I'm designing a sub around the Dayton 12" Titanic MKII driver (pretty popular it seems) and after modeling a few enclosures with WinISD I immediately decided on a vented enclosure because of the higher SPLs at low (~20Hz) frequencies. I've been thinking about the design more and realized I wasn't taking into account the room gain (which apparently is pretty substantial with subwoofers). If the room gain is high enough at the lower frequencies I may be able to use a sealed enclosure to get pretty flat response all the way to 20Hz. Here are my 2 questions:
1) How do I calculate room gain for my particular room?
and
2) I've heard that a sealed enclosure provides better (read cleaner?) bass than a vented enclosure. How does the sound that a sealed enclosure produces differ from a vented enclosure?
1) How do I calculate room gain for my particular room?
and
2) I've heard that a sealed enclosure provides better (read cleaner?) bass than a vented enclosure. How does the sound that a sealed enclosure produces differ from a vented enclosure?
Room gain is more due to boundary effects than room dimensions, which means that placement near a wall or in a corner can get you an additional 6 to 8dB on average irrespective of room size. Larger rooms can result in stronger positive nodes but also require higher SPL to achieve room compression, so the two tend to be a wash.
There are two reasons for the difference in sound. First, below the F3 a sealed box rolls off at 12dB/octave, a vented box at 24dB/octave, so the sealed has a potential advantage for the lowest frequency extension. However, if the F3 is at, say, 20 Hz, the 12dB difference between the two at 10Hz won't matter much anyway. From the same driver you can get to the same F3 in a sealed or VB, but the sealed box will have to be larger.
The other factor is restorative force, which the compressed air mass within a sealed box is more effective at controlling cone motion than a vented box. This generally makes for a cleaner sound.
Bottom line is that you can take advantage of the vented box properties to get a smaller box or get a somewhat cleaner sound from a sealed box but it will have to be larger to match the F3 of a VB.
There are two reasons for the difference in sound. First, below the F3 a sealed box rolls off at 12dB/octave, a vented box at 24dB/octave, so the sealed has a potential advantage for the lowest frequency extension. However, if the F3 is at, say, 20 Hz, the 12dB difference between the two at 10Hz won't matter much anyway. From the same driver you can get to the same F3 in a sealed or VB, but the sealed box will have to be larger.
The other factor is restorative force, which the compressed air mass within a sealed box is more effective at controlling cone motion than a vented box. This generally makes for a cleaner sound.
Bottom line is that you can take advantage of the vented box properties to get a smaller box or get a somewhat cleaner sound from a sealed box but it will have to be larger to match the F3 of a VB.
Well BF doesn't mention you can get an F3 in a larger box than
sealed way below the possibiliities of any sealed alignment.
And generally for a particular driver reflex needs a bigger
box than sealed, you can't choose reflex for a smaller box.
(you can choose a different driver for this to be true)
Using an overdamped reflex alignment you can approximate
a 6dB/ octave roll-off which matches with rooms well and the
necessarily low port tuning will play cleaner than the sealed
box as it has 12dB more low bass SPL capability.
But this is general stuff, the titanic2 driver seems well suited
a sealed box of ~ 2cuft, with possibly some low bass boost.
Reflex alignments that suit room gain seem quite difficult.
An overdamped reflex is heading towards 5cuft.
sreten.
sealed way below the possibiliities of any sealed alignment.
And generally for a particular driver reflex needs a bigger
box than sealed, you can't choose reflex for a smaller box.
(you can choose a different driver for this to be true)
Using an overdamped reflex alignment you can approximate
a 6dB/ octave roll-off which matches with rooms well and the
necessarily low port tuning will play cleaner than the sealed
box as it has 12dB more low bass SPL capability.
But this is general stuff, the titanic2 driver seems well suited
a sealed box of ~ 2cuft, with possibly some low bass boost.
Reflex alignments that suit room gain seem quite difficult.
An overdamped reflex is heading towards 5cuft.
sreten.
m0tion said:
That's the ticket. Ask only one question at a time. Or if you ask more than one question, number them! (Works for me.) Asking about sealed vs. vented and room gain both is too much.
Here's a question: If I assume the sub will go near a wall (and perhaps in a corner), what will the room gain chart look like? I've seen one on the net, but someone here said it was unrealistic. I still do not know what is realistic.
I think most people ignore room gain as there are so many other variables involved. Start by going through this thread: http://www.diyaudio.com/forums/showthread.php?s=&threadid=30038&highlight=m0tion said:
This is somewhat tangential to your question, but you could just ignore room gain, and then if you have too much low bass cut those frequencies. This is better than assuming there will be heaps of room gain and finding out there isn't and having to boost the lows, hence putting more strain on your amp and driver. Especially with ported you need to watch out for boost below tuning frequency.
