Proud new owner of Altec Duplex speakers 604s and 605s

[300man]

OK so I am a little further along with my plans for the 604s. I have talked the project over with a friend who is a accomplished carpenter and cabinet builder. He is recommending 3/4in 12 ply apple or cherry plywood that he can get for about $100.00 a sheet. Due to space constraints in my listening room, I am leaning towards a slightly larger than original (just over 9 cubic feet) Stonehenge III type cabinet.
The project will start 2nd week of Sept.
I am considering using a power amp in the 80W per channel range. Would like to hear opinions on what would be considered the minimum power required to properly drive these speakers. FWIW my listening space is smallish at one end of the living room, it's about 10 X 12 .

 

[rromeo]

I run my 604-8g with a 45 SET amp about 1.75 watts. Works great. Have run them with 70 watt tube amp and prefer the 1.75 watts. I do run a sub with them.

 

[300man]

So we wound up going with 3/4 Cherry Plywood and the build has started. Received most of the XO components (some back ordered) to build the Markwart Cossovers. Found some MIL Spec. 14 gauge silver plated 12 strand copper wire for internal connections of the XO to speaker. Picked up some gold plated binding posts for speaker wire terminals.

OD of cabinets will be 49H X 22 1/2W X 18D.

I'll try to post up some pictures as the build takes shape.

 

[jaaronb]

I’d love to see pics. I’ve currently got my 604-8g’s in little Altec 614 boxes. Still haven’t gotten to hear them in an appropriately sized enclosure.

I started another thread a few days ago about doing an RTA on my 604s, which have a noticeable volume imbalance that persists despite changing diaphragms, crossovers, room position, source, amplifiers etc.

My 604s have different phase plugs - one with Tangerine, one with the older circumferential. They’ve been remagged and gone over by GPA.

Altec experts: Is there anything else - aside from the different phase plugs - that could be causing a 2-4 dB volume differential between the two? It’s driving me crazy!

 

[bowtie427ss]

2-4 db volume differential is wavering on the threshold of human hearing acuity, i'm going to assume you;re at least using an SPL meter or app to make this determination.

Where is the imbalance, above or below XO?

Do they both have the same cone/voice coil assemblies?

What are the numbers stamped on the backs of the cones?

After getting them back from GPA, did you verify the magnetic polarity?

Actual acoustic measurements will eliminate expectation bias and placebo effect.

My first inclination is expectation bias. Since you have been in them and determined that the phase plugs are of different construction, you likely have an expectation bias that they will sound different.

 

[jaaronb]

2-4 db volume differential is wavering on the threshold of human hearing acuity, i'm going to assume you;re at least using an SPL meter or app to make this determination.

Where is the imbalance, above or below XO?

Do they both have the same cone/voice coil assemblies?

What are the numbers stamped on the backs of the cones?

After getting them back from GPA, did you verify the magnetic polarity?

Actual acoustic measurements will eliminate expectation bias and placebo effect.

My first inclination is expectation bias. Since you have been in them and determined that the phase plugs are of different construction, you likely have an expectation bias that they will sound different.

I have taken some quick measurements, and found an overall ~2db imbalance. I suspect that the imbalance is more like 4-6db at the frequencies where it's most pronounced, because it's easy to hear...it throws off the stereo image, and there is less information presented by the driver with the Tangerine plug. I have tried to defeat expectation bias by moving the speakers to different positions, and by not taking note of which (tangerine vs. circumferential) is on left vs. right. I've only marked the back of the boxes to know which speaker is which...the 'quieter' driver always winds up being the Tangerine'd one.

I'm going to do some better measuring this week if I can get to it. I'm just guessing, but it sounds to me like the imbalance is somewhere around ~2k-8k. I'm using the Markwart phase corrected crossovers for the 604-8g.

I didn't verify the magnetic polarity of the drivers - what's the best way to do this?

Both of my 604s were reconed by GPA before I got them, so I presume they have the same cone/voice coil assemblies. Their serial #s are 12493 and 13641.

I guess I'm having a hard time believing the imbalance I'm hearing is totally due to the different phase plugs...but I don't know what else could be causing it.

 

[toddalin]

I guess I'm having a hard time believing the imbalance I'm hearing is totally due to the different phase plugs...but I don't know what else could be causing it.

Your logic is sound. Sounds like your only alternative is to find either of the matching phase plugs (preferably the one you prefer) and try it out in the "other" driver. I've done enough work/experimentation to know that the shape and coverage of any type diaphragm can certainly create the changes you note and do believe that a phase plug is capable of such changes.

Does the 806A use the same circumferential plug? There is one on the "bay" for parts at $10 (+$14 shipping). The Mods don't allow me to list the link so look for "Altec 806A driver parts". Only 1 day left, so if this would work, you better move on it.

 

[bowtie427ss]

I didn't verify the magnetic polarity of the drivers - what's the best way to do this?

Since the difference doesn't appear in the LF it is probably moot point.

Recharging alnico magnets is a two step process. The gausser is first set to the opposite polarity of the driver and used to fully magnetically discharge it. Then, the magnets and gaps cleaned/prepped to accept a new charge. If the operator does not reverse the polarity of the gausser after discharging the magnets, it will apply the new charge at opposite polarity. It's not common, but it does happen. A note with 604s, the HF and LF magnet are energized at the same time, and relative to each other their direction of charge will always be the same.

