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In Reply to: RE: not offset ? posted by tomservo on October 01, 2015 at 17:20:08
thanks Tom - RCA-Fan's graph seems to indicate that in practice this particular destructive interference case is less than the hornresp simulation prediction.
Karlson Evangelist
Follow Ups:
Yes, that's usually the case, measurements of the real thing usually show fewer features and they are of less magnitude than computer predictions.
This has been something i have commented and chuckled about when people model tapped horns which show very sharp features and usually measure fairly differently.
The issue or at least one of them is the model assumes perfect materials and is a simplified case. On the other hand, the value of a computer model is reflected by how well it predicts which you build and measure,even AKABAK which is pretty good,needs some fudge factors or to account for minor secondary effects and even then, i am happy when it predicts the lower part of responses for what i design.
Best,
Tom
I've got a BP4 with a folded rectangular vent which could benefit from a trap to reduce a ~210-220Hz peak - would a 3"ID piece of pvc be able to null it?red trace is the BP4 in question
Karlson Evangelist
Edits: 10/02/15
Hi Freddyi
The big red peak is an organ pipe resonance, this happens at the 1/2 wavelength, the lowest frequency a pipe or duct open at both ends will resonate at.
The easy way around these with a bp speaker is to use a passive radiator instead of a port as they have no pipe resonance.
If you can get inside the cabinet, you could use another duct or pipe with a closed end to make an absorber at that frequency. I put several of those inside the DTS-10 cabinet at work which do this job.
What you would want to do is attach a pipe with a closed end to the port at it's mid point, make the length a bit more than 1/4 wavelength at the peak frequency. If possible, make it so that you can trim the length based on it's effect on the peak (trial and error measurement). A 2inch diameter plastic water pipe ought to be about right.
Hope that helps
Best,
Tom
Danley Sound Labs
thanks Tom - I might be able to poke a stub pipe "sideways" into the vent -- -Oops! there's a brace in the vent- I'm kinda crippled plus the front chamber is difficult to access.a passive radiator would have been cool.
Geddes used to employ an external vent with lengths "Pan - piped"
Will this fix work with a right angle elbow? What happens if the resonator is placed in the rear chamber? Should any damping be used in the pipe?
here's the rear chamber
Karlson Evangelist
Edits: 10/03/15 10/03/15 10/03/15
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