***Desktop Speakers***

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HAL

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Re: ***Desktop Speakers***
« Reply #40 on: 28 Feb 2012, 01:50 pm »
If you reduce the box volume the LF extension of the driver becomes less.  From Skeeter's model looks like F3 is around 65Hz.  If you mate this to a small sub that can go higher in frequency, you can make the box smaller.  The issue is it will be easier to locate the sub audibly.

The program Bass Box will let you put in custom box dimensions after you have the Thiel-Small parameters for the driver, which looks like Skeeter has used in his model. 

skeeter99

Re: ***Desktop Speakers***
« Reply #41 on: 28 Feb 2012, 03:44 pm »
If you reduce the box volume the LF extension of the driver becomes less.  From Skeeter's model looks like F3 is around 65Hz.  If you mate this to a small sub that can go higher in frequency, you can make the box smaller.  The issue is it will be easier to locate the sub audibly.

The program Bass Box will let you put in custom box dimensions after you have the Thiel-Small parameters for the driver, which looks like Skeeter has used in his model.

Hal is correct and some simple adjustments to raise your f3 yields this:



Less than half the space of the previous design and .141 ft^3. It yields a rising response with a peak around 152hz and up 2.2db but then has a fairly smooth roll off after that with an f3 of about 90hz. I just let the box builder figure "optimum" dimensions which are obviously easy to tweak either way. I can easily tweak it, what dims are you looking for?

Scott

Peter J

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Re: ***Desktop Speakers***
« Reply #42 on: 28 Feb 2012, 03:45 pm »
I don't know. Maybe it could be a skinney tower. Do a stand to get it to the floor.
Then put in on either side of the desk. Takes no desk space at all that way.

I've got a drunk that keeps hitting my mailbox. Maybe I could build one of these
to put the mailbox on and have it make a dying sound when it hits it again.  :roll:

I'm thinkin' the sound of a siren might leave a bigger impression on the drunk...

I really want them to live on the desk...really the only way to go if I want them to face me. I'm warming to the idea of fence posts on desktop, and to tell the truth I like contemporary look and now my imagination is ramping up with some cool ways to finish.

I'm wondering how the upper driver will like being within 16-17" of the ceiling...kinda like Danny's AV-R's.

 I'm excited to give this a shot.

HAL

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Re: ***Desktop Speakers***
« Reply #43 on: 28 Feb 2012, 03:58 pm »
Scott,
Thanks for showing the FR change.

The issue is going to be the peaking in the 100Hz to 200Hz range is going to start making things sound nasal since it is not flat.   

Peter J

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Re: ***Desktop Speakers***
« Reply #44 on: 28 Feb 2012, 04:02 pm »
Hal is correct and some simple adjustments to raise your f3 yields this:



Less than half the space of the previous design and .141 ft^3. It yields a rising response with a peak around 152hz and up 2.2db but then has a fairly smooth roll off after that with an f3 of about 90hz. I just let the box builder figure "optimum" dimensions which are obviously easy to tweak either way. I can easily tweak it, what dims are you looking for?

Scott

Scott I appreciate your efforts, I did download WinISD, but try as I might, I couldn't seem to save the new driver info so I could continue. Any clues on that?

 I found something to play with box volume here, but no FR graph like winISD;

http://www.hometheatershack.com/forums/enclosure-volume-calculator/

I've had to define my parameters better as design has progressed, priorities have evolved to:
  1. 5"x5" footprint is ideal for area where they will sit
  2. Keep the whole thing cheap and cheerful
  3. I think I want to optimize box volume if at all possible, hence my latest design
  4. I'll mock them up before commiting to a final finish
  5. I think I've succumbed to the experimentation bug  :o

skeeter99

Re: ***Desktop Speakers***
« Reply #45 on: 28 Feb 2012, 04:09 pm »
Scott,
Thanks for showing the FR change.

The issue is going to be the peaking in the 100Hz to 200Hz range is going to start making things sound nasal since it is not flat.

It definitely could. I have a rising response like that on my desktop speakers I built and its really not too bad since its minimal but other people have far better hearing than I do and it very well could cause issues for them. Very good point.

Scott

HAL

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Re: ***Desktop Speakers***
« Reply #46 on: 28 Feb 2012, 04:11 pm »
Brain is going very slow today due to a cold.  :(

I think Bass Box's crossover software will let you add a notch filter to EQ out the peak in the 100-200Hz range. That might help flatten things out if you want to use the small box.

skeeter99

Re: ***Desktop Speakers***
« Reply #47 on: 28 Feb 2012, 04:20 pm »
Scott I appreciate your efforts, I did download WinISD, but try as I might, I couldn't seem to save the new driver info so I could continue. Any clues on that?

 I found something to play with box volume here, but no FR graph like winISD;

http://www.hometheatershack.com/forums/enclosure-volume-calculator/

I've had to define my parameters better as design has progressed, priorities have evolved to:
  1. 5"x5" footprint is ideal for area where they will sit
  2. Keep the whole thing cheap and cheerful
  3. I think I want to optimize box volume if at all possible, hence my latest design
  4. I'll mock them up before commiting to a final finish
  5. I think I've succumbed to the experimentation bug  :o

I readjusted the dims within WinISD and got a 5"x5"x16.23" box using 1/2" material. Port is 2"x4.42".

I don't know why you can't save your own drivers?? You click on "own drivers" in the new project tab then click the "new" button. It takes you to the "Driver Editor" window where you put in the driver name and all the specs. Once you're done you click OK. You then have to go back to the New Project window, click on "own drivers" again then pick your driver from the pull down menu.

