What kind of stuffing to use?

[ramiro77]

Hello everyone.
I recently finished assembling a couple of floorstanders.
I noticed two peaks in the response.
One at about 400Hz, and the other at 800Hz.
I measured the frequency response, and got the following:



As you will see, beyond the valley at 1kHz, there is nothing unusual.
But I do not comply, and continue measuring. This time, with the microphone inside the bass reflex, appeared the following:



You see, after 200hz, the response falls, then there are two huge peaks at frequencies that I noticed.
All this leads me to think that the problem is internal reflections. But the box is completely filled with glass wool on their faces, and also high density anecoic foam.
So what can i do to avoid this peaks?

[AllenB]

Could they be quarter wave resonances related to the length of the port?

[DavidL]

Looks like the mid/woofer is radiating sound out of the port at higher frequencies. Is the port forward facing? Could you move it to the back of the enclosure? Try stuffing the port with straws and see if it improves any. All ports radiate sound above the frequency wanted to some extent. Is the port a lot longer compared to the diameter? All are a factor.

[ramiro77]

Mmm I don´t think so.
If I put my ear on the walls of the boxes, I can hear that resonances inside.
But the box is made with high thick MDF, and I put many reinforcements to prevent vibration.
In fact, if I touch the boxes, they do not vibrate.
For this reason I suspect the problem is the fill, which is not properly absorbing internal reflections.
Maybe I`m wrong. But as you see, frequency response is nearly flat if i do a near field measurement... And it´s not an acoustical problem, because I can hear the peaks wherever I put the boxes.

[ramiro77]

Originally Posted by DavidL

Looks like the mid/woofer is radiating sound out of the port at higher frequencies. Is the port forward facing? Could you move it to the back of the enclosure? Try stuffing the port with straws and see if it improves any. All ports radiate sound above the frequency wanted to some extent. Is the port a lot longer compared to the diameter? All are a factor.

Hello David.
The port is in the back of the box.
I´ve tried to stuff the ports with a lot of high density foam, and the peaks are still there.
The ports aren´t a lot longer compared to the diameter (4cm x 6.5 cm, two for each box).

[picowallspeaker]

Is the acoustic foam glued to the internal walls ? If not ,it oscillates with the membrane and God knows where it brings...
Ramiro , you should give us also the box dimensions .

[ramiro77]

Hello picowall!
Yes, the acoustic foam is glued to the walls.
The internal dimension of the box is (18.4 x 25 x 65)cm.

[picowallspeaker]

Not properly a floorstander
The frequencies ,400 & 800 Hz , could be due to :
Bad speaker (ugly plastic cone break up ) or bad basket
The cut for the woofer is not as thin as it should , and compromises the sound with primary reflections ( tubey sound ).
The cabinet is dead sound inside ,as you described , so it must be the speakers

[DavidL]

Try completely closing the port. Does the problem still exist? If not then the port was radiating the sound from the speaker.The only place your measurements show the two peaks is the mic inside the port, If that's the case then try moving the port higher in the box. If the port is directly behind the speaker then it's a shorter path for those frequencies to travel through it. Hope that helps, I'm out of ideas if not.

[ramiro77]

I try to plug the port fully. The problem persists.
I'll try something alternative, I will place the Peerless in OB and i´ll see what happens. If the problem persists, drivers are the problem. If not, it´s the box.