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In Reply to: RE: High efficiency + sealed cabinet? posted by Paul Joppa on March 25, 2014 at 18:04:47
This may be a fundamental mistake I have had for all these years. I thought the AR guy developed sealed designs to get the air to act as a spring and needed only smaller cabinets. So the AR speakers were all small and the bass went down deep but not efficient. You have stated that the sealed cabinets should be much bigger.Have I totally misunderstood the concepts? Thanks.
Cheers
Bill
Follow Ups:
There are several variables playing against each other, so it's really hard to make sense of any simple rule such as the ones I posted above. I intended them as examples rather than rules but that's really too much subtlety for a forum post - I apologize if I've sowed unnecessary confusion.Edgar Vilchur was the AR guy. In order to make the box serve spring duties, it is necessary to reduce the suspension stiffness or increase the box air stillness so that the box air stiffness dominates. There are limits to how floppy a suspension can be and still keep the voice coil well centered in the gap. So another way to do that is to use a smaller box to increase the box air stiffness. But then the resonance, which is the low frequency cutoff, becomes high - no deep bass. To get deeper bass, you have then to make the cone mass greater. The greater cone mass is harder to move, so the efficiency goes down. These are qualitative remarks, but djk has distilled the mathematics to put numbers on the effect.
edit: I'll leave the following paragraph, but note that it's incorrect - see the post by djk below for the correct information
> > > "Vilchur originally made a pretty efficient compromise - I don't remember the numbers but the AR-1 must have been around 94dB in a 3 cubic foot box with a ~50Hz resonance. But just at that time, solid state amps were making high power affordable, so smaller speakers with deeper bass and much lower efficiency became the cost-effective standard. Efficient speaker well matched to huge sealed boxes do not make cost-effective speaker systems, which is why it's hard to find suitable drivers on the market." < < <
Edits: 03/28/14
"Efficient speaker well matched to huge sealed boxes do not make cost-effective speaker systems, which is why it's hard to find suitable drivers on the market."
"To get deeper bass, you have then to make the cone mass greater."
The DIY-er can try this too.
I've never rigorously experimented with adding mass to a speaker's cone, but have been tempted, to get an almost suitable driver over the line.
AR-1, 25" x 14" x 11" made of 3/4" stock, about 1.615 cu ft gross.While 92dB/2.83V, they're 4Ω, so they are actually 89dB/1W/1M.
Edits: 03/28/14 03/28/14
could a cheap Visaton BG20 be used to make a knockoff? - wonder how the ~1K crossover sounded? - are there suitable modern woofers that won't rot?
Karlson Evangelist
Thanks for the correction, I was way off. I do remember the WE755 "tweeter" though!
Efficiency and size are directly related.
For any given cut-off frequency the box size will have to double for each 3dB higher efficiency.
2 cu ft 30hz = 84dB
4 cu ft 30hz = 87dB
8 cu ft 30hz = 90dB
16 cu ft 30hz = 93dB
32 cu ft 30hz = 96dB
The multiple drivers will also need to be close to each other to fully couple.
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