Scott

skeeter99

Re: ***Desktop Speakers***
« Reply #48 on: 28 Feb 2012, 04:21 pm »
Brain is going very slow today due to a cold.  :(

I think Bass Box's crossover software will let you add a notch filter to EQ out the peak in the 100-200Hz range. That might help flatten things out if you want to use the small box.

Oh I don't have Bass Box, maybe I should download it. I'm using WinISD.

skeeter99

Re: ***Desktop Speakers***
« Reply #49 on: 28 Feb 2012, 04:31 pm »
Changing the tuning frequency to 75hz smooths out the larger rise to a max rise of .6db centered at 200hz and a f3 of 94.63hz:



This changes the port length to 9" which is pretty long but its all internal so it shouldn't matter.

Danny Richie

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Re: ***Desktop Speakers***
« Reply #50 on: 28 Feb 2012, 08:06 pm »
I'll model this in Bass Box later today. The port size though sound be quite small.

Also keep in mind that there will be some baffle step loss. This will be helped by using two woofers but maybe not completely.

So a bumped bottom end may in reality not be much of a bump.

skeeter99

Re: ***Desktop Speakers***
« Reply #51 on: 28 Feb 2012, 08:10 pm »
I'll model this in Bass Box later today. The port size though sound be quite small.

Also keep in mind that there will be some baffle step loss. This will be helped by using two woofers but maybe not completely.

So a bumped bottom end may in reality not be much of a bump.

Cool! I look forward to seeing what Bass Box comes up with  :thumb: Its fun playing around with the program so it'll be cool to see what pro results look like!

Scott

planet10

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Re: ***Desktop Speakers***
« Reply #52 on: 28 Feb 2012, 08:30 pm »
To get optimum volume (.3 cu.ft.) this is morphing into a pretty overbearing desk accessory...and looking more and more like a fence post...




Do keep in mind that when you get to these kind of aspect ratios that a BR modeler won't do it. You have to use something like MJK's sheets to account for the quarter-wave inside.

dave

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Re: ***Desktop Speakers***
« Reply #53 on: 29 Feb 2012, 12:08 am »
Do keep in mind that when you get to these kind of aspect ratios that a BR modeler won't do it. You have to use something like MJK's sheets to account for the quarter-wave inside.

dave


Hmmmmmmmm...quarter wave?  Dave, I'd love to keep it in mind, but you're dealing with a neophyte designer here, so the truth is, I don't understand what you're describing.

 Any chance you could elaborate? What is BR and MJK's sheets may well be of interest, if only I knew where I might find them. I doubt we're talking bed sheets...

Danny Richie

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Re: ***Desktop Speakers***
« Reply #54 on: 29 Feb 2012, 12:26 am »
Bass box shows these woofers need .1 cubic feet per woofer. And the port size is 1/2" in diameter by 7/16" long. This gives you a -3db of 71Hz.

Peter J

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Re: ***Desktop Speakers***
« Reply #55 on: 29 Feb 2012, 01:05 am »
Bass box shows these woofers need .1 cubic feet per woofer. And the port size is 1/2" in diameter by 7/16" long. This gives you a -3db of 71Hz.

Thanks for doing that, Danny, it gets confusing with different results from various resources. Is the port size you mentioned considering 2 woofers or should that double?

 The little app I linked to earlier was calling for port diameter of 1" with a length of 1 11/16" and a box volume of 1.5 per driver...dang, what a difference. For someone (me) who likes to make well considered decisions, it seems a bit wonky.

I'll run with your numbers, partly 'cuz I like the box size better, but mostly because I trust your judgement.

This quarter wave thing Dave mentioned has got me wondering

Danny Richie

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Re: ***Desktop Speakers***
« Reply #56 on: 29 Feb 2012, 01:41 am »
Quote
Thanks for doing that, Danny, it gets confusing with different results from various resources. Is the port size you mentioned considering 2 woofers or should that double?

Double that for two woofers.

It is just a 3" woofer with .2mm of X-max. It can't move enough air to need a port that is very big.

Peter J

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Re: ***Desktop Speakers***
« Reply #57 on: 29 Feb 2012, 05:37 am »
Round three!

 .2 cu ft volume, 5"x 5" footprint using 5/8ths material, may go with 1/2" material, not sure that additional rigidity of thicker MDF would prove to be a benefit...opinions?



planet10

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Re: ***Desktop Speakers***
« Reply #58 on: 29 Feb 2012, 07:24 am »
Round three!

 .2 cu ft volume, 5"x 5" footprint using 5/8ths material, may go with 1/2" material, not sure that additional rigidity of thicker MDF would prove to be a benefit...opinions?



For Danny's sim to be valid you need to shorten the box and at least increase the depth (increasing the width to reduce early reflections back thru the cone will help reduce midrange colouration). With that aspect ratio you have created a non-optimum mass loaded transmission line. I'd alo try to keep the drivers as close as possible.

You could readily get away with 1/2" quality plywood. MDF needs to be quite a bit thicker for the same stiffness.

dave

Peter J

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Re: ***Desktop Speakers***
« Reply #59 on: 4 Mar 2012, 02:47 am »
Version #4. Got all the parts on hand now. Box volume .2 as Danny figured,  using 1/2" material and also considering Dave's suggestions this is what I came up with.

Bottom 5 1/2" of box is separate and  raises the front driver to get slightly above monitor. Could be legs or some kind of plinth, but I'll ponder that some. My intent is to keep the design simple so it would be easy for others to duplicate. 

Never having messed around with little drivers like these, I'm impressed by their heft...they're stout little buggers.