Hi,
Why wouldn't I build a ported midrange box?
e.g a midrange with an fs around 100hz with t/s parameters specific to ported design. What i'm thinking is extending the bass down to around 60hz in a ported enclosure?
If i model it in winisd i get a 4l box with a 2inch port 12inches long fed with 10watts for 94db flat to 65hz and port velocity of 10m/s at 60 hz.
Of course i could always make the box bigger a bit like a midrange llt but how does the port resonance come into play and how does it affect the mid range?
Why wouldn't I build a ported midrange box?
e.g a midrange with an fs around 100hz with t/s parameters specific to ported design. What i'm thinking is extending the bass down to around 60hz in a ported enclosure?
If i model it in winisd i get a 4l box with a 2inch port 12inches long fed with 10watts for 94db flat to 65hz and port velocity of 10m/s at 60 hz.
Of course i could always make the box bigger a bit like a midrange llt but how does the port resonance come into play and how does it affect the mid range?
So you are really saying you want to use a mid range driver as the woofer in a ported speaker design?
The reasons depend mostly on what you want to do with a woofer.
Other considerations would be intended crossover frequency, the polar response of woofer and mid about that frequency, distortion of the midrange at the frequency, size of the midrange cone also determines how low you can go, baffle diffraction, and a host of other things to consider.
Lastly, look at the group delay and phase plots of the ported midrange. You will need to see how those align with the woofer at the intended crossover frequency.
Personally, I see no reason to run a mid down that low. While the frequency response curves may show a fine frequency response, there are other factors like group delay, phase, and distortion to be concerned with.
A general rule of thumb is to not cross over a driver any lower than one octave above its Fs (resonance frequency). If the Fs of the mid is 50 Hz, then 100 Hz would be the lowest you can expect to crossover.
A better number is two octaves, so a 50 Hz mid should not be crossed over lower than 200 Hz.
When selecting crossover points you need to keep in mind where the crossover takes place in the spectrum and what types of instruments and voice it may intersect. Your ears are most sensitive to those crossover points and phase and group delay anomalies are easier to pick up when they are dividing a band where there is something of interest. Generally, for a 3-way system a lower crossover point of 300 to 500 Hz is typical and for good reasons.
Most mids are in a sealed box. The box size is smaller, the frequency response is more predictable, and more importantly, the phase and group delays are much more linear. Ports disrupt the phase and group delay and placing those disruptions higher up in the midband makes them more pronounced to the ear.
Also, although the software models the ideal frequency response of the driver and looks interesting, the actual response of the speaker may be something else. Check to see if the software is modeling the driver strictly on its Thiele/Small parameters or is it actually using the manufacture's published frequency response (acoustic data). Theory and actual response are two different things.
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I seem to rember about 25 years ago Focal had a lot of drivers for the
diy market. They had a couple of designs that did call for a ported midrange.
diy market. They had a couple of designs that did call for a ported midrange.
To me there would be one reason:
There is sound radiated unwanted from the port, even above fb.
If uncolored midrange is the goal, this can be a major drawback.
An "aperiodic" midrange enclosure with a mainly resistive port
(e.g. to provide higher mechanical damping or for shaping polar
dispersion) would be far more accepatable for me.
Best Regards
Thanks Loren,
That all makes sense, closed with a linkwitz transform to 60 or 80 hz things look a lot cleaner than ported. All ported would allow is higher spl but with worse sound quality.
As for crossing over 1 or 2 octaves above fs is this really necessary I have 10 of these drivers running open baffle at the moment with 9db gain around fs useable output is to about 80hz or so which suits for now and due to the number of drivers excursion is kept to a very acceptable level - this is just a prototype.
I might have a play around with one in an overstuffed box I might grab some 4 inch piping and a U bend. If i model for a 4 litre box and a 47 inch "port" then stuff the port I'm assuming i lose port gain to a certain extent but keep a certain amount of the low frequency sound?
A ported box like this gives a 70hz tuning frequency but is there any actual benefit over a closed box since the stuffing will be attenuating the low freqs to a certain extent?
I can't really comment because I don't know what midrange driver you are using, what the rest of the drivers are, how they are configured, and enclosure design.
As far as how they seem, well, using your ears is pretty subjective and you also have the room, speaker placement, and source material that are part of the system.
The only real way to quantitize what you have is with a good testing program, but that is another ball of wax.
Not saying it is good or bad, just pointing out that Wilson Audio is using ported mid driver for some of their designs (Watt, Sophia, Sasha ..... )
In some cases a higher mechanical damping is advantageous, especially
if the elecromechanical damping is reduced by a passive crossover.
Depending on shape of the cabinet e.g. a rear resistive port can serve
to form a kardioid like dispersion, which can make the loudspeaker more
directional (and directivity less frequency dependent.)
I would not rely on port gain for midrange for the same reasons Loren42
pointed out before and the addtitional sound radiation problem (port resonances)
which is not as acceptable in the midrange like in lower bass regions
... why do you need port gain, Qts of driver too low ?
