Stereo or 2.1 - Which produces better bass punch?

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Hello everyone,


I had successfully designed and built my first 30+30W RMS amplifier about a year and a half ago with the conventional architecture consisting of Diff Amp - Voltage Divider - Driver Stage - Output (Class AB) and Global Feedback. Now I am looking to built something more powerful, let say, around 120-150W RMS in total output.

In the stereo design, I noticed a phenomenon in which the low frequency beats get canceled out to some extent in some parts of the room even when the polarity for both speakers is set correct. I don't know much about acoustics, but I presumed that the multiple sources of sound(2 speakers in this case) create some kind of an interference pattern which is destructive for low frequencies at some locations in the surrounding space.

My question is, should I go for a 2.1 channel amp with a hi-power sub-woofer amplifier to reduce this effect in my next design?

Also I am little curious to know as to why this canceling out thing becomes evident particularly in the low frequency spectrum.

Thanks,
Prasanna (Prax)
 
Hi,

that's the usual room acoustics problem.

In every air filled space resonances occur, at which frequencies depends on the shape of the room (the typical box type room being the worst type) and on its dimensions.

As bass is usually recorded as mono (due to human perception of bass), a 2.1 system will not improve that.

You can try to dampen your room acoustically, like add carpets, book shelves, curtains.

The more the merrier ;)

Have fun, Hannes

EDIT: forgot, changing the position of the speakers can also help!
 
h_a said:
Hi,

that's the usual room acoustics problem.

As bass is usually recorded as mono (due to human perception of bass), a 2.1 system will not improve that.

EDIT: forgot, changing the position of the speakers can also help!


Thanks.

But wouldn't two speakers producing the same monophonic audio from two different positions introduce more directionality than a single sub-woofer banging at the same relative power?

- Prax
 
I have not tried it, but there is a multitude of opinion on this Forum that says that distributed bass drivers have a better chance of sounding right/better than a single or even two bass speaker set up.

If 2.1 were to follow this route then one bass speaker reproducing the 0.1 bandwidth is the wrong way to go.
Maybe 4off 8inch drivers/boxes, each with their own amplifier spread around the room may give a better sound than a 2.0 (stereo) system.
Rather than mid/top satellite pair + one 15inch bass speaker.

This would be an ideal candidate for 6off chipamp monoblocks in tiny chassis.
 
xitronics said:



Thanks.

But wouldn't two speakers producing the same monophonic audio from two different positions introduce more directionality than a single sub-woofer banging at the same relative power?

- Prax


Directionality is not a matter of the number of speakers, but of the music. 2 speakers have the advantage that they power different room modes (resonances), so in average that should give a more consistent bass in the room. Of course using even more speakers improves that to a point of diminishing returns, but is not really practical (equalisation necessary).

Still, it's easier to dampen the room, although that's not to everybody's taste. ;)

Have fun, Hannes
 
I am a bass player and have never heard a 2.1 system that sounded better than a proper stereo set up.
So I agree with Andrew.
Have you ever listened to a subwoofer on its own?
Most sound absolutely crap. Why would you want to add that crap to your music.
The correct way is to start with really good stereo speakers, capable of the frequencies you need (Scanspeak 18W/8545 drivers are one of my favourite drivers for bass) , and amplifier with reasonable amount of damping factor, as well as power output.
Bass notes love powerfull amplifiers.

Edit: Just one other observation. Speakers with multiple bass drivers (eg 5" to 6") sound much more punchy than speakers with single bass drivers (regardless of size). That is it is better to have 2 x 6" drivers as opposed to a single 8" driver.
There are also other factors, cabinet alignment (box volume and port length) for vented cabinets or using sealed cabinets. All of this affects the bass performance.
There is much more than this also, but the things I have mentioned are the things that I have found in my experience make the most improvement.
 
Hi Andrew
It sounds like you are using bi-amping, is that correct?

I should elaborate a bit further about power rating. Most of my experience relates directly to instrument amplification and speaker cabinets, although I have found the same rules seem to apply to stereo amplification.
When I first started out playing bass guitar (over 15 years now) I got myself a Fender Jazz guitar. I didn't know anything about amplification or speaker cabinets at that time. So I had a look at what my friend used (a guitarist). From memory it was 60W Messaboogie combo with a 10" driver.
Well I thought, I am a bass player so I need a big woofer right and if I can afford 100W then I am set.
Well I ended up buying a Fender BXR 100 (a 100W combo with a 15" woofer). Sure this thing played loud (loud enough to cause permanent hearing loss) but I found it lacked tone and punch, basically it was lifeless. I became confused and disillusioned why I couldn't reproduce the tone and punch of other bass players. I tried different EQ settings and affects peddles but nothing helped.
6 months later I walked back into the bass shop not happy, thinking it must be the guitar. I thought maybe I should buy a Musicman bass guitar. So I asked the guy in the shop if I could compare a Musicman to a Fender Jazz. I told the guy I had a Fender BXR 100 combo amp and would like to use that to make a fair comparison. Unfortunately he had sold out of the BXR 100 but he had a BXR 300 (exactly the same amp but with 300W of power). Anyway I plugged in the Musicman and started playing, my immediate impression was this sounds fantastic, alright I was sold. I was just about to trade in my guitar, but I thought to be fair I should play the Fender Jazz through the same amp. So I went ahead and played and then the bomb shell fell, the bloody Fender Jazz also sounds fantastic. What is going on. I asked the guy if he had any other amps with 100W power rating. Every 100W amp I played sounded crap in comparison to the 300W, and I am talking about playing at very quiet levels (much more quiet than you would listen to a cd).
I could go on but to cut to the chase after 15 years of trying out over 50 different amps and cabinets, I have come to the following conclusions:
- a 2 x 10" sounds better than a single 15" (ie multiple drivers over single drivers),
- and 300W or 400W amp sounds much better than a 100W amp.
And finally my favourite bass amps are the Trace Elliot AH500-12 hybrid (2 of the gain stages uses valves, mosfets at the output) amp the other is an Eden WT 550. These are 500W amps.
I mainly play jazz style music so I don't need 500W for the volume. I could probably get away with 40W and still I have ampple headroom in terms of volume but I challenge anyone to find one that sounds as good as the two mentioned above.

