Tannoy DC2528 Transmission Line build.

[tubehunter]

I've decided to try some DIY transmission lines for my Tannoy DC2528 drivers.

I need to decide on wall treatment and foam or wool filling.

Some pictures so far.

http://i514.photobucket.com/albums/t350/halx00/Tannoy%20DC%202528%20Transmission%20line/5B51165C-45C6-42F8-A779-58D6A7F1987A_zps1jniru1o.jpg (http://s514.photobucket.com/user/halx00/media/Tannoy%20DC%202528%20Transmission%20line/5B51165C-45C6-42F8-A779-58D6A7F1987A_zps1jniru1o.jpg.html)
http://i514.photobucket.com/albums/t350/halx00/Tannoy%20DC%202528%20Transmission%20line/E7E5A47A-A687-44AC-9CB6-2EADD1FD4540_zpslrakyjkq.jpg (http://s514.photobucket.com/user/halx00/media/Tannoy%20DC%202528%20Transmission%20line/E7E5A47A-A687-44AC-9CB6-2EADD1FD4540_zpslrakyjkq.jpg.html)
http://i514.photobucket.com/albums/t350/halx00/Tannoy%20DC%202528%20Transmission%20line/4F02DEF2-2503-4A88-A740-F32FB81BFB8B_zpsf6odr6hz.jpg (http://s514.photobucket.com/user/halx00/media/Tannoy%20DC%202528%20Transmission%20line/4F02DEF2-2503-4A88-A740-F32FB81BFB8B_zpsf6odr6hz.jpg.html)
http://i514.photobucket.com/albums/t350/halx00/Tannoy%20DC%202528%20Transmission%20line/ED76E54B-3634-4562-84CC-C7B18052E810_zpsw9ajngk0.jpg (http://s514.photobucket.com/user/halx00/media/Tannoy%20DC%202528%20Transmission%20line/ED76E54B-3634-4562-84CC-C7B18052E810_zpsw9ajngk0.jpg.html)
http://i514.photobucket.com/albums/t350/halx00/Tannoy%20DC%202528%20Transmission%20line/C8349922-8E0B-44DB-B625-BB346C1AAE06_zpscdfdzrnm.jpg (http://s514.photobucket.com/user/halx00/media/Tannoy%20DC%202528%20Transmission%20line/C8349922-8E0B-44DB-B625-BB346C1AAE06_zpscdfdzrnm.jpg.html)
http://i514.photobucket.com/albums/t350/halx00/Tannoy%20DC%202528%20Transmission%20line/69028577-0603-4899-923E-9B477DB1F467_zpsskxtaw73.jpg (http://s514.photobucket.com/user/halx00/media/Tannoy%20DC%202528%20Transmission%20line/69028577-0603-4899-923E-9B477DB1F467_zpsskxtaw73.jpg.html)
http://i514.photobucket.com/albums/t350/halx00/Tannoy%20DC%202528%20Transmission%20line/0989155F-72CB-4589-980D-FB0C0ABDB5E2_zpswavoyqra.jpg (http://s514.photobucket.com/user/halx00/media/Tannoy%20DC%202528%20Transmission%20line/0989155F-72CB-4589-980D-FB0C0ABDB5E2_zpswavoyqra.jpg.html)
http://i514.photobucket.com/albums/t350/halx00/Tannoy%20DC%202528%20Transmission%20line/A02668AB-A331-46CA-82DA-1F4A618045B9_zpssefmzufn.jpg (http://s514.photobucket.com/user/halx00/media/Tannoy%20DC%202528%20Transmission%20line/A02668AB-A331-46CA-82DA-1F4A618045B9_zpssefmzufn.jpg.html)
http://i514.photobucket.com/albums/t350/halx00/Tannoy%20DC%202528%20Transmission%20line/1D8E6D55-26F6-49D1-A051-24391233E78A_zpsibfzq9b6.jpg (http://s514.photobucket.com/user/halx00/media/Tannoy%20DC%202528%20Transmission%20line/1D8E6D55-26F6-49D1-A051-24391233E78A_zpsibfzq9b6.jpg.html)
