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Noob questions for my first project


Neostead
(@neostead)
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Joined: 3 months ago
Posts: 2
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Aloha folks,
I'm excited to join the realm of DIY speakers and start off with my first project. However, aside from one very basic electrical engineering course (enough to understand frequency responses, crossovers and such things, but not much more), I have no practical experience. Thus, I hope to get some answers before starting my first project here!
My intention is to build some mid-scale full range PA-speakers that can serve any purpose from HiFi listening at home to outdoor parties for around 100 (or optimally more) people. Looking for appropriate build plans online, I found Toid's "Soundstage 15" available on this site. Since the plans include everything from casing to crossover layouts, I'm almost ready to dive right in! Before I do, I wanted to clear some questions I've been asking myself though:

1. Batteries - This question doesn't have anything to do with the Soundstage, but I've been wondering: Originally I wanted to build a battery powered active system to be mobile when using the speakers outside. However, I don't ssem to be able to find batteries that aren't either huge (>30kg), super expensive or have a small capacity. So how do manufacturers like "Soundboks" manage to get long 8 hours of playtime at more than 200 Watts out of a small battery pack? And more importantly, is it possible to buy the kind of batteries (and I assume some kind of volage converter) needed to build speakers suitable for medium sized outdoor events without a huge budget?

Now the more important stuff:

2. Loudness - I'm not really sure wether my impression of the "Soundstage 15" being able to go quite loud is correct. Would you assume they're capable enough to get >100 people dancing in an outside location? I've tried to get behind how a speaker's sensitivity and electric Power can translate to SPL, but since I only know the specs of the individual drivers used in this build, I'm not really sure how they work in combination with each other. I'm sorry to relate to the bad-sounding "Soundboks" again, but apparently they get 126dB SPL out of ~210 Watts of power, which to me sounds like an almost impossibly high speaker sensitivity, or is there something I'm missing? This again is closely linked to my last question:

3. Power - How should I power these speakers? The JBL SRX815 have a continuous RMS power of 800 Watts, which already sounds like a lot to me. The drivers used for the Soundstage build can go at 800 Watts (woofer) and 80 Watts (tweeter) RMS. Obviously the input power is somehow distributed through the crossover, but at which levels would I risk harming the speakers? (I guess especially the tweeter is at risk here)

I know these questions are beneath the most basic understanding of audio technology, but I guess everyone's gotta start somewhere.


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Chedwin
(@chedwin)
Eminent Member Registered
Joined: 5 months ago
Posts: 32
 

No shame at all in having basic questions whether starting out or even 10 years in, always better to ask than do it wrong and cause damage

First thing is to decide if you want hifi listening or PA grunt work speakers. No speaker, no matter how well designed can do both. PA speakers are very much max SPL even at the cost of sound quality at times with higher levels of harmonic distorion accepted as OK. This typically results in them not sounding particularly pleasant for hifi listening, compression drivers tend to be very agressive sounding up close.

Second to that I would suggest not attempting active PA speakers if you are not experienced building your own speakers. When your pushing the wattages needed to play loud enough for a crowd the voltage and current handling of the electronics need to be more robust than small bookshelf speakers. You cant really do this both cheaply and safely!

I would suggest building fully passive speakers powered with an affordable PA amp and if you want a mobile solution you can use a small portable generator to power the amp. Im not the right person to recommend a specific amplifier to power these

 

Loudness - I would say you are more than good enough for 100 people with 800W 15inch woofers, ive done plays in 150 seat studio theatre with a pair of 300W 12inch woofer speakers.

I would ignore soundboks as a comparison as they are doing unique and propriatory things to achieve their numbers, I would say they are a completely different category of speaker all together. I understand they are using highly efficient calss D amplification and some form of amplifier switching and dynamic power management to further imporve efficiency. This will have needed serious ammounts of R&D and is even beyond something I would attempt to replicate at this time

 

Power - as stated above im not the right person to suggest an amplifier in this price category but others on here are alot more informed on this

 

Josh Evans
- Professional Live Sound Engineer
- High End Commercial AV Install Technician


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Neostead
(@neostead)
New Member Registered
Joined: 3 months ago
Posts: 2
Topic starter  

@chedwin Thank's a lot for your insights! I feel like the Soundstage will fit my needs more than well, and for the few occasions I would use them for a crowd, a generator is probably the best call. Also, I guess I'll learn a lot more about the whole topic in the process, so I might as well just start with a completely laid out plan!


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123Toid
(@123toid)
Illustrious Member Admin
Joined: 4 years ago
Posts: 1719
 

@neostead 

There are a lot of good questions there.  I would probably nix the idea of using batteries.  Batteries typically run off 12 volts (obviously some more, some less).  But because of this, you are going to have to use a lot of amperage, which will cut down on run-time.  Some batteries even limit your amperage draw, which will cut down on your wattage, loudness, etc. Having said all this, batteries are typically not the way to go.  Most outdoor venues have somewhere to run long extension cords to.  So I would suggest investing in those instead.

As far as how loud they will go, you really shouldn't need any more that 200-250 watts RMS on the Soundstage 15's.  At 200watts in an anechoic chamber (which outside is about as close as you will get) will still play 108dB 10 feet away. And it isn't until 30ft away that you go under 100dB (99.5dB) Way louder than you probably should be playing them anyway. I say all this to say, they should get plenty loud enough for you. And there is nothing wrong with having an amplifier with more power on tap (550-600 watts) or even limiting the power if you want.

The most important thing with any PA speaker is to put a high pass on it. A 4th order high pass around 35hz would be perfect for this.  Most PA amplifiers with dsp on them, will easily be able to accommodate a setting like this. 

https://www.youtube.com/123toid


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