Measuring 604 D TS parameters

[charly1944]

Hi,
I am trying very hard to measure the TS parameters and specially the QTs and VAS of my pair of Altec 604 D.
I am slowly getting familiar with LIMP(ARTA) and understand that i have to enter 3 values:
1.The resistance which in this case is 11.0 Hz for both speakers(The high freq Re are respectively 8.1 and 8.5 ).
2.The membrane diameter:The user's manual indicates that one should take the diameter of the cone plus 1/3 of the surround.Two questions here:
-Is it 1/3 on each side or 1/3 in total?
-Since this is a general recommendation for driver,does it apply as well for a co-axial or is there a correction to be applied when measuring the diameter of a co-ax.
3.Added mass :I have tried to add masses to the back side of the cones but they dont stick long enough to perform the measure till the end.Can i use small magnets without affecting the results of the measures?
Thanks for your help in this meticulous exercise.
Regards,
Charly.

[bowtie427ss]

Is it 1/3 on each side or 1/3 in total?

1/3 of each side would be 1/3 of total, so yes.

Since this is a general recommendation for driver,does it apply as well for a co-axial or is there a correction to be applied when measuring the diameter of a co-ax.

Are you asking what to do about that portion that would be the dust cap in a typical woofer? I'd have to defer to the experts on that one.

.Added mass :I have tried to add masses to the back side of the cones but they dont stick long enough to perform the measure till the end.

Have you tried modeling clay, play-dough, silly putty, plumber's putty, rope caulk?

Can i use small magnets without affecting the results of the measures?

I doubt it, i don't think you can get the magnets located close enough to the voice coil without affecting the motor's own field or interacting with the motor's front plate.

Are you suspending the driver in a free field for your measurements? Nearby objects can cause reflections that will skew your measurements.

[charly1944]

1/3 of each side would be 1/3 of total, so yes.

Are you asking what to do about that portion that would be the dust cap in a typical woofer? I'd have to defer to the experts on that one.
Yes this is precisely is my question.

Have you tried modeling clay, play-dough, silly putty, plumber's putty, rope caulk?
None of those.I have tried a product called PATAFIX.Interestingly it did the job on the my friend old Altec 416 but not on mine!


I doubt it, i don't think you can get the magnets located close enough to the voice coil without affecting the motor's own field or interacting with the motor's front plate.
Any other comments on this one?


Are you suspending the driver in a free field for your measurements? Nearby objects can cause reflections that will skew your measurements.

Not quite.I blocked them between the legs(legs facing the ceiling) of a wooden chair,which is placed on a pretty high wooden stand. The drivers are 4 feet away from the floor and about 8 feet away from the ceiling , are in the same position as when playing in an enclosure with no objects near them.Actually the measurements without any added mass give Fs of respectively 27.9 and 26.7 Hz which are spot on when compared to the 604E Fs mentionned in the Altec unofficial site (27.1 Hz but apparently for a 604 E in 8 ohms since the Re mentionned is 7.0 ohms).So i tend to think the set up works.
Thanks again,
Charly
Apparently i am not using the quote system adequately.Sorry for that!

[GM]

Since this is a general recommendation for driver,does it apply as well for a co-axial or is there a correction to be applied when measuring the diameter of a co-ax.
3.Added mass :I have tried to add masses to the back side of the cones but they dont stick long enough to perform the measure till the end.Can i use small magnets without affecting the results of the measures?

A pressure test is required to accurately determine Sd, but buried somewhere in an old Altec technical paper, the 604's effective diameter is ~12.17" Vs a 515's ~12.75". I know of no ~universal 'correction factor' for co-ax.

I'd be reluctant to use magnets except out near the surround where I've had no problems AFAIK. The main thing is to add enough mass to lower Fs > 25% and ideally Fs/1.56, which is the inverse of finding Vas by increasing Fs in a sealed cab by 1.56x.

GM

[Panomaniac]

I've used neo magnets with a washer on the other side to good effect. Easier than putty and same results. The main problem was weighing the magnets, they pulled themselves down to the scale!

[charly1944]

Thanks GM,
As usual,you are a golden mine!In our first attempt to measure the speakers we used a lower figure for the effective diameter(Actually 11.81 instead of 12.7).No doubt this has impacted the calculation of the TS .We will do next week a complete set of measures entering the right values and if i keep having problems with the added mass method,i will build an appropriate closed box(about 2.27 cubic feet) to end this exercise with decent data.I bought the very useful ,although difficult for an ex-economist,book of D'Appolito.I will keep you informed.

[GM]

You're welcome!

Yes, it should be small enough for high Vas drivers such as the 604.

Smart purchase! It's an excellent measurement reference for beginners.

GM

[charly1944]

Hi,
I finally measured my speakers with a tester woofer 2.
The closed box method gave the following results:
Speaker 1: RE:10.93 ohms;Fs:27.68 Hz;Zmax :285.17 ohms;Qes:0.31;Qms:7.9131;Qts:0.30;Le:1.4841 mH at 1kHz;Vas:527.5 L;Sensitivity:97.2 dB @1w/1m.
Speaker 2: RE:10.62 ohms;Fs:27.83 Hz;Zmax :268.78 ohms;Qes:0.31;Qms:7.5351;Qts:0.30;Le:1.4841 mH at 1kHz;Vas:519.7 L;Sensitivity:97.3 dB@ 1w/1m.
It looks to me that they are pretty well matched but that the Qts are relatively high compared to the specs.Is it important and if yes are they ways to get those Qts down by further burning in the loudspeakers at low frequencies?
Charles.

[charly1944]

HI,
No answer so far regarding the results of my Altec 604 D TS.Those have been reconed by GPA and the QTS are respectively at 0.29 and 0.30 when they should be around 0.21.(Altec 604 E specs) despite 2 weeks of burning in with all kind of music.Is this difference in QTs important and is there a way to fix it?
Thanks for your reply.
Charles.

[GM]

FWIW, I've accumulated quite a few sets of measured specs from all but the original duplex and none have been close to having a 0.21 Qts except the 617-8A ceiling speaker. That said, the E series have averaged ~0.33 with the K-L ~0.27, so apparently the re-cone kits are for the newer series and your old magnets either weren't, or couldn't be, re-magnetized enough to drop Qes/Qts any lower.

Regardless, unless you couple them to a matching impedance, they are plenty low enough for excellent performance and matched closer than many modern drivers.

GM