Subs frequency response...higher end

[Sylar]

I noticed some subs like the FV12 has a frequency response from 20-100Hz. While the VTF 2 has from like 18 to 200Hz. Why such a big difference at the higher end? How much does it impact the listening experience...for music especially?

I just auditioned the SVS PB13 Plus with Usher S520 Bookshelves. The difference was night and day!!
I believe the crossover was at 80Hz. The volume was around -15dB (not sure what the amp settings was like).

 

[55katest55]

Well, since most people set their crossovers at 80Hz it shouldnt matter what the high end is.

The typical frequency range for a subwoofer is about 20–200 Hz for consumer products,[1] below 100 Hz for professional live sound,[2] and below 80 Hz in THX-approved systems.

(from Wikipedia)

 

[Sylar]

Well, since most people set their crossovers at 80Hz it shouldnt matter what the high end is.

(from Wikipedia)

I am aware that ppl usually set the crossover around 80Hz.
But on top of the 100Hz & lower bass, I also like the bass from 150Hz below, played around with my crossover on the AVR. Was wondering if buying subs that do play above 100Hz is a good idea with the idea of playing from 200Hz and below and what the impact would be like.

 

[jonnythan]

Virtually all subwoofer plate amplifiers have a lowpass filter with a frequency set by a dial. Typical ranges are from about 30 Hz to 120 or 160 Hz. With the LPF set to the highest value, most subs start to roll off around 120-150 Hz.

There are two things at work here.

1) For whatever reason, the max crossover on Rythmik amps is 100 Hz, meaning you won't get meaningful output much above that frequency as it's rolling off fast.

2) HSU amps have a switch that lets you disable the LPF entirely. This means that HSU subs can generally play much higher than others without a defeatable LPF.

In practice, neither of these will mean very much unless you have small satellite speakers and need the crossover to be rather high. HSU will accommodate that better.

In general, you'd want to set the crossover on the sub to the highest possible value and let the receiver deal with bass management.

 

[j_garcia]

More likely than not it is a driver and enclosure alignment thing, as well as in some cases, something internal to the amp. It may also be a design choice in that they may intend the sub to have the capability to be dialed in manually to blend with someone's mains. Most subs and/or receivers have pretty steep x-overs for the sub though, typically 12dB/octave min and some 24dB/octave, so they are not really coming into play higher up unless you have the x-over set prety high.

 

[Sylar]

In general, you'd want to set the crossover on the sub to the highest possible value and let the receiver deal with bass management.

...so they are not really coming into play higher up unless you have the x-over set prety high.

I am aware that one wud prefer the filtering in the digital domain in the avr, rather than in the analog domain...hence let the avr take care of the filtering. But my aim here is to get more bass than what my bass capable mains can give me... and I am looking for bass from 150Hz down itself and not 80 or 100Hz down alone.
I would like to know what would it be like, if I set the cross over high around 150 Hz, on a sub like VTF2 which can play till 200Hz, and play bass from mains and sub, or bass from sub alone. Would the HSU sub have a significant advantage over the rythmik here? What would I get or loose out of playing from 150Hz below, with the sub?

Also why is it that when subs are discussed the discussion is usually 100Hz and below and not 200Hz below when there is significant bass from 100 - 200Hz. (lets leave aside satellite speakers and likes which cant play even till 100Hz)

 

[jonnythan]

I am aware that one wud prefer the filtering in the digital domain in the avr, rather than in the analog domain...hence let the avr take care of the filtering. But my aim here is to get more bass than what my bass capable mains can give me... and I am looking for bass from 150Hz down itself and not 80 or 100Hz down alone.
I would like to know what would it be like, if I set the cross over high around 150 Hz, on a sub like VTF2 which can play till 200Hz, and play bass from mains and sub, or bass from sub alone. Would the HSU sub have a significant advantage over the rythmik here? What would I get or loose out of playing from 150Hz below, with the sub?

Also why is it that when subs are discussed the discussion is usually 100Hz and below and not 200Hz below when there is significant bass from 100 - 200Hz. (lets leave aside satellite speakers and likes which cant play even till 100Hz)

The vast majority of speakers play fine down to at least 120. You don't want a sub to play that high since those frequencies are more localizable. You want them coming from thebproper direction.