To sum up I am not saying you need 300W for your stereo set up (40W is probably adequate), but big powerfull transformers improve things quite substantially, so don't skimp in this area.

I realise there are so many other factors. But all things being equal these rules seem to be consistant.
 
I think it's called " headroom".
Looking at little computer 2.1 speakers , sometimes I felt them more present in the low region compared to my 15" woofers , but that trick is easily discoverable because often the little 3" is directly attached to the floor or something...
Now I'm playing with OB and at 2 watts the lows don't even need equalization....
That's strange! Room elastics ? amplifier damping factor ?
 
thanh1973 said:
I should elaborate a bit further about power rating. Most of my experience relates directly to instrument amplification and speaker cabinets, although I have found the same rules seem to apply to stereo amplification.
your "live" music production experience is valuable.
Those who need it cannot do without that type of advice.

Reproduction of recorded music requires a different system philosophy.

I too am an advocate of adequate overhead. I believe it is a priority to ensure "clean" sound.
That example I gave was typically using 50+50mW into a pair of high sensitivity, 18inch drivers and about 500+500mW into a pair of full range, medium sensitivity, small two ways.
100mW into the twin driver bass speaker is ~ quarter of the half watt into each satellite.
But all four of the amplifiers were each of 170W into 8ohms.
 
Hi Andrew
Could you elaborate what this philosophy is.

Hi sensitivity woofers and medium sensitivity satelites is not "all things being equal".
I hope you don't take that the wrong way. I think I agree with just about everything you say, but sometimes I think you enjoy trying to argue every point even though the person agrees with you.
My comments were based on all things being equal (or at least close to equal).
 
the philosophy is make the amplifier system able to play wideband ~1Hz to 100kHz.
Make the amp + speaker system (all drivers) able to produce SPL levels ~110dB at the seating/listening position.
Play an average level that is at least 20dB below the peak abilities of the system.

That philosophy is completely different from the requirements for "live" music.

And none of reproduction gets close to
Bass notes love powerfull amplifiers.
 
This is more evident in the bass frequencies because:
- wavelengths for bass are in feet (or metres if you're metric), so this means a room of given size will cancel them out nicely.
- the bass you hear, compared to midrange, is relatively clean (ie, only one or two frequencies playing), not including harmonics. Midrange, for example vocals, are lots of frequencies, which makes it very difficult to cancel them all.

"but I presumed that the multiple sources of sound(2 speakers in this case) create some kind of an interference pattern which is destructive for low frequencies at some locations"

is correct, however, walls can also reflect the sound, so, while they won't make sound themselves, they will be a "source". When you consider how many walls there are to a room, it's not surprising bass can seem very directional.

A subwoofer MAY sort this problem, to a point where many listening positions are acceptable. Also, subwoofers are fairly flexible in positioning, as they don't affect stereo imaging (unless you have a stereo pair).

Chris
 
What I will say more about this topic is that with an average stereo setup (speakers and amp) I can follow the bass line through out a song can tell you whether the guy is playing an acoustic or an electric bass and write out the sheet music for the bass line.
With a good setup, as well as the things mentioned earlier I can tell you if the bass player uses passive or active pickups, uses a plectrum or fingers, has frets or is fretless, can distinguish between a Fender Jazz, Fender Precision, Rickenbacker, Musicman, Tobias, Warwick, or Spector Bass. I might even be able to tell you what type of amp setup the guy is using.
If you have this sought of ear or desire to hear this sought of detail, then whatever you do don't use a subwoofer.
A subwoofer might increase the volume of the low frequencies but you will lose massive amounts of detail and the character of the notes will be lost.
 
A subwoofer might increase the volume of the low frequencies but you will lose massive amounts of detail and the character of the notes will be lost.

Have you ever heard a good subwoofer with good speakers with the sub xover steep and below 50 hz (ie just using the sub for the very low stuff) in a decent room? The details are in the harmonics, if you use the sub just for the low fundamentals and position it correctly it can sound very good.
 
One problem here is that not all peaople mean the same thing when they talk about subwoofers.
A SUB woofer is for SUB bass, like that last poster understands it. The infamous B**e high-order bandpass modules are not subwoofers for instance. Their lower cutoff frequency is not even reaching the SUB bass range. So systems like this should correctly be called woofer and satellite systems.

While a real SUBwoofer can add more realism to an already excellent stereo setup - this can not always be claimed for satellite and WOOFER systems.

I have once built a small pary PA that is of this type (OK this is not exactly a HiFi setup but my findings might possibly be interesting anyways) which is consisting of a pair of small satellites and a pair of bandpass woofers. Xover frequency is 110 Hz.
I achieve the most SPL in the bass range when I move the two woofers closely together - but the most ACCURATE bass reproduction is achieved when the satellietes are paired with a woofer on each side. Interestingly this happens with the woofers run in mono which I won't have expected personally.

Regards

Charles
 
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