Bass level effect on crossover choice

[brucek]

Perhaps this is just obvious to everyone, but it's something I do with my own system, and so I'll talk about it here.

I may be way off base (my attempt at a pun), so all the smart people are invited to correct my delusion.

Here's the thing:

For those people who enjoy their bass levels much higher than their mains, they might want to consider reducing their crossover frequency.

The result in my system is a cleaner sound.

I think its easier to explain the point I wish to make with graphs, so follow along below.

Directly below is a graph of a set of mains (in blue) and a subwoofer (in blue) crossed at 80Hz and the resulting signal in red.

You'll note this lucky guy has perfect speakers and a perfect room.

Crossed at 80Hz
Flat bass 80 Hz crossover.jpg


Another guy has a very capable set of mains and so decides to cross at 60Hz instead of 80Hz. His graph is seen below.

Not much difference in the resulting signal though, except perhaps he gets a bit more stereo soundstage.
Keep in mind he has perfect speakers and a perfect room, so he didn't have to worry about the rooms effect on the mains response at a lower crossover.
Again we see the mains response in blue and the subwoofer response in blue, both crossed at 60Hz....

Crossed at 60Hz
Flat bass 60 Hz crossover.jpg


The first guy who crosses at 80Hz decides he'd like more bass and so decides to get crazy and turn up his subwoofer 15dB.
Below shows what happens to the resulting signal. The bass starts to result in a increased level at about 120Hz - the graph shows why.
This first guy finds his bass too overpowering in the mid and upper bass regions.

Crossed at 80Hz
HOT bass 80 Hz crossover.jpg


The second guy turns his bass up 15dB and finds it sounds just right because the increased bass doesn't start to even rise above the mains level until about 85Hz - the graph shows why.

Crossed at 60Hz
HOT bass 60 Hz crossover.jpg


Anyway, this is just something I noticed on my system and is a consideration if you decide you want that extra bass, you may want to decrease your crossover frequency.

brucek

[Wayne A. Pflughaupt]

Interesting post, brucek. Goes hand and hand with what I’ve experienced recently: Since switching from larger full-range speakers to bookshelfs, what I ended up with was response similar to your last graph, since the bookshelfs don’t have enough bottom end to smoothly blend with the sub. The result has been a trade off: Upper bass is lacking with music, but with video programming it’s an improvement. I often had problems with the voices, especially male voices, sounding “boomy.” There is much less, virtually none of that now, since response now is remaining flat to a lower frequency.

I guess the only downside to the lower crossover point is less EQ adjustment for the sub. A good compromise might simply be using the receiver’s tone controls to get the same effect as your bottom graph. Many of them these days have adjustable turnover frequencies, and if the tone control also extends to the sub output, then setting a low turnover frequency and then boosting could get the same effective response as your method.

Regards,
Wayne

[azjimmy]

Interesting theory Bruce. This could be why I ended up at 60Hz. I had a response alot like #1, until I switched to 60hz. My sound stage is wider, I do loose some mid bas, but the impact is better.
Hmmm. Something to think about.
Jim

[Chrisbee]

I am left wondering why anyone would arbitrarily raise their subwoofer output by 15dB?

If you are trying (even subconsciously) to match the natural LF roll off of your ears then you ought to try tipping the bass upwards from a higher frequency. A smooth but gentle house curve starting from a higher than normal point will provide the bass you obviously feel you are missing. (Inverse Fletcher-Munsen) Though note how the required bass boost falls to flat around 100dB! Which suggests that subwoofers don't accurately model what the ear hopes to hear. Housecurves may be a way of overcoming the LF output limitations of the equipment chain we use to reproduce film sound. (rather than a symptom of our becoming bass junkies )



With a straight 15dB lift most listeners would think the sound very bass heavy on music. Though they might easily miss the fact that the bass is boosted on films which lack obvious reference points.

I have found that the quality of the bass from a subwoofer is a vital factor in satisfactory (artificial) bass reinforcement. The lower the distortion the higher the level one can "get away with" in the bass. If the quality is high enough it simply seems as if you have moved nearer to the action. (virtual square law effect)

If the quality of the bass is low you end up swamped in ever-higher levels of harmonic distortion with increasing SPLs. On music it quickly becomes intolerable to have the bass set any higher than flat!

With an IB very very high bass levels are easily tolerated (even on music) without one's attention being drawn to the fact. While poor subs and/or those with a peaked response can become absolutely critical as to relative level. They can even require individual sub level settings for different CDs!

[brucek]

Well, aside from the consideration of equal loudness curves (and I do listen fairly quiet), my understanding from reading Professor Pflughaupt is that modifying the response to the 'house' creates a "perceived flat response as opposed to measured flat response". The idea being to raise the level of bass from the crossover up to about 30Hz and then remain flat.... I suppose this considers you listen at sensible levels.

