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Speaker Cabinet - Aerolam/Honeycomb

Discussion in 'Home Cinema Building DIY' started by Alaric, Apr 4, 2004.

  1. Alaric

    Alaric
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    Hi there,

    I'm in a fairly unique situation on this subject, I work for my father in a small business, the main staple of our work is Aluminium honeycomb panel manufacture and variations on that theme.

    For those that don't know what this is, its two sheets of Ali with a fine expanded aluminium honeycomb bonded between. It makes a *VERY* rigid yet light material. Its far more rigid than a solid panel.

    Now, from what i've read some places have used this over the years for speaker manufacture, and the rec.audio FAQ (http://www.faqs.org/faqs/AudioFAQ/part5/) seems to think its about the best material to use.

    Cutting it is not a problem (we have a CAD/CAM router) and i think i can even figure a way to join it by mitering and bonding, though Aluminium chanel is a posibility.

    For a personal project i could get some material probably for free/v. cheap and even for a comercial project i think we are the cheapest manufacturer i know (small business, low overheads).

    Any takers ????

    Either a Co-project for personal / AV-forums usage (i'm no speaker designer, yet) or a comercial venture by any of the bigger boys out there ???

    Thanks,
    Lee

    p.s. We can also do Nomex/foam cores & Glass/Carbon Fibre skins amongst other bits
     
  2. rob_w

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    Hi Lee,

    I remember talking with you about this when I bought your barco800. I'm up for a test run - Have some tempests here which we can pop in a test box.

    Also have true RTA software with calibrated mic to measure. OOh and best of all only at Stansted:D

    What is the resonance of the material ? - the higher the better (if we're talking subs..)

    I'm thinking industrial adhesive for bonding - don't Lotus glue the elise chassis together ?

    Cheers

    Rob
     
  3. Alaric

    Alaric
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    Hi Rob,

    I'm not sure about resonanace, how do i find this out or measure it ???

    I'm looking at getting a callibrated Mic and pre-amp for use with ETF for room accoustic measurements soon as well if this helps (its about £100 IIRC)

    The standard panels are glued with an epoxy resin anyway, and i have access to a lot better glues than are available to jo public :D

    I'm thinking the best way to do things is to cut the edges of the board with a 45 V , bond together with a kind of corner jig, then probably use a Aliuminium angle or even a radius'd angle bead to ensure complete air sealing.

    Can't say i know much about the RTA software, or the speaker design for a given driver, however i'm happy to read and research on a theme.

    Must admit from reading whats been done with other manufacturers, i've not seen any sub development, but i was thinking due to the huge strength and regidity it could be ideal.....Do subs need mass though, as the material is 95% air so is relativly light....Its far stronger and stiffer than solid Aluminium though.

    What sort of sizes are we looking at and wheres some details on the drivers ???

    As for bonded structures, i'm not sure about the elise, but it wouldn't suprise me. I know we supply matreial curently that goes into the caterham, and we did a lot of chasis work for the origional RS200 group B rally car that started the 'rs' trend !

    Cya,
    Lee
     
  4. rob_w

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    Hi Lee,

    The driver I'm using is the Adire audio Tempest.

    http://www.adireaudio.com/diy_audio/drivers/adire/tempest.htm

    Theres loads of info on their site - downloadable 'recommended' box stuff aswell.

    For resonance measuring, a good heath robinson way would be to make up a box, put the driver in an put some sand on the top. Run a sweep and see if/when the sand starts dancing..

    I'd just use butt joins for now, it's only a prototype. maybe use the angle ally on the outside edges to finish, than try to get loads of mitres sitting perfect. You could also glue 3mm/6mm mdf, or veneered ply on the ouside for a less 'industrial' look. Personally I'd just spray it satin black, but I digress...

    What CAD/CAM file format do you use ? DXF ?

    Happy reading:)

    Cheers

    Rob
     
  5. Alaric

    Alaric
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    Hi Rob,

    Making a cabinet and testing the resonance would tell me the resonance of the cabinet, not the material ???

