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Multi-Way Conventional loudspeakers with crossovers

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Old 14th April 2009, 03:49 AM   #11
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Get a sheet of aluminum that's the thickness of the face plates and have it CNC lasered.
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Old 14th April 2009, 05:37 AM   #12
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If you're having trouble flush mounting the drivers...
You could go to a craft store, buy sheets of thick, heavy felt and cut them to the correct shape. That's what I've done for most of my speakers since I'm pretty bad with a router.

Good luck with the speakers, they certainly look cool.
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Old 14th April 2009, 01:33 PM   #13
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great idea using breadboard. makes it very customizable
Dr.EM, what chip do you use for buffer stage?
http://www.linkwitzlab.com/filters.htm#1
is buffer amplifier such as opa633 required? or just a regular opamp will do?
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Old 14th April 2009, 07:13 PM   #14
Dr_EM is offline Dr_EM  United Kingdom
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Hi, thanks for the comments! I do like the look of the mid and tweeter blended together, under some lighting the difference in texture shows up a bit (tweeter finish is rougher), but overall it certainly seems more attractive than two drivers spaced, expecially with that kind of excessive faceplate on the RS52!

I certainly want to do a flush mounting, I am going to try my cardboard template idea again, mabye tomorrow. The faceplates are 5mm on the tweeter and 4mm on the mid, it doesn't seem much difference in practise though.

I had considered felt and it would certainly be easier! The tweeter does have a loss of energy toward the very top though (12k+) and using felt might confound this? Aluminium is a nice idea too, it could look nice but I expect cost might be prohibitive here?

In this test crossover I have just cheap parts, TL074 for most bits, the buffer and BSC is NE5532 (better current drive I believe?). Seems a regular op-amp will do, but something with good drive capability will be best, no low power devices. I followed the guide here for my construction and developed notch filters in Switcher CAD:

http://sound.westhost.com/project09.htm

I have his PCBs so that is where the crossover will end up (along with additional bits for notch filters etc).


Here is a picture of the actual units in construction:

Click the image to open in full size.

for better aesthetics they will go back a bit further, so more layers needed; actually one has been glued on since this and is drying now! Construction is naturally very dense and inert, though debatably not that essential with these enclosed drivers! No bad thing anyhow. I still plan on a real wood front, about 25mm thick. Not sure where to source it from or which wood to use though. Any ideas on good wood types? Needs to be a hardwood, easy to machine with a good looking edge and in a colour complementing the brassy tweeter element (I want brass securing screws too)
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Old 22nd April 2009, 12:41 PM   #15
Dr_EM is offline Dr_EM  United Kingdom
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A quick update again. Just adding more layers to the construction, 2 more MDF ones to go (hopefully that'll give enough mounting depth for the connector panel and capacitor on the back!). The other one is at the same point though not fully flush routered yet, the hoover I use for dust extraction keeps cutting out oddly

Click the image to open in full size.
Click the image to open in full size.

Looks a bit wonky in the second pic I know! It's just confusing angles and the rough cut of that back opening that do it, it's all flat on the outsides really.

Still need the wooden front panel as well as the 2 more MDF layers. Also not decided on the finish for the sides . Still working on the flush mounting!

If anyone knows about Dyson hoovers too then let me know! It keeps cutting out, seems like a thermal cutout perhaps, it works again after a peroid powered down. Sucktion seems a little weaker than usual so am thinking there is an obstruction causing increased motor load but the filters look pretty clean. I cleaned all the other pipes out already.
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Old 24th May 2009, 08:56 AM   #16
Dr_EM is offline Dr_EM  United Kingdom
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Hello again,

These have ended up with 3 more layers than that last photo shows, which with the thick wooden front as well will give reasonable weight and stability (and not look too disproportionate!)

I'll have one ready for sanding and sealing soon, mabye today. I still haven't sorted the real wood , but am thinking of using elm. Anyone here used it? Will the cut edges be "shiny" (unlike with, ie, pine), will I need to be concerned with expansion if it is glued straight to the MDF? It will be aged and kiln dried wood I believe. The sides will be finished with vinyl wood effect most likely.

My main reason for posting was to present these CAD drawings (sketchup) I did:

Click the image to open in full size.
Click the image to open in full size.

It's my first time using any CAD so forgive the poor driver textures and constructional lines! The top section will actually be isolated with shallow profile spikes and rubber pads, I just couldn't figure out how to add these

Not decided which finish I prefer, originally was going for the light fronts (less staining of real wood). The wood texture is taken from a sample of the vinyl wood I wanted, so hopefully is fairly true to life (real grain texture will surely be finer though, I didn't want my textures obviously repeating in this).


Hopefully will have more real progress to show soon, things are moving along, just slowly!
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Old 5th July 2009, 07:52 PM   #17
Dr_EM is offline Dr_EM  United Kingdom
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About time for an update I think!

I have been sanding and sealing these ready to accept the "fablon" around the sides. Here's a pic of 2 completed sides with 7 coats of MDF sealer applied:

Click the image to open in full size.

