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  #1  
Old 07-31-2014, 03:34 PM
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Default Neopro enclosure for outdoor use request

Because of this tasty jam (https://soundcloud.com/omegatypez/to...atypez-bootleg), which starts off with 30< =hz right off the bat, (too much power and my hpf was off ) I blew my dual 2 inch driver box. I used it outdoors and now I wish to make an enclosure for the SA neopro 8. I know the neopro gets very very loud at high frequencies even without an enclosure but what would be the best enclosure for portable-ish outdoor enclosure for it.


Granted a sealed would be the smallest and easiest to build. I have a ported enclosure I salvaged from a HT system that I could just throw it in, but that box is ported a bit high and has low port area. I was considering doing a small folded horn design (or possibly a LAB horn), but would it be worth it for outdoor use? Would making a larger port area ported enclosure be worth it? I mean I want it to make some sick midbass. Max dimensions 12x9x20 inches. Would want to be able to play 60-70 hz if possible. Probably gonna use 1/4 in mdf.

I also have a neopro 6.5 that needs a recone, could perhaps make a dual enclosure, 6.5 in sealed and the 8 in a ported?

Last edited by ylpkm; 07-31-2014 at 04:02 PM.
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Old 07-31-2014, 09:31 PM
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A folded horn will be large and won't play a large bandwidth, plus they usually respond better to an enclosed listening environment to create virtual loading for more gain from the horn mouth. In this case I think a smallish vented enclosure would be the best bet. Do something around .5 ft^3 tuned to 60ish with a 2" vent. With a direct radiator setup like that you could probably even use it as a mono setup by itself with no other speakers needed if you really wanted to. I would go with 1/2" material though. Vented enclosures really need to be air-tight and free of wall resonance, and there's a lot of pressure inside of a vented enclosure around tuning.
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Old 08-01-2014, 07:04 AM
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Would a passive radiator, with the broken 6.5 work? The passive radiator needs to be same size or have more xmax than the active speaker right?
I may just throw it in the HT box for now (when it arrives), and make a small scale super scoop box and see which one sounds better.

Last edited by ylpkm; 08-01-2014 at 09:03 AM.
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Old 08-01-2014, 01:56 PM
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You want to use the 6.5" as a passive radiator? You could technically do it if you removed the motor and added mass to the cone to lower the resonant frequency. Like you said though, you'll have excursion issues. You typically want more displacement capability with the passive than the active radiator.
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Old 08-01-2014, 04:00 PM
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I cant remove the motor without cutting up the cone and spider right? I probably wont go that route. I may just recone it and figure out a dual box at a later time. Probably after I make the Horn box. Hopefully this neopro wont have the triple joint issue as well
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Old 08-25-2014, 03:06 AM
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alright, I decided to go with a ported design. (I was happy with how loud the highs were with the neopro in a .7 cu ft box that was tuned to 40hz) ~1.5 cu ft total for 2 neopro 8's. 2 x 13.5 inch slot port tuned to 55. this is about what the box will look like. For a box that has the speakers in their own air space should I wire them mono, or stereo. Do I lose any output with stereo wiring? It would seem that stereo wiring is better just in case one of them blows/burns the other would work. My amp is a 2 channel that can be wired mono. Opinions?
Box has sides, bottom and back wall, will be doing bracing, port, top, and speaker wall tomorrow. I could tilt the speaker baffles outward left and right, so that it has a wider angle, perhaps it would help the stereo effect if I wire it in stereo.
Winisd predicts I hit about 5mm of excursion at about 100 hz and 47 hz. xmech is 11.5mm (right?) Its good that speakers ride at about xmax at rms right? Is that what the young kids call slammin at those frequencies? Idk whether I should tune lower. Tuning lower causes very close to xmech failure at 100 hz.

and how much does port area affect excursion? in winisd the excursion doesnt change with port area change, I assume in real world it does affect it.

Last edited by ylpkm; 08-25-2014 at 03:49 AM.
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Old 08-25-2014, 03:53 AM
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"should I wire them mono, or stereo. Do I lose any output with stereo wiring?"

