I'm still dumbfounded by the pair of floor-standing speakers I got for free. The driver is a Peerless SKO-165 which claims a resonant frequency of 42Hz. What would you recommend as a port tuning frequency?
The second question is a little more complicated: a single 6.5" driver in a 22 litre cabinet is a waste of space. What are the advantages of increasing port volume? I can attain a frequency of 42Hz with a port of 45 * 90mm. But can achieve the same frequency using 65 * 170mm. What are the advantages of the bigger port.
If you cite WinISD or Hornresp in a brief reply, I'll probably ignore it. In my brain the mention of the aforementioned software translates to 'I don't know'. You see, you are saying, 'There's software for that'. Unfortunately, I comically reminded that several drivers have driven their cars into lakes after blindly following the software.
The second question is a little more complicated: a single 6.5" driver in a 22 litre cabinet is a waste of space. What are the advantages of increasing port volume? I can attain a frequency of 42Hz with a port of 45 * 90mm. But can achieve the same frequency using 65 * 170mm. What are the advantages of the bigger port.
If you cite WinISD or Hornresp in a brief reply, I'll probably ignore it. In my brain the mention of the aforementioned software translates to 'I don't know'. You see, you are saying, 'There's software for that'. Unfortunately, I comically reminded that several drivers have driven their cars into lakes after blindly following the software.
Surtsey,
1) Without knowing more driver parameters than Fs and your acceptable box size and output desire (low or loud) an Fb (Frequency of Box tuning) recommendation would be as useful as following directional software that tells you to drive into a lake.
2)At low power levels, there is no advantage to a larger port size, and a disadvantage in terms of reduced box volume. Increased port volume reduces vent noise ("chuffing", whistling) at high drive levels, and reduces "port compression" that occurs when too much of the slug of air wiggling back and forth that is producing most of the low frequency output at Fb spills out of the port.
Last edited:
Peerless of India.
This thread might be useful: Building my first cabinet with Peerless drivers
Factory data attached: they have 3 SKO165s.
dave
This thread might be useful: Building my first cabinet with Peerless drivers
Factory data attached: they have 3 SKO165s.
dave
Thank you, I already had that data but it doesn't seem to help me. Here's my thinking . . .
I have the driver and the cabinet therefore my only variable is the port (originally tuned to 50Hz). Increasing the port length to 90mm lowers the tuning frequency to 42Hz.
However I am aware that this driver is utilised and performs adequately in cabinets half this volume (Kef Koda 8 F3, 45Hz). Effectively, I have over 8 litres of virtually wasted space. Subsequently, I'd suffer no critical loss of internal volume if I increased the port volume. But my latest inclination is that there is no significant advantage in having a larger port diameter.
Make sense?
If you tune it lower in the same cabinet it won't be flat lower. Depending on the actual cabinet volume that could be a problem or not. I come to a 50L cabinet with a tuning to 38Hz to reach 45Hz F3 with the specs i have (the 8R version). The vent is a 7cm diameter 21cm long vent. Your vent is probally +/-5cm (2") to get that tuning to 42Hz with a 9cm long vent, but that will increase the air velocity way to high (38.3m/s) so you will have port noises on high volume. The 7cm diameter 21cm long vent will have an air velocity arround 19.5m/s which is within reasonable limits.
Last edited:
I've never had a problem with port chuffing in a domestic environment. It's a car thing, possibly a PA thing but not really a hi-fi thing.
Performance tuning follows universal rules. Nothing is for free. e.g. Fuel energy being equal, if you increase power you lose torque. In a subwoofer forum 'flat' is not a practical desire. We would all trade +3dB @ 40Hz for -6db @ 120Hz. 120Hz is not our problem, you need to take that up with the woofer department.
It is possible to hear it.
You'd only hear it clearly if it's a front firing port and you sit in front of the speaker, if the port is down, rear or even upwards firing all you get is a sort of poorly defined smeared out foggy bass in most common rooms and speaker placements. Easily measured as increased distortion.