IM0 for the titanic2 you are looking at a sealed box of around
66 litres or a reflex box of around 100 litres tuned to 20Hz.
The reflex simply has more low bass, a lot more in the octave
20Hz to 40Hz and much higher SPL capability in this region,
12dB at 20Hz, still +6dB at 30Hz.
The titanic 2 is nigh identical to the Shiva 2 parameter wise,
so read up all the stuff on Adire Audio's site on the Shiva.
sreten.
66 litres or a reflex box of around 100 litres tuned to 20Hz.
The reflex simply has more low bass, a lot more in the octave
20Hz to 40Hz and much higher SPL capability in this region,
12dB at 20Hz, still +6dB at 30Hz.
The titanic 2 is nigh identical to the Shiva 2 parameter wise,
so read up all the stuff on Adire Audio's site on the Shiva.
sreten.
Ok, lets put it this way:
When I'm looking at the frequency response graph simulated in WinISD is it better for the response to be down 10dB at 20Hz, or still flat if I want a flat response in my room. If it is flat to 20Hz will room gain give me a big hump in the low end? Should it be down 10dB (or more, or less?) at 20Hz in order to get flat response?
When I'm looking at the frequency response graph simulated in WinISD is it better for the response to be down 10dB at 20Hz, or still flat if I want a flat response in my room. If it is flat to 20Hz will room gain give me a big hump in the low end? Should it be down 10dB (or more, or less?) at 20Hz in order to get flat response?
Ported vs. Sealed follow-up
I don't want to hijack this thread, but the question I have is the same topic.
(My main interest is quality bass.)
Which would you rather have an Adire Audio Tempest in?:
1.) 5 cubic foot sealed enclosure.
2.) 8 cubic foot vented.
If the answer for you (or me) is number 2, would the choice remain number two if instead of 8 cubic feet, it was 4 cubic feet and it had two Tempests, isobaric style? I know it requires more power, but other than that...?
I don't want to hijack this thread, but the question I have is the same topic.
(My main interest is quality bass.)
Which would you rather have an Adire Audio Tempest in?:
1.) 5 cubic foot sealed enclosure.
2.) 8 cubic foot vented.
If the answer for you (or me) is number 2, would the choice remain number two if instead of 8 cubic feet, it was 4 cubic feet and it had two Tempests, isobaric style? I know it requires more power, but other than that...?
If the speaker is fairly close to a boundary, less than a foot or so, you get a fairly broadband loading situation from about 100 Hz and down, not a peaked response. What would cause a bump at 20 Hz would be a boundary 1/2 wavelength away, which for 20Hz is 28 feet or so. At that distance you might get a 3 to 4dB bump, no more.
Your best bet is to get the response you require without room gain factored in; that way if you don't get a lot of room gain you have what you need, if you do get gain it's gravy.
Your best bet is to get the response you require without room gain factored in; that way if you don't get a lot of room gain you have what you need, if you do get gain it's gravy.
Both systems have there place. Small room, sealed is better, for largers rooms refelx is better, who cares about SPL unless you want to bug your neighbours
One claim that is very popular is that you cannot reproduce bass in a small space. While this is certainly true of soundwave propagation, it is completely false if pressure mode is excited within the space. In most rooms, there is a transition point between soundwave propagation and pressure mode (sometimes referred to as 'Room Gain'). That low frequencies can be reproduced in small spaces is clearly shown by headphones and car subwoofer systems. Both of these rely on pressure mode, and the low frequency -3dB point is defined by 'leakage' because the space is not perfectly sealed. In a completely sealed environment, bass reproduction is attainable right down to DC - not that this is actually useful. Most subwoofers ultimately rely on pressure mode to obtain the lowest frequencies in typical rooms, and it is notable that vented systems in particular are unable to excite the pressure mode properly in many rooms.
One of the reasons for this could be that there is a vent that allows the pressure to equalise. In theory, this is meant to be a resonant system, where the back wave of the loudspeaker is inverted in phase and augments the main cone wavefront. That the principle works is demonstrated by many large systems in auditoria, theatres and even outdoor venues, but all of these are large spaces where soundwave propagation is dominant.
When room dimensions become small compared to wavelength, soundwave propagation will not work, and bass can only be reproduced by pressurising (and de-pressurising) the listening space ... pressure mode. In tests I have performed in my workshop, a vented subwoofer seemed to make a lot of noise, but completely failed to produce bass that could actually be felt. A similar driver in a sealed box causes the whole house to vibrate, something that I have not been able to achieve to the same (or even similar) levels using any vented subwoofer system.
