[55 Tony]

Tony, you are correct. I recall hearing these referred to as a push-pull amplifier, where one tube amplifies the positive portion of the output wave and the other the negative portion.

The tri-five Wonderbars and pushbutton radios used this same circuit. (The main difference between them is the signal seeking portion of the Wonderbar.) The manual tune radios used but one tube to drive the speaker.

Some '57 pushbuttons (like the one in my '57) used a single transistor to drive the speaker. They also use an unusual group of tubes in the remainder of the circuit that use a plate voltage of 12 volts instead of roughly 100 volts. These radios are a single piece unit (instead of 2 piece) and do not require the mechanical vibrator tube and transformer. FWIW, I also have a '57 pushbutton radio that is all tubes in my stash of goodies.

As far as output power - 4.5 watts sticks in my mind, but I can't remember where I saw it. I might have that in a paper copy book on these radios.

Yes, it is a push pull design. 4.5 watts sounds about right. I was guessing comparing it to a 4 output tube amp that uses 6V6 tubes which are the same as the 12V6 except they use 6.3 volts for the filaments instead of 12v. The amp I'm comparing it to has two 6V6's parallel, 2 for push and 2 for pull (and a lot more). It's about 12 watt.
Problem with those early transistors is that they were made with germanium not silicon and they sometimes start to crackle and you hear a little static from it. The even degrade just sitting on a shelf, so a new one may be better or worse, If it's available.

 

[stoveboltgeek]

Yes, it is a push pull design. 4.5 watts sounds about right. I was guessing comparing it to a 4 output tube amp that uses 6V6 tubes which are the same as the 12V6 except they use 6.3 volts for the filaments instead of 12v. The amp I'm comparing it to has two 6V6's parallel, 2 for push and 2 for pull (and a lot more). It's about 12 watt.
Problem with those early transistors is that they were made with germanium not silicon and they sometimes start to crackle and you hear a little static from it. The even degrade just sitting on a shelf, so a new one may be better or worse, If it's available.

The transistor in my '57 radio was replaced somewhere along the line. Maybe it died, maybe somebody fried it - who knows.

Germanium is an odd material. When used as a diode, it has a much lower forward voltage drop than silicon (which is nice), but about an order of magnitude more reverse leakage current (not so nice).

 

[Robert Haas]

That is what I got from your statement above. I'm sure you can see how I got there.

I feel the need to respond to this point in case someone who didn't know a thing about stereos wandered across your post and took it the same way I read it, saying a 6x9 shouldn't even be an option as of course nobody goes out seeking poor quality sound. You're a respected member here, very knowledgeable on these cars, and I believe people hold your advice in a high regard. On this point however, you're off base.



What I mean by this is if we get in to an audiophile level discussion of the waves coming off a 6" round speaker vs. a 6x9" speaker, any distortion due to cone shape etc, that discussion is frankly irrelevant when the audio environment is this poor with subpar speaker placement and so many reflections. Of course this is the environment we have to work with, so we do the best we can. Car audio, like everything else, is full of compromises. Anyone building an audiophile stereo to the level to notice any minute difference in the distortion of waves between the 2 speaker shapes is not doing so in a 50s car interior.



Here's where you seem to have a misconception. The 6x9" has a larger cone area and is often just slightly more efficient. As a very important bonus, the larger cone area lets it hit significantly deeper bass notes which is a definite plus if a person is not planning to install a subwoofer to fill in the low end.

Let's look at popular reasonable budget speakers from Crutchfield, all coaxial/triaxial (without separate tweeters). I promise I haven't cherry-picked these examples after looking at the specs, I picked the speakers before looking at the specs. 2 of these speakers I own personally, one in 6.5" (but component), one in 6x9" (but triaxial), I have no strong preference either way, whatever fits the application.

How to use the data below:

dB - Sensitivity - A higher dB number means more efficiency (more measured sound per watt at 1m, except Morel).

Hz - Frequency range. look at the lower Hz number as an indicator of how low the speaker can go. I'm less concerned with the high end as long as it's over 20,000Hz or so as that's usually 'high enough' for most music and most people over 18 start to lose high frequency above 17,400Hz, above 12,000Hz by age 50.

