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Deep End DIY - My first speaker project


acg

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Loving this build! Great work....

 

Just a note about your peaks and dips , I also found a lot of room nodes affected my measurements during my build.

What I ended up doing was a series of 5 sweeps then averaging them to get the final response. Amazing to see the difference between them. (Maybe someone has already mentioned this, haven't read every post)

I did 1 at the front of each arm rest, 1 each side of the headrest and the final was right where the centre of my head would be.

So after each change I run 5 sweeps, average then compare.

 

Anyway, keep up the good work and updates.

 

Dave

 

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23 minutes ago, niss_man said:

Looking at your previous measurement from the listening position, you had a bass null at around 60Hz. Maybe it would be ok to have the resonance at this frequency. The valve amp natural eq (at the higher impedance) would maybe fill this hole up to a certain degree? 

  

 

Yes, I agree.  The reason for stuffing 10 sheets of high density fibreglass in there was to see how far I could influence Fs with an eye on room problems down the track.

 

26 minutes ago, niss_man said:

As for lowering the resonance below 50Hz I think the box volume is the main limiting factor and adding stuffing would not change it much. Simulating with bassbox I find the difference between minimal stuffing and heavy stuffing is only 2.7Hz difference. I would say the reason why the resonance increased to around 65Hz in your plot is you have started to loose volume size in the box when putting 10 layers into it.

 

 

The thing that I find interesting is that I put in high density fibreglass and it did not change Fs for 3 or 4 sheets and then Fs started to rise as more sheets were added.  What I did not see is the textbook lowering of Fs that is expected when adding low density stuffing (mine is high density) so I am wondering if I can still get a lowering of Fs be that only 2 or 3Hz  by adding some low density filling.  I just don't know what people use...and I also don't know if it would be worth the effort either.  Currently Fs is about 47Hz with 4 sheets (or 28cm) of high density fibreglass...maybe I should be happy and leave it at that.

 

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3 minutes ago, nzlowie said:

Loving this build! Great work....

 

Just a note about your peaks and dips , I also found a lot of room nodes affected my measurements during my build.

What I ended up doing was a series of 5 sweeps then averaging them to get the final response. Amazing to see the difference between them. (Maybe someone has already mentioned this, haven't read every post)

I did 1 at the front of each arm rest, 1 each side of the headrest and the final was right where the centre of my head would be.

So after each change I run 5 sweeps, average then compare.

 

Anyway, keep up the good work and updates.

 

Dave

 

 

Crikey, that sounds like a lot of work Dave!

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32 minutes ago, acg said:

The thing that I find interesting is that I put in high density fibreglass and it did not change Fs for 3 or 4 sheets and then Fs started to rise as more sheets were added.  What I did not see is the textbook lowering of Fs that is expected when adding low density stuffing (mine is high density) so I am wondering if I can still get a lowering of Fs be that only 2 or 3Hz  by adding some low density filling.  I just don't know what people use...and I also don't know if it would be worth the effort either.  Currently Fs is about 47Hz with 4 sheets (or 28cm) of high density fibreglass...maybe I should be happy and leave it at that.

 

Can use Poly fill, pillow stuffing.

 

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1 hour ago, acg said:

 

Crikey, that sounds like a lot of work Dave!

Well, just try it and see the difference in the traces when the microphone is moved 1/2  mtr! Not so much changes as the freq increases but you'll definitely see differences when the mic is moved with the lower freq's.  

From memory it was Dave that put me onto it. 

 

Would be interested to see your results if you do give it a try..... If you try it and they're all the same, then measurements become easy, if they're different you either average them or pick one ....

 

Give it a go, nothing to loose.

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6 hours ago, acg said:

 

The thing that I find interesting is that I put in high density fibreglass and it did not change Fs for 3 or 4 sheets and then Fs started to rise as more sheets were added.  What I did not see is the textbook lowering of Fs that is expected when adding low density stuffing (mine is high density) so I am wondering if I can still get a lowering of Fs be that only 2 or 3Hz  by adding some low density filling.  I just don't know what people use...and I also don't know if it would be worth the effort either.  Currently Fs is about 47Hz with 4 sheets (or 28cm) of high density fibreglass...maybe I should be happy and leave it at that.

 

 

To me (being the world's foremost expert on stuffing... NOT) it sounds like it is seeing the fibreglass as a reduction in box volume, instead of an increase of normal stuffing.

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39 minutes ago, Silent Screamer said:

 

To me (being the world's foremost expert on stuffing... NOT) it sounds like it is seeing the fibreglass as a reduction in box volume, instead of an increase of normal stuffing.

 

It sort of is, you are correct.  Well if I add 5 or more sheets the Fs starts to shift which indicates that the driver is seeing a change in box volume.  But those first 4 sheets don't change the Fs at all although they are providing some nice EQ to the system by attenuating the higher frequencies and removing my lovely pipe resonance.  My wife is home...I'll go down and ask her if I can tear apart an old pillow for its filling:  not confident about getting  the green light for that endeavour!

