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Help with some big ol' used DIY speakers

A good friend of mine, passionate about music but new to this hobby, is putting together a system on a dime, a nickel if he can help it. It's a fun project. He recently picked up a pair of whopper DIY, homemade speakers for free (craigslist). He rolled them into his office and this awesome picture tells the story:

https://imgur.com/z2lAvpy

Two questions. First: is there any way to look at those speakers and gauge the kind of amplification they'll need? The guy who built the speakers implied they were rated at 8 ohms and were quite efficient. He said he was using an old 90 watt receiver, and said that even 40-50 watts would be fine. (We're not talking class A here.) I don't think he knows the other specs, such as sensitivity, etc. Maybe it's because I have mini monitors that are underpowered at 200 Bryston watts, but I can't imagine driving those big boys for a house or lawn party with an old 50 watt receiver. I'm hoping my friend can try out a few different amps but that may not be possible. The question is: is there any way to look at those and guesstimate what he needs to drive them? Or, without knowing their sensitivity, is it really just trial and error? Keep in mind the ethos here: free or close to it. So while you can never have too much power, it's also much easier to find inexpensive used receivers or integrated amps at 50-100 watts. (Of course, the watts rating of a receiver or amp doesn't really tell us all that much, but it's likely the best guide as my friend looks around at used equipment.)

The second question is about the wiring. The speakers are in two cabinets, with the woofers below and the tweeters/midrange above. The man who made them simply runs speaker wire from the amp (receiver) to the base cabinet and then more wire from the terminals on the base cabinet to the terminals on the top cabinet. That makes sense, I guess, but without crossovers I assume that the full-range signal would be going to all the drivers. This might not be ideal for the quiet moments of a Chopin etude, but as long as the timing sounds okay, are there any issues with this? I've never done this kind of thing before. I can't imagine my friend would want to plunk down money for an outboard crossover, if that would even work, but maybe. Thoughts?

As you can tell, the goal here is to have some fun putting together a system for as little money as possible ... and to have all kinds of fun cranking tunes and throwing parties!
northman
larryi
4,108 posts
 
If your friend will be listening while seated at the desk, the problem with this setup is that he will not get the sound from all of the drivers to be well integrated at his position.  It might help to toe-in the drivers so that he is at least closer to being on-axis for all of the drivers.  

Given the small space, close proximity to the speakers, and supposedly high efficiency, he could actually go with amps that have considerably less output than 40-50 watts.  I personally would be looking for used low-powered tube gear, particularly something using 6L6, KT66, EL34, or EL84 output tubes.  Even single-ended triode amps are a possibility (300b, or 45, or 2a3 tube), although decent used ones do not seem to be that inexpensive.  If your friend is at all handy, perhaps a kit amp from the Japanese company Elekit would be nice, although not in the Craigslist kind of price range (but there is nothing wrong with a really good amp used with modest speakers).
russ69's avatar
russ69
3,536 posts
 
I would take the owners word on what amp power you might need. But no way of really knowing unless you measure it. 
russ69's avatar
russ69
3,536 posts
 
"...Anyone can tell just looking at them they will play plenty loud with 10 watts..."

I don't think you can say that. Sure, a large speaker with many drivers could be a way to achieve efficiency but no telling what is behind the grill cloth, what the speaker array is, or what crossover is used.  
millercarbon's avatar
millercarbon
12,531 posts
 

Of course not. Blanket statements like that never fly. Anyone refers to anyone who knows a little about speakers, how they work, the different designs, etc. Anyone like that looks at these, and it is instantly readily apparent. First, old paper cone drivers. These were all made back when modern ideas were still way out in the future. They are all pretty efficient. Then sheer cabinet size. Modern speakers are made for women. Women don’t want to see a speaker at all, designers know men are too whipped to buy anything that might turn a woman off, WAF etc etc, so now we have all these teeny tiny little horribly inefficient things. Big box equals big sound, period.

Finally, see that big gaping hole in the top? Anyone knows anything about speakers that big hole says something like folded horn, transmission line, whatever we don’t know exactly but any way you slice it winds up being high efficiency. Same with the big ported uppers.  

So you see it really is the case that anyone can see. Anyone who has a clue. Which would have remained pleasantly unsaid until you had to go and try and one-up me on it. Oh well. Live and learn?
larryi
4,108 posts
 
I too wondered about that big hole in the bass cabinet.  I could not tell if that is meant to be the opening of a back-loaded woofer set up (i.e., transmission line/quarter wave back-loaded horn), or the mouth of a compression midrange driver, or a handy shelf to stash weed and smoking paraphernalia.

Also, the top array looks so much like the back of an old Bose 901, with half the drivers removed (a dead giveaway on that would be a driver on the back of that array).  If it is a 901, but with different drivers, it may be quite efficient, if it is 901 drivers, it would not be that efficient.

In any case, even if it is not that efficient, in that room, I would expect 40 watts would be more than enough.  For any given price point, it is easier to make something that sounds good when you don't demand high power.  
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