Im not a fan of Burr woods they are too blingy for me but should match ok.. The only Burr i really like is Oak or Elm Burr
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Im not a fan of Burr woods they are too blingy for me but should match ok.. The only Burr i really like is Oak or Elm Burr
The Sycamore Cluster is not as dense a pattern as most burrs. Its way more subtle and looks lovely in the flesh. It has a very slight yellowish tinge and conrasts beautifully with the Walnut,
I tried mixing and matching several timbers and looked at Maple, Oak, American Black Walnut, European Walnut, Crown cut Sepele, Red Cheery, Zebrano and many more, but the Cluster Sycamore and Walnut was by far the nicest combination for my own personal tastes. Sycamore is a much under-used timber!
Well, it's usually described as maple, which may lead to that impression but it's not really underused.
I've sold a lot of Sycamore timber in the past (sawlogs and veneer butts) and most of the good quality sticks go to the Continent. There's a big demand for good quality ripple Sycamore in Germany for musical instruments, especially violins & cellos. The slightly lower quality wood goes to make furniture and industrial rollers.
Well, Sycamore whilst part of the Maple family(of which there are many varieties) is used in this context to describe native Sycamore from the UK. This is UK sourced Burr Sycamore veneer and lovely timber at that. Looking forward to seeing the finished article but a heck of a long way to go! Spent part of the day designing the baffle board and jointing (made from 3 different types of timber) including working out the grille design and fitment and how the baffle edges would be finished.
The lining of the interior of the cabinets will consist of carpet underlay glued to the inside over which I'll place 3 inches of long lambswool.
I think they will look great and I've always thought Syc would make a good speaker veneer because it is very hard and, therefore, stiff.
I really don't want to fence with you over silvicultural terminology, but Sycamore isn't native to the UK, although it is considered to have become naturalised. Your veneers may well have been grown in the UK, but they are not native.
Technically correct, so perhaps to keep everyone happy ( ;) ) I'll refer to it as naturalised to the UK. "Acer pseudoplatanus", or "Great Maple" originated in Europe and isn't related to other Sycamores found elsewhere in the world (except perhaps to some of the Great Maples in Aisia). It is very commonly widespread in the UK (as it has been for many hundreds of years).
In fact, although thought to have been introduced by the Romans, It hasn't been widespread here up until several hundred years ago, perhaps a little earlier but whatever it's ancestry it shouldn't be compared with other species sharing the same name found outside of Europe as it is a different tree.
I agree with you though, it's very suited to speaker cabinetry. Durable and attractive, especially when contrasted with darker timbers. I rarely see it used in speaker cabinetry although Bird's Eye Maple is used by many manufacturers. I believe that is most commonly found in Sugar Maple and some Red Maples. The veneer I'm using is not a birds eye Maple though.
Wow..this seems to have turned into a timber blog!
Well, I don't think Tannoys will ever be my thing, but I thought I'd come in here with a maybe-relevant recollection ...Quote:
Originally Posted by Reffc
A few Scalford Shows ago I seem to recall Simon sq12344etc sharing a dem room with a guy who had pair of speakers - Tannoy drivers in a tall enclosure (1.5m-ish?) shaped kind of like you describe, Paul. Quite probably the best Tannoy-based design I have heard.
Maybe worth dropping Simon a line to see if he knows owt about it or can give you a contact?
Thanks Jerry. Perhaps worth a look. I've designed the cabinets to extract the best performance from the 315's, at least on paper/computer! I have made a few changes since I started, as further modelling and speaking with a friend who will be helping me with the build (he has a great deal of cabinetry experience) has refined the design. We will either experiment with a home brewed vacuum forming machine to form curved ply sheets to be laminated for side panels, or I'll make the shape more a conventional box but use internal sloping baffle boards to prevent standing waves formation. Either way, the front baffle board design has been extended slightly to 550mm to reduce baffle-step losses.Quote:
Originally Posted by jandl100
Don't know if this is better here or the DIY section but as I've started, I'll continue!
I've now completed the design for the speaker cabinets and had a mad panic when after placing the timber and materials on order, realised I'd mis calculated for the volume taken up by the acoustically non-transparent 12mm wool felt in each enclosure (ie decimal point in the wrong place!) so 2 litres was in fact 20 litres!
