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Thread: 118H specifications

  1. #1
    Senior Member duaneage's Avatar
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    118H specifications

    I took a pair of 118H drivers off KingJames' hands this week and ran tests on them with my Woofer Tester appliance. I was really surprised at the numbers I got


    FS 39Hz VAS 2.8Cu Ft Qts .9 Qes .97 Qms 6.6 Re 5.55

    These are averaged values between the two. It seems this woofer would not work at all in a small vented enclosure or even a sealed enclosure. WinISD asked for 14 cu ft for a sealed box and 45 cuft (!) for a vented one.

    Could it be these drivers were reconed at some time with the wrong kits? I checked my WT against a known driver and it looks to be spot on

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    118H specifications

    Post individual specs, not averaged specs.
    If you are using WT or WT2, post all the specs.

  3. #3
    Senior Member duaneage's Avatar
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    Thee things seem really tight. The cones have a number on each, 61976. I warmed them up with some program material and retested them. Could these be alnico drivers and could the magnets be weak

    I would like to use these drivers, they seem to have clear midrange performance.

    Here are the T/S for each driver

    Driver 1

    Fs 38.9 Hz
    Vas 4.29 Cu Ft
    Qts .85
    Qes .97
    Qms 6.6
    Re 5.55 ohms
    Le .75 mh
    eff 88.67 db 1w/1m
    Bl 7.2 Tesla/Meter
    Cm 714.472 microns/Newton
    Mm 25.42 Grams
    Rm .880 Ns/m (mechanical)
    Rm 42.36 ohms (electrical peak at FS)

    Driver 2
    FS 37.7
    Vas 4.19 Cu Ft (this came up a bit on a retest)
    Qts .85
    Qes .98
    Qms 6.6
    Re 5.55 ohms
    Le .72 Mh
    eff 89.85 db 1w/1m
    BL 5.92 Tesla/Meter
    Cm 670 n/M
    Mm 25.17 Grams
    Rm .923 Ns/M
    Rm 43.55 ohms


    I played them for an hour at moderate volume with around 15 watts driving them and the pair came out pretty close upon testing. I used 40 Grams of weight for the Delta Mass test for Vas. The Low BL factor and high Qts indicates (to me anyway) a weak magnet. the voice coils are identical in winding resistance and the weight of the cones are identical. The cones move freely and seem to be very compliant.

    Whenever you get a chance Giskard I would appreciate it.. No hurry right now.

  4. #4
    Member WTPRO's Avatar
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    Hello Duaneage

    I would also closely examine the resulting impedance curves to see if they deviate significantly from the T/S simulation. If they do, then you may have a secondary resonance in the test jig. Otherwise I would look into things like a blocked vented pole piece. Running the delta compliance test should also help. Other than this, here is a short list of things to look out for from our FAQ

    - Blocked VPP (tiny almost sealed/lossy box!)
    - Bouncing weights (lower the Idrive, or use clay)
    - Jig resonance (a better test jig)
    - Driver breakin (drive to Xmax for several hours)
    - Compliance -vs- drive level effects

    Some links...
    http://www.woofertester.com/wt2faq.html
    http://www.woofertester.com/compress.html

    A new version (1.04) has also been posted to www.woofertester.com.

    Best regards,
    Keith Larson

  5. #5
    Senior Member duaneage's Avatar
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    Thanks for the post, Keith

    I am using WT1. I want to upgrade to the WT2 as soon as I have a spare buck or two. I suspect the WT is not right since other drivers I am testing are also coming up with higher Qts than what I expect. I have a pari of brand new P206 6 inch woofers and they came out different.

    I am using clay for the test, I test the driver on a carpeted floor so it does not vibrate. I beat the driver pretty hard for about an hour with bass material and moved the cone a great deal. There are no vents for this driver through the magnet structure.

    I have a 1 cuft test box and I am going to test the driver "old school" with an impedance bridge and see if I get the same results. By all rights if I drop this driver on a 1 cuft sealed box the fcb should shoot way up. If it doesn't then I suspect I need a new woofer tester. I can still determine T/S by hand and see what I get.

