Help with Impedance sweep and port tuning
I'm working on an LCR speaker build using 3 Overnight Sensations. Using a DATS V3 my port tuning appears to be way off - DATS is telling me 240hz assuming I'm reading this correctly. Build description claims port tuning at 53hz and WinISD tells me 60hz. Thinking there was an issue with the DATS I reinstalled the software and performed an impedance sweep on my other DIY build, which came back fine.
The LCR build Box volume for each speaker is 0.16 cu ft, port diameter is 1.375" ID PVC and I've been playing with port length between 6-8" although I had to use a 90 degree bend due to cabinet dimensions. I realize the 90 degree bend may cause some resonances but I didn't think it would influence the tuning. With this said I removed the 90 and tested port tuning with a straight port on the exterior of the enclosure. No big change.
Attached is a pic of the last impedance sweep with an 8" port. Any help you can offer is greatly appreciated.
Thx
Phil-
I'm working on an LCR speaker build using 3 Overnight Sensations. Using a DATS V3 my port tuning appears to be way off - DATS is telling me 240hz assuming I'm reading this correctly. Build description claims port tuning at 53hz and WinISD tells me 60hz. Thinking there was an issue with the DATS I reinstalled the software and performed an impedance sweep on my other DIY build, which came back fine.
The LCR build Box volume for each speaker is 0.16 cu ft, port diameter is 1.375" ID PVC and I've been playing with port length between 6-8" although I had to use a 90 degree bend due to cabinet dimensions. I realize the 90 degree bend may cause some resonances but I didn't think it would influence the tuning. With this said I removed the 90 and tested port tuning with a straight port on the exterior of the enclosure. No big change.
Attached is a pic of the last impedance sweep with an 8" port. Any help you can offer is greatly appreciated.
Thx
Phil-
Attachments
The spike at ~3500 Hz is due to the crossover.
A single peak at ~55 Hz looks like the driver in free air. Is the box completed? Is there a missing panel or is the box open somehow?
The review in this link has an impedance plot for comparison. Should have two peaks with a trough at ~55 Hz between them.
https://www.erinsaudiocorner.com/loudspeakers/parts_express_overnight_sensation_mt/
Hope this helps.
A single peak at ~55 Hz looks like the driver in free air. Is the box completed? Is there a missing panel or is the box open somehow?
The review in this link has an impedance plot for comparison. Should have two peaks with a trough at ~55 Hz between them.
https://www.erinsaudiocorner.com/loudspeakers/parts_express_overnight_sensation_mt/
Hope this helps.
"A single peak at ~55 Hz looks like the driver in free air. Is the box completed? Is there a missing panel or is the box open somehow? "
I was thinking this might be the cause - the front panel is not glued up. With this said it seems to be fairly well sealed. I suppose even the smallest leak would throw off what the port tuning will look like. I've held off on gluing up the front panel because once it goes on I won't be able to change the port length.
I do have some scrap wood left so maybe mock up a disposable enclosure.
And thanks for the link to Erin's audio corner. I didn't read it completely but appears there are some tweaks to the crossover that are suggested.
I was thinking this might be the cause - the front panel is not glued up. With this said it seems to be fairly well sealed. I suppose even the smallest leak would throw off what the port tuning will look like. I've held off on gluing up the front panel because once it goes on I won't be able to change the port length.
I do have some scrap wood left so maybe mock up a disposable enclosure.
And thanks for the link to Erin's audio corner. I didn't read it completely but appears there are some tweaks to the crossover that are suggested.
I recently measured a 6" driver in a small sealed box, and there was a 1/4" diameter hole in the bottom for wires to exit. I thought the hole would be inconsequential, but when I measured it with DATS, I found I had a double peak impedance which indicated that the small hole was acting as a bass reflex vent. The lesson is that a box musted be sealed tight to work properly, whether it is a vented box or a sealed box. A vented box should be sealed up so that the only functional vent is the one you installed.
So yes, your non-glued front panel could be leaky enough to disrupt your bass performance and make the vent non-effective, just as @Dave R says.
j.
So yes, your non-glued front panel could be leaky enough to disrupt your bass performance and make the vent non-effective, just as @Dave R says.
j.
Although only a guess, that "0.16 cu ft" may actually be intended as 1.6 cu ft. throwing-out your info. (?)
Last edited:
Thx for the feedback. Nice to see confirmation that even the smallest leak can make a difference. I mentioned playing with a mock up as I've got some scrap MDF but considering I'm on point with the correct internal volume I may just glue it up and call it a day.
Hello Phil,
How are you holding on the front baffle?
Put some gluing clamps on the enclosure to firmly hold on the front baffle, check for gaps and run the test sweep again.
Let us know how it turns out.
I have even put in a few screws for a temporary solution.
Thanks DT
It was a leak! Or, more specifically a number of very small leaks. I originally used gluing clamps to hold the 2 unglued panels in place and even some foam. I suppose I knew there would be some leaking but not enough to make a significant difference. Clearly I was wrong.
I'm getting ~ 51hz with a 6" port and ~ 53hz with a 5" port. Thanks again for those for pointing out the potential issue.
I read the review and testing at Erin's audio corner, which left me a little disappointed in my selection for inexpensive speakers for this project. I did see people making suggestions for possible crossover fixes through a thread on Erin's Facebook page but was unable to determine if there was any definitive change to the crossover design, that had been tested, and made an improvement. I'm embarrassed to say I spent time searching for this before even listening to them. I finally gave up and just listened to them and honestly I think they sound pretty damn good, particularly for how inexpensive they are. They're not my Carrera's but I wasn't expecting them to be.
Thx again
I'm getting ~ 51hz with a 6" port and ~ 53hz with a 5" port. Thanks again for those for pointing out the potential issue.
I read the review and testing at Erin's audio corner, which left me a little disappointed in my selection for inexpensive speakers for this project. I did see people making suggestions for possible crossover fixes through a thread on Erin's Facebook page but was unable to determine if there was any definitive change to the crossover design, that had been tested, and made an improvement. I'm embarrassed to say I spent time searching for this before even listening to them. I finally gave up and just listened to them and honestly I think they sound pretty damn good, particularly for how inexpensive they are. They're not my Carrera's but I wasn't expecting them to be.
Thx again