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-=SHOW OFF YOUR SOUND SYSTEM!!!!=-PART 3

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AndyWave View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AndyWave Quote  Post ReplyReply Direct Link To This Post Posted: 24 August 2021 at 8:25pm
Hi All for a while

Had to build something during covid boreness during 2020. So I attacked a long time back burner project of my home stereo. Had some leftovers from previous PA-systems aaannd.....

I broke all the rules and used 18" as low midrange and married it straight to 1"+waveguide at 800Hz LOL

2,5way passive dipole system with
-2x 18sound 18W1300
-Faital HF10AK+Parts express PHRN 1018

I've later added acoustic resistance matting behind the 18"s to obtain more cardioidish response in the low range.

In the crossover, serial resistance is added to the bass drivers to increase the Qt=0,35 value to something more dipole friendly value of around Qt=0,44
x/o points 180Hz and 800Hz

Driven by
-refurbished all tube Braun CSV13 (2x13W, 1962) 6xECC83 pre, 2x5751 drive, 4x EL84 end
-LAD GAJ-)42 direct drive turntable
-Jelco 370 tonearm+Ortofon concorde cart
-Cheapest present day denon CD-player, not so bad at all...
-for occasional radio (the news!) listening full analog Yamaha tuner from 80'/90's

Jazz vinyls containing double acoustic bass have never sounded so good and real. No more bloody boxes to my castle.Wink











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Tinnitus Rex View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tinnitus Rex Quote  Post ReplyReply Direct Link To This Post Posted: 24 August 2021 at 9:00pm
Erm ,Your not blocking the 18s coil vents are you? You will inflate the spiders and all sorts of no no.


Edited by Tinnitus Rex - 24 August 2021 at 9:05pm
"couldn't we just like... use headphones?"
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csg View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote csg Quote  Post ReplyReply Direct Link To This Post Posted: 24 August 2021 at 9:03pm
With 4 EL84’s i very much doubt it matters provided they are not completely sealed.

Very nice effort. If you are in mono you would be well advised to purchase a specific mono cartridge, ortofon have one in their 2M range
“The fact is this is about identifying what we do best and finding more ways of doing less of it better”
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AndyWave View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AndyWave Quote  Post ReplyReply Direct Link To This Post Posted: 24 August 2021 at 9:27pm
I'm stereo, as my system aswell, just left side showing on pic.

And CSG is right, blocked vents with about 5Wrms reaching per 700Waes/100mm voice coil driver should not cause audible power compression, nor burned coilsLOLLOL.....thermal headroom city.....

In fact center vents are only partially covered by 15mm ply across them. Center vent diameter must be somewhere 40mm from my memory. Enough this nit-picking.

BTW the Braun volume knob has dB scale on it and I usually listen nearby -70dB setting, -55dB if I'm bit drunk and there's Led Zeppelin or Hardfloor on the platter.

Purpose of that picture was more to show that all drivers are integral part of speaker baffle support structure, and that the mass of bass drivers will help to dampen any resonance in the parts made of ply...

- Andy
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Tinnitus Rex View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tinnitus Rex Quote  Post ReplyReply Direct Link To This Post Posted: 24 August 2021 at 9:43pm
When I bench test speakers blocking the vents affects the sound at any level as the spider acts as a second speaker being pressurised because there is nowhere else for the air to go,  why block them at all?


Edited by Tinnitus Rex - 24 August 2021 at 9:44pm
"couldn't we just like... use headphones?"
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doller View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote doller Quote  Post ReplyReply Direct Link To This Post Posted: 25 August 2021 at 7:44am
Nice job Andy. Love the crossover. Home brew max. 
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AndyWave View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AndyWave Quote  Post ReplyReply Direct Link To This Post Posted: 25 August 2021 at 7:59am
Dear mr Tinnitus, I thank You for pointing out such possible design flaw, but in my mind Your sense of relativity fails here.

If You're certain that my solution of covering speaker center vent partially, in this particular solution, with 13Wrms max divided between 2(3)drivers and routed through lossy crossover, and typically used in milliWatt range causes audible additional distortions, please calculate for me the dB level of the distortion caused, compared to a fully unobstructed vent. There is neoprene weatherstripping used between driver magnet assembly and plywood, to prevent any rattle.

You can do it because I have given you Driver spec, schematic of the crossover, size of vent obstruction and and maximum power available. Also very relevant here is my typically used volume setting which causes around 0,2Vrms (0,2V^2)/4ohm=10mW to enter one loudspeaker system through crossover unit. I once measured the rms voltage out of curiosity with my Fluke 118 multimeter.

Personally I don't feel the neccessity to carry on such calculations.

Hopefully my response will not go too much in to Your feelings.

Cheers, Andy

PS
Thank You Doller, those soldering strips and few components used are recycled parts from some old factory crossovers.


Edited by AndyWave - 25 August 2021 at 8:19am
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Tinnitus Rex View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tinnitus Rex Quote  Post ReplyReply Direct Link To This Post Posted: 25 August 2021 at 12:29pm
 Calculations LOL. All good ,Its just my OCD says no to blocking vents ,Im sure it wont matter.


Edited by Tinnitus Rex - 25 August 2021 at 12:32pm
"couldn't we just like... use headphones?"
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AndyWave View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AndyWave Quote  Post ReplyReply Direct Link To This Post Posted: 25 August 2021 at 4:45pm
Thank You for understanding my engineer side of soul. Handshake

BTW, You mentioned some observations about blocking cooling vents, have you conducted any measurements? I'll accept observations by ear also, thats what we use to listen music and sounds afterall.

And maybe we should conduct our heated debate of blocked vents in an appropriate section of forum. LOL

cheers, Andy

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Post Options Post Options   Thanks (0) Thanks(0)   Quote APC321 Quote  Post ReplyReply Direct Link To This Post Posted: 25 August 2021 at 6:14pm
I read the above discussion with interest, so I did a quick test set up to see what the result would be:

I took an RCF L15P/200 driver (which has a central cooling vent diameter of 44mm) and stood it off my workbench on two 75mm x 75mm wooden blocks. These were positioned well away from the vent.

I then set up a tone generator running though an amplifier and put a low frequency tone though the speaker (around 30Hz). This was done at a level to generate movement of the speaker of about 1 cm peak to peak. The speaker sounded "clean" with just a "chuffing" sound of air passing from the vent.

I then got a small piece of 18m plywood and partially obscured the vent with this. Now along with the "chuffing" sound from the vent I could hear a change in the in the previously "clean" sound from the speaker. I guess that this would be caused by some sort of back pressure on the speaker dome caused by the plywood partially obscuring the vent.

Why design a speaker box that reduces the cooling efficiency of the driver, and causes colouration of the sound?

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Tinnitus Rex View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tinnitus Rex Quote  Post ReplyReply Direct Link To This Post Posted: 25 August 2021 at 6:43pm
As above, try it . learning by doing is also better and I commend your project for that.Smile


Edited by Tinnitus Rex - 25 August 2021 at 6:50pm
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AndyWave View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AndyWave Quote  Post ReplyReply Direct Link To This Post Posted: 25 August 2021 at 8:36pm
ClapClap

Despite my particular home stereo project never sees a 10mm cone movement, I must at least knife edge the support plate area behind the vent. Never hurts to be on safe side. It's not at all a big job, few passes with router.....

Other hand on my PA-cabinet projects I have always left sufficient room for the vents.Wink

Thanks guys, and hats off for both of You, Andy


Edited by AndyWave - 25 August 2021 at 8:39pm
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