CrossOver Points

Been getting a lot of questions. Can anyone help?

I believe there are two crossover points: One between the top and bottom tower, and one between the bottom tower and the B1. They are not listed on anything I've found.
Original Post
Cap, I think you may be referring to the two different frequency stats. The L1 by itself, with no subs connected, is rated to run down to 110Hz. Like Chuck said, if you have something plugged into Bass Amp 3 Out or Bass Line Out, the PS1 senses that and kicks in the 180 Hz crossover - so the L1's only perform down to 180 at that point, and the B1's take it from there.
Pardon this real point of ignorance but I was told the Lis when used in conjunction with the B1s are tri-amped. I was also told that there are 250w going to the top radiator, 250w going to the lower radiator and 250w going to the subs.

Someone...please...give me straight scoop on this...please. Without violating any confidentiality agreements, there has to be some usable physical numbers/specs. Something concrete. Something usable.
Cap,

'Sorry to have been unclear on this. We're really not trying to be evasive. Perhaps you could tell us what you want to do with the info, so we could give you something more usable...

Meanwhile, I'll take another stab:

There are indeed 3 amps available, but it's not a triamped system, in the '3 separate frequency bands' sense of the term. With nothing connected to Bass Amp 3 Out, Amp 3 sits idle. With the L1 connected to the PS1, Amp 1 always goes to one half of the L1 and Amp 2 goes to the other half. The important thing to note is that Amps 1 & 2 are both always getting the same signal and outputting it identically to both halves (all 24 drivers) of the L1, with or without bass (B1s, etc.) connected. With no bass connected, the L1 gets 110Hz on up. With bass connected, it's 180Hz on up...

Please let us know if this is still at all unclear, so we might get you all of the info that you need...
Hi Cap - There's that pesky English language getting in the way again. It's confusing terminology. In the world of live sound, the terms "biamped" and "triamped" refer to whether you have a two way or a three way crossover, dividing the signal into two or three chunks of frequencies...it really has nothing to do with how many power amps each freuency range gets. In other words, you can have a 2 way crossover, and take the low freq output and send it to 10 power amps...It's still a biamped system..the signal divided into 2 frequency ranges.

So when someone told you it was "triamped", what they really meant was that it had 3 power amps, but it's a biamped system when used with a B1.
Oh, man. I'm embarassed. Either I assumed incorrectly (99%) or heard incorrectly (1%) that the system was triamped and capable of delivering 750 watts in a double bass system set. (wash cloth please, to remove egg on face).

Okay, it's biamped, 250 watts potential to 24 radiator drivers, 250 watts potential to the subs, and 250 watts dangling if nothing else attached. How am I doing?

With subs attached, the crossover delivers what frequency range to the subs? What frequency range to the radiators?

If using the system barefoot (2 subs, nothing else external, what can be added to grab the other unused 250 watts? Can the dangling 250 watts be bridged into the radiators or subs?

I'm getting some realistic and tough questions asked of me and I'd appreciate some like minded answers...please!!!!!!!!!1
Hi Cap,

How about this: Setting aside what you know or have read for a minute. Think of it this way:


The L1 (Yellow highlight) is a single loudspeaker with 24 drivers supplied by 500 watts.

The pair of B1s (Purple highlight) is a single bass loudspeaker with 4 drivers supplied by 250 watts.

That's 750 watts in total.
edit ... The number of drivers in the enclosures is not actually relevant in this discussion. It would be for discussions about speaker construction.


Now for the breakdown.


B1s
If you break the pair of B1s in half, and use just one of them, it draws 125 watts.

If you don't use the B1s at all, the amp that is normally used to drive them is idle.


The L1 This is one loudspeaker that happens to break down into two pieces for travel.
This is driven by two separate amps, but this is not important because under normal circumstances both amps are driven identically. One drives the top half of the L1 and the other drives the bottom half. Because the L1 should always be operated as a single unit, what happens when you break it down isn't important.



How's that?
Hi Cap,

Now that I've finished with the pretty pictures (that work for some and not for others)... and at the risk of ruining whatever value they may have conveyed...

Let's drop the terms biamped, triamped, and sub from the vocabulary of any discussion of the systems. I'll show you what I mean below.

quote:
Originally posted by Cap:
Oh, man. I'm embarassed. Either I assumed incorrectly (99%) or heard incorrectly (1%) that the system was triamped and capable of delivering 750 watts in a double bass system set. (wash cloth please, to remove egg on face).


The System is capable of delivering 750 watts when used as a double bass system set.

quote:


Okay, it's biamped, 250 watts potential to 24 radiator drivers, 250 watts potential to the subs, and 250 watts dangling if nothing else attached. How am I doing?


The L1 loudspeaker can draw up to 500 watts.
A pair of B1s acting as a single loudspeaker can draw up to 250 watts.

I would try not to mention the number of drivers unless someone asks. It might be interesting to know, but it doesn't help someone to understand how these things perform. For that matter, knowing the number of amplifiers and watts isn't all that helpful either. These kinds of numbers are probably more useful when comparing things that are fundamentally similar. The Bose Systems seem to be in a class by themselves and at least today, I can't think of anything that is similar enough that comparisons by the numbers is actually informative.

Anyway, inquiring minds will want to know, so as a double bass system set, the L1 has 24 drivers and the two-B1-set has 4.

An example of comparisons of things that are fundamentally similar:
A pair of B1s can draw up to 250 watts.
A single B1 can draw up to 125 watts.
What the numbers cannot tell you is if a pair of B1s is twice as loud. (And that, is another discussion).

quote:


With subs attached, the crossover delivers what frequency range to the subs? What frequency range to the radiators?



