How you plan to hear only the bass port without hearing sounds from the woofer? One ear you will cover I suppose, but pen like measurement mics they stick them right in the port's mouth plane.
Ok now I have tried to listen to the port, and I think it worked rather good after getting used to listen to it. I found some interesting things! First, I have sound from 18Hz which I think is rather remarkable, maybe it is not but to me it was 🙂.
Starting at 18Hz it was of course very weak (a 1- on "my" scale) but easy to hear with the ear at the port. Moving upwards to 30Hz, it was quite even and increasing all the way, and suddenly at around 30Hz I heard some sound from the woofer itself, not only the port (it was no sound from the woofers front below 30Hz). Now we are talking 2 on my scale. From 30Hz reaching 39Hz the level is now 3 at 39Hz. Going upwards it increase to 3+ starting at 42Hz to 48Hz. The contribution from the membrane has also increased and is easier to hear than before. 48-57Hz is a little weaker, a 3 on my scale but since the membrane is more active now the total sound is a 4 or even 4+ (around 50Hz).
Ok hope you are still with me on this little trip 🙂.
From 57 all the way to 71 the bass port is increasing rather much to its maximum at 71Hz. Over 71Hz it gets weaker with values 3 and 3+ (up and down and so on) to about 100Hz.
What I do not like is the big maximum at 71Hz, it was loud both from the membrane and port 🙁. Otherwise it seems fine 🙂.
Now the question is, is it possible to get rid of that peak?
Starting at 18Hz it was of course very weak (a 1- on "my" scale) but easy to hear with the ear at the port. Moving upwards to 30Hz, it was quite even and increasing all the way, and suddenly at around 30Hz I heard some sound from the woofer itself, not only the port (it was no sound from the woofers front below 30Hz). Now we are talking 2 on my scale. From 30Hz reaching 39Hz the level is now 3 at 39Hz. Going upwards it increase to 3+ starting at 42Hz to 48Hz. The contribution from the membrane has also increased and is easier to hear than before. 48-57Hz is a little weaker, a 3 on my scale but since the membrane is more active now the total sound is a 4 or even 4+ (around 50Hz).
Ok hope you are still with me on this little trip 🙂.
From 57 all the way to 71 the bass port is increasing rather much to its maximum at 71Hz. Over 71Hz it gets weaker with values 3 and 3+ (up and down and so on) to about 100Hz.
What I do not like is the big maximum at 71Hz, it was loud both from the membrane and port 🙁. Otherwise it seems fine 🙂.
Now the question is, is it possible to get rid of that peak?
Try 71Hz at listening position and move the speakers a little in the front to back axis maybe? Because I see a small suck out at 71Hz in the RTA I took in another room. That's at odds. See if it hits a room node.
Yes I will try that to start with, but I am rather sure it comes from the speaker itself. I will try it to be sure.
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I have now tried to move the speakers +-10cm from back wall and it was a rather small change with respect to the 71Hz tube peak (more that it move a few Hz up or down). I also tried to extend the reflex tube to 150mm (from 135mm) but I heard lower output in the 30Hz band which was not better, so I guess going this direction might be a bad idea (I will not try even longer tube since I had this result, and since you Salas set it to 135mm, correct decision?).
I heard from listening position that the 71Hz peak from the tube is not so peaky at the actual listening positions total sound, so that was a comfort. I also heard that with a 150mm port I got a dip at 72Hz from the tube. Comments on all this, Salas?
I heard from listening position that the 71Hz peak from the tube is not so peaky at the actual listening positions total sound, so that was a comfort. I also heard that with a 150mm port I got a dip at 72Hz from the tube. Comments on all this, Salas?
We had tuned the port in a given room, there it went 135mm. Maybe 130mm & 140mm test in your space for customizing it, if feasible with the telescopic ones you got?
Ok, I think the shortest lenght is about 130mm so I can try that. It is 66mmwide with the telescope part a little wider. My room is 3.8m wide and about 7.3m length. Do you remember the room size you had?
Must be 50m2 including a fully open kitchen annex to its left side, with the main living space maybe 35m2 rectangle.
Hmm, so it is bigger than mine which is 28m2 but with a open wall to my kitchen to the right of my stereo making it a little bigger in total. Well maybe that is not the most important thing.
If I am smart I should probably start now with listening with different amout of filling behind the woofer. If I use 135mm when doing this, then later when I am satisfied with that I should fine tune the lenght, right?
I am afriad that testing with different amount will change the bass output so that should be in place first.
If I am smart I should probably start now with listening with different amout of filling behind the woofer. If I use 135mm when doing this, then later when I am satisfied with that I should fine tune the lenght, right?
I am afriad that testing with different amount will change the bass output so that should be in place first.
The filling can damp mids, and can obstruct reflex circulation losing port bass amplitude, but not damp bass modes. If we could damp bass with just some wool filling then we wouldn't have those sci-fi anechoic rooms with children sized wedges in the KEF brochures from the 70's.🙂
I have read that the more you fill the box the bigger it appears to the woofer, that it can be used to tune the size of the box, if it is made a little to small you can fill more and it appears bigger to the woofer, isn´t it true?
A small apparent volume difference they do make, but the damping materials are there to damp the echoes inside the box mainly. If you use them as masses near diaphragms and ducts when moving relatively freely they can load the total Helmholtz thing and deprive enough wide Q output. Too much expense in energy. Better tune than control. Passive control is always involving energy loss. But do what you wanna do and find out how those things work for yourself. Its fun, nothing electrical to short. Ain't an amp, and you may find your best compromise.
Thanks Salas, this is interesting, I am learning a lot from this project. I will try some and post tomorrow, have a nice evening Salas 🙂.
This is surely a lot of work, particularly using a handheld SPL meter. I understand you are tuning your port, maybe a tool like this spreadsheet may give you some idea of what your changes in room position will do.
Thanks for the link AllenB. I removed the polyester filling behind the woofer and it sound more open and present in the middle range. I had too much here according to Salas build and now I have even less since the sides are bare, so I will try with some filling there later. I wanted to remove all so I could hear easily what happens.
I am also trying now with 140mm tube lenght.
I am also trying now with 140mm tube lenght.
I have settled for a 135mm port after testing 130-140mm. Small difference but anyway. I also put some filling onto the sides behind the woofer and it seems fine. Is it a bad idea to have bare surfaces on the sides near the woofer?
I will give them 50 more hours to settle in before I am ready to glue the baffle in place. Got a feeling it need that, the bass is a tad lean sometimes playing music. But I am rather sure that the 2.5mH coil is enough, more playing will tell. How does the sound vary in quality from a non-ferrite coil vs an air coil used for the woofer, same spec. otherwise?
I will give them 50 more hours to settle in before I am ready to glue the baffle in place. Got a feeling it need that, the bass is a tad lean sometimes playing music. But I am rather sure that the 2.5mH coil is enough, more playing will tell. How does the sound vary in quality from a non-ferrite coil vs an air coil used for the woofer, same spec. otherwise?
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Increased distortion, mainly 2nd harmonic at low signal levels, spiced with 3rd harmonic at higher levels. Both may sound superficially agreeable some times, but it's distortion nevertheless.
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