Why are 8x12 guitar cabs used (full stacks-- 8 12 inch speakers) if a single 35 inch speaker would have the same area (scaling up is quadratic, and therefore makes the drivers a lot bigger at only about 2.5 times the size) and could have more power handling but then have MUCH, MUCH better sound because it isn't 8 sources of the same sound messing with each other? I believe that because of the distance between the speakers, they would act somewhat like active noise cancelling and just mess with everything, but I am not buying the idea that more speakers playing the same music will automatically be worse.
sound less full from 4 speakers than with 2 ?? help!
- Thread starter clairtone
- Start date
Sound production and sound reproduction or reinforcement have different design objectives. Hook a pair of 4 x 12 cabs to your stereo and listen. Who uses 4 x 12s for vocals?jrsh92 said:
The primary objective is SPL. The built-in fixed phaser/flanger is perceived as an enhancement; combing makes part of that metallic "chime" (see next post.) Get back 30 feet, and the multiple sources become more coherent. Get back 100 feet, and they become a point source, effectively, no?
Do the calcs. How much lateral (or vertical) displacement of the listener is required for the differential distance from the acoustic centers of the drivers to equal 1/2 wavelength and generate a cancellation at the highest frequency of interest? Start with just two drivers to make it easier. Then, does having four or eight clustered drivers somehow compensate for this?
Uhmmm, can't make a 35-inch speaker that will play with the requisite bandwidth, I don't believe.
[DARN those laws of physics, anyhow.... :thumbsdn: ]
To illustrate:
I recently did some measurements attempting to add a tweeter to Altec 846B for another thread. Here's what happens when both the horn and tweeter are playing the same frequencies with no crossover. Most of the displacement of acoustic centers here is front to rear, the midrange driver being at the back of the gold horn, but there is also several inches of vertical displacement between the two drivers.
What you see there is called "Combing." Because of the displacement, the drivers play out-of-phase at a specific frequency and multiples thereof, resulting in the reinforcements and cancellations shown in the black curve.
Reversing the phase of the tweeter (just as Clairtone tried with his stack) inverted the comb, clearly indicating phase as the source of the anomalies. (Blue)
You can calculate the total offset from the frequency and the speed of sound in air.
That's what happens when you stack, but across the entire frequency spectrum, the specific frequencies varying with the distance between drivers, and the differential distance between them and the listener.
The "teeth" of the comb are actually much higher. I applied 1/6 octave smoothing to the curves so that the pattern would be more apparent....
[Extra credit: How far is the mic from what in the pic?
]
I recently did some measurements attempting to add a tweeter to Altec 846B for another thread. Here's what happens when both the horn and tweeter are playing the same frequencies with no crossover. Most of the displacement of acoustic centers here is front to rear, the midrange driver being at the back of the gold horn, but there is also several inches of vertical displacement between the two drivers.
What you see there is called "Combing." Because of the displacement, the drivers play out-of-phase at a specific frequency and multiples thereof, resulting in the reinforcements and cancellations shown in the black curve.
Reversing the phase of the tweeter (just as Clairtone tried with his stack) inverted the comb, clearly indicating phase as the source of the anomalies. (Blue)
You can calculate the total offset from the frequency and the speed of sound in air.
That's what happens when you stack, but across the entire frequency spectrum, the specific frequencies varying with the distance between drivers, and the differential distance between them and the listener.
The "teeth" of the comb are actually much higher. I applied 1/6 octave smoothing to the curves so that the pattern would be more apparent....
[Extra credit: How far is the mic from what in the pic?
]Attachments
stickman
Super Member
Clairtone, As discussed in previous posts the likely primary cause of your situation is that the Sansui A + B speaker setting likely does hook the two sets of speakers in series to keep the impedance level high and the amp transistors safe. Unfortunately series connections of two speakers with multiple drivers and crossover networks wreaks havoc with the frequency response of the entire circuit and the increased impedance lowers amplifier output as well. For a test hook both pairs of speakers to the A output connectors only and listen at moderate volumes to avoid risking your amplifier section. This should give you the sonic result you were looking for. If the Sansui is rated for safe operation at 4 ohms you should be safe, if not then using a differtent amp that is rated for low impedance loads would be needed to play both pairs loudly together.
Clairtone, have you tried reversing polarity to one of the pairs (either the pair connected to the 'A' jacks OR the pair connected to the 'B' jacks)? While there is a theoretical detriment in connecting two cabinets per side (as Z. illustrated above), the vast majority of your problem MIGHT be that one of your two pairs is wired, from the factory, in reverse polarity to the other pair...
Regards,
Gordon.
Regards,
Gordon.
An interesting THEORY, but....
JBL 4412 Studio Monitors,
1) The pair each run individually.
2) Connected in series, the Orange one moved out of the measurement area. No frequency response anomalies apparent, just the expected 6 dB attenuation.
3) Stacked, +12 dB to separate the curves. See something familiar? In phase or out of phase at this point? Look at the bass response for the answer.
4) Phase of one reversed, it's kinda clear who's zoomin' who.
5) Devices under test.
6, 7, 8) Wanna stack? Do it right.... :yes:
JBL 4412 Studio Monitors,
1) The pair each run individually.
2) Connected in series, the Orange one moved out of the measurement area. No frequency response anomalies apparent, just the expected 6 dB attenuation.
3) Stacked, +12 dB to separate the curves. See something familiar? In phase or out of phase at this point? Look at the bass response for the answer.
4) Phase of one reversed, it's kinda clear who's zoomin' who.