You might get better acoustic coupling between the two speakers by running a mono signal to them, especially in the lower frequencies. But if the source material is panned to one side or another and you are running a mono signal, you will get combing effects due to the large center-to-center spacing in relation to the size of the wavelength at higher frequencies. If you're only planning to use them up to a maximum of ~200hz or so you would probably get more output by running them mono. If you're going higher than that stereo would probably be a better option, but try it both ways and see what sounds better to you. You also need to consider the impedance of the speakers wired together. Power should be about the same in either a stereo or bridged-in-series scenarios, but will go up quite a bit in a bridged-in-parallel configuration.

"For a box that has the speakers in their own air space should I wire them mono, or stereo [...] It would seem that stereo wiring is better just in case one of them blows/burns the other would work."

I can't quite tell what you mean by your "the other one would work" statement. in either scenario if one speaker blows the other will keep working because it will still be in a complete circuit. The advantage to each speaker having its own dedicated enclosure (and vent) is that if one speaker blows the other won't "see" the enclosure as being much larger and with a big passive radiator via the dead speaker's cone. In some cases on higher power if one speaker blows the other will fail shortly thereafter because of the reduced damping due to those two things. It doesn't really matter what the signal is; whether it's mono or stereo the only thing to consider is how the speaker is coupled to the enclosure's airspace. I noticed you mention earlier that you will be using a single port, which means this will be a shared airspace enclosure. Honestly it's not something I would be too worried about.

"I could tilt the speaker baffles outward left and right, so that it has a wider angle, perhaps it would help the stereo effect if I wire it in stereo."

Depends on what you're going for. You can run into weird combing and lobing patterns if you keep the speakers close in proximity but on differing planes. Shouldn't matter much below ~200hz or so where the speakers are omnidirectional anyway, but at higher frequencies you could get some interesting effects. It would be pretty cool to have two separate enclosures that could be latched together as in you picture, but also pulled apart and placed in more of a stereo arrangement depending on how large the crowd is or the listening area.
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Old 08-25-2014, 04:09 AM
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I am using a full range amp, so the full 50hz-12khz+. Bridged parallel would gain me some watts, situation here is at rms the neopros are already at xmax at 2 frequency areas, 47hz and 90-110hz. I would probably blow the speakers if I go above rms. So no real problem losing some watts in this situation.

(Forgive me, its late, can't sleep, college starts again tomorrow. Halfway through typing this paragraph I self doubted my knowledge) The "other one would work" statement refers to, in a stereo wiring, If one speaker burns and fails to complete the circuit, the other speaker will still work because its path is still complete. Here is my self doubt, this is false in a single voice coil parallel setup correct?

You bring up shared airspace, the speakers only share part of the port. port starts 1 inch from airspace and combine in the center as a 2 inch port area. Or does this still mean shared airspace? Im not trying to be an ass, I genuinely want to know. If one speaker blows, the other one should react to the port difference more so like the port is a folded horn port design, since the port now goes 1 inch for half the port to 2 inches wide the rest of the way. (I mean I can put a separator in the center of the 2 inch port so each one has their own true space. each would have a 1 x13.5 slot port) Does it really matter? I have seen bass builds that use that port design, does it not work for full range?



Last edited by ylpkm; 08-25-2014 at 04:36 AM.
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Old 08-25-2014, 06:02 AM
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"this is false in a single voice coil parallel setup correct?"

Current will still flow as long as there's still path. Series wiring requires current to flow through each component before "moving on" to the next one, but parallel wiring doesn't need that, as each component is a separate "arm" that all see the same voltage from the circuit. The attached picture below might show it a little better, sorry it's kinda sh1tty, I spent like 3 minutes on it. these symbols: -/\/\- are resistors representing speakers in this case.

"the speakers only share part of the port. port starts 1 inch from airspace and combine in the center as a 2 inch port area. Or does this still mean shared airspace?

Don't think about each speaker seeing part of the port. The enclosure will always behave a certain way regardless of how many speakers or what type of speakers you have in it. The response of the speaker can be influenced by the enclosure it's in, but not the other way around. Consider this: let's say one of the speakers dies in your design. The other speaker continues to move, and as the air on one side of the enclosure is compressed and rarefied, it creates a sympathetic resonance with the air mass inside the port. That air mass, as it moves, then creates a sympathetic resonance with the opening into the side with the dead speaker. All areas of the enclosure are still being used. If you're unfamiliar with how ports work; it's in the same way as when you blow over the top of a bottle and hear a tone. It only requires a small amount of energy blowing over the top of the bottle opening (which you could consider the port opening) to make the air in the neck of the bottle rapidly move up and down, so it's that block of air in the neck of the bottle itself that's acting like a speaker.

