[versus rider]

Hi all, has been some time since I posted here, but have been lurking occasionally. My dedicated listening room is now almost finished, just needs a door. My main speakers have evolved over several years from open baffle alphas and lowthers, to a four way OB and finally an open boxed alpha with braced chassis and working very nicely to 200Hz, 200Hz tractrix horn with BMS 4592 mid driver and Raal 140-15D. Lovely easy sound with scale weight. Now here lies the problem and its my daughters fault, I got a free Panasonic 65" plasma from her bank and dueto its width and the rooms lack of width the horns will not fit either side without obscuring the tv. I could and may well still re-design the speakers so the bass drivers are to the inside with the horns at say 30 degrees to the outside so lowering them somewhat, or the other idea is to go back to a lowther driver or similar and so reduce the height and width of the whole speaker. Now will a lowther or similar do the midrange I seek of 200Hz - 2000Hz cleanly, I have DEQX ( Australian unit )so can overcome the shouty problem associated with lowthers or is there something else that can do that wonderful midrange.

[JohnR]

The Seas FA22RCZ may be worth a look, it's symmetrical front to back up to nearly 2 khz. Has good excursion so no worries with EQ for a narrow panel.

[AJinFLA]

The Seas FA22RCZ may be worth a look, it's symmetrical front to back up to nearly 2 khz. Has good excursion so no worries with EQ for a narrow panel.

Hi John, have you seen measurements that show this? That seems rather remarkable given its construction. I would have thought there would be significant asymmetry beginning well below this.

cheers,

AJ

[JohnR]

Hi AJ, here is front and rear at 1m. There are some room effects, driver is only 40cm from floor so the 1 kHz dip is I guess floor bounce. Baffle 38cm wide. Nearfield (10cm) in green.



I didn't measure other angles behind the baffle... what are you referring to by "construction"?

[versus rider]

just reading my original post and spotted an error, alpha is clean to 350Hz, which is the lowest I can realistically run the 200Hz tractrix. Lets say cost is of no consequence for the right driver.

[Rudolf]

Hi AJ, here is front and rear at 1m. ...
I didn't measure other angles behind the baffle...

At first sight it seems quite rational to look for the 0° and 180° responses. At second thought there is almost no measurement less important than 180°. 
And for shure I myself have fallen to the same illogicality in the past. 180° measurements are still on my German dipole homepage today. 

Of course I have to explain:
In general 0° and 180° are very small points in space. And they represent a situation, where the response of any symmetrical dipole is quite special - compared to anything else off axis. Another argument would be: There is no intelligent placement of a dipole where the 180° response would come back as a first/early reflection without any absorption or diffusion. It will always be changed in one or another way.

Really important is the way the dipole null and its wider vicinity is changing with frequency. Is there a deep response hole at 90°? Do I have the full 6 dB attenuation (or even more) at 120°? Or do I experience blooming with a response level gain at 135° instead of a 3 dB loss? These angles are covering a much wider area/part of the total response and are more prone to come back as first reflections.

Rudolf

[AJinFLA]

Hi Rudolf,

Well, to be fair, John did not say it would exhibit dipole radiation up to 2k (it won't as we both know). It will certainly be "dipolar", with some blooming >700hz or so. I'm just a bit surprised that it is indeed relatively symmetric up to near 2k, on axis (0,180) of course.
For true dipole (lateral) response, he would need a smaller diameter driver.

cheers,

AJ

[JohnR]

At second thought there is almost no measurement less important than 180°. 

I guess I don't really agree with this and/or follow your explanation. Even if you are trying to make a perfect dipole, you aren't going to get it if the 180 measurement falls off somewhere. No?

For true dipole (lateral) response, he would need a smaller diameter driver.

Not sure who "he" is but this size seems like a fairly good tradeoff to me, if you're looking for good output from 200 Hz.... smaller will also mean lower sensitivity...

What driver would you use?

