High pass crossover roll-off - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 14 Old 12-11-2019, 08:01 AM - Thread Starter
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High pass crossover roll-off

I recently added a Crown 1502 amp to drive my front towers. I can set a high-pass filter on it with a 60hz roll off, to match the same crossover setting on my receiver. I was experimenting with turning off my sub woofers and playing test frequencies, but my Crown amp LED indicators (output?) were lighting up right from the lowest frequency through the step-up tones up to 60Hz; so these low frequencies were all coming through the Crown amp and the tower speakers. The towers are still set to "small" with the subs turned off (under the receiver's "audio" setting), so why am I still hearing frequencies below 60 Hz through the mains? I assume it isn't a "hard" cutoff at 60Hz, but why do I hear these <60Hz frequencies from the towers? Or does the receiver automatically route all frequencies to the front mains when the subs are turned off, even when the main front towers are set to small?

Marantz SR-7008, Pioneer DV-578A, Technics SL-DD2, Crown XLS-1502; Polk Monitor70s, RTi-A5s, CSi-A4, HTS12; Panamax 4310.

Last edited by Frank123; 12-11-2019 at 08:21 AM. Reason: typo
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post #2 of 14 Old 12-11-2019, 10:05 AM
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High pass crossover roll-off

A crossover isnt a hard barrier, its a fairly gentle slope, usually 12dB/octave) so your speakers if set to small with an 80hz crossover will play around half as low at 40hz and around half as low as that again at 20hz(which they probably cant)

So by turning off the sub you only get less and less bass the lower it goes from the main speakers.

Edit: you use a 60hz crossover so numbers will be ~half at 30hz and ~half again at 15hz.
This is the reason the ‘rule of thumb’ is to set the crossover at double the -3dB point of the speakers.
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post #3 of 14 Old 12-11-2019, 10:15 AM
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Just to add to Leeliemix's excellent comments, if you have bass management enabled in your AVR there is no need to set an HPF on the Crown amp. In fact, it would be detrimental since you would be doubling the slope of the crossover (if you set the HPF in the Crown to 12dB/octave, resulting in 24dB/octave).
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post #4 of 14 Old 12-11-2019, 10:35 AM - Thread Starter
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Quote:
Originally Posted by Alan P View Post
Just to add to Leeliemix's excellent comments, if you have bass management enabled in your AVR there is no need to set an HPF on the Crown amp. In fact, it would be detrimental since you would be doubling the slope of the crossover (if you set the HPF in the Crown to 12dB/octave, resulting in 24dB/octave).
Great, thanks guys! Excellent advice, I will cancel the crossover setting on my Crown amp completely (just use "full band pass" I guess).


So, I am still hearing low bass frequencies below 60Hz, but just at a reduced level, that makes sense now to what I'm hearing. I thought it would be completely eliminated below the crossover setting.



Leeliemix, forgive me but I am not an audiophile veteran; could you explain what you mean by your comment: "This is the reason the ‘rule of thumb’ is to set the crossover at double the -3dB point of the speakers". What is the -3dB point you refer to? Thanks.

Marantz SR-7008, Pioneer DV-578A, Technics SL-DD2, Crown XLS-1502; Polk Monitor70s, RTi-A5s, CSi-A4, HTS12; Panamax 4310.
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post #5 of 14 Old 12-11-2019, 10:54 AM
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Originally Posted by Frank123 View Post
Great, thanks guys! Excellent advice, I will cancel the crossover setting on my Crown amp completely (just use "full band pass" I guess).


So, I am still hearing low bass frequencies below 60Hz, but just at a reduced level, that makes sense now to what I'm hearing. I thought it would be completely eliminated below the crossover setting.



Leeliemix, forgive me but I am not an audiophile veteran; could you explain what you mean by your comment: "This is the reason the ‘rule of thumb’ is to set the crossover at double the -3dB point of the speakers". What is the -3dB point you refer to? Thanks.


Its where the speaker is playing at 3dB lower than ‘flat’ and is usually written in the specifications of the speakers. The woofer(s) isnt able to play as loud anymore and has started to roll off. I dont know what speakers you have so ill write what mine show in the specifications: Frequency range 27Hz - 40kHz (+-3Hz)
These are fairly full range but for surround and sometimes music i use a 60Hz crossover to 4 subs. 60Hz is a little more then double the 27Hz they can do before dipping past -3dB but there is no 50Hz option in my processor so cant try that.


