This is actually a really difficult driver to design a ported enclosure around. The problem is that it wants a really small box with a very large port. Both my friend and I have the neo magnet version and even a 3 inch diameter port produces unacceptable chuffing when pushed hard. A 3 inch or larger port in such a small box has to be VERY long to achieve a 30 hz or lower tuning.
My friend had good luck with this driver by using a ported box with multiple drivers, which allows for a larger box with a large diameter port that isn't extremely long. I've personally had good luck with this driver in front loaded and tapped horns.
My friend had good luck with this driver by using a ported box with multiple drivers, which allows for a larger box with a large diameter port that isn't extremely long. I've personally had good luck with this driver in front loaded and tapped horns.
Please read this whole thread in the link that follows, I have talked about this before, but no one seems to listen
WinIsd and slot ports? - Car Audio | DiyMobileAudio.com | Car Stereo Forum
Please read this whole thread in the link that follows, I have talked about this before, but no one seems to listen
WinIsd and slot ports? - Car Audio | DiyMobileAudio.com | Car Stereo Forum
I think everyone that actually hears about this listens. The problem is that not many people are aware of it. This is old news to me, I've seen a dozen threads that discuss this issue already this year and I was aware of it within the first few months of starting this hobby. Here's the most recent thread on this topic that I've seen. (I haven't actually read it so I don't know if it's accurate or not but I saw it in passing.)
Calculating Subwoofer Port Length - Not So Simple
Now, having said that, I don't think Hornresp and Akabak are as far off as some other programs. After all, a horn is just a big slot port and they usually measure within a hz or two of the predicted tuning.
I don't think I have any sims and measurements saved of my old projects anymore (I haven't built and measured anything for years now) but I don't remember any of my slot ports measuring 30 percent different than predicted by Hornresp.
Actually I do have a sim and a measurement. And it's actually a sim and a measurement of the neo Tang Band 1139si in a dual driver slot port design. How convenient is that? I forgot I have a website, it's been so long since I've looked at it.
Please keep in mind that this was done back in 2009 when I was still a rank amateur and the measurement conditions are suspect. I didn't measure impedance but the frequency response matches Hornresp's prediction very well. It measured a couple hz lower than predicted but still very close.
I even mentioned this issue in the write up.
https://sites.google.com/site/amateuraudio/projects-1/small-ported-sub
Please keep in mind that this was done back in 2009 when I was still a rank amateur and the measurement conditions are suspect. I didn't measure impedance but the frequency response matches Hornresp's prediction very well. It measured a couple hz lower than predicted but still very close.
I even mentioned this issue in the write up.
https://sites.google.com/site/amateuraudio/projects-1/small-ported-sub
Here's another discussion of this tuning issue, they started talking about it in post 151 last night.
Considering a new alignment for 8x LMS 5400 Ultra 18s. Thoughts? - Page 6
They talk about this issue quite a bit at avsforum.
Considering a new alignment for 8x LMS 5400 Ultra 18s. Thoughts? - Page 6
They talk about this issue quite a bit at avsforum.
That's literally the worst subwoofer design I've ever seen. The 1.5 inch port is way too small and causes massive turbulence and chuffing problems.
This Cerberus design is popular on the Parts Express forum but everyone that builds it complains of extraordinarily bad chuffing issues. A bunch of people build it with a 2 inch port (with a longer length to maintain the same tuning) but it still has terrible chuffing.
As I mentioned, even a 3 inch port isn't really big enough.
just a guy,
Googled port TB-1169, cerberus, and port chuffing - the link below from a PE forum discussion indicates that the design has its limitations, but "everyone who builds it complains about extraordinarily bad chuffing issues" is not the case...
http://techtalk.parts-express.com/s...erus-build-using-W6-1139SIF-(ferrite-version)
I am sure there are other threads too, so please feel free to share.
Also came across a post by you on this thread where you are probably referring to the same design? (post #7)
http://www.diyaudio.com/forums/subwoofers/246071-port-calculations.html
I do not want to defend the design or the designer, but do not see any proof that the port issues are overwhelming; Btw, I knocked together a box last year with the 1.5" port - not that I am an expert in anyway, but did not experience issues.
Googled port TB-1169, cerberus, and port chuffing - the link below from a PE forum discussion indicates that the design has its limitations, but "everyone who builds it complains about extraordinarily bad chuffing issues" is not the case...
http://techtalk.parts-express.com/s...erus-build-using-W6-1139SIF-(ferrite-version)
I am sure there are other threads too, so please feel free to share.
Also came across a post by you on this thread where you are probably referring to the same design? (post #7)
http://www.diyaudio.com/forums/subwoofers/246071-port-calculations.html
I do not want to defend the design or the designer, but do not see any proof that the port issues are overwhelming; Btw, I knocked together a box last year with the 1.5" port - not that I am an expert in anyway, but did not experience issues.
