Speaker revolution

[JimmyN2]

Our guitar player turned up the other night for rehearsal with a fantastic new set up.  A Toob 12s, incredibly light at 4.6 kg, and a micro head, unbelievably light yet brilliant tone.  I’m thinking about getting the Bass version 10B or 12B.  
 

Anyone else seen or used them?

 

[chris_b]

Way too small enclosure for full, deep, warm bass at any sensible gig volume level.

[Bill Fitzmaurice]

For guitar, sure. For bass, probably not. Bass speakers require much larger enclosures than guitar to go low. About the smallest you can go with a twelve for good low end is 60 liters. Their 12B is in the vicinity of 20 liters.

[JimmyN2]

Thanks for your thoughts.

I forgot to mention that the band is piano, bass and drums with a couple of saxes and guitar playing jazz of different genres.  The sound I’m after is not necessarily what I hear but what is heard a few feet away.  My current amp is a Markbass cmd121p which I have the bass and low mids cut back and I play an upright stick (Ibanez EUB).

 

I just listened to a Phil Jones YouTube about why he uses small speakers, yet another way of looking at bass projection  

[Chienmortbb]

53 minutes ago, JimmyN2 said:

Thanks for your thoughts.

I forgot to mention that the band is piano, bass and drums with a couple of saxes and guitar playing jazz of different genres.  The sound I’m after is not necessarily what I hear but what is heard a few feet away.  My current amp is a Markbass cmd121p which I have the bass and low mids cut back and I play an upright stick (Ibanez EUB).

 

I just listened to a Phil Jones YouTube about why he uses small speakers, yet another way of looking at bass projection  

I am listening to that now and will comment later. 

[itu]

It is small and light in weight. The sound is fine for home and a small jazz club. Rock and a bigger venue, no way.

[Dan Dare]

4 hours ago, itu said:

It is small and light in weight. The sound is fine for home and a small jazz club. Rock and a bigger venue, no way.

 

It isn't so much the limited volume that will be the issue, but the lack of any real low end (see Bill's comment above). A small PJB cab would be much better in that regard and of comparable price. Granted, it will be heavier, but they're still easy enough to carry.

[nekomatic]

Anyone else expecting this thread to be about Leslies?

 

What is a 'half-open' cabinet anyway? If it's not closed or reflex then it's open, right?

[Chienmortbb]

31 minutes ago, nekomatic said:

Anyone else expecting this thread to be about Leslies?

 

What is a 'half-open' cabinet anyway? If it's not closed or reflex then it's open, right?

It’s a guitar cabinet! Seriously the PJB video has some good stuff in it but does not do what the title suggests, explain why lots of small speakers is better. 

[itu]

1 hour ago, Dan Dare said:

 

It isn't so much the limited volume that will be the issue, but the lack of any real low end (see Bill's comment above). A small PJB cab would be much better in that regard and of comparable price. Granted, it will be heavier, but they're still easy enough to carry.

I have met the designer, and I have tried one. I also know some acoustics, because I studied it in university. Toob is made for g-word. It works somehow, but the design is not bass specific, like @Bill Fitzmaurice said.

 

Photography has its rule:

ISO - aperture - exposure

 

bass cab has similar:

volume - sensitivity - lowest reproducible frequency

 

If you change any of the three parametres, at least one of the two others will change, too.

[agedhorse]

What is magnetic plywood?

[itu]

33 minutes ago, agedhorse said:

What is magnetic plywood?

There are magnet inserts in the plywood.

[Dan Dare]

2 hours ago, itu said:

I have met the designer, and I have tried one. I also know some acoustics, because I studied it in university. Toob is made for g-word. It works somehow, but the design is not bass specific, like @Bill Fitzmaurice said.

 

Photography has its rule:

ISO - aperture - exposure

 

bass cab has similar:

volume - sensitivity - lowest reproducible frequency

 

If you change any of the three parametres, at least one of the two others will change, too.

 

Bill said rather more than that. He observed that extended low frequency performance at any volume demands a larger cabinet. That's an iron rule, I'm afraid. One can bend it a little via reflex loading, porting, etc, but it holds good.  There is no equivalence between the photography and speaker cabinet design "rules" you cite.

