How can I check LIMP measurements?

[duanebro]

I bought several drivers at InDIYana Saturday. I tried to use limp to measure T/S specs. But the results seem off.
I tried a RS-150S-8:
measured qts=.64 (spec .46)
measured fs~64 (spec 54)

I was wondering if there is any way to check Limp and my jig? The jig is just a 1/8" head phone plug and a 22ohm resistor.

[jimangie1973]

Re: How can I check LIMP measurements?

I bought several drivers at InDIYana Saturday. I tried to use limp to measure T/S specs. But the results seem off.
I tried a RS-150S-8:
measured qts=.64 (spec .46)
measured fs~64 (spec 54)

I was wondering if there is any way to check Limp and my jig? The jig is just a 1/8" head phone plug and a 22ohm resistor.

Are you manually calculating the T/S parameters Fs and Qms/Qes/Qts from the impedance curve, or are you using some software tool which inputs the impedance curve? I'm not sure how you could mess up Fs, since it's just the peak. If you have the wrong value for the driver Re, or have the wrong value for the series resistor (22 Ohm in your case) in LIMP, the Q values calculated would be off.

If LIMP was somehow misinterpreting the sampling rate of the A/D, then Fs would be off.

Also, the driver needs to be free of any objects within 2 feet or so. I place my drivers on top of a guitar stand for the test.

Jim

[Jeff B.]

Re: How can I check LIMP measurements?

I bought several drivers at InDIYana Saturday. I tried to use limp to measure T/S specs. But the results seem off.
I tried a RS-150S-8:
measured qts=.64 (spec .46)
measured fs~64 (spec 54)

I was wondering if there is any way to check Limp and my jig? The jig is just a 1/8" head phone plug and a 22ohm resistor.

Actually Duane, those numbers do not sound that far off at all from drivers I have measured. I would be inclined to believe they are correct.

[duanebro]

Re: How can I check LIMP measurements?

Limp calculates the specs from the curve. I am using onboard sound on my laptop, so that could be an issue. My resistor value is correct. But could a different value be better?

[duanebro]

Re: How can I check LIMP measurements?

Actually Duane, those numbers do not sound that far off at all from drivers I have measured. I would be inclined to believe they are correct.

I was wanting to use these in a small 2 way. With a q that high it would seem like sealed would be better. Then I would need a sub or three way. What was your experience with them(how did you use them)? I can't do much more at this point because the power is off.

[rone]

Re: How can I check LIMP measurements?

I was wondering if there is any way to check Limp and my jig? The jig is just a 1/8" head phone plug and a 22ohm resistor.

You could measure a couple resistors to confirm function.

You could also mock up a simulated loudspeaker load (resistor and inductor in series, in series with a parallel combination of resistor, inductor, capacitor) and see what parameters it gets you.

[Jeff B.]

Re: How can I check LIMP measurements?

I was wanting to use these in a small 2 way. With a q that high it would seem like sealed would be better. Then I would need a sub or three way. What was your experience with them(how did you use them)? I can't do much more at this point because the power is off.

I used them in my Dreydel:

http://s109.photobucket.com/albums/n70/jeffbagby/Dreydels/

[PWR RYD]

Re: How can I check LIMP measurements?

I used a pair of RS150S-8's in my latest build (loosely based on Jeff's Dreydels). I measured them with my WT3 and they measured very similar to your results. IIRC Fs ~ 59 and Qts ~ .62

Mine are in a 0.3 cubic foot enclosures tuned to 60 Hz with a 2" diameter port. My wife and I are both surprised by how much bass these little buggers put out.

Anyway, I don't think your measurement setup is necessarily off.

[jmb]

Re: How can I check LIMP measurements?

I agree with the others. These specs seem reasonable. The FS may drop a little with break in but the other specs will likely change such that your enclosure calculations will not be much different than without break in. Manufacturer data is often off, which is why we measure.

LIMP can calculate Resistance, Impedance, or Capacitance. Why not just test know values to be certain that your set up is correct, if you need reassurance. But like I said, my previous measurements of these drivers is also in the same ballpark.

Jay

[duanebro]

Re: How can I check LIMP measurements?

I used them in my Dreydel:
http://s109.photobucket.com/albums/n...agby/Dreydels/

Thank you Jeff. I would/will build those if I find a deal on the seas tweeters. (Anyone have some extras????)

I also tried one of the 12"s my friend bought. qts=.9 I thought that was way high. So I ran a sine wave through it at 20 Hz for a few minutes and tried again- .83 still very high. This is when I thought that something might be wrong with my measurement system. The re is 1.9ohm on this sub. I don't know if this could affect the results. But if this is the case I don't think I could do much with the subs.

[Jeff B.]

Re: How can I check LIMP measurements?

Thank you Jeff. I would/will build those if I find a deal on the seas tweeters. (Anyone have some extras????)

I also tried one of the 12"s my friend bought. qts=.9 I thought that was way high. So I ran a sine wave through it at 20 Hz for a few minutes and tried again- .83 still very high. This is when I thought that something might be wrong with my measurement system. The re is 1.9ohm on this sub. I don't know if this could affect the results. But if this is the case I don't think I could do much with the subs.

There's a version around somewhere using the RS28a of f tweeters too. I am sure I can round it up if you want to go down that path instead.
Jeff

[Pete Basel]

Re: How can I check LIMP measurements?

I was wanting to use these in a small 2 way. With a q that high it would seem like sealed would be better. Then I would need a sub or three way. What was your experience with them(how did you use them)? I can't do much more at this point because the power is off.

Are you saying that you simulated and found a vented alignment that you liked with
the factory specs? If so, I would keep the alignment as is and enter the specs that
you measured to see how far off the actual response is. Also, try comparing this
response to what you're able to do in a closed box, you might find that the misaligned
vented system is better.

You can add some felt or fiberglass right on the back of the driver to lower the effective
Qts. You might have to press it on tight but you should be able to measure a change.
Qts is dependent on Fs so it is likely that part of the error is due to Fs being off.

Be sure to do a calibrate if LIMP has the option, I don't use it so I'm not sure.

[duanebro]

Re: How can I check LIMP measurements?

Are you saying that you simulated and found a vented alignment that you liked with
the factory specs? If so, I would keep the alignment as is and enter the specs that
you measured to see how far off the actual response is. Also, try comparing this
response to what you're able to do in a closed box, you might find that the misaligned
vented system is better.

You can add some felt or fiberglass right on the back of the driver to lower the effective
Qts. You might have to press it on tight but you should be able to measure a change.
Qts is dependent on Fs so it is likely that part of the error is due to Fs being off.

Be sure to do a calibrate if LIMP has the option, I don't use it so I'm not sure.

As an update I measured several caps and inductors and they were spot on! I must agree with the measurement software.

Pete: I haven't even modeled them at all. I just found a great deal on these and so I picked them up. I have been wanting to try out the RS line for a long time but just never had the money. I might just hang onto them until I find a nice tweeter to mate them with.

I actually have a set of tweeters that could work. But I don't know what they are! LOL I went to measure them on limp and found that their impedance is totally flat. 3.2 ohms from 10-20000hz. I didn't try to see what Limp would do with it because it needs an impedance peak to see fs. This is really all I was looking for to see how low they could be crossed. (To try to match them up to a mid.) Flat impedance should make the xo easy though.

[Pete Basel]

Re: How can I check LIMP measurements?

Those tweeters probably use thick ferro fluid.

I'd tune to 45 Hz and it will behave more like a sealed system with much better displacement limited power handling in the 40s. How large of an enclosure did you have in mind?