http://i514.photobucket.com/albums/t350/halx00/Tannoy%20DC%202528%20Transmission%20line/084858BC-C53F-48E0-A937-5154A7D9E713_zpswy8bi9zj.jpg (http://s514.photobucket.com/user/halx00/media/Tannoy%20DC%202528%20Transmission%20line/084858BC-C53F-48E0-A937-5154A7D9E713_zpswy8bi9zj.jpg.html)
http://i514.photobucket.com/albums/t350/halx00/Tannoy%20DC%202528%20Transmission%20line/3913D0A3-5A0B-44F5-99DF-2B3F4C38D1D5_zpsskjcpjah.jpg (http://s514.photobucket.com/user/halx00/media/Tannoy%20DC%202528%20Transmission%20line/3913D0A3-5A0B-44F5-99DF-2B3F4C38D1D5_zpsskjcpjah.jpg.html)
http://i514.photobucket.com/albums/t350/halx00/Tannoy%20DC%202528%20Transmission%20line/81CF56BF-1E18-45E6-8561-F29DC2572112_zpsvixl7fao.jpg (http://s514.photobucket.com/user/halx00/media/Tannoy%20DC%202528%20Transmission%20line/81CF56BF-1E18-45E6-8561-F29DC2572112_zpsvixl7fao.jpg.html)
http://i514.photobucket.com/albums/t350/halx00/Tannoy%20DC%202528%20Transmission%20line/F160BBD9-0957-4742-BDAC-532FC4AEC72C_zpsvfhbmbxw.jpg (http://s514.photobucket.com/user/halx00/media/Tannoy%20DC%202528%20Transmission%20line/F160BBD9-0957-4742-BDAC-532FC4AEC72C_zpsvfhbmbxw.jpg.html)
http://i514.photobucket.com/albums/t350/halx00/Tannoy%20DC%202528%20Transmission%20line/4E299F56-68D6-4203-BA72-AC49CD5C4902_zps23rew7wq.jpg (http://s514.photobucket.com/user/halx00/media/Tannoy%20DC%202528%20Transmission%20line/4E299F56-68D6-4203-BA72-AC49CD5C4902_zps23rew7wq.jpg.html)
http://i514.photobucket.com/albums/t350/halx00/Tannoy%20DC%202528%20Transmission%20line/4081DFC1-415D-4FC8-9928-0342E0670A86_zps7quxxlof.jpg (http://s514.photobucket.com/user/halx00/media/Tannoy%20DC%202528%20Transmission%20line/4081DFC1-415D-4FC8-9928-0342E0670A86_zps7quxxlof.jpg.html)
http://i514.photobucket.com/albums/t350/halx00/Tannoy%20DC%202528%20Transmission%20line/7B40B3F0-5EFA-4C1E-9E63-5BB9E67B8A09_zpsrys7s3re.jpg (http://s514.photobucket.com/user/halx00/media/Tannoy%20DC%202528%20Transmission%20line/7B40B3F0-5EFA-4C1E-9E63-5BB9E67B8A09_zpsrys7s3re.jpg.html)
http://i514.photobucket.com/albums/t350/halx00/Tannoy%20DC%202528%20Transmission%20line/0859FEB0-F8C2-4108-9247-C6FF21892F6D_zpsntfhpzqh.jpg (http://s514.photobucket.com/user/halx00/media/Tannoy%20DC%202528%20Transmission%20line/0859FEB0-F8C2-4108-9247-C6FF21892F6D_zpsntfhpzqh.jpg.html)
http://i514.photobucket.com/albums/t350/halx00/Tannoy%20DC%202528%20Transmission%20line/46872D99-9774-48DF-9816-81E065844C11_zpshduq2nd3.jpg (http://s514.photobucket.com/user/halx00/media/Tannoy%20DC%202528%20Transmission%20line/46872D99-9774-48DF-9816-81E065844C11_zpshduq2nd3.jpg.html)
http://i514.photobucket.com/albums/t350/halx00/Tannoy%20DC%202528%20Transmission%20line/FB511D43-C131-4160-9B4A-1DACE41FA78C_zpsmozqpqmn.jpg (http://s514.photobucket.com/user/halx00/media/Tannoy%20DC%202528%20Transmission%20line/FB511D43-C131-4160-9B4A-1DACE41FA78C_zpsmozqpqmn.jpg.html)
http://i514.photobucket.com/albums/t350/halx00/Tannoy%20DC%202528%20Transmission%20line/F72201DF-1E41-49E2-9BA0-0FA26B2E4A1B_zps7tbgtrud.jpg (http://s514.photobucket.com/user/halx00/media/Tannoy%20DC%202528%20Transmission%20line/F72201DF-1E41-49E2-9BA0-0FA26B2E4A1B_zps7tbgtrud.jpg.html)
http://i514.photobucket.com/albums/t350/halx00/Tannoy%20DC%202528%20Transmission%20line/8536549A-9EC6-417F-A091-7358E76B1EB4_zpsmhforal5.jpg (http://s514.photobucket.com/user/halx00/media/Tannoy%20DC%202528%20Transmission%20line/8536549A-9EC6-417F-A091-7358E76B1EB4_zpsmhforal5.jpg.html)
http://i514.photobucket.com/albums/t350/halx00/Tannoy%20DC%202528%20Transmission%20line/72F82787-04E5-42C2-91F6-BA8CE8B18161_zpsfl0ofqtn.jpg (http://s514.photobucket.com/user/halx00/media/Tannoy%20DC%202528%20Transmission%20line/72F82787-04E5-42C2-91F6-BA8CE8B18161_zpsfl0ofqtn.jpg.html)
http://i514.photobucket.com/albums/t350/halx00/Tannoy%20DC%202528%20Transmission%20line/D153CF25-9F84-455C-8BB0-CEB9259A69FD_zpsnq153emq.jpg (http://s514.photobucket.com/user/halx00/media/Tannoy%20DC%202528%20Transmission%20line/D153CF25-9F84-455C-8BB0-CEB9259A69FD_zpsnq153emq.jpg.html)
http://i514.photobucket.com/albums/t350/halx00/Tannoy%20DC%202528%20Transmission%20line/41AED765-299D-4440-AFAB-B0B5EE901249_zpsqgpyidod.jpg (http://s514.photobucket.com/user/halx00/media/Tannoy%20DC%202528%20Transmission%20line/41AED765-299D-4440-AFAB-B0B5EE901249_zpsqgpyidod.jpg.html)
http://i514.photobucket.com/albums/t350/halx00/Tannoy%20DC%202528%20Transmission%20line/A8898523-6DD3-4E79-A688-29119D465CA0_zps9yimlfcq.jpg (http://s514.photobucket.com/user/halx00/media/Tannoy%20DC%202528%20Transmission%20line/A8898523-6DD3-4E79-A688-29119D465CA0_zps9yimlfcq.jpg.html)
http://i514.photobucket.com/albums/t350/halx00/Tannoy%20DC%202528%20Transmission%20line/6EE23CC2-852A-4C3D-85FF-6DE0FA247164_zpsliaoehqe.jpg (http://s514.photobucket.com/user/halx00/media/Tannoy%20DC%202528%20Transmission%20line/6EE23CC2-852A-4C3D-85FF-6DE0FA247164_zpsliaoehqe.jpg.html)
http://i514.photobucket.com/albums/t350/halx00/Tannoy%20DC%202528%20Transmission%20line/B848B156-068A-4C35-9D29-AAFBD9D853F9_zpsea2j7fma.jpg (http://s514.photobucket.com/user/halx00/media/Tannoy%20DC%202528%20Transmission%20line/B848B156-068A-4C35-9D29-AAFBD9D853F9_zpsea2j7fma.jpg.html)
http://i514.photobucket.com/albums/t350/halx00/Tannoy%20DC%202528%20Transmission%20line/85E530B9-ABAF-422B-950C-B8749F978B59_zpsawla8mqq.jpg (http://s514.photobucket.com/user/halx00/media/Tannoy%20DC%202528%20Transmission%20line/85E530B9-ABAF-422B-950C-B8749F978B59_zpsawla8mqq.jpg.html)
http://i514.photobucket.com/albums/t350/halx00/Tannoy%20DC%202528%20Transmission%20line/DF9EED41-CDB8-4D62-8C59-DC7830C27D11_zpsr5p09pjz.jpg (http://s514.photobucket.com/user/halx00/media/Tannoy%20DC%202528%20Transmission%20line/DF9EED41-CDB8-4D62-8C59-DC7830C27D11_zpsr5p09pjz.jpg.html)

