Bill Fitzmaurice

A bit of semi-interesting stuff is the design of the Altec A-7. The woofer horn had two purposes. One was increased sensitivity in the lower mids, but the other was to time align the acoustic centers of the drivers. The aligning procedure was to wire the HF driver reverse polarity, feed the speaker with a sine wave at the crossover frequency, then slide the HF horn on its sled atop the cab back and forth until the SPL reading was at a minimum. That placed the acoustic centers of the drivers correctly. Swap the polarity on the HF driver back and it was good to go.

The wider the source the narrower the horizontal dispersion. It's why midranges are smaller than woofers, and tweeters are smaller than midranges. Side by side placement reduces the horizontal dispersion by half compared to vertical at the lower end, and raises the potential for combing at the upper end.

Phase shifts like that are normal, and don't matter, as you can't hear them. The dip and shift in the crossover region could be polarity related, the only way to know is to reverse the tweeter polarity and test again. It could also be time align related, which can only be fixed by moving the tweeter to get the acoustic centers of the tweeter and woofer the same. The shift at 100 Hz is probably port related, possibly indicating port tuning at 100 Hz. The 200 Hz dip could be from floor bounce. The best way to take measurements is outdoors, well away from boundaries, taking two measurements. The first is ground plane, with the mic a few cm above the ground. The second is with the cab on its back, the mic suspended above. This measurement will have a dip where the wave reflected off the ground meets the front wave at 180 degrees, the result of the baffle being 1/4 wavelength from the ground. The two are spliced to get the final result. You can do it in one step by digging a hole in the ground, putting the speaker in facing up, back filled with the baffle flush to the ground. It's how Roger Russell of McIntosh used to take measurements. When you take measurements 1/6 octave smoothing is preferred, as that's the limit of what you can hear.

There's no advantage to that over a 410, as it's essentially the same thing. In fact the increased spacing is worse. If you must do it, though I can't imagine why, the bottom cab should be flipped upside down, placing the woofers closer together, but only if the tweeters are not used. If they are used the top cab should be flipped, placing the tweeters closer together.

Not ideal perhaps, but the lobing you get with a typical HF above the LF driver arrangement tilts the HF output downward too. I first saw/heard it done by Henry Kloss in his office at Advent. He used a pair of Advent speakers per side, the upper speaker flipped upside down, creating a W-T-T-W alignment. This was in '72, two decades before another colleague of mine, Joe D'Appolito, perfected the M-T-M speaker.

Running a second no horn cab below adds 6dB to the low frequency sensitivity. For it to sound right requires turning up the HF horn by 6dB, if it has that ability. Lobing isn't an issue if the two cabs are built mirror imaged, so you can set them with the HF horns adjacent rather than separated. I don't see manufacturers doing that, for inventory reasons, but it's simple enough if you build your own.

Of course. But one need not be an arborealist to know that maple and walnut will have higher density than poplar and spruce, while luthiers know which species give them what they, or their customers, want. Also of course. One disadvantage to high density wood is weight, so to keep the weight down you need to go with some measure of hollowing out the body. Mine I made of all rosewood, neck through, with the bouts made in two pieces, each hollowed out to about 6mm thick. This gives the high density advantages of bright tone, tremendous tuning stability and almost endless sustain without being too heavy. I like the looks of it too.

Wood species, and therefore density, makes a lot of difference in tone, as it directly impacts the resonant properties of an instrument. Speaker size alone doesn't. Interestingly I've noticed that a high percentage of those who think that wood density doesn't matter also think that the cone size does. 🤔

Myth. It would be true if voice coils reacted to electron waves within the realm of the speed of sound. They don't. They react within the realm of the speed of light. It's a good thing too, because the frequencies of the notes played are determined by how fast the cone moves. If larger cones moved more slowly you might play a C but it could be heard as a B. 😒

Compared to free-space, which is outdoors and elevated by at least a wavelength, on the ground is half-space, closer than 1/4 wavelength to a wall is quarter-space, closer than 1/4 wavelength to a corner is eighth-space. Each space reduction adds 6dB. This mainly applies to the lows, where speaker output is 360 degrees. 1/4 wavelength at 120 Hz is about 70cm, so ideally that's the furthest out you want the cab baffle from the wall. True. Where either the cab or you relative to each other or a boundary results in a 1/2 wavelength differential between the original source and a reflection there's a cancellation notch. Said boundaries include the floor and ceiling, so often the worst listening position is on the stage, where you can be getting multiple low frequency cancellations from walls, floor and ceiling. Further back in the room where the distance relationships are much longer the lows can be considerably louder than on the stage. This phenomenon was responsible for the myth of wave propagation, the notion that one must be a given distance from the source for a sound wave to fully develop and thus be fully heard. It's easily disproved by listening to the same speaker outdoors, where there are no boundaries that can cause cancellations.

Using more speakers outdoors is appropriate, as you're losing some 6dB or more of boundary reinforcement. That requires doubling the cab count to come out even, especially in the lows. The main issue with using dissimilar cabs is whether they'll integrate to help each other or whether they'll fight each other. You'll want to try it in a practice situation first.

When EQ'd for the same frequency response you cannot tell the driver size. You can have a dozen drivers of the same size with a dozen different frequency responses. When cabs have the same cone displacement, be it from one larger driver or more than one smaller drivers, they have the same maximum output. The only factor that's attributable to cone size alone is the dispersion angle, it grows narrower as the cone grows larger. Even that can be tweaked, and for that matter a pair of tens placed horizontal will have narrower dispersion than a single eighteen. In the end one factor, be it cone size or any of the more than a dozen factors that sum to give the end result, doesn't determine said result. It's that sum total.