    Also within reason i can vary the specification of the material used. We have quite a few miss-shaped panels from one job we do, which are ~300x500mm x 7.65mm and some at ~450x500mm x 13.55mm, both using 1mm skins either side of the core.

    These are more or less scrap (but kept just in case), so i can experiment with these for free. There are various other bits and i'm just about to make a cabinet for my PJ out of a foam cored panel with aircraft grade ali skins (24swg/0.56mm) but i doubt this would be good for speakers !

    I can spec bits and use neigh on anything, but then that costs, and while i'm happy to put cash into things, its better when you have an idea of where they are going.

    The router is a Saber Gerber 408, technicaly a sign making router ! It uses its own custom file formats, but i can convert from dxf to this. I also have a utility that converts dwg and the multitude of versions. Sometimes designs import easily, some need tweaking, but it always give me a start. The wife is an architect, so fully conversant with autocad and probably explains the extravigant designs the cinema acoustic paneling i'll also be making soon :D

    BTW you mentioned you had a calibrated mic, where did you aquire it from and do you use a pre-amp with it, or is it for non computer based use ??? I'm looking at buying a set from the german guy who does the ETF kit, about £100 IIRC - what do you think ???

    Thanks,
    Lee
     
  6. rob_w

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    Hi Lee,

    I think if you measure the cabinet you'd find small vibrations at all freq's, except at 1 where it would go way higher - the materials own resonance. If you like, put a driver in 1 piece of material and run the sweep like that.. I doubt you need to worry at sub frequencies though.

    The offcuts you mention seem a tad small for a sub cabinet. Maybe try building a standard mdf cab and lining it with the special stuff, using a 'lossy' glue (evostick contact type stuff). This would be more 'constrained layer damping' type box - do a search on diyaudio.com....

    I've heard of gerber files - i think - We used to have a small router type machine to mill plastic sheeting at work - probably similar. Use cff2 files a lot.

    I use a behringer ecm8000 mic, with 'trueRTA' software - the software has a calibration file for my mic. I use a behringer shark dsp 1100? preamp for the mic. If the one you mention is based on the 'panasonic electret capsule' then it will be similar to the behringer (same capsule).. not much between them - do a search on the 'mitey mike' too.

    http://www.trueaudio.com/index.htm

    A good book to browse through is the loudspeaker design cookbook. Has most of the basic stuff in. Oh and if you haven't got it yet, download and play with winisd.

    http://www.linearteam.dk/default.aspx?download=winisdpro

    Cheers

    Rob
     
  7. Alaric

    Alaric
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    Hi Rob

    I'm not really interested in building a sub just for the heck of it, so MDF is off the menu. The off cuts i mentioned are just easy test samples. I like the idea of using a driver to work out the resonance in a couple of bits. I may have to 'frankenstin' a couple of old book shelf speakers to play with. Maybe even re-make the a bookshelf speaker with a honeycomb cabinet to see what happens ???

    BTW your 'callibrated' mic by the looks of it isn't....TrueRTA has a 'typical' response for the EMC8000, which will remove the gross errors, but i don't know how truely acurate it is. I say this from the point of someone who just ordered one and a shark, and then got the sinking feeling as the dawning hit me that no one mentioned actual calibration files !

    http://www.etfacoustic.com/NewUser.html

    Explains things better than me half way down.

    I guess i'll have to order a calibrated mic from

    http://home.t-online.de/home/wfrank/shop-us/pd1954442790.htm?categoryId=2

    Which probably means that there will be a ECM8000 up for sale in a few weeks - Unless i've got things wrong - or someone round here is capable of doing calabration for a mic ???

    Cya,
    Lee
     
  8. Nic Rhodes

    Nic Rhodes
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    An interesting idea would be to make just flat aerolam panels (to fit existing tables) and skin with carbon fibre. I would be very interested in that. Finish off well they would look a million dollars (and sound great as well).
     
  9. Alaric

    Alaric
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    Hi Beekeeper,

    I'm a little confused, fit what existing tables ??? Are you talking something like a kit rack ???

    The carbon fibre we have comes in on a roll, pre-impregnated with resin. We have the capability to make flat panels with it (either a composite 'sandwich' with a core, or solid) but they are by no means 'beer money'.

