Which type of box would you build based on this frequency graph? - Page 2 - diyAudio
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Old 7th December 2011, 12:12 AM   #11
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I'm glad I asked - this forum really is a great place to share thoughts


Thanks for all the advice, and the difference of opinion!


Quote:
Originally Posted by badman View Post
...and had a solid budget,
Unfortunately my budget will currently stretch as far as screws, wood, cups of tea and a Sunday afternoon or 2. The real money is being spent on a centre speaker upgrade and a projector, hence I'm trying to make do with loft clutter for the sub idea.

@ sreten

Some interesting ideas there. I've used winISD to come up with the graphs and suggested box volumes. Using a smaller box like you say would be much more practical, but how would I tune it to a certain frequency? I don't see any option to do that in winISD so I guess I need something else.

The other option of using a passive bass boost (I guess this means a HF attentuator?) is a good one, but wouldn't I need a scope and perhaps an SPL meter to tune this properly? (Neither of which I have)

I do like the idea of being able to boost the LF and use a smaller box. But it sounds like I'll quickly get out of my depth. I have no idea how I'd upgrade my monobloc's feedback loop, or even if it has one - they're AB solid state I think.

@ bjorno

The sofa is a 3 seater, and there's a large void that runs up the back, so there's a decent volume in there. However the wooden lining is about 3mm thick so it will resonate like crazy! I thought I could stick some tar sheets/sound deadening to the inside if necessary.

That image you posted looks interesting but is too small to see - have you got a link?

@ Conrad

That's out of my depth, sorry...

@ Zero

Would I definitely need a filter, given that the processor should only be sending LFE signals to the monobloc/s? I was hoping to avoid any additional complications like crossovers, phase, alignment and all those other things I don't fully understand!

Thanks a lot for the graphs. They definitely look feasable. I could make a long flat box that would fit completely under one of the sofa's, and would go up into the lower void slightly. So it would be completely concealed. How much space I've got under there and if I could actually hit 120-150L I don't know yet.

@ weltersys

My thoughts entirely. Thanks.

---

So I think we can agree there isn't really much point going to the extra effort to build a 4th order bandpass.

I'll take a picture of the underside of the sofa tomorrow and post it so hopefully we can decide between gutting out the sofa's void so a ported box can be housed underneath, or just bolting up some wood and a woofer for smiles all round
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Old 7th December 2011, 09:02 AM   #12
Zero D is offline Zero D  United Kingdom
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Originally Posted by judderod

Quote:
Would I definitely need a filter, given that the processor should only be sending LFE signals to the monobloc/s?
In that case no. Just for your information though, BP enclosures really do need a LP filter, or they sound rough etc.

Quote:
Thanks a lot for the graphs. They definitely look feasable.


Quote:
but how would I tune it to a certain frequency? I don't see any option to do that in winISD so I guess I need something else.
Like this

tune.gif

Keep us posted & all the best with it.
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Old 7th December 2011, 03:11 PM   #13
sreten is offline sreten  United Kingdom
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Quote:
Originally Posted by judderod View Post
I don't see any option to do that in winISD so I guess I need something else.
Hi,

You just change the frequency in the tuning frequency box, the
vent length is recalculated for the default / chosen diameter.

rgds, sreten.
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Old 7th December 2011, 03:41 PM   #14
bjorno is offline bjorno  Sweden
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Quote:
Originally Posted by judderod View Post
...That image you posted looks interesting but is too small to see - have you got a link?...
To magnify: You have to click on the X-cross at lower left corner.

b:
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Old 7th December 2011, 04:14 PM   #15
badman is offline badman  United States
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Quote:
Originally Posted by weltersys View Post
Your suggestion of PR make sense for your application, not much for the OPs, regardless of the decade .

Art
Somehow I missed that he already had the woofers.

My PR comments were specific to modern low fs, low Vas subs. As most of us know, higher Xmax tends to drive down sensitivity and Vas and Fs due to the contstraints of building drivers (longer heavier coil)
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Old 7th December 2011, 07:53 PM   #16
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I'd had a play with changing the tuning frequency, but I'm not entirely sure what I'm aiming for. Is the frequency the resonance of the enclosure?

Is it just a case of fiddling with the frequency and volume until the graph has a nice slope?

@ bjorno I guess those pictures are just for looking nice... 374 thousand watts?!!

On to some pictures...

Underside

Click the image to open in full size.


Centre section

Click the image to open in full size.


Left lower void

Click the image to open in full size.


Up the back

Click the image to open in full size.


Back (angled)

Click the image to open in full size.


Looking at these pictures there's a huge volume inside the sofa. Only trouble is some walls are very flimsy, and some walls are just the sofa's foam. No way to calculate anything I guess. How about a big thick sheet that seals off the entire bottom section with the driver in the middle?
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Old 7th December 2011, 08:07 PM   #17
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Quote:
Originally Posted by judderod View Post
I'd had a play with changing the tuning frequency, but I'm not entirely sure what I'm aiming for. Is the frequency the resonance of the enclosure?

Is it just a case of fiddling with the frequency and volume until the graph has a nice slope?


Looking at these pictures there's a huge volume inside the sofa. Only trouble is some walls are very flimsy, and some walls are just the sofa's foam. No way to calculate anything I guess. How about a big thick sheet that seals off the entire bottom section with the driver in the middle?
Play with box volume and available space, choose a size that can be built under your couch, then experiment with tunings.

Box tuning is Fb (Frequency of box), or box resonance.
The resonant frequency of the driver is Fc.

An Fb below Fc will have less output compared to one above in a given size box.
Too high an Fb in a small box, and the box will “boom” (a bump) at Fb.
Too low an Fb, and the response will look more like a sealed box.

You need to juggle box size, Fb, output level and excursion to see what the best compromise for your musical taste, available acceptable size, and your driver's parameters are.

Since you have decided against EQ, "a nice slope" would be a flat response.

Art

Last edited by weltersys; 7th December 2011 at 08:09 PM.
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Old 7th December 2011, 08:56 PM   #18
bjorno is offline bjorno  Sweden
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Quote:
Originally Posted by judderod View Post
...I guess those pictures are just for looking nice... 374 thousand watts?!!
IME, If a T-TQWT is built,measured and compared with the HR graphs: Difference's would be near negligible.

I only read 37.5 W at 24 Hz., You need to build at least 10000 T-TQWT's to withstand that power.

b
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Old 19th December 2011, 11:48 AM   #19
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Sorry Bjorno I thought you were being silly! I get it now. Thanks for the info.

And thanks for the help Art. I worked with the firgures but couldn't get the frequencies low enough. The room I'm working with seems to have a resonance peak at around 43Hz, and if I was going to the effort to build a proper sub, I'd want it to be fairly flat down to about 20Hz as I can easily hear that low. But it's not possible with the driver I have and the space I've got to work with.

So I went for the sofa sub. LFE Sofa

Enjoy
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Old 21st December 2011, 08:18 PM   #20
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Quote:
Originally Posted by bjorno View Post
Hi,

Good idea..LFE-sofa...Why?...IMO,The submitted picture talks for itself:

b

Click the image to open in full size.
How can the distance between S3 & S4 be less than 1/2 the diameter of the speaker?
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