Altec GPA 604-8H-III in MLTL (Bison) Cabinet

[Stevenarrow]

Hey yo,

So i have just finished and set up my new MLTL Bison cabinets with GPA 604-8H-III and crossover. They are not 'finished' but good enough for listening. The plans were provided by the original designer, and i committed to not sharing the dimension. The plans can be purchased.

The box is roughly 10.4 ft^3 (290 litres). They are big. The port is currently facing down. It is 6" in diameter and the legs are 6" tall.

The carpenter didn't follow my plan for bracing, so it is a little under braced at the minute. and I have not finalized the stuffing inside.

My apartment isn't great for hifi. The right side opens to a dining room and the left side is stuck in a corner.


My initial impressions are not great. There is a serious lack of bass. Much less than when the same drivers were in a smaller BR cabinet. I am able to compensate with EQ. However, I was hoping for more, and I am turning to this forum for help.

Is the down firing port the issue? should the legs be longer?
I can move the port to the rear and still be true to the design...
As i mentioned, the box is likely under braced and under damped. I am hoping to get a few measurements this weekend.





Thanks in advance.

 

[Stevenarrow]

 

[Olson_jr]

I have a pair of Altec GPA 604-8H-II in 9 ft^3 cabinets and I found the bass to be greatly improved when I removed the "stuffing" from one side wall and the top or bottom. So I have the back and either the top or bottom stuffed.

That being said, I assume that you have double checked, and then triple checked the polarity of the woofers. (Not that I have ever made that mistake, twice)

 

[TubeHiFiNut]

Paging @billfort @mhardy6647 @marantzfan @Fran604g and all of the other 604 Cognoscenti.

 

[marantzfan]

I agree with @Olson_jr, I had a very similar experience after damping all inside walls. When I removed exactly half, the sound improved dramatically, especially in the bass and mid bass.

 

[Audionut]

My interest is piqued since I am also considering down firing ports, with similar Herman Miller/JBL style legs (as one of my two designs). Forward firing I imagine gives the most bass effect. Your floors look to be hardwood so no issues with carpets muffling the bass. Rear firing if corner loaded.
That’s a good size diameter port, is it a raw opening or is there an adjustable or recessed channel/tube? Can you provide pics of the inside, back and bottom?

 

[shoshin]

My Bisons have bass that comes in strongly at ~25Hz or so; not weak. My build is a bit different (heavy cabinet, jute lining, and full bracing), crossovers are different, and the speaker is raised higher... but I don't expect these to be causing that much difference.

Bisons are designed for high-impedance (2 - 4 Ohm) drive and positioning close to the rear wall. Is that a lovely Leben amp you are using to drive the speakers: if this uses feedback the output impedance may be lower than ideal, which I would expect to cause tight, lean, slightly truncated bass. The speakers appear to be away from the wall which could affect extension and weight.

Yes, the port does not use a tube: cabinet thickness determines the frequency...

Cheers.

 

[mhardy6647]

Re: polarity.

If (if!) any of all y'all* have any significant plans to play DIY with loudspeakers in general, and in particular with vintage drivers (ahem, Altec and JBL, ahem) which 1) had interesting (and somewhat mercurial) polarity conventions and 2) may have been re-diaphragmed at some point with callous disregard to polarity conventions of the original driver -- I would, humbly, suggest investing a C-note in a set of these.

https://www.galaxyaudio.com/products/cpts

I know I've mentioned this before, and I apologize for sounding like a (ahem) broken record, but this seemed like a good time/excuse to mention it again.
____________
* How's that for grammar?

 

[Stevenarrow]

My Bisons have bass that comes in strongly at ~25Hz or so; not weak. My build is a bit different (heavy cabinet, jute lining, and full bracing), crossovers are different, and the speaker is raised higher... but I don't expect these to be causing that much difference.

Bisons are designed for high-impedance (2 - 4 Ohm) drive and positioning close to the rear wall. Is that a lovely Leben amp you are using to drive the speakers: if this uses feedback the output impedance may be lower than ideal, which I would expect to cause tight, lean, slightly truncated bass. The speakers appear to be away from the wall which could affect extension and weight.

Yes, the port does not use a tube: cabinet thickness determines the frequency...

Cheers.

Thanks all for the thoughts. And thanks @shoshin for the direct experience.Do you have photos or a build thread I can check out?

I will have some time this weekend to run through some other tests, checks and placement. A few hockey pucks will get me up an inch as well. I will be using the long weekend coming up to re brace and adjust the stuffing.

Yes, thats a Leben CS600. Currently using KT88s, but likely going to KT77/EL34s in the very near future.

 

[shoshin]

Pics that I thought might be helpful. Most of my pics are still attached to emails... if you are looking for something specific I'll hunt something down.



Those emails are dated late 2012 and early 2013: hard to believe the speakers are approaching 6 years of age. They are keepers.

Give me a yell if you think there is any thing I can help with.

