Omnidirectional Quad Speakers

[barfle]

Damping factor is important with woofers not so much tweeters and midranges. Most crossover networks employ resistors as well. I bi-amp which helps matters especially with damping of the woofers.

Edit: I don't believe (but might be wrong) that there is any problem/penalty when identical speakers are connected in series. Their impedances exactly match, there should be no difference between that and having a single speaker of double the impedance connected. Also the amplifier should be able to better damp a higher impedance load.

I have biamped studio monitors across the front (Emotiva Stealth 8s) partly because they are biamped and have no high-level crossovers. There is less than a foot of wire between the output transistors and the voice coils. Anything that decouples the voice coil from the low impedance output of the amp will affect the damping of the speaker. Of course, there are a handful of systems around that measure the cone movement and send a feedback signal to the amp to overcome those losses. Seems impractical, even today. I occasionally see speaker systems with some sort of feedback loop, but they never seem to take off.

The damping factor, I’m sure you know, is the ratio of the voice coil impedance to the impedance presented to it. If there’s an identical voice coil in series with it, the damping factor can not even be 1.

Again, I suspect I could not hear it. Can anyone?

 

[ar surround]

rear speakers are the only place for omnis and work in extended stereo and of course in surround.

https://cdn2.imagearchive.com/quadraphonicquad/data/attach/40/40719-conn-r.jpg

I can see that. Given the shape of the human ear, sounds from the rear are perceived differently than those from the front.

For example, when I make 5.1 remixes from demixed stereo, I can put a signal (say massed strings) in the left rear, and then duplicate it in the right rear with a good amount of reverb. The ears perceive the resultant sound as massed strings spread across the rear sound stage.

However, if I put that signal in the fronts, the ears hear it coming from the front left with reverb in the front right. Psychoacoustics are fascinating.

 

[par4ken]

The damping factor, I’m sure you know, is the ratio of the voice coil impedance to the impedance presented to it. If there’s an identical voice coil in series with it, the damping factor can not even be 1.

Two voice coils in series will act as a single one, the same current through each and the voltage halved. No difference than having a single cone of double the impedance. In my case with four drivers series and parallel connected the load seen by the amplifier is the same as having a single driver. The "speaker" impedance as seen by the amplifier is the same as with a single speaker.

The output impedance of a perfect amplifier is zero. I don't see where you get a damping factor of less than one. I think that you are looking at it all wrong. The second voice coil is an active part of the speaker system, it adds to the impedance of the speaker not to the output impedance of the amplifier.

In any case I agree that it is mainly a problem with woofers, not really an issue at all with higher frequency drivers. All my woofers are bi-amped and the two in each cabinet are parallel connected.

 

[jimfisheye]

I had a friend who had just bought a pair of 901s, and I have to admit, it was probably the worst effect I’ve ever heard a functioning speaker have on a stereo image. Maybe some of those old Phil Spector “wall of sound” mono 45s would be OK, but IMNSHO, those were awful.

I believe he liked them, but I sure didn’t. To each his own, in that case.

It definitely turned me off speakers that tried too hard to not be point sources. I don’t know if those spherical “omni” speakers would have a similar effect. Probably interesting, but not worth the investment to me.

I want to say it goes something like this.
There was (and still is) a lot of creative license with home audio. That is... A lot of ideas do sound interesting/good/compelling but they don't necessarily sound like an accurate reproduction of the source. Especially in the past, it was considered SOP that the hi-fi let you adjust to taste with a few EQ controls at least. So Bose took that to another place and added room reflection generation that was not ever considered or recorded and mixed into the music. Using the listeners room to generate ambience. Perhaps thinking a dry studio recording might shine that way. Probably had some examples that sounded cool. Going for accuracy is much more a zero to 100 thing. I don't mean to call something that sounds good to someone wrong. Just that accurate reproduction is more unforgiving.

Obligatory...
"No highs, no lows? Must be Bose!"
"Bose! Better Off with Something Else!"