[Macca]

Looks interesting. I take it a Tannoy DC can be used in a TL? I read somewhere that not all drivers are suitable.

[tubehunter]

Well I'll soon find out.:)

Here are the parameters



T&S parameters of the HPD295/2528/ DU296 as supplied by Tannoy UK LTD:



TANNOY HI-FI
THIELE-SMALL PARAMETERS HPD295

Tannoy Ltd.,
Rosehall Industrial Estate,
Coatbridge,
North Lanarkshire,
ML5 4TF
UK


DRIVER TYPE: HPD295/ 2528/ DU296

DATE TESTED: -

NOTES:

Tannoy Ltd. The contents, information and copyright of this document are the sole property of TANNOY LTD
and may not be used for commercial gain without the express knowledge and permission of the owners.
Although believed accurate, no responsibility can be taken regarding the consequences of any errors or
omissions.
All measumements were made with the drive unit suspended in free air, with the free air resonance calculated
by the added mass technique, using a 0.1 ohm current sensing resistor. All figures are ± 10%, to allow for
manufacturing tolerences.



PARAMETER VALUE UNITS

Voice coil resistance, Re: 5,8 ohm
Free air resonant frequency, fs: 26 Hz
Moving mass, Mms: 34,4 gm
Electrical Q, Qes: 0,26 -
Mechanical & Acoustical Q, Qms: 2,2 -
Total Q, Qts: 0,23 -
Force factor, Bl: 11,2 N/A
Total suspension compliance, Cms: 1,1 mm/N
Equivalent volume compliance, Vas: 200 Litre
Mechanical resistance, Rms: 2,55 Mechanical ohm
Effective radiating area, Sd: 360 sq. cm
Sensitivity (2.83V@1m, 20 deg. C): 91,2 dB

[walpurgis]

Interesting design Duncan. You'll get some deep bass out of those.

I glue pieces of dowel between transmission line dividing walls and brace them against cabinet walls. I'd avoid using foam in the actual line. It reduces the effective dimensions at lower frequencies. Teased out long fibre wool is good. Plenty on eBay under crafts. Fabric/felt underlay is good for lining walls, perhaps with some bituminised damping pads underneath.

If you come up with any crossover tweaks, I'd be interested in hearing about them.

[walpurgis]

Looks interesting. I take it a Tannoy DC can be used in a TL? I read somewhere that not all drivers are suitable.

If it works in a reflex box, it's likely to function OK in a TL.

[struth]

Very good Duncan.. will be nice I reckon.

[danilo]

Interesting build. What do they sound like is the important bit?
TL's are simply Bass Reflex boxes in Drag ;-) once the drivers reach 8' diameter.. according to Martin King.
Not saying they won't work well, just that TL is an odd naming.

[Macca]

For it to be a true transmission line the line in theory needs to be infinite (in practice, not). But I don't think anyone has done that in a commercial speaker.

I've had large ported speakers and I currently have TLs (with 8 inch bass) and the difference in bass performance between the two designs is not subtle. Both go low but the TL has so much more power in the low stuff.

[tubehunter]

I should of said 1/4 wave transmission line, all 7ft 6in of it, giving around 35hz tuning I think.

I recently had some IPL s4tl's here and agree the bass is outstanding, this was one reason for this project.

What I like about the Tannoy's is the point source and presence in the mids, it just sounds right.
But I don't feel the passive ABR works, seems to blur the bass lines.

