I've built a FAST System with Fostex FE 83 fullrange driver and 8' Bass driver from RFT Typ L2911 (these bass drivers produced in German Democratic Republic have been a good buy in the past).
I know need some advice to improve the enclosure design and the crossover.
For a first try I'm using the bass driver in a 20 Liter closed cabinet.
Which gives good bass but not lower than 60 Hz I guess. Bassreflex design for this chassis doesn't give good results as I tried out.
So I'd like to go for Transmissionline Design.
Maybe someone could calculate a Transmissionline with chamber + line for me ?
Here are the specs of the bass driver
F-Range: 40 Hz – 9 KHz, 4 Ohm
Qt: 0,57
VAS.: 23 Liter
fc: 50 Hz
efficency: 88 dN
For crossover I took 6db filter
Bass 4,8 mH
FE 83 (in small closed cabinet) 50µF
Maybe a 12db filter should give better results ?
Who could give me advice what to improve here.
Unfortunately the FE83 plays 3 db louder than the bass driver
I know need some advice to improve the enclosure design and the crossover.
For a first try I'm using the bass driver in a 20 Liter closed cabinet.
Which gives good bass but not lower than 60 Hz I guess. Bassreflex design for this chassis doesn't give good results as I tried out.
So I'd like to go for Transmissionline Design.
Maybe someone could calculate a Transmissionline with chamber + line for me ?
Here are the specs of the bass driver
F-Range: 40 Hz – 9 KHz, 4 Ohm
Qt: 0,57
VAS.: 23 Liter
fc: 50 Hz
efficency: 88 dN
For crossover I took 6db filter
Bass 4,8 mH
FE 83 (in small closed cabinet) 50µF
Maybe a 12db filter should give better results ?
Who could give me advice what to improve here.
Unfortunately the FE83 plays 3 db louder than the bass driver
Transmissionline model (enclosure plan) for RFT L 2911
I'v attached a plan for a Transmissionline enclosure which I'd like to choose for the described F.A.S.T. System with Fostex FE 83 and RFT L2911.
This design was used for a 10' driver, Coral Beta 10 in the eighties.
It was tuned to 40 Hz.
For the L2911 the breadth of the cabinet should be reduced.
I wonder if the chamber behind the bass driver should also be reduced, because I read that there is a relationship between sd of the driver and the linke wideness.
The FE83 should get an extra enclosure (closed) with around 1 liter, placed above the enclosure for the bass driver. (datasheet of FE 83 is attached)
I'v attached a plan for a Transmissionline enclosure which I'd like to choose for the described F.A.S.T. System with Fostex FE 83 and RFT L2911.
This design was used for a 10' driver, Coral Beta 10 in the eighties.
It was tuned to 40 Hz.
For the L2911 the breadth of the cabinet should be reduced.
I wonder if the chamber behind the bass driver should also be reduced, because I read that there is a relationship between sd of the driver and the linke wideness.
The FE83 should get an extra enclosure (closed) with around 1 liter, placed above the enclosure for the bass driver. (datasheet of FE 83 is attached)
Greets!
These appear to be a measured pair. If so, then the published specs will calculate a ~35% too small a cab for one and a ~75% too large a cab for the other. This could explain why it didn't do well in vented, which isn't as tolerant of mis-tuning as a TL.
Qms: zwischen 4,32 u. 4,61
Qes: zwischen 0,57 u. 0,62
Qts: zwischen 0,50 u. 0,54
Zmax: zwischen 30,6 und 31,6
Rdc: 3,6
Fs: zwischen 45,1 und 48,8
Vas: zwischen 20,4 und 36,99
Of course this assumes yours fall within these, so Caveat Emptor if you don't measure yours. FWIW, I always try to err on the large side since it's got more tuning options, especially if some form of TL, but if the extra size is a room space/WAF/whatever problem, then I guess go with the published or even the average of them to get the theoretical best trade-off between size, performance: 27.47 L Vas, 47.49 Hz Fs, 0.52 Qts.
Regardless, they all calculate a 36-37 Hz Fb T/S max flat vented alignment, so this is the lowest it should be tuned IME and ideally ~69-88-90 Hz depending on the specs used for a max flat impedance alignment (Fs/Qts).
