OB project, Jame's Quasars copy
#1 OB project, Jame's Quasars copy
I cobbled together these err beasts over the New Year, seeing as I had some old wardrobe doors to dispose of.
They are more or less James's Quasars, but a bit wider to accommodate the Eminence Beta 15s (thanks Phil for the epay heads up) and a pair of Sidcup's finest, two fairly modernish PM6C.
This is my first ever speaker build! And I don't know what I'm doing whatsoever... but they seem to sound quite good, nice present-but-tight bottom end (missus),reasonably balanced midrange (albeit with some of that unavoidable Lowther 'forwardness') and if there's a lack of top treble then I can't notice it....they are also pretty efficient, my 801a amp seems very happy with them.
The phase plugs were an attempt to calm down the midrange peak, but don't really.
Incidentally I also have some old EX3's but I haven't dared drop those in yet (screech alert!)
I remember hearing the original TP1's many years ago and I reckon the Lowther drive unit needs a front horn (or be seriously off axis) as well as a rear horn, but I digress....also my woodworking skills were stretched to the limit with these OBs...
The drive units are in series, with a 30uf cap bypassing the bass driver. I haven't gotten around to ordering any inductors yet.
Aesthetically they are quite err challenging!
I was wondering if folk knew of any idiot's guide for measuring frequency response?
They are more or less James's Quasars, but a bit wider to accommodate the Eminence Beta 15s (thanks Phil for the epay heads up) and a pair of Sidcup's finest, two fairly modernish PM6C.
This is my first ever speaker build! And I don't know what I'm doing whatsoever... but they seem to sound quite good, nice present-but-tight bottom end (missus),reasonably balanced midrange (albeit with some of that unavoidable Lowther 'forwardness') and if there's a lack of top treble then I can't notice it....they are also pretty efficient, my 801a amp seems very happy with them.
The phase plugs were an attempt to calm down the midrange peak, but don't really.
Incidentally I also have some old EX3's but I haven't dared drop those in yet (screech alert!)
I remember hearing the original TP1's many years ago and I reckon the Lowther drive unit needs a front horn (or be seriously off axis) as well as a rear horn, but I digress....also my woodworking skills were stretched to the limit with these OBs...
The drive units are in series, with a 30uf cap bypassing the bass driver. I haven't gotten around to ordering any inductors yet.
Aesthetically they are quite err challenging!
I was wondering if folk knew of any idiot's guide for measuring frequency response?
- pre65
- Amstrad Tower of Power
- Posts: 21399
- Joined: Wed Aug 22, 2007 11:13 pm
- Location: North Essex/Suffolk border.
#2 Re: OB project, Jame's Quasars copy
Bravo Thomas.
That is some phase plug, did you make it ?
That is some phase plug, did you make it ?
The only thing necessary for the triumph of evil is for good men to do nothing.
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
- Mike H
- Amstrad Tower of Power
- Posts: 20189
- Joined: Sat Oct 04, 2008 5:38 pm
- Location: The Fens
- Contact:
#4 Re: OB project, Jame's Quasars copy
Excellent!
-
-
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
-
- Thermionic Monk Status
- Posts: 5643
- Joined: Thu May 24, 2007 11:22 am
- Location: People's Republic of South Yorkshire
#5 Re: OB project, Jame's Quasars copy
Bit harsh on the rug I reckon
Excellent Thomas! We need more threads like this - so I can try to convince the missus it's not just me that's mad. I'm guessing you painted them though - the wardrobes weren't that colour?
I found mine responded well to tuning the crossover. I got a nice improvement limiting bass to the wide bander, I cut around 150Hz IIRC. Similarly, I was originally running the bass helper without any filter and limiting the bass to below the wide bander really helped the coherence. No surprises.
Excellent Thomas! We need more threads like this - so I can try to convince the missus it's not just me that's mad. I'm guessing you painted them though - the wardrobes weren't that colour?
I found mine responded well to tuning the crossover. I got a nice improvement limiting bass to the wide bander, I cut around 150Hz IIRC. Similarly, I was originally running the bass helper without any filter and limiting the bass to below the wide bander really helped the coherence. No surprises.
- Mike H
- Amstrad Tower of Power
- Posts: 20189
- Joined: Sat Oct 04, 2008 5:38 pm
- Location: The Fens
- Contact:
#6 Re: OB project, Jame's Quasars copy
I assumed the colour is the original dark stained finish?
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
#7 Re: OB project, Jame's Quasars copy
Ooooh! Meow!
Thanks chaps.
The phase plugs I picked up many years ago, I can't remember where...they're ceramic. I'm a bit of a magpie....
Yes the wardrobe doors were that dark colour! Not my choice, Ikea jobbies, so a swap with nicer oak ones left me with these bits to play with. Nasty 15mm chipboard, I had to hoover my patio after I cut them out.