Infinity Reference Series
6.5" Round Coaxial Infinity Reference REF-6532ex 93dB sensitivity, 57-21,000Hz range
6x9" Oval Coaxial Infinity Reference 6x9 REF-6532ex 94dB sensitivity 46-20,000Hz range

Morel Maximo
6" Round Morel Maximo Coax 6 - 91dB sensitivity 55-20,000Hz range
6x9" Oval Morel Maximo Coax 69 - 90dB sensitivity, 45-20000Hz range
(note: Morel measures sensitivity at 2.87v @ 1m, rather than 1w @ 1m)

Polk DB series
6.5" Round - Polk Audio DB 652 6.5" 92dB sensitivity, 40-22,000Hz range
6x9" Oval - Polk Audio DB 692 6x9" 93dB sensitivity, 30-22,000Hz range

Alpine S
6.5" Round - Alpine S-S65 88 dB sensitivity, 70-22,000Hz range
6x9"Oval Alpine S-S69 90dB sensitivity, 65-22,000Hz range

Alpine R
6.5" Round - Alpine R-S65.2 88 dB sensitivity, 65-40,000Hz range
6x9" Oval - Alpine R-S69.2 90dB sensitivity 60-40,000Hz range

Kicker CS
6.5" Round - Kicker 46CSC654 - 90dB sensitivity, 40-20,000Hz range
6x9" Oval (3 way) - Kicker 46CSC6934 - 92dB sensitivity, 30-20,000Hz range

Kicker KS
6" Round - Kicker 47KSC6504 - 90dB sensitivity, 43-21,000Hz range
6x9" Oval - Kicker 47KSC6904 - 92dB sensitivity, 30-21,000Hz range

Summary: All but one speaker has better sensitivity (efficiency) in the 6x9" size of the same model. Every 6x9 has significantly lower range, which will be crucial if someone is not planning on installing a subwoofer, as many owners of trifives seem to choose.

This is why I choose to strongly dispute your statement



Someone following your advice would end up with a less sensitive speaker that can't hit the low notes. That isn't efficiency or quality sound in my book.



Well, here I am still saying otherwise. After looking up and posting the data, I don't think I'm being ignorant, do you?

And I don't think it's pride or consumer regret as I have both sizes in my last 2 stereos. I actually spent significantly more on the build that has the round speakers so if I was going to be proud of one of my stereos, it would be that one. I have the Infinity Reference Series (but the 3-way) in 6x9" in my '55 (chosen for the fit, and that I won't be running a subwoofer) I also have the 6" Morel Maximo components in my pickup (chosen for excellent SQ, along with a 12" Sundown subwoofer @ 500w RMS to fill in the lows). I regret neither purchase, or wish I'd have bought either in the other size. Both are a good choice for their application.

I do always enjoy a good technical debate, especially with someone with some technical chops, so if you want to post up the data for a bunch of popular 6x9s that are grossly less efficient than their equivalent 6-6.5" round counterpart, or some data showing that despite hitting significantly more of the audible range, their sound quality is somehow worse, I'll gladly be proven wrong, always happy to learn something new.

Bottom line, you buy what fits the application, and avoid blanket statements like "do not even look at a 6x9 regardless of make or price".

Thank you Carson, a well thought out and detailed response with a substantial amount of research.

I read several of your sitings and the elephant in the room is the mechanics. The mechanical side of how and why a speaker works breaks down to a simple electro-magnet that moves a pliable cone. The materials of that cone dictate the performance and durability of the cone. A oval must move and in doing so must resist distorting its shape. The manufactures must therefore modify the vary design to resist it warping or moving at different velocities through out its "travel" these modifications become a liability. They add weight, and change rigidity in direct comparison with a round counterpart. I concede the range available will be larger as the cones total area has much to do with lower frequency response however to achieve those lower frequencies with higher amplitude the cone will move or "travel" a greater distance thus re-visiting the whole mechanical design issue I mentioned above.

