| MisterB |
I want to build a subwoofer but was wondering wich design is the best :
- Down Firing or Front Firing.
And :
- Sealed or Vented.
I will by a plate amp (like the one at PE) from my local store.
It will be drived by a 10" driver.
Thanks for suggestions.
MisterB |
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| Super |
There is no way to say that either sealed or vented is "best", each has its tradeoffs. A lot of it depends on the parameters of that driver.
Some speakers that arent designed to be downfiring can actually become damaged over time due to "cone sag". If you aren't sure that the driver has a suspension designed to be used in a down firing configuration, make it front firing. |
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| kelticwizard |
Sealed versus Vented? A little background.
Making deep, forceful bass is all about moving air. The deeper the frequency, the more air must be moved. At the same volume level, a loudspeaker has to move FOUR times, (not two times), as much air 20 Hz. as it has to move at 40 Hz. 40 Hz. is one octave higher than 20 Hz.
The amount of air a loudspeaker can move is determined by the area of it's cone times the length of it's back-and-forth movement, (cone excursion). Many of the new 10" subwoofers, for instance, can move more air than the 12" AND 15" woofers of years past because they have much greater cone excursion, even though the 10" obviously has less cone area.
In the lowest octave that the loudspeaker has to play, there is a significant difference in the behavior of the sealed system versus the cone system. If the sealed box and the ported box are both expected to play down to 20 Hz, at 40 Hz there will be a remarkable phenomenon begin to occur.
If we run a signal generator down the tones from 40 Hz on down to 20 Hz, we will see the sealed box move back-and-forth to a greater degree. The lower we go, the more the sealed system has to increase it's back-and-forth motion. At stated previously, at 20 Hz it needs to have FOUR times the back-and-forth movement that it does at 40 Hz.
The ported system? Different story. As we run the test tones down from 40 Hz to 20 Hz, we see that that the ported system does NOT require any greater back-and-forth movement at all. At 20 Hz, the cone of the ported system will NOT need to travel any more than it did at 40 Hz. Why? The port of the ported system tunes the air in the box to a certain frequency. At frequencies within an octave of that tuning frequency, the air in the box is conditioned to react to just a little excitation by the loudspeaker cone. So to speak, the air in the ported box is more "sensitive" to excitation by the cone than the air in the sealed box. This phenomenon only last for the octave above the tuning frequency.
For the lowest octave, where air moving ability is needed the most, the following equivalents are true. Assuming both the sealed and ported systems are set up correctly:
1) A 10" speaker in a ported box is equivalent to a 20" inch speaker, (with equal cone excursion), in a sealed box.
2) A 10" speaker in a ported box is equivalent four 10 inch speakers of equal cone excursion in a sealed box.
3) A 10" speaker in a ported box is equal to a 10" speaker of four times it's cone excursion in a sealed box. So if you have a 10" speaker with a half inch cone excursion, any 10" speaker with a cone excursion than 1/8"-a piddling amount-will produce more bass.
Normally, for any given enclosure volume, you will require a different woofer for a sealed system than you will for a ported enclosure. The "Thiele-Small parameters"-important electrical measurements-will have to be different. Speakers are available that are suitable for either enclosure type for just about any box volume. |
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| kelticwizard |
Why then, do we have such things as sealed box subwoofers?
First, the fact that the lowest frequencies come out the port of the vented speaker means that there is a slight delay in the delivery of those frequencies into the room. Many speaker enthusiasts feel that this muddies the bass.
If you examine the output of a single pulse for both systems, it becomes clear that the sealed system has a slightly cleaner response than the vented. It has been illustrated that at the lowest frequencies, the ear is less sensitive to this situation than at midrange frequencies-that is why there is no such thing as a vented midrange speaker. Nonetheless, it is undeniable that the sealed system produces a snappier response on the chart. Whether you can hear it or not is a matter of individual ability.
Also, deep bass requires large enclosures. A Dayton 12" subwoofer, for instance, requires a 10 cu. foot enclosure to go flat down to 16 Hz. Some owners consider this size impractically large. So they put the speaker in a smaller box. This reduces the amount of volume output possible in the lowest octave. Reduced volume output in the lowest octave requires less air being moved. With less air being required to be moved, the speakers in the sealed boxes can handle it. The speakers in the closed box could not handle the bass outputs that would be possible in a larger box.