If the port is insufficiently dimensioned and poorly placed it's common to blame "bass reflex" in general as being inferior and say that for example closed boxes have a tighter and more correct sound, this was the reason I started looking at bass reflex/TL variations to begin with, to prove that closed boxes where clearly superior.
A well designed box sounds good regardless of type, if you take shortcuts and disregard important data in the planning and execution phase, you end up with an inferior design.
Your solution seems impractical. Of the three variables in a speaker system the port is by far the easiest to adjust.
But if the box is to big you get a bad box alignment. Everything works tigether.
You statement is essentially equivalent to the drunk searching for the keys under the street lamp desipte not losing them there because he could see in the light.
You can search but you will not find…
It is easier to throw some solid fill in the bottom of the box than change the vent.
dave
You statement is essentially equivalent to the drunk searching for the keys under the street lamp desipte not losing them there because he could see in the light.
You can search but you will not find…
It is easier to throw some solid fill in the bottom of the box than change the vent.
dave
Dave, what you're saying seems to have very little basis in reality or logic. On one thread you're insisting an 8" sub needs 30 litres but on this thread you're claiming 22 litres is too big for a 6.5".
Again, I must go with the money on this one. Billion dollar corporations who do not rely on free Internet software for their calculations put this driver in vented cabinets of over 25 litres.
Again, I must go with the money on this one. Billion dollar corporations who do not rely on free Internet software for their calculations put this driver in vented cabinets of over 25 litres.
Vas, Fs, Qts' is all that's required to design a box, tuning.
Sd is used for calculating the Vas spec.
T/S specs explained: Thiele Small parameters equations - How each one affects the others
Basic T/S theory vented box max flat alignment:
net volume [Vb] [L] = 20*Vas*Qts'^3.3
box tuning [Fb] [Hz] = 0.42*Fs*Qts'^-0.96
[Qts']: [Qts] + any added series resistance [Rs]: Calculate new Qts with Series Resistor
For a quick reference,when Qts' is:
~0.403, Vb = Vas, Fb = Fs
< ~0.403, Vb = < Vas, Fb = > Fs
> ~0.403, Vb = > Vas, Fb = < Fs
You want a rule of thump, but in speaker design it does not exist, it's pure math and physics, and if you don't want to understand the basic of it you will never make good speakers but copies of others. GM and Planet10 are long time speaker designers with a very long list of successful designs, and their logic is very logic and based on science, not on assumptions. That is how we work here. It's the same science that those billion dollar corp. use to make theirs (but often with commercial compromises sadly enough).
Thanks for copy and pasting a bunch of data but thiele-small parameters are batch tested and may vary as much as 30% between units. These measurements change once a unit has been bedded-in, and will further change over time.
Your entire philosophy is Jenga Tower based. I understand why people want to knit sweaters from wool and patterns when the store can offer you better, cheaper. However, as the main reason for building our own speakers is to achieve 'the sound we like', a subjective pursuit. We all possess, unique stereo microphones with different frequency responses., and 'room gain' is largely governed by the position of the coffee table.
As I've said before, the object of the exercise is not to build an NS10.
Cheap units can be that bad. Really cheap could be worse.
But it is, if the factor is measuring a representitive sample, an average. The measures you, and me, and almost all other diyers do are almost always collaped from the curves at a different place than the factory data. Experience has shown me that they are a much better starting point. If one is really worried that their drivers are so out of spec a sealed box. Or something where the box plays a larger role in determining the extension the bottom like a TL or horn.
Or do a lot of measuring and working backwards if you want to optimize out of spec drivers).
Sort of like throwing spaggetti at the wall to see what sticks.
dave
I don't believe you, quality wool wear is quite expensive!
If you manage to get someone to knit you a sweater for material cost, or perhaps even given freely, you should count yourself very lucky!