Box tuning help wanted... and sorely needed!

[RobThomas]

Hi,

Please could I get some help with this? I just can’t seem to get decent sounding bass out of this box I’ve built. Singer/Songwriter type music that is mostly vocal and guitar sounds great but as soon as anything in the lower ranges comes in it starts to sound muddled. Some electronic music sounds OK but then if I play it next to a JBL Xtreme or something similar the difference in quality really shows. I’ve tried using a NAD 320 and also a Bluetooth Class D as the backend but it doesn’t make much difference to the sound. This is the first time I’ve tried building a speaker so any help would be greatly appreciated.

Specs:
16mm MDF
Volume: 8.3 Liters
Drivers: 2 X Focal RCX130 Coax Speakers.
The port diameter is 44mm, currently 38mm long

Thanks,
rob

 

[PRR]

Box is rather big. Tuning will be fussy.

Port is mighty small: 1/16th the area of the cones!! Port area should be "roughly similar" to cone area or port air velocity will be high, bass waves damaged.

A larger port with a low tuning must be longer. It is possible for the total volume of the port to use-up all the space in the box.

There's probably a better section for this question.

 

[Michael Bean]

Take a look at this:

HiFi Loudspeaker Design

Mike

 

[Dave R]

Specs:
16mm MDF
Volume: 8.3 Liters
Drivers: 2 X Focal RCX130 Coax Speakers.
The port diameter is 44mm, currently 38mm long

Here's a link to the spec page.
https://www.focal-america.com/wp-content/uploads/2013/12/FT_auditor_RCX_130.pdf

With a Qts = 0.8, it's not an optimum choice for a vented box. And with Fs = 90 Hz, that may limit the bass response.

Be that as it may, could you clarify whether both coax speakers are in the same 8.3 liter box? Or does each one reside in its own 8.3 liter box?

 

[RobThomas]

Hello again,

Michael Bean, thank you that is a very usefull link. We had been using this calculator previously (Subwoofer Vent Length Calculators - Diameter of Vent, Number of Ports, Volume of Box, Tuning Frequency, End Correction Factor). It looks like it's lacking now that I've looked at the one you linked to.

Dave, both speakers are in the same 8.3 liter box.

rob

 

[Dave R]

Dave, both speakers are in the same 8.3 liter box.

rob

I looked at both, and from the response curves, the 8.3 liter box was likely what you had targeted.

The 44mm (dia) x 38mm (Length) port for that combination gives tuning frequency Fb = 88 Hz. The resulting response showed an SPL peak of +7dB at about 120 Hz. It might sound "boomy".

You could increase the 44mm dia vent to 75mm length (instead of 38mm), which yields Fb = 71 Hz. Still some bass lacking below that point. The SPL peak drops down to maybe +5dB at 110 Hz or so. If it still sounds boomy, you could add some stuffing (polyfill, etc.) in the vent to alleviate the boominess and make the sound a little tighter. Experimentation may be the best way to determine the right amount.

Some good simulation programs may help you hone in on a good compromise. However, the bass response with these alone still may not be as satisfying as a woofer/subwoofer with lower bass response.