer Horn
items: Re: Subwoofer Horn
items: Other Drivers and stuff
items: Re: Other Drivers and stuff
items: Hornresp Inputs
items: Throat distortion, air pressure
items: Re: Throat distortion, air pressure
items: B12 Subwoofer Project

Subwoofer Horn
type: item
description: Been trying to get a 2.5 meter horn for 18" driver in a 100x90x48cm 'compact' size (for an 18). Thats the horn dimensions... 100cm high, 90cm deep, and 48cm wide. Used a different folding pattern than what mike.e uses to get it more compact.... and can have big back chamber! Assuming that you measure length like this: Then length would be ~2.47m which is about 2.50m. Acoustic length line is the dotted line. I've heard you measure only on 'inside' dimension though? which is this? Here is response: Any comments/suggestions?! Adrian
creator: Adrian Mack
date: 2004-03-31T23:04:11-00:00

Re: Subwoofer Horn
type: item
description: That's a whopper, but it looks damn good! What woofer did you model it for? There's probably a range of 'em that will work, but which one did you model, if you don't mind my asking? Could you use a 2241?
creator: Wayne Parham
date: 2004-04-01T00:07:25-00:00

Re: Subwoofer Horn
type: item
description: I modelled it up for the Eighteen Sound 18LW1400. I bet there are a lot of woofers that could be direct substitutes though.... like McCauley or JBL. I'm not at home right now, when I get home I'll model up a few other drivers and see what happens. I have a feeling they will perform very similar.
creator: Adrian Mack
date: 2004-04-01T01:33:07-00:00

Re: Subwoofer Horn
type: item
description: Looks great!
creator: Wayne Parham
date: 2004-04-01T01:56:32-00:00

Re: Subwoofer Horn
type: item
description: I think you'd be very pleased with a sub that goes that low. power with 50w then use the 1kw lab gruppen on a tumult for the bottom octave. email me the specs and il fold it my way
creator: Mike.e
date: 2004-04-01T07:00:15-00:00

Other Drivers and stuff
type: item
description: Hey Wayne Just modelled up a few other 18" drivers on the same horn. I found that JBL 2242, Eminence Omega 18, and Eminence Magnum 18LF show the EXACT same response curve as the 18-Sound 18LW1400 response curve in my first post. I almost thought I didn't change the T/S data in Hornresp, because they model up so idential! Great thing about all those woofers is they all have shorting rings/distortion reduced motors, except for the Omega 18. And these 18's are definitly 'top of the line'. JBL 2241, Eminence Kilomax 18, and Magnum 18HO on the other hand didn't model up so smoothly. And strangely, the response curves all looked the same as each other, all peaking and dipping in the same positions! These woofers which arn't so good in the horn showed a curve like this, the woofers being only 0.5db or so out from each other so I'll post one graph only: I guess its not really that bad. Considering that this is a theoritcal model only, it's bound to perform differently in a lot of rooms, though Hornresp is pretty accurate. Getting back to the 'good' drivers (18LW1400, 2242, Omega 18, Magnum 18LF) if it is desired, then throat size can be decreased from 500cm^2 to 400cm^2 if you want to flatten response by about 1.3db more in the 30-40Hz area. Reponse curve in my first post had a 500cm^2 throat, graph below has everything the same except with 400cm^2. It's not much different from the graph in my first post. Reason why in my first post I posted the response curve which had the bigger throat, is because I think the bigger throat will cause less distortion, which I consider of more importance than 1.3db or so flatter response, which may not even be worth it by the time you consider room modes and stuff. Although 500 isn't that much bigger than 400, so it probably wont do anything to distortion (or much). Either way, they both are good. Anyway - I'm beginning to really like this horn... I think I'll take the plunge and try posting it on AA (hope I dont get any response from that …
creator: Adrian Mack
date: 2004-04-01T08:48:05-00:00

Re: Other Drivers and stuff
type: item
description: Looks great! Were those eighth-space models? Really, the 2241 version isn't too bad, and it's a lot cheaper than the 2242. The Magnum series sound just like 22xx JBL's, so that's a good option too. A Magnum 18LF is not much money at all in comparison with the JBL's.
creator: Wayne Parham
date: 2004-04-01T10:19:47-00:00

