Port Conundrum

[dpixel12]

Hello all. I'm new here.
I have a problem I think...Maybe just need some insight.
I've built a 3-way with a 10" woofer with about 1 cubic foot box with a rear slotted port. The mid range and tweeter are sealed. My port diameter is about 4.3" and about 2 inches long and sounds fantastic. It has a nice response from about 45 to 70Hz and not to boomy.
Now when I lengthen the port to (16" for 45Hz tuning) or anything else for that matter, my low frequencies drop off. I do get a slight bump at 45Hz, but not much.
At 16", I loose quite a bit from 55 to 80Hz.
I guess my question is: Should I just go with what sounds good even though it's basically just a hole in the box?
The woofer is a Peavey Pro 10
Some specs:
Vas = 0.89 ft3
fs = 67.7 Hz
Qts = 0.4
Internal Box Dimensions:
L = 12"
W = 10.75"
H = 19.75"

Thanks for looking.

 

[YSDR]

That's the essence of DIY, you can do, whatever you like. After all, your ear is the final judge.
There is nothing wrong with this box alignment, power handling changes with different tuning but you can easily check this with an adequate software.

 

[TBTL]

Listening rooms do not have a flat transfer function from loudspeaker to ear. A non-flat loudspeaker response might be such that it is compensating for that.

 

[dpixel12]

Thanks for the replies. I've been driving myself crazy with different length ports going in different directions, side by side comparisons, measuring with spectrum analyzing software and by ear. I guess I just feel I'm doing something wrong without a correct size port according to online calculators.
@denibeni - can you recommend any software to measure/calculate this power handling?

 

[TMM]

I think your problem is that the woofer just does not want to play low with Fs=67.7Hz.

With those specs for the woofer and box i get tuning at 75Hz for 2" length, a peaking response and not much happening below 65Hz. At 16" length tuning is 39Hz and it's looking more or less like a sealed box because the tuning frequency is significantly below Fs. From the sim that I did, i'd pick around 55Hz tuning - 6.3" long port.

TBTL might be right that the higher tuning matches you listening space. Perhaps your room significantly boosts up around 45Hz and cuts around 70Hz making the higher tuning sound good. The only thing to watch with a high tuning frequency is that the box becomes an acoustic short circuit below the tuning frequency. Excursion of the woofer becomes uncontrolled and if the woofer is driven beyond xmax it'll be easier to burn the voice coil.

 

[dpixel12]

Ok. Now I have to try these in other rooms.

You guys are awesome. Just the kind of insight I was looking for.

@TMM - Yeah, I know this speaker won't play super low. Thanks for doing the sim. I didn't think about the 75 Hz at the 2" length. Sort of makes sense with what I'm hearing and what the room might be doing.

The whole purpose for this project was to be giant studio monitors. I record guitar and bass guitar and do a little mixing. Also to have a fairly decent sounding general listening system. For critical listening, I can eq for a flatter sound if needed.

 

[YSDR]

can you recommend any software to measure/calculate this power handling?

If you have excel:
UniBox - Unified Box Model for Loudspeaker Design - Kristian Ougaard

Enter your driver/box parameters with the desired wattage and check SPL and cone amplitude.

BTW, i think this driver does not go low enough for a (nearly) full range sound. If you want a monitor you need a woofer with around 50Hz or below Fs as a minimum to get good extension for general music (re)production.
This driver is more of a midrange or mid-bass than a standalone bass driver imho.

 

[dpixel12]

@denibeni - Thanks for the link.

BTW, i think this driver does not go low enough for a (nearly) full range sound. If you want a monitor you need a woofer with around 50Hz or below Fs as a minimum to get good extension for general music (re)production.
This driver is more of a midrange or mid-bass than a standalone bass driver imho.

Yes, I'm aware. I chose these drivers because of the power rating and the 50 to 4000 Hz range and the price. I do play some guitar and bass through them, so they had to stand up to some volume/power. I think of these as PA/Studio Monitors. They really do sound very good with some deep lows(with no eq). I wanted a pair of loudspeakers to do it all and I knew there would be some compromises.
I'm running these with a Crown XLS1000, btw.

 

[dpixel12]

Update:
TBTL was right. Another room makes a big difference and not good for bass response. The listening room was 25x14. The new room is 12x11.
I knew rooms make a big difference but I didn't know in the lower frequencies.

