Open Baffle Suggestions

JamesD · Post by **JamesD** » Tue Nov 19, 2013 6:17 pm

yeah, its confusing - you can read it both ways!

IslandPink · Post by **IslandPink** » Tue Nov 19, 2013 6:20 pm

They do refer to a series crossover :

"From 200 Hz up, the PM6a reproduces almost full range. Although the "low end" alnico driver, it has the classic Lowther sound, combining the speed and articulation that Lowthers are famous for with the warmth that an Alnico magnet brings. The crossover is a bit unusual. Set at 200 hz, it is a 1st order (6 dB/octave) series crossover. As both drivers are 96 dB/watt efficient, there is no need for padding resistors. The series crossover looks unusual, but it simply sounds better than the more common parallel crossover in this system (try it both ways if you don't believe me). "

I like the following comments - just up my street :

"The Tone Tubby is extremely fast and articulate. Perhaps just a touch warm, its reproduction of string instruments is especially intoxicating. It only goes down to the 70 hz range, and a subwoofer is used to fill in the rest"

Ray P · Post by **Ray P** » Tue Nov 19, 2013 7:11 pm

The penny is a tight fit but I think it's beginning to drop... I need to reread Martin King again a bit later.

Another question; the angled corners on the Supravox OB are aesthetically pleasing - are they good or bad sonically?

Also, just a reminder that the amps I'm working on are the Transcendent 300B SE-OTL, delivering around 1.5W per channel. I don't live in an aircraft hanger so should be OK if speaker sensitivity is in the upper 90s.

Ray

JamesD · Post by **JamesD** » Tue Nov 19, 2013 7:33 pm

Mark,

Thanks for clarifying that - series connection it is

The Tone Tubby comments are extremely encouraging!

Ray,

The angled corners on the Planneau design are aesthetics only although they do add some stiffness to the design it isn't critical and I wouldn't expect it to add to the sound of the speakers.

I find 1Watt on speakers of 92dB eff. gets loud in a room 15 feet square.

And I used the Quasars (97-98dB eff.) witha 1.5W amplifier in a room 35feet by 27 feet and they were loud.

So I think you will be fine witanything over, say, 95dB/1W eff.

IslandPink · Post by **IslandPink** » Tue Nov 19, 2013 7:55 pm

James - I think I asked this before - do the (slanted) side-wings on the Quasar help to extend the low-bass response ?
Also : How crucial is the extra inductance from the upper driver ( in series crossover ) in extending the lower limit of the bass driver response ? - am I going to lose a lot in that respect, vs. that 'Tiny alnico' combo, from using a bi-amp approach on mine ?

JamesD · Post by **JamesD** » Tue Nov 19, 2013 9:26 pm

The side wings on the lower half od the Quasar reinforce the bass level but they don't in themselves extend the response lower in frequency - this is controlled by the baffle height more than its width - and works with a below floor reflected image of the baffle reinforcing the response down to 40Hz. This is NOT conventional flat baffle theory as it isn't a flat baffle

The side wings also shape the response of the bottom driver so it is not a dipole, as a flat baffle would be, in the bottom frequencies but has the characteristic of a U-baffle and that has a cardioid dispersion pattern i.e. very little rear radiation and so limited room mode (eigentones) excitation.

The Quasar is a real hybrid design and doesn't conform to flat baffle theory or u-baffle theory - it has aspects of both and the design selects the attributes it needs to get the result I wanted. And hey - it works and it is repeatable! It must be Science or at least engineering

The inductor does extend the bass response of the Supravox! Not many people realise that! It adds to the motor inductance and resistance to change the way the system works i.e. modifies the t/s paramters of the Supravox - the series connection of the two drivers also does this so that neither behaves anymore as per their datasheets - most don't spot this subtle aspect of series crossover design - the inductor isn't critical as the second driver effect dominates this interaction - the inductor does filter the mf and hf response away from the bass driver as its primary role.

hope that helps

James

Ray P · Post by **Ray P** » Tue Nov 19, 2013 9:39 pm

JamesD wrote:The angled corners on the Planneau design are aesthetics only although they do add some stiffness to the design it isn't critical and I wouldn't expect it to add to the sound of the speakers.

Cheers James. I'm thinking of the WAF. Perspex isn't going to be acceptable - too 'modern' - a slab of wood will still be frowned upon a bit but there's likely to be least resistance to something with a little more 'shape'. I was thinking more about compromising the sound rather than improving it.

Ray

Ali Tait · Post by **Ali Tait** » Wed Nov 20, 2013 10:03 am

Curve the top into an arch perhaps?

Would look less imposing (a bit anyway!)

JamesD · Post by **JamesD** » Wed Nov 20, 2013 10:47 am

Here is the ex4/285gmf filter I designed. In the end it didn't get built as the EX4s were knackered and a different driver was chosen to replace them.. and looking at it I think this is not at 200Hz... I'll have to check my calculations... it might be 750Hz as we did discuss running the 285 higher than usual.

This is a very simple starting point and doesn't have any correction for the EX4 frequency response.

J

Ray P · Post by **Ray P** » Wed Nov 20, 2013 6:28 pm

James, is that really EX4 units and not DX4s? I ask because the EX units have the filter module on the back to reduce rear HF output and I was under the impression these didn't work well in OB type designs? Instinctively, it feels that less rear output might be a good idea but I'm still learning about this stuff.

Ray

JamesD · Post by **JamesD** » Wed Nov 20, 2013 7:52 pm

The design was done for a friend and he had EX4 units that he got before deciding how to use them and he liked the Quasars and wanted to explore his options for using the Lowthers.

If using EX4 in an OB design is a good idea or not is an interesting question... Looking at the Qts parameter one would think not but when used with a bass helper then it can make sense and if you like the Lowther sound then it certaibly lets that shine through. The relative lack of rear wave means it will tend to a cardioid radiation pattern but that isn't a drawback.

So I think the Lowthers will work fine in a Quasar style OB and will let the lowther sound out.

Dave the bass · Post by **Dave the bass** » Wed Nov 20, 2013 8:03 pm

JamesD wrote:.............and will let the lowther sound out.

"........Aaaaaaaaaaaaarrrrrrrrrrrrrrrrrgggggggggghhhhhhhhh!"

DTB

JamesD · Post by **JamesD** » Wed Nov 20, 2013 8:29 pm

On Guard!!!!

lowthers at 10 paces!!!

SimonC · Post by **SimonC** » Fri Nov 22, 2013 12:57 pm

Aye up James and Ray,

I've been following this thread with interest, having a pair of Beta 15's and have been thinking about what could be paired with them... I know Nick's OB uses the FE167E, and I can't help wondering about the new Alpair A12P after hearing them in Colin's boxes at Owston...

I was wanting to do an MLTL with the A12's, but this thread has got me musing about a semi-quasar A12P/Beta15 OB...

Simon C

JamesD · Post by **JamesD** » Fri Nov 22, 2013 2:52 pm

interesting!

The Beta 15 works very well in a Quasar style OB. The 12P suits a parallel crossover as it doesn't like the series connection with another driver. Mark Fenton's postings on the 12 confirm this.

As it happens I have been working on a suitable crossover for the 12 with the Supravox bass driver and it is attached for your perusal. It needs tweaking for the Beta 15 and I'll have a look at that this weekend.

I think it could be a winning combination!

J

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