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ported and sealed cabs

#21
B-string said:
Rear output from the speaker is also "added" to the front in a ported cab so the ported cab is more efficient, the "sealed" cab has a smoother response.
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Also a misconception. The air within the port vibrates as a mass, in effect acting like another cone, adding to the cab output over a narrow bandwidth in the low end. But most of the additional bass output from a vented cab is due to the lower system resonance. In the midrange, where 'smoothness' is sourced, the two types operate identically. But innate differences in drivers that work best in sealed cabs and those that work best in vented also account for differences in how cabs loaded with them sound.
 
#23
B-string said:
Sorry should have been more precise and noted at lower frequencies only.
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No apology required, even engineers often refer to the output of the port as being the rearwave from the cone.
BTW, this explains why a passive radiator and port are fundamentally the same thing. The air within a port vibrates, acting as a sound source. With a passive radiator the PR cone vibrates, also acting as a sound source. A port's resonant frequency is determined by the volume/mass of air within the duct; the longer the duct the lower the resonant frequency. A PRs resonance is determined by the mass of its cone.
 
#24
We all know, That Bill F is the man here. What I know about the math of it, would fill Bill's thimble. I love my ported cabs, but wanted to just try sealed ones. As some of you who read my post may know I bought a pair of the Chinese Seismic Audio, sealed 215 cabs, for cheap, cause I can't afford the NV215. These two cabs for 300 bucks, have to put out as much spl, as the one NV215 for half the cash, but of course, twice the carry.
What I want to say is, what punch these cabs have, compared to ported cabs! They give you that real smack in the chest at 400 watts, that my ported 810 stack gives me at 1700 watts. I admit, I'm really impressed with that. I run these two 215 cabs with 600 watts at 2 ohms from my Eden WT-405, and it really smacks me in the chest, so I say 'Punch' is the big difference in the two types of cabs, and yes, there is quite a low end loss. But as Bill F. will tell ya, your only hearing the second harmonic at 80 hz, from your low 'E' anyway, so by most ears, very little is lost anyway.
There's my 2 cents.
 
#25
Only thing I'd add here is what I guess you'd call "character" of the low end. If you look at a response graph, the sealed cab will generally start rolling off higher up in frequency (depending on the driver) but have a more gentle slope going down to the bottom, the ported cab will play loud into the deeper frequencies but then have a much more steep decline in response below the tuning frequency. This translates into abstract terms to describe the cab like loose/tight, punchy/deep etc. Not hard and fast rules though, you can make a sealed cab sound deep and loose or a ported cab sound punchy and tight by adjusting box sizes, tunings, etc.
 
#26
At least for us 4-stringers, ported cabs are not operated below the tuning frequency. To avoid the over-excursion catastrophe, the port tuning can't be raised much above the lowest fundamental of 40 Hz.

From what I have been able to gather, cabs with 3 dB points much above 40 Hz have two tuning frequencies: One for the cone / box resonance, and the other for the port / box resonance. Such a design will exhibit (typically) a mild hump at the upper resonance, and a 12 dB/oct rolloff down to the lower resonance. The box is "tuned" by adjusting the upper resonance, not the lower one.

At least that's my take on trying to understand the inner workings of commercial bass speakers of the "big driver small box" variety.
 
#27
fdeck said:
At least for us 4-stringers, ported cabs are not operated below the tuning frequency. To avoid the over-excursion catastrophe, the port tuning can't be raised much above the lowest fundamental of 40 Hz.
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I guess that's dependent on what you consider "much" - common tunings are 50-65 Hz. Realize that most basses have considerably more output in the range of the octave and octave-and-fifth overtones (in the case of 4-string low E, 82Hz, and 123 Hz) than they do at the fundamental, so excursion limitations and port contributions at the lowest fundamentals aren't always too big a problem regardless of tuning.
 
#28
I don't think I'll be in trouble with Bill by saying that the box size and "porting" of a bass reflex box is determinted first by the driver. The theory is to split the free air resonance of the speaker extending it's low range performance, but also causing a higher frequency hump. After the basic setup creative tunning can be done? I agree the lowest frequencies are more for "feel" than what is heard?
 
#29
fdeck said:
At least for us 4-stringers, ported cabs are not operated below the tuning frequency. To avoid the over-excursion catastrophe, the port tuning can't be raised much above the lowest fundamental of 40 Hz.

From what I have been able to gather, cabs with 3 dB points much above 40 Hz have two tuning frequencies: One for the cone / box resonance, and the other for the port / box resonance. Such a design will exhibit (typically) a mild hump at the upper resonance, and a 12 dB/oct rolloff down to the lower resonance. The box is "tuned" by adjusting the upper resonance, not the lower one.

At least that's my take on trying to understand the inner workings of commercial bass speakers of the "big driver small box" variety.
Click to expand...



I've found out with my DIY creations anyway that tuning from the high 40's to the low 50's seem to work pretty well with a lot of bass speakers if they're in a box that's somewhere around appropriate size for the driver. I did have a 210 tuned too high and was getting distortion from what I assume was unloading below the tuning. This was tuned up around 60hz. 40hz tunings seem to be a good way of reducing the lowmid hump in smaller boxes. The 40hz tuning in this particular 210 (eden speakers) took the distortion away and also smoothed out the cab a lot. Has the "punch" you think of as a smallish 210 and doesn't sound like it's trying to put out of bunch of deep bass that it can't do anyway. Sort of and inbetween sealed and ported sound. With a 4-string bass tuned to standard tuning and a box tuned to 40hz I think the cones are doing nearly all the work and the port seems to be calming them down towards the bottom end so they don't unload on low notes.
 
