brief description
Briefly: I use eight drivers of the Acoustic Elegance AEIB-15 woofers (Sadly,No longer available)
These are loaded into a manifold, magnet to magnet; with threaded rods supporting them at their circumfrence and pressure locked with a vented pvc coupler at the magnet assemblies. There are 4 pairs arranged vertically. Each pair is driven by a channel of a Crown K2 power amp. The manifold was constructed inside a jutted out corner of the room, at a 45 degree angle, and behind this fake wall, and opening was knocked out to an adjoining closet to where there's almost 500 cubic feet for them to "breath"
in to. I use an Audio Control Richter Scale III as the electronic crossover.
Right now, the x-over module is set @ 50 Hz, but many of my audiophile buddies have reccomended I raise that a bit higher. The sealed mid-bass units it crosses to are 2 per channel Eminence Definimax 4012HO in a hybrid
ppsl horn loaded deal. The mid-bass units by themselves have response down to about 35 Hz which according to "sims" is impossible. The old rule of thumb I learned about crossing in subs, is that, the main (or satelite) woofers should have response one octave below the intended crossover point. I would have to move my x-over point to 70 Hz for that to be true. Perhaps i'll try someday. If you look at the "cult of the infintely baffled" I have a construction thread called Legend 3215 project, or something to that effect.
Good luck with your friends system, as you say, it's going to be tricky!
Briefly: I use eight drivers of the Acoustic Elegance AEIB-15 woofers (Sadly,No longer available)
These are loaded into a manifold, magnet to magnet; with threaded rods supporting them at their circumfrence and pressure locked with a vented pvc coupler at the magnet assemblies. There are 4 pairs arranged vertically. Each pair is driven by a channel of a Crown K2 power amp. The manifold was constructed inside a jutted out corner of the room, at a 45 degree angle, and behind this fake wall, and opening was knocked out to an adjoining closet to where there's almost 500 cubic feet for them to "breath"
in to. I use an Audio Control Richter Scale III as the electronic crossover.
Right now, the x-over module is set @ 50 Hz, but many of my audiophile buddies have reccomended I raise that a bit higher. The sealed mid-bass units it crosses to are 2 per channel Eminence Definimax 4012HO in a hybrid
ppsl horn loaded deal. The mid-bass units by themselves have response down to about 35 Hz which according to "sims" is impossible. The old rule of thumb I learned about crossing in subs, is that, the main (or satelite) woofers should have response one octave below the intended crossover point. I would have to move my x-over point to 70 Hz for that to be true. Perhaps i'll try someday. If you look at the "cult of the infintely baffled" I have a construction thread called Legend 3215 project, or something to that effect.
Good luck with your friends system, as you say, it's going to be tricky!
Hi Andrew,
Sealed enclosure is a 2nd order highpass, BR 4th order.
This knowledge for me stems from a time when it was still ink on dead trees: Handbook of Sound Engineers, page 530 (second edition 1991): ... a closed box rolls of at 12 dB/octave; a vented box rolls of at 24 dB/octave... There must be something on the interwebs as well.
Two visualizations from a sim (yellow is FR, blue acoustic phase, phase scale left, dB scale right).
BTW, these sims are for the same driver in a similarly sized enclosure. The bass extension of BR versus sealed can easily be recognized. But, it comes at a price.
Sealed gives 180 degrees as would be expected from 12dB high pass.
And vented gives twice that.
vac
Sealed enclosure is a 2nd order highpass, BR 4th order.
This knowledge for me stems from a time when it was still ink on dead trees: Handbook of Sound Engineers, page 530 (second edition 1991): ... a closed box rolls of at 12 dB/octave; a vented box rolls of at 24 dB/octave... There must be something on the interwebs as well.
Two visualizations from a sim (yellow is FR, blue acoustic phase, phase scale left, dB scale right).
BTW, these sims are for the same driver in a similarly sized enclosure. The bass extension of BR versus sealed can easily be recognized. But, it comes at a price.
Sealed gives 180 degrees as would be expected from 12dB high pass.
And vented gives twice that.
vac
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out at infinity. You never get there.
It's only 90 degrees at the turn over frequency, not 180 degrees.
That is the post I reacted to above with the sims and a quote.
Then now you post quoting me on sealed:
out at infinity. You never get there.
It's only 90 degrees at the turn over frequency, not 180 degrees.
This is correct, but not consistent with your earlier statement. It is the characteristic of a second order filter, such as a sealed enclosure is. Be careful with infinity; between 2 octaves below and above the xover frequency, you already have about 90% of this 180 degree phase shift. This is a relevant area in loudspeaker design.
vac
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Scott, you built a house around your subwoofer. Very impressive! Your audiophile friends are right from the perspective of aligning phase, but @70Hz bass is pretty directional already, so from the point of localization perception, the 50Hz xover frequency you have now may be just right.
Thankyou all for the interesting feedback.
The Heuristic I was thinking of was
My reasons for going sealed with bass are simple, they have smaller volumes than bass reflex. If I was considering a Bass reflex enclosure, I suspect I would opt to use Passive Radiator, it appeals more than using pipes, as it would be easier to tune and for low bass Bass reflex pipes get bulky, while passive radiators cost money and surface area. But this thread is a discussion about "Sealed with low Qts" not another "Sealed V Bass reflex" thread, though they can be fun, I should like to draw the subject back.
Thank you for this comment it was very informative.
This was also very interesting. I assume Charles agrees with 6.283.
Sorry if I missed some one, but my fear was that such small speaker volumes possible would have been a worry about the factors of non linear gases behavior. Hopefully I have not missed a comment about this.
A driver to be illustrative the question of low Qts drivers. For example Seas L22RN4X-P.
So getting back to the question, would it be unwise to try a small sealed bass box with something like a L22RN4X-P, Win ISD (Running in Wine on Linux) gives a Q of 0.71 in 14 Liters is appealingly small, but would this make it sound worse?
The Heuristic I was thinking of was
.
My reasons for going sealed with bass are simple, they have smaller volumes than bass reflex. If I was considering a Bass reflex enclosure, I suspect I would opt to use Passive Radiator, it appeals more than using pipes, as it would be easier to tune and for low bass Bass reflex pipes get bulky, while passive radiators cost money and surface area. But this thread is a discussion about "Sealed with low Qts" not another "Sealed V Bass reflex" thread, though they can be fun, I should like to draw the subject back.
Hmmm...really ?
Typically, you will find that low Qts drivers also have a limited xmax because in a vented design you need less excursion capability. If you put such a driver in a CB then xmax might be exhausted very soon leading to increased distortion.
Another variable to look at is the motor itself. There are many underhung designs for vented boxes. But real good bass comes from overhung motors. So a bass driver for a closed box would have both, a decent xmax and an overhung motor.
I'm not sure where heuristics come into play here
Thank you for this comment it was very informative.
This was also very interesting. I assume Charles agrees with 6.283.
Sorry if I missed some one, but my fear was that such small speaker volumes possible would have been a worry about the factors of non linear gases behavior. Hopefully I have not missed a comment about this.
A driver to be illustrative the question of low Qts drivers. For example Seas L22RN4X-P.
So getting back to the question, would it be unwise to try a small sealed bass box with something like a L22RN4X-P, Win ISD (Running in Wine on Linux) gives a Q of 0.71 in 14 Liters is appealingly small, but would this make it sound worse?
It always amazes me how people tend to confuse different issues. There is much talk about how much more group delay BR designs have, when compared to sealed ones, which is true but largely irrelevant. Group delay defines the onset of sound emission, i.e. how late sound emission begins. The potential problem with BR is resonant decay, which is how sound emission from the vent ends, not how it begins. This can be easily seen in anechoic CSD plots. Resonant systems can neither start nor stop oscillating instantly. It takes a while for them to get started and a further while for the oscillation to die down. Group delay describes the former.
i agree bbggg
But group delay IS the same as the resonant system decay, constant inertia and accn force mean that the 'attack' part of the emission envelope is equal to the 'decay' part. In my mind at least this makes group delay significant. One reason lf group delay is less audible is simply the longer attack/decay time at lower frequencies. Ie number of oscilliatory cycles. I believe the listener would be able to hear say 5 cycles 'overhang' at 100hz more easily than at 1k, or even 500hz.
