What's the word on mixing bass?

Very glad to discover this website as I am renewing my interest in audio building. Or possibly audio downsizing.

I've been a confirmed adherent of mixed bass audio for 40 years or so, currently using 5 amplifiers and driving a single amp to a single Klipschorn bass (built in early 50s, I think) in the range up to 140 Hz, with a 50 year old South West Technical amp.

Thought I'd ask: what is the state of current thinking about mixing bass? In particular, are people feeling there is a downside? Or any reason not to use a simple resistor mixer?
 
Peter - many thanks.

I appreciate that kind of information. But... if there's no sense of direction with low bass, what difference would it make what the "composer" thought he/she was trying to do? (That's a real question, not a rhetorical one.)

I'm none too clear where woofer ends and sub begins. In most respects, we divide the frequency compass by equal octaves, thinking that apportions the effort (and in most respects, the design challenges) fairly enough. With bass, there's also the point-of-no-directionality below which we might as well have a single speaker. I'm still inclined to believe the cost-effective approach is to create a single really great woofer because the cost of making two would be steep (that is, double).
 

leadbelly

Disabled Account
2002-12-22 2:13 am
Calgary, Alberta
I'm surprized that you didn't get more of a response. Probably because this has been debated ad nauseam. A little searching would get you some good threads. Personally, I'm on the pro-stereo-woofers side of the debate. IMHO the significant distortion caused by the sub driver makes a mono sub very localizable, and makes stereo subs the preferred option.
 
leadbelly said:
I'm surprized that you didn't get more of a response. Probably because this has been debated ad nauseam. A little searching would get you some good threads. Personally, I'm on the pro-stereo-woofers side of the debate. IMHO the significant distortion caused by the sub driver makes a mono sub very localizable, and makes stereo subs the preferred option.

Thanks.

I searched as best as I could for about a half-hour (and there's that 20/minute time-out too). All variations of mixed, blended, mono, bass, etc., titles and posts, etc. Any help searching such as key words or phrases would be appreciated.

Yes, the distortion products and noise can make the woofers localizable, if they are bad enough. With a low enough woofer crossover, the distortion products should still be barely localizable. But given the benefits of corner location for eking out the lowest notes, easy to get locked-into certain few locations in the room.
 
Picture of Klipschorn? HIding right behind my right D-W in the only good corner in my not large music room... corners big enough for a K-horn are hard to find.

Started life as a utility horn, meaning no veneer and no top. Needs a top to seal off the top edge of the exit mouth and I made one from 25 lbs of particle board. Finished the top and the front with luan mahagonny (striped, nice stuff), bad spelling. Very easy to buy, contact cement, and trim such veneers and then to finish with a gel stain. A nice feature of a Klipschorn is that you can rest a whole lot of cinderblocks or wine bottles on top, always a good move for a woofer, even if least needed for a horn.

Or are you asking for a picture of the antique SWTP amp with the speaker protector circuit (mostly for turn-on turn-off transients) and the extra power supply caps lying on the carpet next to it? Klipsch said "give me 5 clean watts" or something like that.
 
Last I understood, bass was only non-directional when it was mixed that way by the studio, which was apparently common practice. Modern recordings may have stereo information all the way down, and a stereo subwoofer setup is probably to be preferred unless the room precludes it. OTOH, there are some really fine single sub systems, so I wouldn't lose any sleep over it. IMO, subs are great if they can be smoothly integrated with the rest of the system. To me, that means a sealed box mid-bass/main system, not a reflex, and a properly designed crossover. The sub can be any design one likes.
 
Conrad Hoffman said:
Last I understood, bass was only non-directional when it was mixed that way by the studio, which was apparently common practice. Modern recordings may have stereo information all the way down, and a stereo subwoofer setup is probably to be preferred unless the room precludes it. OTOH, there are some really fine single sub systems, so I wouldn't lose any sleep over it. IMO, subs are great if they can be smoothly integrated with the rest of the system. To me, that means a sealed box mid-bass/main system, not a reflex, and a properly designed crossover. The sub can be any design one likes.

As far as I know (and that's pretty rusty) two things have to be kept separate. There can be all kinds of disparate stuff on the channels of a recording, but they get mixed in your room when the frequency is low. If it is true, as I believe it is, that you have no ability to sense direction of a source below maybe 140 Hz, might as well have one quality source. (If you have a super tweeter - and a loudish one - like an ion wind, all the sound seems to come from the little blue glowing tube.)

