Then why can you smell a "burning" voice coil through the port a few meters away?
OMG!
Since you were good enough to link the actual article, (thanks!) I tried to read & comprehend it. Really I did. - But there's less chance of that than a pigmy winning a slam-dunk contest.
Actually, that pigmy has a better shot than I do.
That's why I'm asking for help here.
I don't even know what THAT means. Can you explain it in another way?
(pretend I'm in 5th grade!)
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He's got a point.
Obviously there some small exchange of air molecules, even if the net gain / loss doesn't change.
- But enough for significant cooling? Probably not.
Makes me wonder: Has anyone even installed a high powered fan inside a sub, blowing directly on the motor assembly?
- Heck, that might even break up standing waves! (Just kidding.... Sort of.)
Or liquid nitrogen, or a phase exchanger, or ......
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I have an impression that an idea of just replacing that crap driver with real high-performance, modern subwoofer driver with plenty of magnetic motor strength and plenty of Xmax got lost here. Restricted himself to sealed box, OP's the only solution is to use the best possible driver and try to accomodate DSP processor to shape its response. Magnetic power for efficiency, Volume displacement for bass output. There is no other route in sealed boxes unless you apply horn to it.
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Yes, that's the other piece of the puzzle, but I'm asking that question on a separate thread. (No good answer yet.)
Oddly, I queried B&M about this, asking which of their 18" drivers would best work in a sealed enclosure, and the tech responded that none would be optimal. Then he sent me plans for a small, ported box /driver combo.
Sigh....
I know this may not work, I am REALLY not hopeful, but I want to explore it before compromising with some other design. I figure modern technology may give me the small increases I need. I LOVE the sound of that bag End system, except not enough volume and not enough throw in a big room.
There is no pro driver which will work well as a direct radiator in sealed enclosure without EQ reworking. This is against pro-philosophy which seeks for every tinny dB more coming out of one Watt inputted. Sealed box is least efficient out there (not counting those all OB's, dipoles etc. which are not real acoustic alignments in fact.) Unless treated with DSP in order to bring balance to rapidly rising response of very-powerful drivers they are no-go in sealed especially from pro-manufacturer point of view. Their drivers are designed from the base to work in high order alignments, for example bass-reflex, band-pass or especially horn-loaded.
Read about this crazy 21" driver:
Data-Bass
Data-Bass
And the science behind it:
https://www.powersoft-audio.com/en/docman/922-powersoft-bac-ipalmod-system-introduction/file
Powersoft Guys really know how to handle electricity and they really know how to convert it to real bass.
Read about this crazy 21" driver:
Data-Bass
Data-Bass
And the science behind it:
https://www.powersoft-audio.com/en/docman/922-powersoft-bac-ipalmod-system-introduction/file
Powersoft Guys really know how to handle electricity and they really know how to convert it to real bass.
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What is the status of this issue?
I have a very similar problem. 2 bass reflex cabinets of 1 x 18NLW9400, 150 liters, tuned very high at 47Hz for maximum SPL and efficiency around 45 - 100Hz. Lowcut at 40Hz.
I want to enjoy bass down to about 20Hz, plus the better transient response of closed cabinets.
That is why I am working on 2 DSP setups: 1 for outdoor party with full power and ports in open mode, plus lowcut, one for indoor listening with ports closed / plugged and no lowcut, but a rolloff compensation to make the response almost flat down to ~ 20Hz (at the expense of many dB).
I have done research using hornresp and found no way around the max SPL issue on closed cabinets, even trying many different 18" woofers.
Even if I'd put a second woofer into the same cabinet, I get NO efficiency increase below resonance (but +3dB max SPL due to double power). +6dB output at low frequencies you can only get with 2 enclosures instead of 1 (or a bigger one) AND double power (by using 2 drivers instead 1).
I have a very similar problem. 2 bass reflex cabinets of 1 x 18NLW9400, 150 liters, tuned very high at 47Hz for maximum SPL and efficiency around 45 - 100Hz. Lowcut at 40Hz.
I want to enjoy bass down to about 20Hz, plus the better transient response of closed cabinets.
