Hi everyone,
I'm trying to design an enclosure for a subwoofer I found in my house. I measured the Thiele-Small as best I could (I attach the file) and with some calculations I have calculated the opening for the bass reflex of the box.
I calculated the Fb of this box with this formula:
what would look like this replacing values:
and it would result in 102,393
Then to calculate the dimensions of the bass relfex, I calculate it with a nomogram, this specific one:
In which the value of the cubic feet of the box is located, and then on the other line, the value of Fb. These two points are joined with a line until they intersect with the third line, from there, a straight line is drawn parallel to the X axis.
So every time this parallel touches one of the curved lines there is, a line can be drawn downwards. And there you obtain the value of the area of the opening, and the depth of the opening.
What happens is that my parallel is on the lowest line that can be observed of the third straight line. Therefore, the smallest option for the aperture is an aperture of 12.5 inches in diameter, and about 2.7 inches in depth, which is quite large, and impractical.
My question is, first, is this whole process okay?
And second, if that's okay, is there any way to compensate the area of the opening, by length of the opening? That's more practical.
I'm trying to design an enclosure for a subwoofer I found in my house. I measured the Thiele-Small as best I could (I attach the file) and with some calculations I have calculated the opening for the bass reflex of the box.
I calculated the Fb of this box with this formula:
what would look like this replacing values:
Then to calculate the dimensions of the bass relfex, I calculate it with a nomogram, this specific one:
In which the value of the cubic feet of the box is located, and then on the other line, the value of Fb. These two points are joined with a line until they intersect with the third line, from there, a straight line is drawn parallel to the X axis.
So every time this parallel touches one of the curved lines there is, a line can be drawn downwards. And there you obtain the value of the area of the opening, and the depth of the opening.
What happens is that my parallel is on the lowest line that can be observed of the third straight line. Therefore, the smallest option for the aperture is an aperture of 12.5 inches in diameter, and about 2.7 inches in depth, which is quite large, and impractical.
My question is, first, is this whole process okay?
And second, if that's okay, is there any way to compensate the area of the opening, by length of the opening? That's more practical.
Consider using WinISD http://www.linearteam.org/ Fairly easy to use. Might be easier than what you are doing.
Greets!
No, your box is larger than the 20 ft^3 chart limit.
No.
Use this math to calculate the box size, tuning and use this port calculator to get vent length based on a vent area = driver Sd assuming port end correction is the 0.732 default, otherwise use the attached chart to determine it:
T/S max flat alignment:
Vented net volume (Vb) (L) = 20*Vas*Qts'^3.3
(Ft^3 = (Vb)/~28.31685)
Vented box tuning (Fb) (Hz) = 0.42*Fs*Qts'^-0.96
F3 (Hz) = Fs*0.28*Qts'^-1.4
(Qts'): (Qts) + any added series resistance (Rs)
All that said, vented alignments are normally limited to much lower Qts' (~0.403 where Vb = Vas, Fb = Fs) to limit tuning to around/at Fs since below Fs the driver's excursion limited power handling rapidly drops away.
Attachments
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There is issues that come about with measurement techniques
So there could be a few issues for a realistic model.
Qts seems very high Fs seems very high also for the Sd size
Is this a 12" woofer?
Seems would have to be live sound woofer possibly
Possibly it is very high Qts but likely not that high and Fs would be considerable lower.
Almost impossible to calculate a alignment
SPL is very good, but 723 is a strange number for a 12" or even a 15" Sd
Might be slight errors.
Reasonable port size and length is easy to figure out.
As far as alignment or box size likely not possible
Green entered , Blue auto calculated.
Auto calculated on purpose to double check sheet provided.
They match correctly, but there seems to be questionable values.
@WhiteDragon , you got pretty much the same results as I did with WinISD. It was impossible to find a reasonable vented alignment. In fact, about the only configuration that makes sense is an open baffle.
A few golden rules I was taught over four decades' ago and which have served well ever since:
1. Start with a port area equal to Sd and reduce as required until the port fits the box.
2. Port length should not exceed twice its diameter.
3. Employ a single circular port.
4. Ensure that both ends of the port have similar airflow conditions and radius the edges generously.
5. Don't tune for the very lowest f3 possible above everything else.
6. Move a lot of air - GENTLY. Use absolutely the largest driver(s) you possibly can.
Finally - Never build a ported enclosure if a sealed one will do the job!
1. Start with a port area equal to Sd and reduce as required until the port fits the box.
2. Port length should not exceed twice its diameter.
3. Employ a single circular port.
4. Ensure that both ends of the port have similar airflow conditions and radius the edges generously.
5. Don't tune for the very lowest f3 possible above everything else.
6. Move a lot of air - GENTLY. Use absolutely the largest driver(s) you possibly can.
Finally - Never build a ported enclosure if a sealed one will do the job!
What I was trying to say and hopefully other members can help with
measurements suggestions.
