Possible to use MarkBass CMD 121p as a sub for PA?

roccobladr · #1 09-13-2011, 02:05 PM

I wasn't sure which section this would fit into, but I have a questions about my MarkBass CMD 121p combo. My band will play smaller clubs/private parties sometimes where there is no house sound. We usually use just 2 speakers, but with the increasing amount of samples we use, we are finding a sub to be necessary.

I was wondering if it is possible/would it sound ok if we were to use my bass amp as a sub? I was thinking maybe using the balanced line in or the 1/4" and having the PA send the signal out as a sub or aux (I am not really familiar with this stuff). And I would just have my bass plugged in through either the PA or the 1/4" if it is possible to use the balanced line in and the 1/4 " at the same time.

Anyone do this before or know if its possible?

**lowfreqgeek** · #2 09-13-2011, 02:19 PM

Sure, you can hook it up to use as a "sub", but good luck getting any "sub bass" out of that combo. I owned one for a few days and couldn't get it to play nice with my deep, thumpy basses (like my Rick Turner Electroline with a pickup/preamp that will put out significant signal as low as 2Hz).

You won't really be using it as a sub because you won't be using a crossover with it, so it will just be another speaker. Also, if your bass is active, you might be able to get away with plugging into a 1/4" line input, but you may not have nearly enough gain - and it certainly won't be ideal if your bass is passive. I've done it before when using an active bass with a lot of output (G&L w/EMG preamp).

If you really need a sub, I'd suggest a powered unit that's designed to be a sub, crossover and all... QSC makes some nice stuff, and I believe they have a powered sub.

roccobladr · #3 09-13-2011, 02:36 PM

Thanks for the info...I know it wouldnt be the ideal solution, but for a quick fix it seems ok and I guess better than no sub at all?

I have a Music Man SR5 so it is active. I was thinking about getting a bigger cab so maybe it might pump out some more low end if I had that? (would be an excuse to get the band to help me pay for it

)

will33 · #4 09-13-2011, 02:57 PM

It'd be a great way to destroy it if that's what you're looking to do. No way a bass combo amp can hang with true subwoofer stuff, just not designed for it. If you don't need a lot of output, just fill in the deep lows, you could get away with a compact sub or single sub. That could be something like a lowpassed decent quality 15 or 212 using good drivers. Meaning good low frequency drivers, not something made to sound good with bass guitar, at least not without the use of a mid driver.

I'm in a similair position as you, at least until I get my T39's built. I use one of these. Dayton Audio PA460-8 18" Pro Woofer in 5cu.ft. tuned 40-42hz. That gives it a little bump in output around 60-80hz. It gets the job done indoors where you can take advantage of a boundry or 2. Outdoors, not so much although it still adds a little oomph to the kick and bass up close for the dancers.

I just kinda stumbled into that thing, didn't do much designing. I had the box mostly built as a different bass cab that didn't use an 18, then scrapped the idea. Several months later a friend of mine gave me that driver. He'd gotten it in trade from someone who couldn't pay for some work he did or something. Sat on his shelf for a long time, had no use for it, gave it to me knowing I'm into building speakers etc. Sooo, I had a box with no baffle and a loose speaker. Modeled it, put the 2 together and whadda ya know, it's "ok".

If you don't need huge output, you could look into smallish powered subs. They're fairly spendy but also eliminate the need for a crossover and another poweramp. Some have a crossover built in as well as the amp with outs to send to your tops.

billfitzmaurice · #5 09-13-2011, 03:10 PM

Quote:

Originally Posted by roccobladr

I guess better than no sub at all?

Not necessarily. Most better PA tops go as low as electric bass cabs anyway. Real subs go at least an octave lower than most bass cabs.

roccobladr · #6 09-13-2011, 03:10 PM

Well I don't wanna blow out my amp! haha We just need something that will provide a little more low end. A 700$ paying gig is not exactly worth a whole huge PA setup to me. Like I said, 85% of the time, we will be playing a place that has its own house sound. We just need something to "get by" for these smaller gigs. Is there any type of cab/sub that could be used as a cab when needed for just my own rig, and then be used as a sub for the PA when necessary?

will33 · #7 09-13-2011, 04:03 PM

Some decent quality bass cabs with honest f3's down in the lower 50's could work in a pinch for smallish gigs if you don't send them too much power, just enough to fill in the lows, not knock you down subs or anything. That's still just the speaker, a crossover and separate poweramp are still required. If you do such a thing, run your bass through the pa as well and use a small rig for stage volume. A bass rig trying to fill the house with bass guitar and a sub trying to fill the house with kickdrum/samples etc. will fight each other, cancel each other out and do more harm than good. Basically, once a sub is required, the entire band should be in the pa.

will33 · #8 09-13-2011, 04:24 PM

If you decide to go this route, from a social perspective, I'd advise doing what you need to do to get the required equipment yourself and own it. That whole band members pitching in on communally owned gear, everybody having some percent share thing........it's kinda like communism, usually ends in disaster.

Before commiting to it, it may be a smart idea to rent a powered sub for a gig or two and just consider the money an entry fee or learning experience. Find out what you need to do what you need done before committing to the whole shebang.

roccobladr · #9 09-13-2011, 05:15 PM

Quote:

Originally Posted by will33

Some decent quality bass cabs with honest f3's down in the lower 50's could work in a pinch for smallish gigs if you don't send them too much power, just enough to fill in the lows, not knock you down subs or anything. That's still just the speaker, a crossover and separate poweramp are still required. If you do such a thing, run your bass through the pa as well and use a small rig for stage volume. A bass rig trying to fill the house with bass guitar and a sub trying to fill the house with kickdrum/samples etc. will fight each other, cancel each other out and do more harm than good. Basically, once a sub is required, the entire band should be in the pa.

So if we do go the sub route, would I technically even need to bring an amp? Maybe only to use as a monitor and have it go out through the PA?

will33 · #10 09-13-2011, 06:31 PM

Quote:

Originally Posted by roccobladr

So if we do go the sub route, would I technically even need to bring an amp? Maybe only to use as a monitor and have it go out through the PA?

The house would be hearing you from the PA, you'd need enough amp for you and the guys in your band to hear you well on stage. This could be your little combo setup like a sidefill facing across the band instead of facing the crowd like you see all the time. Most, if not all, vocal monitor type wedges suck for bass, hence the need for a real bass amp, just not a very big one.