Edited October 17, 2022 by Dan Dare

[Chienmortbb]

1 hour ago, itu said:

There are magnet inserts in the plywood.

Magic fairy dust.

[chyc]

2 hours ago, agedhorse said:

What is magnetic plywood?

It carries over to the next line: 'Magnetic plywood MagLeg'. Presumably it's the attachment mechanism of the feet

[Bill Fitzmaurice]

19 minutes ago, Dan Dare said:

 That's an iron rule, I'm afraid.

Hoffman's Iron Law, to be precise. It's not all that far off from what itu said. On the subject of small drivers they give better midrange dispersion, and can be used in multiples for adequate volume, if they're arranged vertically. When they're not, which is usually the case, you lose their advantage in the midrange dispersion and introduce comb filtering in the highs.

[itu]

In photography it is well known that changing ISO, aperture, or time affects other parametres, too. True, these laws are not equal, but represent pretty similar behaviour.

 

Hofmann (https://en.m.wikipedia.org/wiki/Josef_Anton_Hofmann) says, that low frequency reproduction is possible even in small volume, but the sensitivity will be ridiculously low. This can be heard in low cubic volume hifi speakers. Sensitivity may be far less than 0.1 %, while in PA systems it can be over 2 %.

 

It is true that when we want to go really low, a bigger cubic volume (i.e. cabinet) is in order after certain frequency. Adding volume by filling the cabinet with denser material, or making it "look" bigger to the element (for example isobaric trials) have not been as succesful as using bigger cubic volume. The design and construction have to be of exceptional quality, too.

 

By the way, my home speakers have 12" open baffle bass elements. No boxes, as the bass is a dipole. The speakers don't produce anything below 40 Hz.

[Bill Fitzmaurice]

15 minutes ago, itu said:

Adding volume by filling the cabinet with denser material, or making it "look" bigger to the element have not been as succesful as using bigger cubic volume.

That's because stuffing doesn't make the cab look bigger. It lowers the cab Q, which can tame a midbass hump. Making the box larger does that, but making the box larger also lowers the speaker cutoff frequency, stuffing does not. Some 25 years ago a well respected audio expert measured some data and made the conclusion that stuffing made a box act as if it was larger. His conclusion was erroneous, because he didn't measure enough data to reveal what actually occurred. He published his conclusion, and based on his reputation alone much of the professional audio engineering community accepted it at face value without testing to make sure it was true. In both audio and nuclear arms treaties you can trust but you also must verify. 😉

[Dan Dare]

1 hour ago, itu said:

In photography it is well known that changing ISO, aperture, or time affects other parametres, too. True, these laws are not equal, but represent pretty similar behaviour.

 

Hofmann (https://en.m.wikipedia.org/wiki/Josef_Anton_Hofmann) says, that low frequency reproduction is possible even in small volume, but the sensitivity will be ridiculously low. This can be heard in low cubic volume hifi speakers. Sensitivity may be far less than 0.1 %, while in PA systems it can be over 2 %.

 

It is true that when we want to go really low, a bigger cubic volume (i.e. cabinet) is in order after certain frequency. Adding volume by filling the cabinet with denser material, or making it "look" bigger to the element (for example isobaric trials) have not been as succesful as using bigger cubic volume. The design and construction have to be of exceptional quality, too.

 

By the way, my home speakers have 12" open baffle bass elements. No boxes, as the bass is a dipole. The speakers don't produce anything below 40 Hz.

 

In photography, you alter aperture and exposure time to control the amount of photons reaching the film to ensure they are correct for the ISO rating of the film, light conditions, whether you are attempting to capture a moving subject and so on. How is there any parallel between that and the behaviour of a drive unit or speaker cabinet design? Am I missing something?

 

Low frequency reproduction is, of course, "possible even in small volume" - my headphones tell me that. However, the tiny drivers in my cans only need to energise the minute amount of air between them and my eardrums. If you wish to energise the air in a large space - a room, bar or whatever - you need to shift a much higher volume of air over a much greater distance.