    Interestingly we do have some off-cut strips of pre-impregnated 5 harness carbon fibre which are ~300mm x 2500mm which i've yet to figure a real use for, yet at the cost of the material its a *shame* to bin.

    You also mention 'Aerolam', from what i know this is a coined term for an aluminium skined, aluminium cored panel, though are you refering to a different composite combination ???
     
  10. rob_w

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    Hi Lee,

    Did you download the winisd stuff ?

    The mic you linked to looks like a copy of the 'mitey mike'

    http://www.audioxpress.com/bksprods/kits/kd-4.htm

    Based on the same panasonic capsule in the ecm8000, You'd only be paying for a calibration file which, if mass production quality control by panasonic is good, would probably match the true rta file pretty well. Maybe not, but as soon as you measure anything 'in room' 1 or 2 dB's won't really matter..(honest - watch your pink noise signal at 1/24 octaves on a rta - jumps all over the shop - averaging helps a lot but still.. With a sub you'd only need to move the mic a foot or so to change the plot.

    If you do buy it it would be interesting to compare 2 plots to see how a 'generic' calibration does...

    Maybe for a sub you don't need 'perfect' is what I'm saying...

    I'm happy with my results at home. - I reckon I've got a better measuring tool than the radioshack spl meter anyhow. ( does 1 single web published correction chart work with all meters ? )

    Any how it seems as though you want to build 1 sub once, without any testing of boxes etc - if that's the case then look towards sealed boxes for a better chance of success. A sealed box with a Q of 0.5 - 0.6 will do well with 'average' room gain to produce a fairly flat response. Big box though - always compromises with sub design. A ported box tuned quite low (EBS alignment) is said to work great too - I believe the SVS's work this type of way. You'll soon get a hang of the alignments playing with winISD. The Adire site I mentioned before has good info on EBS.

    If you're looking more for a manufacturers input then I'll happily step aside.

    I believe Mr Beekeeper has a very good calibrated test set up (He mention it a few years back IIRC)

    You're welcome to pop down and have a listen to my subs btw..


    Cheers

    Rob
     
  11. avanzato

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    This has reminded me it's time I got a measurement mic so I just ordered the IBF one. It was that or the 'Mitey Mike' kit from Falcon Acoustics. The IBF mic and pre cost £130 or so delivered the Mitey kit is £86.50 but I'd have to build it. It's being calibrated tomorrow and then on it's way to me. Only thing is I'm using TrueRTA so not sure if the calibration file will work.

    IIRC you can measure the reasonant frequency of a panel by attaching a cheap mic to a volt meter, the mic to the panel and playing test tones. When the volt meter reads it's highest that's the reasonant frequency. Does that sound right? I'm a bit vague on it and could be remembering it all wrong.
     
  12. Nic Rhodes

    Nic Rhodes
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    sorry for the confusion here. The material you are suggesting for speakers is great, it is just that most of us just don't know what to do with it but you have that covered.

    I once heard a sheet of the 'honeycomb' skinned with carbon fibre on all surfaces. I plonked it on some basic cones and dropped a player on top. WOW. This combination looks both great and sounds great (like Torlyte) but better. I was mentioning this as I feel than all o9f us with glass shelved units could swap shelves for a good looking but great sounding upgrade. Glass sound 'crap' but medite is better and these composites can be much better again. I just thought it might be an interesting 'side line' for you to make. I fr one would be interested :)

    Aerolam comment was a touch too flippant here, honeycomb with CF skin is what I am 'promoting'. Upgrades to racks but why not a dedicated rack, CF look great and a honeycomb interior. :smashin: :clap:

    I would be happy to help here if I can but am time limited but the results could be seriously interesting :)
     
  13. Alaric

    Alaric
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    Rob -

    Bought the behringer kit the day i posted the previous message, hence the Doh! like comment....don't know if i could use the shark with the German mic i mentioned ??? I know that the behringer mic is pretty good and probably fair for my means, its just i was aiming for a calibrated mic !

