OB project, Jame's Quasars copy

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Re: OB project, Jame's Quasars copy

Post by IslandPink » Fri Jan 12, 2018 5:24 pm

Absolutely. James could probably give us some further insight.
There's no need to change the inductor ( once you have one ) for the two FR drivers. The main change I'd see is the capacitor would need to be larger for the EX3 , as being a low-Q driver it's already rolling off a bit below 200Hz, whereas the PM6C is flat towards 150. The attenuation resistor on the bass driver would be smaller or not required with the EX3.
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Re: OB project, Jame's Quasars copy

Post by chris661 » Sat Jan 13, 2018 5:56 pm

Here's a nice article by Rod Elliott on the comparison between series and parallel crossovers.

http://sound.whsites.net/parallel-series.htm

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Re: OB project, Jame's Quasars copy

Post by thomas » Sun Jan 14, 2018 1:58 pm

OK I have finally ordered, as a start, a reasonably priced pair of 1.5mH air core inductors, from CPCFarnell.

Looking back to my choice of 1.5mH / 30uf, I think I had been looking here

http://www.audio-talk.co.uk/phpBB2/view ... 3&start=45

as James' idea of a fairly high crossover value albeit with the Lowther EX4 seemed a reasonable place to start. However in the meantime I'll have to pick a quiet moment and try bigger caps, and it seems bigger value inductors will have to follow.
simon wrote:
Fri Jan 12, 2018 2:05 pm
What Nick and Mark said, which was my point earlier. But also, I find the louder the volume the more the volume relatively from the bass driver. This was most notable when I took the Quasars to Owston a couple of times ago. Played in the barn of a room (at much higher volume) compared to a bedroom at home the bass completely overwhelmed the sound.

I "fixed" it by using half an Lpad as the series resistor so I can vary the amount of bass to suit now. And by having more bass at lower levels I found I don't push the volume control as much. Which has to be good. But I can easily tweak it if I do want to turn up the volume.
I remember those bass monsters a couple of Owstons ago! Curiously this seems to be my experience too, at low volumes my OB's sound pleasant enough, but when I crank them up the bass seems intrusive.

An Lpad seems a good idea for bass attenuation.

Dim question now, but is your Lpad right by the bass driver, and 'within' the bypassing cap or in series with your inductor?

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Re: OB project, Jame's Quasars copy

Post by simon » Sun Jan 14, 2018 8:59 pm

The Lpad was one of my more recent pragmatisms! I've actually built the crossovers on a board with bananas and Lpads and anything else I could think off to make it convenient.

I've attached two crossovers - the first is James' EX4 version and the second is his 208 version - it should make it clear where to put the resistance.
Attachments
EX4 Quasar Filter.png
EX4 Quasar Filter.png (9.56 KiB) Viewed 1913 times
F208 EZ Quasar Filter.png
F208 EZ Quasar Filter.png (10.66 KiB) Viewed 1913 times

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Re: OB project, Jame's Quasars copy

Post by IslandPink » Sun Jan 14, 2018 9:17 pm

Wow - I'd never seen that - it is a high crossover. You could go a bit lower with the EX3 , but see how it goes.
Actually I don't in that case understand the 7.2mH with the 208Ez, I tried something like that and I couldn't get it to gel - the Fostex is even lower Qt than the EX4, so I'd expect any solution to use a really high crossover.
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Re: OB project, Jame's Quasars copy

Post by simon » Sun Jan 14, 2018 11:18 pm

Aye, they're BIG chokes...

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Re: OB project, Jame's Quasars copy

Post by IslandPink » Sun Jan 14, 2018 11:43 pm

The 7.2 is, the 1.5 isn't.
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Re: OB project, Jame's Quasars copy

Post by simon » Mon Jan 15, 2018 7:20 pm

Yes, I was referring to mine which I use with the 208s

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Re: OB project, Jame's Quasars copy

Post by thomas » Fri Jan 26, 2018 2:55 pm

OK I've been playing....

I've fitted a 2.2mH air core inductor across the PM6C, with a small (1R6 ish) resistor to tame the 'shout', and increased the cap cross the B15 to 40uF.

I did play with a 10mH choke but the bass with that was 'orrible... all slow and tubby.

I suspect the real world sensitivity of the PM6C is more than Lowther say it is.....

Interestingly I prefer the bass with no inductor, but this will do for the time being.....

