Once again, just call him. Until you have spoken with him about the issue, you cannot say what has or can be done. I have seen the graphs and even viewed attached threads, and from what i have seen, some people seem to have solved the issue while others have not.
krzys said:
- First ( before doing that ) check with GPA to see if you might void an existing warranty by opening them up .
- Second, look at your older captures of these drivers on your horns . You should ( if you kept them ) be able to simply turn on the distortion display ( & then compare what you have to the healthy driver specs I posted ) .
- If you need to, then make some new data captures ( of your drivers & horns ) .
- Third , if the distortion specs are out of whack ( & only if GPA says its OK ) then try aligning the diaphragms ( for better frequency response & lower distortion ) .
<> EarlK
krzys - it looks a bit similar to the problem I had with one of my GPA 288H drivers, which was traced to faulty material on the pole-piece. I would have hoped this sort of problem was solved now, as I lost a considerable amount of money in repeat customs charges after sending one of them back from the UK to Oklahoma .....
Hi Earl K and others. I measured both GPA 388 drivers. I found that they are quite different in FR and distortion. One of them displays the distortion pattern of a poor fit example EarlK gave. The other one does not although both present similar but not identical FR. I don't know what to think about.
This once again raises the question of quality and consistency of those drivers. I am not very glad of that. I’m able to EQ them flat with 2/3 parametric filters but it isn’t the ideal situation. I must admit that maybe apart some occasional harshness on loud music I can not hear any major problem.
I contacted GPA and asked if they can send me a spider shim. We will see. I would like to be able to at least check the phragms alignment. This is doable although a very delicate operation. I once damaged a diaphragm on an 806 driver. Somebody knows where I can buy a stainless steel or aluminum screwdriver?
Christophe
Measurements where taken at the horn mouth. SPL is not calibrated. In order: SPL and distortion of both drivers, SPL overlay and group delay overlay
This once again raises the question of quality and consistency of those drivers. I am not very glad of that. I’m able to EQ them flat with 2/3 parametric filters but it isn’t the ideal situation. I must admit that maybe apart some occasional harshness on loud music I can not hear any major problem.
I contacted GPA and asked if they can send me a spider shim. We will see. I would like to be able to at least check the phragms alignment. This is doable although a very delicate operation. I once damaged a diaphragm on an 806 driver. Somebody knows where I can buy a stainless steel or aluminum screwdriver?
Christophe
Measurements where taken at the horn mouth. SPL is not calibrated. In order: SPL and distortion of both drivers, SPL overlay and group delay overlay
Attachments
I didn't 'hone' the response per se, I align honed the driver, steel shim and horn entrance with a three stone brake master cylinder hone attached to an electric drill to make the transitions as seamless/smooth as practical. Then made a tapered wood alignment tool, added indexing marks on everything, so they could be taken apart, reassembled, i.e. a typical motor blueprinting type of mod.
I had easy access to a comprehensive metal fabricating shop at work, so finding a suitable steel shim might be a problem if you can’t make one out of a fender washer or maybe alum. sheet.
There were other tweaks I did that helped in other BWs, grinding down/smoothing welds, rounding over corners, cutting out vane welds, glass beading to a high smoothness, mucho stiffening, damping, etc., but I was trying to make a 'silk purse out of a sow's ear' [Altec 511], just to see if I could and was very pleased with the results, though they were still too 'colored' for SOTA HIFI even back then, so moved on to scratch building horns, ultimately winding up with a huge conical WG that was about the same overall size as a 1803 multi-cell to get good loading down to 500 Hz.
The downside to this was a way too large an acoustical ctc spacing to the vertically oriented dual 15” bass horns, so at that point went back to the tweaked 511s plus added another pair of ~stock 511s [with inductors] stacked on top to get the big horn system’s ‘full’ mids.
GM
krzys,
- For a "Pro" driver those variations are not out of line ( & sadly, still expected from the established names ) .
- I'm in Pro audio and don't consider $ 340.00 ( per compression driver ) as a ton of money / so my sympathies are pretty limited here .
- If you had wanted "matched" drivers ( for audio-phile purposes ), you should have offered GPA a premium price (per driver ) to go through their inventory to find two the same.
- I know GPA can match drivers ( when asked ), here are two of their 902s , as obtained by our dearly departed "Zilch" . IMO, these traces are wonderfully matched !
- I would work on getting the distortion content down for this driver ( fyi, from 500hz to 10K, the third harmonic should average @ 15db below H2 on the "full-body" 288 / the pancake-body 388 is anyones guess ) .
- I published these 2 blow-up pics ( of Brandons "overly small" FR studies ) almost 3 years ago to better highlight the variations in GPAs blind-pulls.
- This was before you bought your GPA 388s .
- So I'm now wondering where you got the idea that these "blind-pulls" from the GPA inventory would give you matched responses ? .
- I don't think it would have been from this post ! Please note my opening line .
- A close scrutiny of AugerPros measurements implied a diaphragm fit up problem for one driver ( indicated within his distortion findings ) from more than 3 years ago .
- Here are Brandon's original words of caution ( regarding distortion ) as found in the first measured GPA 288H .
- The data ( on his site ) for the first driver was removed & replaced by a second set of measurements ( I suppose after it was determined that the first driver with the 2K-4K "problem" was not a healthy specimen ).
<> EarlK
- For a "Pro" driver those variations are not out of line ( & sadly, still expected from the established names ) .
- I'm in Pro audio and don't consider $ 340.00 ( per compression driver ) as a ton of money / so my sympathies are pretty limited here .
