Coming a bit late to the 'party' with the usual disclaimers; Vas, Qts' are 'open' from at least ~430-528 L, 0.34 - 0.42 Qts when including these, so using its mean:
sqrt(430*528) = ~476 L mean Vas
sqrt(25.5*27.4) = 26.43 Hz Fs mean
sqrt(5.12*5.5) = 5.31 ohms Re
sqrt(1.87*1.2) = 1.5 Qms
sqrt(0.42*0.537) = 0.475 Qes
0.361 calc'd Qts
0.5 ohm (Rs) = 0.386 Qts'
sqrt(0.34*042) = 0.378 Qts mean Vs 0.361 calc'd!
pioneer's reflex cab ratio = ~476/1.44 = ~331 L net (personal minimum based on Qts').
Below this point, sealed alignment Vb calcs seem more relevant:
265 L
(a) = ~476/265 = ~1.76
Qtc = sqrt(1.76+1)*0.386 = 0.645
Fc = (0.645*26.43)/0.386 = ~44 Hz
BR Fb = 0.645/0.5 = 1.29
26.43/1.29 = 20.5 Hz
=============
145 L
(a) = 476/145 = 3.283
Qtc = sqrt(3.283+1)*0.386 = 0.8
Fc = (0.8*26.43)/0.386 = ~54.8 Hz
BR Fb =0.8/0.5 = 1.6
26.43/1.6 = 16.5 Hz
These vented tunings come closest to sealed re group delay, etc., but simmed with Fs tuning isn't much different and superior if driven with a high output impedance amp.
All that said, the 3833 and 3836 are supposed to be identical spec wise, but based on a 339 cm^2 (Sd), low Fs and ridiculously low Qms, the posted 3833 specs are pure 'floobydust' in that the T/S specs' Cms, Mmd, BL are just small fractions according to HR, so sure would be nice to get some measured specs!
sqrt(430*528) = ~476 L mean Vas
sqrt(25.5*27.4) = 26.43 Hz Fs mean
sqrt(5.12*5.5) = 5.31 ohms Re
sqrt(1.87*1.2) = 1.5 Qms
sqrt(0.42*0.537) = 0.475 Qes
0.361 calc'd Qts
0.5 ohm (Rs) = 0.386 Qts'
sqrt(0.34*042) = 0.378 Qts mean Vs 0.361 calc'd!
pioneer's reflex cab ratio = ~476/1.44 = ~331 L net (personal minimum based on Qts').
Below this point, sealed alignment Vb calcs seem more relevant:
265 L
(a) = ~476/265 = ~1.76
Qtc = sqrt(1.76+1)*0.386 = 0.645
Fc = (0.645*26.43)/0.386 = ~44 Hz
BR Fb = 0.645/0.5 = 1.29
26.43/1.29 = 20.5 Hz
=============
145 L
(a) = 476/145 = 3.283
Qtc = sqrt(3.283+1)*0.386 = 0.8
Fc = (0.8*26.43)/0.386 = ~54.8 Hz
BR Fb =0.8/0.5 = 1.6
26.43/1.6 = 16.5 Hz
These vented tunings come closest to sealed re group delay, etc., but simmed with Fs tuning isn't much different and superior if driven with a high output impedance amp.
All that said, the 3833 and 3836 are supposed to be identical spec wise, but based on a 339 cm^2 (Sd), low Fs and ridiculously low Qms, the posted 3833 specs are pure 'floobydust' in that the T/S specs' Cms, Mmd, BL are just small fractions according to HR, so sure would be nice to get some measured specs!
Hi @GM ,
Reading your reply i realize i gave incorrect T/S parameters, Sorry for that @Scottmoose
I'm a bit lost now in all the info.
Does this mean it changes the portube size / length ? if so, how big does it need to be?
Or do i need to build a sealed cabinet?
About these Tannoy drivers.
Can i assume that tannoy is a bit "optimistic" with there meassurements of the system 15 dmt?
They state that the 3833/3836 driver does 38hz +/-3db in it's 100L cabinet.
( according to the manual of the "system 15 dmt")
Reading your reply i realize i gave incorrect T/S parameters, Sorry for that @Scottmoose
I'm a bit lost now in all the info.
Does this mean it changes the portube size / length ? if so, how big does it need to be?
Or do i need to build a sealed cabinet?
About these Tannoy drivers.
Can i assume that tannoy is a bit "optimistic" with there meassurements of the system 15 dmt?
They state that the 3833/3836 driver does 38hz +/-3db in it's 100L cabinet.