    The shark is tiny, i expected something bigger from the pics, has loads of gizmo's that i doubt i'll use but... Managed to turn everything off, shame there isn't a bypass button as it takes a while.

    I think your getting confused with my intentions. I have material capabilities that i've read are amazing and difficult to get hold of, yet have in relative abundance...I just want to play and test and see what is/isn't capable...A sub is a cool idea, a mini-monitor is also posible...i don't know how much i'd use as i have what i remember to be a cool set-up (though its still all boxed). Part of me is curious as it could be the start of a business lead (guess i should cold call meridian or mission as they are less than a mile from my home on that one !) - Part of me is just plain curious, as i'm one of those what if geeks.

    I supose a sub is probably the most likely to be in with a chance as its easy to change, where as my surround set-up is all one brand, so chaing a pair would kill the cohesion. However i wonder what will do significantly better than a servo15....Maybe a honeycomb structured box with the servo's drivers ?

    BTW rob, i'm interested in any and all input, besides while i know manufacturers seem to frequent some of the specific groups i'm not sure i've seen any on the diy forum....mr B&Q maybe ?

    Avantzo - TrueRTA apears to both have a few gross error correcting files (Berhinger) and be able to take them. I have notised that some RTA software takes a slightly different format, but with a bit of deductive resaoning (or even changing the extension) it should be able to get any mic file working with any software !

    Beekeeper- As a material it seems very versatile, and thats probably half my problem, constraignts tend to actualy inspire thought, a blank canvas stays that way !

    Its posible to make some carbon skinned panels, however i'm not so sure on the edge trim. I can make an aluminium panel in a tray and make a "solid" looking panel that can just be painted or polished, or probably fablon wrapped (in bonding they are acid etched so the adhesion would be better than most applications).

    I've been considering making a kit rack as its something i don't really have (I used to use some ikea wooden shelving!) Its posible with aluminium to bond in a milled insert so that you don't compress the honeycomb structure through localised compression. However i'm still not sure about the legs....I guess i could use the M8's we have and M8 threaded bar similar to the flexy ???

    Cya,
    Lee
     
  14. rob_w

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    Hi Lee,

    just a quick response as I'm in the middle of a big listening session....

    If you're serious about this then you really need to build a 'special' box and a 'normal' one for comparison - and use them both for a couple months each for comparisons. Mini monitors are a cool idea, although the parrallel sides of a 'box' type enclosure will undo some of the good work of the 'stiff' benefits - in midrange stuff the wavelengths are small enough to cause standing waves in the enclosure - at sub freq's the wavelengths are too big to cause them......

    You really should come down and have a listen of my subs - will give you an idea of whats achievable with diy methods...

    I've only ever seen a couple of 'off the shelf' servo systems for diy stuff, and one was a velodyne sub with servo for the ICE market - approx 1995, approx £900 If my fuzzy memory serves me right....

    I said it was going to be a small post, oh well :)

    Rob
     
  15. Nic Rhodes

    Nic Rhodes
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    The Behringer mike is pretty accurate, if you look around it is the same one supplied with Velodyne DD or by other serious players like Beyer. I use one :)

    re legs, I will have a think. Ikea desks like LACKs are EXCELLENT for audio and I mean excellent, think of them as 90% or Torlyte performance for 5% of the price :)
     
  16. stuthemong

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    few things, alaric, sounds fun - I live in offord cluny :) - i am in cambridge doing exams for the next month or so, but after if you want a muppet to hold stuff etc... give me a shout.

    IMO the best application for this would be car audio speaker enclusures, most guys dont like the weight of 18mm * 2 layer MDF in their boot, I am certain that if the boxes are built like brick outhouses, people would be very interested.

    I have a behringer ecm8000, and ub802 (IIRC) for DRC duties, although i have found that with no acoustic treatment it aint really a good alternative.

    If you need a hand designing boxes i can happily help you (BBP 6 user, so you cant complain on that front :D)

    Robwells: i am hereby inviting myself to your house at some point this summer. We'll trade - i get to hear your subs (could you tell me your setup), and you can listen to my total McIntosh amp/speakers in car PC install. Deal? ;) EDIT - and you appear to have a barco - ill bring some Haagen Dazs then too.....