Got some bitumen sound deadening in with some foam on top.
I going to leave the fronts screwed only until I decide on line filling or more foam if needed, after auditioning.

http://i514.photobucket.com/albums/t350/halx00/Tannoy%20DC%202528%20Transmission%20line/FCC6FF08-3A3E-4F66-82EA-D0D9CCB3B933_zpsqekmf0um.jpg (http://s514.photobucket.com/user/halx00/media/Tannoy%20DC%202528%20Transmission%20line/FCC6FF08-3A3E-4F66-82EA-D0D9CCB3B933_zpsqekmf0um.jpg.html)
http://i514.photobucket.com/albums/t350/halx00/Tannoy%20DC%202528%20Transmission%20line/B12C7A86-88DF-40EA-94EA-AD50FEFE6EB5_zpsesnb6a7n.jpg (http://s514.photobucket.com/user/halx00/media/Tannoy%20DC%202528%20Transmission%20line/B12C7A86-88DF-40EA-94EA-AD50FEFE6EB5_zpsesnb6a7n.jpg.html)
http://i514.photobucket.com/albums/t350/halx00/Tannoy%20DC%202528%20Transmission%20line/F73A6A28-54B0-4924-A86F-C31A813F2DDF_zpsbx8dpplo.jpg (http://s514.photobucket.com/user/halx00/media/Tannoy%20DC%202528%20Transmission%20line/F73A6A28-54B0-4924-A86F-C31A813F2DDF_zpsbx8dpplo.jpg.html)
http://i514.photobucket.com/albums/t350/halx00/Tannoy%20DC%202528%20Transmission%20line/E22B1B1A-B7AF-4F99-AADF-B473469CFFC3_zpsghc9wgdf.jpg (http://s514.photobucket.com/user/halx00/media/Tannoy%20DC%202528%20Transmission%20line/E22B1B1A-B7AF-4F99-AADF-B473469CFFC3_zpsghc9wgdf.jpg.html)
http://i514.photobucket.com/albums/t350/halx00/Tannoy%20DC%202528%20Transmission%20line/3CB71F74-F476-45C0-942F-A8FBB469EA82_zpsaqlb9byy.jpg (http://s514.photobucket.com/user/halx00/media/Tannoy%20DC%202528%20Transmission%20line/3CB71F74-F476-45C0-942F-A8FBB469EA82_zpsaqlb9byy.jpg.html)

[tubehunter]

"Oh God ! What have I Created?"



:eek:

[Macca]

Working then?

[Marco]

Like it so far, Dunc, I shall be following this with interest! :cool:

Marco.

[struth]

Need to get you to make me up a flat pack dunc :eek: super job

[Ian Walker]

"Oh God ! What have I Created?"



:eek:
Dunc...Are you alright there?

Has one just run across the room and eaten you!! :lol:

[danilo]

Had my interest until you said 1/4 wavelength.
http://www.quarter-wave.com/index.html

[Reffc]

Had my interest until you said 1/4 wavelength.
http://www.quarter-wave.com/index.html

Nothing wrong with a decent 1/4 wavelength design. Castle Acoustics with design leadership from Andy Hill are probably best known for their very successful implementation of the 1/4 wave design starting with the Chester Mk1 in 1988 (or thereabouts) and the Harlech, Howard and Winchester loudspeakers. Great sounding designs if you've ever managed to hear any.

[ScottL]

There is absolutely nothing wrong with a quality quarter-wave speaker, other than the fact that there is about a metric ton of myth and nonsense that has been attached to them. FWIW, a few basic points:


'Transmission Line' is in the majority of cases something of a misnomer. It has become a convenient catch-all phrase for all QW enclosure types, which means you can see it being trotted out for enclosures that are functionally opposites of each other. Since it's been ingrained into hi-fi terminology now, it's too late to get rid of it. Technically it comes from the electrical transmission line, so if the definition is applied strictly, it should be a line that is designed with the sole object of providing the flattest possible impedance, with zero other considerations. Of course, as noted, it's almost never used so narrowly. Bailey employed it in the title of his old '68 Wireless World article, and caused a massive amount of confusion by then proceeding to describe a line that was in fact partially resonant.