But group delay IS the same as the resonant system decay, constant inertia and accn force mean that the 'attack' part of the emission envelope is equal to the 'decay' part. In my mind at least this makes group delay significant. One reason lf group delay is less audible is simply the longer attack/decay time at lower frequencies. Ie number of oscilliatory cycles. I believe the listener would be able to hear say 5 cycles 'overhang' at 100hz more easily than at 1k, or even 500hz.
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I think he does, although I should have said "some" or "a few" instead of "There are many underhung designs ".
BTW, the ScanSpeak Illuminators are another example but not the Vifa NE series as I initially thought.
I think it could sound fine but again the low end output might be limited.
in my limited experience low qts is not a huge issue, and fs makes more of a difference. Qts <0.3 would generally make sealed less appealing. EBP is the common value used, but ive often ignored this if the f3 is acceptable. What u lose in extension you gain in 'attack' so as usual its a compromise
This is very consistent with what I quoted for a single pole filter.
It appears to me that if you don't like the message, you don't bother to read it through.
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back on topic
Greetings: Please keep in mind this is only an eight inch driver, so it won't move much air even with a 14 mm p-p. The Seas spec sheet says it does not reccomend this driver for a sealed system, but the EBP says it can do either.
Keep in mind, that for the degree in which the Qts is raised to the Qtc is the same degree as the Fs is then raised to the Fc. The F3 varies according to the alignment of a vented system. In a sealed, the F3= Fc IF the Qtc = .707
For a sealed enclosure this driver wishes to see 15.848 litres giving an Fc/F3
of 55 Hz @ Qtc .707
For a vented enclosure this driver wishes to see 24.7 litres giving an F3 of
37.6 Hz. The Fb (vent frequency) is 31.6 It's lower than the F3 point because this would be a quasi 3rd order vented alignment.
Of special note this driver has a relativly low Fs (listed as 21Hz) for it's size.
I've never seen an eight inch driver with an Fs this low.
Greetings: Please keep in mind this is only an eight inch driver, so it won't move much air even with a 14 mm p-p. The Seas spec sheet says it does not reccomend this driver for a sealed system, but the EBP says it can do either.
Keep in mind, that for the degree in which the Qts is raised to the Qtc is the same degree as the Fs is then raised to the Fc. The F3 varies according to the alignment of a vented system. In a sealed, the F3= Fc IF the Qtc = .707
For a sealed enclosure this driver wishes to see 15.848 litres giving an Fc/F3
of 55 Hz @ Qtc .707
For a vented enclosure this driver wishes to see 24.7 litres giving an F3 of
37.6 Hz. The Fb (vent frequency) is 31.6 It's lower than the F3 point because this would be a quasi 3rd order vented alignment.
Of special note this driver has a relativly low Fs (listed as 21Hz) for it's size.
I've never seen an eight inch driver with an Fs this low.
Sorry Andrew, you see it wrong. Sealed has a second order character and BR a fourth. With the associated 12dB/octave and 180 degrees phase shift for sealed and 24dB and 360 degrees for BR.
I have this from old textbooks, measurements and sims, but I also took the liberty of Googling on your behalf, and the first quote that came up:
In an acoustic suspension, sealed box, or infinite baffle application, there is an optimum system Q value to obtain the flattest frequency response, and a phase response identical to a 2nd order Butterworth filter. Not coincidentally, the roll-off is identical to a 2nd order Butterworth filter at 12 dB
Essay
Of course, by changing the size of the box, you can change the systems Q, but you can never get away from the 180 degree phase shift of a two pole filter.
Before confusing the readers of this post more, may I please ask you to do some further research before replying, possibly on the basis of clear references?
vac
Andrew, let's keep it technical. I read both posts and even corrected them, by quoting from the Loudspeaker Engineers Handbook and showing two sims that demonstrate it. Subsequently, you posted again, and so I looked for it on the interwebs, and posted a quote and a link that shows you are mistaken. Why not do the same, and quote from your literature, show a sim or post a link to a website, instead of this? I don't mind myself, but you confuse people.
vac
vac
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