Lime Prisms

[Mr Evil]

There were various unrelated bits and bobs that I have had lying around for many years, and I thought it was about time I put them to use. These included: four Celestion SR1 full range drivers; a pair of Eminence APT-150 horn tweeters; a bunch of polypropylene capacitors and a few inductors, enough for a passive crossover; lots of MDF from when I recently made a horn subwoofer. We needed a pair of speakers for use in the garden now that the weather is better, for parties and stuff - the aforementioned components are suitable for this.

Attached is a photo of the finished pair of speakers from the front. The woofers' cones are paper, they are only silver because I painted them to cover some slight discolouration they seemed to have suffered from damp.

[Mr Evil]

Here's a second photo from above so you can see the triangular cross section. The top panels are removable to allow access to the crossovers (I intend to convert them to active crossovers, but I don't have enough parts to make four amplifiers at the moment). One top panel is dull because I haven't put the final coat of paint on it yet. There are handles on the sides because they are quite bulky (1m tall) and heavy to move otherwise.

[Mr Evil]

This is a picture of what WinISD thinks the bass response should look like. If I had used a normal alignment to give a flat frequency response then they would have needed a subwoofer, but like this it's possible to use them alone, with EQ.

[Mr Evil]

And finally, here's the measured Thiele-Small parameters and an impedance graph for the woofers. I couldn't find any such information on these drivers anywhere, so perhaps this will be useful to someone.

Re = 11.0Ω
Le = 0.5mH
Sd = 22.7e-3m^2
Fs = 70Hz
Qms = 4.3
Qes = 0.50
Qts = 0.45
Vas = 15.7l

They are full-range drivers and so they could have been used on their own, but the addition of the tweeters helps them to reach past 10kHz.


The finished speakers sound quite bright because of the much higher efficiency of the tweeters, despite the padding I added. They sound about right when listened to off-axis though. As expected, the bass is not so impressive by default, but with a little EQ they fill out nicely. The main thing is that they are quite efficient and very robust so they will survive outside, including when it rains as long as it's not too heavy before we escape inside.

They are totally unoptimized because of the mish-mash of parts, but I'm pleased with them because they were constructed entirely from parts I already had, meaning that the cost was effectively 0 (apart from the lovely green and black paint, which I bought especially for these speakers).

[PeteMcK]

love projects like this, (not sure about the colour though ...)
what freq did you tune the box to ?

[jackinnj]

Originally posted by PeteMcK
love projects like this, (not sure about the colour though ...)
what freq did you tune the box to ?

The color is perfectly apropos of life in the UK -- if you don't move fast enough moss grows on your feet and other appendages. You are quickly resigned to a life of watching Mrs. Marple, trying to get yourself admitted to P.G. Wodehouse "Drones Club", tut-tutting Captain Peacock, minding the china with the hand-painted periwinkles or figuring out which one is Ting and which one is Tong.

Kidding aside, in my view, this looks like a really snappy design and kudos to Dr. (Mr.) Evil.

[jackinnj]

Originally posted by PeteMcK
love projects like this, (not sure about the colour though ...)
what freq did you tune the box to ?

The color is perfectly apropos life in the UK -- if you don't move fast enough moss grows on your feet and other appendages. You are quickly resigned to a life of watching Mrs. Marple, trying to get yourself admitted to P.G. Wodehouse's "Drones Club", tut-tutting Captain Peacock, minding the china with the hand-painted periwinkles or figuring out which one is Ting and which one is Tong.

Kidding aside, in my view, this looks like a really snappy design and kudos to Dr. (Mr.) Evil.

[PeteMcK]

lol.. forgot that our cultural context colours our view....

[Mr Evil]

Originally posted by PeteMcK
love projects like this, (not sure about the colour though ...)
what freq did you tune the box to ?

It's tuned to 50Hz, with a box volume of 50l. A tuning of 60Hz would have given a flat response.

And sadly jackinnj is right about the colour. If you surround yourself with nice bright colours you can almost imagine that the summer sky you are sitting beneath is actually blue and sunny, not dropping more rain on your head.