audio-talk

I'm just finding my way into this job , but ran into this error message while trying to edit component values :

I can't see anything on the screenshot, but if you can send me the file Mark, I'll take a gander & see if it works OK at this end.

Looks like I need to do some de-bugging at my end. Thanks Scott.
Perhaps load on the laptop and see if it works OK there.

Meanwhile I took the whole shebang inc. the Mk.1 cabinet round to Jon's today, and Dave the cabinet-maker came round. We had a mini audio-fest and Jon was very happy with it, as was Dave. We are just clarifying our plans re . the crossover box and final mods to the box for the 'nice' versions. I will continue to do final tweaks to the crossover.

Not sure you are aware of this Troel's speaker design. But, if not you may find helpful regards measured performance and XO design of the Purifi driver in a small studio monitor speaker similar to what you are doing

http://www.troelsgravesen.dk/Purifi-6R.htm

Thanks Colin but someone spotted that before, see page 2.
I did a simulation ( page 3 ) and didn't like that box/alignment for bass, at least.
I might re-look at the crossover in case there's anything I can learn from it.

I'm doing a minor tweak for the final version of the cabinets.
I was wondering about making the box non-rectangular, but i know that would be a lot more work for Dave.
I was also thinking about having a perspex layer on the inside surfaces.
In the end a compromise formed in my head, where i could use some thick (15mm) perspex in places, to effectively make the internal volume a bit narrower at the back than at the front - should smooth out the box modes a little. I should still get a useful contribution of the perspex over a decent area, I find that perspex is very dead (damped) in the HF region.
I think that the perspex should be bonded onto the wood using silicone sealant (and a couple of screws), to provide a constrained layer.

The height of the box has been increased 2cm to make up for the 'lost' volume from the perspex.

If you sand the perspex on the side to be fixed to the box with a really agressive grit like 40 grit you can stick it on with normal wood glue. Make sure you hoover all the dust off it though first or use a tack cloth to make sure its really clean and free from detritus or it will fall off
I made some td150 arm boards like this.
Other option is to use sheet adhesive which is usually paper sized sheets (a4 usually). Its usually pressure sensitive adhesive so you can get a really good bond with it if you run the corner of a hardwood block across it to press it onto the thing you want it to stick to

Thanks - I'll run the options past Dave. Wood glue is usually to hand, of course !

Another option for a damper would be the stick on lead flashing sheet. I have used it in he past with some success. Not sure about the loss curve for acrylic and it’s effective frequency, few 100 Hz upwards I think. Alternative would be a constrained layer damper( CLD) which are more effective, however the two surfaces need to be more rigid than the glue in between. OSB board has good damping, so two different timber sheet materials with a polymer adhesive in between, so a box within a box. Steel or aluminium sheet, best as stiffer, acrylic somewhere in-between. With steel sheet, 1mm will be enough, and probably the cheapest option.

Had to help a guy at the Scalford show, move some tannoys around his room, he had lead lined them with code 3 lead sheet, don’t know how he got them up the stairs. Lead probably cost more than the Lockwood drivers.

Some discussion on DIYaudio about damping too.. https://www.diyaudio.com/community/thre ... ar.392930/

In the home theatre field, people try to reduce the amount of sound that leaves the room (annoying neighbours etc)
They use a damping glue, Google ‘green glue noise proofing compound’, typically between sheets of drywall.
I don’t know what it would do to the sound of a speaker between Perspex and the cabinet, but possibly worth an experiment.

Different visco-elastic materials work over different frequency ranges at different temperatures. Green glue is claimed to work over mid and low frequencies (in some places they claim all frequencies, presumably meaning all audible frequencies)
Also note it takes 30 days to cure to its most effective state - presumably the long polymer chains forming as it cures.

Sorry, posted twice

All good ideas thanks. I have limited time for experiments now, Jon is keen to get the final version up & running, but i will look more at what i can do to the other surfaces in the interior.
Steve, my idea was pretty much CLD, with the rigid plywood , then a silicone layer, then the perspex.
I know the perspex damps well, from the experiences with wood and perspex on the OB's ( and James's lead on that ).

What I learned from listening to Kevin Scott speak about the Vox Olympian horns, is that you can take out some colouration, in the form of greying of tone, from plywood, by painting the surface with varnish, preferably several layers. I have found so far that even two layers of yacht varnish on the throat of a horn or the inside of a plywood box, will improved the transparency of the upper mids. I don't know if the polyurethane acts as a barrier or just a damping ( filter ) ; I know that the sound will otherwise penetrate some way into the wood, then come out scrambled, and I think it must be the higher frequencies that do this.

The green glue looks no more expensive than silicone, thanks Max, we could get some of that. I could try some thinner perspex sheet in the Mk.2 test cabinet, with some of that, while Dave's building the final boxes.

IslandPink wrote: ↑Sun Dec 04, 2022 4:11 pm The green glue looks no more expensive than silicone, thanks Max, we could get some of that. I could try some thinner perspex sheet in the Mk.2 test cabinet, with some of that, while Dave's building the final boxes.

Not sure where you are looking for green glue - £15 a tube is expensive. Polysulphide caulking is what we use in aircraft intakes, or loaded epoxy.

CLD will only work if there is relative motion to shear the green glue between the stiff membranes. IHMO, mass loaded vinyl will work best with stiff cabinets.