Result is that each cabinet has had to grow to 180 litres in volume...not too far off the Lockwood volume! Couldn't source the cluster Sycamore but managed to get some of this instead:
http://i1140.photobucket.com/albums/...ps1cf9725b.jpg
10 large sheets of Grade A quality Ripple Sycamore on order instead!
I've tweaked the design to now use two 100mm diameter ports to generate a smoother response in-room (in theory) tuned to 34Hz (just a few dB down at this which should be interesting!).
Each cabinet is growing and will measure 1.28m tall weighing in at over 75kg each (without drivers). After some trial work at the workshop with the guy who's helping with the build (it's a two man job for various reasons) we've perfected a DIY jig to bend 6mm panels and laminate them in twos to form a single 12mm thick curved panel...two each of these then glued and clamped forming a 24mm cruved panel side. The end result in plan view will resemble a large kettle drum on it's side!
Sourced some very bling bell-mouthed ports of exactly the right size from Germany and they're now winging their way to me along with 3.5m2 of acoustic foam, 3.5m2 12mm dense wool felt, the same amount in 2mm mastic sheeting and a box of long lambswool. The cabinet fillings have cost an arm and a leg but I want this to be a no-holds barred high quality speaker build.
Some CAD mock ups of the speakers to follow so watch this space!
Quote:
Originally Posted by Reffc
All sounds very exciting, looking forward to the final result :)
CAD mock up's completed. First one shows the bare cab cut for driver and ports:
http://i1140.photobucket.com/albums/...ps2ee5a572.jpg
There'll be some sneaky design such as burying small neodymium magnets set into the ply front baffle underneath the veneer, with corresponting magnetic strips set into the grill beneath the cloth so that the front lines of he woodwork will remain unspoilt with the covers removed. With the full length cover on, the cabinet will look like this:
http://i1140.photobucket.com/albums/...ps2bd96a43.jpg
Not unlike my older Horning Agathon Ultimates in front profile except larger! A shade under 1.3m tall but with rounded side panels.
Quote:
Originally Posted by Reffc
Looks gorgeous Paul.
Does it come in 15in? :idea:
It can certainly be arranged Tom. A 15 inch driver would add 50mm all round on the dimensions (gross volume of 230 litres). No shrinking violets!Quote:
Originally Posted by montesquieu
Tannoy seem to have gone to long slotted ports rather than the round tube approach which in some setups can be a bit 'obvious' (chuffing and wheezing). Any rationale for going either way? Is there method in calculating the opening size and placement?Quote:
Originally Posted by Reffc
The reason they've done that I think is largely cosmetic Tom, but I did find hat the crudely cut port (no shaped entrance etc) being narrow was a little wheezy and could make the bass a little slow sounding.Quote:
Originally Posted by montesquieu
I've used a standard Helmholtz model to check the ports and have gone with an arrangement similar to that recommended by Alex Garner of Tannoy: Two 100 diameter ports 200mm long. I've placed these fairly high in the cab as that helps with bass speed (apparently) although I'm unsure of how it affects the mid-point standing wave (or vice-versa)which tries to form in tall cabs (max amplitude at the mid point) but have designed a lot of wadding around a central chamber at this point to negate that effect. I've also used WinISD to check and that model came out with a similar result (suggesting 3mm longer ports, but what is 3mm between friends?:lol:)
Your cabs look rather long. Will they be baffled to break up standing waves along the major dimension?
The length isn't an issue on its own, as the formation and control of standing waves is a little more complex than just analysing the length. The internal length is 1.16m, reduced to an effective length of 1.13m due to internal acoustically non-transparent damping and wadding. In the middle, there will be additional wadding to help damp down the amplitude of any waves forming along the length although there will be holes or gaps to allow the lower ports to be driven properly. The internal dimensions have all been selected so that there are no equal multiples with respect to each other (this is very important) and the side panels curved to reduce internal reflections in that plane. There are also internal ribs which protrude 50mm into the cabinet asymmetrically spaced and these have internal cross bracing which also helps break up standing waves. In theory, they should be very well damped and controlled in this respect.Quote:
Originally Posted by walpurgis
Veneer's here...all 10 sheets!
http://i.ebayimg.com/t/Fiddleback-Ri...j,w~~60_12.JPG
Bellmouth ports :carrot:
http://i.ebayimg.com/t/SPEAKER-CABIN...UPw~~60_12.JPG
Slow progress, as too many other things to do! Still, managed to get all materials now and totalling up the cost needed some smelling salts and sweet tea to bring me round!
