High/Low pass for a sub/speaker configuration

[Boerd]

Hi there,

I am looking for an answer to a simple question:
If I have a speaker that goes down to 40Hz and a sub, do I need a high pass for the speakers (such that they only get 40Hz + signal)?
I've heard that sending the entire signal to a speaker that can't go down to 20 Hz introduces distortion. How much of this is true?

Thanks a bunch for your time.

 

[mtrycrafts]

Hi there,

I am looking for an answer to a simple question:
If I have a speaker that goes down to 40Hz and a sub, do I need a high pass for the speakers (such that they only get 40Hz + signal)?
I've heard that sending the entire signal to a speaker that can't go down to 20 Hz introduces distortion. How much of this is true?

Thanks a bunch for your time.

No, you would not get distortion. the speaker would not respond to the lower signals, that is all.

What is your setup? How are these two connected to something?
Just because that speaker is claimed to go to 40Hz, doesn't mean it is functional to that frequency.

 

[Boerd]

No, you would not get distortion. the speaker would not respond to the lower signals, that is all.

What is your setup? How are these two connected to something?
Just because that speaker is claimed to go to 40Hz, doesn't mean it is functional to that frequency.

Vienna Acoustics Baby beethoven + REL R 505 sub.
What happens with the signal that can't be reproduced by viena acoustics ? Does it waste amp power?
VA go down to 30Hz (theoretically)...

Thanks for your time

 

[Swerd]

Vienna Acoustics Baby beethoven + REL R 505 sub.
What happens with the signal that can't be reproduced by viena acoustics ? Does it waste amp power?...

No it doesn't waste amp power. If a speaker cannot produce sound, or to be more technically correct, if a speaker can't move in response to an audio frequency signal, no electrical current is drawn from the amp at that frequency. Zero current (I) means zero power (P), P=I²R, where R is resistance.

The answer to your original question depends whether you are using a HT receiver or a stereo amp or receiver. HT receivers have built in crossovers for separate subwoofers that can also high-pass filter the audio sent to your other speakers. Most 2-channel rigs lack that.

 

[fredk]

To add to what has already been written, how your speakers interact with the room will also affect the best crossover point. Having speakers that reach low gives you more flexibility in where you set the crossover. This assumes you have a receiver that has an adjustable crossover point.

FWIW, your Vienna acoustics speakers may well meet their stated specs. Not all manufacturers exagerate. See if you can find some independant measurements of your speakers.

 

[fredk]

No it doesn't waste amp power.

Doesn't that depend on whether or not the speaker has a highpass filter set?

If the signal goes to the speaker, it will attempt to reproduce the signal and thus use power. A number of sub plate amps have a highpass filter for this exact reason. It protects the driver by preventing it from unloading trying to reproduce very low frequencies.

 

[Boerd]

Doesn't that depend on whether or not the speaker has a highpass filter set?

If the signal goes to the speaker, it will attempt to reproduce the signal and thus use power. A number of sub plate amps have a highpass filter for this exact reason. It protects the driver by preventing it from unloading trying to reproduce very low frequencies.

This is what I heard before...
I use a Primare i21 amplifier BTW - no sub output - no high/llow pass for a sub.

 

[Swerd]

Doesn't that depend on whether or not the speaker has a highpass filter set?

If the signal goes to the speaker, it will attempt to reproduce the signal and thus use power. A number of sub plate amps have a highpass filter for this exact reason. It protects the driver by preventing it from unloading trying to reproduce very low frequencies.

It depends on whether the speaker can actually draw current from the amp at the frequency in question. Most woofers naturally roll-off below a certain frequency. When in a cabinet, there is additional roll-off due to the interaction of the woofer with the cabinet. The shape and steepness of that roll-off can vary depending on the cabinet volume and tuning. It works as a non-electronic high-pass filter.

The best way to know if a speaker can draw current or not at low frequencies is to look at an impedance vs. frequency curve. High impedance means low current draw. Some speakers might distort or even get damaged trying to produce low frequencies, but many others - by design - cannot draw enough current from an amp at low frequencies to matter.

A subwoofer's high-pass filter is usually set a some frequency higher than the natural roll-off point of the speaker itself. The main reason is to allow better blending of sound between the speaker and subwoofer. But it could also protect a speaker's woofer from trying to produce lower frequencies that it really can. Those cases may be uncommon, and I believe that it may be evidence of poor speaker cabinet design.

 

[Boerd]

Thank you guys.

 

[Swerd]

Thank you guys.

I tried searching for measurments of Vienna Acoustics Beethoven Baby Grands that might show an impedance curve, but had no luck. They seem like well-made speakers and look really nice http://www.viennaacoustics.at/products/beethoven_baby/beethoven_baby.php

I did find a frequency response curve, but that review did not have an impedance curve.

