Coen: this could help you.
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Coen: this could help you.
Thanks, i ran into that site yesterday. I've made some uncalibrated measurements with ARTA and the behringer ECM8000 to get the big picture. So far pretty consitent with AB and Earls measurements. A bump aroud 650Hz, a deep notch at 8kHz and a strong resonance around 12kHz. I will post some pics after calibration.Quote:
Originally Posted by vuki
Coen
These are the frequency response graphs of the 288's I measured on a 511E horn for my DIY project that I'm building. These graphs are both the 0 degrees on axis measurements.They both have the 23763 diaphragms.While driver #2 has the 8 Khz notch, driver #1 does NOT... It also has a pretty flat response. :cool:
I was told when I bought them from an attorney handling the estate of an Altec engineer both drivers had a pretty close matched set of diaphragms.One pair received the 23763 and the second pair received the 25884 and that they were rebuilt and never put into use after rebuild.And I have to agree with that statement.
http://www.hostboard.com/forums/hbmc.../2012/05/2.png
http://www.hostboard.com/forums/hbmc.../2012/05/3.png
Both mine have the sharp 8Khz notch. What you see above is smoothed, so the notch appears wider and shallower than in a raw plot.
Sure wish I could figure out why one of your drivers dos NOT have the notch!
Pano,
Just how deep is the 8K notch on your drivers ?
Here's a close look of mine . The 8K notch is only +/- 2.5db ,, which is nothing, really .
http://www.hostboard.com/forums/hbmc.../2012/05/4.png
Another ( higher rez ) shot ( raw file//no smoothing ) ;
http://www.hostboard.com/forums/hbmc.../2009/06/1.png
:)
Interesting. So what are you saying? The notch is related to the diaphragm? That would be nice :). For now my units seem a lot rougher. They're the radial tangerine ones though....Quote:
Originally Posted by Altec Best
Those are some nice 288-Cs you're having there. Maybe I should get some of those, only if they wern't so expensive.
:(
Any preference toward one of the diagrams? Those graphs are shure good reference material. Did you put the mic close to the horn (like 2-6 inches) or at a 1meter (40 inch) ?Quote:
I was told when I bought them from an attorney handling the estate of an Altec engineer both drivers had a pretty close matched set of diaphragms.One pair received the 23763 and the second pair received the 25884 and that they were rebuilt and never put into use after rebuild.And I have to agree with that statement.
Coen
Make a driver+ horn measurement with IMP function at 1m. Make SPL measurement of the whole loudspeaker at listening position with pink noise as source signal and with averaging.
Pretty damn deep on mine. Here is the raw response on a 1005 horn
Attachment 1335
Here are some graphs with calibrated in and output. Never mind the details, for now this is about the big picture. I couldn't reproduce the graphs of yesterday night, that might be the result of the calibration. Oh and no mic FR compensation.
I have measured (coarsly) with two different methods and the results are very similar. Even when the difference in mic distance is taken into consideration.
Attachment 1333
25cm from the horn, Log sweep, Impulse setting in ARTA. 100dB is -below- the noise floor of the 16 bit dac. For starters I used the mobo codec. Very little distortion (0,03%), limited DR (16 bits).
and the second one with noise and RTA (averaged).
Attachment 1334
15cm from the horn, RT Freq analyser (noise cut off at 300 Hz)
By no means does this resemble any of the above measurements. Different horn and different driver though. Probably better matched.
Looking at my graphs I'd say this response could have been designed as a compensation for the natural HF fall of CD style horns... Just wyld guessin' here, OTOH they have been reported excellent on tractrics style horns.
So what should I think of this? Any quick tips to get a better measurement or does this indicate something?
Thanks,
Coen
Quote:
Originally Posted by Coen
If what you just posted can be believed / then yeh / that's going to be pretty unlistenable ( IME ) .
The problem I have now, before I can comment on the 2 response curves that you've shown, I need to be convinced that the data you just got is worthwhile .
I ( we ) don't want to be chasing phantoms ( that are actually caused by some fault in the setup process / such as, inline EQ in the test chain ) .
How about measuring something else & then posting those results ( like some 2-way HiFi speaker that you figure is smooth & is enjoyable to listen to ) .
How are you driving signal into these devices ? ( it should be with a simple basic amp, plus a 40 to 50uF in line cap just before the driver offering DC protection ) .
:)
http://www.hostboard.com/forums/atta...p-288-1005.png
Oh yeh, that misfit . I remember now . Obviously, that was as good as it got , right ?? ( Mind-you , looks great up to 8K )
It's seeing curves like that really damp-down my enthusiasm for acquiring new GPA diaphragms ( since the cause of that suckout is still not determined ) .
( Maybe it's a function of the 1005H horn loading on the driver/phragm combo ).
Did you ever try to fitup one of ABs diaphragms into your driver, as a "yardstick" reference ?
:)
No, never tried other 'phrams other than the symbiotics that came with them. May have that graph somewhere. Jean-Michel Le Cleac'h and I went back and forth via email quite a got and never could figure it out. I just gave up and roll them off at 7K.