Your point about applications and the consumer wanting to only use the available space allotted. This is a very important arena in terms of products available. Building a system with only a single speaker or a pair of same will be a compromise. The simple and easy choice is to drop in a speaker that sort of matches the factory hole and plug it in. The down side is that dropped in speaker will not have the lasting durability due exclusively to the points above about the physical obstacles it must overcome. Oval speakers fail sooner due to this one design obstacle. I will not call it a design flaw, it is designed and engineered to highest level but much of those specific resources are focused on bolstering a difficult engineering problem.

You make a great point that round speakers are for the most part designed to be used as components where individual frequencies are received by appropriate sized speakers and lower frequencies desired would need a sub woofer and you are not wrong. Yet even a top dollar state of the art oval speaker will not be able to deliver truly low frequencies. To do so would tax its design to failure. So it will need to be filtered or supplemented. Bypassing through a crossover will protect it, but that filter will introduce other less desirable anomalies as well.

A auto stereo system relying on just 2 speakers on the package shelf will perform just fine for a consumer just desiring a little sound (emphasis on LITTLE) Hiding a sub-woofer somewhere in the car allows the consumer to build a round speaker-ed component style system that will out perform and more importantly out live a compromised system using oval speakers. The sub-woofer market is booming with stealth category components. way, way back a long time ago speaker design laid out the 3 laws of design and they gave birth to the 3 way speakers seen in every audiophiles living room in the 1960's Those speakers all had a woofer, a mid range and a tweeter, all mounted in furniture grade cabinets and hooked up to amplifiers that would make a modern arc welder blush. The same people that grew up with those monsters in their homes designed the first 3 way speakers for cars where they put all three elements into a single speaker and the Triaxle speaker was born. Technology moves at a rapid pace, 60 years ago compared to today is practically impossible in most things, speakers included.

 

[55 Tony]

The transistor in my '57 radio was replaced somewhere along the line. Maybe it died, maybe somebody fried it - who knows.

Germanium is an odd material. When used as a diode, it has a much lower forward voltage drop than silicon (which is nice), but about an order of magnitude more reverse leakage current (not so nice).

Testing a Germanium diode is even weirder. With a multi meter diode test, they always show open both ways, but if I take a low voltage (but higher than the multi meter diode test voltage) LOW CURRENT power source it's a different story. I've used my Sencore capacitance tester set on 3 volts on the low current setting for small caps and check for leakage and it clearly conducts one way. Does the voltage drop increase when they get old? I know when they fail, they never short, only open. I didn't think of it till now, but with the load on it like I did, I can measure the voltage across it.

 

[vich57]

I never liked Germanium junction devices (diodes, transistors, etc.).
They have a 0.3v junction voltage instead of Silicon's 0.7v, but they fail much more easily.
Since Carbon is the next element above in the periodic table, I had thought that Carbon semiconductors could be nearly indestructible and run much hotter without issue.
But since Carbon electrons are in a tighter orbit, Carbon would have to be heated way too much to make it work.

 

[Carson Blocks]

@Robert Haas

I feel like you're moving the goal posts here, Robert.
First it was the sound quality of 6x9s that was unacceptable which I think I debunked as a non-issue in any reasonable automotive application.
Then it was the efficiency was too low, which turned out to be exactly the opposite of what you stated.
Now it's durability, nevermind that any reasonably modern, decent quality automotive speaker regardless of size lasts quite well under normal use and that most failures are due to voice coil abuse or the foam surround failing due to heat and UV damage (especially in a rear deck location) and not actually failures of the cone due to being flexed due to an oval shape.

Please feel free to actually post some evidence that modern 6x9 speakers suffer from a significant cone durability problem when not abused outside of their operating envelope.

The whole 6x9 vs round sound thing is an "audiophile" old wives tale and you're not the first guy to get caught up in it. I believe the origin is that a possible minute difference in edge cases is theorized, and it sounds good to a logical engineering-minded individual, so well-meaning people start repeating it as if it's gospel as we can all fall in to the "well, technically..." trap and neglect to consider what the actual difference may be in a practical application, which is really why most of us buy speakers, right?

It gets asked and debunked often on popular car audio sites, here's the write-up people usually link to in order to debunk the myth, written by a guy whose knowledge eclipses mine by a fair amount, but I understand the gist of what he's saying. Myth: Oval/"odd" shaped speakers can't...