This one is at full depth now, minus the real wood front (32mm or so).

I haven't been able to get the wood effect covering I wanted (and shown on those CAD pictures), but have ordered and recieved a different one. I'm not sure about it really, It's not nearly as dark as the one I intended nor is it light enough to do the "inverted" scheme.

Another concern is that the speaker shrinks a bit towards the back, about 2mm difference from the front to back overall. This may make applying the covering difficult. Should have took all the layers from template really, rather than from each other

I have now my M8A woofers ready, I am undecided on if I will begin building bass cabs now or when these are finished. I also have a new RS52 to replace the superglue damaged one. I have cut this one already and took some photos in case any are interested. Bear in mind it is easier if you can swing a smaller arc in one go than to do this following a guide technique! I think the pictures are faily self explanatory but feel free to ask on any details! Annoyingly, the paint (powedercoat?) finish chipped a little this time, either the finish has been made poorer since my others (which were fine) or my cutting bit has bluntened too much

Click the image to open in full size.

I am taking measurements with HOLMImpulse to perfect the crossover too
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Old 21st July 2009, 07:38 PM   #18
Dr_EM is offline Dr_EM  United Kingdom
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Been working on recessing the drivers. The mid is not a problem being round, but the tweeter is awkward! I've ended up running the router around the edge of the tweeter faceplate to create a template (the faceplate can be detached naturally!). Works quite well, now I've done this test I feel more confident about doing a "real" one.

What makes this harder still is the the 2 cutouts must be made in exact locations so the drivers sit closely together! I'll probably produce an overall template for use on the real solid wooden baffles rather than trying to line the 2 seperate cutouts together on the baffle.

This test baffle is made from (cheap) 12mm ply and 18mm MDF, giving around the thickness I want from the real wood eventually. I will probably buy a larger roundover bit too, this is a bit shallow. I also cut the recess a bit deep on this and the tweeter cutout is a bit ropey. This baffle will do for my measurements I hope

Click the image to open in full size.
Click the image to open in full size.
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Old 11th August 2009, 10:00 AM   #19
Dr_EM is offline Dr_EM  United Kingdom
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Well yesterday was measuring day. A day filled with confusion and frustration for a noob to it like me

I have changed several things in accordance with what I saw. I've only really be trying to "fix" these mid-top sections. Integration with the woofer is still off (more on that later).

Firstly, the effect the baffle has on the mid unit's response is more pronounced than the sim showed:

Click the image to open in full size.

And measured:
Click the image to open in full size.

So I employed a broader and deeper notch filter than prviously used, adjusted in accordance with feedback from measuring:

Click the image to open in full size.

This seems to work faily well. It still leaves a relative dip at 4kHz, but I don't think it's significant enough to warrant further intervention. Problem, the circuit introduces a lot of hiss through the mid. Are the resistor values simply too large?

The crossover between mid and tweeter is now much better. Before the mid was effectively rolling off early. Inverting tweeter polarity now reveales a deep, sharp notch (which I stupidly forgot to save an image of, it's around 25-30db anyhow).

The tweeter seems to exhibit a mystery 6kHz peak. It's not on the datasheet, nor are there any simulated artifacts at this frequency. I'm hoping for possibly an acoustic fix for this, some carefully used felt perhaps.

To reduce it's relative effect I've added a treble shelving filter to the tweeter. It;s natural response drops by 6db after ~10kHz, so the filter is designed to combat this then allow me to lower the tweeter level (which I haven't actually done yet) and hence the 6kHz peak.

Here is the mid and treble combined output. It's probably better than it looks here, observe the scale:

Click the image to open in full size.

I have yet to lower the treble level. It sounds quite hot to me even though it's still down in the very top frequencies.

Here is combined with the woofer. This is with the woofer technically incorrect phase . With correct phase a notch is revealed, around 1kHz oddly, not the 820Hz Xover point. Don't know what's going on here really, I think all measurements below 1kHz look dodgy. Shows some 50Hz noise too, not from the speaker itself mind

Click the image to open in full size.

I don't wish to repeat this process, moving 2 amps, a desktop PC, crossover, speaker, DAC, cabling, mixer, mic, stand etc downstairs for the day
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Old 20th September 2009, 12:48 PM   #20
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I've "undone" most the measurement based adjustments as I think there's something quite radically amiss with it. I've got the prototype crossover set around the simulations now and it just sounds much better.

It's causing me some issues now though. Basically, the woofer cuts in and out seemingly randomly and for that matter it even seems to fade in and out, the change is seamless. To make it more bizzarre, it'll invariably come back on if I increase the signal level through it (currently using PC as source and hence level control, though the 3 xover outputs are fixed attenuated to a more reasonable level). No problems when the volume is set fairly high. Any ideas what on earth is happening here? It's got me baffled and is getting rather annoying. Using quad TL074 Op-amps, NE5532 input buffer+BSC and a TL072:

Click the image to open in full size.

Any ideas? Must be a dodgy chip I figure, I can't see how it could fade in and out otherwise
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