porting mid-bass question on port size
- Thread starter 2004alpinewhite
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- #2
By the way I'm going to be band-passing the driver between 100-300/350 hz... So possibly a higher frequency? I dont know much about ports.. thanks!
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- #3
Or is the point to find my enclosure size when its all said and done, then calculate the port size that will yield me the same frequency as the one shown in the specs?
helotaxi
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Kilroy was Here
If you're planning on crossing it with a high pass at 100hz (WAY too high IMO) then don't even bother to port it. You're wasting the extended low end output that a ported setup would afford you. Additionally if you can't get at least that amount of airspace, don't try ported. The results would be disappointing at best.
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- #5
How is 100 hz too high for a mid-bass driver? My sub will be low-passed at 100.. Anything below 100hz isn't audibly locatable. It won't pull away from the front stage at all as long as its below 100hz and not overpowered. I am just trying to get all of the mid-bass up front instead of coming from the rear. If I go sealed, this isn't exactly possible..
And why do you think that anything less than that is soo small? I mean, its only a 6.5" driver.. Its recommended airspace for ported design is .6. It could obviously get by on just slightly less.. We're talking like .5 cubes for a 6.5..
Another question.. I have always heard that if you take an mdf box and line the inside of it with fiberglass that it effectively increases the airspace inside the chamber. Even though its not physical, the box performs as if it was larger.. Is there any rationale behind this at all? If so, then if the dimensions were meant for a mdf box, could I not get by with slightly less?
On the same tangent.. What qualities to different materials actually produce? Say, for instance, you can have just mdf with silicone, or mdf lined with fiberglass, possibly lined on top of that with sound deadener, and then fiber fill on top of that! What is the real difference? It seems that by packing more and more into a box you're only decreasing the airspace, so how do they help? And in what ways?
helotaxi
5,000+ posts
Kilroy was Here
If you want the soundstage as good as it can be, lower is better on the frequency division between the midbass and the sub. Ideally the subs would be crossed below 60hz. If you look at the response graph for those mids in the ported box, they'll play flat down to below 50hz. If they'll do it it'd be dumb not to use it. If you go with a smaller box the sound will end up muddy, not what you want from the midbasses at all. Sealed will work just fine with those mids, I know, I used them for 3 years in rather small sealed pods crossed at 63hz. The midbass response was terrific.
The reason for lining the box with fiberglass is to kill standing waves. Stuffing it with polyfill makes it act slightly bigger. Works best with sealed boxes.
Box material isn't that important. The mounting baffle needs to be solid. The box should flex as little a possible. With a mid, the forces involved aren't that high. My pods are 3 or 4 layers of fiberglass mat over the knit cloth that I used to shape the pod. No ringing. No flexing. You don't need to make it out of MDF.
The reason for lining the box with fiberglass is to kill standing waves. Stuffing it with polyfill makes it act slightly bigger. Works best with sealed boxes.
Box material isn't that important. The mounting baffle needs to be solid. The box should flex as little a possible. With a mid, the forces involved aren't that high. My pods are 3 or 4 layers of fiberglass mat over the knit cloth that I used to shape the pod. No ringing. No flexing. You don't need to make it out of MDF.
^^^He is exactly correct.
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- #8
Ok, well I will definately mess with the crossover points once I get it all installed to see how it all sounds, but it does make sense that the more of the music that's up front the better the staging will be. When I used this driver in my last vehicle it was in a door enclosure. It was deadened and the driver was mounted firmly in metal. I really wasn't happy with the low response.. I suppose that the crossover they sent with it may have affected the output though..
If I do go with the ported box and try to get it lower than 100hz, is there any way to pre-determine approximately how the driver will react with a specific box size and port? In other words, if I only get .5 but use polyfill and a port tuned to 50hz, how can I know what to expect from the driver? I know I could probably get the full .6 cubes if I start doing cutting and building further into the door, but if its at all avoidable then I'd really like to avoid it..
If I do go with the ported box and try to get it lower than 100hz, is there any way to pre-determine approximately how the driver will react with a specific box size and port? In other words, if I only get .5 but use polyfill and a port tuned to 50hz, how can I know what to expect from the driver? I know I could probably get the full .6 cubes if I start doing cutting and building further into the door, but if its at all avoidable then I'd really like to avoid it..
helotaxi
5,000+ posts
Kilroy was Here
I'm just curious why you are so set on going with a ported setup. The driver will play plenty low and give you the same output sealed and do it in a smaller box. Space is an issue and sealed will sound better, too.
The next thing that you have to worry about if you try to go smaller, other than it won't sound right, is to get the same tuning in a smaller box, you need a bigger port which means the box is smaller still and needs an even bigger port. By the time you get it all sorted you're going to be looking at a tiny box that is horribly wrong for the driver. If you can't give it the space it needs to properly port it, go with sealed. They really do sound good sealed.
The next thing that you have to worry about if you try to go smaller, other than it won't sound right, is to get the same tuning in a smaller box, you need a bigger port which means the box is smaller still and needs an even bigger port. By the time you get it all sorted you're going to be looking at a tiny box that is horribly wrong for the driver. If you can't give it the space it needs to properly port it, go with sealed. They really do sound good sealed.
