Classix 2.5 bass question

[stev]

Hi everyone, noob speaker builder here. I recently finished a pair of Classix 2.5's and overall they sound phenomenal, however I'm a little underwhelmed by the bass I'm getting. The bass is tight, defined, and articulate, but I was expecting a little gratuitous chest-thumping. This is very "hear it", not "feel it".

First off: are my expectations out-of-whack? I'm new to the hifi world (though have lots of experience with live sound reinforcement), and I understand it's a subjective question. If I compare them to the bass I get from my tiny Isetta (first speaker I built), I'm a little disappointed given how much bigger these are.

Mostly I'm wondering if I've done something wrong. I've verified that the polarity of all the woofers is correct. Given how good they sound overall, I doubt there's anything wrong with the crossover (I've also connected just one driver at a time and to my ear the crossover is correct). The amp I'm using is a QSC GX3. My cabinets may be *slightly* undersized (maybe 1/8 inch short on height). My ports are the Precision Port 3-inch flared (which claim an effective length of 2.5 inches) connected to 6 inch lengths of 3 inch diameter port tube for 8.5 inches overall ported out the front.

Any thoughts or recommendations would be appreciated, thank you!

[johnny5jz]

I know there are some pics of the 2.5s using the flared port, but I am not sure how there is room. With the 8.5 inch port, there is only 1.75 inches between the back of the port and the back wall. If you use the aero port to the correct dimension, you would be too close to the back wall. My aero ports were around 9.5+ inches if I remember correctly. I ended up scrapping them for a straight port. If you have a DATS, run an impedance sweep to verify the port resonance frequency.

[Carbon13]

Could be over stuffed? How much fill do you have?

[johnny5jz]

First, what is the overall length of your Aeroport?

[johnny5jz]

Per the precision port website "Overall length of flare is 3" of which only 2 1/2" is usable because of the flare." per this, the port would actually be 9.5 inches overall, putting it 3/4" from the back wall. That could definitely lower your tuning frequency and also make the bottom end a little thin. If the port is 8.5 inches overall, it would raise the tuning frequency and could make it a bit boomy, but at a higher frequency.

[stev]

Carbon13 I put a big handful behind each woofer. Am I correct in assuming the fill is there to tame some boominess? I'll try pulling it all out and seeing what happens.

johnny5jz sorry, I'm a little confused. I think the design calls for an 8.5 inch long port. I read that exact section on the Precision Port website, and my logic was the flared port (2.5 inch usable length) + 6 inch length of straight tube = 8.5 inch long port. Maybe I'm misinterpreting something there?

Thank you both for the responses!

[stev]

Could my problem be that I've surface mounted the port to the front of the cabinet without taking into account the thickness of the front panel (3/4")? Essentially ended up with a port that's 3/4 of an inch too short?

[johnny5jz]

Then the overall length of the port is 9.5 inches and is too close to the back of the cabinet. The kit I bought also came with the precision port, but I did not use it. The kits now have been modified to a 2.5" precision port 5.75" long to mitigate this. You can either buy the 2.5" precision port or put a standard 3" port in place.

[johnny5jz]

Could my problem be that I've surface mounted the port to the front of the cabinet without taking into account the thickness of the front panel (3/4")? Essentially ended up with a port that's 3/4 of an inch too short?

No, the port length is independent of the baffle thickness. The 3" precision port was a mistake in this kit originally. Like I said, it was communicated to the vendor and corrected.

[stev]

Then the overall length of the port is 9.5 inches and is too close to the back of the cabinet.

Can you help me with where the 9.5 inch number is coming from?

[johnny5jz]

Each end of the flare is 3.0 inches long. Only 2.5 inches of this is used in your port calculation leaving you with an extra .5 inches on each side. This makes the actual overall length 9.5 inches instead of 8.5. Flare ports are always a bit longer than straight ports, because the flare itself does not count in your actual port length. Hope that makes sense.

[stev]

Ok. I probably didn't clarify, I'm only using the precision port on one end of the port (outside). Outside flare (2.5 inches) + 6 inch straight port tube, no inside flare.

[johnny5jz]

You are still .5" closer to the back wall. Try a 1/2" or larger piece of plywood between the port flange and the front of your speaker cabinet. See if that makes it any better. Also make sure there is no stuffing or damping material between the back of the port and the back wall of the cabinet.

[djg]

This came up before. The builder ended up with a down firing port since it didn't appear there was enough room front to back to fit the proper size 3" Precision Port.

The new kit comes with a 2.5" x 5.75" Precision Port.

If you whine at the kit supplier they may send you a new port package. They are nice people. Of course your hole's too big, but it's DIY.

Another solution would be a 90 degree elbow in your 3" port.

[stev]

I appreciate all the responses. I bought all the components individually so no one to blame but me. If I'm understanding, the issue isn't that my existing port is the wrong length (9 inch overall, 8.5 inch effective) but rather that the existing gap between the inside end of the port and the back of the enclosure (1.25 inches less egg crate material) is insufficient?