That is why I am working on 2 DSP setups: 1 for outdoor party with full power and ports in open mode, plus lowcut, one for indoor listening with ports closed / plugged and no lowcut, but a rolloff compensation to make the response almost flat down to ~ 20Hz (at the expense of many dB).
I have done research using hornresp and found no way around the max SPL issue on closed cabinets, even trying many different 18" woofers.
Even if I'd put a second woofer into the same cabinet, I get NO efficiency increase below resonance (but +3dB max SPL due to double power). +6dB output at low frequencies you can only get with 2 enclosures instead of 1 (or a bigger one) AND double power (by using 2 drivers instead 1).
The driver manufacturer sensitivity graph is the driver's sensitivity in an infinite sealed box. Smaller boxes will boost an ever increasing frequency according to the driver's surface area and mass Vs the compliance of the driver. The max SPL with sealed is always proportional to the displacement. The size of box determines power Vs displacement at different frequencies. Below box resonance the driver works harder compressing the air you don't hear so your box resonance should be your lowest often used frequency. If you insist on using sealed large pa drivers will get you the most possible efficiency in a big box.
For small excursions air at sea level will compress about 1 percent per 0.01 bar or 1000 pascals. So let's say the bulk modulus of air is around 1 bar. On Everest a smaller box will get lower (equalise the pressure) but won't get as loud due to the air being thinner.
A modelling program is probably your best bet. Hornresp and win isd can do sealed boxes easily.
Sealed boxes are best for confined spaces like cars because the air is trapped the woofers can compress it like air in a pump cylinder at low frequencies instead of it wafting out of the way.
For small excursions air at sea level will compress about 1 percent per 0.01 bar or 1000 pascals. So let's say the bulk modulus of air is around 1 bar. On Everest a smaller box will get lower (equalise the pressure) but won't get as loud due to the air being thinner.
A modelling program is probably your best bet. Hornresp and win isd can do sealed boxes easily.
Sealed boxes are best for confined spaces like cars because the air is trapped the woofers can compress it like air in a pump cylinder at low frequencies instead of it wafting out of the way.
As I mentioned in another thread:
Turn your driver around if you insist on closed in high power scenarios. There's minimal power compression when the unit is in free air. Build a curved grill or extend the box planar style to envelop.
IMO, sealed boxes in LF applications in PA is a recipe for an extreme amount of extra boxes, power, mass, cost, etc - for minimal gains.
'Better' drivers (BL, low QTC, etc) in reflex are a much more sensible approach. Or build FLH if you want complete accuracy.
Turn your driver around if you insist on closed in high power scenarios. There's minimal power compression when the unit is in free air. Build a curved grill or extend the box planar style to envelop.
IMO, sealed boxes in LF applications in PA is a recipe for an extreme amount of extra boxes, power, mass, cost, etc - for minimal gains.
'Better' drivers (BL, low QTC, etc) in reflex are a much more sensible approach. Or build FLH if you want complete accuracy.
Yea... A live sound man with good ears!
I used to crew for a Jazz Funk band in the 80's and we used stacks of sealed box subs to form line arrays which sounded amazing and had massive throw which covered all the way to the back of the venue with tight super accurate bass and low mids.... "Better than Earth Wind and Fire sound" was one review headline!
If I was in your business today (I'm too old to carry 60Kg subs now!) I would use the attached drivers... Twin stacks of 4 cabinets (8 cabinets in total) will hit 120dB to 126dB peaks all day and all night in a typical 500 seat / 1,000 standing dance floor venue... Even the audience at the back (20 to 30 meters) will have great sound and the front row wont have to suffer ear bleed (an illegal!) 140dB crap sound!
Power compression is key
PS
The Precision Devices drivers are the gold standard for live sound with legendary build quality and reliability and the customer service to back it up... But they are twice the price of Beyma, RCF, B&C and 18 sound and they also offer some great low Qts (0.2 to 0.25) drivers that will also work really well in sealed box with DSP/Eq.
