Single or double bass modules??

I currently have a double bass PAS. Yesterday, I did a test playing back some test tones through a single bass and double bass configuration. There is no difference! I measured db levels through a db meter and could find absolutely no difference in the loudness of bass between having one or two bass modules. Can someone explain this? If this is true, then everyone might be better off having just one bass module as it's easier and faster to set up. Sound is exactly the same.
Original Post
iibw,

That's an interesting result! Two B1S are getting more power from the PS1 and are physically moving twice as much air. Can we get some details about your testing - frequencies of the tones used, type of meter and settings, speaker placement (stacked, etc.)? Also, were you using Amp 3 Out with the proper 4-conductor Speakon cables?

I ask because I've done a similar comparison using only my ears (no test equipment) and the difference between one and two B1s is dramatic, especially on my acoustic guitar. While testing, did your ears tell you anything different from what the meter told you?
iibw,

Great experiment and your observation is exactly right and here is why:

We have carefully voiced the system to have the "best" spectral balance. Ideally, this spectral should not change, no matter how many bass modules are attached. More bass modules simply allow you to play louder and have more headroom. Adding the second B1 will not change the spectral balance but play louder.
The PS1 senses how many B1 bass modules are attached (0, 1 or 2) and adjusts the internal EQ accordingly. In the case of attaching the second B1 the PS1 will drop the bass level by about 6 dB so that the overall acoustic output stays the same.

You can actually notice the change: When you attach (or detach) the second B1, the systems mutes for about a second, adjust its EQ and then comes back again. That's perfectly safe to do while the system is playing.

This actually pretty useful: When you have lightweight gig or a rehearsal, you need to only bring one B1. For heavier duty you can bring the second one along. In either case your sound will not change and you don't need to adjust anything.

If you repeat your experiment with the system cranked to full volume you will actually find a 6dB difference. That is your second B1 at work.

Hope that helps (if not, please post again)

Hilmar
Hi Chuck, thanks for your response. I did the test because my ears were telling me that the sound was the same with one or two B1s. I have two B1s stacked side by side, connected from amp 3 out with the original 4 conductor Speakon cables. I used a radio shack sound level meter, and played a test tone CD at 40kHz, 80kHz, 120kHz, 220kHz at 90dB and results were all the same, no increase in dB reading at any frequency. The meter was about 10 feet away from the B1s, on a table.
I was curious because when I went to the Bose Center, the tech there said the same thing, that he noticed there was no apparent bass volume change with 1 or 2 B1s on their setup.
I'm wondering if a vertical stack would make a difference...I'll do the same test with the B1s stacked vertically and post the results.
Hilmar

I hear what your saying, but I don't really understand. I associate "spectral" with light instead of sound. This might be clear as a bell (or a bass drum)to some, but I'm not getting it.

When I read the post by iibw, I figured his test signal was above 180hz, thus no difference in output.

Could you try again otherwise it would appear there is no need to have 2 B1's.

Thanks, Oldghm
I used a radio shack sound level meter, and played a test tone CD at 40kHz, 80kHz, 120kHz, 220kHz at 90dB and results were all the same, no increase in dB reading at any frequency.

Sorry, the above should have read 40Hz, 80Hz, 120Hz at 90dB... not kHz!!
[QUOTE]Originally posted by Oldghm:
Hilmar

I associate "spectral" with light instead of sound.

Oldghm, I think Hilmar's use of "spectral balance" refers to the balance of tonal range from deep bass all the way up to high treble sound. He is saying that whether you have one or two B1s, the sound is the same; always balanced between the highs and lows. The only difference is the ability to play louder.

In my opinion, if you're not driving your system at or close to maximum volume, you won't need the second B1.
I went back and read again and again seems to me there is contradiction...."adding the second B1 will not change the spectral balance but play louder".... "In the case of attaching the second B1 the PS1 will drop the bass level by about 6db so the overall acoustic output stays the same"

I'm so confused now I'm not sure the yellow paint thing makes sense.

Oldghm
I like to use my Takamine acoustic as a reference to see what speaker systems can do. It has a pickup under the bridge that sounds kinda like a kick drum when I smack the bridge with the butt of my palm. When I compared one B1 vs two, I started with one and set it as loud as I could bear. Adding the second had me reaching for the remote and turning the system down a bit. The difference with two B1s wasn't so much more bass in the spectrum, rather more volume and it seemed punchier overall - I know, hardly empirical data...

Hilmar, does this make sense, or are my eyes deceiving my ears (and my rib cage)?
Hi everyone

quote:
if you're not driving your system at or close to maximum volume, you won't need the second B1

That quote from iibw is really what its all about. Very well put.

Oldghm
On the spectral balance: By spectral balance we mean the correct proportions of lows, mids and highs. This is what we try to maintain.
Let's look at an example. For the sake of argument lets assume we want equal amount of level at 100Hz and 1 kHz. Say its 90 dB in the room. If you add a second B1 (without compensating) your acoustical level at 100 Hz would go up to 96 dB (because you double the acoustic volume for 3 dB and you double the total electrical power for another 3 dB). That would sound too "bassy". To compensate the PS1 drops the electrical output by 6dB so that the acoustic output goes back to 90 dB where it belongs in the first place.
The only difference between one and two B1s is in the maximum acoustic level you can get at 100 Hz. Lets say you crank the systems playing bass guitar. At a certain volume level (say 105 dB) the B1 is out of steam. The limiter kicks in and would prevent it from getting damaged or sounding bad. But the L1s still can go louder (since there isn't much high frequency energy in the bass guitar signal). Now if you add the second B1, you can still keep increasing the low frequencies to about 111 dB. Up to 105 dB output the 1 and 2 B1 configurations would sound the same. Only at high levels there will be a significant difference.
It not only depends on how loud you want to play but also on your input signal. If you are a singer, you really don't need a second B1, because the bulk of the energy is in the mid and high frequencies and the L1 will reach its way before a single B1 is maxed out.
I hope that all makes sense to you. If not, please post back and I'll try to explain it differently.

Chuck,
Nothing in the world is perfect, so 1 B1 and 2 B1s will never sound "exactly" the same although it should be pretty close. There will always be some minor differences depending on the room and where you are standing. Sometimes is just that the second B1 (stacked on the first) is a little closer to your ears and feels louder at the playing position. There is also more headroom, i.e. at any given output level 2 B1s don't have to work as hard as a single B1.

Hope that helps

Hilmar

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