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Bill Fitzmaurice

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Posts posted by Bill Fitzmaurice

  1. 8 hours ago, Downunderwonder said:

    If we accept that Ampeg are selling us a bass cab and not a mid cab then I don't think it's wrong to infer SPL from sensitivity and power handling by assuming the xmax is available.

    In most cases the xmax isn't available. The mechanical power limit of drivers averages around half the thermal limit. Some are higher, some are less. Some even have a mechanical capacity equal to or greater than the thermal. But those are high cost premium drivers that are seldom seen in electric bass cabs. Here again don't take my word for it, verify it yourself with speaker modeling software. As a for instance, the Eminence Deltalite II 2510 is the most popular neo ten inch platform. The thermal rating is 250w. The mechanical limit in the critical 80-100Hz region is 100w. And the 2510 is better than most. The most popular ceramic ten platform is the Eminence Beta 10. The thermal limit is 250w. The mechanical limit is 60w. 

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  2. No doubt Ampeg is one of the more honest manufacturers. Their power ratings are conservative. But the fact remains that without xmax or Vd one simply cannot calculate max SPL. Try it yourself, using any of the common loudspeaker design programs, leaving xmax/Vd out of the parameters. You can calculate response, impedance, phase, group delay, port velocity, but when you go to the max SPL chart it's left blank for the lack of the required specs.

     

    This isn't picking on Ampeg by any means. AFAIK Barefaced is the only manufacturer that provides that critical bit of information.

  3. A rig of that sort will only sound as good as the crossover allows it to. That means having sufficient high pass slope to prevent over-excursion of the midranges. It also means low passing the woofer cab, otherwise the woofers and midranges will fight each other where they're operating in the same frequencies. MIdrange drivers are a good idea, but as is the case with all good ideas it's the execution that determines success versus failure. If the bright box doesn't have a jack to send a low passed signal to the woofer cab the execution was flawed. If they didn't do that then the high pass filter, if it has one, is also likely to be inadequate. 

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  4. 47 minutes ago, alexa3020 said:

    To achieve mutual coupling, woofer center to center needs to be less than 1/2 wavelength - is that right?

    So what distance do woofers on bass need to be apart ideally?

    Correct. At 3kHz, for instance, 1/2 wavelength is 2.25 inches. That means it's impossible for electric bass woofers to fully couple to 3kHz. The highest tens will go is roughly 675Hz, so 'ideal' spacing is impossible. That's why vertical placement is key, so that the effects of spacing beyond 1/2 wavelength won't be heard on the horizontal plane. 

    Quote

    Also, does that mean that a traditional 410 (2 stacks of 2) is better than 4 speakers in a vertical array, because of the greater distance between the bottom speaker and top speaker in a vertical array?

    The opposite. The CTC from the top woofer to the bottom woofer doesn't matter, it's the spacing between adjacent woofers that counts. 

    • Like 2
  5. 6 hours ago, alexa3020 said:

    Is there much difference in dispersion etc, if I stack a tweetered 210 vertically (tweeter top center between the 2 10 inch drivers when cab horizontal)?

    I don't hear a huge difference standing next to it. 

    There are two factors in play. In the lower frequencies where the two woofers are spaced close enough to mutually couple, which means they act as one, the dispersion angle across the sound field with vertical alignment is twice that of horizontal alignment. In the higher frequencies where they're too far apart to mutually couple their outputs alternately reinforce and cancel each other as you go across the sound field when placed horizontal, what's referred to as comb filtering. When placed vertical the response is constant across the sound field. Standing next to the cab you wouldn't notice it. Further away standing in one spot you wouldn't either. But when you're even a few meters out they will sound different as you walk across the sound field. Where comb filtering occurs they'll sound different in the highs with as little as a few inches of listening position shift.   

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    I've been surprised how much a second identical cab adds to perceived volume and audibility - reading about it the dB change is one thing, but there's no substitute for hearing it. Even with valve amps where the power from the amp should be the same into a correctly matched load, it's still generally bigger sounding.

