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Do I lose 3db of sensitivity if I seal my cabinet?

Trdat

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I am curious if it is as simple as losing 3db when I seal cabinet from a ported to closed. And is this throughout the whole frequency range...?

I have a deltalite 15inch which is being used for midrange duties between 140hz and 950hz and want to close the cabinet. Is it just a 3db loss?
 

McFly

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How big is the cabinet, probably no noticeable loss at those frequencies. Depends on Q when sealed.

There is no 3db loss as soon as its sealed, just a much earlier, and slower/gentle decline toward bass frequencies. Since that 15 isnt going that deep, id bet you wouldn't notice.

Stuff some socks in the port see what happens
 
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Trdat

Trdat

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How big is the cabinet, probably no noticeable loss at those frequencies. Depends on Q when sealed.

There is no 3db loss as soon as its sealed, just a much earlier, and slower/gentle decline toward bass frequencies. Since that 15 isnt going that deep, id bet you wouldn't notice.

Stuff some socks in the port see what happens

Hey I had a feeling it wasn't as simple as a 3db loss. My cabinet is massive, 120 litres I initially designed it to have a roll off similar to a sealed cab that way without subs I get tight bass when playing all the way down. And when adding subs I have the opportunity to seal it as a full midrange. I am now convinced adding dual subs is on another level. So I am considering sealing the Deltalite but of course not at the cost of sensitivity.

The QTC of the cabinet closed will be around 6.5. Essentially, the lowest it will play is around 90hz unless I filter the crossover width wide to get it to play all the way down but that still will be around -20db at 50hz a very gradual roll off. I do this to get double bass from sub and 15inch. Sounds unbelievable.

So you think in the midrange I'm not losing sensitivity? Or much...?
 

sergeauckland

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Above the resonant frequency of a bass reflex vent, a loudspeaker behaves identically to a sealed box, in that the vent doesn't affect anything. You can see this easily if you play a, say, 1kHz tone on a vented loudspeaker and block the vent. There will be no change to the output of the 'speaker.

At frequencies below the vent resonance, the bass driver is unloaded, so there's no restoring force, which is why bass reflex loudspeaker cones flap about on Vinyl playback if the phono stage doesn't have good LF filtering.

A 15" unit used up to 950Hz I suggest is bad idea as it will be beaming significantly by then, I wouldn't let a 15" unit go above 200Hz or so, and cross over to a 4 or 5" by then. As a 'rule of thumb' I would have each driver covering no more than a decade, so LF 20-200, MF 200-2kHz, HF 2kHz up, although probably better as a 4-way or even 5 way if one genuinely wants to get down to 20-20kHz flat with any roll-off outside that.

Tannoy 15" Dual Concentrics have their crossover frequency at 1kHz, which I've always felt was just plain wrong.

S.
 

tomtoo

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I did hear alot. And iam open mindet. But hell I have never seen a 15“ as a midrange. That must be the most crazy hell of a PA system that ever was build.
 

Rock Rabbit

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You don't loose any sensitivity, it is calculated @ 1 kHz 1 meter (3 ft distance).
Frequency range is not the same as useful frequency working range, that 15" can throw over 123 dB SPL in the range 50-500 Hz without cone excursion limitation (250 watts input), over 500 Hz it loose efficiency and dispersion.
Adequately used as woofer the box volume for vented or closed is the same (211 lets or 7.45 ft3), but vented f3 is some 47 Hz for a closed box it goes to 80 Hz at Qtc=0.7
https://www.diyaudioandvideo.com/Calculator/SpeakerBoxEnclosure/
 
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Trdat

Trdat

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Above the resonant frequency of a bass reflex vent, a loudspeaker behaves identically to a sealed box, in that the vent doesn't affect anything. You can see this easily if you play a, say, 1kHz tone on a vented loudspeaker and block the vent. There will be no change to the output of the 'speaker.

I know what you say is true. I personally have experimented with an open and closed box for an 8inch between various mid frequencies and it seems the closed box always gives a tad bit better transients. I'm not arguing with you or science it could be the way I have perceived it with some bias, and it could very easily be the slight puff from the vent which makes it feel like it has a lag opposed to the no vent with the closed box. In saying that I will take what you mention in consideration and not worry about it.