    I like the convenience of the WT1, it is just too dated today. The new one allows import of data into apps and I like that.

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    Hi again

    Actually a soft and plush carpet can be rather misleading. It turns out that the compliance of the carpet is proportional to the surface area of the magnet that is in contact. This and the total mass of the driver can produce a resonance right where you dont want one. In my case I try to do my testing on the corner of a rather massive sub-woofer cabinet. Being stiff at the point of contact, any driver-to-box resonance will be quite high.

    In your case using clay can have another advantage. If you suspend the driver from an appropriate jig (or wire/rope setup) so the axis of motion is sideways, any secondary vibrations going up or down are more or less blocked.

    I saw someone here post a trick where they would put saw dust on the side of a cabinet and then run test tones to find vibrations. If you take this and apply it to your situation, if you drive the speaker with an apreciable level while it is in your jig you can often spot jig resonance problems.

    To give you an idea how much the entire structure can be pushed around simply hang the driver from a string and drive it modestly hard. You may be surprised to see just how much vibration you can feel in the total structure. When I push drivers real hard, it is not uncommon for them to literally start bouncing off the corner of my test cabinet. This all comes back to Sir Isaac's law that for every action there is an equal and opposite reaction. That is, to push the voice coil and cone, the magnet structure see's an opposite push. And, if you examine the weight being pushed around, though 25 grams may seem small compared to say 500 grams total weight, the ratio is nowhere close to zero. And, by the way, the WT2 is easily good enough to see this effect.

    Hope this helps
    Keith

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    Senior Member duaneage's Avatar
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    well tonighti am doing some testing by voltmeter and test box to see what I come up with for the drivers. I felt the frame while under test and it did not vibrate much. The drive levels are very low.

    I don't know what the published specs are for this driver according to JBL so I cannot say for certain what is going on. But considering they had this driver in a 1.5 cu vented box I don't think the numbers I got are right. I mean .85 Qts is really high for ANY JBL driver, let alone a 118H

    Drivers may be bad, you never know.

  8. #8
    Senior Member duaneage's Avatar
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    I tested a driver again with the impedance bridge method and here are the results.


    The Vas was calculated with a 1 cu ft test box. I placed the cutout for the driver hole into to box to compensate for the cutout and also placed a small wooden block to further compensate for the cone area. The calculated Vas on one driver was 4.09 cu ft, very close to the 4.29 cu ft that the WT1 called out.

    FS was found to be 36.5 at 100mv and 35.6 at 1.0 volts. I was not able to get proper signal readings at 100mv so I had to up the voltage to 1.0 I calculated Qts Qms and Qes two ways. I used the AC current method and got .74 and used the impedance method and got .68 Both were lower than the .85 the WT1 found but these two methods are notoriously inaccurate. At 1 volt the readins for f1 and f2 were very different and this affected the Qms value a lot.

    A better method is to calculate BL and Cms and determine Q from the resonance peak. I don't have what I need to determine BL outside of the WT1, I need a few things to set that test up.

    I'll wait for Giskard to weigh in with his 118H measurements but I don't think I'll be building boxes for these just yet.

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    Hm... I just read your post and need to think it over, but it seems like you are getting good corelation. Anyhow, I was preparing another post as you posted yours. I suspect it may still be of interest, so Ill post it.

    - Until you appreciably crank up the drive I doubt you (or anyone) would be able to feel movement of the magnet and basket. Basically the ratio of moving mass to frame displacement is the inverse of the weights we are talking about. On the other hand this is pretty easy to measure electrically.

    - Typically Fs is not affected as much when it comes to jig resonance. The usual problem is the impedance peak amplitude and width gets distorted... and therefor affecting Q. The good thing about the Q/Fs test is that it is a free air test making it a lot easier to try other jig setups.

    - Just how high is the impedance peak? It may just be possible that the WT1's current source output is saturating. I dont recall any option in the WT1 that adjust Idrive like we can in the WT2. If you directly connect an AC ammeter to the WT1 and set the frequency to 60Hz (many meters are only accurate at 50/60Hz) you measure the current.