Re: Other Drivers and stuff
type: item
description: Yep, they were modelled in eigth space. Theres probably other drivers from other brands too that will work, I just did the Eminence and JBL's though because a lot of people use them here.
creator: Adrian Mack
date: 2004-04-01T10:29:32-00:00

Hornresp Inputs
type: item
description: I think I'd be pretty happy with 30Hz too. Maybe I'll try putting a high pass filter at 30Hz one day on my sub and see if I notice any difference with music, but I think my room will gain so much on the low end anyway making the experiment not worthwhile. It means the basshorn will have gain on the low end too though :D Here are the inputs: Let me know if you can come up with a better folding scheme! Adrian
creator: Adrian Mack
date: 2004-04-01T10:33:09-00:00

Re: Other Drivers and stuff
type: item
description: Gotcha. Looks great! I'd go with the Magnum 18LF or the JBL 2242. What's the best deal for you? I assume it's 18Sound?
creator: Wayne Parham
date: 2004-04-01T10:51:14-00:00

Re: Other Drivers and stuff
type: item
description: Well I own an 18LW1400 so I'm already half way there, or 3/4 in terms of $$$, just need wood! its in the big vented box right now I showed you before.... I like the 18-Sound driver a lot, you probably can tell by now :p I like that there are so many direct drop in's which can be used on this horn.
creator: Adrian Mack
date: 2004-04-01T11:04:18-00:00

Re: Other Drivers and stuff
type: item
description: Super cool. If you have the driver, your cost now for building a speakers is mostly in your time for making the cabinet. And then the wood too, as you say. Now that I think about it, that's a lot of real estate, so the wood ain't gonna be cheap. But at least you have the woofers. Hey, here's an off-topic thing that caught my interest. I hope maybe you'll have some input. I'm wondering where the onset of non-linear distortion happens from compression/rarefaction asymmetry. Do you happen to know of any references to reliable research data on the subject? I'm guessing it happens when the compression cycle of sinusoidal pressure reaches 1.5 to 2 atmospheres, 'cause that would put the rarefaction cycle between 0.5 and 0.0. This assumes (1.0) atmospheric pressure is the baseline, 'cause I'm wondering where the start of trapped-air distortion and other air pressure related acoustic nonlinearity begins. Since you can't go below 0.0, but you can go above 2.0, somewhere in the 1.5 - 2.0 range must start the onset of asymmetry. I just don't know where it is. Check this out. Let me know if you know of any good data on the subject.
creator: Wayne Parham
date: 2004-04-01T11:44:03-00:00

Re: Subwoofer Horn
type: item
description: Hi wayne,i have just the same situation,but my horn MUST fit in my little car! which is only 80cm wide! it seems near impossible to make my jbl fit in there while still reaching 30hz,40hz is definitely possible though :-S lab12 it is!
creator: Mike.e
date: 2004-04-01T12:22:12-00:00

Re: Subwoofer Horn
type: item
description: Put wheels and a windshield on Adrian's horn and you can drive it like a car! You won't need a flat 'cause you can live inside it!
creator: Wayne Parham
date: 2004-04-01T13:08:04-00:00

