Port tuning of the Classix 2.5, with the Precision port

[JensToft91]

Hi all

Some of you may have seen my cabinet tickness question. I made a new thread, in case someone searches for this problem in the future.

I ended up making the Precision Port 1 inch longer than specified in the Classix 2.5 design, because of the instructions that followed with the port. It says here, that the total length should be 1 inch longer than the calculated length using the known formula. Instead of calculating the vent, i just added 1 inch to the specified 8,5 inch port.

Paul Carmody about the tuning: "This tunes the enclosure to approximately 40 Hz, and will get an F3 around 35 Hz".

I have measured the response of the woofers close up, and get a tuning around 35 hz.

Should i shorten the port, and aim for 40 hz exactly?

[fpitas]

Hi all

Some of you may have seen my cabinet tickness question. I made a new thread, in case someone searches for this problem in the future.

I ended up making the Precision Port 1 inch longer than specified in the Classix 2.5 design, because of the instructions that followed with the port. It says here, that the total length should be 1 inch longer than the calculated length using the known formula. Instead of calculating the vent, i just added 1 inch to the specified 8,5 inch port.

Paul Carmody about the tuning: "This tunes the enclosure to approximately 40 Hz, and will get an F3 around 35 Hz".

I have measured the response of the woofers close up, and get a tuning around 35 hz.

Should i shorten the port, and aim for 40 hz exactly?

It really depends on how you like the bass. Room gain will fill in the droop you show to some extent, but often with a smallish speaker people like a bit of a bass hump. Have you listened? Also, if you're near-micing the woofers you're probably missing a lot of the port contribution.

[JensToft91]

The drop is because of the port tune. Measured close up, the output of the woofer will drop as it reaches the port tune (the resonanse stops the woofer from moving).
The point of the lowest output, is the port tune. At least to my understanding :-)

[fpitas]

The drop is because of the port tune. Measured close up, the output of the woofer will drop as it reaches the port tune (the resonanse stops the woofer from moving).
The point of the lowest output, is the port tune. At least to my understanding :-)

True as far as it goes. But you are missing some port contribution from the way you're micing. Generally you would also close mic the port and "sew" the two responses together to get reality.

[JensToft91]

That's true. As I'm searching for Paul Carmody's tune of 40 hz, the close-mic test should be just that. (The woofer dip). The full response is the woofer+the port as you say.

I went ahead, and did the work. (difficult, because i added braces around the port.)

This is a 3 cm difference. My Precision port is now 22 cm long. 0,16 inches longer than the 8,5" port specified.

[wogg]

If you have DATS or can otherwise measure impedance, that gives you a little easier interpretation of where the tuning landed. Also, the old rice on the cone sweep when the rice moves the least bit. All of that isn't super exact.

Personally, I'd leave it. Most of my cabinets are tuned a little lower than "ideal", that allows a little deeper extension at the cost of a little bass knob adjustment and keeps the cone under control a little deeper as well.

[Geoff Millar]

Am following these threads with interest as the 2.5s are on my 'to build' list! The ports to which I have access here are in between Precision Ports and straight PVC tubes, they're Jantzen brand, tapered and slightly flared at one end:


I assume these will give different tuning results to Precision Ports and straight tubes? I used them in my recent builds including the Classix II and they seem to sound fine, although I don't have measuring equipment.

Geoff

[JensToft91]

Wogg:

The bass on the OS was excellent, so I really want to follow his designs. But I do follow you, though!

Geoff:
The tuning will be the same with slightly flared ports and the PVC. It's only because the precision port has such a big flare, that it changes the tuning.

Stay with PVC og slightly flared, and follow his 8,5 inch recommendation. I had to move the precision port under the cabinet, because it got longer (not enough space in the cabinet)

[Geoff Millar]

Thanks for that; I used Precision Ports with my first DIY build but they're now silly prices.

Geoff

[fpitas]

Am following these threads with interest as the 2.5s are on my 'to build' list! The ports to which I have access here are in between Precision Ports and straight PVC tubes, they're Jantzen brand, tapered and slightly flared at one end:


I assume these will give different tuning results to Precision Ports and straight tubes? I used them in my recent builds including the Classix II and they seem to sound fine, although I don't have measuring equipment.

Geoff

As we've discussed, the tuning is to some degree a personal preference. The effect in real life will also depend on your room and where you position the speakers.

[Geoff Millar]

Thanks Francis

Geoff

[JensToft91]

So I've finished the speaker, with the buttom port.

The buttom port is too close to the floor, so it affects the tuning, making it lower.. The higher one is measured on it's side.
It looks like a bit of woofer break-in lowered the tune? Can this be true? It measured 40Hz exactly yesterday. Now it measures 37hz, same conditions.

I'll remove the buttom port, and install a rea port instead.

The speaker sounds awesome though!

[djg]

Nice job. Really.

[JensToft91]

Thank you so much!

[fpitas]

Yes, break-in is real enough. Mechanical parts that flex soften with time. Why go away from a bottom port? Just lengthen the feet a little.

[JensToft91]

I tested this, and it didn't help. I also removed the back part of the base plate. Actually, as I'm writing this, it sounds weird, that raising it didn't help.

I'll try it without the base plate

Edit: I have to raise it higher than I like, to remove the effect. I know it's not much - but i know it will bother me! Rear port it is :-)

[Chris Roemer]

There's nothing "magical" about Paul's tuning. If they sound awesome, just enjoy them for a bit.

[JensToft91]

I do have trouble dealing with small technical details that "prove me wrong".

I just hooked it up to my Crown amp, and cranked it. I can't complain about the bass at all. Like, not AT ALL. I have a pretty big subwoofer, 400w SVS cylinder, and this speaker had med checking twice. My girlfriend event asked if it was only that speaker playing.

But back to my problem about details. Measurements like these have me worrying, if i am missing something. Like, would a 40 Hz tuning be even better? Am i even able to tell the difference? Is it worth ruining a pretty good build to try?

WinISD have the curves within 3 dB, so i shouldn't be able to tell the difference anyway.

It's a 5 Hz difference, and i hate that a detail like this is overshadowing what is possibly the best speaker I've heard.

I think i need to try the 40 Hz tuning, maybe with an even shorter port underneath. Then i dont have to cut any holes.

[djg]

Wait 'til you build some really good speakers.

[fpitas]

Try it as a learning experience. Even if you hear the difference there's no telling which you might prefer until you build a few speakers and get to know your own preferences.

[JensToft91]

djg: The thing is. It's not the best speaker I've heard "objectlively". I've heard really, really expensive systems - but i don't like the "HiFi"-sound. I find it way too revealing and ear-piercing. This speaker does exactly what I've been looking for. A soft, but not a dull sound.

[wogg]

...But back to my problem about details. Measurements like these have me worrying, if i am missing something. Like, would a 40 Hz tuning be even better? Am i even able to tell the difference? Is it worth ruining a pretty good build to try? WinISD have the curves within 3 dB, so i shouldn't be able to tell the difference anyway.

Nope, unlikely you'd hear a difference. Move the speaker 2 feet in any direction and you'll make a bigger difference at the listening position.