***Desktop Speakers***

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jeffh

Re: ***Desktop Speakers***
« Reply #80 on: 20 Mar 2012, 02:32 am »
How about using this UltraTouch Insulation from Creative Sound Solutions to line the cabinet?





mikeeastman

Re: ***Desktop Speakers***
« Reply #81 on: 20 Mar 2012, 03:06 am »
I used  UltraTouch in some acoustical panels and used some I had left over to stuff a sub I just built. You can get it from Homedepot also.

planet10

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Re: ***Desktop Speakers***
« Reply #82 on: 20 Mar 2012, 05:22 am »
We almost exclusively use UltraTouch for our boxes. It is a joy to use and works very well.

There are 2 types -- the 1/2" felt Bob sells, and less dense bats as used for wall insulation (in various thickness -- i expect this is what Home Despot sells (only in the US, not in Canada)

We use the felt for lining reflex enclosures (and for near the drivers in other boxes). The insulation bats are good for sealed or aperiodic boxes.

dave

tvyankee

Re: ***Desktop Speakers***
« Reply #83 on: 20 Mar 2012, 05:19 pm »
hello,

i remember a while back listening to speaker that looks like the speaker you are making. i sure it is not the same but thought you may want to look at it.

http://www.6moons.com/audioreviews/fj/om.html

Danny Richie

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Re: ***Desktop Speakers***
« Reply #84 on: 20 Mar 2012, 05:29 pm »
hello,

i remember a while back listing to speaker that looks like the speaker you are making. i sure it is not the same but thought you may want to look at it.

http://www.6moons.com/audioreviews/fj/om.html

Wow, $4,000 a pair.

I have a kit along those lines for $249: http://gr-research.com/av-o.aspx

And then this one is a step above at $529: http://gr-research.com/o-3.aspx

And I still have completed X-Omni's with no grills for $275 a pair. http://www.audiocircle.com/index.php?topic=99297.0

LarryB

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Re: ***Desktop Speakers***
« Reply #85 on: 20 Mar 2012, 06:11 pm »
The FJ speakers are sold through dealers (in fact, a friend of mine carries their line); if they were sold direct, the $4,000 FJ Ohm would be apprioximately $2,000.  To determine how the FJ Ohm compares sonically to Danny's speakers, one would have to hear them side by side; it would undoubtedly make for an interesting comparison!

Larry       

Peter J

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Re: ***Desktop Speakers***
« Reply #86 on: 22 Mar 2012, 03:21 pm »
Danny I wonder if you could elaborate on the cancelation you mentioned in your measurements? I'm trying to wrap my head around it conceptually and reconcile with what I'm looking at in the graphs.

Does the cancellation you see take place where the different driver meaurement lines intersect? What's the sonic effect? Does it create a null at that frequency (frequencies) that makes it (them) inaudible?

Danny Richie

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Re: ***Desktop Speakers***
« Reply #87 on: 22 Mar 2012, 03:46 pm »
Okay, the green line is the front driver and the red line is the upper driver.

So looking at the blue line of the two of them playing together we see that they are coupling below 900Hz and we see an increase in output (1+1=2).

However, at 1,700Hz and 4,900Hz we see cancellation effects (1+1=-2). Funny math huh? At 1,700Hz it is a half of a wave length back and 180 degrees out of phase. At 4,900Hz it is likely 1.5 wavelengths back and out of phase.

2,300Hz to 4kHz they are in phase and creating gain again. In this range they are actually a wavelength apart but in time with one another.



When they couple they are twice as loud and when they cancel they have less output than one woofer, sometimes less than half of the output of one woofer.

Peter J

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Re: ***Desktop Speakers***
« Reply #88 on: 22 Mar 2012, 06:36 pm »
uhh... right.  Just when I think I have a little handle on the cancelation and doubling, you go and introduce wavelengths and phase shifting...  :o  Funny math indeed.

Phase confuses me some, I guess I think of it in absolute polarity terms, which is what I know from simply hooking up speakers, but there appears to be much more to it. So phase shift can occur within crossover components?

You know, this makes me feel almost stupid, good thing I'm not sitting in your chair! I'm better off sticking to the wood parts.

S Clark

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Re: ***Desktop Speakers***
« Reply #89 on: 22 Mar 2012, 07:59 pm »
Waves superimpose upon themselves... in other words, their amplitudes add.  Imagine that two waves approach one another.  If the crest of one wave goes through the trough of another, the amplitude will cancel.  It's the same kind of thing as when two woofers are hooked up wrong, with one wired backward.  When one woofer kicks in, the other kicks out.  One creates a pressure zone, and the other a vacuum zone.  When they meet, they cancel.  On the above graph, at about 1700 Hz, one woofer is kicking in where the other is kicking out.  It happens again at around 5K Hz.  If it weren't for phase shifts, we could all design crossovers like pros.  They are tricky little devils, and a pain to deal with.

