I think this is a common issue with enclosures approaching towers. When the port is located near one end it turns the enclosure into a MLTL. Here is the port response I measured from one of my towers I was having issues with.. compared to an example graph of a transmission line output:
Notice the similar plateaus and valleys (just not so extreme in amplitude). I see roughly similar behaviour in your port response.
Did you use PVC pipe for your port? If so, cutting down the port and adding a long 90deg bend (maintaining overall port length) may help by placing the inner opening farther away from the bottom of the cabinet.
Notice the similar plateaus and valleys (just not so extreme in amplitude). I see roughly similar behaviour in your port response.
Did you use PVC pipe for your port? If so, cutting down the port and adding a long 90deg bend (maintaining overall port length) may help by placing the inner opening farther away from the bottom of the cabinet.
So I don't think it is a panel resonance issue, just the natural resonance of the enclosure length. The wave hitting the bottom of the enclosure and reflecting back creates a pressure spike that the port provides an outlet for and is either constructive or destructive with the woofer output depending on frequency. The idea would be to move the inner port opening farther away from the end so it is less effective at doing this. Without having calculations it becomes more of a "try it and see what happens" thing unfortunately.
For my build I went through similar hair pulling out with room measurements and the like. Eventually came to the epiphany of standing waves in the enclosure giving transmission line like response. I tried a different diameter port to tune the enclosure differently and added fibreglass insulation to the bottom of the enclosure and acoustic foam at the top, which made marginal difference. I would have had to get creative (somewhat destructive) to try a port bend so I just accepted it as a design flaw for now. Live and learn.
For my build I went through similar hair pulling out with room measurements and the like. Eventually came to the epiphany of standing waves in the enclosure giving transmission line like response. I tried a different diameter port to tune the enclosure differently and added fibreglass insulation to the bottom of the enclosure and acoustic foam at the top, which made marginal difference. I would have had to get creative (somewhat destructive) to try a port bend so I just accepted it as a design flaw for now. Live and learn.
Alright, so I think part of my problem was that I was running the woofer too hot. I also spent some time today playing with positioning. Unrelated to my problem but angling them in super benefited the speakers. I guess you wanna be pretty on axis with a tweeter like this on this baffle.
I've been playing a lot of stuff today and having the woofer at an appropriate level, I'm not really hearing the problem anymore... I'm a little confused and I'll still plan on adding a few braces and securing the port, but everything kinda sounds fine now? I think what happened is I got a little fatigued from loud long listening and kept pushing the woofer up throughout the day.
I've been playing a lot of stuff today and having the woofer at an appropriate level, I'm not really hearing the problem anymore... I'm a little confused and I'll still plan on adding a few braces and securing the port, but everything kinda sounds fine now? I think what happened is I got a little fatigued from loud long listening and kept pushing the woofer up throughout the day.
Your ears get tired or acclimated much faster than many realize. I usually try to keep fine-tuning sessions pretty short, and spread them across multiple days to try to make sure I'm not off in the weeds.
Having known good references to bounce back and forth with is also handy. Sound isolating earphones are good for this if you don't have extra amps/speakers/sources in the same room. Switching needs to be fast to be most effective, and the levels need to match.
Having known good references to bounce back and forth with is also handy. Sound isolating earphones are good for this if you don't have extra amps/speakers/sources in the same room. Switching needs to be fast to be most effective, and the levels need to match.
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You're right about all of that. I was surprised how one woofer level sounded great at night, but the next morning was way too loud.
Nothing special just some large, comfortable ones (no markings) on sale ages ago at a local HIFI 'big box' store that historically have performed good enough for a wide range/quality of YouTube, etc., videos and the LP is an HP 450 G3 Workbook with Win7Pro, DTS.
Alrighty, honestly not really hearing much of a problem lately since dialing in the woofer xover more. I also believe it is partly my room. I've been toying with an OB speaker and it's kind of been revealing in how my room sounds, has the same issues around that area. Granted I have never messed with OB, sounds pretty neat but highly diffuse, maybe not for me.
I did grab a few things to try. I got a 90 degree pvc bend to see what that does, I will be cutting the current port down. Someone suggest moving the ports opening away from it's current location. I also grabbed a thick rubber door mat that I plan on zip tieing around the port. All in all about $20 and probably the limit of effort I want to put into fixing this potential issue. Will share results soon.
I did grab a few things to try. I got a 90 degree pvc bend to see what that does, I will be cutting the current port down. Someone suggest moving the ports opening away from it's current location. I also grabbed a thick rubber door mat that I plan on zip tieing around the port. All in all about $20 and probably the limit of effort I want to put into fixing this potential issue. Will share results soon.
First little test, I wrapped the port in the rubber mat with two layers, idk if my measurement setup is off but it looks really jagged. I went ahead and plugged the entire port with some memory foam, should be decently sealed. I'm kinda new to impedance measurements. Green is sealed, orange is port open. What happened to my two humps? I'm a tad confused to say the least.
I can't test the PVC pipe bend because my 4" inch bends don't fit the 4" pipe...
I wish I could afford DATS but all I've got is my cable and resistors. This makes me feel like I should cut the port and cap it off, but I don't want to jump to conclusions.
I can't test the PVC pipe bend because my 4" inch bends don't fit the 4" pipe...
I wish I could afford DATS but all I've got is my cable and resistors. This makes me feel like I should cut the port and cap it off, but I don't want to jump to conclusions.
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Lower your graph as much as possible to see if the tuning has dropped into the low-mid 20s.
Here is port wrapped in rubber vs. non. I think points to the port vibrating being a problem. I may need to look into securing the port in some other manner. As far as the humps go, can you generous folk fill me on what the humps are indicating? I'm reading about them but not quite understanding. Please be kind I know these are basic questions.
~13543/2/10 = ~677 Hz (344 m/s, 0.254 m using this 'open cylinder' calculator), so a bit lower as measured once its pipe end correction is factored in and the ~140-150 Hz? spike still seems likely a reflection off the pipe and some part of the box internals since the rubber wrap quells it.
Sorry to say this > but I am now convinced that your port diameter is just too large to start with.
Its proximity to cabinet wall & woofer only exacerbates the problem.
But don't despair, there are ways to change this without 'chopping up' your boxes.
I say, get clever with reducing your diameter (could look good) and re-establish length for tuning.
GOOD LUCK🙂
Its proximity to cabinet wall & woofer only exacerbates the problem.
But don't despair, there are ways to change this without 'chopping up' your boxes.
I say, get clever with reducing your diameter (could look good) and re-establish length for tuning.
GOOD LUCK🙂
Yeah, from the get-go with 4" it can only handle ~50 of its 120 W rating at ~18 m/s, so going smaller just reduces it more.
It's interesting to consider and I note your attention to detail. Resonance could be analysed anywhere along the continuum from driver to outside atmosphere, and in isolation the port is indeed an open cylinder.
The resonance in question has the pressure driving the port appearing at the interface of the box volume and the inner mouth of the port, assuming a minimum phase box. In that respect I'm inclined to see a configuration similar to a driver at one end of a line, open at the other end.