Re: Other Drivers and stuff
type: item
description: Hi Wayne The non-linearity you speak of (called throat distortion in horns) is caused by the fact that the speed of sound is temperature dependant (with speed increasing with temp). Imagine a sound wave, the "pressure" half of the wave is actually warmer than the rarified side. AS a result, the "hot" side travels slightly faster than the cool side and so after enough distance (and sufficiently high SPL) the nice sine wave progresses into a saw tooth wave. If I recall, at about 1100 degrees C, the speed has doubled. This was a real problem in the acoustic Levitators I used to work on as once one had a saw tooth (or sufficiently distorted sine wave) then one also produced acoustic pumping (an effect like a fan). These operated in the range of 155 - 175 dB SPL @ 21Khz generally. This effect is also seen in a sonic boom, here, on the leading edges, the air is compressed over 1atm at supersonic flight. Here, because of the same temperature/speed relationship, what finally reaches the ground as radiated sound is also a saw tooth (on the front edge), over all, the waveshape of a sonic boom is like a capitol letter N. Throat distortion is pretty much a non-issue in bass horns though, cone and coil drivers generally cannot produce enough acoustic pressure to cause this. While dozens of bass horns I have measured had sometimes even gross distortion, the driver is the primary source. This distortion is the sum of the VC motor and mechanical system's non linearity. The "bad" effects of the latter can be minimized by choosing a driver with a low Fs which then requires a small Vb to end with the right compliance. Depending on the sealed volume more means that a more linear spring is dominating over the drivers relatively non-linear suspension (by comparison) spring. Generally, stay away from High Fs driver for bass horns if low distortion is a goal. The BT-7's for example of relitively high throat pressure, are the same horn (essentially) as the LAB sub but at full rated power ha…
creator: Tom Danley
date: 2004-04-01T14:13:36-00:00

Re: Other Drivers and stuff
type: item
description: Do you have any references to test data handy? I was hoping for maybe some test results that quantified the onset of air-compressibility non-linearity distortion. I'm not sure if it's the same thing as throat distortion or not, but it is from air passing through the cooling vent. This question is purely because of the fact that Jerry's analysis made a 0.75" diameter port possible, and some of us were discussing how much effect this might have. Jerry said he would test them and find out. About motor distortion, I've always been impressed with the performance of flux stabilized motors. They provide about -15dB improvement in 2HD, and it's not just a figure - I find it immediately obvious. You can walk into a room with a sound system and immediately hear whether the woofers are flux stabilized or not. It just sounds cleaner. Back when the LAB12 was first being made, I wondered why it wasn't built with flux stabilization. I think you and I discussed this back then. I got the impression you weren't interested in a better magnetic structure, but maybe I misunderstood you. In any case, that's the point I wanted to make. The motor is responsible for most of the 2HD in the entire system, so to me, it makes sense to make flux as symmetrical as possible if high-output and high-quality are the goals. Since the improvement from flux stabilization is 10dB to 15dB reduction in 2HD, it amounts to a significant improvement around the same magnitude as horn loading. That's like 10x to 35x and sometimes more - Certainly nothing to sneeze at. So I questioned the decision not to use shorting rings in the original LAB12. The Magnum was already in the works, so I wondered why the LAB12 wasn't made with flux stabilization. And here lately, I just thought I'd ask Chris at Eminence about it. In hindsight, I don't know why it hadn't been done before now. But I guess there were cost concerns. Jerry tells me that the flux stabilized woofer is being readied now for testing. If you are expecting …
creator: Wayne Parham
date: 2004-04-01T15:04:12-00:00

Re: Other Drivers and stuff
type: item
description: >>Do you have any references to test data handy? I was hoping for maybe some test results that quantified the onset of air-compressibility non-linearity distortion. EV does, EV discovered this on there MTL-4 high cabinets, the 4-10's that were driving the mid-bass horn were developing to much air-compression causing non-linearity in the throat section of the horn and causeing the harmonic distortion to rise dramatically when driven near full power. Bill W.
creator: Bill Wassilak
date: 2004-04-01T16:04:18-00:00

Re: Other Drivers and stuff
type: item
description: Interesting. I didn't really expect to find throat distortion on cone-driven horns, because the compression ratio is low to prevent the cones from ripping. Titanium can stand up to higher compression, but the paper cones punch the voice coil through. I was more concerned about what might happen in the cooling vent, and whether it might introduce 2HD from pneumatic non-linearities at high output levels. This is all in response to the flux-stabilized LAB12 project I asked Eminence to work on. Jerry McNutt said that he and John Sheerin modeled the magnetic structure and found that there were two solutions for putting a flux stabilization ring on the motor. One involves making the vent hole smaller, which might increase power compression and introduce non-linear distortion from the trapped air. The other option doesn't require a reduction in cooling vent size, but it will take a couple months more to develop. If the vent is made smaller, the compression ratio between the cap and the vent will change. The concern is whether or not this feature will adversely affect power handling, thermal compression or introduce distortion. Tom Danley is going to test the flux stabilized LAB12 next week, so we can know the distortion of this version of the woofer. If it works out, perhaps Eminence will make a better low-distortion version of the LAB12 available fairly quickly. If not, the second option is to install shorting rings in the plates, outside the voice coil. It has the advantage of allowing the vent to be made larger. This option will take 6-8 weeks though, so production would have to wait a little longer.
creator: Wayne Parham
date: 2004-04-01T17:51:37-00:00