 

[barfle]

Two voice coils in series will act as a single one, the same current through each and the voltage halved. No difference than having a single cone of double the impedance. In my case with four drivers series and parallel connected the load seen by the amplifier is the same as having a single driver. The "speaker" impedance as seen by the amplifier is the same as with a single speaker.

The output impedance of a perfect amplifier is zero. I don't see where you get a damping factor of less than one. I think that you are looking at it all wrong. The second voice coil is an active part of the speaker system, it adds to the impedance of the speaker not to the output impedance of the amplifier.

In any case I agree that it is mainly a problem with woofers, not really an issue at all with higher frequency drivers. All my woofers are bi-amped and the two in each cabinet are parallel connected.

Yes, assuming all four drivers in a series/parallel setup are equal in equal environments, the amplifier would see a single load. But each speaker would have isolation from the amplifier by its series companion.

A damping factor of less than one would happen with an impedance equal to the driver being in series with the driver. The driver would see both the added impedance plus whatever impedance the amplifier had. Assuming the driver is 8Ω with an equal impedance in series with it (as perhaps by an identical driver), plus the impedance of the amplifier (let's just say it's 0.1Ω for argument's sake, then the damping factor for that driver would be 8/8.1, which is approximately 0.988.

Now, two voice coils in parallel will both see the amplifier's output identically, although with the current being shared, that would effectively halve the damping factor.

Again, I doubt if I could hear the difference.

 

[barfle]

I want to say it goes something like this.
There was (and still is) a lot of creative license with home audio. That is... A lot of ideas do sound interesting/good/compelling but they don't necessarily sound like an accurate reproduction of the source. Especially in the past, it was considered SOP that the hi-fi let you adjust to taste with a few EQ controls at least. So Bose took that to another place and added room reflection generation that was not ever considered or recorded and mixed into the music. Using the listeners room to generate ambience. Perhaps thinking a dry studio recording might shine that way. Probably had some examples that sounded cool. Going for accuracy is much more a zero to 100 thing. I don't mean to call something that sounds good to someone wrong. Just that accurate reproduction is more unforgiving.

Obligatory...
"No highs, no lows? Must be Bose!"
"Bose! Better Off with Something Else!"

Bose is interesting. I have a pair of their noise-cancelling headphones that I've owned for about ten years. That's a lot longer than any other noise-cancelling headphones, and they're still great. We also have a wave radio/CD changer that we inherited from my dad. It sounds pretty good, although I'd guess that measurements would show me plenty of deficiencies. It's actually in my wife's den, and she's not much of a music listener.

I only heard the 901s that one time, and I was really disappointed with what I heard. He had them set up reasonably correctly, so I'm pretty sure I heard what Bose intended. As I noted, I believe the owner liked what he heard. I didn't, but it wasn't my system. IMNSHO, a failed experiment. Worthy of trying, but just not something I would spend the few dollars I had at the time on.

I've had three sets of "main" speakers over the years. I had a pair of Pioneers that I bought in the Army on an E-4's pay that I sold to my girlfriend (later wife) when I was able to get the engineering prototypes of a University (Altec) E-8. I still have them, but when I found out about the Emotiva Stealth-8, I bought three of them, since the old Universities never went into production and a third unit was impossible. I have the only ones ever built. Somehow the surrounds are still good after 50 years, even if the capacitors in the crossovers have died, as did the foam grilles (now cloth).

 

[par4ken]

Yes, assuming all four drivers in a series/parallel setup are equal in equal environments, the amplifier would see a single load. But each speaker would have isolation from the amplifier by its series companion.

A damping factor of less than one would happen with an impedance equal to the driver being in series with the driver. The driver would see both the added impedance plus whatever impedance the amplifier had. Assuming the driver is 8Ω with an equal impedance in series with it (as perhaps by an identical driver), plus the impedance of the amplifier (let's just say it's 0.1Ω for argument's sake, then the damping factor for that driver would be 8/8.1, which is approximately 0.988.

