is this a good design?
driver: http://www.europe-audio.com/document.asp?document_id=1709&link=datasheets\seas\h1305.pdf
interior volume 58.75x30x50=88.88liters
length of port: 107.58
port entrance and exit: 13.75x13.75
tuning at: 24.3 hz (requiring final volume of 80.5liters)
8.38 liters being left for driver, 2.5*2.5 cross and T bracing. and padding
external dimentions high=80 wide=35 deep=55
all wood 25mm ply (or mdf) all corners rounded off nicely
here is a rougth scetch up (please excuse my poor angles and reprensentation)
image hosting jpeg
and simulation
jpg image hosting
is this a suitable port
i understand that a pipe will have a resonence, and a way up the spectrum it will have another one that is louder. does this occur with reflex ports like this preposed one? and will i have decresed its effect by having the port entrance a way away from the woofer
driver: http://www.europe-audio.com/document.asp?document_id=1709&link=datasheets\seas\h1305.pdf
interior volume 58.75x30x50=88.88liters
length of port: 107.58
port entrance and exit: 13.75x13.75
tuning at: 24.3 hz (requiring final volume of 80.5liters)
8.38 liters being left for driver, 2.5*2.5 cross and T bracing. and padding
external dimentions high=80 wide=35 deep=55
all wood 25mm ply (or mdf) all corners rounded off nicely
here is a rougth scetch up (please excuse my poor angles and reprensentation)
image hosting jpeg
and simulation
jpg image hosting
is this a suitable port
i understand that a pipe will have a resonence, and a way up the spectrum it will have another one that is louder. does this occur with reflex ports like this preposed one? and will i have decresed its effect by having the port entrance a way away from the woofer
With information provided your -3dB point will be at 50Hz, not realy desireble. The worst thing is that low frequency will start dropping already at 150Hz. Your tuning point is far too low. You can keep box size at 80 Liters and tune port to between 34 - 35Hz. that will give you flat response and -3dB cut off point at 35Hz. Using standard circular port. Kind of port you are intending to use is not easy to tune and can cause a lot of problems...Good luck...
Forgot to say, port diameter 75mm, length 85mm; or port diameter 50mm, length 24mm... ( tune to exact length if you have that ability...).
i was looking for a smooth roll off that was like a sealed cabinet, ownly 3db louder over an extended range. this then means i am -6db at 30hz, and with soft equailisation and/or room gain it should be "flat"to 30hz
in my mind tuning to 34 would end up with with too much bass at 40/50 hz
-3db at 50hz and -6db at 30hz is a very smooth roll off
so apart from the fact that it is tuned too low. will it work as i desire?
what i am really asking is if the port will work and provide the plot, shown in blue, which offeres a amplified responce over a sealed cabinet (yellow)
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WaVe,
I think you may be over-sizing the port but i would need to run simulations to confirm. I see you have 14mm of Xmax in the specs for the simulation, the driver actually only has 7mm of Xmax. The specs listed are for peak-to-peak (both ways) but your simulation is assuming "14mm one-way" linearity. I'm not sure if you were trying to design a port to accommodate an acceptable air velocity based on a 14mm Xmax or not. I'll try to run a sim later on to figure out what's going on here.
I think that Tomom is on the right track in suggesting a more compact port with more of the space allocated to box volume rather than port volume, however, I think you should disregard his input regarding the rolloff... Your simulated rolloff looks great IMO. To be honest, there is a TON of room for tinkering in this area but it all comes down to personal taste, and application. A nice controlled "slight bump in efficiency" over sealed is a very good approach IMO. The nice thing about such an approach is that, while bass may fall off in some applications and feel a bit weak, it is unlikely to ever sound "boomy" and annoying. A subdued but low distortion bottom end is more apt to come across as being [subjectively speaking] poised and controlled, compared to a "boomy" alignment.
I think you may be over-sizing the port but i would need to run simulations to confirm. I see you have 14mm of Xmax in the specs for the simulation, the driver actually only has 7mm of Xmax. The specs listed are for peak-to-peak (both ways) but your simulation is assuming "14mm one-way" linearity. I'm not sure if you were trying to design a port to accommodate an acceptable air velocity based on a 14mm Xmax or not. I'll try to run a sim later on to figure out what's going on here.
I think that Tomom is on the right track in suggesting a more compact port with more of the space allocated to box volume rather than port volume, however, I think you should disregard his input regarding the rolloff... Your simulated rolloff looks great IMO. To be honest, there is a TON of room for tinkering in this area but it all comes down to personal taste, and application. A nice controlled "slight bump in efficiency" over sealed is a very good approach IMO. The nice thing about such an approach is that, while bass may fall off in some applications and feel a bit weak, it is unlikely to ever sound "boomy" and annoying. A subdued but low distortion bottom end is more apt to come across as being [subjectively speaking] poised and controlled, compared to a "boomy" alignment.
