should i be worried about chuffing when design my 15" 2-way pa speakers ?I've seen a lot of 2-way enclosure designs both DIY and "Pro Grade (JBL,EV,Mackie) with a minimum of 2-4 ports around 3" in diameter rated at 600w rms all the way to 1200w.so is chuffing really an issue i should be worried about?
Chuffing happens mostly when the port dimensions are too small which causes the air velocity to be too high. You can simulate the air speed with WinISD, the result of the air speed is quite accurate.
Big ports got disadvantages too though, they take up (a lot in some cases) of the volume because the air in them doesn't add up to the effective enclosure volume. And in a 2-way speaker, the backside dispersed mid-garbage of the driver does come out too.
Big ports got disadvantages too though, they take up (a lot in some cases) of the volume because the air in them doesn't add up to the effective enclosure volume. And in a 2-way speaker, the backside dispersed mid-garbage of the driver does come out too.
fwiw I've heard chuffing and seen what I call "vent rectification" with a 15" JBL woofer in a 3.7 cubic foot box tuned with two 4" ID x "4 PVC pipe vents at 20vrms / 37Hz sine. The woofer's position moved forwards from normal center. My Karlson with similar area vent and system tuning did not chiuff, nor woofer move out of normal position (plus excursion was half that of the reflex) Ports for high output reflex probably should have flared ends.
it was my ports causing the offset -
http://mariobon.com/Articoli_storici_AES/jbl/JBL_2002_AES_Reflex_Ports.pdf
” Could ports c and d have hidden asymmetry?
All the ports were surface mounted in the enclosure. This
means that one end of the port has a baffle and the other
end does not. Thus all the ports were asymmetric. This
suggests a preferential airflow in one direction over
another, analogous to a fluid flow diode effect, and it can
be thought of as “port rectification.”
http://mariobon.com/Articoli_storici_AES/jbl/JBL_2002_AES_Reflex_Ports.pdf
” Could ports c and d have hidden asymmetry?
All the ports were surface mounted in the enclosure. This
means that one end of the port has a baffle and the other
end does not. Thus all the ports were asymmetric. This
suggests a preferential airflow in one direction over
another, analogous to a fluid flow diode effect, and it can
be thought of as “port rectification.”
Oh sorry, I misunderstood it.
If the offset of the membrane moves with rising excursion and no DC is in the amp signal, it is partly a possible asymmetry in the driver suspension and/or partly the effect of the port. If the driver closes in to the power compression, it gets worse as the Qt rises with the VC temperature. Klippel released several papers on that topic.
For the port: A too high air velocity in the port greatly increases the asymmetries. The port surface should aim for SD/3 as a rule of thumb. A typical 15" driver got ~855cm² cone surface, so 285cm² should be the target. Your ports got a surface of 157cm², that's a bit above the half of the suggested surface. So a larger port (or more than the two) would likely solve the problem. You can simulate the port air velocity with WinISD and other tools to get a correct dimension of the port as the effect of the asymmetries is way weaker then.
If the offset of the membrane moves with rising excursion and no DC is in the amp signal, it is partly a possible asymmetry in the driver suspension and/or partly the effect of the port. If the driver closes in to the power compression, it gets worse as the Qt rises with the VC temperature. Klippel released several papers on that topic.
For the port: A too high air velocity in the port greatly increases the asymmetries. The port surface should aim for SD/3 as a rule of thumb. A typical 15" driver got ~855cm² cone surface, so 285cm² should be the target. Your ports got a surface of 157cm², that's a bit above the half of the suggested surface. So a larger port (or more than the two) would likely solve the problem. You can simulate the port air velocity with WinISD and other tools to get a correct dimension of the port as the effect of the asymmetries is way weaker then.
I'd say it depends.
To give you an idea, most 2-way speakers aren't expected to put out much bass - it would be a surprise to use them to re-inforce a mic'd kick drum without any subwoofers.
You could run an acoustic act through the speakers, all the way up to the limiters, and never have a problem with port chuffing.
You could switch to dubstep and immediately have a lot of problems.
The thing to remember is this: when you're doing simulations of port velocities etc, the software is telling you what happens when you put in a sine tone at that input voltage. If it's 90v RMS into an 8ohm load, that's approximately a kilowatt.
It's up to you to decide if 40Hz at 90v RMS is a likely input signal for the driver.
If it'll happen often, you'll need a big port. No way around that.
If it'll happen because some crazy person wants to play dubstep without any subwoofers, that's the perfect time for the salesman to connect a subwoofer and show the difference.
So, most companies probably under-size their ports on the assumption that if the customer wants bass, they'll simply add subwoofers.
If you're designing a 15" 2-way to run without any subwoofers and play bass-heavy content, you'll need to put in a bigger port than most. Again, it's up to you to look at the likely program material, and figure out how much of a problem you'll have.
IIRC, going above 17m/s will start to incur friction losses in most ports.
I have a pair of Faital Pro 10FH520 drivers in each of my main speakers, and have found that when they have a single 3" port you get a low tuning (44Hz-ish) that will give audible chuffing problems at high power.
I rarely run with that setting, though - only for small venues where I want the low-frequency extension. For larger venues, I can unblock some more ports and get louder, but missing the LF extension. That's when the subs come out.
Chris
thank you chris661 you have help me alot .Here is more details to what i am doing.as i said i am making a 15" 2-way system ill be using a Eminence Kappa Pro 15A for the woofer and a Eminence PSD:3014-8 1.4" Titanium Compression Driver for the highs.my pa system will indeed have a sub-woofer Eminence kappa 18lf to be exact.
The 12" will beam at a higher frequency, that means you can xo higher with the same dispersion and chose a different HF driver (the Eminence PSD:3014 is really not very good). If you don't need the low xo ability of the 15", 2x10" + 1,4" would also be a nice option, that's still the midrange and highs would sound much better and it's still ~40% more cone surface than a 12". A 2x10" + 1,4" will not go as low as a 15" though.
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