is two full range drivers in one baffle a problem?

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Barber pole is a way out...slight change in the direction. Saw bose 802s on the same pole and was wondering why they all we were at a slight change of angle. This would be the reason.

Just a sec here, trying to figure out the phase shift. If for example, you take two sine waves and change the phase shift for one wave by pi/2 (90 degrees), do the two waves add-up? Or, will they require a change of pi (180 degrees). The sine wave represents the sound from one Fostex.

I believe that the poor off-axis response is due to the wedge dispersion and lobing effect from using a line-array. This is good however, for use when you want to minimize reflections for PA use in a room with relatively poor acoustics. You get the same power of a larger driver without the reverberations.
 
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Bose(o) said:
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Just a sec here, trying to figure out the phase shift. If for example, you take two sine waves and change the phase shift for one wave by pi/2 (90 degrees), do the two waves add-up? Or, will they require a change of pi (180 degrees). The sine wave represents the sound from one Fostex.

Two sine waves of the same frequency will add together. I believe, but am not sure, that if you add two sine waves together of equal frequency but 90 deg phase difference, that you get a result that is half the amplitude of what it would be if they were in phase together.

If they are 180 degrees out of phase, they cancel out completely.

I think I mentioned once, about anti-noise. Certain airplanes have a system where the noise of the engines is picked up by mikes, sent through an amp, reversed in phase, and played in the passenger compartment. Although there are some time delays, the phase is close enough to 180 degrees that the sound of the jet engines is substantially reduced. Anti-noise = sound waves 180 degrees out of phase.
 
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kelticwizard said:
I think I mentioned once, about anti-noise. Certain airplanes have a system where the noise of the engines is picked up by mikes, sent through an amp, reversed in phase, and played in the passenger compartment. Although there are some time delays, the phase is close enough to 180 degrees that the sound of the jet engines is substantially reduced. Anti-noise = sound waves 180 degrees out of phase.

Panasonic uses this noise-cancellation technique in their high-end video projector. You can actually be in the same room as the projector!!

It is interesting that the 1st publication of this idea was actually intended to be an April Fool's Joke :D

dave
 
Two drivers in paralell will give 6dB+ for the same voltage in.

Two drivers in paralell with a 90degree phase distance will give 3dB+.

And obviously at 180degree they cancell out.

At 270degree (the case with 3rd order butterworth) the situation is virtually the same as with 90degrees, so the sum is 3dB+.

/Peter
 
peranders said:


Are you sure about that? Double power = 3 dB increase in sound pressure. I think you mixed up voltage and power.

We've covered this countless times before. Where the distance between the 2 drivers is small relative to the wavelength, you get a 3dB increase for the same total power input. So for 2 drivers in parallel at lowish frequencies, for a given voltage input, you get 6dB increase in on-axis output relative to a single driver.
 
Great to be back in the special triangles of things eh? Thanks a lot guys I understand now...Unfortunately with noise-cancellation you get a white noise that is evident in almost any noise cancellation (headphones for example). And that, nois-cancellation is always a bit behind in time.

So, by reversing the polarity on the tweeter you get a +3dB. increase where the waves are identical because reverse polarity=pi/2 (90 degrees).

Thank you!

Sorry about the somewhat off topic part of things.
 
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Bose(o) said:
Unfortunately with noise-cancellation you get a white noise that is evident in almost any noise cancellation (headphones for example). And that, nois-cancellation is always a bit behind in time.

I did not know that, since I never had occasion to experience "anti-noise". Still, I would guess that the residual white noise is much lower in amplitude than the sound of jet engines. I believe that it actually is used on some aircraft-not certain.

Yes, noise cancellation is always a bit behind in time, therefore it is not 180 degrees cancellation. But even 170 degrees out-of-phase goes a long, long way towards cancellation.


Bose(o) said:
So, by reversing the polarity on the tweeter you get a +3dB. increase where the waves are identical because reverse polarity=pi/2 (90 degrees).

If you reverse the polarity of a tweeter, or of anything, you have just done a 180 degree change, not 90 degree.

What you might have in mind is the reversal of a tweeter in a 12 dB symmetrical crossover. But there, at the crossover point, the drivers are already 180 degrees out-of-phase. The crossover components make them 180 degrees out-of-phase. If you left them like that, cancellation would occur at the crossover frequency and you end up with this large hole there.

So when you reverse one driver, (usually the tweeter, but it could be the woofer), you reverse the phase effects of the crossover, and the woofer and tweeter are now back in phase.
 
dave,

the market is "full" of well designed transistor amps that doubles the MAX power down to 1-2 Ohms. There are many amps that might not do that, but still output the double current for half the load up to some power limit.

A voltage output amp that does not double the power when the load impedance is lowered by a factor of 1/2 would have serious output impedance and therefore would be a bad design... no?

Such an amp would also give serious deviations from a flat fr. response with a real world speaker load and its non-flat impedance.

Am I missing something in your post..?:)

/Peter
 
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Pan said:
the market is "full" of well designed transistor amps that doubles the MAX power down to 1-2 Ohms. There are many amps that might not do that, but still output the double current for half the load up to some power limit.

Let's just consider 8 ohms to 4 ohms. 1st with tube amps with output transformers there are taps for impedance matching. They usually put out less power at impedances more or less than the taps, and approx the same off of each tap into the appropriate load. OTL amps will put out less power into 4 ohms than 8 (and usuallly more into 16 or 32 ohms). That takes away a small portion of the amps out there.

Now lets take amps that art in the majority. Cheap receivers, HT amps, etc (this is probably >75% of the amps out there). Most say 6 ohms (or 8 ohms) or higher speakers. And for those that have a multi-speaker switch, this connects 2 speakers in series (ie Sony). These all have wimpy power supplies and just can't deliver enuff current for 4 ohms.