Some of the stuff that is different on any channels of the recording is accidental and due to factors of the room where the recording took place. Some of that wave informs the listener about the concert room (if any), but that is not because of any directionality of the sound or the disparity between the two channels.

Likewise, some of the stuff that reaches your ears as a results of identical low frequency material coming out of speakers in different places in your room, is also accidental and of no significance - or a distortion - when it reaches your head.

So why not just mix the bass and avoid some of the false room effects and the losses arising from having multiple channels doing the same thing (when you could invest time and energy into one excellent woofer doing all the woofing well)?

My mixed bass corner horn (cross-over around 140 Hz, 24 db/8ave) sits right behind my right speaker. But there is no sense that any bass emphasis is coming from that side.

BTW, I share your preference for sealed and distaste for the very fashionable tuned boxes. A Klipschorn has a sealed box behind the driver.
 
It's the "inaudible below 140 Hz" thing that I think was dis-proven a while back. Apparently we can detect directionality at low frequencies. Just how low and under what conditions, I'm not sure. No question that room effects at low frequencies confuse the issue beyond belief, and it seems a valid argument for mixing the bass. I don't even have a sub right now, but the few I've built have all been singles. Still, given the right room and conditions, a dual setup might localize drums better- has anybody had both and could you tell the difference?
 
I am no longer surprised at new scientific findings - today Vitamin E is good for you yesterday, but today, maybe bad for smokers. There's some direction finding with a single ear (even with an immobilized head) and that was a bit of a surprise albeit now 50 yrs ago. So maybe you are right. But I would like to see the basis of your claim that directionality exists much at XX Hz.

To be sure, even woofers make rude noises and hiss and the speaker is detectable in that sense. Likewise, no doubt possible to tell if one or two woofers are playing, the difference between mixed bass and stereo, and so on for basic discrimination tests.

I guess my belief is that iif there were two woofers in a room and your head was more or less steady in one location, you couldn't answer which was playing an 80 Hz note even if you knew they sounded different (which they probably would).

You believe otherwise?
 
bentoronto said:

I guess my belief is that if there were two woofers in a room and your head was more or less steady in one location, you couldn't answer which was playing an 80 Hz note even if you knew they sounded different (which they probably would).

You believe otherwise?

I'd for the most part agree with that statement. However there are things that can make subwoofers playing at or below that range easier to localize. It could be harmonic distortion, mechanical noise at higher excursions, or port noise if it's a ported box. I once had a subwoofer using a fairly inexpensive driver and if I pushed the crossover frequency above 120hz the harmonic distortion became strong enough for me to locate the subwoofer. I think that if you are going to go with a single subwoofer in your room there are are several things you could do to make it less easy to localize;

-Keep the crossover frequency as low as your mains will handle
-Use a driver with low harmonic distortion
-Keep the subwoofer between your mains or as close to them as possible.
-Use an adequately sized port to avoid port noise
-Put your subwoofer behind a couch, a stuffed chair, or some other objcect that will absorb some of the higher frequency harmonics
-If you have carpet in your room and the driver is suited to it, build a downfiring subwoofer.
-Use a bandpass enclosure, it will actually filter out some of the mechanical noises and harmonic distortion(I owe credit to Zaph for making this observation) It's even more important to have an adequately sized port in this case since all of your output is through the port.

As far as stereo bass is concerned it's my opinion that the only things that make stereo bass audible as actually being in stereo are the exact same things that you want to avoid in a subwoofer such as harmonic distortion). Even if I am wrong an by chance the human ears can detect very low frequency sounds in stereo there is one other very important point to make. Any instument that makes sound has harmonics, and it will be those harmonics that your ears are able to locate. So unless you listen to recordings made up of low frequency sine waves mixed in stereo then I don't see much of a point to stereo subwoofers.

Jason
 

leadbelly

Disabled Account
2002-12-22 2:13 am
Calgary, Alberta
JasonB said:
Any instument that makes sound has harmonics, and it will be those harmonics that your ears are able to locate. So unless you listen to recordings made up of low frequency sine waves mixed in stereo then I don't see much of a point to stereo subwoofers.

Unlike the rest of your post, that last part completely misses the point. Harmonics which are present in the source are taken care of by the sub low pass filter; these localizable higher frequencies do not magically make it past the filter because they come from a bass instrument. The distortion of the sub woofer itself, which is in general a relatively large value on the order of 1%, imparts distortion on the sound and makes the sub localizable.
 