    Long before I knew a Hz from a dB I knew that two cabs made a world of difference. This was in 1967, when I got a second cab for my '65 Bassman. With one cab the Bassman was barely usable. With two it was tolerable. Wanting to know why was the impetus for my heading to the engineering section in my college library the following year. There I found 'Acoustical Engineering' by Harry Olson. Even though it was written in 1957 it remains to this day the Bible of loudspeaker designers. A year later I began designing and building my own.

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  6. 7 hours ago, Steve Browning said:

    For years I always removed anything between the cab and the floor. After getting a 2x18 that was immovable without I indeed found there was not the blindest bit of difference. Years of shifting utterly wasted.

     

    Get some decent 10cm casters with brakes and don't look back.

    By the same token isolation doesn't work either. Isolation can reduce the vibrating of a cab atop a soft floor, which is vibrating as the result of acoustic resonance excited by the speaker output. What it can't do is reduce the vibration of the floor, as that's acoustically sourced, not mechanically.

    http://ethanwiner.com/speaker_isolation.htm

    https://www.bassgearmag.com/submit-article-bass-amplifier-isolation/

  7. 29 minutes ago, DGBass said:

    I just meant my particular MDF box cab🙂 And I guess you are saying the answer is Yes, it could make a difference to the sound although the yes word isn't specifically mentioned.

    Yes, because what works in one speaker works in all speakers. The physics are the same, no matter what it's made of. MDF may not benefit from bracing as much as thinner, lighter materials, but it's not two inches of concrete either. OTOH bracing is what allows me to use cabs made of 3mm and 6mm plywood, with no ill effects either from a sonic standpoint or a physical standpoint, that being to my ancient arthritic spine. 😁

  8. 1 hour ago, Dan Dare said:

     

    Bill, should you allow for the wadding when working out cab volume, or does it not affect it? Thanks.

    it has no effect when used as lining, as it doesn't affect the low end where the cabinet defines response. When used as stuffing it does affect the low end, and should be taken into account during the design phase. If you want to make a sealed cab as small as possible stuffing is a must. However...

    In 1995 a respected audio enthusiast named Ton Nousaine did some experiments with stuffing. Noting that it reduced a midbass response peak, similar in fashion that a larger box reduces a midbass response peak, he erroneously concluded that stuffing gave the same result as making the box larger. It does not. Stuffing and larger boxes both lower the speaker Qtc, which reduces a midbass peak. But a larger box also lowers the speaker frequency response and increases low frequency sensitivity. Stuffing does not. It actually reduces sensitivity. His error was due to not collecting adequate data to fully explain what he observed. Unfortunately he published his theory, which was widely accepted on the basis of his reputation, and the myth that stuffing a sealed cab gave the same result as making it larger was the result. That myth persists, to the extent that if you google 'stuffing loudspeaker' you'll find numerous references that continue to get it wrong, as they keep repeating the same flawed initial conclusion. The error would be obvious if they used loudspeaker modeling software to confirm what's going on, but they don't, because they don't know how.

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  9. 1 hour ago, DGBass said:

    The question about whether the inherent sound of such a cab will change by extensive bracing and wadding is still open.

    That question was answered during the golden age of loudspeaker design, 1938-1973. The hi-fi guys knew it, the PA guys knew it. A few electric bass cab manufacturers knew it, those being manufacturers that also did hi-fi and PA, like JBL and EV. The mainstream musical instrument manufacturers didn't, operating in a vacuum as it were. JBL and EV never really cracked the musical instrument market, because they didn't make amps, and in those days amps and speakers were almost always sold as a set.

  10. Where coloration is concerned Eminence intentionally imparts it, as it's been part and parcel of their tone going all the way back to the CTS days. One could even say it's part of the history of the sound of the electric bass, much as Celestion holds that position with electric guitar.

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  11. Only if it's 40cm or more closer, and that wouldn't affect it down low. You get full boundary reinforcement when within 1/4 wavelength of the boundary. 1/4 wavelength at 100Hz is 85cm, and the lower you go the longer a wavelength is. 

  12. That's one way to look at it. The other is that they really didn't know what they were doing where cabinet design is concerned. Fender certainly didn't, not until the 1990s. Even today Fender isn't state of the art by any means. There are two reasons to brace. One is to silence panel vibrations that detract from the speaker sound. The other is to improve the efficiency of the speaker. Energy wasted causing panels to vibrate doesn't end up in the audience.

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