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Deep End DIY - My first speaker project

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Thanks guys for the pendulum stroke explanations.  All I know is that it works a charm, along with those extra watts.

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Upperbass horn:                 167kg each

.

:blink:

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What is the height as they are standing now

They would be taller than most people by the looks of them

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Don't let one of those roll down the stairs Anthony!

Or the top of the Toowoomba Range ...

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What is the height as they are standing now

They would be taller than most people by the looks of them

 

50 x 32mm = 1.6m tall.  Just showed my wife and the first thing she asked was "will they fit in the room?".  "Affirmative" was my reply "I've checked it all out in CAD"

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Don't let one of those roll down the stairs Anthony!

Or the top of the Toowoomba Range ...

 

Got to get them up 16 stairs so who knows what will happen!!

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I should add that I modelled the horns in HornResp and used the export function to import the profile into AutoCAD where I fitted a spline and modified the mouth so that it terminated properly at square to the centreline (HornResp does not quite get this right). I believe that the mouth termination could be of some importance, especially considering JMLC's efforts.

 

I don't quite follow what you did with the horn contour near the mouth.  Could you explain this a bit more please?  More importantly, how did you go about checking the directivity over the desired bandwidth of each horn?

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Same blades. Looked up the specs: the Makita is 450w with 18mm stroke; Bosh is 620w with a fancy pendulum stroke (whatever that means).

Ahh that makes sense. Reminds of the old bogan car sticker "If you want more inches, stroke it". Speakers are looking awesome. Can't wait to see the size of this lathe.

Simon

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I would not mind seeing these speakers, but no way will I be close when they need to go up the stairs!

 

Your preparations are excellent and I don't want to sound negative, but can your study's floor handle the weight?  

 

Fascinating project !

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I don't quite follow what you did with the horn contour near the mouth.  Could you explain this a bit more please?  More importantly, how did you go about checking the directivity over the desired bandwidth of each horn?

 

@@svenr ... have a look at the attached PDF file...hopefully that will clear things up a little.  I will answer the directivity question later on.

 

Horn Mouth Modification.pdf

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Hi Anthony, I hope you have invested in a very good dust mask! MDF isn't harmless.

 

Looks like a great project and I don't envy your task of machining all those rings on the lathe. I've used that kind of process in the past on a much smaller scale and it definitely needs to be a labour of love.

 

I find that Bosch tend to provide more useful features for a given price point than Makita. I've used a couple of Bosch Jigsaws and the pendulum option is very handy. I also like the Bosch variable trigger which other don't typically provide around the price point.

 

Good luck with your project!

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Hi Paul,

Yep, I have a good dust mask. The lathe work is a little daunting, mainly because I have little experience and secondly because I have now verified that I will eventually be turning about 150kg. I have done plenty to minimise the amount of material to remove with the lathe but am now considering a more flashy arrangement to turn the big horns because I now have two mates that have put up their hands for some horns and the lathe will get many more hours than initially intended. May as well get it right from the start.

Cheers,

Anthony

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turning 150kgs on a lathe would scare me stupid. something's just aren't worth the potential risk. good luck

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turning 150kgs on a lathe would scare me stupid. something's just aren't worth the potential risk. good luck

 

I see your point guru, but each of us has to pick our poison I suppose.  For instance I am more comfortable with a large moving mass that I can monitor by eye than I am playing with mains voltage (or higher - like in valve amplifiers) that I cannot see.  The horns will not be spinning very fast and 90% of the job can probably be done spinning them by hand, so they should be very much under my control.

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 More importantly, how did you go about checking the directivity over the desired bandwidth of each horn?

Hi @@svenr, by directivity I assume you mean minimising honk or beaming?

Tractrix profiles are "known" to have less extension at the lower cutoff frequency, compared to say an exponential curve, so it is generally advisable to set the crossover points somewhere above the lower octave of the horn in question, and then leave some room in the horns upper octave as well.

The Upperbass horn is limited by a diameter of 1m so that I can get the midrange horn immediately above it at ear height, and is therefore limited to about 115Hz. The UB is also the only horn that I anticipate that I will try to grab every hertz of lower frequency extension and with a bit of floor gain perhaps I can get below 100Hz before it starts to sound wrong. The crossover point to the 250Hz Fundamentals Horn will hopefully be about 600Hz so the bottom octave of the FH will not be required except at attenuated volumes determined by the crossover slope. Likewise the 400Hz Midrange Horn will be crossed into at about 1000Hz so the bottom octave of the MH will not be used but also only the middle octave will be used in the FH horn (600Hz - 1000Hz). The MH will extend to about 10kHz before signing over to the ribbon tweeter so there will be some direct radiation involved, so we will see how that goes.