It should be noted that some high quality subwoofer manufactuers, such as REL, have both sealed and vented models in their best line of subwoofers.
If all this sounds complicated, maybe the best thing to do is to tell us what size you plan to make your subwoofer box, what subwoofer speakers you have your eye on and the people on the forum can explain your choices to you. Have you downloaded a loudspeaker program yet?
Oh, yes, I thought I would just mention that Super is right about up/down versus front firing. The long excursions of today's subwoofers make it necessary to make certain that the manufacturer says up or down firing is possible. |
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| Andrew Steele |
hey kelticwizard,| quote: | | At 20 Hz, the cone of the ported system will NOT need to travel any more than it did at 40 Hz. Why? The port of the ported system tunes the air in the box to a certain frequency. At frequencies within an octave of that tuning frequency, the air in the box is conditioned to react to just a little excitation by the loudspeaker cone. |
you mentioned an octave above the tuning frequency the excursion of the woofer will not be any greater than the start of the octave, ok, so what happens below the tuning frequency? I know that below the tuning frequency, excursion becomes uncontrolled, I am just wondering If there was any certain rate of increase of excursion, just looking at it all I would take a wild guess at x8 but I may be wrong....
Also, what about resonant frequency, is it bad to tune a box to below the woofers Fs? if so, how does it affect it? |
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| kelticwizard |
Andrew:
More about the excursion below Fb later.
As to the question of tuning a box below the speaker's free air resonance, the answer is yes, you can do it. In fact, Thiele came out with a whole list of alignments that do just that. For various reasons, it is somewhat more desirable to find a speaker with an Fs that is below or at the desired lowest frequency we want the speaker to play, but we are not speaker manufacturers and cannot get drivers custom made for our enclosure needs, can we? We have to go with what is available. Fortunately there are a lot of drivers available.
If possible, try not to make the Fb too far below the speaker's Fs. If you have driver with an Fs of 30 Hz, a Qts of .4, and a Vas of 2 cubic feet, and you put it in a box with a VB of 2 cubic feet and tune it to 21 Hz, then the response will be 9 dB down at 21 Hz, and the entire bass will droop. You will need a big amp to make up the difference, but it is one way to get big bass from a comparatively small box. Forget about getting anything beneath 21 Hz on this speaker-big dropoff.
If I increase the Vb on this speaker to 3 cu feet, I will be 6 dB down at 21 Hz and my bass will droop a lot less.
If you are going to increase your box volume over Vas, and tune your box to below Fs, ideally your Qts should be above .4. but you can get away with anything being slightly off in ported boxes if it is not too severe.
If I had my druthers, I druther have my speaker's Fs at or below my box Fb. But I would not abandon a project if I could not find a speaker to fit that requirement.
Have you downloaded a speaker design program? Test it and see what curves you get.
By the way, do you have anything specific in mind? |
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| Javaman |
kelticwizard
I guess I'll jump in here with a couple of design options I've been considering - perhaps they could be used for discussion or illustration.
Both are suggested alignments from Parts Express:
1.) Dayton MKII 10 inch - 1.4 cubic foot EBS tuned to 25 Hz - anechoic F3 bout 28
2.) Dayton MKII 12 inch - 2.0 foot sealed - thinking I'd EQ round 20-25Hz maybe as much a 5-6 dB
I am dealing with the all important SAF here, so my options are limited and musical fidelity is paramount to me, but I do want some serious low end.
Seems based on modeling with WinISD that #1 is more of a gentle rolloff ported design that a real EBS. Does anyone have opinions of the relative performance for these two designs??
thanks
peter |
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| SsZERO |
Quick question here:
I built an enclosure from a design originally meant for a downfiring setup...will there be any problem if I simply lay the box on its side for a front firing setup? I would rather lay it sideways, because it fits better in my room that way. Also, I want to be able to see the sub. It looks cool. :)
-= SsZERO =- |
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| Super |
| As long as no ports are blocked and it isnt in danger of tipping, theres no problem in turning it on its side. Go for it. |
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| SsZERO |
Cool! I asked this before, but I didn't fully understand about wiring the voice coils in parallel. I have two leads from the amp, + and -, would I split each lead into 2, like with a y-cable, then attach two + to each + connector on the sub and the 2 - to each -connector?
