Bill Fitzmaurice

Decibels is a matter of speaker sensitivity and frequency response. On average fifteens have higher sensitivity and lower frequency response than tens, so on average two fifteens will go louder and lower than two tens, even when driven with less power.

Since it's loaded with Eminence OEM probably built on the Alpha 10 chassis 95dB is a reasonable expectation. So is a high Fs and short xmax.

22 hours ago, Hobbayne said:

BTW why has Irish accent turned American?? ☺️

Not any American I know. 😉

It's also harder to mess up parallel. That's the only reason I can think of for Ampeg using 32 ohm drivers in the 810 SVT.

You can in Italy. For that matter it's mandatory.

Wire it parallel for 4 ohms. Tube amps aren't bothered by lower impedance loads than the tap rating. It's higher impedance loads that they don't care for.

The Rumble 200 plus extension would be louder. It's not about watts, it's about decibels.

4 hours ago, BassmanPaul said:

The seller described the Bassman as the best bass amp in the world. Ho ho ho!

 

Even in 1961 it was second best to Ampeg. 🙄

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. 

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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. 

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.

If they're identical sensitivity and maximum output go up by 6dB, the equivalent of quadrupling power. Intelligibility of the mids and highs for you increases by having the source closer to ear level.

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/

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. 😁

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.

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.

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.

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. 

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.

A good front to back method is to have a brace or two attached to the baffle at driver attachment screw locations. That way the driver is more securely connected to the box as well.

The Fs is a bit high, Vas a bit low for best results, though that's probably Greek to you. Nonetheless they'll work well enough in a number of my designs. For specific recommendations ask on my forum. They'll also work in other ported designs where the Eminence Beta 10 is recommended.

6 hours ago, Bunion said:

They’re in ampeg cabs too the stop the horn from blowing, my old 210 is a normal car tail light but I think they’ve updated them now to something more fancy 😄

They've been using 24v aircraft bulbs for quite some time.

4 hours ago, Phil Starr said:

These are really common, it's a really simple solution to protecting the speakers, mainly the tweeters. The bulb has a very low resistance when cold but as the current increases it heats up and the resistance rises reducing the current to the tweeter. In the quieter sections it cools down and full power is restored. 

Correct. In effect they work like a compressor, taming transient peaks that otherwise might cause the tweeter to fail. In extreme cases of overpowering they'll blow, turning them into fuses, although that's not their intended purpose. Those extreme cases are usually the result of using distortion effects, which increase the high frequency power content well beyond what most bulbs or tweeters can handle.

Wadding, more properly referred to as damping, serves two purposes. One is to reduce internal reflections in the cab, which cause peaks and valleys in response. How much will give the best result varies from cab to cab, with between one and two inches usually being good.

The other purpose is to lessen midbass boom, which takes more material. In sealed cabs with high Q drivers, which have a tendency for boomy response, the cab might be fully filled. In extreme cases it may be not only filled but also compressed. Well designed ported cabs don't use high Q drivers, so they usually don't boom and don't require filling the cab to tame it. Of course not all ported cabs are well designed, so more than an inch or two of damping could be beneficial. A ported cab would never be stuffed and compressed, as that would mess with the cab tuning and could kill the low frequency output. 

How damping affects response and impedance can be software modeled by changing the Qa value. 100 is a bare cab, 50 is lined, 10 is filled, 5 is filled and compressed. It's an approximate result, as different materials have different indexes of absorption. It also is only accurate to roughly 2 to 3 octaves above the box frequency, as are all the results with speaker modeling software.

The only reason to not use any damping is cost. 🙄

It makes no difference. The connection to the floor which gives boundary loading isn't mechanical, it's acoustical.

14 minutes ago, Marcus Cornall said:

 

Its just like the thing Bill said about 'the tube sound' coming from the power stage.- I have not seen that simple truth stated on any of the things I have read up on trying to understand it on my own.

 

 

Amp manufacturers, certainly those who don't sell all tube amps, won't tell you that. To some extent one can get some of that tube response by over-driving a tube in the pre-amp, but it won't come close to an over-driven tube output stage. It's not just the tone and response that's different, it's also the perceived volume created by compression. That perception is the reason for the never ending 'tube watts' debate.