 

[Audionut]

@shoshin a question as to the speaker cutout being off centered. I’ve seen this a few times on other builds and was wondering if this was by design? I like the beveled edges BTW and great looking setup!

 

[shoshin]

@shoshin a question as to the speaker cutout being off centered. I’ve seen this a few times on other builds and was wondering if this was by design? I like the beveled edges BTW and great looking setup!

Thanks for the kind words re the system! A few $$$ invested in it... but I love the way it sounds... and I enjoy the DIY/bespoke/crafty aspects of it.

Scott, the designer, provided the option of offsetting the driver according to some golden ratio; from the plans: "Offset drivers/mirror imaged pair will have diffraction effects spread-out and give more versatility in room positioning".

Oh, to answer the OP's original question: No, I don't think the issue is the bottom port (this is preferred, actually) and the legs are long enough. Your floor is carpeted - I wonder if this limits the bass propagation? Maybe try resting something non-absorbent under the speakers? If you can, move the speakers back close to the wall and experiment with cabinet lining. You could also try some resistance in series with the speaker to see if it makes a difference.

Edit: added question and suggestion regrading carpeted floor.

 

[Stevenarrow]

Been chatting with Scott a bit on this. Seems like I may be dying a death of a hundred cuts... positioning, cabinet bracing, lining, amp impedance... hardwood floors, so thats not the quick fix...

Pulling the cabs out a bit further has helped, and ensuring there are no record crates near the lower port has helped. Lower the amp impedance to 6 from 8, has helped. Im starting to hear it now. Next weekend is set a side for re-bracing, installing the XO inside and experiment with the lining.

Thanks for the help all.

 

[Stevenarrow]

D'Angleo - Brown Sugar (https://www.discogs.com/DAngelo-Brown-Sugar/release/7032080) shaking this place right now.

 

[shoshin]

Been chatting with Scott a bit on this. Seems like I may be dying a death of a hundred cuts... positioning, cabinet bracing, lining, amp impedance... hardwood floors, so thats not the quick fix...

Pulling the cabs out a bit further has helped, and ensuring there are no record crates near the lower port has helped. Lower the amp impedance to 6 from 8, has helped. Im starting to hear it now. Next weekend is set a side for re-bracing, installing the XO inside and experiment with the lining.

Thanks for the help all.

Glad you are getting it sorted. Scott is really a great guy and very helpful. Seeking his advice would have been my first move... I'll remember to ask more question in future, rather than diving in with solutions.

 

[shoshin]

Hi Steven,

Hope you don't mind me posting some pix of Bison bracing and lining used in my build. Lining is >10mm thick goat hair and jute, like United Bonded's Wunderfelt, applied to one side and rear only.

Not sure it will help you now, but might help someone in the future.

Back panel


Lower right-hand side


Driver bracing


Ludo being helpful

Cheers!

 

[Stevenarrow]

Nice. My bracing is a little more conventional: side to side, front to back and altec style stiffeners. Using 2" fibre glass top, side and back. Getting a little more bass than before. Positioning helped a lot.Working on a new set of legs/stands.

 

[shoshin]

Bracing is probably a bit overkill on mine. I've never really experimented with the lining - results have been okay... I may experiment in the future though.

Yes, positioning matters with these speakers - they are designed for wall-mounting and reasonably unobstructed airflow around the ports... though in any given situation, it pays to experiment if you are getting unacceptable results.

Sounds like you are getting it sorted.

 

[Stevenarrow]

Bracing is probably a bit overkill on mine. I've never really experimented with the lining - results have been okay... I may experiment in the future though.

Yes, positioning matters with these speakers - they are designed for wall-mounting and reasonably unobstructed airflow around the ports... though in any given situation, it pays to experiment if you are getting unacceptable results.

Sounds like you are getting it sorted.

Yeah, i have an asymmetrical set up at home, so one channel backs into the kitchen area. Not ideal. But bringing them out into the room helped for me.

 

[doglv]

Lots of good advice to try.

It was my experience that less stuffing was better then too much. Lots of theories on bracing but, again, my experience was- more was better.

Moving the speaker around should yield various results. The bottom port should be fine and preferred by many... including Shindo.

Not sure about your legs. Is it a suspended floor? One experiment is to put something super heavy on the bottom of the floor inside your speaker and see how it sounds. If the legs (verticle) aren't permanent and the floors are suspended I can show you pictures and describe my "base". I tried many scenarios and have a good and cheap diy one that I love.

Swapping the polarity around every-which way you can is worth the exercise.

I assume they are 8ohm drivers? Does your amp have multiple ohm leads/ taps? Have you tried a different amp?

I just plugged up a cheapo 8 watt 60 year old Heathkit amp to my 15" woofers and that little thing lit those woofers up like I've never heard before. Amp/speaker relationship are like marriages... they're either great or they suck, either way, there's a lot of mystery involved.