Hi,
I'm planning to build a Speaker along a well-known two way classic design and use the original components. But our living room doesn't allow the original dimensions. So the box will be somewhat lower and not as wide, compared to the original, but much deeper to keep the internal volume of 140 litres. Internal measures of my project will be 400 mm width, 700 mm height, and 500 mm depth.
The original speaker is vented by two tubular ports of 102 mm diameter and 210 mm length. The dimensions of my baffle doesn't allow me to arrange the same tubular ports on it.
May I arrange the two ports at the back wall instead? Or may I substitute them by two triangular ports of the same aera in the lower corners, that is glueing two mitred boards to the bottom board and each side wall?
If so, may I keep the original length?
If not, how do I calculate the suitable length of my triangular ports?
Best regards!
I'm planning to build a Speaker along a well-known two way classic design and use the original components. But our living room doesn't allow the original dimensions. So the box will be somewhat lower and not as wide, compared to the original, but much deeper to keep the internal volume of 140 litres. Internal measures of my project will be 400 mm width, 700 mm height, and 500 mm depth.
The original speaker is vented by two tubular ports of 102 mm diameter and 210 mm length. The dimensions of my baffle doesn't allow me to arrange the same tubular ports on it.
May I arrange the two ports at the back wall instead? Or may I substitute them by two triangular ports of the same aera in the lower corners, that is glueing two mitred boards to the bottom board and each side wall?
If so, may I keep the original length?
If not, how do I calculate the suitable length of my triangular ports?
Best regards!
Putting the vents on the backside is typically OK. If you go with the triangular ports, it should work well as long as the area of the surface of the triangle is the same as the circular surface area of the port and the length the same. I would keep them at right triangles too.
Mike
Mike
Hi!
No problems placing the ports at the back of the enclosure, provided your speakers will not be standing hard up against the rear wall of the room. If a port is up against a wall, the vibrating mass of the air inside the port could be affected by the air trapped between the speaker and the wall, which could alter the resonant frequency of the port.
Regarding the triangular corner ports - something nags at me that, due to their proximity to the internal walls of the enclosure, their dimensions would have to be calculated to take account of that proximity. I would research this a little further.
This was exactly my concerns! I suspect the enclosure walls, which form two of the three triangle sides, will virtually extend the ports' length.
As I don't know the math, I think I'll go the way of matching by measuring the system's impedance, prepare boards of several lenths and tweak until it fits, i.e. two summits of the same height. Is this a good idea?
Best regards!
As I don't know the math, I think I'll go the way of matching by measuring the system's impedance, prepare boards of several lenths and tweak until it fits, i.e. two summits of the same height. Is this a good idea?
Best regards!
I've had a wee fish around the web and the best I've come up with is to experiment with the length of the triangular port. Make it longer than calculated for a 'normal' port then whittle it down to size. There apparently needs to be an end correction, but I haven't come up with the maths to determine it!
If it's like squaring a round horn, then due to friction the area needs to be greater, with the sides being the round horn's diameter rather than its circumference/4.
If stuck in corners with two sides being the cab walls, then there's a huge end correction for 'shelf' vents that can sometimes require making the vent just a [larger] baffle cutout. Audio pro designer bjorno has posted some math for a shelf vent, but no clue how to adapt it to triangular unless it's as simple as halving the end correction [making the 'shelf' longer], but I'm no mathematician, so leave it to others to figure out.
GM
I found the attached image a while ago when trying to work out differences in port length for shelves etc. It doesn't specifically refer to triangular ports, but does address square corner ports which might be closer than other approximations?
I should point out I haven't built anything based on these calculations, so can't verify their accuracy.
I should point out I haven't built anything based on these calculations, so can't verify their accuracy.
Attachments
Just a thought. Obtaining two impedance humps of the same amplitude is the 'classic' way of tuning a bass reflex cabinet.
However, this particular tuning may not have been employed in your speakers.
Perhaps you should obtain an impedance plot of the original speakers then try to reproduce it in your modified enclosures?
Thanks! I keep 'misplacing' my link to it. 🙁
K = 1.728 is what I'd try as 'close enough' since tuning to a specific Hz isn't normally critical except for tuning to Fs [equal humps] when coupled to a high output impedance tube amp.
GM
The wall thickness of the hull must be considered in the length of the port. And the shape of the port - round, triangular, square - does not matter - the area of the port is more important.
Hi David,
your image supposedly is an excerpt of a German book or paper. Do you know which one, so that I could investigate some further?
Hi Datsun,
both triangular ports together will represent the same area as a square of 12.8 cm length, which is exactly the same cross section area of two circular ports of 10.2 cm internal diameter.
I think I won't opt for vents in the back wall, what would be the easiest way to do, as the enclosure yet will be 55 cm deep, and placing them in an appropriate distance from the wall most certainly will heavily struggle with WAF 😉.
Best regards!
Hi Kay,
Unfortunately I only found it via a google search, and it was on this site - you can see the URL of the thread at the bottom of the image - that's all I know about it I'm afraid.
I forgot to say - if the port has a low resonance, below the voice range, and the speakers have small legs, then it can be brought to the floor.
What do you recommend as an appropriate clearance between the enclosure's bottom and the floor, if the vents were showing downward?
Best regards!
Best regards!
Any - from the store accessories for home furniture.
A more "advanced" option for floors with a small height difference: SoundCare SuperSpike 1 - €15.90 : AUDIO-HI.FI, Интернет-магазин с доставкой в Россию
If the floors are perfectly smooth, then:
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I have seen a clearance of 80 to 100mm being recommended on this forum, but have no evidence to substantiate the figures.
And without evidence, this is understandable - you need to recalculate the port area along the length of its circumference and get the height of the legs.
For example, for a port with a diameter of 5 cm, the height of the legs is at least 1.25 cm.
Sure? I think that the distance between the bottom panel with ports and the floor is of the same importance as the distance between the rear panel with ports and the wall?!?
Best regards!
Been looking around and have found it suggested more than once that the gap should be at least equal to the diameter of the port.
Kay, sound pressure from the port should not experience resistance when exiting the speaker. Just mentally imagine a strip with a length of the port circumference and an area not less than that of the port - the height of the legs will be several centimeters.
If the port has little pressure, then it is more convenient to put it on the back wall of the loudspeaker - here the corners of the front wall will help.
If the port has good pressure, then it is placed on the front side of the speaker.
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