I have seen something from Pi-speaker...ups, found it
http://www.pispeakers.com/Speaker_Crossover.doc
seems like your first cap needs to be much smaller...O point something
http://www.pispeakers.com/Speaker_Crossover.doc
seems like your first cap needs to be much smaller...O point something
question about
My wife has a pair of JBL MRX515 PA speakers that she uses for performing and also as rehearsal monitors. They have a horn/waveguide with ~70 degree beamwidth (specs here). These speakers sound pretty good (driven by a 500W analog mixer), but I am wondering whether they could be improved by using a foam plug in the horn/waveguide. If I were going to experiment with that, would one of these foam types be appropriate (e.g., protectair 30ppi)? What is the best way to cut and shape it?
-Doug
My wife has a pair of JBL MRX515 PA speakers that she uses for performing and also as rehearsal monitors. They have a horn/waveguide with ~70 degree beamwidth (specs here). These speakers sound pretty good (driven by a 500W analog mixer), but I am wondering whether they could be improved by using a foam plug in the horn/waveguide. If I were going to experiment with that, would one of these foam types be appropriate (e.g., protectair 30ppi)? What is the best way to cut and shape it?
-Doug
I used a razor blade knife to cut mine. But it doesn't look really pretty. I dunno how Dr. Geddes gets his looking so good...lol. You would think it would be easy to cut pretty...I did. I was sort of wrong.
But the foam...the foam is good stuff. You wouldn't think you would have any high frequency response left with it in there, but again, that will suprise you.
But the foam...the foam is good stuff. You wouldn't think you would have any high frequency response left with it in there, but again, that will suprise you.
Back in the 1970's I helped a friend build a Burt Rutan design called the LongEZ ( an airplane using foam as the core). The foam panels (wings, fuselage etc ) were cut using the hot wire method. We used an electric model train transformer to power the stainless steel wire stretched across a bow. Later in the project we used a battery charger as the power source. It is very simple and extreemly effective. Hope this helps.
Ray
Ray
Thanks, Earl (and others)... I suppose I could set up something with a hot nichrome wire in a fume hood (I have access to a hood in the lab where I work). A sharp serrated knife might be be just as easy. It does sound like it will be a challenge to get the shape right, x2. So is there a good place to get a reasonable sized block for reasonable $?
-Doug
-Doug
Re: question about
Doug,
Before buying Summas, I'd considered modding a pair of JBL two ways. The JBLs which I purchased sound quite good, though they don't image at all. I googled your speakers, and it looks like they may use a relative of one of my favorite compression drivers.
I really like the BMS compression drivers, and JBL sells a version of one. According to this thread on Lansing heritage, your JBLs may use a relative of it:
http://www.audioheritage.org/vbulletin/showthread.php?p=199585
If that is the case, then your speaker would make an excellent candidate for the foam plug, as the BMS driver in question has the most extended high frequency response of any compression driver I've personally seen.
I'll leave the research to you, but it's certainly an interesting speaker.
If you'd like to learn more about this, take a look at some of my other posts. I also used the BMS in a foam filled waveguide back in 2006:
www.audiogroupforum.com/csforum/showthread.php?t=62789
DougSmith said:
DougSmith said:
Doug,
Before buying Summas, I'd considered modding a pair of JBL two ways. The JBLs which I purchased sound quite good, though they don't image at all. I googled your speakers, and it looks like they may use a relative of one of my favorite compression drivers.
I really like the BMS compression drivers, and JBL sells a version of one. According to this thread on Lansing heritage, your JBLs may use a relative of it:
http://www.audioheritage.org/vbulletin/showthread.php?p=199585
If that is the case, then your speaker would make an excellent candidate for the foam plug, as the BMS driver in question has the most extended high frequency response of any compression driver I've personally seen.
I'll leave the research to you, but it's certainly an interesting speaker.