HAL

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Re: ***Desktop Speakers***
« Reply #90 on: 22 Mar 2012, 08:11 pm »
Ok, but when I grow up, I want to go to Scott's class about building speakers.   Having Scott and Danny as teachers sure would have been cool!

Maybe my designs would not have been so bad over the years!   :D

dmatt

Re: ***Desktop Speakers***
« Reply #91 on: 22 Mar 2012, 10:04 pm »
Isn't a benefit of this wave cancellation effect the "noise-cancelling headphone"? 
The microphone in the headphone listens to the ambient noise and plays it back in the headphones 180 degrees out of phase -- thus cancelling the noise :o for the headphone wearer (as explained by Danny and Scott). 

This has nothing to do with your cool speakers, I'm just tossing out another example that you may have experienced.

- David

Atexanathome

Re: ***Desktop Speakers***
« Reply #92 on: 23 Mar 2012, 02:21 pm »
Wow, $4,000 a pair.

I have a kit along those lines for $249: http://gr-research.com/av-o.aspx

And then this one is a step above at $529: http://gr-research.com/o-3.aspx

And I still have completed X-Omni's with no grills for $275 a pair. http://www.audiocircle.com/index.php?topic=99297.0

I notice that the reviewer devotes a lot of space to flowery descriptions of the sound, but I'm not seeing anything in the review about the position of the speakers in the room. He mentions his room size, but nothing more than that. Nothing about how position in the room changed the sound or imaging. Position in the room is important for any speaker, but it seems especially critical with dipoles and omnis.

Danny Richie

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Re: ***Desktop Speakers***
« Reply #93 on: 23 Mar 2012, 02:24 pm »
Welcome to AC Atexanathome.

Danny Richie

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Re: ***Desktop Speakers***
« Reply #94 on: 23 Mar 2012, 08:52 pm »
Okay how's this?

One woofer is mounted right over the other now and the best response was obtained on axis with the front firing woofer. Green is the front facing woofer. Blue is the lower one, and red is the two together.



Because I am on axis with the front firing woofer and not dead center between the two of them, there is some cancellation going on in the 1.5kHz to 4kHz range but only a slight amount cause by a slight phase rotation. This is because the mic is slightly further away from the upper woofer. So it smoothed out the peak in the response of the front woofer. No notch filter needed.  :D

Okay now how's this (below)? I added a .47mH inductor in line with the upper woofer to minimize how high it plays and to reduce upper frequency range interference a little. This time the light blue line shows them playing together.



Here is the response on a typical 10db scale like you see everywhere else.



Here is the horizontal off axis. Looks pretty smooth and consistent.



Here is the vertical off axis. As the mic moved up 4" per measurement you can see more coupling in the 1kHz to 3kHz range. Not too bad though.



Here are the impedance curves with and without the .47mH inductor on the upper woofer. Red is without the inductor and green is with it.



Another thought on this is that a rear firing ambiance tweeter could be added with a single small cap and resistor (adjustable) to give it back a little air. That will help with the over all sound since the top end is a little soft. It would also not effect the on axis response, just the overall in room response and balance. It will also lower the impedance in the top end and balance the impedance load.   

These would be good speakers for a small untreated room, especially with the speakers placed well out into the room. They would create a pretty large sound field.

LarryB

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Re: ***Desktop Speakers***
« Reply #95 on: 23 Mar 2012, 09:07 pm »
Danny:

In the second graph I do not see the high frequency roll-off from the inductor in series.  What am I missing (other than a brain! :)  )

Larry

Danny Richie

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Re: ***Desktop Speakers***
« Reply #96 on: 23 Mar 2012, 09:10 pm »
Danny:

In the second graph I do not see the high frequency roll-off from the inductor in series.  What am I missing (other than a brain! :)  )

Larry

Check the bright Blue line in the top two graphs. Note that in the second graph the upper woofer (Blue line) does not play up as high.

LarryB

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Re: ***Desktop Speakers***
« Reply #97 on: 23 Mar 2012, 09:21 pm »
Aha, it's the lower woofer (dark blue line) that does not play as high in freuency.

When you wrote "I added a .47mH inductor in line with the upper woofer" you really meant the lower woofer, correct?  Or am I still confused? 

Danny Richie

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Re: ***Desktop Speakers***
« Reply #98 on: 23 Mar 2012, 09:35 pm »
Aha, it's the lower woofer (dark blue line) that does not play as high in freuency.

When you wrote "I added a .47mH inductor in line with the upper woofer" you really meant the lower woofer, correct?  Or am I still confused?

No, it is the upper woofer (up facing woofer) that has the inductor in line with it.

LarryB

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Re: ***Desktop Speakers***
« Reply #99 on: 23 Mar 2012, 10:55 pm »
But those responses look identical.   I'm still confused.