Hello, I'm a true newbie to DIY speakers, and I did a search for the term "Pyramid." If you can direct me to where this has been discussed before, I'd much appreciate it.
I inherited a pair of triangle pyramid cabinets that were designed for a 10" woofer and a 3 1/2" driver for high frequencies. In the course of history, they were modified to hold two 5 1/2" drivers. The drivers were destroyed by a little brother's ignorant thumb (Augh!). There were no other electronics inside.
I'll give you the measurements, then describe what I'd like to do.
It's built with 3/4" presswood of some sort.
I went to Parts Express to search for parts (go figure) which might make these speakers into a nice 2-way system for about $200 or so. I'd like to replace the front-panel with a substantial Vifa driver (P21WO-20) that has decent frequency response so that with a decent tweeter (D27TG-05) the system might cover the whole range without a big dip somewhere in the midrange.
Firstly, is that a decent proposal? That's an 8" woofer in an enclosed configuration. I could go to 6 1/2", but I want that bottom end if at all possible.
Secondly, I haven't got a clue as to crossover configuration. I can solder and I understand impedance and capacitance, etc., but can I just buy one designed to crossover at 2500 or 3000 Hz? That would make my life much easier.
BTW, I'd like to see a discussion of the benefits of an equilateral pyramid as far as the whole "parallel surfaces" thing is concerned. No ports or anything, either. Hmm...
Thanks!
I inherited a pair of triangle pyramid cabinets that were designed for a 10" woofer and a 3 1/2" driver for high frequencies. In the course of history, they were modified to hold two 5 1/2" drivers. The drivers were destroyed by a little brother's ignorant thumb (Augh!). There were no other electronics inside.
I'll give you the measurements, then describe what I'd like to do.
It's built with 3/4" presswood of some sort.
- inside height from middle bottom to top peak is 14"
- the length of each joint is 16"
- According to V=1/3Bh, that comes to roughly 520 cu. in. right?
- 520 cu. in. comes to .3 cu. ft. or 8.5 liters
I went to Parts Express to search for parts (go figure) which might make these speakers into a nice 2-way system for about $200 or so. I'd like to replace the front-panel with a substantial Vifa driver (P21WO-20) that has decent frequency response so that with a decent tweeter (D27TG-05) the system might cover the whole range without a big dip somewhere in the midrange.
Firstly, is that a decent proposal? That's an 8" woofer in an enclosed configuration. I could go to 6 1/2", but I want that bottom end if at all possible.
Secondly, I haven't got a clue as to crossover configuration. I can solder and I understand impedance and capacitance, etc., but can I just buy one designed to crossover at 2500 or 3000 Hz? That would make my life much easier.
BTW, I'd like to see a discussion of the benefits of an equilateral pyramid as far as the whole "parallel surfaces" thing is concerned. No ports or anything, either. Hmm...
Thanks!
Member
Joined 2002
You can kinda make out where the 3 1/2" driver went. The 10" filled up most of the remaining panel.
Actually that looks like a tetrahedron... beauty.
You might actually get more bass from a 6" driver in such a small box. Personally i like an even smaller midbass (and add a sub later). A Vifa P13 perhaps.
dave
You might actually get more bass from a 6" driver in such a small box. Personally i like an even smaller midbass (and add a sub later). A Vifa P13 perhaps.
dave
yes, tetrahedon. That's the shape. I said "triangle" to get that across. I'll do a search for tetrahedon now!
I'd like some more input, though. I'm sure I can learn a lot about why the 6" has better low-end response in this thing.
I'd like some more input, though. I'm sure I can learn a lot about why the 6" has better low-end response in this thing.