    Stu!!!!!!!!!
     
  17. Alaric

    Alaric
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    Hi There,

    Rob - I was actualy talking about butchering my existing Paradigm Servo15 if the honeycomb material proved better for subs. Though how you get driver specs from it i don't know !
    I'd love to take you up on the offer sometime, though i don't know when i'll have that much free time....i wonder i its posible on an evening as i'm sure the wife would happily loose me for a while then, but the weekends are normaly DIY on the cinema or bathroom as we're heavily pushing both projects. The cinema is in the middle of being plastered (by the wife!!!) as i speak...er type.

    Beekeeper - The old rack i built from ikea was just one of the garrage style squarish bolt the slatted shelves into 4 pre drilled planks of wood. It was fairly wobbly even with the bracing rods. The Behringer mic is the ecm8000 and it looks a nice solid piece of kit, i just wish they provided indervidual calibration. There are a few links for people who do this stateside (post mic, get disc and mic back) but i've not seen anyone in the UK.

    Stu - I'm in the centre of huntingdon, with work in sawtry. I like the weight saving idea for car audio, though i always get the feeling most people into it are for extream unruly bass...I doubt i'd ever sacrifice my boot for a sub enclosure, but as a business idea its probably good as i guess its un-tapped and i could see a craze happening with it....particularly with a non-structural gimmicy carbon fibre wrap !

    BBP6 ??? You've lost me there.

    As for Barco's....Both Rob and I have them, though at a guess his is being capable of being run.....I curently have a spare BD800, a BG801s and even a DLC-BG6300 and non of them are set-up due to room building !!!!

    http://www.the-dreaming.com if anyone wants a look, however we had a 8month break from it and have started moving it forward - we now have the ceiling plasterboarded, with light fittings and are just taping and skiming the walls

    Cya,
    Lee
     
  18. rob_w

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    Ok quick post as (usual) it's way past my bedtime:)


    Stu, yes I have a Barco, but right now its out of action (had it set up on the floor for the last year, but finally ripped it all out and am about to put in a beam or two to hang it off - give me 4 weeks and it should be almost there) By the summer it should all be done :smashin: - you can bring the beers for the barbie....

    btw - I'm sure the absorption panels are good down to about 300~500Hz, but below that you need bass traps/ helmoltz resonators/ panel absorber type stuff - I've almost finished a pair of absorbing panels for my left / right walls 1st reflection....

    Lee, weekdays are good - pm me to sort out a day..

    Do a search on speaker workshop for a way of testing a drive unit - however for a servo15 I'd be inclined to just replicate the volume and front baffle dimensions, and build a pukka 'braced to hell' cab for it. It would be nice to hear it in a low Q (0.51) box - massive box at a guess though.....


    BBP 6 ? my moneys on bass box pro 6, but I usually lose when gambling:D


    And so to bed :)

    Rob
     
  19. stuthemong

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    yeah robwells, bass box pro 6. the best speaker box designing software i have found, it actually properly models the entire speaker response (excursion, thermal limits), unlike any freeware programs. Its superb.

    re: DRC. yes you are right, the sound absorbing panels will have no effect around the bass freqs *but* they have significant effect at mid freqs. The DRC seems to do a good job with the bass (essentially EQing much flatter - though ill never get perfect without traps), but it messes up the mid from the speakers, actually making the system sound worse. When i can sort out the correction on the mid - the sub will fall in line if that makes sense!

    Lee, cool about those barcos, i have never seen a DRT, and got bored of my AE-100 as it was sheat. I have considered going for a ae500 et al. but i think ill still be ****** off with the awful contrast so have seriously been thinking about a CRT. I would love to have a demo when its running!

    Also, there have been a few people making fibreglass sub boxes, a few sold, but they are never gonna be *that* strong. I'd have to have a look at this stuff to see how strong it is, but at a guess anyone wanting an *extreme* install could use this to wall their cars, / make massive boxes. If it is better than MDF strneght wise, people would pay IMO.

    anyhoo. BREAKFAST!

    Stu
     

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