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post #6 of 14 Old 12-11-2019, 11:34 AM
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Leeliemix is giving great advice again, however I believe by "double" he actually means to say "two octaves" above the F3 point. For example, if the in-room F3 of your speakers (the point where the lower end of the frequency response drops by -3dB) is 60hz, you would want to use a crossover of at least 80hz (not double, which would be ~120hz).
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post #7 of 14 Old 12-11-2019, 11:55 AM - Thread Starter
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Originally Posted by Leeliemix View Post
Its where the speaker is playing at 3dB lower than ‘flat’ and is usually written in the specifications of the speakers. The woofer(s) isnt able to play as loud anymore and has started to roll off. I dont know what speakers you have so ill write what mine show in the specifications: Frequency range 27Hz - 40kHz (+-3Hz)
These are fairly full range but for surround and sometimes music i use a 60Hz crossover to 4 subs. 60Hz is a little more then double the 27Hz they can do before dipping past -3dB but there is no 50Hz option in my processor so cant try that.


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Sounds good, thanks again !

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post #8 of 14 Old 12-11-2019, 12:11 PM
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Quote:
Originally Posted by Alan P View Post
Leeliemix is giving great advice again, however I believe by "double" he actually means to say "two octaves" above the F3 point. For example, if the in-room F3 of your speakers (the point where the lower end of the frequency response drops by -3dB) is 60hz, you would want to use a crossover of at least 80hz (not double, which would be ~120hz).

(Not really a reply to @Alan P but for the OP)
For a high F3 like 60Hz then 120Hz crossover might be a bit high yes but thats only because we can locate the sub fairly easily up that high and that subs often dont do very well higher up. But for those that end up double at up to 80hz thats usually a good way to go (and maybe 100/120hz depending on speaker and sub placement, if sub is between the front speakers for example a higher crossover can work well).
These are just starting points, whats best depends on speakers/sub/placement/room and personal preference.

P.S. I hope we arent drowning you in information @Frank123
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post #9 of 14 Old 12-11-2019, 12:13 PM - Thread Starter
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Quote:
Originally Posted by Alan P View Post
Leeliemix is giving great advice again, however I believe by "double" he actually means to say "two octaves" above the F3 point. For example, if the in-room F3 of your speakers (the point where the lower end of the frequency response drops by -3dB) is 60hz, you would want to use a crossover of at least 80hz (not double, which would be ~120hz).
Thanks Alan! Again, I really appreciate your advice.
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post #10 of 14 Old 12-11-2019, 12:47 PM
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I don't think localisation is an issue when setting x-over at 100hz, I have tried it in my setup, with 120hz it may be but depends on your setup. if the sub is physically located fairly close to the front speakers, a higher x-over shouldn't have any downside.
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post #11 of 14 Old 12-11-2019, 02:31 PM - Thread Starter
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Originally Posted by Leeliemix View Post
(Not really a reply to @Alan P but for the OP)
For a high F3 like 60Hz then 120Hz crossover might be a bit high yes but thats only because we can locate the sub fairly easily up that high and that subs often dont do very well higher up. But for those that end up double at up to 80hz thats usually a good way to go (and maybe 100/120hz depending on speaker and sub placement, if sub is between the front speakers for example a higher crossover can work well).
These are just starting points, whats best depends on speakers/sub/placement/room and personal preference.

P.S. I hope we arent drowning you in information @Frank123
My Polk Monitor 70’s have a spec freq range of 30Hz to 25Khz so I will keep the 60 Hz crossover setting on the AVR. Next lower option is 40Hz, which I don’t think the speakers would handle as well as the sub?

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post #12 of 14 Old 12-11-2019, 02:45 PM
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Quote:
Originally Posted by Frank123 View Post
My Polk Monitor 70’s have a spec freq range of 30Hz to 25Khz so I will keep the 60 Hz crossover setting on the AVR. Next lower option is 40Hz, which I don’t think the speakers would handle as well as the sub?
Take another look at the specs...it says the -3dB point is 40hz.

60hz is the absolute lowest acceptable crossover, but I would experiment with 80, 90 and 100hz as well and go with the one that sounds best to your ears. The less work the mains have to do, the less distortion. That being said, your subwoofer is definitely the weakest link in your system...have you considered an upgrade?
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post #13 of 14 Old 12-11-2019, 02:52 PM
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High pass crossover roll-off

I see those polks differ from site to site between 30 and 40 hz in the specifications so not sure whats what but that changes a bit depending on room also so. It could be worth trying 80hz to see if better but it depends on your sub also. If your amp handles them well at 60hz XO thats fine.

Edit: removed a spare ‘e’, and i see Alan beat me to it
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post #14 of 14 Old 12-11-2019, 04:19 PM - Thread Starter
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Originally Posted by Alan P View Post
Take another look at the specs...it says the -3dB point is 40hz.

60hz is the absolute lowest acceptable crossover, but I would experiment with 80, 90 and 100hz as well and go with the one that sounds best to your ears. The less work the mains have to do, the less distortion. That being said, your subwoofer is definitely the weakest link in your system...have you considered an upgrade?
Absolutely. Will be the next one.

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