First speaker build - questions about values

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#21
Cooljazz, the realisation that this is a notch filter + a first order, increases the requirement for both measurements and the components to be matched to the response. Notch filters are more sensitive to component tolerance than other filters also its likely the resonance the notch is designed to cut in the teeter will also vary from tweeter to tweeter.

Regards,
Andrew
 
#22
Thank you guys,

I must confess I don't fully understand the comments you made, I'm still trying to figure out the theory behind all this.

One thing a have a question about is the port length/diameter. I did the calculations and with a box volume of 60 liters and a bass tube of 64mm dia. and 120mm length, the tuning frequency I get is 36Hz.
A 2mm wider port gives me a tuning frequency of 37Hz.
How important (audible) is this? I will make the tube a bit longer so all the math checks out, but i'm just curious.

Another question is this: I can get the drivers as matched pairs (at extra cost). What does that even mean and is it worth it?
Is it matched impedance, sensitivity, something else?

Cheers,

Erik Jan
 
#23
The bass resonance will change more than 1hz due to temperature variation in the driver, so I wouldnt get too hung up on the last degree in port tuning.

As for matching drive units, it will probably help but dont pay a massive amount extra for it. You wpuld need to ask to know what they are matching, but I would hope sensitivity and resonant frequency.

Regards,
Andrew
 
#24
They tell me they match the driver frequency response to within 0.2dB. A 2dB change in volume is not or barely noticable so even if unmatched drivers have a difference of 10 times that of the matched drivers, it wouldn't make much difference would it?

Is that correct or am I missing something?

Ej
 
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