-= SsZERO =- |
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| Andrew Steele |
| what impedance is each coil, because if each coil is 4 ohms, wiring them in paralel would make a load of 2 ohms, and this is too low for most home amps. but if theyre 8 ohm coils, that will be cool, as it will present a 4 ohm load to the amp. and by the way, the way you said you'd wire it above ^^^ is correct. |
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| kelticwizard |
Javaman:
I haven't forgotten you. I have been meaning to answer you since the other thread. I think I have another subwoofer that gives better performance in a 1.4 cu ft or 2.0 cu ft box than the Dayton Titanic 10. It's the Peerless XLS 10 inch tuned to 25 in a 1.4 cu ft box or 22 in a 2.0 cu ft box.
www.peerless.dk
The delay is that I have difficulty getting Boxplot's graphs to get into an image format that this forum can print. Working on it. Will be back.
Peerless is sold by Madisound and I think Parts Express has started carrying them. About the same price as the Titanic, I think. |
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| kelticwizard |
Looks like I wrote too soon. I was dealing with the old Titan. The Titan II is down 3 dB at 27 Hz and 5 dB at 25 Hz when tuned to 25 Hz. This is excellent performance.
In a 2 cubic foot box, the performance is even better. The 12 inch would have too high a cutoff in a 2 cubic foot box, I think. |
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| Javaman |
Many thanks kelticwizard
I had looked at the Peerless - in fact I build a sat/sub setup many years ago using their CC line drivers for the mid and a Madisound
1250 (I think it was) in a huge sub box. Didn't sound half bad for a first effort. Anyhow I digress......
The Titanic 12 MKII in the 2ft^3 sealed does rolloff early ( F3 at around 38Hz) but I was hoping with some fairly aggressive EQ boost, say 5-6dB round 22-25Hz, I could get some serious bass and still have all the inherent advantages of a sealed design. What do you think? I know, I know no free lunch........
My application is primarily music and this is why I was also attracted to the EBS alignment. It looked like a smoother rolloff than most ported designs for a nice blend with some room gain and still met the <= 2ft^3 box limitation. Would it be wise to use any EQ with this type of design?
Also I noticed Peerless has a small PR alignment in their 10 inch XLS docs that seems to go really low but I am a little reticent to use a PR design for a music application. Do you think is would sound good? I am afraid it would be a little tricky to tune just right.
adios
peter |
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| Javaman |
I lied. It's the Peerless XLS 12 inch application notes that detail a 35 liter box tuned to 20Hz with 625g on a passive radiator. Their sim. with BassBox Pro (sounds like a fishing program to me) shows an F3 around 25. I don't get anything remotely like that using plain old WinISD.
Is a PR simulation that much different from a regular vent?
I'd fire up the table saw tonight if I really felt I could get that kind of performance from such a small box and have good musicality as well.
Don't PR designs have the worst transient response and worst group delay? And how much does it matter?? I can't think of any high-end products that use PRs.
Geez I've gone all the way around the horn and I am back to the basic "what's the best 2ft^3 sub I can build?" question again! Help! |
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| Andrew Steele |
I like using BassBox Pro, its a good program, and no, there are no fishing simulations in there...
Simulating in BassBox Pro the Peerless XLS 12 8ohm with the matching passive radiator does indeed show that group delay is all over the place, it actually looks worse than any ported group delay I've seen...
You may be right Javaman, but I have not had any real experience with passive radiators. |
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| kelticwizard |
Javaman:
Have not built passive radiators. Essentially they are "vent substitutes". They should sound similar to vents.
