Help interpreting speaker data

[Terry McGee]

I'm thinking of building some cheap bookshelf-style speakers for above the test bench and was attracted to some low-price ($30) 5" woofer/midrange devices. But, as a newbie to enclosure design, I'm having difficulty interpreting the data provided on-line. Most of the parameters are clearly stated:

Specifications
• Nominal impedance: 8 ohms
• Power nominal: 50WRMS
• Frequency response: 70Hz - 7kHz
• Sensitivity: 88dB (1W@1m)
• Qms: 1.404
• Qes:0.717
• Qts: 0.474
• Fs: 67.63Hz

The missing ingredient, Vas, is given at the bottom of the Impedance vs Freq graph as "Vas=7.266m M". See:

http://www.jaycar.com.au/products_up...0parameter.pdf

Can someone familiar with similarly-sized drivers suggest what unit of measurement must be intended here? Being a Volume, I'd be expecting Litres, Cubic Metres or something similar. But what's an "m M"?

They also give the dimensions according to some convention I'm not familiar with:

Dimensions:
• A= 145
• B= 136
• C= 120
• D= 56

Would I be right in assuming that:

• A= 145 is outside diameter of basket
• B= 136 is diameter of the circle of mounting holes
• C= 120 is diameter of cone (5" = ~125mm)
• D= 56 is front-to-back (ie depth)?

Terry

[planet10]

Some of the units are strange on the graph. For that size driver Vas is likely 7-some litre. SOmewhere they will have a key to ABCD, your interpretation is likely correct except that C is likely the cut-piy diameter.

dave

[Terry McGee]

Great, thanks Dave. I'll plug that in and see if it makes sense.

You had me puzzled with "the cut-piy diameter". Oooh, I thought, another loudspeaker technical expression I'm unfamiliar with. But, checking the keyboard, I note that the letters "o.u.t." are all one to the left of the letters "p.i.y.". (Pesky, finding those dashes, isn't it!)

So, I'm going to proceed on the basis that 120mm is the cut-out diameter. It certainly makes more sense than my guess!

Terry

[planet10]

Originally Posted by Terry McGee

You had me puzzled with "the cut-piy diameter". Oooh, I thought, another loudspeaker technical expression I'm unfamiliar with. But, checking the keyboard, I note that the letters "o.u.t." are all one to the left of the letters "p.i.y.". (Pesky, finding those dashes, isn't it!)

Very perceptive of you, and exactly what happened... i took grade 11 math insteadof grade 10 typing, and when on the laptop in low light my already poor typing becomes worse.

dave

[taj]

I never would have figured that out. I'd be torturing my poor already-abused brain on p.i.y. acronyms for the next month.

..Todd

[Terry McGee]

Heh heh. The only good thing about getting old is you get very, very sneaky....

Terry

[Terry McGee]

Hmmm. Proceeding on the basis of the dimensions given, I get a 12.37 litre box, a port diameter of 25mm (1") and a port length of 1.61cm, suspiciously close to the thickness of the wood I specified, 16mm (5/8"). I guess that's just telling me to drill a 25mm (1") hole in the box? Or should I get suspicious?

Terry

[planet10]

Originally Posted by Terry McGee

Hmmm. Proceeding on the basis of the dimensions given, I get a 12.37 litre box, a port diameter of 25mm (1") and a port length of 1.61cm, suspiciously close to the thickness of the wood I specified, 16mm (5/8"). I guess that's just telling me to drill a 25mm (1") hole in the box? Or should I get suspicious?

Terry,

That is an OK looking sim.

dave

[Terry McGee]

Thanks Dave

I'll go chop down a tree in anticipation...

Terry