Re: Other Drivers and stuff
type: item
description: >> I didn't really expect to find throat distortion on cone-driven horns, because the compression ratio is low to prevent the cones from ripping. Titanium can stand up to higher compression, but the paper cones punch the voice coil through. I think this is more of a problem pushing low frequencies, that compression ratios come more into play. On Tom Danley's BT-7 I think they have like a 3:1 ratio and when they were in development they had problems tearing cones apart at first, and I've heard other people talk about it when they start going over 3:1 ratios. On Ev's MTL's they crossover at 160Hz but I'm not sure what the compression ratio is on these, but they weren't ripping cones, just causing distortion to rise. After they discovered this they came out with mod kits for them to address the issue which I think was a 1/4" spacer between the 10's and horn's throat to reduce the distortion at the cost of 2-3db reduction in SPL's. I've been following the threads on the new lab 12, but at first I thought you were talking about non-linearity in horns rather than the speakers vent hole. Bill W.
creator: Bill Wassilak
date: 2004-04-01T18:24:10-00:00

Re: Other Drivers and stuff
type: item
description: Aahh, cool beans, interesting story on the EV horns. Are you gonna be at Jim Denton's house on Saturday?
creator: Wayne Parham
date: 2004-04-01T19:17:11-00:00

Re: Other Drivers and stuff
type: item
description: Planning on it, don't know what time I'll show up, going to Kidd Rock Friday night so don't know how burnt I'll be. Bill W.
creator: Bill Wassilak
date: 2004-04-01T19:31:40-00:00

Re: Other Drivers and stuff
type: item
description: That's cool. A buddy of mine had three tickets to Kidd Rock and he couldn't go so he asked me to sell 'em on eBay for him. I couldn't go either, so I put 'em up and they sold. Pity, I like some of the stuff they've been doing, especially about three years ago. So dude, just chill out and sleep it off. You don't have to be there until 2:00pm, so if you can't make it there by then, I'm gonna razz you for a year.
creator: Wayne Parham
date: 2004-04-01T19:47:53-00:00

Re: Other Drivers and stuff
type: item
description: Hi Wayne Aside from thumb rule formula linking SPL to horn bandwidth, I have not seen much in print. Most of the experience I have had with this issue was in trying to "fix" it in our levitation sources, ultimately, there is no fix, one simply had to reduce the distance (in wavelengths) traveled at high SPL's. I guess one could say for what we were doing, the answer really was to have a converging sound field that only reached maximum SPL where it was focussed. It was pretty cool though, at the center of focus, the sources could light a cigarette with acoustic friction (at about 165-170 dB) Flux rings had been / are pretty much associated with "more expensive" drivers and the advent of accurate magnetic computer models with experience has made many ceramic structures that were the equal of what one could get with the traditional materials (alnico). On the other hand, as long as the lines of flux are not "pinned" down totally , the magnetizing force in the Voice Coil modulates the set point of the magnetic circuit. The extent it is modulated also is the amount that the magnetic circuits' non-linearity in its BH curve alters the relationship between the two. Interestingly, when I went to work at Intersonics in 1979, the sound source they were using at the time was called a St Clair (developed by the department of mines I think). It was a bar of aluminum, held at the exact center by a thin flange and driven by a shorted turn.. In this driver, the driven coil is wound around the center pole and the bar is set in motion by the "shorted turn" at one end (turned out of the same bar). I had made several tweeters (a small aluminum dome) with this approach, using the edges of the dome as the S.T. and coil wound on the center pole. These worked fairly well and I thought there was a possibility of making a compression driver this way. We applied for a patent on it but after a while there was a budget cutback and the application was abandoned. Some years later, Tannoy was able t…
creator: Tom Danley
date: 2004-04-02T13:51:01-00:00