 

[GM]

Hello all. I'm new here.
I have a problem I think...Maybe just need some insight.
I've built a 3-way with a 10" woofer with about 1 cubic foot box with a rear slotted port. The mid range and tweeter are sealed. My port diameter is about 4.3" and about 2 inches long and sounds fantastic. It has a nice response from about 45 to 70Hz and not to boomy.
Now when I lengthen the port to (16" for 45Hz tuning) or anything else for that matter, my low frequencies drop off. I do get a slight bump at 45Hz, but not much.
At 16", I loose quite a bit from 55 to 80Hz.
I guess my question is: Should I just go with what sounds good even though it's basically just a hole in the box?
The woofer is a Peavey Pro 10
Some specs:
Vas = 0.89 ft3
fs = 67.7 Hz
Qts = 0.4
Internal Box Dimensions:
L = 12"
W = 10.75"
H = 19.75"

Thanks for looking.

As a cab alignment reference point: with a ~0.403 Qts, Vb = Vas, Fb = Fs, so combined with a little wiring series resistance, then for a max flat T/S alignment [flat, no 'bump' in the response] the cab will ideally need ~0.89 ft^3 net tuned to ~67.7 Hz, though based on it having some obvious 'boom', the specs apparently off quite a bit, typical of Pyle and many other manufacturers unfortunately.

Regardless, otherwise it's performing as it should with the different tunings, so if you want more bass you'll ideally either need to start over with a woofer with an Fs at least as low as you want or tune it low and back them into solid corners to get boost the low end.

GM

 

[dpixel12]

Thanks GM.

You guys helped me to understand things better, which is what I was looking for. I'm going to try a 50 - 55 Hz tuning as TMM mentioned. The room that they'll be in make them sound really nice with a lot of low end. I guess how they sound in the room is what matters. If I move to another room and need more bass, I'll change the woofers or get a sub. I'll update this thread when I make the changes in tuning. Thank you everyone.

 

[YSDR]

If you make the port from multiple sections, you can easily close one or more sections to fine tune the speaker for different rooms or placements.

 

[YSDR]

I mean divide the slot port to more smaller port instead of one big for example.

 

[dpixel12]

I mean divide the slot port to more smaller port instead of one big for example.

Dual Exhaust?

Generally, what impact would a smaller port make with keeping the same length?

 

[YSDR]

Generally, what impact would a smaller port make with keeping the same length?

It lowers the tuning.
If we are talking about rectangular ports, the theoretical ideal cross-section shape is square. You can have multiple square (or nearly square) ports next to each other instead of one elongated rectangle if you divide it to equal parts. Stuff a port or two with a sock and voila, you have a better match for another room.
But check that the overall cross-section area is not too small.

 

[dpixel12]

It lowers the tuning.

Does it attenuate low end at all?

What kind of effect would a larger opening have vs. a smaller opening with a port length adjusted to have the same tuning? Would one be louder around the tuning frequency? Or would the optimum opening size be the loudest?
I know about chuffing with smaller ports due to the increased pressure.

 

[YSDR]

Does it attenuate low end at all?

With different tuning some frequencies are attenuated, another frequencies are amplified. I really recommend that you try a box simulation software, play the settings, and look at the result.
There is not a magical port area size, but if it is too small then chuffing and compression occurs. If it is too large then sometimes (depending on the design) it needs to be too long and the result is higher freq pipe resonance. But a good software tell you all.

 

[GM]

What kind of effect would a larger opening have vs. a smaller opening with a port length adjusted to have the same tuning? Would one be louder around the tuning frequency?

When port area [Av] = ~ 1/2 Sd, its efficiency begins to increase, hence theoretically the minimum optimum [assuming vent mach is < ~13-17 m/s depending on who you ask] and by Av = Sd it is audible in the tunings the pioneers used, so recommended this size as 'optimal' when tuned to the driver's actual Fs [equal impedance peaks, AKA Altec, JBL 'West Coast Sound'].

Note that the higher the port efficiency, the wider its gain BW as shown on an Onken 360's Av = Sd multi-port system, which would be even greater if less vents were used and of course greatest if only a single round vent: http://www.ispra.net/audio/images/onken/hiraga/32a.jpg

GM

 

[dpixel12]

Update:
I now have great bass! I chopped 5.5" off the 16" port length and there it is. More than I expected and lower without loosing other frequencies. I guess the online calculators were throwing me off or I didn't know what I was doing. I always built sealed cabs in the past, so I never payed attention to the t s parameters that much. I should have reached out for help sooner. Anyway, thanks to everyone. You've all been so much help. I'll post some pics when I get a chance, but tomorrow is workshop day to clean these things up.