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5 hours ago, nzlowie said:

Well, just try it and see the difference in the traces when the microphone is moved 1/2  mtr! Not so much changes as the freq increases but you'll definitely see differences when the mic is moved with the lower freq's.  

From memory it was Dave that put me onto it. 

 

Would be interested to see your results if you do give it a try..... If you try it and they're all the same, then measurements become easy, if they're different you either average them or pick one ....

 

Give it a go, nothing to loose.

 

Duly noted and stored in my memory banks for later retrieval.  I will give it a go.  Thanks Daves...haha.

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Sounds like the lowest octave is fairly well sorted out.

Will need plenty of stuffing for the other 7 cannons :)

 

Spun up those bass horns yet  ? 

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Have not got back to the Upperbass Horns.  This morning I will pick up my steel (for the amplifiers and vibration isolation platforms mostly) from the powerdercoater and will probably start building up the Bass Cannon stack as I get time.  All up I have 5 Cannons prepared and once they are together I will measure things again and make the final call on whether I will push ahead with the concept and get the remaining 11 Cannons cut.  It's looking like it will come together so I am fairly confident at this stage.

 

So, apart from deciding on the Bass Cannons I want to tidy up all the amplifier parts lying about my room which means a bit of building will need to happen.  I keep moving the mess into the spare bedroom but we keep having visitors and I am sick of moving all that stuff back and forth up and down my stairs.  I'll start nibbling away at the Upperbass Horns again soon and hopefully will get actually turning wood in the next month or so.

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On 8/29/2017 at 0:39 PM, acg said:

Is it the type of stuffing I have used?

 

I don't know what type of stuffing you used :)   (sorry if I missed that post)    Seems like it might be quite dense?   (EDIT:   I just caught up, and it seems you confirmed that)

 

You really do want to get all the 'unpexedcted wiggles' out of the impedance curve of a driver.    I wouldn't bother too much with listening tests as they really don't provide reliable information for a number of reasons.

 

Aside from that, you'll find that the biggest most critical aspect of the subwoofer performance is where it is placed in the room.

 

 

 

On 8/29/2017 at 1:44 PM, BioBrian said:

I'm still mystified about why flattening the impedance hump with an LCR in the crossover (Dave, my speaker thread) is not a brilliant idea.

 

It's not a "bad idea" .... but the question is why are you doing it?      Adding large and expensive components between the driver and amp can only hurt - so what are you trying to achieve by changing the impedance seen by the amplifier?

 

If it's "to make the crossover components work as expected" .... then you can factor the impedance trap into the crossover design .....  I'd be a bit anti passive speaker level filters at these frequencies regardless though.

 

 

On 8/29/2017 at 1:44 PM, BioBrian said:

I've read that valve amps don't like low impedance speakers; also that drivers in series is not good, but never heard why

 

That's a generalisation based on typical value amplifiers which aren't designed for low impedances.

 

 

Edited by davewantsmoore
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Down here we can get wool batts, which expand from their packaging to about 75 mm thickness. I just found the calculations I made on them some time ago: 12 kgs per cubic metre. No idea how they rate among audiophiles, but they (suit my organic bent, and) can be pulled apart to be 2 or 3 times more fluffy. Measurement proves that they can get rid of internal box reflections, at least in the mid-range.

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S

3 hours ago, davewantsmoore said:

 

You really do want to get all the 'unpexedcted wiggles' out of the impedance curve of a driver.

 

 

I was thinking about this today.  Those impedance wiggles have brought in some corresponding waves in the SPL response and although this all happens in the frequencies that are being line level filtered it is probably still an issue.

 

How to correct it though?  Because the wiggles happen when there is a certain threshold of high density stuffing in the tube all that I can think of is to try different types of stuffing....

 

1 hour ago, Beeman said:

maybe try untreated sheep wool as stuffing?

 

...such as this stuff. Not sure where to get some to try.  We don't have sheep (we only buy the odd clutch of them to fatten and eat) and my brother in law has been chased out of sheep by wild dogs otherwise I am sure I could have got some wool "straight off the sheeps back" at shearing.

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I've noticed in a lot of the sub builds on AVS that people recommend using really cheap pillows, like these -  http://www.ikea.com/ca/en/catalog/products/30269817/  you don't even have to rip them open and get the polyfill out, just stuff 'em in. Maybe worth trying and comparing to the denser sheets you're using now?

Edited by jamiebosco
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So I've been stuffing around this morning, literally and have some interesting results.

 

I have received advice that the stuffing is more effective near the middle of the tube and not at the far end of the tube as I have been placing it.  Moving one and then two sheets to somewhere near the middle of the tube bears this advice to be true.  See the graph below: orange is no stuffing in the tube; magenta is 4 HD sheets at end of tube; blue is 2 HD sheets at middle of tube...