Coen, holy rising response, Batman! If your measurements are correct, that's got to sound awful. As Earl mentions, let's see something else to be sure. Do you have an EQ or something in front of them? A passive EQ with a big HP shelf?
I tried to get the horn equal distance from the ceiling and the floor with Mic dead center in front of the horn.To limit room reflections.I also measured at low volume from my amp to minimize that as well.IMO it is better to keep the Mic close to speaker to minimize adding any noise into the measurements.Three feet one meter is fine,but in a living room with walls,furniture,etc... It's best to keep the Mic close to the speakers IMHO.It helps, otherwise you will need to adjust the gating on the measurements as well... Zilch used to measure just a couple of inches away.Quote:
Originally Posted by Coendert2011
@ Pano, WOW there is something wrong with those ! Are they all aluminum Frams ? If so what model #? It looks like that dip goes off the chart.Literally ! :Can't belive it:
Coen, do the IMP measurement from 1m distance without crossover (just dc blocking capacitor).
Thanks all for the thinking along.
My setup is quite simple. The motherboard terratec codec to a 75W Hafler mosfet amp (with attennuators and dc servo) and then to the drivers. Behringer mic -pointed straight on-axis to the hornmouth- is connected to behringer 8in-2out mixer with some gain, all eq to 0 and then to the codec again. All wiring is simple low L, low C stuff. The terratec codec can do 24/192 out and 16/192 in, not bad! Levels are quite low though:1V rms out and 1V peak-peak in.
So, as you can see no filter and no eq in the chain. I pondered a little on the results and came to the conclusion that I have been integrating reflections as well. The rta is averaged and the imp has a long sequence. So next measurement will be imp with a 3mSecond window, now I only need a meter of free space. 330Hz as a lower boundary is fine with me. I am still a little sceptical wheter this changes the FR a lot. Probably a notch and peak or two, but we'll see. I'll keep the mic close to the hornmouth.
I wondered though if the on-axis position is the best. The center fin of the horn is in front of it and the two adjacent sectors might have some lobing and peaking at certain frequencies even at a close distance. Otoh off axis measurements can probably not be compared to all other material...
One one account the measurements make sense: they sound awfull allright!
I am struggling a little with the correlation with my first auditory inspection. This seems consistent with the measurements, but should that be the case? I mean hearing sensitivity varies with frequency and loundness, right?
Thanks for the cap suggestion in an moment of unattention this may save the phragms!
Thanks, Coen
I found another 288-(16)K Freq graph here: MachMat mainpages.
Attachment 1336
Much smoother on the circular "Oris" tractrix horn. The black line shows the un-eqed measurement and shows the rising response up to 1KHz, The upper part looks a lot flatter though. Save for the reflections, the 511-E throat blobs may have something to do with this too.
Coen
IMPulse measurement from 1m distance would tell a lot. 3ms window is just about right. Do it also with the crossover and then do the RTA of the complete loudspeaker at listening position.
Since there is clean 6dB/oct. rise in your measurement I suspect that it is something with the measurement setup (wrong generator signal?) because if corrected (by 6dB/oct.) you would get nice 288k response :)
Thanks,Quote:
Originally Posted by vuki
I will fire them towards the ceiling for maximum free space and measure at 1 meter like you suggest. I have planned to recheck the complete setup to eliminate all hidden faults. The strange thing is that it is a high pass characteristing which implies a series capacitance or a shunt inductance. Where to look for those?
Fyi i used the same settings in a loop feedback configuration (as part of the calibration process) and the response was completely flat. Let's first put the amp in that loop...
Coen
IMHO that high pass is too linear to be caused by passive component. I still think it's measurement setup. Try the Impulse measurement.
Thanks,Quote:
Originally Posted by vuki
First measurement was done with IMPulse setting. The Impulserespose was measured with a log sweep. In fact to have ARTA determine if there are any excessive distortion components. At the level of my measurements these all appear to fall into the noise floor of the ADC.
The high pass can be acoustical as well. Think of the lower horn cut-off or bass reflex which both have inductive air-impedances in their modelling. Checking all bolts and nuts is also part of the setup inspection!
Coen
Really now, who wants to look at such tiny pics ?
http://www.hostboard.com/forums/atta...0p-288-103.jpg
Fellas, it's time to learn how to create "links" that go from this site over to an interesting image that is hosted on another site . So;
> Right Click on the Image ( of interest ) at the other site ( webpage ) .
> Choose, "Copy Image URL" from the menu .
> Come back to this site & open the text editor.
> Paste the "friggen" URL ( belonging to the image ) into this sites text editor .
> Write [img] in front of URL
> Write [/img] after the URL
> Now look at the original picture in it's proper, glorious size .
http://www.machmat.com/mysys/images/288-103.gif
:)
PS : Thanks for the link to the other site .
