Should Altec 288 compression drivers sound like this? (ringing)

[Steve71]

I have two Altec 288K compression drivers mounted to Mantaray horns (MR-64 & 94) that I'm using for home use.

They do quite a few thing amazingly well, but I'm getting a lot of ringing on some recordings. The Beatles Magical Mystery Tour for example has a lot of sibilance and some of the "haaa" harmony's are shrill. Sounds like it's in the 2-3khz band.

I don't think it's a room mode because it's persistent when I walk around the room, but then again it's a lot less noticeable at lower volumes.

The 288's are crossed over at 500hz with a 24db per octave slope. Raising the crossover doesn't help much. But apart from being crossed over, they have no EQ.

Is this normal 288/MR sound without EQ?

[CONVERGENCE]

Your cross over slope should be set at 12DB buterworth . The M94 specs recommends a xo at 800 HZ.

You don't say much about your woofers :type ,box ext. would help.

I made a montage of the history of the Beatles on Ampex 440 . I used
604 8G in 612 box monitors and replayed the whole thing in a theater on Altec A-5 and never heard any ringing on the magical mystery tour song.


.....................

[Steve71]

Your cross over slope should be set at 12DB buterworth . The M94 specs recommends a xo at 800 HZ.

You don't say much about your woofers :type ,box ext. would help.

I made a montage of the history of the Beatles on Ampex 440 . I used
604 8G in 612 box monitors and replayed the whole thing in a theater on Altec A-5 and never heard any ringing on the magical mystery tour song.


.....................

Thanks for the response CONVERGENCE.

The x-over is a Behringer CX2310 and I'm crossing over to two VMPS subs.

I do realize this is far, far from ideal, but it's just an evaluation system so I could test the 288's before I sell of my old speakers to fund the rest of the horn project.

I tried running the crossover as high as 900hz with the VMPS's on mute but I still get that shrill sound on certain vocals... I muted the subs to eliminate any possibility of comb filtering

Assuming this isn't normal then, does it indicated that the diaphragms are past their useful life?

FWIW at moderate volume it sound fine on most recordings and even sounds fine at high volume on Jazz and classical.

And when I say "shrill" I mean it sounds like the typical distorted midrange ring that you hear (on vocals and distorted guitars) at a rock concert.

[CONVERGENCE]

Oh that is quite a bit of distortion ;not normal.Then the diaphragm should be replaced by new ones preferably from GPA.

[Zilch]

Do we have some cause for believing that 288s don't require CD compensation on MantaRays, which are CD?

[Steve71]

Oh that is quite a bit of distortion ;not normal.Then the diaphragm should be replaced by new ones preferably from GPA.

It's sure looking that way... I had a read through the thread below, and it looks like Alu diaphragms are only good for 10 years at most. These 288's came out of a church so who knows when the last time the diaphragms were replaced. Now I just have to decide to go with 288 or 299 diaphragms.

http://audioheritage.org/vbulletin/showthread.php?t=790

[Steve71]

Do we have some cause for believing that 288s don't require CD compensation on MantaRays, which are CD?

It's my understanding that constant directivity horns require some eq on the top end because they spread the HF content over a much larger area than the non CD horns. When I get serious about building these horns into real speakers, I'll be measuring and compensating.

However the ringing/distortion I'm hearing is a separate issue, no?

[Zilch]

However the ringing/distortion I'm hearing is a separate issue, no?

I'd call it a separate issue until proven otherwise.

If the midrange is as exaggerated on those as it is using the smaller drivers without compensation, you may be hearing more of it than if the response were properly balanced.

That's not to suggest that the excitation would be any different for a given SPL, however.

[Earl K]

Should Altec 288 compression drivers sound like this? (ringing)

No ! Just the opposite / in fact, they are one of the best behaved compression drivers ever retailed .

- ie ; they don't have any frequency dependant "hot-spots in the "CSD domain" that need taming / unlike most JBL drivers of similar vintage .

- Once properly EQed, healthy 288-xKs are among the best sonically balanced drivers available . Your 288(s) may not be healthy ( they are afterall , about 25 years old ) .

- These drivers ( especially on Constant Directivety horns ) need EQ to be flat out to 13Khz . ( I'll assume you may like a relatively flat HF response / like most of the population does )

Is this normal 288/MR sound without EQ?

- I don't have any MRs horns here / so I can't comment on whether the horns are adequately damped or not ( they are aquaplas over a lightweight metal such as tin ) .

- These horns are relatively huge ( in size & voicing for home use ) & so demand to be paired with a likeminded ( similarly sized ) hornloaded midrange below them ( ie; twin 515x in 210 or 817 cabinets / plus subs ) .

- I'd suggest ,getting some test gear & then learning how to make custom EQ compensation filters / assuming you want to keep DIYing .

[Steve71]

Once properly EQed, healthy 288-xKs are among the best sonically balanced drivers available . Your 288(s) may not be healthy ( they are afterall , about 25 years old ) .