Any difference with "drone cones"and vented systems is possibly due to the fact that the drone cone itself has a resonance, and this resonance detracts, not adds to the bass output of the speaker, forcing it to roll off at a greater slope. Looking at some charts, it seems that the slope of the effect of the passive radiator tuning starts about an octave and a half below the tuning frequency of the system, or Fb. So if your drone cone resonance, (as opposed to your enclosure resonance, or Fb), is 2 octaves below Fb, there probably should be no effect worth worrying about.
The Peerless drone cones are tuned to 6 Hz, I believe, and adding mass to them should tune them even lower. After, all, adding mass to a normal loudspeaker cone lowers it's resonance frequency, so this should be the same. This might be why Peerless tirelessly promotes these drone cones to go with their XLS systems.
I should add that Pioneer makes a drone cone that is very inexpensive. It is just Styrofoam with a foam surround attached to the frame. Theoretically, this should be all you need in a passive radiator, but web sites have stated that drone cones with a spider are superior. Why, I don't know. Maybe it has something to do with the weight-drone cones can get fairly heavy if you use more than one and you want to tune low.
Normally a 10 inch speaker is fine with a 3 inch vent, but the Dayton and Peerless XLS are not ordinary 10 inch speakers. If you want to go to a 4 inch diameter vent, it will be about 32 inches to tune at 2 cu ft box to 22 Hz or a 1.4 cu ft box to 25 Hz. Both vents take up less than a quarter of a cubic foot . You might wish to negotiate your size limits up slightly to accommodate.
Madisound sells 3 inch ports, flared at both ends, which should bring the vent volume down to less than 10% of box volume, yielding a negligible increase in Fb. A flared pipe is equivalent to a larger pipe, unflared. Apparently, from what I can see, the flared ports are designed to fit over a straight piece of PVC pipe.
If you use a 4", at 30+ inches, you will most likely want to use an elbow, easily obtained from building supply stores. If you use the flared 3" pipe, it will be shorter.
If I were building it, I would go with the Dayton Titanic 10 inch Mark II in a 2 cubic foot box. If it is already established that you can go to 2 cubic feet for a 12 inch, it seems to me that you ought to be able to go that high for a 10 inch.
For a long time, a .25 inch throw, either way was considered a very long throw woofer. With more than .5 inch excursion, the Dayton or Peerless really is equivalent to an old 15 inch, only with cubic foot requirements equivalent to a regular 10 inch. If these speakers can do that, the least you can do is give them a LITTLE extra room, LOL.
I am obviously not in a position to know your space requirements. But going down to the low twenties in a 2 cubic foot box is quite an accomplishment, in my opinion.
Let me know how this turns out.
There is another possiblity. The Blueprint 1001. The webpage is down, but you can Email for specs. As I recall, it had specs similar to the Dayton, but it cost only 79 bucks. At least that was the old price. The Email address is:www.blueprintdrivers@hotmail.com. Blueprint invites inquiries.
Hope to hear from you soon. |
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| MisterB |
Well.. Tanks for all the answers and informations...!!!
You guys know a lot more than me!!
So I think I will do a front firing sub, vented.
I will let you know when the project will be on his way.
MisterB |
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| Javaman |
kelticwizard
I thinks I'll take you advice and go with a ported Titan 10 inch design, thanks.
Did you like the 2 cubic foot box for it's smoother rolloff, rather that something smaller?
Also I was also wondering about the port diameter. Seems Unibox recommends an air speed < mach .08 while WinISD and older programs seem to draw the line at around .16. Who's being too conservative/optimistic?
Using the .16 number I could get away with shortening the Madisound 3 inch flared port. With the 17 inch long 4 inch port I'd be splicing in some extra length and I am sure the interior would end up with ridges. Wouldn't this cause turbulence and noise?
Thanks again for your help.
regards
peter |
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| kelticwizard |
| quote: | Originally posted by Javaman
Did you like the 2 cubic foot box for it's smoother rolloff, rather that something smaller?
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I like the 2 cubic foot box for a couple of reasons.
Sometime during the eighties, an article was published in the Journal of the Audio Engineering Society where all the bass content of videotapes and CD's were analyzed in an exhaustive search to find the lowest notes your subwoofer would actually have to play. All of the lowest notes were on CD's, (the present-day DVD might change that, I don't know), and it was found that there were only FIVE CD's that had usable bass content below 16 Hz.