A good rule of thumb to calculate efficiency is to work backwards from the max thermal power SPL ie for the attached, at 40Hz in 61 litres with 800 watts AES power:
800 watts = 115dB
400 watts = 112dB
200watts = 109 dB
100 watts = 106 dB
50 watts = 103 dB
25 watts = 100 dB
12.5 watts = 97dB
6.25 watts = 94 dB
3.12 watts = 91 dB
1.56 watts = 88 dB
Also a big point on Power compression (thermal compression) of the Precision Devices 18 inch drivers... Just 1.6dB to 2dB at full power! Thats the lowest in the industry and under half the 18 inch Beyma compression.
The PD drivers soak up a genuine 800watts to 1,000 watts AES continuous with 6dB peaks of 3,200 watts to 4,000 watts depending on model.
You really need amps with 4,000 watt ratings into 4 Ohms ( assuming you stack 4 of the 16 Ohm PD drivers and wire them in parallel for a 4 Ohm load)
PS
The Precision Devices drivers are the gold standard for live sound with legendary build quality and reliability and the customer service to back it up... But they are twice the price of Beyma, RCF, B&C and 18 sound and they also offer some great low Qts (0.2 to 0.25) drivers that will also work really well in sealed box with DSP/Eq.
A good rule of thumb to calculate efficiency is to work backwards from the max thermal power SPL ie for the attached, at 40Hz in 61 litres with 800 watts AES power:
800 watts = 115dB
400 watts = 112dB
200watts = 109 dB
100 watts = 106 dB
50 watts = 103 dB
25 watts = 100 dB
12.5 watts = 97dB
6.25 watts = 94 dB
3.12 watts = 91 dB
1.56 watts = 88 dB
Also a big point on Power compression (thermal compression) of the Precision Devices 18 inch drivers... Just 1.6dB to 2dB at full power! Thats the lowest in the industry and under half the 18 inch Beyma compression.
The PD drivers soak up a genuine 800watts to 1,000 watts AES continuous with 6dB peaks of 3,200 watts to 4,000 watts depending on model.
You really need amps with 4,000 watt ratings into 4 Ohms ( assuming you stack 4 of the 16 Ohm PD drivers and wire them in parallel for a 4 Ohm load)
Hydrogen Alex,
If you were competing in the business of providing low frequency for dancers today you would quickly find that using sealed cabinets using eight times the drivers and power to achieve the same low frequency SPL easily available from a single driver is not economically viable.
If we ignore room gain, which will affect any cabinet equally, it does not matter whether you use 8 drivers or one driver to produce 126dB at 40 Hz ("one meter"), the level will only be 100 dB for the audience 20 meters back.
Art
Sorry but you are wrong!
All point sources drop of at 6dB per doubling of distance...
All line arrays drop off at 3dB per doubling of distance...
So your point source ported sub which is producing 136dB at 1 meter ( illegal and instant ear damage!) will drop to:
130dB at 2 meters (133 dB with line array)
124 at 4 meters (130 dB with line array)DDn
118 at 6 meters (127 dB with line array)
112 at 12 meters ( 124 dB with line array)
106dB at 24 meters ( 121 dB with line array)
So you can see that the line array ( 4 subs per stack, one left stage, one right stage) will massively outperform any point source over 90% of the dance floor on a like for like starting SPL at 1 meter.
I used to set this up three times a week for a Jazz Funk band it the sealed box line arrays sounded amazing!
All point sources drop of at 6dB per doubling of distance...
All line arrays drop off at 3dB per doubling of distance...
So your point source ported sub which is producing 136dB at 1 meter ( illegal and instant ear damage!) will drop to:
130dB at 2 meters (133 dB with line array)
124 at 4 meters (130 dB with line array)DDn
118 at 6 meters (127 dB with line array)
112 at 12 meters ( 124 dB with line array)
106dB at 24 meters ( 121 dB with line array)
So you can see that the line array ( 4 subs per stack, one left stage, one right stage) will massively outperform any point source over 90% of the dance floor on a like for like starting SPL at 1 meter.
I used to set this up three times a week for a Jazz Funk band it the sealed box line arrays sounded amazing!
Alex, a line array is formed when the effective line length exceeds 10x wavelengths.