Here is a sketch on the traditional back-of-an-envelope, the Hz figures are probably all wrong, I was attempting to make sense of things, assuming each driver is an 8R load.
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WP_20180126_14_46_18_Pro.jpg

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Re: OB project, Jame's Quasars copy

Post by thomas » Sat Jan 27, 2018 7:22 pm

This afternoon I had a most enjoyable time mucking about with the OB's, with young Dave the Bass as a critical listening ear.
Listening was via naim cd player and my Tower of Power....about 1.5w ....heady stuff! Dave liked things LOUD so we cranked it up a bit....
Starting off with a bit of 'Hadouk' the OBs seemed pleasant enough, with a reasonably polite balance and wide but low soundstage.
A bit of 'Big Jim Sullivan' demonstrated the lack of treble extension which we tried to improve initially by reducing the resistor by the PM6C.
A rummage to dust off two working rather old EX3's was thwarted when we discovered, upon dissection, that the suspension of one had succumbed to the Lowther foam rot.
Instead we got back some treble by reducing the inductor from 2.2mH to 1.5mH, which to me made no intuitive sense whatsoever. Perhaps the larger inductor had some capacitance?
A bit of the Lowther shout was coming in too, so I'll play with the resistor value a touch to damp the PM6C down a little more.
Taking out the inductor completely to me made the bass cleaner, but as Dave pointed out the mids became ragged. Treble extension, as much as Lowthers do it, was as good as it could be.
We felt that with some judicious tweaking it may be possible to juggle the legendary Lowther midrange, decent OB bass and reduce to acceptable limits the Lowther 'shout'.
One thing that my OB's lack ultimately, is high frequency extension, and for that Dave has promised to loan me some Fostex supertweeters I'll wire up in parallel with a protective 3u3 cap......
All in all a really instructive and fun afternoon...It was good to have the opinion of an extra pair of ears, but I think I let Dave down on the lack of cake action...(sorry DTB!)

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Re: OB project, Jame's Quasars copy

Post by Dave the bass » Sat Jan 27, 2018 8:30 pm

Top afternoon of Tunes and Tweaklings, cheers MrT.

Pics of what was goin' down... he's got a v. nice listening room that can 'carry' O.B.'s.
Image

This looks daft but sounds flippin' good. Its the only time I've personally thought "Lowthers, yeah! Now I hear what you do!"
Image

Only the finest Chipboard wardrobe doors used in this construction :)
Image

The power of the tower!
Image

Ouch! Le EX3 est Mort.
Image

Le Homme est les miserable!
Image

Interesting afternoon, ta for the lay-persons guide to Lowther maintenance Thomas, Fostex FT17H's available on Tuesday.

IMO its the soundstage width and linear sound-placement of the music that the whole caboodle does thats so very very impressive. The bass 'tone' quality (copyright ILPS wordy Phrasing's Dept!) seems to be very tweakable using that 1.5mH inductor but its the wide band Lowther that really impressed me most. Getting that last little bit of HF extension handed over to a little Horn tweeter might solve that odd soundstage stage height observation. That was an odd one weren't it, like an odd filter that allowed the mid range to sit physically higher in the sound stage than HF content.

Cracking project you've got going there Thomas, keep it up.
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Re: OB project, Jame's Quasars copy

Post by IslandPink » Sat Jan 27, 2018 8:33 pm

I don't know what to suggest really as I don't really like the solution with the smaller inductors - it's putting the crossover very high at 500Hz as you've pointed out - not great cos the bass driver is now doing frequencies up to at least 1000Hz quite strongly from a U-shaped part of the baffle, which will give colouration. Also the peaks in the kHz from the Eminence are not supressed enough - there's a big ( 10dB ) peak at 2kHz for instance, which is just going to spoil the treble.
Given you have the right sort of Qt ( ~ 0.4 ) on the PM6C I'd really try to find a way of getting a bigger choke like a 6.8 to 8.2mH on there and doing the job properly.

Oooh - cool pics ! :D
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Re: OB project, Jame's Quasars copy

Post by thomas » Sat Jan 27, 2018 10:42 pm

That's an aweful pic of me, Dave!

Mark, I guess I am going to have to bite the bullet and try a larger inductor as I am 110% certain you know a whole lot more about this sort of thing than I would ever hope to know! I'm psyching myself up to acquiring a pair of something like a 7.5mH air core, at some stage....

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Re: OB project, Jame's Quasars copy

Post by steve s » Sun Jan 28, 2018 7:12 am

Good result Thomas there is a lot of time to be spent on crossovers.. once you think you have it sorted some points something out that lets you know it's not...
I have a little meter for measuring inductance, its invaluable for modifying/ winding your own and seeing how the inductance changes when you put a washer and screw through the middle to mount it.
It was only cheap and seems accurate against known values
Putting some damping on all of the back of the baffles is a must in my view if you have not already done it.
A couple of layers of black car carpet works well and is cheap enough, use some spray glue
I agree lowthers can sound pretty good with support, i too have pm6c and ex4 drivers,
well run in pm6c have quite a balanced sound, i have found the ex4 need more work to get them something like ( which i think i once did with two 12" supporting and off axis placement ?)
Good work ...
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Re: OB project, Jame's Quasars copy

Post by simon » Sun Jan 28, 2018 10:58 am

thomas wrote:
Sat Jan 27, 2018 10:42 pm
I'm psyching myself up to acquiring a pair of something like a 7.5mH air core, at some stage....
Guilty yer honour. Gotta be done if you're going to get the best from them. Shame we're not closer or you could try mine.

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