A TL / QW type speaker is not a bass reflex. It differs in that the dominant resonant mode is derived from standing waves / eigenmodes not Helmholtz cavity resonance. If we compare the physics of (for example) a mass-loaded transmission line (MLTL) to a BR, the practical transition from one to the other can be said to occur when one dimension of the enclosure is stretched sufficiently for the eigenmodes generated to modify the enclosure alignment away from what would be obtained from the same Vb and vent dimensions under Helmholtz conditions (which assumes an internal uniform air particle density and no standing waves). Most MLTL designs are quite highly forced (significant mass loading) to keep the dimensions in check, but they still generate & exploit standing waves to an extent.

Internal stuffing material does not significantly slow the speed of sound. It does a bit, but not much. That was Bradbury's theory -a very nice, elegant piece of maths, based on aerodynamic drag. Unfortunately it was wrong, as Augspurger, King & a number of others have subsequently illustrated. Naturally, different materials have different absorption properties, so stuffing densities tend to need to be adjusted on this basis, and some of the details will differ a little.

The fundamental resonant frequency of a line is a function of axial length and taper, so simply taking c / (desired Fp / 4) only works for untapered pipes, and only then when you have factored in end-correction etc. A tapered pipe (narrowing toward the terminus) will have a lower fundamental than an untapered pipe for the same physical length. An expanding pipe (horn) will have a higher fundamental than an untapered pipe of the same physical length. In both cases, how much lower or higher depends on the degree of taper.

Line cross sectional area has no functional relationship to driver Sd. Unfortunately that's one myth that has got itself particularly ingrained, and is arguably the cause of more unsuccessful QW enclosures than anything else, since it often ends up causing an insufficient internal volume.

Tuning to the driver free air resonant frequency F0 is rarely optimal; like any other type of enclosure, line tuning depends on your particular objectives and the driver characteristics. Another one that's responsible for a lot of poor performing QW / TL boxes.


Rgds
Scott

[walpurgis]

Good quote Scott.

Having built several very effective 1/4 wavelength tapered TLs (and 1/4 w/l horns) I'd agree with what is said.

[danilo]

Erm OK.. Have any obtained and Tried... Martin Kings' worksheets ?
He's a Mathematician... his developed modelling/design formulas are More than simply good. State of the Art imo.
He claims/proves that once at 8" drivers, a 1/4 w and or a folded tube variant IS effectively a BR box.. with the attendant Math.

Nothing less than naive to design a 1/4 w or Folded line contraption.. without consulting Kings' works
They are a Proven design tool... learn the programs (easier said than done TBH ) and the results are as predicted.
A genuine 'cut once' solution to an Old problem
Those were Freely available.. until recently.
Sadly he has, due to persistent abuses removed the Free aspect.
Still available, if you ask nicely and pay a 'reasonable' fee.

Just trying to help here ;)

[walpurgis]

I was perfectly happy using principles described by G A Briggs over fifty years ago.

[ScottL]

Have I obtained & used Martin King's Mathcad worksheets? Yes. As it happens Martin is a friend and we remain in sporadic contact; I was one of the earlier adopters / users of his worksheets, and I've been using them, along with a battery of other software when needed for 14-15 years now. All of the designs I have done on the Frugal-Horn site were modelled at some stage, and in some cases refined, in his worksheets. The same applies to all of the designs on my Woden Design site, and the (literally) several thousand that I have created for others over on diyAudio & other forums, be they back-horns or other QW variants such as TLs and the like. So I'm familiar with Martin's seminal work. It's unfortunate that he discontinued supply of the sheets due to their being exploited by some for commercial gain without paying the very modest license fee, although I can't say I blame him. I supported Martin's stance then, I do so now, and will continue to do so.