Covered the ports in the same 12mm dense wool felt that will be applied to the inside of the speakers:
http://i1140.photobucket.com/albums/...ps8206dde7.jpg
I've also modified the front baffle board design in an attempt to bring down the resonant frequency of the panel, and introduced an extra coupling brace. The baffle is now 25mm Birch ply with an inside panel of 6mm MDF glued to it and 2mm Bitumen sheeting applied to the MDF internal face plus 12mm dense wool felt. I'm taking no prisoners. These panels will be as acoustically dead as I can get them!
Hi Paul
Have you considered Deflex Panels rather than all that wadding - I had good results with them years ago - they kill the box reverb without deadening the sound.
http://www.madisoundspeakerstore.com...tandard-panel/
I have Martin, but at £17 each (280 by 210mm) I would need 50 of them so way too expensive! What I have designed is tried, tested and cheaper. Bitumen sheeting helps damp resonance and also helps to pull resonant frequency down below the critical mid range. 12mm dense wool felt helps with acoustic damping, the foam panels help with absorption of mid frequency to high frequency reflections and the long lambswool helps with attenuation of LF. You want the cabinets to be as dead as possible resonance wise and internally very well damped so that there are no reflections colouring the information coming from the front of the driver. You can over do damping, but not as you may think. Add too much and the driver sees a virtual volume greater than the actual volume so that you can reduce SPL in bass output, but I'm with the school of thought that there's frequently not enough internal damping in loudspeaker boxes.Quote:
Originally Posted by Macca
Fifty! You don't need to coat the whole interior with them! I guess we differ about damping - I think most speakers have too much. I alwyas used 3 quarter inch chipboard all round for cabs so pretty dead sounding anyway.Quote:
Originally Posted by Reffc
There's various schools of thought but I want the panels to be as acoustically dead as possible and the construction is designed to be very dense and very stiff. I much prefer Birch Ply for cabinets to the chip board, but most timbers can be made to work with adequate bracing. I'll be using three internal cruciform braces. I know that the design works because there's been very similar and very successful designs carried out in the past using similar design/technique to that I'm using. Chipboard just doesn't have enough panel stiffness for my liking.
Your system damping ideas make sense to me Paul. It's good to hear somebody describing accurately what the various types of materials are useful for and how to use them. So many people cock that up.
Thanks Geoff. I must admit, I've seen (heard?) many more under damped cabinets than over damped! Most problems seem to revolve around inadequate front baffle mass/stiffness. You need both high mass and stiffness to lower resonant panel frequency AND to limit panel excursion to minimise distortion. It always puzzles me to hear comments about over damping the inside, when it does require at least 70mm depth acoustic foam and wool all the way round, with twice that behind the driver!
Well I'm a firm believer in bracing everything I can sensibly do inside a cabinet, as well as the damping of course and I too like the front baffle to be as substantial as possible. I often brace the main driver to the rear panel as well.