"so like the port is a folded horn port design, since the port now goes 1 inch for half the port to 2 inches wide the rest of the way"

Even if we were to imagine that the other side of the enclosure was somehow blocked off, you would still be left with a much larger area of port with the same length, which would raise tuning - probably by a lot. Folded horns (and true transmission lines) use much more complicated impedance transform to produce their output than just expanding a vent, as there isn't a discrete definition of "port" areas and "enclosure" areas, its a continuous transform that requires a lot of math to get right, lol.

"I can put a separator in the center of the 2 inch port so each one has their own true space"

That would work to fully separate the two and make them independent. Unless you're really worried about blowing speakers, it's not required. I guess if you can add it in and it won't take much extra effort than it's worth it.

"Does it really matter? I have seen bass builds that use that port design, does it not work for full range?"

Nope, it should work well. At frequencies an octave or two above port tuning the speaker acts exactly the same as it would in a sealed enclosure.


More question from your edited post:

"Winisd predicts I hit about 5mm of excursion at about 100 hz and 47 hz. xmech is 11.5mm (right?) Its good that speakers ride at about xmax at rms right?"

Excursion in a sealed enclosure will grow larger and larger the lower in frequency you go. Theoretically, to maintain the same amplitude an octave lower than a certain frequency, you need 4x the excursion, so for example if you wanted the same SPL at 30hz and 60hz, and at 60hz the excursion was 5mm, you'd need 20mm of excursion at 30hz. Vented enclosures fix this by reducing excursion around the tuning frequency substantially (think back to the bottle example: it only requires a small amount of air movement over the top of the bottle to produce a loud tone from the air in the neck of the bottle). The downside is that the excursion characteristic when plotted by frequency is exactly what you are seeing: excursion shoots up right above and below tuning. That's usually a fair tradeoff though, as excursion is still much lower than a sealed enclosure given the same output. It's not generally a good idea to design for a lot of excursion, but unless you plan on listening to sine waves at full blast around those excursion peaks it's shouldn't be an issue. On music you'll be fine. Still, I highly recommend you use a high-pass filter no lower than 40hz to protect the speaker from bottoming out on low notes.

"Is that what the young kids call slammin at those frequencies?"

Lord I hope not.

"Idk whether I should tune lower. Tuning lower causes very close to xmech failure at 100 hz."

For those speakers: don't tune lower. You'll just loose output where it's actually important. Trying to play low bass from a couple (relatively) small speakers outdoors is like farting in the wind.

"and how much does port area affect excursion? in winisd the excursion doesnt change with port area change, I assume in real world it does affect it."

It doesn't, at least not in your scenario. Vents with too small an area can act as aperiodic dampers, and there's a good case for larger ports and especially flared ports with regards to increasing port efficiency, but for something like your project it won't be a major thing. You've got PLENTY of port area, you could probably reduce the area by half and shrink the port by the appropriate amount if you wanted to. Keep vent velocity below about 33m/s (100ft/sec) and you'll be fine. WinISD should graph vent velocity for you. If it doesn't make sure you have the "sd" parameter filled in in the TSP section. sd is radiating (cone) area.
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  #10  
Old 08-25-2014, 11:18 AM
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Thank you, very informative post. The amp does have a hpf and lpf, the speaker hits overexcursion at 45hz based on the Winisd prediction (without a roll off or filter), where should I set the HPF.

Winisd predicts I could set the HPF at 45hz (even if box is at 55) because I added the HPF in Winisd (4th order right because ported has 4th order roll off?)
Would that be safe to do? or should I play it safe and tune at 55.
The port velocity stays below 20m/s in my design.
Another question. Some songs rendered in stereo have something in one channel that isnt as profound in the other (or even there). So if I choose to wire it in stereo without the port separator, would I technically be stressing the speakers whenever the stereo effect actually happened? Like say vocals were only on the right side for part of the song (just as an example). Or does it not matter since only low bass is the only thing that would be mainly causing the port velocity and/or usually low bass is uniform across stereo files correct?

Last edited by ylpkm; 08-25-2014 at 11:23 AM.
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