I'm assuming the cap bypass across the bass driver is a bog standard filter which with an assumed 8r gives an f-3db of about 600Hz or so. I was going to start clipping in extra capacitance to drop this, once I have got to grips with how they sound now. James quotes 100uf for his AER/supravox drivers.
I was going to get a pair of 1.5mH inductors to put across the PM6Cs but that was just before xmas and hifi collective never got back to me for some reason.
I can see this whole thing is going to take me a fair bit of trial and error....
-
- Thermionic Monk Status
- Posts: 5643
- Joined: Thu May 24, 2007 11:22 am
- Location: People's Republic of South Yorkshire
#8 Re: OB project, Jame's Quasars copy
Ah, okay. They look black on my phone. ("No Johnny" - a Fast Show reference there for the kids!)
My crossover bits weren't cheap. Big chokes with low DCR are surprisingly expensive...
My crossover bits weren't cheap. Big chokes with low DCR are surprisingly expensive...
#9 Re: OB project, Jame's Quasars copy
Sorry to depress you, but the "kids" have never head of the Fast Show
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
- Dave the bass
- Amstrad Tower of Power
- Posts: 12276
- Joined: Tue May 22, 2007 4:36 pm
- Location: NW Kent, Darn Sarf innit.
#11 Re: OB project, Jame's Quasars copy
Dang! Beat me to it!
Top Ikea Conversion work there MrT, that phase plug though.....
"The fat bourgeois and his doppelganger"
- IslandPink
- Amstrad Tower of Power
- Posts: 10041
- Joined: Tue May 29, 2007 7:01 pm
- Location: Denbigh, N.Wales
#12 Re: OB project, Jame's Quasars copy
Oooh.. ebonised, is it ?
Classy ! & good effort, always nice to see a new speaker.
PM6C sounds like a good choice, I had a look at them myself - only 92.5db/w , so around the same as where I am at the moment with 2x FX120.
Given this is an 8R (ish) driver the 'proper' Quasar-style crossover for this will be similar to what I tried for the Fostex FF225WK which has similar efficiency, size , Re and Qts.
If you get an 8.2H choke then it should be close to this :
You need the big choke and cap values to put the crossover around 150 to 200Hz.
You should be able to get a pretty good result using a laminated E-I core choke ( talk to Colin ) , that will help keep the cost down a lot compared to a big air-core like the ones I have and James used. I'd recommend you use at least 6.8mH though, otherwise you'll have the crossover too far into the midrange, the Eminence with the deep side-wings down there needs to be rolled-off fairly early to avoid colouration.
With the proper crossover, you should get a lot of improvement from where you are now. You will be able to fine-tune the cap value by ear, just checking upper bass tone and overall dynamics. It was fairly easy to judge with the Supravox and FF225WK.
Oh yes, the padding down of the bass driver will be required as it'll otherwise be too efficient relative to the PM6C. You might want to start with 3.3R to the Eminence.
Classy ! & good effort, always nice to see a new speaker.
PM6C sounds like a good choice, I had a look at them myself - only 92.5db/w , so around the same as where I am at the moment with 2x FX120.
Given this is an 8R (ish) driver the 'proper' Quasar-style crossover for this will be similar to what I tried for the Fostex FF225WK which has similar efficiency, size , Re and Qts.
If you get an 8.2H choke then it should be close to this :
You need the big choke and cap values to put the crossover around 150 to 200Hz.
You should be able to get a pretty good result using a laminated E-I core choke ( talk to Colin ) , that will help keep the cost down a lot compared to a big air-core like the ones I have and James used. I'd recommend you use at least 6.8mH though, otherwise you'll have the crossover too far into the midrange, the Eminence with the deep side-wings down there needs to be rolled-off fairly early to avoid colouration.
With the proper crossover, you should get a lot of improvement from where you are now. You will be able to fine-tune the cap value by ear, just checking upper bass tone and overall dynamics. It was fairly easy to judge with the Supravox and FF225WK.
Oh yes, the padding down of the bass driver will be required as it'll otherwise be too efficient relative to the PM6C. You might want to start with 3.3R to the Eminence.
"Once you find out ... the Circumstances ; then you can go out"
#13 Re: OB project, Jame's Quasars copy
Thanks for the pointers there Mark. Looks like with the variables to play around with this could take me quite a while with trial and error.
Obviously I can clip in capacitance to my hearts content, but is it worth buying a handful of cheap(ish) inductors and trying adding them incrementally in series and only splashing out on an air core when I'm happy with the set up?!
Obviously I can clip in capacitance to my hearts content, but is it worth buying a handful of cheap(ish) inductors and trying adding them incrementally in series and only splashing out on an air core when I'm happy with the set up?!
#15 Re: OB project, Jame's Quasars copy
Quick experiment. One half of the primary of a 30va Vigotronix VTX-146-030-215 toroid is just under 8H at 100Hz.Not very constant with frequency, its only 2H at 1kHz, but might be worth a play.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.