You read wrong information then, 'Sd' per se isn't used in speaker cab design, only in calculating its peak SPL capability. MJK does use it as a convenient way to define a cab design's cross sectional area (CSA = width x depth) in his MathCAD software and decades ago David Weems published a rule-of-thumb TL design routine based on Sd and a driver's Fs that by and large yielded mediocre results at best, but to amateur DIYers back then it was better than nothing.
Today, MJK's CLASSIC TL and/or Rick Schultz's ALPHA TL design routines for T/S specs are what you want to use.
WRT XO advice, there's not enough information to comment beyond the fact that it's 'best' to have ~one octave of ~flat response on either side of the XO point/slope order to ensure it's attenuated enough to be out of hearing range, so let's say the HF is ~flat to 150 Hz before rolling off, then 4th order = 300 Hz, 3rd/424 Hz, 2nd/600 Hz, 1st/2400 Hz.
From this we see that without response measurements of both drivers, especially the (mid-bass) woofer's, XO design is a real crapshoot to get right enough for the DIYer even if done by ear if it's not at least 2nd order or in our acute hearing BW centered at ~2 kHz.
GM
These appear to be a measured pair. If so, then the published specs will calculate a ~35% too small a cab for one and a ~75% too large a cab for the other. This could explain why it didn't do well in vented, which isn't as tolerant of mis-tuning as a TL.
Qms: zwischen 4,32 u. 4,61
Qes: zwischen 0,57 u. 0,62
Qts: zwischen 0,50 u. 0,54
Zmax: zwischen 30,6 und 31,6
Rdc: 3,6
Fs: zwischen 45,1 und 48,8
Vas: zwischen 20,4 und 36,99
Of course this assumes yours fall within these, so Caveat Emptor if you don't measure yours. FWIW, I always try to err on the large side since it's got more tuning options, especially if some form of TL, but if the extra size is a room space/WAF/whatever problem, then I guess go with the published or even the average of them to get the theoretical best trade-off between size, performance: 27.47 L Vas, 47.49 Hz Fs, 0.52 Qts.
Regardless, they all calculate a 36-37 Hz Fb T/S max flat vented alignment, so this is the lowest it should be tuned IME and ideally ~69-88-90 Hz depending on the specs used for a max flat impedance alignment (Fs/Qts).
You read wrong information then, 'Sd' per se isn't used in speaker cab design, only in calculating its peak SPL capability. MJK does use it as a convenient way to define a cab design's cross sectional area (CSA = width x depth) in his MathCAD software and decades ago David Weems published a rule-of-thumb TL design routine based on Sd and a driver's Fs that by and large yielded mediocre results at best, but to amateur DIYers back then it was better than nothing.
Today, MJK's CLASSIC TL and/or Rick Schultz's ALPHA TL design routines for T/S specs are what you want to use.
WRT XO advice, there's not enough information to comment beyond the fact that it's 'best' to have ~one octave of ~flat response on either side of the XO point/slope order to ensure it's attenuated enough to be out of hearing range, so let's say the HF is ~flat to 150 Hz before rolling off, then 4th order = 300 Hz, 3rd/424 Hz, 2nd/600 Hz, 1st/2400 Hz.
From this we see that without response measurements of both drivers, especially the (mid-bass) woofer's, XO design is a real crapshoot to get right enough for the DIYer even if done by ear if it's not at least 2nd order or in our acute hearing BW centered at ~2 kHz.
GM
Thank you Greets! for your detailed answer to my transmission line project questions.
Unfortunately, I am not able to check the paramaters of the bass driver.
That's why I would trust on the rightness of the values I got from the manufacturers datasheet (qts 0,57, VAS 23 Liter, fs 50 Hz).
I'm not familar with mathsheet calculations from Martin J. King.😕
Maybe, you could give me some help, what to change on the design I posted.
Concerning X-over I would like to go for 12 db filters.
X-over frequenzy around 200 Hz.
Unfortunately, I am not able to check the paramaters of the bass driver.
That's why I would trust on the rightness of the values I got from the manufacturers datasheet (qts 0,57, VAS 23 Liter, fs 50 Hz).
I'm not familar with mathsheet calculations from Martin J. King.😕
Maybe, you could give me some help, what to change on the design I posted.
- How many liters should the chamber behind the bass driver be ?
- The wideness of the inside enclosure should be around 220 mm.
- Is there anything more to change/improve on the line dimensions ?
- How many liters should the small closed enclosure for the fullrange Fostex FE 83 driver have ?
Concerning X-over I would like to go for 12 db filters.
X-over frequenzy around 200 Hz.
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