Unless you are a millionaire building a room specially designed for music listening, it makes little sense to design your system to cover the 5 CD's out there-somewhere-that might actually use it's capabilities. So, 16 Hz is the sensible goal.
And what kind of subwoofers actually can go down to 16 Hz? Big ones. With big price tags. That take up a LOT of space in your listening room, and leave a lot of empty space in your bank account. Four, five cubic feet or more, that cost thousands of dollars. That is what kind of subwoofer is 3 dB down at 16 Hz.
In a 2 cubic foot box, the Titanic 10 Mk II, assuming the numbers are correct, will be 3 dB down at 23 Hz. That is only half an octave above 16 Hz, (the sensible goal for even a shoot-the-moon subwoofer). And it accomplishes this in a "standard" 2 cubic foot box.
A "standard" 2 cubic foot box? Well, I have been following audio since the seventies, and even at that time, the normal size for a "full-size" speaker was 2 cubic feet. Advents, AR's, and a host of others. It seems that early on, designers discovered that 2 cubic feet was the best combo of enclosure volume and unobtrusiveness. And people had 2 of those speakers per room, not one. Those speakers did not go down to 30 Hz, let alone 23 Hz.
Here, you have the capability of generating bass only a bit behind the best subwoofers out there, in a box size that for decades has been considered "standard", even for 2 units in a room. If you go to the 1.4 cu ft box, your 3 dB down point will just nudge below 30 Hz, which is very good. But there are a lot of speakers out there now that go down to 30 Hz, albeit in bigger boxes. There really aren't that many that go down to 23 Hz.
Heck, it's your place, it's up to you to decide what is visually acceptable and what is not. But since you asked, those are my thoughts on the matter. |
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| kelticwizard |
A couple of more things. Parts Express website has a Titanic 10 Mk II White Paper. In that White Paper, they recommend a port size of 3". This is for an unflared port size. Flared ports give better performance, that is why people bother with them. If the manufacturer says the unflared is acceptable, I would think that a flared 3" port gives you an extra margin of safety.
I personally have never used flared ports, so I could not tell you absolutely how to fit them over 3" PVC pipe. Madisound sells them, and they have a tech line. So you might want to give them a holler just to make sure. From the picture, it looks like a straightforward fit. You might want to put a brace on the interior of the box to anchor the port inside. You might find a muffler clamp handy for this.
The White Paper also says that the Titanic 10 can be used in a downward firing sub. It says the suspension can handle it. Myself, I don't like the idea, since you are putting an extra weight on the suspension for every minute of every day. Seems to me, sooner or later that is bound to take it's toll. But I am not an engineer, and the people at Parts Express are, and they say, "Go ahead".
Also on the White Paper, Parts Express provides a chart of the Titanic 10 Mk II's free air, (unenclosed), response. Subwoofer crossovers routinely go up to perhaps 200 Hz. Not this one. It has a natural 6 dB/octave rolloff after 80 Hz. An interesting point is that if you wanted to hook this up on a passive crossover, (which I am sure you are not), all you would have to do would be to add a choke in series to get a 12 dB/octave filter. Anyway, I enclose the response graph. Boy, they really DID intend this thing only for subwoofer use!
Let us know what you decide size-wise and otherwise. Good luck!! |
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| Javaman |
Kelticwizard
2 foot size looks like just the ticket. I am going to post a question to Parts Express about the 3 inch ports. Unibox predicts the air speed going way over their .08 threshold starting at about 29 Hz and going straight up from there. I would hate to have this puppy start whistling at every crescendo - but if I could use a 3 incher, then by coincidence the Madisound flare is almost exactly the correct length. I'll let you know what they say.
adios |
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| Javaman |
Contacted PE about the 3'' VS 4'' ports and they replied more or less: "Gee I guess 4 would be better but then it gets too long...."