The data is not correct
Nobody would manufacture a driver as shown.
Curious if it was damaged or overheated or whatever surround material it has
If treated cloth it may have hardened.
Wild guessing of course but something will explain the odd data.
Assuming it is typical 3 to 4 mm excursion driver
use 2x 3" or 2.5" round ports and calculate length and your done.
Velocity would be fine for its actual linear range.
If trying to make a slot port then the error factors with sharing walls
need to apply.
Can help you with that with accurate data.
Looking at Qts yes it could very well be more suitable sealed.
Whatever box it came from should be a big hint for design guide
measurements suggestions.
The data is not correct
Nobody would manufacture a driver as shown.
Curious if it was damaged or overheated or whatever surround material it has
If treated cloth it may have hardened.
Wild guessing of course but something will explain the odd data.
Assuming it is typical 3 to 4 mm excursion driver
use 2x 3" or 2.5" round ports and calculate length and your done.
Velocity would be fine for its actual linear range.
If trying to make a slot port then the error factors with sharing walls
need to apply.
Can help you with that with accurate data.
Looking at Qts yes it could very well be more suitable sealed.
Whatever box it came from should be a big hint for design guide
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While I agree in principal, but having seen some pretty weird spec'd drivers for a variety of specialty apps; till we know more about what it was designed for I'm not inclined to dispute it, though fully aware from reading many BB/net forum threads/postings and witnessed incorrectly measured specs over the last ~ 6 decades, I know there's plenty of room for minor errors to turn them into floobydust.
Indeed, the Sd suggests a 15" driver (or very close) but the moving mass is only 17 grams? That really doesn't sound right.
Yes and 75 Hz for Fs would be rather poor 15"
With such high Qts
It is almost looking like " open baffle" not in a modern sense.
Would be a open back 1940's radio speaker with very very light thin cone.
And rather aged surround. To even support the data.
Which would explain the high sensitivity. AKA stiff suspension with small magnet for such high Qts
Otherwise something closer would be underhung guitar speaker.
Also designed for open back as well. And yes many large guitar speakers be about 65 to 75 Hz Fs
Pictures would help
With such high Qts
It is almost looking like " open baffle" not in a modern sense.
Would be a open back 1940's radio speaker with very very light thin cone.
And rather aged surround. To even support the data.
Which would explain the high sensitivity. AKA stiff suspension with small magnet for such high Qts
Otherwise something closer would be underhung guitar speaker.
Also designed for open back as well. And yes many large guitar speakers be about 65 to 75 Hz Fs
Pictures would help
Indeed! Very similar specs to my 1939 RCA AM, SW, 78 rpm player console's 12" field coil, which is open back, bottom plus vented slits beside the baffle.
Many thanks for all your comments.
It's probably what WhiteDragon says, since I made the measurements of the T/S parameters at home following a YouTube video (
), and I couldn't follow it completely, since it does not have the same materials.
The speaker is a Thonet & Vander model Laut BT. It is the subwoofer of the system. My intentions were to be able to get better performance out of it, putting it in a larger box. Now I don't know what to do, because if my T/S measurements are wrong, I won't be able to do the enclosure calculations, neither for this subwoofer, nor for any of my other woofers.
Any recommendations to be able to measure the parameters in a better way?
It's probably what WhiteDragon says, since I made the measurements of the T/S parameters at home following a YouTube video (
The speaker is a Thonet & Vander model Laut BT. It is the subwoofer of the system. My intentions were to be able to get better performance out of it, putting it in a larger box. Now I don't know what to do, because if my T/S measurements are wrong, I won't be able to do the enclosure calculations, neither for this subwoofer, nor for any of my other woofers.
Any recommendations to be able to measure the parameters in a better way?
The Laut BT is a modestly priced 2.1 woofer/satellite desktop system, as far as i can see, and the woofer is a 6.5 inch unit in a ported box. I'm not sure how you got an Sd of over 700 sq cm!
The original box looks to be about 10 litres volume. I'm not convinced the woofer will be worth the trouble of redesigning the box. A single 6.5 inch woofer is never going to shake the rafters.
The original box looks to be about 10 litres volume. I'm not convinced the woofer will be worth the trouble of redesigning the box. A single 6.5 inch woofer is never going to shake the rafters.
Maybe not, but plenty good enough to use for learning to do measurements, though curious too about Sd since the video does a good job of it, then Sd (cm/in^2) = dia^2*pi/4
Also, re measuring Vas, using large enough cans, jars to add weight to lower measured Fs 1.56x is what I gleaned from studying the pioneers Vs the more common 1.25x I've seen in several papers and a book PE sells IIRC.
Also, re measuring Vas, using large enough cans, jars to add weight to lower measured Fs 1.56x is what I gleaned from studying the pioneers Vs the more common 1.25x I've seen in several papers and a book PE sells IIRC.
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