- These drivers ( especially on Constant Directivety horns ) need EQ to be flat out to 13Khz . ( I'll assume you may like a relatively flat HF response / like most of the population does )

- I don't have any MRs horns here / so I can't comment on whether the horns are adequately damped or not ( they are aquaplas over a lightweight metal such as tin ) .

- These horns are relatively huge ( in size & voicing for home use ) & so demand to be paired with a likeminded ( similarly sized ) hornloaded midrange below them ( ie; twin 515x in 210 or 817 cabinets / plus subs ) .

- I'd suggest ,getting some test gear & then learning how to make custom EQ compensation filters / assuming you want to keep DIYing .

Thanks for all that valuable info Earl. Now I can't wait to get the new diaphragms. There is just soooo much to love about the 288/MR's. I'm very happy to hear that it's just the old diaphragms and not an inherent horn characteristic. On one hand I associated that familiar sound with horns from all the concerts I've been to, but on the other hand I remember going to the cinema in the late 70's as a child and loving the sound.

Matching the rest of the speaker is going to be a exercise in WAF management. I was hoping for a single 515 in a conical 80hz horn, but I haven't really looked into matching dispersion patterns at the crossover frequency. Horn subs are out until I finish the basement, so I'm not sure what I'll be going with. I'd like to play down into the mid teens for HT, but finding something that will work that low, but keep up with the horns (for home use) & fit in my room might be an exercise in futility.

I was planning to use a Beringer DEQX and tri amp everything. That way I can apply the necessary delays and eq.

Big plans, but still lots to learn. If these new diaphragms sound as good as everyone says, I be putting up my B&W's for sale ASAP.

[johnaec]

I was planning to use a Beringer DEQX and tri amp everything. That way I can apply the necessary delays and eq.

Careful! Don't get the Behringer DEQ series and the DEQX mixed up! The Behringer stuff is strictly entry level, while the DEQX products start at several thousand dollars, and are a whole different animal: http://www.deqx.com/

Many people have had a certain amount of success with some of the Behringer stuff, and it's certainly fun to play around with, but the DEQX products are substantially more refined and capable.

John

[Earl K]

Thanks for all that valuable info Earl. Now I can't wait to get the new diaphragms. There is just soooo much to love about the 288/MR's. I'm very happy to hear that it's just the old diaphragms and not an inherent horn characteristic. On one hand I associated that familiar sound with horns from all the concerts I've been to, but on the other hand I remember going to the cinema in the late 70's as a child and loving the sound.

- You're welcome, but ,,, it's still not determined that you need new diaphragms ( ie; you may just need to implement some EQ ) .

- You should test the (FR) response of your diaphragm/horn combo ( & compare against a known FR plot of a "healthy" specimen ) .

- Here's the on-axis response of a 288-8G on a large, 90° radial horn ( it's a bit "idealized" IMO ). Also in the pic , is the response of the same driver on a 2" Plane Wave test tube . The response of a driver on a Constant Directivety horn ( such as your large MR series ) should more closely resemble the response from the Plane Wave.


- Here's what a brand new, GPA manufactured, 288 diaphragm looks like when measured on a "pure" exponential type horn ( an Altec multicell in this case, 805 or 1005 / though I forget the exact model ) . Ignore the UHF "contamination" above 15K .
- Thanks to sfogg ( Shawn ) for this response plot .



- Here's what Shawns' old diaphragm measured like before replacement . Pretty awful , huh ?



- Since I've never listened to the 299 diaphragm ( with the harder "Pascalite" metal ) / I don't know what to suggest, if you need to buy replacements .

[Steve71]

Careful! Don't get the Behringer DEQ series and the DEQX mixed up! The Behringer stuff is strictly entry level, while the DEQX products start at several thousand dollars, and are a whole different animal: http://www.deqx.com/

Many people have had a certain amount of success with some of the Behringer stuff, and it's certainly fun to play around with, but the DEQX products are substantially more refined and capable.

John

Obviously I was either confused or in a hurry when I typed DEQ . What I mean to type was Behringer DCX2496 (three way digital crossover). Thanks for clearing that up.

[Steve71]

- You're welcome, but ,,, it's still not determined that you need new diaphragms ( ie; you may just need to implement some EQ ) .
- You should test the (FR) response of your diaphragm/horn combo ( & compare against a known FR plot of a "healthy" specimen ) .

Once again thanks for all that info Earl. Unfortunately I don't have any measuring equipment at the moment. I do have RoomEq software on my PC hooked up to my AVP via digital co-ax. Even just using the mouse to sweep through 500-15khz, I can hear that the output from 3K to 7K is up about 10db (double the perceived volume). However I don't seem to get as much roll off after 10K as the graph for the warn out diaphragm would suggest.

I really should get some measuring equipment to be sure... might try to track down a Radio Shack SPL meter.

[scott fitlin]

1. You hear the BEHRINGER through those Altec 288,s. Not really good enough for these drivers, IMO.

2. What amp are you using, and how much power does it produce?