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The thing about the Parts Express forum is that it is mostly populated by older gentlemen who listen to classic music that doesn't have any real bass in it, and no content below 40 hz at all. And they don't like to listen particularly loud. In cases like that port chuffing may not be too much of an issue and some people were happy with it, but there were still plenty of complaints about this design. The PE forum is probably the best place in the world to learn passive crossover design (and I did) but their philosophies regarding enclosure design drove me completely nuts.
Even the designer's page for the Cerberus design says it has chuffing problems, it was a conscious compromise.
I have personal experience with a very similar design. My buddy made something similar to the Cerberus but with a 2 inch port. I told him before he built it that it would have problems but he did it anyway. It was so bad it rustled papers on the other side of the room and the turbulent noise sounded like a narrow vaccuum cleaner hose sucking air. He ripped the port out and put in a 3 inch port, it was very long to maintain the same tuning and mostly stuck outside the box. It still produced unacceptable port noise at high volume. That design was so bad he just burned it.
A 3 inch port has 4x more area than the 1.5 inch port in the Cerberus design and the 3 inch port still isn't big enough. I'm not joking or exaggerating, the Cerberus is truly the worst subwoofer design I've ever seen. It is severely limited in performance by the low performance port. You could get the same results from a much less expensive driver in a good design.
I'm not going to go searching for threads, I've seen plenty and I also have personal experience, so you can take that for what it's worth or leave it.
Your quote this from the other forum:
"Yeah, I was off initially because I said ~40% reduction----I'm getting old and some brain cells aren't quite as active as before, but none the less, a 30% reduction in required length is a big difference because it allows you to go BIGGER on the port area (without the penalty of a ridiculous vent length) to kill (lower) vent velocity and maintain port linearity to much higher levels."
30% less length if wall slot ported, is that correct? Is this considered gospel?
If 30% of the port is removed after construction and gives that 30% back to the cabinet volume, how do you account for that? Slot ports are voluminous.
"Yeah, I was off initially because I said ~40% reduction----I'm getting old and some brain cells aren't quite as active as before, but none the less, a 30% reduction in required length is a big difference because it allows you to go BIGGER on the port area (without the penalty of a ridiculous vent length) to kill (lower) vent velocity and maintain port linearity to much higher levels."
30% less length if wall slot ported, is that correct? Is this considered gospel?
If 30% of the port is removed after construction and gives that 30% back to the cabinet volume, how do you account for that? Slot ports are voluminous.
Please read this whole thread in the link that follows, I have talked about this before, but no one seems to listen
WinIsd and slot ports? - Car Audio | DiyMobileAudio.com | Car Stereo Forum
Soundnovice, Ok, I understand you are looking for a compact design. Several years ago I built the "Volvotreter 38hz" tapped horn. Because the tapped horn is narrow, I lay it on it's side and keep it placed underneath a dresser, where it supports a pair of FH3's, crossed-over at 80-100hz. In our 15x20ft bedroom it sounds very rich and full playing music. Playing movies, I am amazed at how much "rumble" and "Boom" this little tapped horn can make!
...just in case you reconsider.
That's what I personally measured with my DATS. I don't know if you consider empirical data "gospel".
I never removed anything after construction. This was constructed with a higher Fb initially in design. It was afterwards that I discovered the much lower than calculated Fb. Turned out sounding real nice, so I left it as-is.
Thanks. OK, to flesh out my previous post:
I have attached an image of the sim of the cabinet I have running.
GREEN LINE - 26L and tuned to 34hz with a 70cm port. This is the ideal prediction before real world port correction.
PURPLE LINE - 26L and tuned to 31hz with a 91cm port. This is the presumed real world response of the green line cabinet with 30% longer port.
If I decrease the port that is 70cm (but acts like a 91cm port) by 30% will I be on track?
I have simmed a cabinet volume gain of about 1.5L (due to reduce port volume) and that has little effect on the curve.
Many thanks,
Attachments
I've seen worse, starting with all those "TH" designs that feature 10+dB resonance spikes just outside the passband
.From the driver's specs, it looks like a good PR design might be the best fit for it.
I'd love to see some linearity tests done on a Cerebus subwoofer. I'll bet that the output from the port drops dramatically long before the driver's reached its limits....
The Cerebus sub uses the 5" driver, so the port is undersized for sure, but at least they're not using the 6.5" driver.
FWIW, I used the 6.5" ones in 14L boxes tuned around 40Hz for a while. With a 50mm diameter port, air velocity was an issue when pushed.
Looks to me like PRs are the way to do it, unless a TH or similar is an option.
I did find these drivers need an absolute rocket up them to get going. Budget on a few hundred watts per cone IME.
Chris
FWIW, I used the 6.5" ones in 14L boxes tuned around 40Hz for a while. With a 50mm diameter port, air velocity was an issue when pushed.
Looks to me like PRs are the way to do it, unless a TH or similar is an option.
I did find these drivers need an absolute rocket up them to get going. Budget on a few hundred watts per cone IME.
Chris
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