Now, two voice coils in parallel will both see the amplifier's output identically, although with the current being shared, that would effectively halve the damping factor.

Again, I doubt if I could hear the difference.

Back EMF generated by either speaker appears across the two outside terminals of the series connected pair and is controlled by the amplifiers low output impedance. The same as with a single speaker.

Only if the two series connected speakers were different from one another could there be any ill effects. Because the series connected pair has a higher impedance than a signal speaker I would argue that the damping would actually be greater.

Quite frankly I think that you are over analyzing things. The "speaker" consists of all the connected drivers, it is not like the impedance of one series connected element is simply increasing the driving impedance of the amplifier. The amplifier doesn't know how many speakers are connected just the total impedance that it sees. The separate drivers are just a part of that load. With all drivers being equal all is balanced and all is well.

Even if your analyses is correct I do agree with your statement "Again, I doubt if I could hear the difference.".

 

[LuvMyQuad]

I only heard the 901s that one time, and I was really disappointed with what I heard. He had them set up reasonably correctly, so I'm pretty sure I heard what Bose intended. As I noted, I believe the owner liked what he heard. I didn't, but it wasn't my system. IMNSHO, a failed experiment. Worthy of trying, but just not something I would spend the few dollars I had at the time on.

I owned a set of 901 series 3 in my late teens - early 20s. When I eventually upgraded i took them into a dealer and A/B'd them against a pair of Dahlquist DQ-10s. The difference was pretty shocking. The high end was just not there with the Bose. Like a heavy handed treble control was switched in. So much so, i had to check to be sure the EQ module was in the circuit properly. Without the EQ module switched in, the sound was beyond dull. Prior to this I never considered the high end to be lacking, but i really didnt have anything to compare it to. I believe a big part of the discrepency was the difference in room treatments between my listening room and the dealers room. Mine was untreated with a reasonably reflective rear wall. The dealer had a treated room with some adsorbing treatment on the rear wall.

I ended up buying the Dahlquists.

 

[multi_est]

Sugden made more than just turntables then! Connoisseur was the best bang for the buck back in the day!

it was the so called Yorkshire triangle.
Some of the stuff is still up there way beyond anything produced now.
eg.
I use Calrec microphones for recording, and occasionally for calibration. .it was originally part of the Calrec studio line up with their mixing desks, a competitor to Neve, and who's mics were involved in the Ambisonic B tests with Gerzon, and of course the soundfield mics.

The calrec mics we use were a BBC favourite for many years, but became hard to service.

After a good deal of excellent results they turn out to be as good and highly regarded today as the old and superb Neumann KM83 range. BELOW.
When I compare directly with my (now obsolete) Neumann KM100 series, they are actually better but more noisy.

When I lined up the Calrec mic against my Neumanns, the traces were nigh on identical without the LF roll off of the Neumann A remarkable performance for a cardio.

Idem many of the large ALLAN speaker drivers.
The 10" + TC and the "SUPER" range with the huge magnets compare well with top of the range moderns.
Problem was ALLAN fitted them in smallish cabinets. (I have a pair of their restored flamencos for home cinema).

What such large drivers need are giant size cabs.

I use a pair of the cambric "supers" in each of my monster 235L b-r cabinets. 1 x 12" and 1 x 15", and the old CG8T cambric dual cones in the mid range arrays.

The CG8T was reckoned to be way better than the Coral betas which the Jap audio freaks wanted for full rangers, but suffer from melting if over powered.
That works great filtering off the bass and used for mid range.

fyi. Below the use of multiple paralleled smaller drivers causes no image problems, but it may be hard to have a cabinet that size which works.
Frequency response is after all proportional to total cone area.

With my dual 12+15 setup, and the giant magnets they are very sensitive.
I drive them with a pair of large Bogen industrial valve amps which are rated to 100W per channel.
It's the only system I know of able to reproduce live organ music properly.