One claim that is very popular is that you cannot reproduce bass in a small space. While this is certainly true of soundwave propagation, it is completely false if pressure mode is excited within the space. In most rooms, there is a transition point between soundwave propagation and pressure mode (sometimes referred to as 'Room Gain'). That low frequencies can be reproduced in small spaces is clearly shown by headphones and car subwoofer systems. Both of these rely on pressure mode, and the low frequency -3dB point is defined by 'leakage' because the space is not perfectly sealed. In a completely sealed environment, bass reproduction is attainable right down to DC - not that this is actually useful. Most subwoofers ultimately rely on pressure mode to obtain the lowest frequencies in typical rooms, and it is notable that vented systems in particular are unable to excite the pressure mode properly in many rooms.One of the reasons for this could be that there is a vent that allows the pressure to equalise. In theory, this is meant to be a resonant system, where the back wave of the loudspeaker is inverted in phase and augments the main cone wavefront. That the principle works is demonstrated by many large systems in auditoria, theatres and even outdoor venues, but all of these are large spaces where soundwave propagation is dominant.
When room dimensions become small compared to wavelength, soundwave propagation will not work, and bass can only be reproduced by pressurising (and de-pressurising) the listening space ... pressure mode. In tests I have performed in my workshop, a vented subwoofer seemed to make a lot of noise, but completely failed to produce bass that could actually be felt. A similar driver in a sealed box causes the whole house to vibrate, something that I have not been able to achieve to the same (or even similar) levels using any vented subwoofer system.
Take a look at the critical
Q sub here: http://members.ozemail.com.au/~joeras/sub_index.htm . it deals with room gain and its effect, among other things . this is almost the same as the sub I designed ,and have been using for 5 years . mine is +,-
2DB 100 to 30 hz and -4@20 in 1.4 FT3 sealed with EQ, in room, 1 W/@1M on Dr. Bruce Edgars calibrated LMS sys.,and produces enough energy that a lady i demoed too thought there was an earthquake as the building was shaking from the heartbeats on DSOM! I drive my stereo pair with 200W/chanel.
Q sub here: http://members.ozemail.com.au/~joeras/sub_index.htm . it deals with room gain and its effect, among other things . this is almost the same as the sub I designed ,and have been using for 5 years . mine is +,-
2DB 100 to 30 hz and -4@20 in 1.4 FT3 sealed with EQ, in room, 1 W/@1M on Dr. Bruce Edgars calibrated LMS sys.,and produces enough energy that a lady i demoed too thought there was an earthquake as the building was shaking from the heartbeats on DSOM! I drive my stereo pair with 200W/chanel.
yup Ice you do: I personally have never heard a ported woofer that i would now own tho way back , i did own some but was never satisfied till i did good bi amped sealed units . I use HSU ASW1202 drivers as the XLR drivers this guy uses were not avail. and i use 2 of them, one on each side of my listening chair 43 inches away, since I listen near field. as i say mine is very similar, but not identical to the "critical Q", altho my results are nearly so. the sats are also 43 inches away so are time aligned,even tho thier position is on a 45 deg. angle, the subs obviously are at 90deg.
deliberately resonate speaker sys. dont reproduce music but make thier own sound. a speaker should never
produce any sound that isnt comeing down the wire and helmholtz resonaters certainly arent coming down the wire LOL. speakers should NEVER produce sound , they should only reproduce sound ! thers a massive difference! well designed sealed gets the closest except for VERY well designed horns, and there arent many of those that are suitable for rooms i can afford, much less horn subs i can afford, or even lift or move! LOL someone recently posted trying to convince me that sealed is also a resonate systems but the logic was so flawed i didnt even bother to answer . a sealed sub has a well DAMPED resonate cavity and there is no open comunication with the room air and an UNDAMPED cavity as there is with ported. MASSIVE DIFFERENCE!
deliberately resonate speaker sys. dont reproduce music but make thier own sound. a speaker should never
produce any sound that isnt comeing down the wire and helmholtz resonaters certainly arent coming down the wire LOL. speakers should NEVER produce sound , they should only reproduce sound ! thers a massive difference! well designed sealed gets the closest except for VERY well designed horns, and there arent many of those that are suitable for rooms i can afford, much less horn subs i can afford, or even lift or move! LOL someone recently posted trying to convince me that sealed is also a resonate systems but the logic was so flawed i didnt even bother to answer . a sealed sub has a well DAMPED resonate cavity and there is no open comunication with the room air and an UNDAMPED cavity as there is with ported. MASSIVE DIFFERENCE!
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