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post #1 of 5 Old 06-12-2019, 02:05 AM - Thread Starter
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Subwoofer crossover

Hi
On this website bobpariseau.com/blog/2018/6/5/choosing-a-crossover-frequency-awesome-bass-begins-here

The author states that: So the LOWER limit for the Crossover Frequency would be TWICE the bottom end of your regular speakers. If they are rated down to 30 Hz, the Crossover Frequency should be no lower than 60 Hz. If they are rated down to 50 Hz, the Crossover Frequency should be no lower than 100 Hz.

Does he mean the bottom end Hz at -3db?

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post #2 of 5 Old 06-12-2019, 11:02 AM
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Why not ask Bob?

I'm sure he means the -3dB point. But few speaker manufacturers are honest about the lower end, especially since clean, low bass at high volume requires big, heavy, expensive cabinets and drivers.

Keep in mind that particular rule of thumb applies with a *total* crossover slope of 12dB/octave. Not all crossovers have a 12dB/octave *electrical* slope (24dB/octave is very common in pro gear), and the *acoustic* roll-off contributes as well.

The problem with mains speakers contributing to the low bass is that the mains have to be located best for imaging and the quality of sound above the sub crossover. Those locations are rarely the best place for them to contribute to low bass. Seperate subwoofers can be moved around for the best bass response.

All these things, and more, are just rules of thumb which sometimes have to go out the window to get acceptable bass response. Look up "subwoofer optimization" for some approaches.

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post #3 of 5 Old 06-12-2019, 11:10 AM
 
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Rooms alter the sound and that's why modern systems measure what's going on with a mic and make decisions based not on just what speakers you have but more importantly how your speakers behave with your placement of them in in your room. Move them to a different room or change their placement and you can get a completely different crossover decision.

Here it is graphiclly. The exact same speaker (actually a subwoofer) but with 4 different placements in the exact same room. Did the sub change? No. Did the room size or shape change? No. The only thing changing is the location of the woofer placement within that room:

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post #4 of 5 Old 06-12-2019, 12:52 PM - Thread Starter
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Thanks
I couldn’t find his contact details.
I had not seen the “2x” guesstimate before and was just pondering my setup last night. I have Tannoy M1s (ckaimed 55hz at +/-3dB) at the front and a new SVS SB2000 for LFE. I set the crossover in the AVR to another ROT, 80Hz, which is not 110Hz. I’ll have to get REW out again and look at the integration with all speakers outputting the sweep.
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post #5 of 5 Old 06-12-2019, 03:05 PM
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An octave is 2x and for a typical 12 dB/octave crossover puts the power one octave away from the crossover frequency at about 1/10th the power at the crossover frequency. That is also roughly the half-loudness point -- something about 10 dB lower in power/SPL is perceived as half as loud (in the midrange; the curves compress a bit in the lowest frequencies). The rule of thumb is to limit the power away from the crossover point into the "off" driver and limit audible interaction among drivers (or main speakers and sub).

There are other variables, of course, that may influence the crossover choice but the 2x rule is a good starting point most of the time.

FWIWFM/HTH - Don
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