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Long ports have strong resonances. Are you using this as a sub, or as a woofer - where will it be crossed over? The organ pipe resonance of your design is at ~160Hz.
Your woofer is really only 7mm xmax so it would handle about 50watts before linearity would become a concern above resonance with your design.
A 10.16cm diameter port about 44cm long would give you the same 24.3 Hz resonance and still would not chuff (15m/sec at 50 watts). The spurious resonance of a 44cm port would be at about 390Hz
A 7.62cm x 23cm port gives a velocity of 26m/sec (more on the edge - a radiused edge would be appropriate) and resonates at 740Hz.
FWIW, I have a commercial design here that has a predicted 60m/s port velocity at 100W with a straight cardboard tube and I have never heard it chuff except when using test tones.
Your woofer is really only 7mm xmax so it would handle about 50watts before linearity would become a concern above resonance with your design.
A 10.16cm diameter port about 44cm long would give you the same 24.3 Hz resonance and still would not chuff (15m/sec at 50 watts). The spurious resonance of a 44cm port would be at about 390Hz
A 7.62cm x 23cm port gives a velocity of 26m/sec (more on the edge - a radiused edge would be appropriate) and resonates at 740Hz.
FWIW, I have a commercial design here that has a predicted 60m/s port velocity at 100W with a straight cardboard tube and I have never heard it chuff except when using test tones.
FWIW, I ran a sim for you in TLwrx. The speaker output agrees with your sim. Acting as a transmission line, your port will have resonances about 150Hz, 300Hz, etc, but these are easily damped with a bit of light stuffing. In reality, your port will have almost negligible output (except for the resonant spikes), the important thing is the control over the woofer. I've been using this approach myself, lately.
As far as Xmax concerns go, are you really going to be pushing 100 watts through the speaker? This is something else I've had to deal with, mostly by de-rating the system's power handling.
As far as Xmax concerns go, are you really going to be pushing 100 watts through the speaker? This is something else I've had to deal with, mostly by de-rating the system's power handling.
It will be crossed at 500hz to this midrange... H1262-08 - Seas MCA15RCY midrange - Europe Audio
As far as i now, know all tubes have a fundimental resonence, followed by a load of higher harmonics that are usally in a fibonacci type sequence
From what i have learned, bass reflex and transmission line speakers both work with the same unlerlying principle
My biggest priority is not messing up the 100hz-500hz range that the driver will be producing. The second is not to have a boom or a tuning at 34hz. The third is obviously bass
I dont understand how in the sims this port works over such wide range. As all pipes have a fundimental.
However assuming that it does work..
Because this port has a minimal effect on a wide range of frequencys, as apposed to a strong effect on a narrow range of frequencys, i was rightly or wrongly assuming that i would have many inaudiable harmonics, as apposed to fewer more intense harmonics....
I tend to push the amount of watts into a speaker that it is happy with.. i do this by observing the cone motion. If it starts moving too much i turn it down abit.
In the final speaker i am trying to find a happy balance between range quality and volume
Keriwena. You say you have been using this approach lately? I am interested, please elaborate. Will the harmonics really not be an issue? As you seem to disagree slightly with Ron E. If you say the port contribution to the sound is negligible, what is the advantage of this “control over the woofer” that you mentioned.
This is all getting very interesting now
No, the port resonates first in combination with the box - that is the port tuning frequency - then comes the L/2 (and multiples) organ pipe resonance chain above this which is due only to the port. A TL has the latter resonances (at L/4 in this and multiples), but it doesn't have the simpler mass-spring resonance of a ported enclosure.
I would go with a smaller diameter (area), shorter port, mounted on the rear of the enclosure.
I don't understand what you are trying to say here - hopefully the above clears it up for you.
The first attachment is your proposed enclosure, simmed as a box with a t-line attached. Next is the same thing, but with the pipe reduced to .55m. The total output (blue line) looks much better, but if you look at the speaker (green line) you'll see it drops off suddenly, to be replaced by the port output (dashed line). Trouble is, the port has dreadful transient response. It sounds great with cellos, too fat with electric bass, and it makes kick drums sound like they not only put in a pillow for damping, but all the bed covers. More of a thum than a thump. Certainly not the thwack of a well-tuned kit.
So, I've been using lower pipe tunings, as you did, to get more extension from the speaker itself, rather than rely on the output of the port. With a bit if judicious EQ, the result is much closer to what you'd actually hear in the studio.
The third attachment shows the same plot as the first, along with a plot with minimal damping in the pipe. As you can see, those resonances are easily tamed.
(It's probably worth noting the pipe output in these graphs actually measures about -9 dB lower than is shown. That means those nasty spikes predicted by the blue lines don't really occur.)
