Film-Tech Forum ARCHIVE: Use QSC LF-4215 as Sub

This is topic Use QSC LF-4215 as Sub in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Alban Birch (Member # 4121) on 01-26-2013, 06:20 AM:

Hi
Something went terribly wrong and now I'm stuck with 3 SC-443s and only 1 SB-5218. what we needed was 3 SC-423s and 2 SB-5218s. So the mainchannels are oversized and the Sub undersized.
What do you guys think of using the 3 LF-4215s as subs together with the SB-5218, which will leave me with SC-423Hs as mainchannel.
Amps are all DCA
3 1622
1 2422
1 1824
Surrounds are only 4 SR-26s
The room shall 5.1 bi-amped

Thanks

Posted by Steve Guttag (Member # 268) on 01-26-2013, 07:24 AM:

Without knowing the room, it is impossible to say what the result will be.

Combining the LF-4215s with the SB-5218 is probably not wise. The LF-4215 does not have the bottom end. The cabinets were not tuned for that. You could possibly tune them separately to extend their response but you will likely need a lot of amplifier and not have a very efficient system.

If you just combine them...you will have an exaggerated mid-bass with very little true bottom end.

Look at the response of the LF-4215

Now compare it to the SB-5218

Now super-impose the two but allow for that the LF-4215 is going to be louder given the same power.

Posted by Marco Giustini (Member # 4544) on 01-26-2013, 08:44 AM:

Wouldn't be easier just to buy the missing sub?

Posted by Steve Guttag (Member # 268) on 01-26-2013, 10:28 AM:

With just 4 surrounds...the room better be tiny anyway! So who is to say that they need more than the one double-18 sub?

Posted by Alban Birch (Member # 4121) on 01-26-2013, 12:55 PM:

I have the possibility to EQ 2 different Subchannels thanks to an AP20
No discussion about the why not buy or exchange against the LFs, the missing Sub please. Not doable.
Sorry 4 SR-26 per side.
Speced another 4 SRs for the back that's why we habe the 1824 instead of a 1222

Posted by Marco Giustini (Member # 4544) on 01-26-2013, 01:35 PM:

I wouldn't ruin the front channels removing the LF. Live with one sub and wait till you have some money for the second one.

You still did not mention the lenght of the room, one double-sub may be acceptable for the time being.

Posted by Bajsic Bojan (Member # 4928) on 01-26-2013, 02:03 PM:

@Marco

He will not remove the LF completely from the screen channels, but will use the main speakers appropriate for the room (and the amplifiers). The 443s are the same as the desired 423, but with an additional box of 15" drivers (the LF 4215 box).

He wants to use these 3 "now-spare" boxes of LF drivers to serve as a subwoofer.

That might not be a good idea as Steve mentioned.

Are you sure you cannot trade back the 4215s for one subwoofer? Even at no cost to the provider? I mean, the SB costs the same as one LF4215 list. If really desperate, trade in for two?

Posted by Marco Giustini (Member # 4544) on 01-26-2013, 03:04 PM:

Got it, thanks!

Is he sure that a room that needs 4x18" wouldn't appreciate 4x15" as well? [Smile]

Anyway what Bajsic says is correct: trade the extra LF back and buy the sub. If the dealer is not willing to do it, trade them yourself as brand new!

Posted by Alban Birch (Member # 4121) on 01-27-2013, 07:05 AM:

2x18" and 6x15" to be precise

Posted by Marco Giustini (Member # 4544) on 01-27-2013, 08:07 AM:

SC443 have 4x15" cones and SB5218 have 2x18" each. You claim you'd need 2xSB5218 - hence the 4x18". And I was wondering whether your room - the dimentions of which are still unknown - would appreciate 4x15" (SC443) rather than 2x15" (SB423) - per channel.

Am I missing something here?