Some more progress. Came out of hospital this morning and told to rest, so naturally my time has since been spent in the workshop where the speaker side panels were busy "cooking" in the DIY laminating machine. This consists of a table top with a hinged alloy frame and inlets for vacuum pipes connected to an electrical motor and vacuum pump. It generates 14lbs/sqr inch pressure on whatever former is placed into it (there's a tough plastic cover attached to the hinged frame which pulls down over the former). Once the motor's started, the plastic pulls down evenly across whatever piece of work you want to put in there, and holds it for gluing/forming for as long as needed. Each of these panels was in for around 4 to 6 hours:
Machine in action with one of my speaker side panels being formed from 6nr 4mm Birch ply sheets glued with PVA:
http://i1140.photobucket.com/albums/...ps85d822aa.jpg
Vacuum pump turned off and former lid removed:
http://i1140.photobucket.com/albums/...ps817ec489.jpg
One of the panel edges had rippled slightly but not as bad as it looks since the panel width is oversized to allow for this edge rippling which can sometimes occur. It'll be trimmed up and will be fine:
http://i1140.photobucket.com/albums/...psd42937be.jpg
One of the laminated panels at rest for a day or so after gluing up to allow for any further movement before final trimming:
http://i1140.photobucket.com/albums/...ps4b797c81.jpg
Each of these sides weighs approximately 15kg! You can imagine what each speaker will weigh with two of these, the front and rear panels (front panel is 30mm thick!), bracing, damping and drivers. It will be a two man lift per speaker for sure.
A little more progress in between jobs...these are now taking shape!
First dry mock-up of first speaker cabinet today. Due to very slight deviations (a few mm) along the length of the curved side panels, making a template and using the same uniform shaped ribs didn't work, so each rib has had to be custom tweaked by a few millimetres to ensure an exact fit. the square panels and uprights are not part of the build; they're just there to aid stability of the mock up. This is just the beginning and there's loads of work left to do, but at least you can start to get a feeling for the height. These are about 4 feet tall:
http://i1140.photobucket.com/albums/...psbaf6f442.jpg
Close up of one of the ribs:
http://i1140.photobucket.com/albums/...pse0832513.jpg
More to come next week.
Cor! You don't hang about do you.
It's getting more interesting by the day.
(just seen a really nice looking pair of Mansfield cabinets on eBay by the way)
:lol: Yes, they are my Mansfields. Someone bought them and asked for a cancellation because he thought it was for the speakers including drivers despite the block capitals stating it was for cabs only. He has not offered to pay my re-listing fees either, despite being invited to. Some people...Grrrrrrrrrrrr.Quote:
Originally Posted by walpurgis
The speakers under construction still have I guess around 2 to 3 weeks left before they're finished. Once the panels are all cut, formed and tweaked for fit, they have to be veneered before final construction as they wont fit in the the vacuum former used for pressing the veneer whilst gluuing unless in individual panels. The veneer has first to be trimmed and bookend matched. The veneer is pretty stunning in the flesh.
Yes, I too have come across the occasional eBay genius. It happens.
I don't know what type of adhesive you plan using for the veneer on the bendy bits, but I've built large cabinets with expensive veneer onto curved surfaces and found using a good contact adhesive (Thixofix) on both surfaces and allowed to go only just tacky dry was best for me.
Obviously great accuracy is needed to get the veneer lined up before the glued faces come into contact and 'grab', as you only get one chance.
The trick is to first lightly press the veneer down, then rub firmly along the grain with a softwood block, working from the centre of the panel outwards. This gets the veneer tightly down onto the panel with no lifted areas. I'd suggest a couple of trial pieces if you adopt this method.
Should any bubbles or lifted areas become apparent, they can be persuaded to stick down with a hot iron as long as they have had a proper adhesive coating originally.
I've had beautiful results.
I'll be using PVA in all probability Geoff. The veneer is too expensive to risk mucking it up so the veneering will be done in the same way as the curved panels were formed. The PVA will be evenly applied to the plywood face, the veneer placed on and rubbed down from the centre outwards, then placed inside the vacuum former and left for at least 4 hours to set before removal. The PVA is more than strong enough and this method allows complete confidence that sufficient even pressure is applied to prevent bubbling up of the veneer. It's very time consuming as only one panel can be done at a time but hopefully by this time next week, there'll have been enough time to book match and glue the first few veneers. I'll post some photos when done.
Side panels now veneered using the vacuum former and work started tidying the panels up ready for the first lacquer coat. Photos to come. Veneer looks great and really suits the profile.
Have had a think about the internal damping and reckon I can get away with slightly less except for behind the drive unit, by introducing some "V" deflector panels. The volume lost will be balanced by the volume gained omitting the wool felt to the side panels so I plan for two Vee deflectors: one in the base, to reduce unwanted standing waves along the length of the cabinets, and one set of two (ie "W" deflectors) on the rear panel behind the drive unit. The chamber containing the drive unit will be fully lagged and damped using bitumen, wool felt, acoustic foam and long lambswool. The front and rear baffle panels will also have wool felt applied to deaden them but I'll now omit this felt from the side panels as I don't want to risk over damping the panels.