They have two woofers, probably driven in parallel in a ported cabinet. The HT Labs frequency response curve (purple trace) shows shallow bass roll-off below 80 Hz, a shoulder at around 40 Hz, and then steep roll-off below 40. That is consistent with a ported cabinet tuned to around 40 Hz. Usually such designs have steeply rising impedance below the port tuning frequency. I think it's safe to guess your speakers do that.

I couldn't find an impedance curve, but there is no reason to believe these speaker are not well designed. I wish I could hear them.

 

[Boerd]

Please take a look at these (bigger brother of the ones I have):
http://www.stereophile.com/floorloudspeakers/506vienna/index4.html

 

[jostenmeat]

Hi there,

I am looking for an answer to a simple question:
If I have a speaker that goes down to 40Hz and a sub, do I need a high pass for the speakers (such that they only get 40Hz + signal)?
I've heard that sending the entire signal to a speaker that can't go down to 20 Hz introduces distortion. How much of this is true?

Thanks a bunch for your time.

I've been led to believe that ideally you will want a high pass for the speaker, unless you are assured that they will not be replicating the same bass frequencies, for then you suffer unpredictable amplitude and phase interactions.

THAT SAID, it seems that most people, myself included, use compromised bass mgmt most of the time. People skin this cat in many different ways, including using multiple subs all over the place (which has the same "issue" of duplicate bass).

I've been led to believe something like the discontinued Outlaw ICBM could be desired in a situation like yours. Or perhaps the Behringer DCX (more difficult to understand).

While I'm trying to speak in terms of what I think is supposed* to be the ideal, I also have the impression that for people like you and me, there is no substitute for experimentation. If it sounds good, it sounds good, and there's probably a reason for that. If the bass is bloated, or is masking the other audio, obviously that's not good.

I'd just keep playing around with the REL's low pass, phase, gain, etc, and just as importantly, the position of the sub itself.

 

[fredk]

unless you are assured that they will not be replicating the same bass frequencies

Theres the rub. Every room is different. I have read about a few people that run their mains full range as well as crossing the sub higher with good results. There are also a couple of people running MBM units that overlap with the mains.

Geddes even suggests that the ideal arrangement is multiple MBM units (~50 - 150Hz) and a single subwoofer.

 

[jostenmeat]

Theres the rub. Every room is different. I have read about a few people that run . . .

Yep. And I've read of a guy who found his favorite tweaking after using BOTH the sub's lowpass in conjunction with his receiver's xover. Yeah, cascading xovers, but as he noted, they're not brick walls.

 

[nibhaz]

Yep. And I've read of a guy who found his favorite tweaking after using BOTH the sub's lowpass in conjunction with his receiver's xover. Yeah, cascading xovers, but as he noted, they're not brick walls.

Was this by chance on a THX certified Processor?

THX controllers use a 2nd order Butterworth on the high-pass filter for the speakers, and 4th order Linkwitz/Riley for the sub. This is based on the assumption that the speakers are sealed and have an – 3db cut off at 80 Hz. The speaker’s natural roll off combined with the 2nd order Butterworth should create a 4th order Linkwitz/Riley slope on the speaker side of the crossover point. If your speaker isn’t sealed and it’s -3db point is lower than 80 Hz all bets are off…hmm cascading filters…interesting.

 

[jostenmeat]

Was this by chance on a THX certified Processor?

No idea.

THX controllers use a 2nd order Butterworth on the high-pass filter for the speakers, and 4th order Linkwitz/Riley for the sub. This is based on the assumption that the speakers are sealed and have an – 3db cut off at 80 Hz. The speaker’s natural roll off combined with the 2nd order Butterworth should create a 4th order Linkwitz/Riley slope on the speaker side of the crossover point. If your speaker isn’t sealed and it’s -3db point is lower than 80 Hz all bets are off

This is interesting info. I think I've read of some older units that had a shallower slope than 4th order (I think 2nd) for the sub's output, and in fact none at all (full signal) for the speakers, as the mftr assumes the natural rolloff of the speaker to be sufficient. Don't quote me on that!

…hmm cascading filters…interesting.

Yeah, I know. I'd never recommend it, but I just brought up the story to highlight my point that people skin the cat in so many different ways. The guy brought this up when I was asking a somewhat complicated question in the Audio theory forum of AVS.

 

[fredk]

THX controllers use a 2nd order Butterworth on the high-pass filter for the speakers

Wel now, thats interesting. I want to try the Geddes method, but was concerned about the speaker crossover. I will also try the mains full range to see how that measures.

 

[lsiberian]

It's interesting to read the opinions on the matter. I think it's important to play it safe with speakers especially ported ones. I've found the sound to be unpleasant in many speakers below a certain crossover. I suggest you listen and see what sounds the best to you. This is one of those ear determined things in my mind. That being said unless I have 8" drivers I won't push too far down.