Why do my 288-8Ks sound like cr@p?

[vuki]

Crossover that works wonders for one driver can be totally wrong for the other. Brand and composition of capacitors, resistors and inductors (especially wires) certainly won't do any wonder to the sound of the loudspeaker, but their values will. Diaphragms seem to be OK otherwise freq. response wouldn't be so nice. Distortion (if it is correctly measured) could be caused by misalignment - fixing this shouldn't be a problem with your measuring setup.
Anyway, IMO the right way to proceed would be to measure drivers' responses with crossover and complete loudspeaker. This would tell you a lot more than guessing and listening.

[vuki]

Coen ,

As far as I'm concerned you've nailed it ( a bad batch of diaphragms , ( metal related ) ; too thin, wrong Alu mix, wrong metal prep, etc. etc. ) .

Distortion in that elevated area is particularly noticeable to the human ear ( & I really have no idea what internet based cool-aid Vuki is drinking when denying the audiblilty of distortion / I have my suspicions that it starts and ends with the initials E.G. ) .

I'd love to see some sweeps of your 802s ( Fr & Dist ) on the same 511Es ( that would be a learning experience for all of us ) . When you have time .

Thanks for the educational thread ( now you know & now we know ) ><

I guess that 2kHz distortion hump would be at least somewhat reflected on freq response of the driver, wouldn't it?

BTW Beer is my drink of choice.

[Coendert2011]

I guess that 2kHz distortion hump would be at least somewhat reflected on freq response of the driver, wouldn't it?

BTW Beer is my drink of choice.

Good point, however these are the distortions @ 2kHz, so D2 is 4kHz and D3 is 6kHz! You can see the little response bumps in the smoothed curve at these frequencies. furthermore the level is worst case about 30dB below the response line, if distortions were absent the response line would marginally be lower.

Coen

[Coendert2011]

Coen ,

As far as I'm concerned you've nailed it ( a bad batch of diaphragms , ( metal related ) ; too thin, wrong Alu mix, wrong metal prep, etc. etc. ) .

Distortion in that elevated area is particularly noticeable to the human ear ( & I really have no idea what internet based cool-aid Vuki is drinking when denying the audiblilty of distortion / I have my suspicions that it starts and ends with the initials E.G. ) .

I'd love to see some sweeps of your 802s ( Fr & Dist ) on the same 511Es ( that would be a learning experience for all of us ) . When you have time .

Thanks for the educational thread ( now you know & now we know ) ><

Thanks for the kind words and helpfull support!

Not having witnessed the breakup myself, this is a typical case for Occam's Razor. This just makes to much sense notthe be the cause. I am curious myself on the 802s!

Coen

[Coendert2011]

Crossover that works wonders for one driver can be totally wrong for the other. Brand and composition of capacitors, resistors and inductors (especially wires) certainly won't do any wonder to the sound of the loudspeaker, but their values will. Diaphragms seem to be OK otherwise freq. response wouldn't be so" nice. Distortion (if it is correctly measured) could be caused by misalignment - fixing this shouldn't be a problem with your measuring setup.
Anyway, IMO the right way to proceed would be to measure drivers' responses with crossover and complete loudspeaker. This would tell you a lot more than guessing and listening.

Vuki, believe me I know what you are talking about. I've been working on the current co for the 802s over more than a year. Small shifts in co points and slopes make huge differences to the sound. The same can be said about the b.r. tuning of the 828 cabinets (with 515-8G). I've been biamping with software crossovers (Thuneau allocator) to find the sweet spot. In the end i liked the passive correction I use now best.

So I am confident that the c.o. is of very little importance to the bad-sound problem as discussed in this thread.

I will start a new thread when optimising the co for the NEW 288s with new diaphragms, this should be interesting!

Coen

[Altec Best]

As far as I'm concerned you've nailed it ( a bad batch of diaphragms , ( metal related ) ; too thin, wrong Alu mix, wrong metal prep, etc. etc. ) .

I'd love to see some sweeps of your 802s ( Fr & Dist ) on the same 511Es ( that would be a learning experience for all of us ) . When you have time .

This is probably the most probable cause.As I have a Brand new pair of the same diaphragms 23763's and they are pretty flat.And sound great BTW ! I'm almost certain they are from the OKC plant from the 80's from what info I have been able to piece together.


I have adapters for the 511E's to mount the small formats (802's) and have been wanting to measure the Brand new 802G's I have with the lite Frams for awhile now.Just haven't had much time to do anything with work taking most of my time now.. Can't even finish my project that has been taking much too long now..

But I'm starting to see some light at the end of the tunnel so to speak.

[Coendert2011]

Today I've put the mic in front of the 802-16D. Horn is the same one used for the 288 measurements with the addition of the 21216 throat adapter (1" to 1.4").

This produced some very interesting results:

Here is the FRD with distortion (at 20cm):


Here is the THD:


And here is the smoothed version (stretched):


IMO the cleanness and smoothness I like is best correlated to the distortion. It remains verly low and constant in the horn loading region and I don't think it will get much lower at less power. Note that since they are 16 ohm dias, the power is half of the 288 measurements.

The FR is a tad more hilly than I would have expected, but it makes sense to my listening experiences.
I recognise the peak at 2.2KHz leading to a somewhat forward character on voices and midrange instruments. The 8K hump (heh a hump at 8K!) may give the sound a certain boost at the usually very low listening levels I practice. The unevenness in the midrange is comparable to the 288, while the latter has some serious HF issues (the sharp 8K notch and 12k peak).

The thing is I have not been bothered by this at all, but I see the room for improvement here!

I'm curious what a 802-G would bring to the table!

Coen

[Earl K]

Coen,

Thanks a lot for those .

It's really nice to see this type of data .

Especially when coupled with your original comments & preferences. // it makes for a type of Double Blind Test /

ie; one has "great looking FR" - but sounds unlistenable while the other only looks, "acceptable", but sounds great ) .

All good stuff !

I'll post more tomorrow .

[vuki]

802-8g + 511
22UF.jpg

902 (gpa 8 ohm dia) + 511
902.jpg

[Coendert2011]

802-8g + 511
22UF.jpg

902 (gpa 8 ohm dia) + 511
902.jpg

Nice work!

Those pics are unfortunately awefully small. Left of 1kHz is hi passed away?
Interesting peaks on 10 and 12kHz. So these could be related to the 802-g radial phase plug that is in our 288-ks as well....

Did you use any compensation for the bumps/nothces?

Coen