There was some talk years ago about damping materials causing the speaker to 'see' a larger cabinet volume than it does without them. How factual this is I don't know, but it may be of interest.
Its perfectly true Geoff. When you stuff something like long lambswool onto a speaker enclosure, the path travelled by the backwave from the speaker driver is increased, fooling the speaker into thinking it's in a larger cabinet than it is. You can increase apparent volume by up to 25% by stuffing the whole enclosure. Whilst this is usually a good thing for sealed cabinets (the larger the cabinet the smoother the response and the less rolled off the bass) it isn't a good thing for ported cabinets. This is because you have tuned the ports to a specific frequency and the act of increasing apparent volume will lower the resonant frequency of the tuned enclosure. "great" I hear you say, but not necessarily so.Quote:
Originally Posted by walpurgis
Every driver has what is called a "free air resonance" which is it's natural harmonic resonant frequency when unloaded (ie free air or dipole conditions). If the cabinet tuning falls on or very close to this frequency then all sorts of horrible LF distortion is the result. Its important to also realise that a manufacturer's stated FAR for a loudspeaker driver is often not the same as that measured! Some Tannoy MG 12 inch drivers I know have a FAR of approximately 50Hz which is way above the stated FAR, so its important that cabinets for MGs are not tuned or resonate at 50Hz or close to that figure.
I'll bet you're sorry you asked now!
Tuning a reflex cabinet should be done as precisely as possible and the cabinet should not be over damped. The only area which you can really go to town on the damping is behind the driver to prevent unwanted reflections straight back through the driver. Everywhere else should just get the minimum needed to absorb HF reflections and mid frequency reflections. A few inches of acoustic foam or a single 35mm layer of baff/wool elsewhere is fine.
Because mine are long cabinets, I have to be concerned with half and quarter wavelengths at LF's and work out where the nodes and anti-nodes form. To reduce the possibility of these forming I have added the sloped or "Vee" panels to the design (all will become clear when the photos are posted) and also introduced damping at the critical areas such as around the ports barrels themselves and in the centre of the chamber.
Closed infinite baffle boxes are far easier to design for, especially if large. Predicting what happens with smaller boxes is more tricky and these do by and large need to be much more solid and heavily damped than large cabinets.
Beware any floor-stander that feels light. Probably an indication of being under-braced and under damped using thin panels. Particular attention needs to be paid to the front baffle which should be as acoustically dead as possible (very heavy and well damped).
You've been browsing your textbooks again Paul.
No, I'm not sorry I asked. It's nice to see that somebody else has a good grasp of speakers. They're my favourite Hi-Fi subject.
Having built around fifty speaker systems in the past I have actually learned a lot. I'm aware that to have port resonances tuned close to that of a main driver can create problems. That applies to all vented systems, not just reflex (Hemholtz) types. You can end up with a huge bass hump, cancellation and all sorts of dodgy harmonic effects.
I personally like transmission line or acoustic column (which are not quite the same thing) speakers and have built several. Horn speakers are nice, but I don't like the immediate 'backloading' Lowther tend to use as it creates all sorts of colourations due to the too close proximity of reflective surfaces. A big flare/horn coupled reflex or quarter wave horn can sound great though.
The original 12" Tannoy Monitor Gold, with the pleated paper cone surround was basically a Monitor Red with higher power handling and at one time had a quoted free air resonance of 23 Hz. which I never believed, nearer 40Hz. I'd guess. The next version with the rubber roll surround had a lower resonance and may well have been around 30Hz. The last 12" gold had the unfortunate 'Tanoplas' foam surround which was slightly more pliant and might well have produced a resonance getting down into the twenties. Although I've owned these, I never bothered to measure their characteristics.
The quoted resonance for the little IIILZ was the biggest porky, Tannoy claimed 30Hz, but my guess would be getting on for twice that. You just could not get proper deep bass out of them. I've used these in pretty big cabinets and their limitations were obvious.