 

[multi_est]

I have biamped studio monitors across the front (Emotiva Stealth 8s) partly because they are biamped and have no high-level crossovers. There is less than a foot of wire between the output transistors and the voice coils. Anything that decouples the voice coil from the low impedance output of the amp will affect the damping of the speaker. Of course, there are a handful of systems around that measure the cone movement and send a feedback signal to the amp to overcome those losses. Seems impractical, even today. I occasionally see speaker systems with some sort of feedback loop, but they never seem to take off.

The damping factor, I’m sure you know, is the ratio of the voice coil impedance to the impedance presented to it. If there’s an identical voice coil in series with it, the damping factor can not even be 1.

Again, I suspect I could not hear it. Can anyone?

errr..........look up CURENT DRIVE.
You will see damping factor is largely irrelevant especially as speaker impedances go all over the show over the entire frequency range.
(It's why I use an array for each band with a multi cored complete tri wired harness,- 1 pair for each band, using difference transformer secondary windings for each one.)

If you do studio style traces on scope etc to measure what's going into the amp then compare it with what is present at the speaker terminals then compare it with what measurement mics can see, you would be quite shocked most of the time.

It's why I always measure amplifier response, especially valve amps into first a pure resistive load then how it actually behaves when faced with a speaker inductive load, then bang IMD tests thru them all.
The differences are often quite flagrant.

 

[barfle]

I owned a set of 901 series 3 in my late teens - early 20s. When I eventually upgraded i took them into a dealer and A/B'd them against a pair of Dahlquist DQ-10s. The difference was pretty shocking. The high end was just not there with the Bose. Like a heavy handed treble control was switched in. So much so, i had to check to be sure the EQ module was in the circuit properly. Without the EQ module switched in, the sound was beyond dull. Prior to this I never considered the high end to be lacking, but i really didnt have anything to compare it to. I believe a big part of the discrepency was the difference in room treatments between my listening room and the dealers room. Mine was untreated with a reasonably reflective rear wall. The dealer had a treated room with some adsorbing treatment on the rear wall.

I ended up buying the Dahlquists.

It was over 50 years ago, so the details of the room have been lost to me, but I doubt he had much room treatment. 1971 or so wasn’t exactly the era of figuring out room nodes in apartments (at least I think it was an apartment). I’m pretty sure the front wall had some posters on it over (probably) 1/2” drywall.

I just felt the stereo imaging was so terribly messed up that I really didn’t notice if they had any highs (or lows), and my audio sophistication was pretty typical of a 23-year-old at the time.

 

[barfle]

errr..........look up CURENT DRIVE.
You will see damping factor is largely irrelevant especially as speaker impedances go all over the show over the entire frequency range.
(It's why I use an array for each band with a multi cored complete tri wired harness,- 1 pair for each band, using difference transformer secondary windings for each one.)

If you do studio style traces on scope etc to measure what's going into the amp then compare it with what is present at the speaker terminals then compare it with what measurement mics can see, you would be quite shocked most of the time.

It's why I always measure amplifier response, especially valve amps into first a pure resistive load then how it actually behaves when faced with a speaker inductive load, then bang IMD tests thru them all.
The differences are often quite flagrant.

I am quite aware that speaker impedances are bariable based on frequency. That’s why it’s called “impedance” instead of “resistance.” And I know the difference between those terms and “reactance.” But I was trying to keep things reasonably simple.

 

[par4ken]

Bose 901's had almost a cult following locally around here. A local dealer sold them and ran them at the "Disco" at a local bar. I always felt they lacked low bass and upper treble. People that thought they were so great just didn't know any better! It didn't help matters that they played cassette tapes in the bar rather than records. They sounded OK only because they were turned around backwards. All those rear facing drivers were pointed forward. I can only imagine how bad they would sound facing the proper way! A friend had 301's that sounded OK.