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Tapped horn drivers

post #1 of 14
Thread Starter 
I have spent the better part of this weekend searching, reading and more searching and found a lot of cool and informative info on tapped horns. Except one thing that still eludes me.

What driver specs should I consider when looking to do a tapped horn? I see a lot of designs on specific drivers but not why that driver made a good choice. Surely just not any driver is suited for such a design.

I have a couple drivers sitting around that are intended for vented enclosures and a couple others that I'm considering. However I'd like to have a set of guidelines on the TS params (if there are any) so I can quickly look at a given speaker and mark it off the list or not before trying to model it.
post #2 of 14
There is no specific or tight nit set of driver characteristics required for horn applications. If the horn is designed around the driver, nearly any driver that could work acceptably well in a reflex enclosure can probably have a horn built around it. Some people will argue otherwise, however, I've run across very few driver characteristics that were "unusable" in a horn.

In the real world, there are practical limitations. Large drivers often force horn designs into lower gain territory simply because the physical size is limited by personal needs/preference/portability/buildabilty.

I'm pretty quick with hornresp, if you want to share with us the drivers in question, I'm sure you'll get some ideas on how to go about wrapping them up in a horn from myself or others or both.

Regards,
Eric
post #3 of 14
Here's what I look for: low Vas, relatively high Fs, and Qes of around 0.3. But it's all about tradeoffs... some drivers work better than others, and sometimes you have to compromise.
post #4 of 14
Thread Starter 
Thanks mdocod. I have the 6.5" and 8" versions from the first link below. The 10" is easy enough for me to get. The thread that lilmike had about the 25hz 6.5" Exodus horn was really interesting. I'm not sure if this 6.5" would work that low. I'm also concerned about xmax on these drivers in this scenario. Ultimately I'd like to do 20hz which I'm guessing would require the 10" at least.

As an alternative I'm considering the JL 12w6, also linked below. Right off the bat it has a 25hz Fs, so if what I've read over the weekend is correct, this should be able to do an 18hz or so horn, not regarding size anyway. On the high end 40hz a minimum, with 60hz being nice to have. From all the horns I've seen so far, I should have no problem with the high end requirements. Most I've seen will easily go up to 80-100hz. 80 would probably be my highest point.

As far as size goes, as you might guess, these are car audio drivers. The application would be automotive, but it would be a truck via a blow -through so I have tons of space to utilize. Just in front of the wheel wells alone there some 17ft^3. I could easily fit say 4 of the exodus style enclosures. maybe 4 8" driver versions, or 2 10". Not sure about multiple 12-13" drivers.

http://store.12velectronics.com/products/-Imagine-I6SW-6.5%22-Subwoofer.html

http://www.jlaudio.com/12w6v2-d4-car-audio-w6v2-subwoofer-drivers-92121

My goals for this particular project are:

1) Yes it is car audio, but I'm not after SPL (although if it does get loud, all the better). Ultimately it is a competition sound quality vehicle and I would like to get that really low extension. Yes most music doesn't go that low and I know that. There are a few test tracks that hit an 18hz pipe organ, etc. and few SQ cars do that well. I have 8" midbass that plays down to 40hz easily, so for competition the horn would most likely see 40hz and down. basically a one to one and a half octave enclosure. Daily use I'd probably change the crossovers to run up to 60hz because, well, I like to jam a little every now and then smile.gif

2) Yes I could easily build some big sealed enclosure, or ported. or even IB with a few 15's. That's all done and quite frankly not that interesting. I want to do something unique. Even bandpass is fairly common. I have the 6.5" mentioned above in a series tuned 6th order as my center console right now. Does pretty well from 38hz to about 75hz.

3) I'd like to use this as a learning exercise for later home theater possibilities and learning hornresp itself.
post #5 of 14
Thread Starter 
Quote:
Originally Posted by Oklahoma Wolf View Post

Here's what I look for: low Vas, relatively high Fs, and Qes of around 0.3. But it's all about tradeoffs... some drivers work better than others, and sometimes you have to compromise.

Can you define "low" for vas?

interesting on the Fs. I guess that depends on how low you want it to play ultimately? I forget where but I saw a "rule of thumb" about targeting the horn for about 66% of the Fs. So a 25hz horn would need about a 38hz Fs. is that correct?

The Qes is good info. I've seen some similar size speakers with widely different values here which is what lead to my weekend long search.

Based on those two, the 8 and 10" I linked to above would meet those basic requirements. the 10 has a qes of .34 and the 8 a .29. vas is 49.5l and 18.5l respectively.


P.S. I'm in broken arrow smile.gif
post #6 of 14
What OklahomaWolf said is a good start. You've also got to look at the amount of cone area for the motor force that's available. There is also a LOT more to a proper design than a flat frequency response.