#30
Yeah, Will, although that's really dependent on driver and box. Myself, I tend to choose drivers and box sizes that tune around 40-45 Hz without compromising LF output for the sake of excursion issues. But in the case of say the Kappalite 3015 (non-LF) it's got pretty long xmax for a "full-range" driver, so even in a 3 cf net box it seems to live well tuned between 50-55 Hz. That makes full use of its LF extension without unloading ever a problem for any sane user. Also a driver a lot of sealed cab users would like since its LF extension is "tight".

Driver dependent and user output desires being the point of all this I suppose ; }
 
#31
billfitzmaurice said:
No apology required, even engineers often refer to the output of the port as being the rear wave from the cone.
BTW, this explains why a passive radiator and port are fundamentally the same thing. The air within a port vibrates, acting as a sound source. With a passive radiator the PR cone vibrates, also acting as a sound source. A port's resonant frequency is determined by the volume/mass of air within the duct; the longer the duct the lower the resonant frequency. A PRs resonance is determined by the mass of its cone.
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Are there any sonic benefits to using a passive radiator over a port? Can the cabinet be smaller? I'd think that a passive radiator would be more expensive than a port; trying to see why they'd be chosen by a cab designer.
 
#32
Good points all around. Just going by my own experiences with my own hodge-podge of stuff here. The Kappalite3015 sure looks nice, ie. loud, even response and good xmax. High on the list of replacements when I need one although since acquiring some knowledge about this kind of stuff I haven't and really don't think I: ever will blow a driver/damage equipment etc. Just waiting for the Black Widow to wear out (like that'll ever happen):).
 
#33
will33 said:
If you look at a response graph, the sealed cab will generally start rolling off higher up in frequency (depending on the driver) but have a more gentle slope .
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Generally, yes, but not necessarily. Model an Alpha 10 in 2 cu ft sealed and 2 cu ft vented/50 Hz Fb and you'll see identical rolloff slopes down to 30 Hz, but the vented has 3dB higher sensitivity from 35Hz to 100 Hz.
Are there any sonic benefits to using a passive radiator over a port
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No. PRs are usually used when the overall box size is too small for a duct of the required length to fit inside. IMO that also means the cab is just plain too small for the driver size being used, and that a better result would be had with a smaller or different driver.
 
#35
B-string said:
I believe passive radiators were pre ductport tunning and required larger cab volumes than ductporting with higher losses than ductports?
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I can't say exactly how far back either exists off the top of my head, though the first ducts I saw on bass cabs were on Kustoms circa 1968. It's safe to assume that ducted ports existed in the hi-fi realm at least ten years prior to that.

For a given radiating area the PR uses a smaller cab than a ducted port, as it takes a lot of air within the duct to equal the mass of a PR cone, and that air adds to the cabinet volume.

The PR probably came about back in the 40s, when it was believed that a reflex port had to have the same area as the driver cone, and with no duct that translated into huge reflex cabs. A PR would have given a lot smaller box. But when it was realized that a port didn't need to have more than 1/4 the area of the cone, and that a duct would lower the Fb, the PR was essentially rendered obsolete.
 
#37
greenboy said:
I guess that's dependent on what you consider "much" - common tunings are 50-65 Hz. Realize that most basses have considerably more output in the range of the octave and octave-and-fifth overtones (in the case of 4-string low E, 82Hz, and 123 Hz) than they do at the fundamental, so excursion limitations and port contributions at the lowest fundamentals aren't always too big a problem regardless of tuning.
Click to expand...

Quite true. I would consider 50 Hz to be the upper limit that I would be comfortable with. Above that, it no longer falls into my admittedly limited understanding of how a bass speaker should work.
 
#38
will33 said:
...Sort of and inbetween sealed and ported sound. With a 4-string bass tuned to standard tuning and a box tuned to 40hz I think the cones are doing nearly all the work and the port seems to be calming them down towards the bottom end so they don't unload on low notes.
Click to expand...

That's the scheme that I have arrived at too, and it seems to work nicely.
 
#39
Hey will33 and fdeck,

Here's illustration using the 3015 in a 3 cf net box, at 45 Hz tuning, and at 55 Hz.

First max power, which shows how much power up to the thermal limit of the driver can be applied at various frequencies:

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You'll notice that the 450-watt driver can't be driven by more than 320 watts at 70 Hz before reaching xmax, and at 82 Hz (first overtone of low E), 360 watts. In contrast, the 55 Hz tuning allows it to reach 405 watts before exceeding xmax at 82 Hz, which is the predominant overtone of the electric bass at low E, which means that's where the bass demands the most power. You'll also note that the dip is less wide, impacting less content.

So while the 55 Hz tuning unloads at a higher frequency, for electric bass even with some low EQ that happens at frequencies where there is a lot less output from the bass, and indeed by my experience using the driver in that size of box with some low bass boost, I never unload the driver or even hear signs of stress when driving with 300-400 watts and a 5 string bass with a drop A Hipshot. And where I do demand more power, the driver is less stressed.

Next, the maximum SPL graph.

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You'll notice that at 55 Hz (first and predominant overtone of my Hipshot when doing drop-A0) and above there is more output available, and less excursion limiting in the crucial midbass. Having used both tunings with such a cab for weeks, I can safely say that the 55 Hz tuning is more effective even for 5-string. And for synth bass? Well, at the point where that is being used heavily, it's time to go to a 3015LF in a cab with a dedicated midrange driver : }

Of course my example here differs for different drivers, which is why it's wise to design (and test) on a case-by-case basis.
 

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