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- #10
Well, the recommended sealed enclosure is .3 cubes. Would it be even more beneficial to have a larger sealed enclosure? If so, how can I figure out the ideal volume to go with. I have the capability to get like .5 cubes very easily. How can I estimate what size enclosure will give me certain advantages on the sound curve?
More quick questions. If size wasn't the option at all and you had the option to go with a .3 cub sealed box and a .6 ported box made to perfect specs, which would you go with and why? Do you really think the sound produced by the driver would be incredibly higher quality in a sealed enclosure? Also, if going with the sealed enclosure, would I probably need to pass it a little higher and take a little more upper range out of the sub?
Cross over the lower the better.
Lower frequencies definitely ARE localizable for a number of reason, not the least of which are harmonics, vibrations and simple overpowering volume.
I can make my sub seem to disappear with my midbass when crossed over properly between the two as low as 40Hz. However, if I run my subs up higher, over 63 or 80Hz for instance, they definitely are more localizable.
You really should consider (IMO) crossing your midbass lower... the up-front bass will be much nicer, kickdrums in the chest, not the back, etc.
Just my opinion, but I LOVE having my midbass crossed as low as possible, and in fact, I'm currently running them without a HPF at all! And at 300W RMS per driver!
Lower frequencies definitely ARE localizable for a number of reason, not the least of which are harmonics, vibrations and simple overpowering volume.
I can make my sub seem to disappear with my midbass when crossed over properly between the two as low as 40Hz. However, if I run my subs up higher, over 63 or 80Hz for instance, they definitely are more localizable.
You really should consider (IMO) crossing your midbass lower... the up-front bass will be much nicer, kickdrums in the chest, not the back, etc.
Just my opinion, but I LOVE having my midbass crossed as low as possible, and in fact, I'm currently running them without a HPF at all! And at 300W RMS per driver!
- Thread Starter
- #12
Well what size sealed enclosure would be good for actually trying to produce notes that low properly? I really don't think a .3 cub enclosure is going to produce the low end that I'm looking for? I mean I could be wrong, but can anyone tell me how large or small would be recommendable for a driver with these specs? Is there even any way of knowing?
helotaxi
5,000+ posts
Kilroy was Here
The .3 will work fine. I never measured mine but I'm pretty sure that they're smaller than that.
- Thread Starter
- #14
That's not the question. The question is: Is it possible to estimate the possible gains from larger airspace? Also, I have already started construction of the box. It was originally meant to be ported, so its already got lots of airspace. So is there a certain level where the larger the volume, the worse the sound? How do I find that level, if it exists?
There is a free box design program called WinISD that will help you model a driver's performance in various sized enclosures. I think it's linearteam.org or something like that.
However, I would simply email CDT and see if you can get some tech help on the issue. I am not telling you that you need to go with sealed and shouldn't port them... in fact, I think porting would be a great thing for midbass drivers, provided you have a good enough high-pass filter on them. I've considered it for mine.
From what you've said, though, worrying about "low end" performance seems a bit... odd to me when you're planning on crossing them over at 100Hz. There is no low end above 100Hz.
If you can get .45 or .5 cubes of airspace, then you can still get those things tuned down to 60 or 70 Hz easily, I would assume, and believe me, that is WORLDS better than crossing several-hundred dollar components at 100Hz. Ugh.
Up-front bass FTMFW!
The .3 sealed box response on that .pdf is probably gonna get a bit of a low-end bump from the car's cabin gain, son don't look at that graph and think it's automatically gonna be wimpy below 100Hz, where it begins to roll off. You could very well go with a .3-.4 sealed box and have those things HAMMERING at 80 or even 60Hz. You might be really really surprised....
What kind of power are you going to be running to these? I assume you're going 3-way active front, since you're only running them up to 350Hz?
Email CDT and tell 'em your dilemma... not QUITE enough airspace for 50Hz tuning, but still want to port. //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif
Seriously, though, let me know how they work out in these enclosures, I've got a buddy with these exact drivers who is wanting to build enclosures for his, wondering how they're going to sound. Your experiences could be greatly motivating to him. //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif
However, I would simply email CDT and see if you can get some tech help on the issue. I am not telling you that you need to go with sealed and shouldn't port them... in fact, I think porting would be a great thing for midbass drivers, provided you have a good enough high-pass filter on them. I've considered it for mine.
From what you've said, though, worrying about "low end" performance seems a bit... odd to me when you're planning on crossing them over at 100Hz. There is no low end above 100Hz.
If you can get .45 or .5 cubes of airspace, then you can still get those things tuned down to 60 or 70 Hz easily, I would assume, and believe me, that is WORLDS better than crossing several-hundred dollar components at 100Hz. Ugh.
Up-front bass FTMFW!
The .3 sealed box response on that .pdf is probably gonna get a bit of a low-end bump from the car's cabin gain, son don't look at that graph and think it's automatically gonna be wimpy below 100Hz, where it begins to roll off. You could very well go with a .3-.4 sealed box and have those things HAMMERING at 80 or even 60Hz. You might be really really surprised....
What kind of power are you going to be running to these? I assume you're going 3-way active front, since you're only running them up to 350Hz?
Email CDT and tell 'em your dilemma... not QUITE enough airspace for 50Hz tuning, but still want to port. //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif
Seriously, though, let me know how they work out in these enclosures, I've got a buddy with these exact drivers who is wanting to build enclosures for his, wondering how they're going to sound. Your experiences could be greatly motivating to him. //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif
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