2 octaves will be below E140's Fs
Baron030's chart really demonstrates the limitations of small boxes. Additionally, you need to know that 2 octaves down from a guitar's E string is about 20 hz. Its going to be off the map, meaning you won't hear it. E 140's have an Fs of 32 hz. http://www.jblproservice.com/pdf/thi...parameters.pdf You would really need the low filter to protect the transducer.
A small box will also impact the E and A string fundamentals. The charts show -3 db or worse until the mid 100's. You probably would have to equalize the highs down and lows up to make it work. You could get "icepick" highs otherwise.
I think you mentioned earlier, that you are overdriving the amps. It will have a larger impact as the frequency drops.
Quote:
Originally Posted by
Baron030
Hi
Here is chart that shows why you can’t change the laws of physics. Pictured are 3 different enclosure sizes and they are all tuned to the same 40 Hz. As you can see the smaller the box the greater the roll off, so there is no way you are going to get really deep bass out of a small box using an E140 driver. It’s all about compromises between enclosure size and depth of bass. Since, you are using a device that can shift frequencies down 1 or 2 octaves. You might run into an issue with cone over excursion. Pictured below is a cone excursion plot with and without a sub-sonic filter. What happens at frequencies below the port tuning frequency is that the air loading on the cone to drops dramatically. This causes the cone to flop back and forth wildly without really generating a lot of sound. Oh, it may look impressive to seeing the cone flopping in and out, but you are not going to hear it. Here is a link to a sub-sonic filter that could be built to protect your drivers:
http://sound.westhost.com/project99.htm Baron030:)
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E120's have higher sensitivity
Speaker design for guitar is really a personal matter, so there's no right or wrong answer. If you get the sound you want, its right. If this were sound reinforcement or reproduction you would likely seek a flatter, uncolored response.
Having said that, the low end in the proposed system will be less than it could be. Baron030 already pointed out the the output drop below the mid 100 hz, but there's also a difference in sensitivity between E140's (100db) and E120's (103 db). http://www.jblpro.com/pub/components/eseries.pdf You will have to think about the difference in volume of what's coming out of the E120's and the frequencies rolled off by the E140 cabinet. If you play harmonics on the G B and E strings on the seventh fret or above, those tones are going to cut through the mix. The crossover point will make a difference as to where the difference in volume occurs, but doesn't necessarily solve the problem.
Again, whether this is good or bad, isn't decided on paper. Its up to you and your audience.
You could add attenuation to the crossover to give it flexibility.
Quote:
Originally Posted by
parker_knoll
I'm using E120s crossover over for the mids and highs, so that should avoid the icepick.
It looks like the speaker itself is roughly 6 litres volume, less when front mounted. if i go for a box with internal dimensions of 60cm x 50cm x 40cm that gives me 120 litres, which, less the speaker, delivers pretty much 4 cubic feet. I think i can work that, and it doesn't seem overly small. it works with Baron's graphs. would you define that as a small box?
As i said i have the low filter so that's all good.