A 1.5 volt battery connected to the LF terminals will visually move the cone forward or backward. With the + terminal of the battery connected to the + terminal of the LF, the cone should move outward.

but it sounds to me like the imbalance is somewhere around ~2k-8k.

Particularly in the low end of that range is where i find tangerines sound different from the annular slit design. Note that Altec didn't drive tangerine equipped small format drivers below 1200hz.

I'm getting the impression that your hearing is particularly acute in that range, and you are detecting a difference that is more subtle to the average ear. Perhaps your room and source material are also playing a role in making the anomaly stand out to you.

 

[jaaronb]

Since the difference doesn't appear in the LF it is probably moot point.

Recharging alnico magnets is a two step process. The gausser is first set to the opposite polarity of the driver and used to fully magnetically discharge it. Then, the magnets and gaps cleaned/prepped to accept a new charge. If the operator does not reverse the polarity of the gausser after discharging the magnets, it will apply the new charge at opposite polarity. It's not common, but it does happen. A note with 604s, the HF and LF magnet are energized at the same time, and relative to each other their direction of charge will always be the same.

A 1.5 volt battery connected to the LF terminals will visually move the cone forward or backward. With the + terminal of the battery connected to the + terminal of the LF, the cone should move outward.

Particularly in the low end of that range is where i find tangerines sound different from the annular slit design. Note that Altec didn't drive tangerine equipped small format drivers below 1200hz.

I'm getting the impression that your hearing is particularly acute in that range, and you are detecting a difference that is more subtle to the average ear. Perhaps your room and source material are also playing a role in making the anomaly stand out to you.

Thanks for this info Bowtie - very helpful. I took some quick measurements this morning using an iPhone RTA app. I took them from right at the horns, and realize I should've probably done it from 1-3 feet out. Still, pretty clear what's going on here and what I've been hearing. The question is how much of this is due to the phase plugs vs. other stuff.

Check it out:



If the differences here are due to the phase plugs, it looks like a pretty compelling case for the superiority of the radial/Tangerine type.

 

[toddalin]

Thanks for this info Bowtie - very helpful. I took some quick measurements this morning using an iPhone RTA app. I took them from right at the horns, and realize I should've probably done it from 1-3 feet out. Still, pretty clear what's going on here and what I've been hearing. The question is how much of this is due to the phase plugs vs. other stuff.

Check it out:

View attachment 1410109View attachment 1410110

If the differences here are due to the phase plugs, it looks like a pretty compelling case for the superiority of the radial/Tangerine type.

This is the kind of thing that would be expected. You said that you preferred the "circum" phase plug, and this is understandable because it puts more energy up above the crossover point and you perceive this as a nice, bright "air." Again, the ear perceives louder as "better," even if it is not the case.

If these were crossed over at 500 Hz, you would turn them down to keep them from being too bright/peaky (and fatiguing) also further "lowering" the dip, and more perceive the dip and the speaker would sound "dull" or muffled in the midrange.

BTW, this is almost exactly the same thing that happens with the Heils and the very reason I developed the "Heil Wedgie" to go in front of the diaphragm.

 

[300man]

So my buddy the cabinet builder is well on his way to building a couple of beauties!

I went over to his shop today to see and get the latest progress report. WOW they look BIG. I thought i had my brain wrapped around what they would look like in person. I was wrong...I walked in to a small office and both cabinets were there in all there glory. I thought they were up on stands like maybe milk crates then realized they were on the floor! They are pretty much small phone booths, which is not a bad thing.

We front loaded one of the 604s and snugged in down, so we could mark the mounting position for a magnet support brace. We also fit and determined the location for a support brace below the speaker and port. About 2 inches below the cabinet midline.

The bad thing is I did not bring my camera! But the next time I visit there will be pictures that I will post here.

I am still waiting on the last of the crossover components which should be delivered tomorrow.

 

[carpe-diem]

Love to see some pictures of the new cab.

 

[300man]

Love to see some pictures of the new cab.

I will be taking pictures and hope to do this by Sunday or sooner. Both JM simplified crossovers are well on the way to being completed.

 

[300man]

Here are some pictures I took with my phone.

 

[300man]

Some more pics of the completed crossovers. Just waiting for the final finishing work on the cabinets. Should be loading and wiring in everything soon!

 

[300man]

Got the cabinets this evening! Insulated them and front loaded the 604s. Took a couple of pictures with my phone, but will take proper pictures once I compete them. The plan is to wire them up and do a bit of testing tomorrow!

 

[toddalin]

Purty!

Will they get grills?

 

[300man]

Thanks Todd,

Yes the cabinet maker made custom full length frames. I just have to choose material and apply it.

So i worked nonstop on the speakers and had them playing last night. Today i was moving them around and playing different types of music. Added a bit more insulation...had what i thought was a slight hollow sound. It's amazing that small tweaks can make such a difference when you go in the right direction...or wrong lol.

Still a work in progress but i will say that strings, percussion, voices and horns sound excellent.

 

[300man]

Here are some better pictures taken with a real camera. The Altecs are starting to smooth out more ( about 5 hours of play time now) and they have some milage on them...I have re-positioned them well over a dozen times. The nice part about there location is i can rotate them 180 Deg and with a little more wiggling they face a room with more casual furnishings.

 

[rromeo]

Nice! I am considering getting some similar cabs built. Do you mind if I ask how much it cost to have them made? You can PM if you like.