Yes, I have a soft spot for 1/4 wave loaded speakers. Castle made quite a few along these lines and I owned three pairs (Chesters and few pairs of Howards) and the Howard S2's were amongst my all time favourite loudspeakers although the treble could be a little coarse.
Tannoy claim 26Hz for the HPD and a similar figure for the MG which simply cannot be true. The HPD was engineered for more (and lower) bass so I can't and don't believe that the later MGs achieve the same power handling or bass response (they don't). The problem with HPDs is that unless the cabinet is optimised to make the best of that response, they can sound toppy and require some increase in the HF series resistor, and really benefit from a notch filter at the crossover point. (in fact ALL Tannoys benefit from a notch filter to cure the impedance characteristics at the crossover point to tame the honk!). Once you have the HPDs in proper cabinets, they start to make far more sense as the balance is restored. You simply cannot achieve this in undersized cabinets with them, without getting a very peaky bass response. 150 litres or more for a vented enclosure is needed. Anywhere between 150 and 170 litres is fine. If you make the cabinets any bigger, the bass starts to roll off and if you tune for a lower resonant frequency, you cross over the drivers own FAR, which ruins the performance. It's no accident that Alex Garner chose 150 litres as the optimum for the HPD 12 inch drivers (and it's also pretty much the optimum for 12 inch MGs, although their response stays a little smoother down to say 130 litres, so they can be used to good effect in smaller enclosures but wont have the bass of the HPDs).
The other thing to remember when DIY-ing loudspeaker cabinets is that baffle width and shape matters! if the front baffle is too narrow, then the frequency at which baffle step loss occurs is higher than for a wider baffle. The can be easily calculated but the important thing is to remember that when radiating into full space as opposed to half space a 6dB loss occurs at the transition frequency from half to full space. Most crossovers for commercial speakers are designed to compensate for the "apparent" rise in frequencies occurring at twice the width of the baffle (so for a baffle of 600mm wide, maximum amplitude occurs at 1.1kHz which also happens to be close to the crossover point of many Tannoy crossovers).
This last point does mean that crossovers may need to be tweaked to account for the amplitude rise. It's also another reason why the same Tannoy drivers and crossovers can sound much brighter in some cabinets than in others. There's a hell of a lot to take in when considering cabinet and crossover design!
Finally had a chance to cobble together an update. Not a great deal of progress as it's been really time consuming getting all the laminations done then doing the veneering and shaping each individual brace for an exact fit.
Anyway, some photos:
Cabinets look enormous sat on these 3 inch trolley plinths! Just the right size for a 100 BHP Mercury outboard motor on the back of each!
Base and top panels cut, joints formed and glued to veneered side panels:
http://i1140.photobucket.com/albums/...pse18bf4e4.jpg
Side view of one of the veneered side panels. Its only up to a 20 or 30 sheen, so the grain will come out more with some more finishing work. That won't happen until I have the interiors fitted out and the front and back panels are completed. Still, I like the ripple Birch. Very contemporary and light and I reckon it'll be a nice contrast with the Black Walnut front edges:
http://i1140.photobucket.com/albums/...ps897524cf.jpg
Close up on one of the panels. The veneers have been cut and matched as well as possible before going into the vacuum press for gluing:
http://i1140.photobucket.com/albums/...ps4e739b12.jpg
Front view...braces removed for the moment whilst top an bottom panels are glued:
http://i1140.photobucket.com/albums/...psb1199de9.jpg
Side view:
http://i1140.photobucket.com/albums/...ps9a8675a5.jpg
Detail of top panel joint:
http://i1140.photobucket.com/albums/...psb3d61153.jpg
Front of cabinet. 30mm deep baffle panel will be glued into this recess formed by the sloped face and the straight (internal) face beyon the step you can just about make out behind the strapping. A really awkward cut to make:
http://i1140.photobucket.com/albums/...ps494d03ea.jpg
Rear view:
http://i1140.photobucket.com/albums/...psa8e677a0.jpg
The cabs will sit there until the glue has set and hardened so 24 to 48 hours before they're touched. Next job will be to fit the rear panel after first forming a cut-out in the lower panel for the removable section housing the crossover and binding posts. On the base internally there'll be a sloped internal baffle cut to shape from 24mm ply and the void between it and the cabinet base packed with wool felt. The slope is being put in to ensure that the internal base is not parallel to the top panel to help avoid standing waves. Won't have that issue with the curved sides!