What would be the corner freq. of such high-pass - 20khz? Notice that distortion curves are also very uniform along 6db/oct. line.Quote:
Originally Posted by Coendert2011
Hm, on the second look that would be more like 3dB/oct?
http://www.hostboard.com/forums/hbmc.../2012/05/5.png
Something like the above is what I would expect to see ( from a "healthy" 288 mounted on a radial type horn ) .
Not this ;
http://www.hostboard.com/forums/atta...5cm-sc-003.jpg
:)
Well, forget those first measurements.
Did them too tired and way too sloppy. Bad location, loose bolts, on second sight weird settings and a wrong connection that I still don't understand (why it worked in the first place).
Now I've got much better graphs. FR seems ok, but distortion is a little high and uneven compared to above (not playing real loud here).
Thanks to Earl here you are with a nice pic:
http://www.hostboard.com/forums/hbmc...2012/05/58.jpg
Pretty nice eh?! However: D2 and D3 are dancing all over the place....
I did another much louder measurement to eliminate the influence of ambient noise, with this result:
http://www.hostboard.com/forums/hbmc...2012/05/59.jpg
Here is a group shot of the Gremlins:
http://www.hostboard.com/forums/hbmc...2012/05/60.jpg
Ammounting to this high performance compressiondriver THD graph:
http://www.hostboard.com/forums/hbmc...2012/05/61.jpg
Yes folks that is almost 10% distortion....:eek:
For the fans: here is the smoothed version in low quality jpeg:
http://www.hostboard.com/forums/hbmc...2012/05/62.jpg
New diaphragms and a little compensation for the 600Hz peak will probably make this an outstanding hifi combination!:cool:
Coen
Yeh baby !! , now that's some good work .
- Notice ( on mine ) D3 ( 3rd Harmonic Distortion / ugly stuff ) is 60 to 70db below the fundamental ( 1K to 5K ) .
- Your D3, ( 1K to 5K ) is about only 30 odd db down ( with that big sub 2K peak getting close to being only 24db down ) .
- Anyways, nice work !! .
- IME, distortion specs like these nicely supports all of your earlier mentioned, auditory-impressions .
- ( FWIW, before ordering new diaphragms ), I would play about with those diaphragms a bit ( loosen off the screws holding the guide-pins / Pano knows what I'm talking about ) to see if you can lessen the distortion ( by shifting the centering of the diaphragm in the gap ) .
:)
PS ; Thanks for the big pics !
Yeah, I was going to ask, do you have the centering pegs? I think I saw them in your photo. Getting the 'frams centered without them is near impossible, as I found out. :(
I see the ~8.3Khz dip in yours, too.
Did I tell you, or did I tell you? :rolleyes:
Do the same measurement with crossover. Do the RTA measurement of the complete loudspeaker at listening distance. Post the schematic of the crossover.
I don't think the distortion is the cause of bad listening impression. Also, it seems to me that diaphragms are OK.
No no centering pags or 'spider shim' used. I left the factory alignment in place.Quote:
Originally Posted by Panomaniac
One can improve here.
I will perform a higher resulution measurement on the dip to see how deep it goes.
Coen
Ok!Quote:
Originally Posted by vuki
Cross over is second order Linkwitz-Reilly on 650Hz that works wonders on my 802 setup. C=12uF paper in oil 600V cornell dubilier, L=3.3mH heavy copperfoil air inductor. This is a fantastic filter for my 802 setup.
Driver with horn sounds equally bad with and without the co and with and without my diy altec 828 cabinets. I don't expect any difference by inserting the filter nor by adding the bass cabinet. Been there, done that.
Fyi I experimented with various caps like different pios and polypropylene and different cables (stranded, solid core, silver, copper etc). NOTHING cures or even ameliorates the harshness. The high distortion makes a whole lot of sense.
To me it is no longer circumstantial that the phragms are not up to spec, probably the whole batch isn't. They might have have been tin thin or had a bad heattreatment, bad coating, bad whatever, but they break up as hell. Factory misalignment may also play a role, but both drivers suffer the same illness, so it is not exemplary. This is supported by the post of Todd W.
For now I'm curious how my other 288 and 802s perform on the graphs. I do like this sound of the latter.
If I find some extra time I will go through the trouble of measuring in situ. But
Thanks anyway for your suggestions!
Coen
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 ) >< :)
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.
I guess that 2kHz distortion hump would be at least somewhat reflected on freq response of the driver, wouldn't it?Quote:
Originally Posted by Earl K
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.Quote:
Originally Posted by vuki
Coen
Thanks for the kind words and helpfull support!Quote:
Originally Posted by Earl K
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
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.Quote:
Originally Posted by vuki
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
Quote:
Originally Posted by Earl K
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.
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):
http://www.hostboard.com/forums/hbmc.../2012/05/6.png
Here is the THD:
http://www.hostboard.com/forums/hbmc.../2012/05/7.png
And here is the smoothed version (stretched):
http://www.hostboard.com/forums/hbmc.../2012/05/8.png
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
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 .
:)
802-8g + 511
Attachment 1343
902 (gpa 8 ohm dia) + 511
Attachment 1344
Nice work!Quote:
Originally Posted by vuki
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
