118H specifications

[duaneage]

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

[4313B]

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

[duaneage]

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.

[WTPRO]

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

[duaneage]

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.

[WTPRO]

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

[4313B]

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

Best regards,
Keith Larson

Nice update!

[duaneage]

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.