[Rudolf]

I guess I don't really agree with this and/or follow your explanation. Even if you are trying to make a perfect dipole, you aren't going to get it if the 180 measurement falls off somewhere. No?

If we attenuate one source of a perfect two-point-source dipole, we will loose the figure-8 pattern too - that's right. But I have seen at least one real world driver which rolls off in the back without loosing the 90° null.
It is the Visaton FRS5X, which of course has several shortcomings under other aspects - which doesn't make it a recommendation for versus rider.

In practical life I find a nice figure-8 with an rolling-off back wave more interesting than a perfect 0°-180° match with a bloom to the sides. This is not saying that the Seas FA22RCZ does have the latter - I don't know the driver. I simply would find a 60° or 120° measurement a better complement to the 0° measurement than the 180° result.

Rudolf

[versus rider]

I should point out my original post was incorrect, I will cut off the lower frequency at 350Hz. At this time I am leaning towards Lowther and Voxativ drivers. I have had lowthers in the past and know they are difficult break in and can take several months to produce reasonable bass but only requiring 350Hz at the bottom end should be ok. The other problem with Lowthers is a hump at around 1600Hz, correct me if I have that wrong, but with DEQX PDC I can overcome that. I intend to listen to Voxativ soon but they are more expensive. Other drivers of this quality would interest me more than some of the run of the mill kind. My main speakers have been disassembled for some time now and the cabs have been in the workshop awaiting finishing, so seeing them in the gallery on auto-tech horns made me think how I would miss them with the 200Hz tractrix doing mid range. Whatever replaces them would have to be very special.

[JohnR]

But I have seen at least one real world driver which rolls off in the back without loosing the 90° null.

Oh OK, interesting. I didn't do a full set of measurements, never actually finished that speaker and the Seas are waiting for another project. I lean towards planars above a few hundred anyway... speaking of which...

I should point out my original post was incorrect, I will cut off the lower frequency at 350Hz.

The BG Neo10 may be worth a look. studiotech uses them with good success, no personal experience. If they're not too run of the mill for you...

While this has been an interesting discussion, have you considered just getting a smaller TV?

[AJinFLA]

Not sure who "he" is

The OP

but this size seems like a fairly good tradeoff to me, if you're looking for good output from 200 Hz.... smaller will also mean lower sensitivity...

What driver would you use?

I wouldn't use a [cone] driver, dipole, over such a bandwidth. Now that VR's raised the low end requirement, I agree, probably the Neo 10. I've used the Neo8 to 2.3k, but no lower than 500hz.

cheers,

AJ

[versus rider]

Oh OK, interesting. I didn't do a full set of measurements, never actually finished that speaker and the Seas are waiting for another project. I lean towards planars above a few hundred anyway... speaking of which...

The BG Neo10 may be worth a look. studiotech uses them with good success, no personal experience. If they're not too run of the mill for you...

While this has been an interesting discussion, have you considered just getting a smaller TV?

ahhh just mounted the tv and the picture is superb and huge. The problem may just go away as the wife has said she would like the room and that the workshop would make a good music room, this was my initial intention to use what is now the workshop. Now where to build a workshop?

[JohnR]

Now where to build a workshop?

Put a wall in the middle of the wife's room and claim half of it? 

I have to say, I'd rather have a listening room than a workshop. While it's a PITA to drag tools out and put them away again, I guess I'm getting used to it.

[versus rider]

Put a wall in the middle of the wife's room and claim half of it? 

I have to say, I'd rather have a listening room than a workshop. While it's a PITA to drag tools out and put them away again, I guess I'm getting used to it.

dragging a 7' tall bandsaw, large table saw and heavy planer out, to where I don't know is just not on. together with a small bandsaw, bobbin sander, metal and wood lathes, compound mitre saws, etc, etc. I still think I stand a chance of gathering enough materials to build an extension on the back of the house. However this doesn't solve the problem at hand. Hopefully I will get to try the voxativ drivers next week, along with some other 8" drivers I have from old projects.