Using an Altec 3156 in an A7

[Fitts]

I was wondering if anyone could share with me their experiences or offer any recommendations on using an Altec 3156 in an A7 cabinet?

Thanks,

[Murray Keidge]

Hello Dave,
Yes, I have done it and sound does come out. What I found was that the sound quality was certainly not that of the 515-8GHP in the A7, however the 3156 does work.

I noticed that it "kicked" more suitably if you are using it for "rock & roll" and the 3156 is less likley to fail if being used at very high levels as compared to the 515-8GHP.

Of course, the heavier cone, voice-coil assembly, and stiffer spiders of the 3156 are the primary reasons as to the different performance.

My suggestion would be to get two A7's and fit one with the 515 and one with the 3156 and see which you prefer.

My preference is still the 515-8GHP for sonic performance, particulary when being used in critical listening situations.

However, it is your call in the end.

Murray.

[Jim D]

I have used 3156 in full front loaded and combination bass horns. They work pretty well in the large front loaded horns and as Murray says really impact. As for combination horns like the A-7 box, they do not work as well as either the 515 or 416. The 416 with it's lower damping often has better bass response than the 515. The 3156 really will whap you, but lacks the detail of the other two speakers in the mids. The 515-416 are underhung voice coil drivers and are therefore more articulate than the 3156, and yes Murray is right, the 3156 is much tougher. The old 515 has the most mid detail, the least bass. The 515 g has the next best mid detail with the 515-16g the best of them, the 8G has slightly more bass, the 8GHP is more like the 16G.. The 515B would be next, than the 416s and last the 3156. Jim

[ngccglp]

Sorry I have to revive this thread.

I changed my A7 (416-8B, 802, 511B, N501A) to A5 (515-16G, 288-16G, 1005, N500F). I am using the Unison Research S2K (uses pair of KT88s) which is rated at 15W.

I was not satisfied with the bass of the 515. Though I could hear better bass articulation, it does not go as loud and deep enough when compared to my 416-8B. Also, with the N500F set at max attenuation (-4dB), the 288 is still much louder than the 515, causing the sound to be bright.

Does this mean I need more power for the 515-16G? I was kinda dissappointed as I was expecting the 515 to pump out more bass with its 16 ohms rating.

Any advice? Thanks.

[GM]

Greets!

Actually, this should be a new thread IMO.

The 515 is primarily a midbass driver from a T/S specs POV and originally meant to be optimally driven with a matching output impedance (OPI) amp, which means its effective Qes doubles! With my measured 515Bs this equates to going from a T/S max flat alignment of ~2.49 ft^3/37.9 Hz Fb (little/no useful LF output) if driven with a typical vanishingly low OPI SS amp to ~20.19 ft^3/20.2 Hz Fb of room rattling organ music!!!

So from this it's apparent that when driven with a typical SS amp, it takes two 515Bs in ~20.19 ft^3/20.2 Hz Fb cabs to ~match them down low, with the benefit of its midband efficiency being doubled. Now you know why the various '40s designed VOT cabs have so much back chamber Vb and why blocking off the upper portion of the cab's rear chamber was recommended when the old tube systems were swapped for higher power, lower OPI SS.

WRT level matching the horns, all compression loaded drivers want to 'feel' a resistive load, so a non-inductive resistor in series with the HF horn is a good idea if not driven with a matching impedance amp, then adjust the level if needed via the XO. If no super tweeter is used, then a bypass cap is required to 'lift up' its HF response. This value is user dependent, so you'll have to experiment with different values using cheap ones and then replace it with an equivalent high SQ one (or combination of values to get it). PIO motor run caps is the way to go IMO since these are the closest modern day equivalent to the audio caps of yesteryear, but as always YMMV.

Anyway, back to the 'weak' 515........ I gather from the manufacturer's specs that the S2K has fairly low OPI, so adding some series R to it will cause Fb peaking, requiring the vent area to be reduced to one or more tube vents to flatten its in-room Fb to a lower frequency, which will require the HF horn to be further attenuated, with the trade-off being a loss of system dynamic headroom. It also means that you may not have enough amp DF or power to even use what's left since a goodly percentage of it is being burned off as heat from the resistor.

On a related note, I'm not very amp design literate, but it's my understanding that SE class A means no nfb (among other things), ergo since it has some its OPI can't be 4-8 ohms as listed AFAIK (IOW these are just nominal tap ratings), so I'm curious about this amp's specs and/or would appreciate some clarifications on the subject. For sure if the OPI were this high, then I don't see how you would be having the HF shelving problem and the cab would be hammering you with very 'boomy' midbass (at least by my standards).

BTW, the 16 ohm impedance just means that the amp won't need to provide as much current (IOW 'easy load'), which means the amp won't 'lay down' (hard clip if SS) as quick when it's called upon to provide mass quantities of it, though its voltage gain must be up to the task also.

GM

[ngccglp]

Thanks GM.

I tried to dig up the user manual on the amp but could not find any useful spec.

Now I have reverted to this combination: 416-8B, 288-16G, N501A, JBL 2405 tweeter (parallel to the 288). I don't know why, though the crossover is not meant for the 288, its the most pleasant and balance combination.

But I really wanted the N500F on the 288 and 515 to work as that is spec for the A5. In fact, my observation is consistent with your comment that the 515 is a mid bass driver. I could hear double bass notes clearly.

Is there any other things that I should experiment with?

[GM]

>Is there any other things that I should experiment with?
=====
Greets!

Yeah, jack it up about 6ft and slide something better suited for wide BW HI-FI apps in its place. I mean the 825 cab was designed to be used with baffle boards and an 800 Hz multi-cell in limited BW small cinema, auditorium, etc., apps driven with matching impedance amps, a far cry from its later A5, A7 variants.

Anyway, there's threads discussing various tweaks and I'm burned out on repeating them.

GM

[cclark65]

I use 3156 drivers in some 816 knockoff cabinets from 100 to 500hz. Gives me plenty of midbass.

[Jack6428-2]

I?m always interested when the topic comes up on which 15 incher to use in the 828/825 cabinets.

My basic setup is / will be:

- 802G driver on 12 inch square Mantaray or 311-60 horn for 5K Hz and up
- 290 driver on 311-90 horn for 300, 400, or 500 Hz to 5K Hz
- 15 incher for 80 or 90 Hz to the 300/400/500
- 3182 or 3184 for subs (separate cabinet)
- 4 way active crossover with 4 separate amps each channel or 3 way active crossover with the 802G and 290 in parallel with capacitor added in line before the 802G to only give 5k Hz and up to the 802G

Questions are:

1. What 15 incher to use? -- I have:
* 3156
* 515B
* 515 Hollywood (Gold Hollywood labels - not ?red, white and blue? but have never been told what the differences are if any. They are phenolic spyders and semi rigid surrounds - same as red, white, and blue. They were originally 20 ohms but were reconed to 16 ohms)
* 515GHP
* 421A, 421LF, 421HII, 3154 (I?m assuming these are not ideal)

2. What freq range to run the 15 inchers?

3. Crossover as 4-way or 3-way with extra cap. If 3-way with extra cap, what cap value?

Thanks - NG