If you'd like to learn more about this, take a look at some of my other posts. I also used the BMS in a foam filled waveguide back in 2006:
www.audiogroupforum.com/csforum/showthread.php?t=62789
I don't think that this kind of foam can be obtained at reasonable prices because even the base materials are very expensive. A ft^3 block would be about $25 uncut. And then when you cut it there is a lot of waste. I'm running a little short so I don't want to sell any of what I have. You can buy it in sheets, but then layering it poses some issues.
I've tried a couple of methods with layers of foam. The first was to glue the layers together. This doesn't work - don't bother. There isn't enough surface area to make a good bond.
The next method I tried was to wrap the layers in panty hose. That works pretty well.
What I would like to try next is to just hold it together with something that's acoustically transparent. For instance, you could bond the layers with bamboo skewers. Yes, the same ones you use for cooking shish kebabs
It sounds a bit silly, but with a diameter of 1/8", bambook skewers are acoustically invisible all the way 28khz!
Another option is plain ol' sewing thread. Just sew the layers together.
The next method I tried was to wrap the layers in panty hose. That works pretty well.
What I would like to try next is to just hold it together with something that's acoustically transparent. For instance, you could bond the layers with bamboo skewers. Yes, the same ones you use for cooking shish kebabs
It sounds a bit silly, but with a diameter of 1/8", bambook skewers are acoustically invisible all the way 28khz!
Another option is plain ol' sewing thread. Just sew the layers together.
This is a "For What It's Worth" :
When we set up to cut a wing panel we attached a template of the airfoil to each end of the foam slab as a guide. We also made equally spaced, numbered tick marks around the perimeter of the template and called them out as the wire passed each one. This kept us together and produced a symetrical cut. Your wave guides are obviously not long enough to require two people but maybe there is something here that will help you.
Ray
When we set up to cut a wing panel we attached a template of the airfoil to each end of the foam slab as a guide. We also made equally spaced, numbered tick marks around the perimeter of the template and called them out as the wire passed each one. This kept us together and produced a symetrical cut. Your wave guides are obviously not long enough to require two people but maybe there is something here that will help you.
Ray
Member
Joined 2003
Earl,
I think you would find quite interesting to know what is said about you here, in France, into the Son-QC francophone forum about audio. I don't know if you read French, but, as you are the main subject of a new thread, it is normal that you are informed about the content !
Here is the text that is describing you about a remark from a reader about the criticisms you made about the Bjorn Kolbrek's article on Voice Coil and the accuracy of the Webster equation :
(copyrighted material removed by moderators)
The less I can say is that it's not very fair to criticize when one is hidden into a foreign forum ! But, I'm sure, you won't be very surprised !
Jipihorn
(sorry for english syntax mistakes I can make...)
I think you would find quite interesting to know what is said about you here, in France, into the Son-QC francophone forum about audio. I don't know if you read French, but, as you are the main subject of a new thread, it is normal that you are informed about the content !
Here is the text that is describing you about a remark from a reader about the criticisms you made about the Bjorn Kolbrek's article on Voice Coil and the accuracy of the Webster equation :
(copyrighted material removed by moderators)
The less I can say is that it's not very fair to criticize when one is hidden into a foreign forum ! But, I'm sure, you won't be very surprised !
Jipihorn
(sorry for english syntax mistakes I can make...)
Thanks for the heads up.
From Jean-Michael I'm not surprised at all. He has been trying to make the situation clear as mud with false statements from the begining. The foam further reduces the already low HOMs from the OS waveguide making these waveguides by far the lowest HOM content anywhere. The subjective opinions bear out that this is a major benefit. He didn't seem to mention that part.
He should talk about humility!
From Jean-Michael I'm not surprised at all. He has been trying to make the situation clear as mud with false statements from the begining. The foam further reduces the already low HOMs from the OS waveguide making these waveguides by far the lowest HOM content anywhere. The subjective opinions bear out that this is a major benefit. He didn't seem to mention that part.
He should talk about humility!
I have read some of Jean-Michael's work, and there are a few articles that was very inspiring. Everyone talks about HOMs, but no body has ever done any sensitivity analysis or measurements as to how sensitive HOMs are to manufacturing tolerances. I don't even think that anyoneone actually has a standard way of identifying the severity of HOMs.