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Multi-Way Conventional loudspeakers with crossovers

Port Conundrum
Port Conundrum
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Old 16th May 2018, 03:17 AM   #1
dpixel12 is offline dpixel12  United States
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Join Date: May 2018
Default Port Conundrum

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.
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Old 16th May 2018, 05:52 AM   #2
denibeni is offline denibeni
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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.
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Old 16th May 2018, 08:39 AM   #3
TBTL is offline TBTL  Germany
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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.
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Old 16th May 2018, 11:24 AM   #4
dpixel12 is offline dpixel12  United States
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Join Date: May 2018
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?
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Old 16th May 2018, 11:31 AM   #5
TMM is offline TMM  Australia
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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.

Last edited by TMM; 16th May 2018 at 11:38 AM.
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Old 16th May 2018, 12:20 PM   #6
dpixel12 is offline dpixel12  United States
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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.
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Old 16th May 2018, 05:39 PM   #7
denibeni is offline denibeni
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Quote:
Originally Posted by dpixel12 View Post
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.
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Old 16th May 2018, 08:00 PM   #8
dpixel12 is offline dpixel12  United States
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@denibeni - Thanks for the link.

Quote:
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.
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Old 17th May 2018, 12:36 AM   #9
dpixel12 is offline dpixel12  United States
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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.
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Old 17th May 2018, 07:44 AM   #10
GM is offline GM  United States
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Location: Chamblee, Ga.
Quote:
Originally Posted by dpixel12 View Post
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
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