 

[j_garcia]

The vast majority of speakers play fine down to at least 120. You don't want a sub to play that high since those frequencies are more localizable. You want them coming from thebproper direction.

Yep that's why. Below about 120Hz, sound is not really localizable. Meaning you are more likely to hear the transition around the crossover point higher than you would if that x-over was lower. Not to mention in that range, the lower midbass, you want your mains playing that sound because they will still likely handle it better than the sub.

 

[TLS Guy]

Well, since most people set their crossovers at 80Hz it shouldnt matter what the high end is.

(from Wikipedia)

Oh yes it does.

Crossovers are not brick wall.

The low pass crossovers in receivers are 24 db per octave, fourth order.

So I sub needs a good frequency response an octave above the crossover setting.

So, if set the crossover at 80 Hz, then the sub will only be 12 db down at 120 Hz, and the output will not be 24 db down until 160 Hz. The sub output is not negligible until it drops below the 24 db point. At the 12 db point the contribution of the sub will be just slightly less than half as loud as the mains.

For 100 Hz setting it will be 12 db down at 150 Hz and 200 db down at 200 Hz.

A sub absolutely needs a smooth frequency response an octave above the crossover point.

A sub will a poor response in the 100 db to 200 db range is a lousy sub, especially if it has a peak in that pass band.

The correct function of the use of subs seems to me to be the most miss understood topic on these forums.

 

[j_garcia]

The correct function of the use of subs seems to me to be the most miss understood topic on these forums.

I think it may actually be the crossover that is the most misunderstood. I agree with the fact that even with a steep slope, you will still have sound 1 octave up at least. The speakers get a gentler slope, so they need to extend well below the x-over point also.

 

[TLS Guy]

I think it may actually be the crossover that is the most misunderstood. I agree with the fact that even with a steep slope, you will still have sound 1 octave up at least. The speakers get a gentler slope, so they need to extend well below the x-over point also.

Also thee is misunderstanding of the acoustic power curve of music by frequency.

 

[Sylar]

A sub will a poor response in the 100 db to 200 db range is a lousy sub, especially if it has a peak in that pass band.

The correct function of the use of subs seems to me to be the most miss understood topic on these forums.

You mean 100Hz to 200Hz.

...but all rythmik subs have a response till 90 or 100Hz only. they expect a perfect crossover at 80 or 100? Does that mean u dont recommend rythmik subs?
I used to think that the transition from passband to stopband would require about 20Hz max.

 

[TLS Guy]

You mean 100Hz to 200Hz.

...but all rythmik subs have a response till 90 or 100Hz only. they expect a perfect crossover at 80 or 100? Does that mean u dont recommend rythmik subs?
I used to think that the transition from passband to stopband would require about 20Hz max.

Yes, I meant Hz not db!

Brick wall filters have far too much time delay and phase aberration and are also prone to ringing.

The low pass filter on the receiver is always fourth order, 24 db per octave. So yes you need at least an octave above the crossover frequency.

The high pass filter on receivers is second order. So if you set the crossover to 80 Hz, the mains will be down 12 db at 40 Hz and not down 24 db until 20 Hz.

The reason behind this is that they fondly hope that speakers will naturally roll off at 12 db per octave below 80 Hz. Only a small sealed bookshelf will do that. Then the crossover will be composite fourth order, as long as the sub has a wide enough pass band.

Unfortunately it is seldom you get a good symmetrical splice between mains and sub.

Now if a sub rolls off around 100 Hz, say second order, then you have a composite sixth order low pass filter. Not perfect, but it makes the rig weak in the 100 to 150 Hz range. That is actually the range where not only most of the bass is, but the region the ear perceives as bass. It is an area where small driver speakers with incomplete BSE have trouble. So having a sub with a response an octave above the pass band is a good thing.

Now the big unknown is whether there are cone break up modes, in the octave above the set crossover frequencies. When drivers roll off they seldom do it gracefully and cone break up is the usual rule, but not always. With cone break up you get peaks and valleys. This is a bad thing. It will be audible until the crossover gets the driver 24 db down.