A 15" unit used up to 950Hz I suggest is bad idea as it will be beaming significantly by then, I wouldn't let a 15" unit go above 200Hz or so, and cross over to a 4 or 5" by then. As a 'rule of thumb' I would have each driver covering no more than a decade, so LF 20-200, MF 200-2kHz, HF 2kHz up, although probably better as a 4-way or even 5 way if one genuinely wants to get down to 20-20kHz flat with any roll-off outside that.

I've been told that a 15 inch starts beaming around 700hz and good crossover should be around 600hz, haven't heard of 200hz. I do have a 5 way system with the 15inch that takes it up to 300hz and an 8inch that takes it to 800hz then a mid to 3000hz and the soft dome tweeter from 3000hz but for my PA style(waveguide) system unfortunately my waveguide is too small to take the compression driver below 900hz. I will one day upgrade to a larger waveguide and a 2 inch compression driver to make a system with less compromise. For now I have to do with the B52 PHRN 1014 Parts express waveguide and the DE250.
 
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Trdat

Trdat

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I did hear alot. And iam open mindet. But hell I have never seen a 15“ as a midrange. That must be the most crazy hell of a PA system that ever was build.

Well, it's really a 15 inch with a compression driver with added subs so essentially the 15 inch ends up with lower midrange duties.
 

Rock Rabbit

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I know what you say is true. I personally have experimented with an open and closed box for an 8inch between various mid frequencies and it seems the closed box always gives a tad bit better transients. I'm not arguing with you or science it could be the way I have perceived it with some bias, and it could very easily be the slight puff from the vent which makes it feel like it has a lag opposed to the no vent with the closed box. In saying that I will take what you mention in consideration and not worry about it.



I've been told that a 15 inch starts beaming around 700hz and good crossover should be around 600hz, haven't heard of 200hz. I do have a 5 way system with the 15inch that takes it up to 300hz and an 8inch that takes it to 800hz then a mid to 3000hz and the soft dome tweeter from 3000hz but for my PA style(waveguide) system unfortunately my waveguide is too small to take the compression driver below 900hz. I will one day upgrade to a larger waveguide and a 2 inch compression driver to make a system with less compromise. For now I have to do with the B52 PHRN 1014 Parts express waveguide and the DE250.
You're totally right there's a tradeoff in box selection, sealed has better transient response but a higher slow roll of, poor transient for a vented box ...but an extra octave in bass range (for this particular 15"). Then comes the "king" of transient response in a transmission line...but the bass is anemic. Maybe the solution is a dipole woofer (open baffle)
https://www.linkwitzlab.com/woofer.htm
https://www.linkwitzlab.com/models.htm
 

sergeauckland

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You're totally right there's a tradeoff in box selection, sealed has better transient response but a higher slow roll of, poor transient for a vented box ...but an extra octave in bass range (for this particular 15"). Then comes the "king" of transient response in a transmission line...but the bass is anemic. Maybe the solution is a dipole woofer (open baffle)
https://www.linkwitzlab.com/woofer.htm
https://www.linkwitzlab.com/models.htm
Not really,

Transmission lines are inefficient as (theoretically) all the rear energy gets absorbed, but the bass of a proper TL is extended and flat, not at all anaemic. Sadly, all too many so-called TLs are nothing of the sort as a true TL is very large, so many so-called TLs are only 1/4 wavelength labyrinths.

The problem with dipole woofers (open baffle) is that they have NO bass at all under the half-wavelength path length, so need HUGE amounts of EQ to make them usable. The problem then with HUGE amounts of EQ is that it needs HUGE amounts of amplifier power to overcome the amount of EQ, which in turn needs HUGE Xmax capability in the drivers.

There's really no 'perfect' bass loading although TL comes very close if a large and expensive enclosure can be accommodated, with a sealed box being the next best, albeit also quite large if the bass is to be reasonably extended. Reflex (vented) loading is probably the most common as it allows a 'sensible' amount of bass level and extension in a 'sensibly' sized box but at the expense of flabby bass.

There's no such thing as a free lunch, something somewhere has to pay, whether in level, extension or size and cost of the box or amplification.

S.
 
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