Otto

ed · Post by ed » Wed May 14, 2014 11:56 am

This is Otto.

here's the David and Goliath shot.

It is a twin port reflex box but while I'm finishing the cabinet I thought I'd have a play with an OB.

The OB is a mule to get a feel for how an OB fits into my music room. I've always thought that the room is too small for OB so I'm about to find out(hopefully) if it really is too small(4mx4m). The bass driver is medium Q(chosen for the reflex cab), so not theoretically ideal for OB, but it should give me an idea if the room is overpowered.

The OB also makes it easier to fiddle with the crossover. It obviusly won't be exact but it will put me in the right area for the filter side.

IslandPink · Post by **IslandPink** » Wed May 14, 2014 6:09 pm

Very interesting .. in a rather ominous, 1960's sort of way !
Maybe medium-Q will be your friend, in the context of a smaller room ?
This looks very well made and finished for something you're just playing around with .

Dave the bass · Post by **Dave the bass** » Wed May 14, 2014 7:49 pm

Schweet, are they going in the room where the 'stats used to live?

DTB

ed · Post by ed » Wed May 14, 2014 8:11 pm

Dave the bass wrote:Schweet, are they going in the room where the 'stats used to live?

DTB

yep...that's exactly the plan....these AMTs are the only thing that vaguely sound like electrostatics...IMO.....we shall see.

I'm truly excited by this challenge cos they're 102db SPL on the datasheet, which means that if I succeed I can also dispense with the PP amp(sorry Steve C).

might be an opportunity to have another go at the 71A as well, this time with Rod Colemans heater boards...oh the possibilities.

Cressy Snr · Post by **Cressy Snr** » Wed May 14, 2014 8:28 pm

ed wrote:
Dave the bass wrote:Schweet, are they going in the room where the 'stats used to live?

DTB
yep...that's exactly the plan....these AMTs are the only thing that vaguely sound like electrostatics...IMO.....we shall see.

I'm truly excited by this challenge cos they're 102db SPL on the datasheet, which means that if I succeed I can also dispense with the PP amp(sorry Steve C).

I didn't know you had a PP amp Ed.

Those baffles look fab.

ed · Post by ed » Wed May 14, 2014 8:47 pm

IslandPink wrote: This looks very well made and finished for something you're just playing around with .

very rough round the edges if you look closely....it's all smoke and mirrors in the end

http://www.vitalstates.org/diy/misc/ob2.jpg
http://www.vitalstates.org/diy/misc/ob3.jpg
http://www.vitalstates.org/diy/misc/ob4.jpg

I was disappointed with the cut out for the beymas...the corner radiii are not very tight which makes it tricky to route.....I should have paid more attention

just kidding.

I forgot to mention....my local B&Q are offloading all their BB at £40 a sheet, which makes it the same price as the timber merchant...and nearly the same price as their 8 ply external stuff. I would normally have used the external stuff for a test set-up.

Scottmoose · Post by **Scottmoose** » Wed May 14, 2014 9:43 pm

Lovely work as ever Ed.

For what it's worth, a minor point re Q and baffles that often seems to be overlooked: Q alone doesn't mean much. It's what it does in combination with Fs that counts. A very low Q driver for e.g. can be fine on a baffle providing Fs is low enough (i.e. it has a reasonably low mass-corner).

Greg · Post by **Greg** » Wed May 14, 2014 10:21 pm

Looks good, Ed. Are you bringing them to Owston?

A reflective note......we have seen a similar cabinet build profile in the 'Metronome', but it did not nudge me to consider anything outside of a metronome. Your design does something different to me. Surely that build signature at bottom right corner is not a modern take on KKK?

Just kidding; it was simply where my mind took me

ed · Post by ed » Wed May 21, 2014 5:19 pm

I've been listening for a few days now and I have to say I'm initially disappointed with the OBs. The bass is to die for but the top end is not as tinkly as I expected. The whole picture sounds a bit constrained to my ears.

I started with a crossover idea borrowed from somebody who had used the beyma before, so it's early days and I've only just started to fiddle. The impedance correction is a bit heavy at the moment but it sure works. As it's the top end that I'm not happy about I'm not sure it will make any difference when I get the boxes finished......

At the end of the day I wasn't expecting miracles, and it still might be that the room is too small for OB.

The calibrated spl at measurement point 1 watt/1 metre says 99.2db although this isn't reflected by the mls.....ho hum.

Scottmoose · Post by **Scottmoose** » Wed May 21, 2014 5:33 pm

Interesting. What's the bass driver Ed?

ed · Post by ed » Wed May 21, 2014 5:41 pm

it's a fane 12/200

I went through all the fane 12s and 15s and the eminence and the beyma and the volt and many more. I was pretty stuck to the idea of 12" and the 12/200 simmed the best by a country mile into a reflex box of 100ltrs.

steve s · Post by **steve s** » Thu May 22, 2014 8:38 am

My second pair of beymas seemed to take ages before they came alive, at least a couple of weeks, a bit like getting lowthers run in i had not noticed it with the first pair too much, it was comparing run in with new that was obvious to my ear

ed · Post by ed » Sat May 24, 2014 1:49 pm

having listened almost continuously for a week and measured everything that made a squeek I've got some ideas about OBs with beyma AMT in my room....

1. dull as ditchwater, maybe duller
2. way too much bass, controlled but boomy and very reflective
3. tried with 4 amps....se 2a3, se sv572, Pass F4, kt88 PP....all with similar presentation...sv572 preferable
4. total lack of sparkle
5. A/B/C in and out with vofo and markaudio monitor and vofo has it by country mile
6. tried without compensation network and they were slightly brighter but still bass heavy..BUT, need the compensation network as the target amp will be SE valve.

considered moving the xover point up slightly but that would only give the 12" more to chew on than it already has.....it's already OTT!

verdict: OBs, not for me

anybody want 2 OB frames...free..will doubtless need rejigging for other drivers?

will carry on with the reflex boxes, hoping they will tame the bass. If they don't then there will be 2 beymas for sale....probably very attractive price. oh waily waily ..the price of experience

pre65 · Post by **pre65** » Sat May 24, 2014 1:59 pm

Seeing how you are struggling with OB grieves me Ed.

I feel so lucky that my OBs, lashed together with seemingly mismatched drivers and a series crossover borrowed from Nicks baffles, works as well as it does.

IslandPink · Post by **IslandPink** » Sat May 24, 2014 2:54 pm

That is a shame.
However that alcove bit behing the speaker in the pic is quite confined and doesn't look great for OB . Perhaps that's a big part of the bass problems ?
I'm a little concerned too about the midrange and the interfacing of the 12" bass driver to the Beyma . You refer to dullness , would you say it's a lack of tone, and if so, in the bass or more in the midrange ?
What's your crossover freq for these, ED ?

audio-talk

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