crossover cut off question

[JOHN FICKEL]

I'm looking for opinions . I have RF-7ll 's for my mains, RC-64ll for the center, and RS-62 for my surrounds. The 7's play down to 30hz, while the center plays to 59hz and surrounds play to 50hz. Where would you cross the sub, 60hz or 80hz? If I decided cross at 60hz do you think that is too low for my center speaker, and surrounds? Thank you I've tried both ways and liked both, but what is the proper cutoff?

 

[j_garcia]

I would still cross them all at 80. X-over is not a brick wall, it has a slope, so you will still get sound down to about 40Hz with an 80Hz x-over. So it would still be applicable to the mains. If you can do them independent, set the mains only to 60.

 

[JOHN FICKEL]

I would still cross them all at 80. X-over is not a brick wall, it has a slope, so you will still get sound down to about 40Hz with an 80Hz x-over. So it would still be applicable to the mains. If you can do them independent, set the mains only to 60.

Ok thank you for your response. I can't do them independently. I'm using a Yamaha RX-Z9. Thank you again for explaining the slope. I don't think a lot of people are aware of that. So if one were set the crossover at 60hz, the mains will see well below 60hz. At that point u might as well set them large? Thank you again

 

[slipperybidness]

Some clarification.

When you set your crossover at 80Hz, what you are really saying is "The -3dB point is 80Hz". The rolloff of the bass actually STARTS above 80Hz, and at 80Hz you have hit the -3dB point. Below the -3dB point, the signal continues to diminish. Exactly how much it falls off is determined by the crossover itself, with a typical value of -6dB per Octave after once you have gotten below the -3dB point.

A picture is worth a thousand words. The 80Hz is the "cutoff frequency" or "corner frequency" depending on which text you read.
http://www.google.com/imgres?imgurl=http://www.intechopen.com/source/html/40131/media/image16.png&imgrefurl=http://www.intechopen.com/books/computational-intelligence-in-electromyography-analysis-a-perspective-on-current-applications-and-future-challenges/signal-acquisition-using-surface-emg-and-circuit-design-considerations-for-robotic-prosthesis&h=277&w=318&tbnid=EvQorRgW6LTL-M:&docid=NLvW3n0CMX6vGM&ei=GecCVt-FIcXVggSq2auAAw&tbm=isch&ved=0CB8QMygCMAJqFQoTCJ_2tdbcjcgCFcWqgAodquwKMA

 

[j_garcia]

I don't think that's how it works on a receiver - 80Hz would be 0dB reduction and drop off there based on the slope. On the speaker side, the slope is usually 6db/octave and it would start at 80Hz with the -6dB being 40Hz (half the output, but you'd still hear some sound). On the sub side however, it is usually 12/dB per octave so it rolls off faster above the cutoff point, minimizing the blend to the mains and keeping it below localization.

 

[slipperybidness]

I don't think that's how it works on a receiver - 80Hz would be 0dB reduction and drop off there based on the slope. On the speaker side, the slope is usually 6db/octave and it would start at 80Hz with the -6dB being 40Hz (half the output, but you'd still hear some sound). On the sub side however, it is usually 12/dB per octave so it rolls off faster above the cutoff point, minimizing the blend to the mains and keeping it below localization.

I'm not saying that you are wrong, but it would seem odd to me to define the crossover frequency (ie cutoff freq) on an AVR in a manner that is different than EVERY other instance in the electronics field. And, clearly the slope from 0dB to -3dB is not the same as the slope from -3dB on down. And, clearly the slope from 0dB to -3dB is not a constant slope like it is from -3dB on down.

The electronic rolloff is controlled by the crossover design, yes you have given more/better examples on that than I did.

https://en.wikipedia.org/wiki/Cutoff_frequency

Also, be careful with the -6dB vs. -3dB.....are we discussing power or voltage?

 

[JOHN FICKEL]

Ok thank you both. I have a much better understanding of this now. Thank you. Gene if you are listening please do a video on this with Graphs.

 

[JOHN FICKEL]

So if I understand this correctly if I cross over at 60, now the center which is only capable of 59hz would see frequencies down to about 30hz ? And obviously that's a lot lower than what the center channel was rated for

 

[JOHN FICKEL]

But those frequencies would be at a -3 to -6db output ?

 

[j_garcia]

Yes, the speaker will see those frequencies, but at a much lower output, so it may bk. I tend to err on the side of it can handle it for sure. Worth trying as you said you've done, so it depends on a variety of things like how loud you listen and whether or not the manufacturer's ratings are honest or optimistic.

 

[markw]

John, this is not an exact science. And, manufacturer's specifications are approximations at best. And, the specs are allowed to vary somewhat during the manufacturing process.

Go with want sounds best to you. It won't harm the speakers. And, if you can't hear the difference, don't sweat it.

 

[KEW]

I wouldn't consider it gospel, by any means, but I would consider it an intelligent starting point:

Google "SVS Merlin" and you will be able to specify your speakers and Merlin will suggest SVS subs (which you can ignore) and farther down it will suggest the proper roll off point.

Note it gives two scenarios.
One is for using an AVR for bass management, the other is for the situation where you are using an old school stereo and the speakers are running full range so you are tuning the sub to your speaker's natural roll off.

 

[JOHN FICKEL]

Ok thank you all. I go back and forth between 60 and 80, and always seem to go back to 80hz. Only because the bass sounds more to my liking at LOW volumes. I will continue to play around. Thank you all again. I just wanted to make sure 60 didn't hurt anything