Nearly any decent driver can be made to "work" in a tapped horn of some kind. Just cause you can does not mean you should. There are precious few that work well enough for me to draw a fold.
post #7 of 14
Thread Starter 
Quote:
Originally Posted by lilmike View Post

What OklahomaWolf said is a good start. You've also got to look at the amount of cone area for the motor force that's available. There is also a LOT more to a proper design than a flat frequency response.
Nearly any decent driver can be made to "work" in a tapped horn of some kind. Just cause you can does not mean you should. There are precious few that work well enough for me to draw a fold.

So that leads to the next question. What in the sims tells me to move on to another driver? ragged FR response? Impedance? A smooth response is obvious to see, so would over excursion. The rest, I'm not quite so sure what I"m looking at as it relates to good/bad for a particular combo.

Is there a general ratio of BL to cone that would be considered good? For example the three hybrid drivers all use the same basic motor which measures at ~13.6.
post #8 of 14
Quote:
Originally Posted by pocket5s View Post

So that leads to the next question. What in the sims tells me to move on to another driver? ragged FR response? Impedance? A smooth response is obvious to see, so would over excursion. The rest, I'm not quite so sure what I"m looking at as it relates to good/bad for a particular combo.
Is there a general ratio of BL to cone that would be considered good? For example the three hybrid drivers all use the same basic motor which measures at ~13.6.

I'll be honest - I am still learning what works and what does not. I have seen that smaller drivers can get away with a higher Qes. I think this is partly because the Mms is lower. Also - look at more than just BL, BL^2/Re is a good start. I divide this ratio by cone area, BL^2/Re/Sd. Numbers depend on units, but if in typical metric or SI units, I look for this ratio to be greater than 0.12 and less than 0.25. Even this is not a guarantee of a good driver. The cone has to be strong, and the driver has to have sufficient displacement to make the SPL you're after.

Real specs matter here. I can't emphasize this enough. Specs that come from the marketing department are often useless. If I did not measure the driver, I had better know and trust the source. Complex cabinets are not as tolerant of deviations in driver specs.

All of the output graphs in Hornresp are valuable. I look at all of them when designing a sub. Sure, I start with as flat an SPL curve as I can make happen, but that is the first thing I compromise to get the rest right. The time domain side of things matters too, and you can't exactly "see" those issues in the SPL plot.

Then, there is also the simple fact that at some point (and it will be different for every driver and horn combination) the predictions will not match the reality due to losses that Hornresp can not account for. Certainly, there are commonalities as to when things come off the tracks, but I have not developed any hard and fast rules yet. I can only afford to waste so much time and plywood building things that don't work.... Compression ratio is part of it, expansion rate is another.

Acoustic impedance and reactance are most often overlooked. They do matter. Group delay is usually not too big of a deal for subs, provided nothing is outrageous, but needs to be looked at too.

There is a lot more to it than I can distill into a single post. Like I said - I am still learning, and though I have theories, I still can not fully explain some of the things I have measured.
post #9 of 14
Thread Starter 
That is all very helpful actually.

About 30 minutes ago I took your simple tutorial as a base, plugged in the TS for the I8SW driver and well, it didn't look pretty smile.gif had a huge bump at 40hz, like 8db or so. looked like a ported box tuned really strong for one frequency. I played around with the sliders a bit but it never flattened up. Either I did something wrong or that driver just isn't suitable, which is ok.
post #10 of 14
Some drivers are trickier to work with and will just give you less than ideally flat response. In the real world, most rooms are going to cause +/-6dB or more variations below 200hz anyway, so having a sub that had similar variations isn't actually as bad as one might think. In an ideal situation, it's sometimes possible to use a peaking response from a horn load to counteract a lull in response cause by room reflections. Worst case scenario, things aren't perfectly flat, and most of us are non the wiser.

The I8SW has some options... Trying to get it down to 20hz isn't something I would suggest as the harmonic distortion of a driver operating so far below Fs is apt to be pretty piss poor. Again, I'm not sure why the preference towards "high Fs" is being called, for. If you want to build a horn that plays down to 20hz, a good starting point is a driver that can play down there with low distortion, which is generally going to be a driver with low Fs.










That's a pretty usable response, from a pretty small box (internal volume just over ~3ft^3). High pass setup ~25-30hz to protect from over excursion, and a low pass at about 80-90hz, with dynamic reach to ~110dB in this passband makes for a pretty impressive performance from a single 8" woofer.

When I have a chance later on, I'll try to come up with some ideas for that JL you have in mind.
post #11 of 14
Thread Starter 
I played around a little bit today with dual 8's using lilmike's tutorial as a basis. It started out with higher peaks than the drivers he use but I think I was able to smooth it a bit. Overall it was about the same size as well, just a couple liters bigger. the 6" just wasn't working. It looked like a one note wonder.

I was going to try the jl, but their site doesn't give all the ts params, so I didn't know how to proceed. And I had to get some work done as well smile.gif

I'll look over yours a little more closely and see how it compares. That will be a good learning exercise for me. I'll admit I've seem some distortion plots but not sure how to interpret them yet.

