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Bass Boom - change port length?

3158 Views 5 Replies 3 Participants Last post by  jtalden
I have just built some bass reflex cabinets for a pair of Tannoy Monitor Gold HPD 315s. They are loosely based on designs discussed on the Hilberlink Tannoy, and are roughly 150 litres in volume with 2 100mm diameter, 100mm long ports. (As apparently recommended by Alex Garner of Tannoy)

I am very happy that the sound is much better than my previous speakers, but I did notice that on certain tracks, the kick drum can get a bit tiring. I have set up REW, and calibrated the Behringer ECM 8000 mic and Behringer UCA202 sound card. I have been experimenting with blocking one or both of the ports and analysing the results. The least lumpy curve is obtained if I block the lower port, but looking at the SPL chart, there is still a sharp kick up from about 18Hz. (See image) Is this likely to be causing my "kick drum fatigue"?

This is my first bass reflex design, so I'm not sure if this problem can be alleviated by changing the port length; any advice would be appreciated.

On a side issue; I have used REW on Windows 8 and on Ubuntu. With the setup as close to the same as possible, (calbration, room setup, mike position) I get wildly different-looking phase curves. The Windows ones jump all over the place, whereas the Ubuntu ones (seen in the attachment) show a relatively flat line to 600 and then a reasonably regular curve up from there. Could anyone tell me why they are so different?


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Pretty decent curve overall. :T The quick and easy solution is parametric equalization. If you’re averse to that, then a slew of bass traps could reduce the severity of the 50 Hz peak, but probably not totally eliminate it.

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