While I'm at it, shelf style ports have two issues. The short height dimension can lead to chuffing, and they don't do double duty as braces unless located between the drivers. While this isn't a bass cab, it's a sub, I use the same design features in direct radiator bass and PA mains cabs: https://celestion.com/blog/build-this-21-inch-bass-reflex-enclosure-featuring-the-tsq2145/

Those dimensions give an approximate volume of 50L per driver with 55-60 Hz tuning, so the tuning is too high and the box is too big. A dividing shelf doesn't do anything other than to add bracing to the panels that it connects. You should have bracing, but as far as that's concerned a shelf is one of the least effective methods.

Unless the low pass inductor is seriously undersized, resulting in high DCR and potentially going into saturation, a low pass filter won't cause clipping of the low notes. That's usually the result of inadequate driver xMax/Vd, sometimes by the cab size and tuning. If you went with the WinISD default of 41 L per driver with 58Hz tuning you'd run out of excursion at only 80 watts per driver at 50Hz and lower. Without knowing the cab specs that's all I can offer. If I was using that driver I'd ignore the WinISD default and go with 30L per driver and 45Hz tuning. If you did use the WinISD default making the port(s) long enough to get to 45Hz tuning would be better, and since the net box volume should be smaller as well you've got the room for it.

And that's why the riders for major touring acts specify Ampeg SVT.

It's simple, whoever bought the rig wasn't a bass player. 😒

You need a cable with 1/4" on one end and Speakon on the other. What's labeled as Direct Output goes to a mixing console, not a speaker. Read the manuals. If you don't have them do a search to find them. BTW, you're in the wrong forum. This is the PA section. 😒

A perfect example of why I stopped going there 13 years ago. It's like watching the Gallaudet University Marching Band, led by Stevie Wonder as the Drum Major. 🤥

Normally I'd agree there, but...the SP212 isobaric configuration means that while it has two twelves it only has the output of a one twelve. A proper 212 will give the OP what he needs, save the SP212 for those gigs where it's enough on its own.

A few items of disagreement. First off, he loaded that cab with replacement Celestions, so what the frequency response is one cannot say. Second, most of the power with electric bass is in the 2nd and 3rd harmonics, so when you play a 41 Hz open E what's mainly there is 82 and 123 Hz. By and large a speaker f3 of 50 Hz is sufficient, even for drop tuning. The SVT 810 f3 is 58 Hz. And lastly where hearing yourself is concerned that's mainly in the upper midbass through the midrange, roughly 200 Hz to 2kHz. As for "In terms of the angled / stacked speaker cabs, I’d have to disagree in my experience. The only times I’ve done that I’ve hated the sound - too harsh and right behind my head." when you aim the cab at your head rather than your calves you hear what the audience hears. If you don't like what you hear neither will they. The EQ should be set so that it sounds good on the speaker axis, not 30 degrees or more off axis. To remove the room from the equation I always walk out onto the dance floor for sound check, adjusting the EQ so that it sounds good there. If that results in less than optimal tone on stage I live with it, I'm playing for their enjoyment, not my own.

If this hasn't been a problem in the past then it wasn't your gear, it was the room, although a 4x10 arrangement doesn't help. You'd be better served with a pair of 2x10, stacked vertical, to get the upper drivers closer to ear level. At the very least your 4x10 should be tilted back and/or elevated, otherwise the directional mids that are the source of clarity are passing by you unheard.

They are.

More than a few DIY experimenters have turned that hobby into a lucrative profession. Included in that list: James Lansing, Paul Klipsch, Edgar Villchur, Henry Kloss, Conrad Sundholm, Thomas Danley and Alex Claber, and if I may, myself. All of got into speaker design because they were dissatisfied with what was available commercially and thought they could come up with something better. Audio design in general, and speaker design in particular, has always been advanced by the work of amateurs, unimpeded by corporate politics. Villchur's example is perhaps the best. He had a Masters degree in Art History. He got into audio as a radio repairman while in the Army in WWII. That piqued his interest in audio, which he followed up on after the war. When he came up with the idea for the acoustic suspension speaker he shopped it to all the major players. They all said the same thing, that if his idea had any merit that their own engineers would have already done it. That was circa 1950. Undaunted, Villchur built a prototype of his new speaker out of a plywood box. The dimensions of the face of the box were taken from a picture frame that he had hanging in his house. His wife, Rosemary sewed the pattern for the flexible surround out of mattress ticking. After proving his concept to himself, if not others, he and his student, Henry Kloss, proceeded to create their own company, Acoustic Research, in 1954. In 1966 AR’s loudspeaker sales represented almost one-third of the entire market. Not bad for a couple of tinkerers.

As one who does both commercial and DIY designs I have to disagree. One major advantage to DIY is being able to build designs that are labor intensive without concern for the cost of the labor. There's a reason why high end outfits like Danley Sound Labs get top dollar/quid for their products, and it's not just the cost of the components, it's also the cost of the labor to build them. A DIY build of a sophisticated design can easily match the performance of a high end speaker costing $5k at a fifth that price or less. Where commercial has the advantage of economy of scale is in the low to midrange price range, but even there DIY can still be the better route. You can buy a simple ported or vented box or you can build one for the same price but loaded with premium drivers, whereas buying a commercial one with premium drivers would raise the cost considerably. Now that's not to say that all DIY designs are gems by any means, I see cringe worthy junk all the time. But to be fair I see plenty of cringe worthy commercial junk too. Maybe not in the $5k range but certainly in the $500 range. And lest I forget...well, I did actually...DIY doesn't have expenses for marketing and distribution, office staff, accountants, lawyers, offices and factories, the guys on the loading dock...it's a long list that all contribute to the price you pay.