It is always best policy to have driver have a pass band an octave higher than the crossover point for a fourth order filter and two octaves for a second order filter and four octaves for a first order filter.

 

[DD66000]

So, if set the crossover at 80 Hz, then the sub will only be 12 db down at 120 Hz, and the output will not be 24 db down until 160 Hz. The sub output is not negligible until it drops below the 24 db point. At the 12 db point the contribution of the sub will be just slightly less than half as loud as the mains.

You're off a bit. An octave higher from a given frequency is double, and an octave lower is half.
So if the XO is @ 80 hz, with a 12 db/octave slope, then its -12db @ 160 hz.

For 100 hz XO, then its -12db @ 200 hz.

Actually; if the XO is -3db @80 hz, then it would be -15db @ 160 hz. For a 12db/octave slope.

 

[its phillip]

If the slope is 24dB/octave like he said, then his math is correct.

 

[DD66000]

If the slope is 24dB/octave like he said, then his math is correct.

Yep, you and TLS are right, as I was reading it, I was thinking 12db/octave.

 

[TLS Guy]

If the slope is 24dB/octave like he said, then his math is correct.

Thank you. My math is correct. The low pass filters on receivers are 24 db per octave roll off. The high pass is 12 db per octave.

 

[defmoot]

It is always best policy to have driver have a pass band an octave higher than the crossover point for a fourth order filter and two octaves for a second order filter and four octaves for a first order filter.

I'm interested in learning about these concepts. Can anyone point me to a good reference?

Thanks.

 

[defmoot]

^^^
Okay. Found much to begin with in the "Subwoofer terminology" and "Myths" stickies.

Thanks to all who contributed to them.

 

[davee70]

It is always best policy to have driver have a pass band an octave higher than the crossover point for a fourth order filter and two octaves for a second order filter and four octaves for a first order filter.

Does anyone know if the Velodyne DD series satisfy these criteria? I have a DD-15 and added a DD-12 to fill in a broad dip I had in the 60 to 80 Hz region. Like the original poster, I am interested in the high end of the frequency response for listening to music.

I recently replaced my surrounds with two NHT Classic 3's, which are acoustic suspension type. I chose them because they have a 2" aluminum dome mid-range driver like the 2" drivers in the Energy Veritas 2.3i's I have in front. And they do in fact blend very well, excepting in the mid-bass region where the Veritas have two 6.5" woofers that are ported and the NHT has one 6.5" woofer that's not. So in order to achieve a better balance in the mid-bass region I am thinking of having the XO for the NHT's at 150 Hz and 6 db/oct for the DD-12 and 12 db/oct for the DD-15. The crossovers themselves will be custom made, the reason being is that I want the XO that's right for the speakers and not have to rely on the sub or the receiver or the player to do it with one size fits all.

My question then is, do either of these driver's (which feature "high gain servo" control) meet TLS Guy's criteria (low distortion levels 4 octaves for the DD-12 and 2 octaves for the DD-15 above a XO at 150 Hz)? Or would it be better to use a higher slope and/or lower XO frequency and not try to use the XO to match the mid bass response of the NHT's to the Veritas?

I'm sure there have been measurements done on the D-12 and DD-15 but I am having trouble finding them and I'm doubtful that any of them looked at distortion in the 200 Hz to 300 Hz and higher region. Most reviews, even if they do look at distortion, usually focus on the lowest frequencies in the driver's range, not the highest.

My ears tell me the above XO settings will work okay but I'm interested in others opinions and experience with similar drivers. I do not seem to be bothered by the directivity issue that has been mentioned as justification for low XO frequencies and high slopes. It seems to me that one's perception of the overall quality of the sound that's most important. I think distortion is likely more important than direction but it's not so easy to detect just by listening alone.

Edit: I should probably explain that when I refer to XO I actually mean low-pass filter. I have all speakers high-pass filtered at 80 Hz, 12 dB/oct. Therefore, in the case of the NHT's, I am not relying primarily on the subwoofer response in the octave below the 150 Hz XO frequency. In this range, both the speakers and the subwoofers make large contributions to the sound.