Scalable DIY PA system based on Econowaves and Bag End style DIY sub

[tag_]

I have an idea for a scalable DIY PA system that I would like some feedback on. It would start with Econowaves, in particular this variant: Econowave DSP

I want to use active crossovers for efficiency and using the MiniDSP to implement the crossovers adds the benefit of flexibility.

The idea is that for low volume applications, you could use the Econowave DSP as-is, then when more power is needed the crossovers could be changed to higher order and the 12" would be crossed over with a sub.

For even more power the Econowaves would be doubled and stacked, with the lower ones inverted (horn on bottom), the 12s in parallel and the lower horn not used. It this configuration by my estimation SPL output at max power for the mids would be about equivalent to the max SPL output of the compression driver.

The sub would be an Eminence Sigma 18 in a 3.3 cubic foot sealed cab, operated Bag End style below resonance with a DIY dual integrator based on this design

The sub crossover point would be 91.4 Hz based on the resonance frequency of the sub, 12 dB/octave so the 12s would be configured to have a -3dB point of 122 Hz.


Based on the driver specs I did this power/spl comparision I did.

D220Ti: 109 dB 2.83V/1m, 80W RMS max
equivalent to 640W 100 dB 1W/1M

Beta 12: 98 dB 1W/m 250W max
2 in parallel, 101 dB 1W/1m 500W max

Sigma 18: 99 dB 1W/1m, 650 W max

My big question is what are the power limits when you take into account the small sealed boxes and the low crossover point for the D220Ti? Any thoughts about the concept in general?

[Paul O]

Re: Scalable DIY PA system based on Econowaves and Bag End style DIY sub

My big question is what are the power limits when you take into account the small sealed boxes and the low crossover point for the D220Ti?

In a sealed box the Sigma is displacement limited to 200w and output SPL is pretty low for a PA sub over the desired pass band, in comparison in a ported box the driver will take another 100w before reaching xmax and produces more SPL between 20hz and 100hz with the most gain of about 8db at 50hz. Bottom line is a sealed box is pointless for PA applications unless it's attached to a large horn.

Now as for the low crossover point on the CD, at low input power levels(10-20w) I don't see it being a problem but once you need more output it'll start to get nasty. With DSP you have options of course it would be pretty easy to develop several processings for different power levels, but I'd be more inclined to simply build 1 that does away with the baffle step completely and EQs flat above 100hz to mate well with the sub, that will maximize sensitivity from the driver combo so then all you need is enough SPL from the sub/s to fill in the spectrum. That of course is another vote against using sealed subs, you're gonna want/need subs that are capable of at least 3db more output than the tops which with these drivers is gonna be a tall order, A side benefit of using this method is that with an underlapped sub/main crossover you may also eliminate the need for some or all low freq EQ boost on the tops.

[tag_]

Re: Scalable DIY PA system based on Econowaves and Bag End style DIY sub

I'd be more inclined to simply build 1 that does away with the baffle step completely and EQs flat above 100hz to mate well with the sub, that will maximize sensitivity from the driver combo so then all you need is enough SPL from the sub/s to fill in the spectrum.

Can you elaborate on this? I think this is what I want to do, are you saying to take the baffle step compensation out of the DSP?

[tag_]

Re: Scalable DIY PA system based on Econowaves and Bag End style DIY sub

My thought is that the max spl will be limited by the max spl of the compression driver because I can always add mids and subs but using multiple horns/waveguides is more complicated because of cancellations and such. I like the idea of econowaves because they also are good for non-pa applications. Weekend warriors could use them around the house, with individual band members owning sets, then combine them on the weekends and add subs to play small clubs.

[Paul O]

Re: Scalable DIY PA system based on Econowaves and Bag End style DIY sub

Can you elaborate on this? I think this is what I want to do, are you saying to take the baffle step compensation out of the DSP?

Yes eliminate the baffle step EQ... or maybe I should say go at it in a different way. In PA applications and especially when there is active DSP processing available it makes no sense to throw away 6db of sensitivity and potential SPL output over the whole audio spectrum to achieve flat response, when and where necessary add a small EQ boost instead.

[Paul O]

Re: Scalable DIY PA system based on Econowaves and Bag End style DIY sub

My thought is that the max spl will be limited by the max spl of the compression driver because I can always add mids and subs but using multiple horns/waveguides is more complicated because of cancellations and such.

I don't see how.. unprocessed they have an 8-10db advantage over the other drivers 1 on 1 and even if you doubled everything up you're still gonna need to turn them down. Subs will always be the limiting factor.

[wg_ski]

Re: Scalable DIY PA system based on Econowaves and Bag End style DIY sub

The missing piece of information here is that you don't NEED as much SPL at 2kHz as you do at 200. tag_ is assuming he does, which is incorrect. If you did, the compression drivers really would be the limiting factor.

[tag_]

Re: Scalable DIY PA system based on Econowaves and Bag End style DIY sub

you don't NEED as much SPL at 2kHz as you do at 200. tag_ is assuming he does, which is incorrect.

You mean because of the frequency content of the source material? If the target Max SPL vs. frequency curve isn't flat then what does it look like?

[mdocod]

Re: Scalable DIY PA system based on Econowaves and Bag End style DIY sub

Tag,

PA bass systems are a delicate balance of amplification and box gain. Some systems are designed to be more compact, and use more watts to overcome size, others use more box gain with less watts. Some use more watts AND more box gain. Reflex boxes, and more sophisticated bass horns and transmission lines offer more acoustic coupling with less drivers. Accomplishing the same same thing with a sealed system CAN be done, but is not practical from size/weight/portability/cost standpoint as the number of drivers required to achieve the same SPL would be substantially higher. In a sealed system, acoustic output and driver displacement are directly related.

A sounds reinforcement build with sealed subs would be either a large wall of inexpensive drivers, powered by reasonable levels of amplification, or a more practically sized wall of expensive high displacement drivers, powered by esoteric levels of amplification. A dedicated passband bass horn system can match the output of the sealed system with a smaller combined physical size, less amplification, and lower cost.

Regards,
Eric

[wg_ski]

Re: Scalable DIY PA system based on Econowaves and Bag End style DIY sub

You mean because of the frequency content of the source material? If the target Max SPL vs. frequency curve isn't flat then what does it look like?

Most source material simply has less total energy up high. Power/SPL requirements peak in the mid-bass, and exactly where is highly program dependent. But it always falls off with increasing frequency. 3 dB per octave is as good a rule of thumb as any.

But as average power requirements go down, peak requirements can be just as high. For this reason, it's good to have extra headroom for your HF drivers. You might use a 200W amp with a 40W horn driver, and set the limiters or compressors to give 40 watts average. I use a GX5 to drive 75 watt 2" horns.