5) Devices under test.
6, 7, 8) Wanna stack? Do it right.... :yes:
Attachments
clairtone
ballers clique
GordonW said:
I thought to myself maybe the polarities of one set of speakers are reversed inside the speakers, so I connected one set in reverse to the other but that wasn't the answer either.
yes i said that earlier, I think im gonna go with what zilch said and build an external crossover just use the 220's for bass
Precisely.Cosmos said:
Unless you are in the plane equidistant from both sources playing the same program material, they are out-of-phase to some degree.
Assuming I am measuring on-axis with the lower tweeter (which I was,) which drivers are generating phase delay in the stack under test?
Zilch said:
That's for IDENTICAL speakers.
For ANY difference between speakers (even as small as one having stiffer surrounds than the other), I've WATCHED speakers "pump and breathe" (one woofer going in, the other going out, etc), among other possible anomalies, even when wired IN POLARITY, when wired in series.
And, just FORGETTABOUTIT if the speakers are different brand/model/type from each other. Series wiring of dis-similar speakers is ASKING for weird things to happen.
Anything that upsets the impedance/EMF balance between the speakers, and all bets are off, in series wiring... been there, done that, too many times...
Regards,
Gordon.
I can't run every potential combination here, of course, but I DO have some Bose I might try.GordonW said:
:I'm pretty sure you'd agree though, Gordon, playing just about ANYTHING in the same frequency range with Maggies is just asking for phase interference difficulties of a high order, and from the description, that's what Clairtone is hearing.... :yes:
Zilch said:[Extra credit: How far is the mic from what in the pic?
No takers, Z? How about a 13.5" differential in distance between the acoustic centers and the mic? Or did you mean absolute distance from source->mic?
And speaking of phasing and interference...ever played with a Bessel Array? I've been thinking about doing that lately.
Ray
For whatever reason, I didn't catch that one of the speaker pairs was a Magnaplanar.
That being the case... NOTHING is going to "mate" with those. Completely different dispersion pattern- dipole (planars, such as Maggies) vs. "semi-hemispherical" monopole (for any speaker with cone drivers).
Forget trying to play them over the same frequency range... use a subwoofer and/or a supertweeter with the Magnaplanars, and call it a day.
Regards,
Gordon.
That being the case... NOTHING is going to "mate" with those. Completely different dispersion pattern- dipole (planars, such as Maggies) vs. "semi-hemispherical" monopole (for any speaker with cone drivers).
Forget trying to play them over the same frequency range... use a subwoofer and/or a supertweeter with the Magnaplanars, and call it a day.
Regards,
Gordon.
With regard to two identical or differrent speakers wired in series, it is quite easy to understand. Let's say the impendance of each speaker is
Z=R+jX,
where R is the resistive part of the impedance and X is the reactive part of the impedance.
When you have two speakers in series, Z(total) = Z1 + Z2 = (R1+R2) + j(X1+X2).
When these two speakers are identical, R1=R2 and X1=X2, Z(total)=2(R1+jX1). So the impedance doubled, but the phase relationship is still the same.
However, when these two speakers are not identical, (X1+X2)/(R1+R2) doesn't equal to either X1/R1 or X2/R2, so the phase relationship changes.
Coupled with acoustic interference between two sets of speakers, you will have some interesting results.
Z=R+jX,
where R is the resistive part of the impedance and X is the reactive part of the impedance.
When you have two speakers in series, Z(total) = Z1 + Z2 = (R1+R2) + j(X1+X2).
When these two speakers are identical, R1=R2 and X1=X2, Z(total)=2(R1+jX1). So the impedance doubled, but the phase relationship is still the same.
However, when these two speakers are not identical, (X1+X2)/(R1+R2) doesn't equal to either X1/R1 or X2/R2, so the phase relationship changes.
Coupled with acoustic interference between two sets of speakers, you will have some interesting results.
Oooooo, Ray you are GOOD! :thmbsp:spkrdood said:
It was both, actually, in different posts, and you have the first one exactly correct. The combing is coming from a 1 ms. delay.
The "Distance from what to what" one in post #23 was mic to tweeter, which is closest, and assuming I have the time window beginning when it first arrives at the mic, the delay of 4.29 milliseconds to start times the speed of sound (13.56 in/ms, I use,) says the mic is 58+ in. from the acoustic center of the tweeter, ~1.48 meters.
From that, we can calculate the SPL at 1M, and knowing the tweeter impedance and sensitivity, how much power I'm driving it with, the applied voltage, all that good stuff....
The answer in post #30 is, from tweeter axis, ALL the 4412 drivers are interfering with each other, and it's such a mess I can't begin to sort it out, although one delay is clearly dominating above 10 kHz. The lack of bass response (Blue) indicates that the final (Black) connection is the correct woofer (and, presumably, system) phase connection....
Never tried it, but I hope you'll document your work with that here so we can all learn and enjoy!! :yes:spkrdood said:
Zilch said:
Don't know if I'd go that far, but I do it for a living so I have to know enough to fool the masses.
Wasn't sure if you put in a little buffer for electrical propagation or not so I left that one alone. My system has a bit of latency so I have to pad my times a little. Wish I still had the TEF20 from my last corporate gig but that's a little much for my currently anemic wallet.
I'll see what I can do. It's just something I've been kicking around. I have a stack (24 or so) of 4" full range-ish drivers that I've been thinking about putting into a line array but the Bessel has always made me curious. We'll see where it goes.
Ray