Thanks again
post #12 of 14
Quote:
Originally Posted by pocket5s View Post

Can you define "low" for vas?

The lower it is, the smaller the horn can be to a point. But, you have to watch the compression ratio and make sure you're not going to tear apart the diaphragm either. Like I said, it's all about tradeoffs sometimes.

Anyway, those are just the three parameters I look at to quickly determine whether or not it's a driver worth throwing into my Hornresp database and playing around with. Whether or not I feel like folding it depends on a fair bit of other things, like how well I can make it fit my goals.
Quote:
Originally Posted by mdocod View Post

Again, I'm not sure why the preference towards "high Fs" is being called, for.

Simple answer - I try to have the biggest excursion maxima within the horn's passband somewhere near the driver's Fs, which is usually north of my desired tuning frequency.
Edited by Oklahoma Wolf - 7/23/12 at 9:46pm
post #13 of 14
Hello Pocket5s,

The parameters are on JLs site. Everything hornresp needs can be found under the "parameters" "tab."

quote:
"Free Air Resonance (Fs) 25.0 Hz
Electrical “Q” (Qes) 0.48
Mechanical “Q” (Qms) 7.1
Total Speaker “Q” (Qts) 0.45
Equivalent Compliance (Vas) 2.82 cu ft / 79.9 L
One-Way Linear Excursion (Xmax)* 0.65 in / 17 mm
Reference Efficiency (no) 0.25%
Efficiency (1 W / 1 m)** 85.9 dB SPL
Effective Piston Area (Sd) 77.8 sq in / 0.0502 sq m
DC Resistance (Re)*** 6.75 Ω"


The only thing not listed there is Le, which doesn't matter in this case.


Tapped horns can be approached different ways. The example I gave above with the I8SW is barely really reaching into the gain possible if the horn were to flare out much wider (much larger box volume). The design proposed, would be considered by many to be a tapped, tapered, transmission line. Work in hornresp for awhile and one starts to realise that these are all just different degrees of sophistication applied to different amounts of box volume to accommodate a driver characteristic in a desirable way. There are different ways to label many of these boxes.

The premise of "tapping" a line/horn, is actually misconstrued and misunderstood by most. Hornresp can simulate all sorts of box configurations, and in time, one must realise that the function of the "tap" is primarily for the purpose of gaining some control over the shape of the response by changing the point where wave-fronts combine constructively or destructively as they traverse the horn/line. The tap position in a line is a "tool" for one to use to fine tune the response of the horn. The same sort of ability to "shape" response via effecting the wave-front timing and summation, can be accomplished in non "tapped" designs by having the horn end (or line or port end) terminate at various distances to the listener.

The reason I bring up the above, is that, I see what appears to be a "tapped horn fever" spreading in the DIY crowd, much of it I believe is based on a false premise that somehow the "tapping" of the horn, results in some miraculous improvement over other types of box sophistication. In truth, the taping of a line or horn should be viewed as a fine tuning tool. Some drivers, are going to model better in alternative reflex, horn, line, or tapered line configurations when particular box volume constraints are in play. The tapped horn configuration, can represent the best use of available box space where certain drivers and volume limits are up against each-other. I don't think it's wise to set out with a handful of drivers, bound and determined to get each and every one into 1 type of box design.



With that in mind, what sort of box volume limits do you have in mind for these drivers? If you give 40-50ft^3 of space to work with, there isn't much reason not to build a 120-140+dB bass horn (depending on bandwidth/driver etc). If limited to just a few cubic feet, you'll have to live with the reality that a few cubic feet can only buy so much (if any) gain, depending on the driver using that space, and how well the space is used by the designer to maximise the potential box gain.

Regards,
Eric
post #14 of 14
Thread Starter 
Thanks Eric. I knew some of the specs were available, but didn't know what effect if any the missing ones would represent. I see all the boxes to fill and well, wanted to fill them smile.gif

I understand your thoughts on the box configuration being a tool, makes complete sense. If the drivers in question just don't really work well in a tapped horn that is fine too. If they did, then I would probably pursue a test enclosure and see what happens for the sake of experimenting.

As for amount of space available, I have about 17ft^3 set aside. That is the front of the truck bed to the wheel wells. I haven't specifically measured but best guess would be 25 or so if I utilized the whole bed.

Originally I was going to go with a couple 12 or 13" jl subs in a bandpass box playing up to 40hz or so. During SQ competition they would be turned down and the crossover set to 35-40hz to further attenuate them. My 8" midbass speakers would play down 40hz. Out of SQ comp, say everyday driving and the occasional SPL run, I would run them up to 60hz or so and let them run for fun. Note that SPL is not a goal, but if the icing is there, I'll eat it smile.gif

Having said that, I like the idea of a low distortion, low extension enclosure that is out of the car audio norm. I don't have to worry about trunk space like most do. yes I would like to keep some of the bed in the thing, but I'm not opposed to using the space if it is appropriate.
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