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Old 5th December 2013, 07:32 PM   #11
just a guy is offline just a guy  Canada
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Quote:
Originally Posted by zman01 View Post
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...

Cerberus 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)

Port calculations?

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.
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.
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Old 6th December 2013, 04:47 AM   #12
soundnovice is offline soundnovice
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ported box no doubt can reach deep and be efficient, but transient response is said to be not as good as in horn and sealed boxes. Also if i am correct ported box volume is generally bigger than hor/sealed boxes.
i am considering small multiple subs as in Gedlee's method.
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Old 28th December 2017, 01:13 PM   #13
grahamgraham is offline grahamgraham  United Kingdom
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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.

Quote:
Originally Posted by OscarS View Post
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
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Old 29th December 2017, 03:27 PM   #14
plund is offline plund  United States
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Originally Posted by soundnovice View Post
what would be most suitable box for Tang Band W6-1139SIF 6.5" subwoofer?
i have come across 38hz tapped horn and ported designs for this, but i am looking for really compact subs. target low freq. would be around 40hz
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.
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Old 29th December 2017, 04:12 PM   #15
OscarS is offline OscarS  United States
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Originally Posted by grahamgraham View Post
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?
That's what I personally measured with my DATS. I don't know if you consider empirical data "gospel".

Quote:
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.
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.
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Old 30th December 2017, 08:37 AM   #16
grahamgraham is offline grahamgraham  United Kingdom
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[QUOTE=OscarS;5291132]That's what I personally measured with my DATS. I don't know if you consider empirical data "gospel".


Ah, OK, thanks for the reply. So if I have already constructed my cabinet and need to reduce the port size internally, is there a ratio or rule of thumb as to how the shortening of the port and the subsequent gain in cabinet volume will interact?

What I guess I am asking is:

Can I shorten my port by your indicated maths and achieve the right effect with the added cabinet volume increase?
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Old 30th December 2017, 09:12 AM   #17
grahamgraham is offline grahamgraham  United Kingdom
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Quote:
Originally Posted by OscarS View Post
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,
Attached Images
File Type: jpg graph tb 6 d.jpg (159.8 KB, 190 views)
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Old 30th December 2017, 01:15 PM   #18
Brian Steele is offline Brian Steele  Grenada
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Originally Posted by just a guy View Post
That's literally the worst subwoofer design I've ever seen.
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....
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Old 30th December 2017, 04:07 PM   #19
chris661 is offline chris661  United Kingdom
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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
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Old 30th December 2017, 06:28 PM   #20
zman01 is offline zman01  Bangladesh
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box for Tang Band W6-1139SIF
Quote:
Originally Posted by chris661 View Post
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.
Chris,

The web page says 6.5" driver for he Cerebrus:

Cerberus
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