When any connection is used to supply signal to a low-frequency output (B1 or Bass Line-Out), the crossover works like this:
Low frequency band-pass: 40-180 Hz (for the B1s or Bass Line-Out)
High frequency high-pass: 180 Hz and up (for the L1)

edit: added
If there is no connection for a low-frequecny output (B1 or Bass Line-Out) the crossover works like this:
High frequency high-pass: 110 Hz and up (for the L1)
(end edit)

I'd use the term bass unit instead of sub. The term sub may have a very specific meaning to some (e.g. A large enclosure for 12-18" drivers capable of producing 20-80 Hz at 120 dB +/- 5% THD, thus capable of reproducing sounds below the normal range of hearing) and be somewhat less meaningful to others (e.g. something I attach to the little speakers on my computer).

The B1s work within the range of normal human hearing, not sub-normal.

quote:


If using the system barefoot (2 subs, nothing else external, what can be added to grab the other unused 250 watts? Can the dangling 250 watts be bridged into the radiators or subs?



When using the System configured with two B1 bass units, all the amps in the PS1 power stand are being used.

Follow-up statement. The output that is available for the B1s (marked Amp 3 Out) is designed to work with the B1 bass unit. Connecting anything else to it is not recommended.

quote:


I'm getting some realistic and tough questions asked of me and I'd appreciate some like minded answers...please!!!!!!!!!1


Was that any help - or do we want to approach this from a different angle?
quote:
Originally posted by Cap:
If using the system barefoot (2 subs, nothing else external, what can be added to grab the other unused 250 watts? Can the dangling 250 watts be bridged into the radiators or subs?


Actually, "barefoot", it is 500w which are unused.

If using the PS/1 without the L1 inserted at all, then BOTH of those 250w amps are available to drive something else (note the AMP1 and AMP2 outputs next the AMP3/BASS output - Speakon connectors).

As noted previously, AMP 1 & AMP 2 deliver exactly the same signal (When the L1 is inserted, this is a high-pass down to 110 Hz if B1's are NOT plugged in to AMP 3; high-pass down to only 180 if the PS/1 senses that B1's [one or two] are plugged in to AMP 3). The AMP 3 the only one that provides a different output (which depends on whether it detects that B1's are attached or not).

[edit]: I suspect (see my next note) that all three amps actually detect that "B1" presence, and do the right EQ thing to drive 1 or 2 B1's.
quote:
Originally posted by ST:
B1s
If you break the pair of B1s in half, and use just one of them, it draws 125 watts.
If you don't use the B1s at all, the amp that is normally used to drive them is idle.


Minor correction: Remember that power amplifiers are rated as "watts into a particular impedance"; e.g.: 250w @ 4 ohms. As I recall an earlier posting on the 'techy' stuff of the PS/1, all 3 amps are really identical as far as power rating is concerned. The only differences are in what "signal" they are driven with.

Thus, that amp 3 is 250w @4 ohms. When you only have one B1 attached, it is not really "cutting back" to only 125w. It is just that the impedance (resistance of the attached speakers) is now 8 ohms, and way power is calculated & delivered is such that this same amp is now rated as 125w @ 8 ohms.

Nothing really new, here. This is how most modern power amps behave: when you halve the impedence (e.g.: go from 8 to 4 ohms), you double the "rated watts" ... within a useful range. Most amps will only deal with two or three variations in "load". That is why you can't plug in 4 B1's (which would be then a 2 ohm load) and get 500 watts out of AMP 3 (it detects the low output impedance and shuts itself down to prevent damage).

I hope this makes it clear why you can use the PS/1 -- without an L1 attached -- to drive 3 to 6 B1's. The amps are identical. They sense when 1 or 2 B1's are attached. They are all rated at 250w into 4 ohms.

Perhaps another way to think of the PS/1: It is not a tri-amp system. It is a triple amplifier; it contains 3 virtually identical amplifiers. It's just that it is normally used with two amps driving into each L1 segment and the 3rd driving any attached B1's (or other external bass speakers).

[edit]: I would guess that if you were to use two-wire Speakon connections from all 3 AMP outputs (without an L1 inserted), you would get the full-range identically from all. (I'm not sure about AMP 3, though.) ... subject to correct by the -at-Bose folks who *really* know.
Well hey....

Could you use just the lower half of the L1 inserted and then drive 4 b1s? (2 into the B1 out and 2 connected to the Amp 2 out?)

Owning 2 double base PAS systems already, could I invest in 4 more bass modules and lose the top half of my L1s occasionally? Might that produce more bass for my Jr. High cafeteria/stage dance gigs?
quote:
Originally posted by TheDJGuy:
... Could you use just the lower half of the L1 inserted and then drive 4 b1s? (2 into the B1 out and 2 connected to the Amp 2 out?)

Owning 2 double base PAS systems already, could I invest in 4 more bass modules and lose the top half of my L1s occasionally?...


Using half the L1's, I think you'd lose a lot of the clarity and dispersion advantages.

Rather than keeping the two system "symmetric" (that's conventional PA thinking, which I'm learning to avoid Big Grin ), how about just using one L1+2B1's on one PS/1 (i.e.: a 'double bass system), and then 6 B1's on the other PS/1 (i.e.: a bass-only system).

Put them both in the center of the "stage" (side by side) and stack the B1's in two stacks 4 high (alternatively, a row of 8 "on their sides" jammed together horizontally across the "stage", making a horizontal "bass column").

I'll bet you'll get enough high-end from the single L1 to satisfy the room.

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