Nowhere does Martin claim an MLTL is identical to a bass reflex TTBOMK. A bass reflex assumes Helmholtz cavity resonance, which is based upon there being a uniform internal air particle density and no eigenmodes (standing waves). An MLTL (a moniker my friend GM created around the turn of the century to differentiate between straight / untapered pipes and Martin's then-new ML-TQWT for the now-defunct Fostex FE164) either deliberately generates and uses, or specifically accounts for the presence of standing waves in the design. That is the fundamental difference between the two. As I noted, strictly, the shift from BR to QW (MLTL) loading can be said to occur when one dimension is stretched sufficiently relative to the others that the standing waves generated will change the alignment for the same size of vent. You can see the effects of dimensions easily enough in Martin's worksheets -that's one of their great assets. Take a driver suited to reflex loading & design a simple BR for it, without any damping so the differences are easier to see. Use golden ratio or whatever. Fix that enclosure volume & the vent dimensions, and change the overall cabinet HxWxD ratio so that one dimension is significantly stretched relative to the others. You'll see how the response can change as a result of the internal standing waves, without there being any other changes to driver, vent dimensions etc. The attached for example (apologies for the small size -for some reason I can't get the full sized image to upload). I did this quickly for a generic driver; it's a deliberately under-damped alignment to make the differences more obvious. The upper row shows it as a reflex tuned to 60Hz. I've included FR and the driver + vent outputs. Lower row shows the same driver in the same cabinet volume with the same vent, but with the cabinet dimensions changed so that the height is significantly stretched relative to the width & depth. Fb (box tuning frequency) has dropped by 12Hz, you can see the harmonic modes coming in at odd multiples of the fundamental.

The 8in driver size mentioned is an interesting one though, and I entirely agree with the point I assume Martin is making. Like most other things in life, we deal in shades of grey (hopefully not 50 ;) ) rather than black & white. That means that for most people, there are certain practical limits for cabinet size; particularly height. As a quick & dirty ROT, most 8in drivers (not all) want a larger box volume than smaller units, and can frequently be tuned lower. And if the maximum permissible cabinet height is fixed at a certain modest point, then the relative difference between the HxWxD dimensions is reduced, which in turn tends to reduce the influence / generation of standing waves and their impact on the overall behaviour / frequency response et al. So, the larger the driver (assuming it needs a greater box volume) & the lower it can be tuned, the longer the pipe has to be for the standing waves generated to significantly affect the response; to put it another way, for a given Vb you need to maintain a high ratio of length to cross section for QW action to dominate the tuning frequency / basic alignment shape. So, in a lot of cases, an MLTL for an 8in driver is actually a bit short for a low tuning frequency (or 'highly forced' if you prefer); they exist in a grey region where you don't necessarily have all that much of a difference on FB per se, but the ratio of dimensions is sufficient for standing waves to still be generated, which will likely have some impact on the shape of the response in the octave above Fb, and should be accounted for in the design, whether in terms of adjusting the vent dimensions slightly to hit the desired alignment, and / or altering the driver & vent tap locations, and likely some of the damping to reduce any unwanted harmonic modes. That's one of the mot important things Martin's worksheets hammers home: that whatever name you want to hang on it, a quality design needs to account for all physical effects. They're not a panacea, they don't design boxes for you, and the damping assumptions are based on Martin's own measurements of hollow-fibre fill (Dacron) but unfortunately not all types of hollow-fibre fill are one & the same, so you get some variability there; likewise with different materials. You can fudge it very closely though when necessary based on prior experience of using different materials & what the relative levels / positions of damping in Martin's worksheets will best represent them, so it's not too much of a deal, especially when room modes / variability is factored in. They're certainly one of the best enclosure design tools of the last 20 years or so, and hopefully Martin will release some again in the future.

Rgds
Scott

[Reffc]

As Scott rightly says, as the drive unit size increases, then practicalities such as cabinet height come into play which for most people may limit the viability of a 1/4 wave design. However, I am not aware anywhere of Martin or his work actually singling out 1/4 wave design per se as being a poor substitute to other types of loading. As Scott has already stated, there are many benefits of 1/4 wave design, such as phase coherent bass response with very shallow roll-off slopes making for a very efficient way to extract decent bass from a small drive unit (subject to it's lower resonance limits in said box), and of course for flattening impedance. These are all commendable goals for loudspeaker design. Irrespective of which model you care to choose to design any loudspeaker, ultimately they are a jumble of compromises, some being more compromised than others, and each having it's own merits. There are many very fine examples of 1/4 wave designs, many of which are very successfully being produced today.