Re: Other Drivers and stuff
type: item
description: Cool beans. I understand the woofer used in the BDEAP horn is slightly different than the LAB12, so perhaps it doesn't make sense to combine the flux stabilized versions into one project. But they are similar enough the basic woofer structure will be the same, and the efforts to develop them are the same. So in a sense, you and I are cooperating on this one. I do want to address the comments about 20Hz EQ though. Not to pick a fight, but to clarify. You yourself describe the potential of pushing a horn-loaded LAB12 into non-linearity by EQ'ing the bottom end. That's exactly the point I've made in the past, and what I hope to address with the flux stabilized LAB12. Since the woofers in a horn act as direct radiators below horn cutoff, it's really the woofer alone that sets performance limits at those low frequencies. Certainly EQ is an option to bring up the bottom octave, where the horn becomes ineffective. Or if 140dB isn't required and 120dB will do, a smaller direct-radiating package is a viable option and EQ isn't necessary. In either case, having a high-quality subwoofer with a shorting ring will really shine in this application. Horns are great, but if you're looking for operation down to 20Hz, a subwoofer such as this can be used in other smaller enclosure types as well. For maximum power, a horn is the best option. It offers about 15dB greater output above cutoff, which is significant. But the smaller package of using the subwoofer as a direct radiator is a viable alternative, and performance is quite good, particularly at the lowest frequencies.
creator: Wayne Parham
date: 2004-04-02T15:05:14-00:00

Throat distortion, air pressure
type: item
description: Hi Tom > This effect is also seen in a sonic boom, here, on the leading > edges, the air is compressed over 1atm at supersonic flight. Here, > because of the same temperature/speed relationship, what finally > reaches the ground as radiated sound is also a saw tooth (on the > front edge), over all, the waveshape of a sonic boom is like a > capitol letter N. > Throat distortion is pretty much a non-issue in bass horns though, > cone and coil drivers generally cannot produce enough acoustic > pressure to cause this. When a direct radiator, I agree that a loudspeaker of this world cannot increase the general air pressure of the entire atmosphere very much (which I'm pretty sure step response shows, showing sound pressure when voltage step function is applied). In a basshorn though (or any horn), cant you think of the piston being a moving 'pump', forcing air through the throat? A smaller throat would be creating more compression at the peaks or crests on a sine waveform, and so theres more distortion if air pressure is increased to much due to a small throat (caused by high SPL). On the other hand, a larger throat would create less compression at both low and high SPLs because of less restriction, so less changing in the temperature/speed relationship (causing volume changes to be unequal when pressure is changed), so less changing of waveshape. I dont know if a basshorn has the ability to increase air pressure much past 1 atmosphere, I guess it must compress to some degree though. I think I'm getting mixed up with midrange and HF horn throat distortion though... does one need more acoustic pressure to compress the peaks of a very long low frequency wavelength? Why is this? Is it because, for example a 600Hz wave vs 20Hz wave. The peak area/region on the 600Hz wave is a lot smaller than the peak region on a 20Hz wave, which would be very wide. So at the same SPL level, the compression of air atmosphere in the 20Hz wave is more 'spread out' than on the 600Hz wave, so th…
creator: Adrian Mack
date: 2004-04-02T16:51:27-00:00