- If you had wanted "matched" drivers ( for audio-phile purposes ), you should have offered GPA a premium price (per driver ) to go through their inventory to find two the same.
- I know GPA can match drivers ( when asked ), here are two of their 902s , as obtained by our dearly departed "Zilch" . IMO, these traces are wonderfully matched !
- I would work on getting the distortion content down for this driver ( fyi, from 500hz to 10K, the third harmonic should average @ 15db below H2 on the "full-body" 288 / the pancake-body 388 is anyones guess ) .
- I published these 2 blow-up pics ( of Brandons "overly small" FR studies ) almost 3 years ago to better highlight the variations in GPAs blind-pulls.
- This was before you bought your GPA 388s .
- So I'm now wondering where you got the idea that these "blind-pulls" from the GPA inventory would give you matched responses ? .
- I don't think it would have been from this post ! Please note my opening line .
- A close scrutiny of AugerPros measurements implied a diaphragm fit up problem for one driver ( indicated within his distortion findings ) from more than 3 years ago .
- Here are Brandon's original words of caution ( regarding distortion ) as found in the first measured GPA 288H .
- The data ( on his site ) for the first driver was removed & replaced by a second set of measurements ( I suppose after it was determined that the first driver with the 2K-4K "problem" was not a healthy specimen ).
<> EarlK
More than me, I have zero sympathy since inflation adjusted, their pricing is for the most part somewhat lower than what I paid way back when after a discount and by the mid '70s, Altec's QA had dropped to the point where I quit buying/recommending them except for replacements where cost effective.
WRT distortion testing, I've no experience or even considered it since I don't recall seeing anything published by Altec in either cut sheets or in tech bulletins beyond recommending that in any type of high power app the speaker's components be limited to a decade, implying that in any consumer app short of a frat party it was a non-issue, so wondering what the distortion looks like when the driver is BW limited 2nd order to 500-5k, etc..
GM
GM said:
- Looks to me like 1K to 10K is a more realistic BW ( for distortion products, when aligning diaphragms ) .
- ( Obviously from above ) Altec did publish a few distortion specs ( for their later drivers bolted onto their horns ) / granted, specs are few & far between .
- I suppose I might moderate the goal ( of a 15db spread between H2 & H3 ) down to 12db ( to match Altecs own stats ) / but heck / all these newer horns/waveguides ( sans diffraction slot ) are widely touted for their lower distortion , so why not shoot for a 15db spread to see if it's achievable ?
<> EarlK
LOL! OK, you really did hone them.Make sense, I just didn't take you literally. Porting and polishing the horns, eh? Real audio hot-rodding is cool.
Wait until you see the tuned extractor pipes!
An externally hosted image should be here but it was not working when we last tested it.
For chrome you pay extra:
An externally hosted image should be here but it was not working when we last tested it.
The pipes are the ports.
Courtesy of Pellegrene Acousticsacoustic waveguides
I didn't think to chrome these but it would have been a nice surprise when they took the lid off haha.
Best,
Tom Danley
pix at 2739
http://www.diyaudio.com/forums/subwoofers/97674-collaborative-tapped-horn-project-274.html
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Mark, you have no idea how timely this post is for me. I'm looking into this litz / cotton world and frankly unless I want to spend $1k for a larger quantity than I need (new), finding litz to the 99.99 spec is not so easy. ...nor is the cotton.
I was hoping I could start with a kick-*** DIY cable and only then invite the commercial stuff to compete (and with a return policy). But because of the low price of the TQ cables you mentioned above, one possibility is to start out with the TQ and then have the litz/cotton attempt to compete. I will have to rearrange things in my house before I can proceed with the right length of cables. In the meantime, I can follow things and see how they develop. Same goes for this speaker.
Above I forgot to ask my questions. I'll ask now...
Mark, how is the testing going with the TQ black?
And how do the highs compare to the litz/cotton?
And finally, on your litz cables, how many pieces of shrink tubing do you have, how big are they, and how far are they spaced apart?
Wire
Hi Charlie
Well, the HF-end of the Blacks is not quite there ( not as good as Bud's litz ) but I've got one length on burn-in with a signal generator currently, as I'm told it takes anywhere from 100-300 hrs at normal volumes to reach its best . I hope it comes around, as the coherence from mids to bass is really something .
For Lynn's benefit, what I'm hearing with this wire is like going from an RC RIAA network to an LCR one, in a phono, in that there is a much better dynamic and tonal integration between the bass and mids .
For info, on the litz, I am currently using what Bud suggested, which is one piece of heatshrink about 1.5" long , every 0.5m or so ( sorry to mix units ) . As I have said, I have no theory at all about what this is doing, except that it makes a big difference to the sound !
It may be that I will experiment a bit more with extra pieces now, given what I've been hearing from the TQ wires.
Hi Charlie
Well, the HF-end of the Blacks is not quite there ( not as good as Bud's litz ) but I've got one length on burn-in with a signal generator currently, as I'm told it takes anywhere from 100-300 hrs at normal volumes to reach its best . I hope it comes around, as the coherence from mids to bass is really something .
For Lynn's benefit, what I'm hearing with this wire is like going from an RC RIAA network to an LCR one, in a phono, in that there is a much better dynamic and tonal integration between the bass and mids .
For info, on the litz, I am currently using what Bud suggested, which is one piece of heatshrink about 1.5" long , every 0.5m or so ( sorry to mix units ) . As I have said, I have no theory at all about what this is doing, except that it makes a big difference to the sound !
It may be that I will experiment a bit more with extra pieces now, given what I've been hearing from the TQ wires.