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Old 3rd May 2015, 08:23 AM   #1
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Default amplifier loading in a small enclosure....

a quick question to which i have been trying to search an answer for....

i am thinking of building a pair of very small full rangers with helper woofers. i am wondering if i use a very small sealed enclosure, limiting the bass in the full range (F3 around 120H), if this acts as a kind of high pass filter in terms of the load on the amplifier. i am using a small 2A3 set amplifier for the full rangers, and trying to find ways to maximise its dynamics, without sacrificing quality, or adding filters and stuff inline....
the helper woofers would cross over around 120Hz and be powered by a separate (solid state) amp.
simply stated, i want it all - deep solid bass, and warm lovely fluid midrange, soundstage and transparent clarity. but all this will be at good levels of listening, not painful....
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Old 3rd May 2015, 08:36 AM   #2
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The small sealed box acts as an acoustic highpass filter. The load on the amplifier won't change - it'll still try to wave the cone around at low frequencies, but the cabinet won't let it. The driver gets the short end of the deal as it has to dissipate the extra LF current, resulting in a little more heat in the voice coil, and probably a little more distortion.

At low volumes, you probably wouldn't notice the extra stress on the FR driver. Turn it up, though, and I'd expect problems to be apparent. Easy way around it: put a crossover in there. Even a capacitor on the amp's input would help dramatically.

Chris
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Old 3rd May 2015, 09:14 AM   #3
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ok - that is a shame - i was hoping the speaker and amplifier were in cahoots in terms of the load. i shall look into simple passive high pass line level filters as you suggest....

thanks for the response!
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Old 4th May 2015, 04:53 PM   #4
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If you have a 2A3 amp it will likely have a series cap somewhere in circuit already acting as a high pass. Just shrink the size of that cap so that it acts at the frequency you want to roll off the speaker at.

This coupled with the 2nd order of a sealed box will give you a 3rd order filter. The rising impedance of the box will reduce the load on the amp for a bit. Note that the driver will determine were the roll-off is.

dave
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Old 4th May 2015, 09:17 PM   #5
sreten is offline sreten  United Kingdom
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Hi,

Build a 1st order filter into the amplifiers via the input capacitor @ 120Hz -3dB.
Then use the output to also drive an attenuator with a built in reverse 1st order
boost +3dB @120Hz to use as drive to the subwoofer amplifier. Works a treat.

rgds, sreten.

TinaTi will help with the simple modelling,
SPICE-Based Analog Simulation Program - TINA-TI - TI Software Folder .
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Last edited by sreten; 4th May 2015 at 09:20 PM.
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Old 4th May 2015, 11:49 PM   #6
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Too get better bass I make a 4 inch hole in the rear of my cabinets.
It doesn't let out too much sound but reduces pressure inside the cabinet.
My last build was Fane Sovereign 15-600LF and it sounds great with the 4 inch hole in the back of the cabinet, loads of bass.
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