My contention was that for those who have set up their system at a particular level and then increase it may experience too much bass at the higher bass frequencies (as demonstrated in my graphs). I offer a solution that worked for me.

I'm one of those people who like a lot of bass, but not so the response is chesty or muffly sounding. Lowering the crossover may be a solution to those who enjoy a lot of bass down low.

Here's my response showing the difference between mains and sub.......... did you ask who would arbitrarily raise their bass level by 15dB - how about 30dB................ I use a 60Hz cross.


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FULL_RANGE_WITH_FILTERS.jpg

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brucek

[Chrisbee]

Bruce

Your 30dB lift looks rather like my 16-46's natural in room response.

[Wayne A. Pflughaupt]

Chrisbee wrote:

I am left wondering why anyone would arbitrarily raise their subwoofer output by 15dB?

I got the impression that was merely a “for the sake of argument” example! Until I saw brucek’s real curve, that is...

By the way, Chris - the Fletcher-Munson curves became obsolete in 1956. The Robinson-Dadson curves eventually became the ISO standard in 1987. See the 5th paragraph here.







Regards,
Wayne

[Wayne A. Pflughaupt]

Chrisbee wrote:

If you are trying (even subconsciously) to match the natural LF roll off of your ears then you ought to try tipping the bass upwards from a higher frequency. A smooth but gentle house curve starting from a higher than normal point will provide the bass you obviously feel you are missing. (Inverse Fletcher-Munsen) Though note how the required bass boost falls to flat around 100dB! Which suggests that subwoofers don't accurately model what the ear hopes to hear.

From what I’ve seen, a house curve is a compensation for the room, not our hearing deficiencies. This is because hearing compensation is a static factor, while the house curve needed will vary from one room to another. Thus, hearing compensation only enters the picture in that the house curve needs to be adjusted for your regular listening level. Still, I like having a remote control for my sub, to turn it down when playing at louder than normal levels, and up for lower than normal levels.

Keep in mind that the SPL level we measure in a room as 100 dB is typically C-weighted. Since we need the bass boosted in a residential room, the bass is what’s delivering the 100 dB reading to the meter. Switch to A-weighting at that volume level, and you’ll see the SPL drop significantly – 10 dB or more typically. 100 dB A-weighted - now that's freakin' loud!

With a straight 15dB lift most listeners would think the sound very bass heavy on music. Though they might easily miss the fact that the bass is boosted on films which lack obvious reference points.

That’s certainly something else to consider! That 15-dB sub boost might indeed sound terribly bass heavy with high-volume music, but with movies it won’t necessarily be obvious, because (as you note) they don’t really have a reference point.

Regards,
Wayne

[Chrisbee]

Interesting that the later curves show a greater need for bass. Bring it on!

[eddthompson]

surely equal loudness curves are slightly moot?

if your sat in front of an orchestra you will hear it as you would.

if you record it with a flat frequency response, the play back with a flat responce, surely you would hear it as you would sat in front of it.

ive always prefered the sound of a flat responce, anything else is surely like using "rock" eq mode on your amp.

the only thing i still dont totaly understand if the room curve.

edd

[brucek]

surely you would hear it as you would sat in front of it.

The point of the equal loudness curves is to show how the human ear responds to various frequencies at different sound pressure levels.

Since the ear becomes less sensitive to low frequencies at low volume levels, then as you turn down the volume the "perceived" response will not be flat anymore, even though the actual playback is flat.

A house curve compensates for the actual effect a room has on the sound pressure, not the perceived effect.

brucek

[Chrisbee]

Edd

You have to remember that no present system is capable of reproducing the original sound.

The dynamics and bass extension of the real world are impossible to recapture with present equipment and transducers. And quite probably we should be thankful for that! Nobody wants a real Colt 45 or a bomb going off in their home! We are already approaching the levels where hearing defenders would be compulsory in industry. Fortunately most of the acoustic energy is in the bass where it does least (or no) harm. As a famous speaker manufacturer claims in their ads: "Nobody screams for more treble!"

[eddthompson]

brucek wrote:

The point of the equal loudness curves is to show how the human ear responds to various frequencies at different sound pressure levels.

Since the ear becomes less sensitive to low frequencies at low volume levels, then as you turn down the volume the "perceived" response will not be flat anymore, even though the actual playback is flat.

A house curve compensates for the actual effect a room has on the sound pressure, not the perceived effect.

brucek

So recordings should state at which volume they should be played at (say 80db) and if you play louder or quiter you can compensate, pitty that aint gonna happen

im still a bit lost on room curves, i guess the idea is any noise we hear, in general is affected by a sort of room curve, and as such using my example of an orchestra, you hear it as affected by the room curve (when going to see one), where as if is recorded flat, that room curve is lost, so at home you need to apply a room curve that suits you room to regain it. is this perhaps why some of the 1950s twin mic recordings sound so great, they left the acoustics/room curve on the recording?

struggling to form coherent passages here


edd