However I did find an interesting article by Dick Pierce from Speaker Builder posted on the Adire site. It was mostly about when ports are too BIG but near the end he addresses the too small question:
"At the other end of the limit-consideration of the minimum diameter-I suggest that things are not as neat and tidy as some of the literature might suggest. Usually, as mentioned, the criteria used is to limit the particle velocity to some small fraction of the speed of sound to limit potential nonlinear motion. However, I don't recall either a rigid theoretical study nor careful measurements confirming the existence and magnitude of these suggested effects.
Further, the maximum particle velocity will occur for a given SPL only at the Helmholtz resonance Fb, and is reduced on either side of that. It is at Fb, remember, where the port is producing most of the system's acoustical output, and the output from the driver is at a minimum. Outside of the range of Fb, more and more of the system's output is from the woofer, and less from the port. Rest assured that the nonlinear behavior of even the best woofers is far worse than all but the tiniest of ports at the kinds of sound pressure levels where the port velocity might be an issue."
If I read this correctly he's saying don't sweat it about small ports unless they are really small and besides no one has done a real study of port air mach speeds anyway.
Also their is a thread here about port sizing and someone makes the point that when ports are too long the acoustic mass of the air in the port takes on a life of its own causing (phase?) problems.
So when is the port size too small and what is a 'chuff' anyhow???
regards
peter |
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| kelticwizard |
Javaman:
"Chuffing" is the sound of air coming out of a port that is too small, but not so small as to manufacture whistling. If the woofer is big enough, and the port small enough, I have read that the port acoustically closes down completely. It has to be pretty small to do that, though.
Much of what was written in your quote makes sense. Since I am not engineer, I did not want to contradict a simulation program, but I WAS wondering how, if high air velocity is caused by trying to squeeze a large amount of air through a port, the velocity of air could rise as the output of air coming through the port is falling-which it certainly does in a properly tuned box as you move away from the tuning frequency.
For this reason, I like to go by "rules of thumb" and general judgment. For most 10 inchers, a 3 inch port works fine, for 15 inchers, go to a 4 inch port. The Titanic 10s move as much air as many a "long throw" 15 incher, however, so the larger port would be indicated. I figured the flared 3 inch port would approximate a 4 inch port, but I have no evidence this is so. Various audio reviews have stated that systems that use flared ports exhibit less port noise than you would expect from a port of a given size, I know that much. Thomas W, in his 6 cu ft enclosure for a Blueprint 1503-a driver with a 2 inch front-to-back excursion-said to use a flared 6 inch ports or unflared 8 inch port, which would tend to indicate an equivalence of sorts. So the flares must actually work.
One possibility is, since the port can be anywhere on the box, put the port pointing toward the wall and down to the floor. Since the unwanted noise is higher in frequency than the wanted port output, by the time it gets done bouncing around the walls, absorbed by any caprpeting and comes to the listener, it will be reduced in volume. The higher the frequency, the more it gets reduced by bending and stuffing material, such as rugs.
After all this, would you still feel more comfortable with a 4" port? Okay, the volume of the 3" port of 17.5" length, (what is required to tune a 2 cu ft box to 22 Hz), is 1/13th of a cubic foot-virtually negligible. The volume of a 4" port of 32" length is .23 cu ft. Not entirely negligible.
At 22 or 23 Hz, instead of being 3 dB down, the output will be 4.5 dB down. It is up to you to decide if that is acceptable. Personally, I don't think that is so bad. However, if you don't like it, you can:
A) Retune to 24 or 25 Hz-you will be 3dB down there)
B) Compensate for the difference in the design. It won't take much. If your box was going to have internal-not outside- measurements of 12" square by 24" high, then the new box will have internal measurements of 13" square by 24" high. Is this acceptable?
One more thing. We have been playing with numbers on this thread as if they written in stone. Take 1.5 dB here, add 2 dB there, etc. These are really just general guides. Even good quality manufactuers sometimes exagerrate the specs a little. It has been my experience that if you use good quality manufacturers and build a good strong box, the yield should be somewhere in the ballpark. I can't gurantee anything. To which I would add that the space occupied by the speaker itself is usually negligible, but might not be in this case-the Titanic looks big. But I still think you are going to be happy at the bass you get coming out of this box. |
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