Maybe back in the old days (50s-?) of poor quality paper cone speakers, they might not have sounded as good as their round counterparts or lasted as long, I wasn't around to hear those when they were new. I only started dabbling in the car audio hobby in the late 90s. Nowadays they're the best choice rear deck speaker for people who don't want to run a sub, due to the significantly lower range.

 

[55 Rescue Dog]

Back in time, having a speaker in the dash, and one 6x9 speaker with a reverb/fader in the rear was awesome! An 8-track was a huge plus too. Of course, with no air and the windows down, it sounded better going slow, or the best when parked by a lake...
I actually think the sounds my stripped-down 55 makes all by itself, is a mechanical symphony!!!

 

[delray_fan]

I think I’ve now learned way too much about car stereo systems…..My car came with the radio delete and I like leaving it stock. So don’t laugh but my very utilitarian stereo system is Bluetooth speaker that fits in my cup holder which I can remove when I get to a show.👍

 

[geoffcb]

In my '57 sedan I have 6" x 9" 2 way speakers towards the outer part of the parcel (package?) shelf. We used this size years ago as it was the biggest speaker for bass response that you could fit in a compact area. But nowadays I cut off frequencies below 60Hz anyhow, which are routed to the subs. If I was starting again, I'd use good quality 6" speakers to match the fronts that are in the kick panel area - those subs behind my rear seat do all the low end work. But I'm stuck with this size unless it's modified. Some other points:

* I always thought that a properly tightly attached speaker frame will reinforce the larger holes to some degree?

* I have a hi-fi tube amp (we call them valves!) at home, which sounds great due to low third harmonic distortion, but you wouldn't want it in a car! Too much power consumption, heat and fragility! My Pioneer uses MOSFET output and sounds fine. My sub amp is probably Class D and is very efficient and powerful. No, I don't go doof doof doof!

* If only our dashes could take 2 DIN sized AV head units...

Geoff

 

[johnonetrillion]

So don’t laugh but my very utilitarian stereo system is Bluetooth speaker that fits in my cup holder which I can remove when I get to a show.👍

The forerunner to my current Bluetooth set-up was exactly this: a portable Bluetooth speaker that my sons had hanging from the coat hook in the rear … as we drove our road trip most of the way down the US west coast: Seattle > LA > Temecula > Long Beach. I remember the day we left Santa Cruz headed to Monterey … stinking hot day with strong westerly winds – with Jimi Hendrix Live in Monterey (of course) blasting. A great few hours!

 

[Shadetree55]

So, we have two men who are clearly intelligent, strong personalities, and well-versed in their facts, but have opposing viewpoints. They debate the topic by presenting their facts - and without getting nasty.

I would say they're behaving like gentlemen, in the classic sense of the word.

(Note that I've stayed out of that portion of the discussion, as I have nothing of value to contribute. Fact is - if I'm driving somewhere and the radio is on, it's because my wife turned it on. I can tell a good-sounding stereo from a crappy one, but that's about the extent of it.)

me either---this will be me when I get my 55 back together

 

[55_2_drive]

Back in time, having a speaker in the dash, and one 6x9 speaker with a reverb/fader in the rear was awesome! An 8-track was a huge plus too. Of course, with no air and the windows down, it sounded better going slow, or the best when parked by a lake...
I actually think the sounds my stripped-down 55 makes all by itself, is a mechanical symphony!!!

I will agree with you there: among the most beautiful sounds in life is the roar of a V8 at full throttle. Even better if it's supercharged.

 

[upsrod]

I think I’ve now learned way too much about car stereo systems…..My car came with the radio delete and I like leaving it stock. So don’t laugh but my very utilitarian stereo system is Bluetooth speaker that fits in my cup holder which I can remove when I get to a show.👍

View attachment 366126

I think I’ve now learned way too much about car stereo systems…..My car came with the radio delete and I like leaving it stock. So don’t laugh but my very utilitarian stereo system is Bluetooth speaker that fits in my cup holder which I can remove when I get to a show.👍

View attachment 366126

Every Tri-Five was a radio delete car, the dealer installed the chosen radio!

 

[KENTON]

I've done way too much drag racing & beating on tin to even know what song is playing, lol.