    - Compliance compression with drive level is a real phenomena, and by the way, something we are working on. However, even though I have seen compliance vary by as much as 2:1 over very low to very high drive levels, the change in Qt is something more like 1.4:1. Anyhow, it shouldn't be doing this (IMO).

    Best regards

  10. #10
    Senior Member duaneage's Avatar
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    The WT1 found the peak about 43 ohms, My testing at a high drive level of 1 volt found it to be 27. The source impedance of the sig generator ( a Wavetech) is 50 ohms.


    For a drive like this I should be getting a wider, higher peak maybe near 60 ohms or so. But without published specs I cannot be sure

  11. #11
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    Hi Duanage

    I suppose you have done the amplifier with 1K resistor trick in the past to simulate a constant current and I also have to agree that it is a pain in the butt to set up. Never the less, there are some ways to rig a low impedance signal generator to act a bit closer to a constant current. What you can do is add a smallish (~20 ohm) series resistor and watch the current accross that. However one thing to be very careful about is that a lot of DVM's have 50/60Hz pass band filters (IE reject noise) making them not so desirable for T/S testing.

    Both the Woofer Tester 1 and 2 use true current sources to drive the outputs, have signal amplifiers in them, and use tunable DSP filters to reject out of band noise. As you have seen, this makes T/S testing (and a number of other things) a cinch.

    My guestimate is that the WT1's maximum impedance tops out over ~1K ohm, so I dont think you are going to have a problem. When I built the WT2 I knew it was going to have a lower Vdrive capability (a limitation of being USB self powered), but I also wanted to have a higher available Idrive so we could test very low impedance drivers and cables. Given these two factors, and knowing the Zmax at full Idrive on the WT2 is ~300 ohms, the WT1 should top out at ~1K. BTW, you can safely put a handheld DVM on the speaker as you are testing it to see the voltage. What is on the banned list is grounded instruments like oscilloscopes and a lot of benchtop DVM's. The reason is that neither side of the current driver loop is ground referenced.

    If you want to know what the theoretical 118H Zmax should be, put the published TS specs into your box simulator. You will then want to set the box size to something very large (1000 cuft), the tuning frequency to something low (.1hz) and if you can adjust this, box loss (Qbox) very high. I put a simple box simulator in the WT2 software for this reason.

    Best regards

  12. #12
    Senior Member duaneage's Avatar
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    I tried another sig gen ( an HP) that has 600 ohms of source resistance and the problem was the signals were too low for accurate frequency counting. I will try it again tonight, I will make some better connections than the alligator leds adn see what I get.

    I don't doubt the Woofer Tester 1, I think the drivers are either not something I can use.

  13. #13
    Senior Member GordonW's Avatar
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    Have these drivers been refoamed? If the original black rubber surround is in place, there could definitely be an out-of-spec condition, since that rubber gets significantly harder as it ages.

    If tney've been refoamed, they might need break-in... I'd recommend playing them at about 3/8" total cone excursion (3/16" in, 3/16" out) at around 20 Hz on a signal generator for a half-hour, before measuring. Let them sit about 2 minutes between the exercise and the test... that way, you'll be getting a pretty good approximation of general-use conditions.

    I'll bet that the Fs and Qts will go down, and the Vas will go up... though, with the small magnet and voice coil on the 118H, it's bound to be a somewhat high-Q driver in the best of cases (I'd guess at least a Qtc of .5, even fully broken in)...

    Regards,
    Gordon.

  14. #14
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    Quote Originally Posted by WTPRO
    A new version (1.04) has also been posted to www.woofertester.com.

    Best regards,
    Keith Larson
    Nice update!

  15. #15
    Senior Member duaneage's Avatar
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    I'm gonna give them another try with a 20 Hz signal for an hour and see what comes up. If Im don't see better numbers ebay they go. Someone with a pair of L56 speakers probably won't mind if they at least work.

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