So I hope this explains the choices to minimise honk or beaming by keeping the horns operating comfortably within their 3 octave ranges, with only a couple of exceptions that hopefully will not prove to be too detrimental. Otherwise, if I do not know how to explicitly model directivity.

Cheers,

Anthony

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@@acg - with directivity I was referring to beaming, i.e. the decrease of the spatial angle of radiation with rising frequency.  This is a very important aspect for the selection of crossover frequencies as well.  An uneven directivity profile will cause a spectrally unbalanced reverberant sound field and cause coloration of the perceived sound.

 

Honking in contrast is due to resonances in the horn and you would have seen this in Hornresp as very narrow peaks in the on-axis frequency response.  They should of course be avoided during the horn design or by attenuation in the crossover design.

 

Will be good to see the on-axis measurements of the horns once you are ready.  Great project btw - five way systems are hard to design but will perform very well if done properly.

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Thanks svenr, you've just given me a little "key point" in my understanding of honking, which is a subject that I have not overly tried to find out too much about.

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I would not mind seeing these speakers, but no way will I be close when they need to go up the stairs!

 

Your preparations are excellent and I don't want to sound negative, but can your study's floor handle the weight?  

 

Fascinating project !

You know JV that you are welcome anytime at castle ACG, especially and particularly on the day the big horns go up the stairs.

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My measurement gear turned up today and I could not help myself but pull out my Fane Studio 8M's to see how well the drivers match impedance wise.

 

What I ended up is as follows (using DATS):

 

post-139669-0-32635000-1421639927_thumb.

 

Here is the datasheet:

 

post-139669-0-00556100-1421639978_thumb.

 

Impedance wise it looks to me as though the two drivers are well matched.  However, even though the T-S measurements of the drivers seem to match they do not correspond particularly well to the datasheet. The biggest surprise for me is the free-air resonant frequency: measured 106Hz;  datasheet 81Hz.  I will have to do a bit of reading to try and figure out why they would be so different.  Can anybody offer a clue?

 

The drivers are brand new genuine 2004 production (not from the 2011 group-buy).  To measure I set a roll of packing tape on my desk, then placed the driver face-up with the magnet centred on a roll of tape so that the vent was not blocked.  Vas was measured using the "Added Mass" method whereby I added a plastic cup to the cone (which perhaps should have been something that did not enclose a volume of air over the dust cap).  All input welcome.

 

 

Cheers,

 

Anthony

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The biggest surprise for me is the free-air resonant frequency: measured 106Hz;  datasheet 81Hz.  I will have to do a bit of reading to try and figure out why they would be so different.  Can anybody offer a clue?

 

driver "break in" .... as you use the driver its moving parts like the surround and spider will soften or loosen up ... and the Fs can drop by quite a lot.

 

Applying power gently at the drivers current Fs is a good way to break the driver in.     (Produces the most movement for the least power/heat .... stick to perhaps 1/2 of xmax)

 

EDIT:  only read half your post.    Forget VAS for now, and also play around with your mounting method of the driver to ensure that your "roll of tape" isn't doing anything to the measurement....   also keep in mind that very high sensitivity drivers are affected more (than lower sensitivity) drivers by poor mounting, vibration, external noise, etc. etc. when sweeping them.    (So you do need to be quite careful).    I typically make sure I can at least repeat my sweep reliably with the same result.

 

 

Also, "click on stuff" in DATS until you can get the graph to show the curve in more detail (it will help you evaluate it) ....  although FWIW - from what I can see they look as expected.

Edited by davewantsmoore

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Thanks Dave.  Driver break-in...of course!  

 

Perhaps I should set up a rig to run these Fanes in while I build the Upperbass Horn for them.  That way I could tune the backchamber with run-in drivers rather than having to wait some time listening to sub-optimal upperbass.

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rig

 

Don't go overboard.... it won't take long, and you don't have to be precise.     Just keep the power at approximately Fs.    Don't go too close to xmax.    I'd be remeasuring them after only a few 10s of minutes.

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I thought drivers need around 100 or more hours to break in.

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I thought drivers need around 100 or more hours to break in.

Nar.

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