Just to clear it up for our friend, let's ask which "speaker drivers" he plans on using in his cabinets.
Best Regards,
TerryO
Depends on your intent. If you are making an isobaric sub with shallow drivers with them both in a sealed box, yes you wire them "out of phase" (actually "reversed polarity to each other") so that the cones move in the same direction at the same time. But if the chamber they are both in has an opening for sound to radiate out of, then perhaps you want them wired "in phaase" (same polarity) so that they both pump air in or out of the opening at the same time.
It depends, in OB for bass no, for mid and high, yes, in sealed is reverse :
http://www.diyaudio.com/forums/full-range/253992-true-dipole.html
Phil.
This is accurate in the theoretical sense for open environment. If, however, the intent is to have one of them facing a reflecting surface, the phase reversal of the reflection does not result in the loss.
In the real world the effect is far less pronounced for any number of reasons, not least of which is reflection from the floor beneath the speaker, which an open environment precludes. Many guitar amplifiers are open back, which produces reversed phase waves. Many players know that if they stand near it, 90 degrees off axis, they can avoid the full SPL. However, anywhere else there is hardly ever a discernible difference. The primary frequency of the lowest note on a guitar in standard tuning is ~82 Hz, well into the bass range for most considerations.
Back to back speakers
I wonder if I have misunderstood some of your points.
Does "the phase reversal of the reflection" mean that sound reflecting from a surface has it's phase reversed?
Are you saying that the open backed combo amp produces a flat response down to 82 Hz, and if so is this done without any bass boost?
Does the reflection from the floor boost the out of phase rear radiation differently to the in phase front radiation? If they are both boosted, how does this effect cancellation?
I wonder if I have misunderstood some of your points.
Does "the phase reversal of the reflection" mean that sound reflecting from a surface has it's phase reversed?
Are you saying that the open backed combo amp produces a flat response down to 82 Hz, and if so is this done without any bass boost?
Does the reflection from the floor boost the out of phase rear radiation differently to the in phase front radiation? If they are both boosted, how does this effect cancellation?
The waveform structure itself is maintained. However, the reflection acts (in the perfect, theoretical sense) in reversing the vector and producing an apparent spherical wavefront with a virtual source behind the reflecting surface, at a distance twice that of the original source to reflecting surface distance. The wavefront will no longer automatically oppose the amp front wave. The on axis longitudinal wave may or may not, depending on the distance and frequency. However, detecting that is a problem in that it would have to be done at the surface of the cone, and detecting only what's coming from 180 degrees away from it. The single most accurate measurement situation possible falls prey to the practicality requirements of reality. In that reality, the wave front from the virtual source will have a curvature different from that of the wave front coming from the front of the speaker. Any areas of cancellation (and by definition, and equal number of amplifications due to constructive interference) will appear in 3D space as expanding toroids traveling along the axis -- they do not have places, they have vectors. There is no "where" for them to be detected except as transient variations. And the reapplying the concept of complex wave forms with a range of fose requencies, those variations will appear only as drops of transient differences within the bucket of the constantly changing range of frequencies being produced. It defies detection by ear and requires far better equipment than the vast majority of people have access to just to detect them.
In real life the output is not a frequency, but a band, convolved into a complex wave form, even if what's played is a single sustained "note". The harmonics inherent in strings negate thinking about the actual possibilities in theoretical terms. Those terms are akin to Platonic Ideals, and don't exist. More about that below.
Yes, guitar combo amps produce 80 Hz. At least most of them. The amps themselves can produce, if not the typical 20-20k, at least a range far wider than the notes' primary frequencies. My larger Peavey, Kustom and EV speakers go down to about 40, and so serve equally well as bass speakers. My Fender Frontman 65R, a very typical 1x12 combo, goes down to 60 Hz. Smaller (ie. "modeling") amps also have the wider range in the amps, but may or may not in the speakers. Mine do. My Peavey Blue Marvel 8s go down to 60, and my home brew cabs made with GRS BOFU clones go down to 40. All this, with no "bass boost".
However, I said nothing about flat, nor would I ever. Guitar speakers are promoted according to their "color", that being what frequencies are more or less from flat, or are enhanced by harmonics, and how that frequency band profile changes with increasing power and SPL. My Peaveys are PA woofers and are far flatter than almost all guitar drivers. They have 3% total harmonic distortion. My old JBL studio monitors had 5% THD. Most commercially available guitar drivers have 10% to 20% THD, and that's designed in. In any case, the range given for a particular driver is still given as the standard +/- 3 dB, so if it says it goes down to 80, it does so within that range of SPL.
As for floor reflections, they appear as sources below the floor. You only get to see the portion above the floor. They too will appear as expanding toroids (or portions thereof) of + or - interference that varies across the frequency band and with time. If you want to try to imagine these regions in space, think of rainbows -- virtual spatial regions in the sky that appear because of reflection. Some people call it diffraction. So be it, we can use that word rather than the entire phrase "frequency dependent variation in angle of reflection".
All told, if you listen to speakers facing opposite directions, one facing a wall it will be louder than if the wall weren't there. If you play real music through them and walk around listening, and you might find places where a small portion of the frequencies vary sometimes, but you won't find dead spots. And if any such spots occured with guitar combo amps other than right next to them, they'd all have backs on them by now.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.