I know I read an article on this several years back, but I've no recollection where. Frankly, the more I think about it, the less I'd trust research on the matter. As said above, the reason being that any sub, even with motional feedback, is going to have some harmonic distortion. The minute the sub emanates anything out of band, you'll be able to localize it. So, it seems to come down to "how do single vs stereo subs sound with music?"
 
I suppose somebody should mention the reason mixed-bass is a positive benefit: stereo phone cartidges have their vertical rumble cancelled and with benefits to reducing uncorrelated/undesired bass sounds (I may have that garbled). Dunno if summing the bass helps counter any distortions in the digital recording world?

A bigger room would put the woofer further from your ear and so many noise components that are constant (not increasing with sound level) would be inaudible, esp whenever anything loud and bassy is playing. That's a good reason not to use an overly-powerful amp to drive speakers if the absolute noise floor from the amp is correspondingly raised from a small-power but clean amp.

The nice even-harmonic distortion products from the the single woofer would almost certainly be overwhelmed by the very same frequencies made by the source instrument and coming out of the highly localizable upper-range speakers.

If your best single-woofer placement is near your ears, the room is small, the amp is noisy, the woofer distorted, or you have all the money and listening room space in the world... don't go with mixed bass.

Today's favorite bass: Vangelis: Mission to Mars (he also wrote the great music for Chariots of Fire (about Olympic racing... not spaceships). Guess what segment is real loud and bassy?
 
leadbelly said:


Unlike the rest of your post, that last part completely misses the point. Harmonics which are present in the source are taken care of by the sub low pass filter; these localizable higher frequencies do not magically make it past the filter because they come from a bass instrument. The distortion of the sub woofer itself, which is in general a relatively large value on the order of 1%, imparts distortion on the sound and makes the sub localizable.

I should have clarified myself a bit better there. I agree that the actual harmonics of the instrument will not make it to the subwoofer, however they will be played by the main speakers. And it will be these harmonics played through the mains that will give you the impression of stereo bass even with a mono subwoofer.

I also agree with your point that it's mainly harmonic distortion that makes it possible to locate a subwoofer playing low frequencies, but I'd be curious to see if a typical subwoofers harmonic distortion would be high enough to mask the natural harmonics of the music that are being played through the mains and ruin the stereo image.

Jason
 
bentoronto said:


The nice even-harmonic distortion products from the the single woofer would almost certainly be overwhelmed by the very same frequencies made by the source instrument and coming out of the highly localizable upper-range speakers.

If your best single-woofer placement is near your ears, the room is small, the amp is noisy, the woofer distorted, or you have all the money and listening room space in the world... don't go with mixed bass.


Two excellent points, your comment about the natural harmonics being played be the mains overpowereing the harmonic distortion is what I was I was alluding to in my post above to Leadbelly. And the second point, I've heard cheap subs that come with HTIB systems placed well away from the mains and the highish crossover points and large amount of harmonic distortion really draw attention to their location.

Jason
 

leadbelly

Disabled Account
2002-12-22 2:13 am
Calgary, Alberta
bentoronto said:
The nice even-harmonic distortion products from the the single woofer would almost certainly be overwhelmed by the very same frequencies made by the source instrument and coming out of the highly localizable upper-range speakers.

JasonB said:
Two excellent points, your comment about the natural harmonics being played be the mains overpowereing the harmonic distortion is what I was I was alluding to in my post above to Leadbelly.

You're both dreaming in Technicolor if you think that the harmonic distortion spectra from the sub will mesh so cleanly with harmonics present in the source. Thanks for the chuckle :)
 
leadbelly said:




You're both dreaming in Technicolor if you think that the harmonic distortion spectra from the sub will mesh so cleanly with harmonics present in the source. Thanks for the chuckle :)

Meshing, no.

We both agree that is is harmonics that let the ear determine the location of a low frequency sound. My point is that the natural harmonics of the note played through the main speakers will be much more of an indicator of location to the ear than the harmonic distortion of the subwoofer itself will be. There are always exceptions, but if you are using a quality subwoofer, crossed over and located properly and not overdriving it it should not be an issue. If you are using a cheap subwoofer, to high of a crossover, poor placement, or are overdriving it then yes I could see that the harmonic distortion generated by the subwoofer could draw attention to itself and cloud the stereo image.

Jason