Subwoofer question

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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.
 

kelticwizard

diyAudio Moderator Emeritus
2001-09-18 2:33 am
Connecticut, The Nutmeg State
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.
 

kelticwizard

diyAudio Moderator Emeritus
2001-09-18 2:33 am
Connecticut, The Nutmeg State
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.
 
a few questions...

hey kelticwizard,
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?
 

kelticwizard

diyAudio Moderator Emeritus
2001-09-18 2:33 am
Connecticut, The Nutmeg State
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?
 
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
 

kelticwizard

diyAudio Moderator Emeritus
2001-09-18 2:33 am
Connecticut, The Nutmeg State
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.
 
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
 
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!
 
hey

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.
 

kelticwizard

diyAudio Moderator Emeritus
2001-09-18 2:33 am
Connecticut, The Nutmeg State
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.
 
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
 

kelticwizard

diyAudio Moderator Emeritus
2001-09-18 2:33 am
Connecticut, The Nutmeg State
Javaman said:

Did you like the 2 cubic foot box for it's smoother rolloff, rather that something smaller?

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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