So, I've been using lower pipe tunings, as you did, to get more extension from the speaker itself, rather than rely on the output of the port. With a bit if judicious EQ, the result is much closer to what you'd actually hear in the studio.
The third attachment shows the same plot as the first, along with a plot with minimal damping in the pipe. As you can see, those resonances are easily tamed.
(It's probably worth noting the pipe output in these graphs actually measures about -9 dB lower than is shown. That means those nasty spikes predicted by the blue lines don't really occur.)
Attachments
thankyou for the advice. 🙂
the current preposed box size is acceptable. so that aside..
a narrower port with the same tuning would still be offering me (my deduction below)
(bassed on your previous comment of the neglegable port output) would i be getting more from the port?
what im trying to say.. what is in essence the advantage of having a smaller diameter port?
i admit i liked the idea of how the area above the port was flat, and how the port fitted perfectly in the bottom of my box....
i am willing to "tweek" the design though, if a wiser voice so suggests, and i understand "why"
ok it was just theoretical deduction.
a port tuned higher was offering a peek that was for example 35-40hz. this port was creating only 2-3db- but over a broader range of frequencys. so i deduced if a port with a high resonence in a narrow frequency range had strong harmonics, then a port with a lower resonence over a broader frequency range would have thus weaker harmonics. this was just a deduction. pay it no heed.
im assuming that simulation 3 was the output with driver and port combined and isnt -9db😱
firstly: i must say. this is great progress and i appreciate you running these simulations for me
secondly:
i think you where saying, keep it how it is because a 55cm port would make is sound "rubbish" and just add some light dampening, to take care of resonances...
i admit i may be having abit of trouble deciphering what your conclusion was, so i may be wrong...
according to ron E and confurmed by my sim: a 55 cm port that is 10x10 will have the exact same responce as my preposed 108cm by 13.75x13.75
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The area of the port has nothing to do with the shape of the port resonance (tuning frequency) or its bandwidth. A smaller diameter, shorter port just moves the organ pipe resonances out of your passband. Tuning low is your choice, you can still use a shelf, just make it smaller...make it 13x5cm or 26x2.5cm something like that....
simulation with 4" diameter (or equivalent area) port. The port output is the inverted "U" shaped response - it would look the same for (essentially) any size port of the same tuning. Not shown are the organ pipe resonances, which move higher in frequency as the port gets shorter..
I agree with Ron E ( and from my experience) that long ports have undesirable (and unpredictable sometimes) resonances; in particular bends in ports should be avoided if anyhow possible. Yoy can acheive same result by using 50mm diameter and 50mm lond circular port, or 75mm diameter 140mm long one. That would tune it to 29Hz and give you curve you are aiming for, -6 at 30Hz and about -2 at 50Hz. I have attached simulation.
Smaller port diameter allows you to have less deep box basicly, but if diameter too small, it may become noisy and eventualy you will hear noise of air rushing through...
Smaller port diameter allows you to have less deep box basicly, but if diameter too small, it may become noisy and eventualy you will hear noise of air rushing through...
you have convinced me... 🙂 this pdf🙂 is just what i was looking for. it is for my desired tuning, and it looks promising, it will take some chewing. but the impedance higher up the responce looks clean, which should hopefully allow for a half decent arguementation to my chosen midrange
i will redesign the box to accomidate for the 10cm x 10cm x 55cm port. you sound like you know what your talking about. (and the 5 and 10 numbers sound nice and in keeping with my 2.5mm thickness
i will re up a new box scetch tomorrow
im still curious though how if both ports are the same internal volume and tuning, how the shorter one has harmonics that start higher in the frequency range... (however i will be researching this of my own accord)
i agree with Keriwena's opinion. i dont want the port tuned higher. he explained it fairly well. my view was also expressed somewhere along the line...
i will factor in your view about non curved ports though, but im not sure it will fit uncurved. i dont want to be making it smaller that 10x10
The two ports will have different internal volumes. Tuning in a BR port is a function of surface area of the opening to the length. To get the same tuning as a port with larger opening surface area and longer length you need to shorten the length in conjunction with the "mouth" area. (a simple ratio)
Now the pipe resonance has to do with length, a 34" port has a pipe resonance ~200Hz, a 17"Long port has a pipe resonance of 400Hz, 8.5" = 800Hz, etc. Pipe resonance only deals with the length of the port not the opening surface area or port tuning.
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how about the amplitude of the pipe resonances? does the larger or smaller port have the loudest resonances,
or are they equalIf your only demand is to attenuate low frequency as per your diagram, you would me much better off to use closed box. Much less complicated work (box), no frequency shifts etc...Any port will augment low end frequncies, BR or TL, so what is the point of introducing them in the first place if you are happy with subdued low end...just my opinion.
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