( according to the manual of the "system 15 dmt")
I admit being (nearly) completely baffled by this webpage 😕 It seems to substitute "sensitivity" for "efficiency" when convenient, handwaves on very rough (erroneous) math, and pins high importance on closed-box f3 (by itself meaningless, since a point and a tangential line do not at all define a falling curve, even with predetermined final slope). Is there a more complete explanation & comparison of different cab types? 🤔
I believe it; your response strongly implies what we refer to as 'can't see the forest for the trees', so all I can think of is to focus solely on the circular graphics and what each implies in that you can only have two out of the three basic design options and it doesn't matter what type of cab alignment it is.
I believe GM is referring to Hoffman's Iron Law. In other words, pick two out of the following three, but ye laws of physics dictate you can't have all of them:
1/ Small size
2/ Low [deep] bass extension
3 High acoustic efficiency
Or to put it another way:
-You can get deep bass out of a pint-sized box, but the price is low acoustical efficiency
-You can get bass extension with high acoustical efficiency, but the price is a large box
-You can have a small box with high acoustical efficiency, but the price is bass extension
What you can't have is low bass extension with high acoustical efficiency in a small box, so you need to pick which performance compromises you are willing to accept / best meet your criteria. For a given driver, those will then determine the general sizing of enclosure & its tuning. Or in some cases tell you that you may need a different driver. 😉
1/ Small size
2/ Low [deep] bass extension
3 High acoustic efficiency
Or to put it another way:
-You can get deep bass out of a pint-sized box, but the price is low acoustical efficiency
-You can get bass extension with high acoustical efficiency, but the price is a large box
-You can have a small box with high acoustical efficiency, but the price is bass extension
What you can't have is low bass extension with high acoustical efficiency in a small box, so you need to pick which performance compromises you are willing to accept / best meet your criteria. For a given driver, those will then determine the general sizing of enclosure & its tuning. Or in some cases tell you that you may need a different driver. 😉
Thank you both. The other link GM just posted is non-baffling as it ties together efficiency n0, Fs, Vas (rather than F3, Vbox), in terms of moving air which makes sense.
Yeah, for the life of me I couldn't think of Hoffman, but remembered John's article, so posted it though have yet to read it beyond seeing the simple, useful graphics.
As for John's 'erroneous' math, haven't looked at it either, but knowing his pro level education, experience, contributions to the DIY community that make mine look entry level at best, not to mention explaining some of the more math intensive (for me) concepts that I pass on nowadays when appropriate, find it hard to believe it's incorrect, especially considering all the 'smart' guys from the basslist that no doubt would have politely 'corrected' him way back when first published.
Confession: I haven't had chance to look at the maths myself, but agreed, given John's rather extensive background hard to believe it's out. Will have a proper gander later out of interest.
Yep, lead & asbesdos. Lovely combination. 😉 The lead's normal enough for lots of these older houses; the asbesdos came as a mild surprise. Fortunately, it's in the pseudo-coving, so removal has been a bit more straightforward than expected.
Yep, lead & asbesdos. Lovely combination. 😉 The lead's normal enough for lots of these older houses; the asbesdos came as a mild surprise. Fortunately, it's in the pseudo-coving, so removal has been a bit more straightforward than expected.
Writing with my general hat on, I've just quickly gone through the https://trueaudio.com/st_trade.htm page, and I can't see anything wrong with it, let alone 'handwaving'. The carefully-referenced formula
Efficiency = k * f(3)^3 * V(B)
(where k is the so called "efficiency constant")
(f(3) is in Hz, and V(B) is in cubic meters)
With its k factors
For closed boxes: k = 2 * 10^-6
For vented boxes: k = 4 * 10^-6
Is from Small, demonstrating the mathematical relationship between conversion efficiency, box size and low frequency extension. F3 is used by Small because his work, and that of Benson, Thiele and Novak (and to a large extent Thuras) is derived from electrical filter theory. John's explanation and simple pie-charts are all perfectly correct as far as I can see -no surprise there.
Efficiency = k * f(3)^3 * V(B)
(where k is the so called "efficiency constant")
(f(3) is in Hz, and V(B) is in cubic meters)
With its k factors
For closed boxes: k = 2 * 10^-6
For vented boxes: k = 4 * 10^-6
Is from Small, demonstrating the mathematical relationship between conversion efficiency, box size and low frequency extension. F3 is used by Small because his work, and that of Benson, Thiele and Novak (and to a large extent Thuras) is derived from electrical filter theory. John's explanation and simple pie-charts are all perfectly correct as far as I can see -no surprise there.
Last edited: