Used it where?
As Dave suggests, a simple reflex box calculator does not apply to your speaker.
You have little option but to experiment as I have suggested.
P.S. T/S stands for Thiele/Small parameters: https://eminence.com/pages/support__understanding-loudspeaker-data
Is 0.821 cuft correct for the box vol? I looked up the speakers (https://www.hifiengine.com/manual_library/castle/stirling-3.shtml) and the listed external dimensions were 870 x 200 x 240 mm, which becomes 0.04176 m^3 which is 1.47... cu ft. But these are external dimensions so box vol is prob smaller, and maybe 0.8 cu ft is correct...
But either way, you don't have to model it. If you can find a free tone generator app for your phone / computer and play in a sine tone you can look for the woofer motion to null. Here's how:
At low volume, adjust the tone generator to something low, below the expected tuning frequency. Turn the volume up until you can see the woofer cones moving. Get enough motion for clear visability, but not so much that you damage your woofers. Look for a mote of dust or some point on the woofer cone that is easy to keep an eye on. Slowly increase the frequency of the tone generator, and watch the motion of the cones. Cone motion will be highest below tuning frequency, then come to a minimum at tuning frequency, then rise again above vent tuning, then slowly decrease as you get to higher frequencies (200+ Hz). So where the cone motion is at min, look at the tone generator, that's the box tuning.
Pure tones for long amounts of time will heat up your voice coils, especially at tuning frequency where the cone motion is at a min, so do the test and then turn off the stimulus. Don't leave it playing.
This is the lowest tech way to find the tuning frequency. One might also do it acoustically, close mic'd to the woofer, or do an impedance sweep (Dayton DATS, Woofer Tester, other methods).
If you can model that would give you a nice port length to get started with, but if you can't, you can just pick a length and start. All else being equal, longer ports give you a lower tuning F, and smaller diameter gives you a lower tuning F. Too long and the port won't fit in the box, too small of diameter and the port chuffs / whistles with the air flow.
But either way, you don't have to model it. If you can find a free tone generator app for your phone / computer and play in a sine tone you can look for the woofer motion to null. Here's how:
At low volume, adjust the tone generator to something low, below the expected tuning frequency. Turn the volume up until you can see the woofer cones moving. Get enough motion for clear visability, but not so much that you damage your woofers. Look for a mote of dust or some point on the woofer cone that is easy to keep an eye on. Slowly increase the frequency of the tone generator, and watch the motion of the cones. Cone motion will be highest below tuning frequency, then come to a minimum at tuning frequency, then rise again above vent tuning, then slowly decrease as you get to higher frequencies (200+ Hz). So where the cone motion is at min, look at the tone generator, that's the box tuning.
Pure tones for long amounts of time will heat up your voice coils, especially at tuning frequency where the cone motion is at a min, so do the test and then turn off the stimulus. Don't leave it playing.
This is the lowest tech way to find the tuning frequency. One might also do it acoustically, close mic'd to the woofer, or do an impedance sweep (Dayton DATS, Woofer Tester, other methods).
If you can model that would give you a nice port length to get started with, but if you can't, you can just pick a length and start. All else being equal, longer ports give you a lower tuning F, and smaller diameter gives you a lower tuning F. Too long and the port won't fit in the box, too small of diameter and the port chuffs / whistles with the air flow.
A port length calculator , well , several calculators .
I was aiming to get myself an estimated starting point , using the 2" minimum suggested , but , all the calculations I have done say it is not possible .
I want to spend as little time as possible finishing them as I want to be listening and I can not do this until the placement is sorted , and I can not find there optimum position until they are finished .
Hi and thankyou for your reply , the measurements are actually 845 x 200 x 245 and the wall thickness of 25mm was taken into account , that said I do not know for sure that the answer is correct as I have no idea what I am doing .
I thought this would be a simple enclosure refurb , as a carpenter this is easy ...........
How thickis the material?
I’d guess 15mm, so 30 litres, just over a cubic foot insternal (less any bracing). Doesn’t account for any difference in height due to the plinth and spacers.
Just under 28 litres if 18mm, ie a ft3
dave
If it's of any relevance at all, I've extracted the following information from my David Weems book.
For a tuning frequency of 45 Hz and a port of diameter 2 inches, he calculates the following port lengths:
0.75 cu ft: 4 inches
1 cu ft: 2.75 inches.
Hi Galu and thankyou .
So , Ive been having a mare these last few days , but , I think I may finally be happy .
I bought a 2.5" parcel tube 1m long and have spent the last few days , cutting and listening and cutting and listening and found that I preferred 2.5" x 4" , but , could not find any substantial plastic tubing at said diameter , so , out of frustration and anger I bought 2 5" long flared ports which are approx. 1.75" in diameter and flare to 2.5" and I think they are better , or maybe Ive just had enough haha .
But as always with these things , I have discovered , or caused , another issue .
As they are small floor standers the tweeter does not sit at ear level and although the soundstage is wide and deep , it now seems quite low , almost as though I am looking down at the band .
I have tilted the speakers back as far as they go , and this made a big difference , but , its still not quite right .
My thoughts on solving this are to make a box , big enough to bring the tweeter to ear level , approx. 250mm , that will fix to the underneath of the plinths and fill said box with sand .
Is this a good idea ? is it ridiculous ? please help I have no idea .
And finally , to celebrate my achievement I had these made , can not get real ones unfortunately .
So , Ive been having a mare these last few days , but , I think I may finally be happy .
I bought a 2.5" parcel tube 1m long and have spent the last few days , cutting and listening and cutting and listening and found that I preferred 2.5" x 4" , but , could not find any substantial plastic tubing at said diameter , so , out of frustration and anger I bought 2 5" long flared ports which are approx. 1.75" in diameter and flare to 2.5" and I think they are better , or maybe Ive just had enough haha .
But as always with these things , I have discovered , or caused , another issue .
As they are small floor standers the tweeter does not sit at ear level and although the soundstage is wide and deep , it now seems quite low , almost as though I am looking down at the band .
I have tilted the speakers back as far as they go , and this made a big difference , but , its still not quite right .
My thoughts on solving this are to make a box , big enough to bring the tweeter to ear level , approx. 250mm , that will fix to the underneath of the plinths and fill said box with sand .
Is this a good idea ? is it ridiculous ? please help I have no idea .
And finally , to celebrate my achievement I had these made , can not get real ones unfortunately .
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I'm surprised that Castle hasn't placed the tweeter at a typical arm chair seated ear level. That begs the question, what are you sitting on?
Visually, a 10" extension in height could make the speakers look out of proportion. Audibly, you can but try it and note the effect.
Before committing yourself to constructing a sand-filled box, I suggest you experiment with raising the enclosures by any means at your disposal. For example, my garage is overflowing with piles of old electronics magazines that I would use to do the job temporarily!
P.S. Nice badges.
Visually, a 10" extension in height could make the speakers look out of proportion. Audibly, you can but try it and note the effect.
Before committing yourself to constructing a sand-filled box, I suggest you experiment with raising the enclosures by any means at your disposal. For example, my garage is overflowing with piles of old electronics magazines that I would use to do the job temporarily!
P.S. Nice badges.
Haha just a ordinary 2 seater couch mate .
Yeah Im surprised myself about that .
Excellent idea my friend , just so happens I have a stack of carpet tiles that will be ideal , I can start with a few and gradually increase the height until I find the spot .
I am a tad concerned about how they will look , was thinking maybe I will do the extension the same dimensions as the speakers and make a new plinth rather than extending the original plinth .
Watch this space
Yeah Im surprised myself about that .
Excellent idea my friend , just so happens I have a stack of carpet tiles that will be ideal , I can start with a few and gradually increase the height until I find the spot .
I am a tad concerned about how they will look , was thinking maybe I will do the extension the same dimensions as the speakers and make a new plinth rather than extending the original plinth .
Watch this space