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Here are the T/S Params
QES 0.63
QMS 2.84
QTS 0.516
FS 89.98
VAS 1.62L
MMS 5.3
RE 3.8
BL 4.24
SD 43.9
when you put it through the likes of win isd it indicates a very ported alignment as best of course it still works in a closed or open alignment it just sub optimal.
Weird driver (i have 64 of them) as it has removable rear magnet so you can actually alter the design to a certain extent i.e. removing the magnet should increase QTS a little e.g. QTS 0.6 which will help in open or fully closed alignment.
Its a full range 4" driver from wharfedale which i purchased for line array use I have built a rough prototype using 10 of them which works very well with the secondary magnet removed but i'm just wondering if an alternative to open baffle may suit better?
QES 0.63
QMS 2.84
QTS 0.516
FS 89.98
VAS 1.62L
MMS 5.3
RE 3.8
BL 4.24
SD 43.9
when you put it through the likes of win isd it indicates a very ported alignment as best of course it still works in a closed or open alignment it just sub optimal.
Weird driver (i have 64 of them) as it has removable rear magnet so you can actually alter the design to a certain extent i.e. removing the magnet should increase QTS a little e.g. QTS 0.6 which will help in open or fully closed alignment.
Its a full range 4" driver from wharfedale which i purchased for line array use I have built a rough prototype using 10 of them which works very well with the secondary magnet removed but i'm just wondering if an alternative to open baffle may suit better?
Hi,
which is Your desired XO frequency ?
what kind of filter do you like to use ?
Woofer concept ?
Or do you want to use that driver as a woofer ?
I did not quite understand ...
which is Your desired XO frequency ?
what kind of filter do you like to use ?
Woofer concept ?
Or do you want to use that driver as a woofer ?
I did not quite understand ...
Hopefully 60hz,
active crossovers and due to extra excursion probably 4th order LR although a 2nd order butterworth looks better on paper.
More of a mid woofer without having to buy more drivers trying to lower the crossover point to subs is what i want i currently have xover set to 80hz.
Subs will be a pair of dayton dvc's probably horns of some description.
active crossovers and due to extra excursion probably 4th order LR although a 2nd order butterworth looks better on paper.
More of a mid woofer without having to buy more drivers trying to lower the crossover point to subs is what i want i currently have xover set to 80hz.
Subs will be a pair of dayton dvc's probably horns of some description.
I was under the impression that most subs dont sound their best over 80 to 100hz at the moment i'm testing using a very rubbish posted sub just to get a 'feel' for the crossover configuration of the mids. The sub in question sounds pretty poor above 80hz theres also the issue of alignment and postioning i.e. if my subs are not near the mids there may be sound integration issues so high up the bandwidth.
A crossover frequency of 100Hz, even with a mono sub
should not be a problem cocerning "intergration" and
positioning ... at least this is my experience.
What is the problem with your sub over 80 Hz ?
Distortion, Noise, Cabinet resonance ?
IMO a usable sub should be sufficiently "clean" up to 300 Hz ...
which is normally no problem, if the cabinet is stiff enough.
should not be a problem cocerning "intergration" and
positioning ... at least this is my experience.
What is the problem with your sub over 80 Hz ?
Distortion, Noise, Cabinet resonance ?
IMO a usable sub should be sufficiently "clean" up to 300 Hz ...
which is normally no problem, if the cabinet is stiff enough.
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Noise and resonance,
It a pretty naff little sub from a 5.1 sony system which is possibly why I think i have to cross lower with the mids.
If crossing at 100hz isnt an issue then i'm sorted i can let the mids roll off naturally and cross at 100 or there abouts.
Whatever sub i build with the daytons (probably bill fitzmaurice horns) should be good this high I guess.
It a pretty naff little sub from a 5.1 sony system which is possibly why I think i have to cross lower with the mids.
If crossing at 100hz isnt an issue then i'm sorted i can let the mids roll off naturally and cross at 100 or there abouts.
Whatever sub i build with the daytons (probably bill fitzmaurice horns) should be good this high I guess.
Usually, sub drivers do not operate up that high (300 Hz) cleanly. It's not the cabinet, it's the driver.
To get lower Fs one of the tradeoffs is usually a heavier cone, which is fine in the low frequency domain, but lacks the transient response needed for upper bass and there may be cone breakup issues as well, depending on the make of the driver.
On that vein, I don't know if the original poster has a frequency plot for his 4" driver, so it is a little hard to say what the driver does down to the upper bass region.
The driver has an Fs of 89 Hz, so it is unlikely that it extends down below 100 Hz without significant rolloff, even in a vented enclosure.
The high Qts of .5 leans toward the sealed cabinet domain, not the vented. A Qts of .3 or lower is better for vented.
Which is what i would have suggested... 🙂
You can make a lower tuned highpass for the midwoofers (maybe 1. Order)
to limit the excursion even further.
As Loren42 said too, the big box low tuned alignment for your high Q
driver is not very attractive.
Too much excursion (with al the related problems), steep rolloff ...
A well suited closed box or a smaller box with a resisitive leakage is
more sane for the driver.
My experienced max XO frequency for a mono subwoofer is about
120Hz, depending on behaviour of the subwoofer and the room.
When using stereo subs near the midwoofers, you may even go higher.
Best Regards
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