Are there any benifits in using that shape enclosure for ported speaker boxes? I ask cos I am doing woodwork next year and would like to make some speakers... ported, using 6inch Response speakers (from jaycar) and am not sure if the teacher will allow me to make just simple rectangular prism boxes.. 😀
ALSO!!!!! while I am here... how do the ReSponse 6inches compair to the Vifa P17WJs (sorry, couldn't find a link to info on them.. 😀)
ALSO!!!!! while I am here... how do the ReSponse 6inches compair to the Vifa P17WJs (sorry, couldn't find a link to info on them.. 😀)
kneadle said:
An 8 generally will need a bigger box than a 6. If you put a speaker in too small a box you end up with a high Q -- a big bump in the response which doesn't sound good. The smaller driver, with its requirement for a smaller box could well have a more realistic Q.
dave
Hmm. I tried all the calculating I could understand with pebox, and it seemed like the 8" I picked out could fit in a .3 cu. ft. box.
Maybe Im ignorant, though. That's why I'm here.
Oops! Upon double checking, I see that I was wrong! The 6 1/2" P17WO-20 (for skinnyboy: http://www.partsexpress.com/pe/show...36&St3=79409795&DS_ID=3&Product_ID=7856&DID=7 )
is actually made for a .28 cu. ft. sealed configuration, the size of my box within 2/100ths.
But that's my next question: Is a tetrahedron actually behaving like a .30 box or like a 1.0 cu. ft. box? Do you get my drift??
Maybe Im ignorant, though. That's why I'm here.
Oops! Upon double checking, I see that I was wrong! The 6 1/2" P17WO-20 (for skinnyboy: http://www.partsexpress.com/pe/show...36&St3=79409795&DS_ID=3&Product_ID=7856&DID=7 )
is actually made for a .28 cu. ft. sealed configuration, the size of my box within 2/100ths.
But that's my next question: Is a tetrahedron actually behaving like a .30 box or like a 1.0 cu. ft. box? Do you get my drift??
I pulled a random Vifa P17 & P21 out of the database that comes with MacSpeakerz and with the 8 i got a big peak and an F3 of 105Hz, with the 6 a Q of 0.77 and an F3 of 90.
It doesn't matter what shape the box is -- its behavior is determined by its volume.
dave
kneadle said:
It doesn't matter what shape the box is -- its behavior is determined by its volume.
dave
OK, to test my fledgling DIY knowledge:
Q .77 is good, right? The Pebox helpfile says that people like Qtc 8.0-1.1 for the skewed bass response, but I wanna stay nearer to flat.
F3 values are a little beyond me. Aha! Found it. That's where the bass starts to roll off. 90 isn't terrible, and it's certainly better than 105. Isn't that cool? The smaller rolls off later than the bigger.
Hmm. I wonder where 45 will show up with this tetrahedron.
And what about a crossover? What in the heck am I doing there?
Q .77 is good, right? The Pebox helpfile says that people like Qtc 8.0-1.1 for the skewed bass response, but I wanna stay nearer to flat.
F3 values are a little beyond me. Aha! Found it. That's where the bass starts to roll off. 90 isn't terrible, and it's certainly better than 105. Isn't that cool? The smaller rolls off later than the bigger.
Hmm. I wonder where 45 will show up with this tetrahedron.
And what about a crossover? What in the heck am I doing there?
It might look interesting but a speaker cabnet shaped like that is a serious accident waiting to happen. The sharp point on the top will be a magnet for the face of someone tripping over the speaker cables. Better make sure your umbrella insurance is paid up before you have any parties...
One good "point" about the design is no one will ever leave a beer sitting on top of it!
MR
One good "point" about the design is no one will ever leave a beer sitting on top of it!
MR
kneadle said:
It will do.
Depends on the midbass & tweeter you choose. Careful choice of a midbass with a smooth roll-off you might get away with only an XO on the tweeter.
dave
Hmm... I had a discussion with my stupid physics teacher and a know it all, know nothing car audio enthusist who didn't have a car, earlyier this year about spherical speaker boxes... my physucs teacher was quite certain that you would get very poor bass from it.... is this the case???
My friend and I also had a "discussion" about a car decked out FULLY with subs, and he recconed it'd do over 160dB (I think thats what it was, maybe higher) He brought the mag to school, and sure enough... hats what it said in the mag.. 🙂 hm... possible???