It'll be a week to 10 days before I update with more photos and should be close to completion by then.
:lol:Quote:
Originally Posted by Reffc
Top work though Paul - I really admire people who can do this sort of job to a decent standard - apart from the time issue, I just know I'd cock it up somehow. Look forward to seeing the next instalment but they look very professional so far. :thumbsup:
Thanks Alex. I am getting help with them as parts of the construction are much easier as a two man job, but it's not all been plain sailing with some scrapped panels due to the odd mistake, but we're getting there! I've a fair amount of internal work to do to them following the rear panel being fitted before the baffle can go on. To help speed things up, I'll be getting on with the internals whilst my colleague gets on with the front panel.
Looking good!
But will you be able to move them? They're going to weigh something.
Great work so far, I'm excited to see the end result!
BTW, when leaving things to dry, do you have the heating turned right up (guessing no) and do you worry about damp this time of year?
I don't leave the heating up (too miserly) so rely on leaving things for longer! No worries about damp. The glue will set irrespective and the lacquer is water based after all! The ply is top quality Birch ply and it won't be subjected to particularly high humidity in the workshop.Quote:
Originally Posted by realysm42
Hi GeoffQuote:
Originally Posted by walpurgis
They're going to weight far more than I anticipated! The weight of each side panel is 15Kg, so there's around 35 to 40Kg in each hollow shell and that's before front and rear panels are fitted, all the internal bracing and sloping internal base, all the bitumastic sheeting, the drivers, the fittings, and the grill. 70 to 75Kg each is probably a good estimate but I'll weight them when done. No way are they a single person lift. It'll be minimum a two man lift per box.
Looking really nice Paul :)
Cheers Jon.
A little more progress. Sloping internal base is now in and braced very sturdily from underneath. Braces for one speaker are also in and rear panel is about ready to glue into place. Net internal volume works out at 158 litres, so the braces, front baffle internal laminations, ports and driver and bitumen sheeting take up a surprising 20 litres of volume.
I'm teetering on the edge of revising the porting arrangements to more an EBS design by lowering resonant frequency to 28 Hz to flatten out the bass response and remove the slight peaky response of the twin ports tuned for 33 Hz. The Alex Garner recommendation was 35 Hz with two ports but the response models as quite peaky and could lead to boominess in room. I know that I have a lift at 28/35/72Hz of over 6dB and that twin port tuning (200 long 100 dia) results in bass being just 3dB down at 38 Hz and -7dB at 30Hz.
A 120mm long single port is just -5dB down between 30 and 50 Hz before gently rising to zero at 500Hz. Seems a better tuning arrangement to me. The tuning is a remarkable 28Hz at -6dB which is some serious bass!
I'd be happy to take advice off anyone who's tried either of these tuning points for a cabinet between 150 and 170 litre volume plus any subjective impressions of in-room response. Need to know before midweek next week as that's when I'll be sorting the front baffles and ports!
The two tuning options are shown below. Green line is twin port 33.5Hz and red line is single port, 28Hz tuning:
http://i1140.photobucket.com/albums/...psf4f91ae6.png
Updated pics of the internal sloping base and bracing now completed for one of the cabinets.
http://i1140.photobucket.com/albums/...ps289016ce.jpg
http://i1140.photobucket.com/albums/...ps276ca6f0.jpg
Got the other one to do then the back panels will be glued into place. I'll be sealing and painting the rear panels rather than veneering. They'll be finished in a high gloss piano black finish. I'm going to add a small brass plate with the name of the loudspeaker at the back. trouble is, I haven't thought of a name yet....could this be an AoS competition I feel coming on? :scratch::pub:
You could call it the 'Ohmygawdthisisgoingtotakefourofus'
"The Gloucester".
:lol::lol::lol:Quote:
Originally Posted by walpurgis
That's closer to the truth than you might imagine!