Re: Throat distortion, air pressure
type: item
description: Hi Tom >> This effect is also seen in a sonic boom, here, on the leading >> edges, the air is compressed over 1atm at supersonic flight. Here, >> because of the same temperature/speed relationship, what finally > >reaches the ground as radiated sound is also a saw tooth (on the > >front edge), over all, the waveshape of a sonic boom is like a > >capitol letter N. >>Throat distortion is pretty much a non-issue in bass horns though, >>one and coil drivers generally cannot produce enough acoustic >>pressure to cause this. >When a direct radiator, I agree that a loudspeaker of this world cannot increase the general air pressure of >the entire atmosphere very much (which I'm pretty sure step response shows, showing sound pressure .when voltage step function is applied). >In a basshorn though (or any horn), cant you think of the piston being a moving 'pump', forcing air >through the throat? Yes, unlike a sealed tire pump etc however, on the throat side of the radiator, the "pressure" is not proportional to displacement but rather the velocity. This results in the curious situation where if one looked at the points of minimum and maximum acoustic pressure, one finds that instant in time is where the radiator displacement is zero (but has greatest velocity). >A smaller throat would be creating more compression at the peaks or crests on a sine >waveform, and so >theres more distortion if air pressure is increased to much due to a small throat (caused >by high SPL). On >the other hand, a larger throat would create less compression at both low and high SPLs >because of less >restriction, so less changing in the temperature/speed relationship (causing volume >changes to be >unequal when pressure is changed), so less changing of waveshape. I dont know if a >basshorn has the ability to increase air pressure much past 1 atmosphere, I guess it must compress to some >degree though. I think I'm getting mixed up with midrange and HF horn throat distortion though... What your saying is…
creator: Tom Danley
date: 2004-04-03T19:26:21-00:00

Re: Other Drivers and stuff
type: item
description: Hi Wayne The standard Lab 12, the version we use and the shorted turn samples your talking about that Eminance has built are all the same driver with the exception if the dimensions of the center pole and in one case the addition of a shorted turn and in the other a different VC. You could say they were different drivers but unless you took them apart down to the core and measured, you couldn't tell the difference as all the radiator, suspension , frame, physical construction and magnetic parts are all the same. Part of the design (what makes it a LAB 12 and different) here was to make a very ridged cone, one that acts like piston in operation in a horn as well, not just the driver parameters I had specified. My thought in not calling it by an unrelated name (like mag 12 etc) is that one does not see this generally when one say offers some other minor change, say a dual coil version of a woofer with a proven track record like the LAB 12 has. Also since the LAB sub project drove the need and then the design / spec's I gave Eminance for the LAB-12, it is perhaps also a part of the objection that one would simply be taking a unique, successful, proven design, make a small change (that was on the wish list but couldn't have been implemented at its conception) and try to infer it as a fundamentally different driver. Since "MAG 12" is not a new driver design and is identical in every way to the LAB 12 (except for adding the ST), why not just call it the LAB12 ST? This is perhaps just my view, for example, our version of it has our logo and decals and a somewhat stronger motor and different VC, but I still refer to it as our version of the LAB 12 and not something new.. So far as co-operating, understand any help I have given (doing the LAB sub project etc) or other things is aimed at the DIY'rs and not part of "my job". It is a somewhat sensitive area too as it is frequently pointed out that my designing things for DIY'rs (like the LAB sub) that may compete with our produ…
creator: Tom Danley
date: 2004-04-11T17:45:58-00:00

B12 Subwoofer Project
type: item
description: The name "LAB12 ST" would suit me fine, but it may be confused with the existing woofer. I tenatively chose the "MAG12" name in early discussions, making a reference to Eminence's flux-stabilized "Magnum" series. But that may also be confusing since Eminence has introduced a "Magnum 12" midwoofer. It is actually an Eminence executive that has voiced his opinion that "LAB12 ST" and "MAG12" might cause market confusion. I don't believe either name violates any trademark, but I haven't asked an attorney to research it either, so I don't guess I really know. In any case, it's not the name I'm particularly interested in. I'm thinking about calling the woofer simply B12. The main thing I'm concerned about is its specs. Woofers with ferrite magnets are improved significantly when flux stabilization rings are used, so that's the part I'm interested in. Now it's down to the matter of where to put the ring, in the core or in the plate. Hopefully the first prototype will meet specs with the ring in the core, so Eminence can roll them out pretty quickly.
creator: Wayne Parham
date: 2004-04-11T20:13:01-00:00