Altec Malibu 843B upgrade advice? (same drivers as 9844 I think)

Hello,

I have a pair of Altec Malibu's with the die-cut wood grills. I drive them with McIntosh MC-30s, Scott 299-D, or misc. solid state.

Drivers are 806A and 414Z qty. 2.

They sound "good" except for one complaint, which if resolved, I think they would sound great.

Sounds in the frequency range of a snare drum typically don't sound right to me. The best comparison I can think of is when you clap your hands, there is a snap or a ring to it. If you were to clap with gloves on, that's what I think it sounds like today.

Maybe I should leave them alone and enjoy as-is? I actually really like the highs and the bass.

Upgrade options?

1. Add a tweeter and an external crossover, to let the horn handle just the midrange?
2. Use a 3-way crossover, and split the woofers somehow?
3. Would upgrading from the 806A to the GPA driver (is it a 902?) solve the problem for me?

I read a long thread on a 9844 project, and it made me dizzy. The lesson I learned is that there's more to designing a crossover than just the driver performance specs. You'd have to do the work of the original engineers and take into account the response characteristics from the cabinets etc. It's beyond me!

Whatever I do, I want to keep the efficiency high, I have a few old amps I want to try in the 3-15WPC channel range.

Any suggestions?

Thanks!

If they have the original crossovers, they may need a refresh. The caps in the crossovers tend to go bad with age, and replacing them can make a big difference.

Francis

Also, it occurred to me to point out that those are fairly directional speakers because of the vertically stacked woofers, and the horn. You'll need to be within the "sweet spot" to get the most out of them, probably within about +/-15 degrees of on-axis vertically.

Francis

Thanks for the suggestions, is anyone aware of a rebuild instruction thread on the N800F? I only know that they are "potted" which sounds discouraging... Is there a GPA or other vendor direct replacement?

I have the Malibu's in a pretty small room, sitting pretty close to horn height. Yes, the axis makes some difference, I think they sound best in my room with toe-in to intersect about 2 feet in front of me.

Sorry, never tried to get an N800F apart. I know people do it, but not the details. Never tried to buy a new one from GPA, either; give them a call.

Ears at horn height and toed-in like you described sounds good for listening.

Francis

Greetings TW from the left coast,

One other thing you might consider: inserting the 30904 eq/ attenuator between the X/O and the HF driver. (you'll have to recalculate for 16 Ohm) I used it in my diy 846b's an it makes a huge difference. I always liked the 9844, and actually preferred it to the 9845. What you have is a classic with that grill.

Quote:

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Originally Posted by Ed Kreamer

Greetings TW from the left coast,

One other thing you might consider: inserting the 30904 eq/ attenuator between the X/O and the HF driver. (you'll have to recalculate for 16 Ohm) I used it in my diy 846b's an it makes a huge difference. I always liked the 9844, and actually preferred it to the 9845. What you have is a classic with that grill.

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Thanks for the ideas! How would I go about the recalculation for 16 Ohm?

I spoke to Bill at GPA today who was really helpful. His theory about what I'm hearing is the "bump" in response from 800-4000Hz.

Upgrading to a 902 driver would expand the HF extension, but he didn't think it would cure the issue I am describing.

I bet the attenuator you are referencing addresses a similar issue.

One of Bill's suggestions was the Model 19, N1200 crossover, and I really liked that idea, giving me control over the MF response.

We figured out unfortunately that it's for an 8Ohm system, and I'm pretty sure my 414Zss and 806A's are all 16Ohm. How could I compensate for this?

If I could adjust components in that system it would be worth a try. I see posts that the parts for a DIY N800F are about $120, which might not help much anyway, and for the extra cost I could go N1200.

I remember that Altec used the N800F on 8Ohm and 16Ohm systems. Could I "get away with it" using an 8Ohm crossover system on my drivers?

If I should start a new thread about crossovers or in the DIY section let me know.

Thanks again!

The 30904 attenuator/EQ will attenuate the 800 - 4000Hz frequencies to match the horn response beyond 4000Hz. You would then use the horn adjustment of the N800F (bring the level up somewhat) to get the right horn level. To convert to 16 ohms, double the resistors and halve the capacitors in value. Using an 8 ohm crossover in a 16 ohm system typically won't work well.

Francis

I wanted to say thanks to all for the advice on the 30904. I have the schematics for what it would take to make this work for 16ohm but haven't got around to it.

The next step in the project is to use my Behringer crossover that has the "CD Horn" EQ in it, and test different crossover points from 800-1200. GPA thought that a 1200 crossover point might sound better as well on the 414Z. The end result is that once I find the right balance, I want to go back to a newly built passive crossover with an equivalent 30904 and a crossover point based on the testing results as detailed above.

The project is on hold until I figure out what bad thing I have done here:

http://www.audioheritage.org/vbullet...555#post412555

Thanks!

Hi TW-

When you add the 30904 circuit, be sure to build only the top section that concerns the HF horn, actually called 30923. The bottom half of the circuit is a Zobel network designed for different woofers.

The 16 ohm values for the 30923 section are:

C1 - 3uf
R1 - 7.8 ohms
R2 - 13 ohms

I added a Beyma CP21F horn slotted super tweeter to my Altec build with a simple 1st order crossover at 10kHz to augment the HF response. Best move I made besides adding the 30923. The HF response is no longer rolled off, and is nicely crisp and smooth.

GeeDeeEmm

GeeDeeEmm, this is great, thanks! Now that I've said "I have the schematics" I know I have the 30904 printed out somewhere, and I take it the top half of that is the same as 30923 (at 8ohms, before conversion to new values). I was going to disregard the LF side and that is confirmed now based on your advice, because I was not sure how the zobel would work with the two 414Z.

Did you do the lpad on your 30923?

The Beyma reminds me of the tweeter in the Jubal. How does the Beyma compare to say a Fostex T90A (besides the price) and how did you mount it?

If you are referring to inserting an L-pad in the R-2 position to vary the amount of midrange cut, yes I did do that. But, I found that the adjustment was not necessary for the sound balance that I was seeking, so I removed the L-pad and returned the circuit to stock. I love the way it sounds.

It's been many years since I've heard the Fostex T90, so I really can't do a fair comparison. I chose the Beyma slot tweeter based purely on the frequency response graph, which shows it having a very level plot extending all the way to 18kHz. Having used them, I have no reason to doubt that. I crossed them in first order at 10kHz, which is roughly where the 802D begins to roll off. I'm planning to experiment with lower frequencies later.

You can see these speakers in my avatar. The Beyma is mounted behind the grill cloth, just above the 416Z woofers.

GeeDeeEmm