For indoor venues with a solid (I'm talking several feet of concrete, minimum) floor and ceiling, it's possible to make an effective line source. Without those acoustically reflective surfaces, you've still got a point source.
Chris
For indoor venues with a solid (I'm talking several feet of concrete, minimum) floor and ceiling, it's possible to make an effective line source. Without those acoustically reflective surfaces, you've still got a point source.
Chris
Sorry Alex, you have a lot of "catching up" to do...
Line arrays drop off at 3dB per doubling of distance due to destructive interference in the near field, while in the far field the level drops at 6dB per doubling of distance.
The near field for a "line array" of only 4 to 8 small cabinets at 40 Hz is so short that it can be ignored.
Meyer Sound Copyright © 2002
Line Arrays: Theory, Fact and Myth
https://www.epanorama.net/sff/Audio/Pro_Audio/Installations/Line Arrays - Theory, Fact and Myth.pdf
"With a practical, real line array of sixteen cabinets (each using 15” low-frequency cones), a slight “cylindrical wave-like” effect can be measured at about 350 Hz, where there is a 3 dB drop between two and four meters from the array. More than four meters from the array, however, the sound spreads spherically, losing 6 dB per distance doubling."
Happy reading!
Art
I built Art's Keystone and while it is a larger cabinet I find it much easier to move than my Behringer active 18 about same size as the QSC. Single Keystone rocked a high school Prom with heavy low bass content. Chris already said it, TH is the way. KS is easiest to build and Art did great with design and testing. I'm solo too and a good hand truck will help immensely if stairs are common.
Eight times the drivers and power? That is a difference of 18dB. No bass reflex will give you 18 dB over a closed box (same driver assumed). More like 8 dB. And only around the resonance. Many Minus dB below and zero dB far above the resonance. And that 8dB small band boost can only be gained if port compression does not "eat" your extra dBs, i. e. if you use big enough port.
Another thing to consider with sealed is that the impedance curve for the box has only one hump (which gets smaller the more damping you put in) while a reflex has two humps and a tapped horn has three. This is a good example of how damping (panel flex) affects the resonant peak sizes for a tapped horn:
The Subwoofer DIY Page - Projects : Using Impedance Graphs
The more peaks, the higher the average impedance is over the subs bandwidth and the less power is dissipated in the box for a given acoustic output. Speakers cannot be approximated as resistors apart from far below their first resonant frequency. This brings me to the IPAL drivers and other drivers with high Bl^2/Re (effective motor force), these drivers may have a low impedance magnitude at DC but they cause cabs to have massive peaks in the impedance increasing efficiency:
dB v2
but its worth remembering in a reflex or tapped horn you would get more peaks and more efficiency!
if you use a high motor force driver to move a cone back and forth a given distance (IE produce a set SPL at a set frequency from a sealed box) you will have less power dissipated in the motor of the driver in comparison to a cheap low motor force driver. The voltage sensitivity of such systems below resonance however is very poor so you will need big amps.
I know lambda labs sometimes installs sealed sub systems in clubs but they are huge arrays of drivers and amps. Very expensive!
YouTube
The Subwoofer DIY Page - Projects : Using Impedance Graphs
The more peaks, the higher the average impedance is over the subs bandwidth and the less power is dissipated in the box for a given acoustic output. Speakers cannot be approximated as resistors apart from far below their first resonant frequency. This brings me to the IPAL drivers and other drivers with high Bl^2/Re (effective motor force), these drivers may have a low impedance magnitude at DC but they cause cabs to have massive peaks in the impedance increasing efficiency:
dB v2
but its worth remembering in a reflex or tapped horn you would get more peaks and more efficiency!
if you use a high motor force driver to move a cone back and forth a given distance (IE produce a set SPL at a set frequency from a sealed box) you will have less power dissipated in the motor of the driver in comparison to a cheap low motor force driver. The voltage sensitivity of such systems below resonance however is very poor so you will need big amps.
I know lambda labs sometimes installs sealed sub systems in clubs but they are huge arrays of drivers and amps. Very expensive!
YouTube
Center stack all 8 subs as close as possible and you ll get ~2 free extra dB (3 in theory, but not in practice)
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