 

59aa01ac3e7af_MiddleplacedHDSheets.thumb.jpg.d37c81eb11c09b231cc2aeda2991bb97.jpg

 

The impedance wiggles are still there so I cut up some less dense Greenstuf R1.5 batts, removed the HD batts, and put the Greenstuf (GS) sheets in about the middle of the tube.  I experimented with 1, 2 and 5 sheets and with each sheet added the Fs reduced which indicates the driver is seeing a larger box, which is good.  Colours in the graph below are: Orange = no stuffing;  Magenta 4 HD sheets at end of tube;  Blue = 2 HD sheets at mid of tube; Yellow = 5 GS sheets at mid of tube...

 

59aa02eea56c9_MiddleplacedGSSheets.thumb.jpg.2e53caff2bdd4153138c13ab9a5ccf11.jpg

 

Now that yellow line is better behaved around the wiggles but has also widened the large resonant peak in the graph.  If we look at the SPL graph below we notice a few things:

 

59aa0570d73dc_HDvsGS.jpg.e952e520b864af8db2cf174c8743e098.jpg

 

I've added REW "dB Offsets" to make the three lines meet roughly at their maximum volume circa 150Hz.  The blue line shows a relatively even attenuation at the frequency rises past 200Hz but adding 4 sheets of HD (gold line) at the end of the tube makes some impedance wiggles in this area and causes the SPL response to vary quite a bit.  Interestingly this gold line is is the flattest below 150Hz and has more relative bass SPL than any other stuffing configuration.  Having 2 HD sheets in the middle of the tube (magenta line) has an even more uneven response above 150Hz and loses relative bass output.  5 sheets of Greenstuf R1.5 in the middle of the tube (green line) gives the closest response to "empty" both above and below 150Hz.  

 

So, I have gleaned a few take home messages from this mornings measurments:  

  1. I should definitely try to eliminate the impedance wiggles because it makes the 150Hz+ much more linear
  2. Less dense stuffing helps to minimise those impedance wiggles, but at this stage they are not all gone
  3. I should try to find some stuffing that is even less dense than the Greenstuf R1.5
  4. Stuffing at the far end of the tube seems to improve relative bass output of the Cannon.

 

 

 

 

Edited by acg
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Hi. It would appear that we're going hell here for leather trying to crush out serious resonances  which are inherent in this kind of enclosure shape, and in dealing with the lack of bass efficiency encountered in a sealed enclosure. May I be so bold as to suggest installing a large diameter, long BR port mounted on the back plate , thus converting the cannons to a bass reflex enclosure.Hello bass extension, and it is likely that some of the impedance issues could be minimised. Certainly not a complete redesign.

Cheers

G

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On 31/08/2017 at 9:20 PM, jamiebosco said:

I've noticed in a lot of the sub builds on AVS that people recommend using really cheap pillows, like these -  http://www.ikea.com/ca/en/catalog/products/30269817/  you don't even have to rip them open and get the polyfill out, just stuff 'em in. Maybe worth trying and comparing to the denser sheets you're using now?

 

I have now done that and it does work well.  The Cannon tube is perhaps half full and the Fs gets down to 44Hz which is excellent...the 150Hz+ SPL response is the the smoothest of all measurements so far...but the impedance wiggles are not quite as smooth as with the Greenstuff R1.5.  Perhaps I need more poly fibrefill but to be honest to further smooth out the wiggles but at this stage the result is fairly similar to the Greenstuff, and the Batts are a much more suitable solution for the long term.

 

I have been advised that I should try BASF Melamine foam and I do have some sitting down in the garage, so this afternoons task is to cut some circles of that stuff and try it out.

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23 hours ago, georgepapa said:

Hi. It would appear that we're going hell here for leather trying to crush out serious resonances  which are inherent in this kind of enclosure shape, and in dealing with the lack of bass efficiency encountered in a sealed enclosure. May I be so bold as to suggest installing a large diameter, long BR port mounted on the back plate , thus converting the cannons to a bass reflex enclosure.Hello bass extension, and it is likely that some of the impedance issues could be minimised. Certainly not a complete redesign.

Cheers

G

 

I don't mind suggestions.  Ported bass enclosures are not my cup of tea and I don't mind a bit of extra effort trying to figure out how different stuffings affect the electrical characteristics of my driver and sealed enclosure.  This experimenting has given me a range of options to EQ the final result when I finally get around to embedding the entire system in my room so it is not an entire waste of time. Plus I am learning a lot.

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1 hour ago, acg said:

I have been advised that I should try BASF Melamine foam and I do have some sitting down in the garage, so this afternoons task is to cut some circles of that stuff and try it out.

 

I have tried various combinations of melamine and it does not work as well as the softer stuffing.  At this stage, it looks like the Greenstuff R1.5 wall batts are the way I will go.  There is still some potential to smooth out the impedance response a little further with another sheet (or perhaps two) of the GS...so I will give that a go when it comes time.  The next thing that I should probably do is to fire up the breadboarded Melquiades SET amplifier (with the Bass OPT in place) and see what sort of frequency response I get with that amplifier.

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