Hi,
I have a pair of unused Fostex FE126E's and I am looking for a project for the summer. I don't really have that much experience at all, so any advice would be helpful.
I've been looking at TQWT enclosures, and I would probably like to build something similar to the cabinets described here: http://www.geocities.com/agalavotti/tqwt.html
These are designed for the FE164's, so I would need to alter them for appropriate use with the 126's.
Does anyone have existing TQWT plans for the 126's?
Thanks in advance.
I have a pair of unused Fostex FE126E's and I am looking for a project for the summer. I don't really have that much experience at all, so any advice would be helpful.
I've been looking at TQWT enclosures, and I would probably like to build something similar to the cabinets described here: http://www.geocities.com/agalavotti/tqwt.html
These are designed for the FE164's, so I would need to alter them for appropriate use with the 126's.
Does anyone have existing TQWT plans for the 126's?
Thanks in advance.
reikso2h said:
Because it's designed for a back-loaded horn enclosure, check the spec sheet:
http://www.madisound.com/catalog/PDF/fostexdrivers/fe126e.pdf
As Scottmoose suggests, throw them in a BIB. I have mine in a 48" tall, 12" deep, 5" wide (internal) BIB, using 1/2" ply. It's slightly shorter than recommended, but I think the sound is fantastic nonetheless. You're certainly not going to find an easier build...
Of the four FE-126E drivers I have measured, the average fs is 94 Hz and the average Qts is 0.41. I do not consider the FE-126E to be a low Qts driver, don't blindly trust the manufacturer's spec sheet when evaluating a driver or designing an enclosure. My measurements fall in line with others that I have found on the Internet.
Based on these values the FE-126E would be appropriate for a resonant enclosure like a TL or TQWT and even a BR if it is tuned to the mid 90's. In fact, I would consider the BIB and the "BLH" designs for the FE-126E to also be resonant enclosures where standing wave resonances are used to augment the bass output. I do not consider any of these designs to be functioning as a well designed horn for the bass frequencies. They are really hybrid TL/horn systems.
So in my opinion, the FE-126E is suitable for many different styles of enclosures as long as you recognize that for most of them you are not going to get much low bass. Make sure you use actual measured T/S parameters and do the design work to learn what compromises are required and what type of bass performance is achievable. A sub woofer or woofer would probably solve the bass issues and still allow the full range driver sound desired.
Based on these values the FE-126E would be appropriate for a resonant enclosure like a TL or TQWT and even a BR if it is tuned to the mid 90's. In fact, I would consider the BIB and the "BLH" designs for the FE-126E to also be resonant enclosures where standing wave resonances are used to augment the bass output. I do not consider any of these designs to be functioning as a well designed horn for the bass frequencies. They are really hybrid TL/horn systems.
So in my opinion, the FE-126E is suitable for many different styles of enclosures as long as you recognize that for most of them you are not going to get much low bass. Make sure you use actual measured T/S parameters and do the design work to learn what compromises are required and what type of bass performance is achievable. A sub woofer or woofer would probably solve the bass issues and still allow the full range driver sound desired.
Always measure the T/S parameters of your drivers. If you are going to all of the effort to design and build an enclosure, it just seems like a big mistake/risk to assume the critical driver parameters used to predict the bass output. All of that work only to find out in the end it does not perform as expected because what you started with as an input was in error.
That pretty much falls in line with what I've got (albeit the Q on mine is somewhat lower, at about 0.33, when I last had the facility to check drivers).
The problem that can't be circumvented though, assuming you want to tune fairly low) is the limited Xmax, which is why a horn of some kind (hybrid or otherwise -very few people would want a ~optimal W. M. Leach hyperbolic 50Hz horn for them, and if they did, they'd find the HF had vanished) is preferable if the driver is being run sans support. They should be passable in other types, if, as Martin says, you tune to a higher frequency, treat them gently & support with woofers if you need the LF, but they wouldn't be my choice for those duties.
The problem that can't be circumvented though, assuming you want to tune fairly low) is the limited Xmax, which is why a horn of some kind (hybrid or otherwise -very few people would want a ~optimal W. M. Leach hyperbolic 50Hz horn for them, and if they did, they'd find the HF had vanished) is preferable if the driver is being run sans support. They should be passable in other types, if, as Martin says, you tune to a higher frequency, treat them gently & support with woofers if you need the LF, but they wouldn't be my choice for those duties.
MJK said:
I am leary of all T/S parameters, even the ones i measure myself.
Here is were my dilemma comes from... the Fonken was designed using factory specs. When the actual enclosure with the drivers is measured it produces pretty close to expected based on the sim. It looks nothing like the sim with the values that i have measured. The measured values are quite different than factory (attachment shows average of something like 120 stock FE127)
Similar happens with the A126. And Brynn, And anything else we have put the FE126 into.
Another instance to watch is to see what happens when the latest batch of group buy JX92s go into the already designed GM cabinets. They shouldn't work at all based on the numbers Zaph has measured.
What do i do now? I design based on a guess of what the parameters are and then measure, rebuild until i'm happy.
So for the FE126 go look at what people have been happy with and build one of those.
dave
Attachments
Driver TS specs
For those of us interested in enclosure design it would be really beneficial to have an area (such as in the 'Best Posts') where TS parameters of drivers could be shared. Of course there will be variability in the measurements for the same driver due both to production variability and measurement accuracy. Nonetheless, it would become quite evident, at least ballpark, where the TS parameters would likely fall. This would allow intelligent selection and purchase of drivers, and matching of drivers with enclosure types.