Then we are many amps (representing only a very small amount of the market) that are rated to double power into 4 ohms, but if you look at a test of these, it turns out they are often underrated into 8 ohms, so in fact they put out less than double into 4 ohms.

I'm pretty sure that i have read somewhere that there is an actual theoretical/practical reason why an amplifier no matter how good can actually never double its power into 4 ohm vrs 8 ohm -- they can only come close.

And then there are all the amps that are in between the budget amps & the high end SS amps. Consider the gainclone* & the Zens discussed here. Both have attached to them "they don't really like low impedance loads" (can someone point to actual measured results). I take this to mean they won't double power into 4 ohms. And those are both good amps.

* (the choice of 25V DC rails on the 3875 is a direct attempt to minimize this issue)

So there are actually only a small subset of amps out in the field that will actually double their power from 8 ohms to 4 ohms, and this doesn't consider that fact that speakers do not resemble resistors and amps have an even tougher time driving them.

So the 2 speakers in parallel question always needs to be answered:

The 2nd driver adds 3 dB, and then you need to consider how much power your amp puts out into the new impedance. If you have a SS arc-welder special this will approach an additional 3 dB (at greater distortion mind you). If you have an OTL you might actually lose more than 3 dB (but if you connected them in series you might get more than 3 dB power gain).

dave
 
2 FR

so let's get back to Brad's question ( or more precisely, my take on the reason for it)

to quote from another forum:

Personally, I don't believe in absolutes in audio... ie, "Any crossover" or thing in the signal path will (have to) degrade the sound. There are too many good sounding speakers out there with crossovers done RIGHT to prove my point.

Sounds like you're trying to rationalize or justify why a product that sounds as musically involving as some things you've recently heard (and posted about) either measures poorly or seems contrary to CURRENT fads or "popular" wisdom.

Pose such questions to 10 real experts, and you better take of yer shoes to count the answers and carbon-dated research papers supporting their positions.

Don't waste your time obsessing over any of this s h i t , (can I say that on this forum); just enjoy the freaking tunes, dude!

If Ed's 4x4 horns (double-D leopard skin grilles optional ;) ) sound better and louder than a single pair, then they do. Too bad the Torii wasn't available at your recent listening session. It may not be the perfect amp for all time, but it could just be a problem solver for you.
 
Not sure exactly what you're saying or thinking I'm trying to say. Is the question related to Ed's speaker? Yes. I really like the sound of Ed's horn... but I want more of it. So I was wondering if there was a way to configure two of them to get higher efficiency without mucking things up. It sounds like the answer is mostly no.
There are always compromises I guess.
 
dave

"These all have wimpy power supplies and just can't deliver enuff current for 4 ohms."

Of course they can deliver the current to 4 ohm. Maybe not enough to double the rated power at 8 ohm, but that is another thing.

We must separate the issue of max rated effect and an actual situation at low levels, that is totally different things.

If a solid state amp with follower ouptut, rated 100W, can not give 200W at 4 ohm, that does not mean it can not drive 4 ohm loads at low levels with 6dB + spl compared to the 8 ohm case.

An example;

A el cheapo amp rated 100W @ 8 ohm and 160W @ 4 ohm. What this says is only that there is a upper limit in current output, nothing else. This very amp, if it puts out 2V rms into 8 ohm, will not have a behaviour in 4 ohm reflected by the 100W/160W rating. At the low level of 2V rms it will easily double the current into 4 ohm. What will affect the result is output impedance/damping factor.


"I'm pretty sure that i have read somewhere that there is an actual theoretical/practical reason why an amplifier no matter how good can actually never double its power into 4 ohm vrs 8 ohm -- they can only come close."

I would guess that in a well designed SS amp its so small of a problem that for all practical reasons we can assume a 6dbB gain.

Talk to you later,
now it´s time for a late night dinner for me:nod:

/Peter
 
2 horns

Sorry I wasn't clear enough, Brad; I was trying to say that

1) Ed's twin horn enclosure might give you the extra SPL and/or bass extension you're seeking, particularly in combination with the power and higher impedance performance of the new Decware amp.

2) The specific reference to vertical stacking of Fostex full range drivers in your thread-start made me think about Ed's horns, 'cause I'm aware of your experience with them , and concerns we'd probably share about power levels, etc.

3) The Signature mono-blocks can sound lucious and very 3-D, but inappropriately matched, may still have some power issues for some applications. (larger rooms, inefficient or higher impedance speakers, silly-loud listening levels, etc) The new Torii power amp would appear to address many of these questions for a lot of folks - particularly those of us who play with building or tweaking speaker systems. I know I'm quite interested.


Oops, maybe I repeated myself about the new amp, but I think it's seriously worth a listen.
 
I spoke with Steve about the Torii's. Seems they are better match for ~90db speakers and below. Since I will be going higher rather than lower than the Horn's ~92db in the future, I'm not interested in the Torii - then again I haven't heard it yet!!!

With high efficiency speakers Steve says you should get better microdynamics with the Zens than the Torii. The reverse is true for low to mid efficiency speakers.

It's all about system matching and synergy isn't it?
 
BBaker,
When these two drivers reproduce a frequency whose wavelength is equal to the distance between thier centers, thier outputs will sum. When they reproduce a frequency for which they are spaced one half wavelength, the two outputs will be 180 degrees out of phase, and they will cancel.
If you manage to get them 3" apart center to center, they will sum around 4500 hz, and cancel around 560hz. So just lay an inductor on one of them puppies somewhere below 560 hz. Most people pick a point that compensates for baffle step losses.
Looks like the barber pole is frequency tapered towards it's ends in a similar fashion.
I'm for the KISS principle.
Little hung over, so check the math...
regards, Jason :clown:
 
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