My friend and I also had a "discussion" about a car decked out FULLY with subs, and he recconed it'd do over 160dB (I think thats what it was, maybe higher) He brought the mag to school, and sure enough... hats what it said in the mag.. 🙂 hm... possible???
You need not to make a pyramid with only 4 sides.
make them left and right sloop 10-15 degrees angle.
And the same with the backside.
Baffle, bottom and top still is at usual.
This will reduce standing waves inside.
Also avoid to make any of deeepth, width and height
have same measure.
Worst box is a cube like a dice, with all sides equal.
/halojoy
a geometrical fenomena never to be solved
by anyone at any time ever
make them left and right sloop 10-15 degrees angle.
And the same with the backside.
Baffle, bottom and top still is at usual.
This will reduce standing waves inside.
Also avoid to make any of deeepth, width and height
have same measure.
Worst box is a cube like a dice, with all sides equal.
/halojoy
a geometrical fenomena never to be solvedby anyone at any time ever
halojoy said:
AHHHH DANG!!! I shoulda know that before I made my sub box a cube.. 😛 now what am I supposed to so with it???? I suppose I could chop off the front at an angle and make a box with an angled front..... I SPENT 20BUX ON THAT MDF!!!! lol.... Hmm.. sell it to my friend..... 😀
I do not think that is as important for sub-frequencies.
Cube Sub-box would be very easy to make.
at 100 Hz a wave is 3.4 meters long
and below 100 even longer.
It is no way it would fit in your box,
and what is a bigger problem:
It wouldn't even fit in a normal living room
So when waves get longer than 4-5 meters,
they start climbing around the wall
causing them to deform.
A 50 Hz wave is 6.8 meter.
wavelenght, meter = 345/Hz
But in the mid register irregular or circular shape
would be an improvement.
Waves can be "standing" in there and resonances
can occur.
at least this is what
/halo thinks
Cube Sub-box would be very easy to make.
at 100 Hz a wave is 3.4 meters long
and below 100 even longer.
It is no way it would fit in your box,
and what is a bigger problem:
It wouldn't even fit in a normal living room
So when waves get longer than 4-5 meters,
they start climbing around the wall
causing them to deform.
A 50 Hz wave is 6.8 meter.
wavelenght, meter = 345/Hz
But in the mid register irregular or circular shape
would be an improvement.
Waves can be "standing" in there and resonances
can occur.
at least this is what
/halo thinks
The thing with the wavelength and the room size is indeed quite a hot topic in this context:
1.) for really long wavelengths it is not possible to build up standing waves in a small box, so cube shaped subwoofers are definitely O.K. if used properly.
2.) If there is no "room for a wavelength" it is still possible to generate sound. For our hearing it is not necessary to have a soundWAVE to hear sound. Sound PRESSURE alone is sufficient. So it is still possible to generate low frequency sound in a small room. If the room in question were airtight the SPL could easily be calculated using the ratio of room volume and linear displacement of the woofer.
3.) This leads to the answer for the car-audio question: It is indeed possible to generate SPLs of 160dB and even more in a car if you are able to move enough air. If this is reasonable is another question. If you use the same car audio system in free space the SPL will drop significantly.
For short wavelengths, irregular shapes like the tetrahedron are definitely advantageous (also round ones). The main reason it isn't done more often is costs.
Regards
Charles
1.) for really long wavelengths it is not possible to build up standing waves in a small box, so cube shaped subwoofers are definitely O.K. if used properly.
2.) If there is no "room for a wavelength" it is still possible to generate sound. For our hearing it is not necessary to have a soundWAVE to hear sound. Sound PRESSURE alone is sufficient. So it is still possible to generate low frequency sound in a small room. If the room in question were airtight the SPL could easily be calculated using the ratio of room volume and linear displacement of the woofer.
3.) This leads to the answer for the car-audio question: It is indeed possible to generate SPLs of 160dB and even more in a car if you are able to move enough air. If this is reasonable is another question. If you use the same car audio system in free space the SPL will drop significantly.
For short wavelengths, irregular shapes like the tetrahedron are definitely advantageous (also round ones). The main reason it isn't done more often is costs.
Regards
Charles
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