 

A small hi-fi speaker might reproduce sufficient low frequencies in a domestic environment (they are usually measured in an anechoic chamber by a measurement microphone placed one metre from the cone to produce their spec's, which tells you little about how they will perform in anything other than a small, quiet living room), but they won't cut it for live music.

 

Your 12" open baffle speakers may produce sufficient bass in your living room, but, as anyone who has tried to play bass through an open backed guitar cab will attest, it is not sufficient when playing in a band context in a room of any size. Remember also that most recorded music is compressed to a greater or lesser extent, which reduces the dynamic range and creates an impression of loudness. Play your bass through a bass amp driving the average pair of domestic "mini-monitors" and you'll destroy them in short order.

 

Bill will correct me if I'm wrong, but I was under the impression that the idea of isobarik loading was to eliminate out of phase reflections rebounding from cabinet walls and striking the driver cone. Isobarik cabs employ two drivers working in parallel, one directly behind the other, so the column of air between them acts as a piston. It is that, not stuffing, that is supposed to enable isobarik cabs to fool a driver into thinking it is in a larger box. If you stuffed the cab, it would impede the movement of the column of air between the two drivers, so isobarik cabs are not stuffed. Is that correct, Bill?

Edited October 17, 2022 by Dan Dare

[Bill Fitzmaurice]

With isobarik the result of using two drivers is halved Vas, the volume of air having the same acoustic compliance as the driver suspension. This allows halving the internal volume of the cabinet, not counting the space taken up by the second driver and the air space between the two drivers, without any loss of low frequency response. As always there is a trade off. In this case since the cone area and excursion radiating to the outside air is that of only one driver the maximum output is the same as with one driver in the net doubled cab volume. One could stuff the chamber of an isobarik, with the same result as with a standard alignment, lowered Q.

 

Isobarik was a reasonable alternative to huge enclosures fifty years ago, when driver Vas was generally much larger than today. For instance, the fifteen inch Altec 421 8LF Vas was  600 liters. The modern equivalent Eminence 3015LF Vas is 159 liters.

[itu]

9 hours ago, Dan Dare said:

Low frequency reproduction is, of course, "possible even in small volume" - my headphones tell me that.

Exactly. I think I tried to open this up by comparing the difference in sensitivity (<0.1 % vs. >2 %). It would not be feasible to use flat response in PA systems, because the system would be so ineffective. If we compare pure power, this would equal 20 kW vs. 1 kW. This is one reason I very much doubt the FRFR talk.

[Bill Fitzmaurice]

13 hours ago, Dan Dare said:

Low frequency reproduction is, of course, "possible even in small volume" - my headphones tell me that. However, the tiny drivers in my cans only need to energise the minute amount of air between them and my eardrums.

What you've hit upon here is Pressure Vessel Gain, more commonly referred to in audio as Cabin Gain. It has to do not with the volume of air but the dimensions of the room. There is a sensitivity gain at a rate of up to 12dB per octave as frequency goes down below where the longest room dimension is one-half wavelength. In a living room that's 5 meters long cabin gain starts around 34Hz. In a car that's 2 meters long it starts at 85Hz. Cabin gain is what allows the silly high bass levels achieved in auto dB competitions. A club is too large to have any cabin gain, but in an ear canal it covers almost the entire audio range.

[Dan Dare]

2 hours ago, Bill Fitzmaurice said:

What you've hit upon here is Pressure Vessel Gain, more commonly referred to in audio as Cabin Gain. It has to do not with the volume of air but the dimensions of the room. There is a sensitivity gain at a rate of up to 12dB per octave as frequency goes down below where the longest room dimension is one-half wavelength. In a living room that's 5 meters long cabin gain starts around 34Hz. In a car that's 2 meters long it starts at 85Hz. Cabin gain is what allows the silly high bass levels achieved in auto dB competitions. A club is too large to have any cabin gain, but in an ear canal it covers almost the entire audio range.

 

Thanks Bill. That's very interesting. I didn't realise that volume of air was not the main determinant. I'll Google Pressure Vessel/Cabin Gain and do some reading.

[Bill Fitzmaurice]

It's logical to assume that the air volume of the room is the main factor, especially as decibels measure the intensity of an acoustic pressure wave. But cabin gain is something else entirely. This will help: