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say I currently have two active cabinets, with 15" woofers on them.

Would adding an additional 15" subwoofer to the setup improve the lows, or just produce more of the same volume?

How about 12" subwoofer?

The question is: what is the perceptible difference beetween the woofer in full frequency cabinet and subwoofer?

Thanks!

  • Please keep in mind that systems that have a sub woofer also have a special channel to power it. I believe these are generally active dedicated circuits vs. a passive crossover found in most 3 way cabinets. – filzilla Nov 19 '13 at 20:07
  • I understand that. However, my question was more like this: if the current 15" speaker doesnt provide much "pressure" (you know feeling the bass in your belly), would same size subwoofer add that? – mrQQ Nov 22 '13 at 13:13
  • that's a fair question. I think one would need to compare the transfer curve of the amp output vs. the response of each subwoofer to qualify. – filzilla Jan 8 '14 at 17:47
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The size of the driver is just one specification that you need to consider. Power handling, voicing, and crossover type will affect the performance.

As an example, I have a pair of first generation JBL Eon PA speakers that use fifteen inch drivers. I also have a JBL Prosumer ten inch powered subwoofer. Neither product could be called esoteric, or super high performance. The bass produced by the Eons when pushed is really lacking. The little ten inch sub on the other hand can make the house shake to where you would think Godzilla was stomping on the roof..

So to answer your question, Yes... a dedicated subwoofer will probably generate more bass energy, than a set of stereo speakers. This will be especially true if the stereo speakers utilize a passive crossover. This doesn't mean you will achieve better overall sound. There will undoubtedly be an overlap of frequencies between the full range speakers and the sub which will tend to muddy up the lows. A proper Sub/Satellite system should be designed to work together.

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The cone size is only one variable determining the lowest frequency to be produced by a speaker (read more here). As such, a 15'' sub is likely to output lower frequencies than one on a multiway speaker.

But the only way to know for sure is by looking at the frequency response of each device.

  • How do you figure the sub will output lower frequencies than same size driver on a multiway speaker? – mrQQ Nov 30 '13 at 18:16
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    The only way to know for sure is to look at the frequency response specification of each speaker. If it is branded as a 'sub' - it should, but may not be. – Izhaki Dec 1 '13 at 20:09
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Subwoofers usually have comparatively small air volume for their output power, implying that they work with resonance to some degree. Which implies that their impulse response has characteristics of its own and a somewhat sluggy onset and what you get to hear resembles a bit a virtual bass drum triggered by the real bass drum.

Large-scale(!) woofers tend to reproduce rather than produce a bass response. Whether or not you consider either desirable is your own musical taste. You would not want the same action a solid subwoofer/shaker produces in your headphones and popping your tympani.

With regard to an accurate representation of the electrical signal, large woofers (with large volume behind them) tend to deliver more accuracy than an subwoofer. This is only partly seen in the frequency response: you need to look at waterfall diagrams to figure that out.

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Something else to consider is your coverage area. If you have a way on your active cabinets or mixer (or a setting passing through woofer) to high pass and filter out some low bass, you are recovering amplifier power to dedicate to low-mids through highs.

In this way you can produce a higher dB max SPL in this range covering a larger space once the woofer takes some of the heaving lifting work off of the other cabinet's amps. Even if you maintain the same SPL level, your system will have more overhead and can play with lower distortion THD. This is fairly obvious in my home setup with 8" woofer bookshelves and a 12" woofer. When I turn the woofer off and send full range to the speakers, I am spreading available amp output across a broader frequency. The same principles apply to my PA pro level gear. This all works because every octave decrease towards the low end requires dramatically higher amplifier power.

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