For example, a Qts of 0.25 (Fostex spec sheet) for the FE126E suggests that horn loading would be optimal and that series resistance would need to be added for use in reflex and TQWT enclosures. On the other hand, a Qts of 0.41 (or even 0.33) is in prime reflex territory. Unfortunately the relatively high Fs (90 Hz give or take a few Hz) would not provide much bass extension. Again, the measured Fs (90 Hz) vs the Fostex spec (70 Hz) really changes the outcome of an actual project.
Along these same lines, it would be very beneficial to know the TS parameters used in the response models for the Spawn Family.
Regards,
Bob
For those of us interested in enclosure design it would be really beneficial to have an area (such as in the 'Best Posts') where TS parameters of drivers could be shared. Of course there will be variability in the measurements for the same driver due both to production variability and measurement accuracy. Nonetheless, it would become quite evident, at least ballpark, where the TS parameters would likely fall. This would allow intelligent selection and purchase of drivers, and matching of drivers with enclosure types.
For example, a Qts of 0.25 (Fostex spec sheet) for the FE126E suggests that horn loading would be optimal and that series resistance would need to be added for use in reflex and TQWT enclosures. On the other hand, a Qts of 0.41 (or even 0.33) is in prime reflex territory. Unfortunately the relatively high Fs (90 Hz give or take a few Hz) would not provide much bass extension. Again, the measured Fs (90 Hz) vs the Fostex spec (70 Hz) really changes the outcome of an actual project.
Along these same lines, it would be very beneficial to know the TS parameters used in the response models for the Spawn Family.
Regards,
Bob
Re: Driver TS specs
These would only be useful if they were actually usable to produce an enclosure. As i have said my measured parameters for both the FE126 (similar to Martin's -- i can get an average of 80-100 drivers) & FE127 would not work to produce useable cabinets -- at least within the envelope of my experience (and we have probably built at least as many boxes as anyone else, so have a good sample set of boxes).
dave
AstroSonic said:
These would only be useful if they were actually usable to produce an enclosure. As i have said my measured parameters for both the FE126 (similar to Martin's -- i can get an average of 80-100 drivers) & FE127 would not work to produce useable cabinets -- at least within the envelope of my experience (and we have probably built at least as many boxes as anyone else, so have a good sample set of boxes).
dave
Just a further note: both the FX120 & F120A have factory specs quite close to FE127e. Yet when i measure them those 2 are close, but have Vas ~20% higher & Fs 10-15 Hz lower than FE127. Note: my sample set of each of them was 2.
I am now in a position of having to make some educated guesses before i do a 1st iteration of design for them...
dave
I am now in a position of having to make some educated guesses before i do a 1st iteration of design for them...
dave
planet10 said:
There is a physical reason for everything that happens and it should be possible to produce an accurate math model for most of these enclosures. If you have measured the T/S parameters, then you should be able to rerun a math model and calculate a matching impedance curve to your measured impedance. That will check your T/S validity which should be the first step. The other thing to keep in mind is that there is variabilty from measurement to measurement so don't get to obsessed about producing repeatable results to 6 significant digits. I always run at least 10 averages when making final measurements. The hardest things I have had to do as an engineer is running test programs, getting valid measurements is really tough.
When I have finished building an enclosure, I always measure the impedance and SPL at 1 m. The math model of the driver in the enclosure should match the electrical impedance very closely which means that the low frequency motions of the driver have been correctly predicted. If your predictions are off then the math model needs work and you usually learn a lot by struggling to correlate the measurements with the predictions. I have never found that the math model and the measurements would not eventually converge for low frequencies. This stuff is not rocket science but it sometimes requires creative modeling and insight to gain an understanding of what is going on in and around the enclosure.
Determining what calculated and/or measured response actually sounds good is the trick. If you have a speaker that really sounds good, measure the impedance and SPL and use this as a target for the future. Nothing says that the speaker has to measure ruler flat, sometimes something with a very ugly resposne plot sounds great.
Interestingly enough, sometimes the enclosure design is not too sensitive to the exact T/S parameters. If you design an enclosure based on a specific set of parameters, go back and rerun the simulation with a set of "off" parameters. Change the Vas or the Mms, recalculte a new set of consistent T/S parameters, and put them back into the simulation and recalculate the response. Sometimes a design is just not that sensitive to misalignment.
Great thread here guys.
If the Fs/Qts ratio is similar for factory specs vs measured, the enclosure response should be similar for both sets of numbers.
Dave, can you post your calculated vs measured impedance for the Fonken. If you are using the same system to measure, the results should be similar unless there is a problem somewhere.
If the Fs/Qts ratio is similar for factory specs vs measured, the enclosure response should be similar for both sets of numbers.
Dave, can you post your calculated vs measured impedance for the Fonken. If you are using the same system to measure, the results should be similar unless there is a problem somewhere.
gmilitano said:
Take me a while to figure that out... and i may need to actually measure exact drivers as the data i have handy is average for the sim and specific for the Fonken. It was more that the FR measured was about what i expected from the sim given the liberties i took with the vents and unknown BS etc.
Here thou is the average of 80 FE126e
dave
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