Low-distortion OB

[Rudolf]

5 dB less means it radiates ~32 % of the power it radiates on-axis. And the question was about a rear-firing tweeter, i. e. at 180 °. Figure 8 from your link looks as if the rear tweeter was already 10 dB down between 7 and 8 kHz. And that is inspite of a frequency response rise on-axis.

Yes, that is perfectly normal for a rear-firing 1" tweeter. But dipole radiation is not about recovering the rearward energy of a driver in the first place (Fig.8 shows that at 1 m on axis it is the same for both tweeters or the front tweeter alone ), but about forming a figure 8 radiation pattern. With the diagram I tried to explain that this works up to 10 kHz.

I assume that it may not be necessary to run a rear-firing tweeter to its upper frequency limit. Maybe it is good to run it until 3 kHz, maybe until 10 kHz, or maybe it should run as high as it can.

I suppose you are mainly talking to yourself with this?

You will have to make your own tests, if you are interested in knowing the truth.

I´m in the process of doing that. That´s why I ask people who have assumptions WRT the issue.

Don't be surprised, if it turns out to be a question of the listening room layout and of personal taste. Anyhow I would not go to the lengths of using a low-pass on a rear-firing tweeter. I would wonder whether it makes sense to add a rear-firing tweeter, if the speaker was already dipole up to 3-4 kHz.

Assumptions again. But it looks like you have an idea what driver (planars excluded) might work as a dipole up to 3-4 kHz. I´m strongly interested in that - honestly.

But then there is always gainphile's proposal from post #75 to check it out.

Indeed. I checked it out 6 months ago - and kept it ever since. It does make a difference to the listening experience and it works even from 2 kHz up. And yes - it does make a difference for the power response too, which can be measured. You should try it in the spirit of your signature.

Rudolf

 

[human.bin]

i'm puzzled again. btw i've my beloved wizzered fullrangers so no problem.

gainphile what's working better the pluto's clone or the new OB?

 

[a_tewinkel]

The biggest disadvantage I see in using two tweeters is the very wide dispersion pattern (hardly figure of 8) and rising power response up to the frequency where the tweeters start beaming. There is hardly any dipole cancellation with wide tweeter baffles. This extra high frequency energy can sound annoying when not corrected for.

 

[gainphile]

i'm puzzled again. btw i've my beloved wizzered fullrangers so no problem.

gainphile what's working better the pluto's clone or the new OB?

I've forgotten how they sound, but at one stage I kept flipping between the omni and dipole and after a few weeks the bass quality and box resonance gets pretty obvious. The midrange, though was great from day-1. It actually drove me to experiment with dipole midrange (notches, baffle size, etc).

Now that SL has published Pluto 2.1 I may revisit them again. He now has 200Hz notch which may explain the coloured low-midrange ("box sound"). I have old measurement which realates to this, due to standing waves. Yellow=no damping, green=damped. It works, but not perfect. With dipoles there's simply none of these.

It's *THE* speaker to showoff your friends though, people can't believe the amout and depth of bass coming out of them perky 5", admitedly I equalized them to 30Hz or so he..he..

 

[CFT]

Hi gainphile,

I've been enjoying my pair of Pluto for almost a year, and now I own a set of full range drivers that I would like to put them on OBs as a second system.

1) OB size and mounting
I was thinking of putting together something like the proto-type mini OB as described on Linkwitz's site. No xo and speakers driven directly with a T-amp.

Or any other dimensions that you would suggest for my 8" FR? Any particular mounting technique that I should be aware of? Need any OB offset boost circuit?

2) Sharing Pluto's woofers
Put in a 12 dB/oct LP @ around 75Hz (?) to the Pluto's input RCA. with speaker phase reversed (?), as the FR's complementary woofers.

Do I need any phase delay or anything additional?

Thanks for any advice

 

[gainphile]

Hi CFT,

Is this your 1st OB? then I would do the following with your 8" fullrange:

1. Using 25cm x 115cm baffle, mount the driver and run fullrange directly using an amplifier. You will hear the sound as very open. No box coloration and even may start to learn pluto pipe resonance sound (not a good idea he..he..). But it will be shouty, not realistic. That's called a dipole peak.

2. So then this dipole peak needs to be equalised. I wouldn't try using passive XO as it may get expensive/difficult. To equalize you'd need a DIY measurement tools (cheaply) to find out the notch frequency, depth, and Q. Once the notch implemented you should get flat, open, oncoloured sound OBs are renowned for.

3. Then simply cross to your "pluto sub". But remember to put shelving lowpass on the 8" so that the low-freq is flat. I personally did not like combination of OB and sealed sub though.

 

[CFT]

Thanks gainphile.

OK, so I do need the notch and OB boost filters....hmmm. I was thinking of the mimimal approach....but that will require some measurements though.....

I noticed that the OB peak wasn't that pronounced in the proto-type mini OB here:
http://www.linkwitzlab.com/proto.htm

Perhaps that's speaker specific and the OB boost filter also touches on that peak as well. Any particular comment on that OB size BTW?

As for crossing over to the Pluto bass, would you think I can find some higher xo point that I could have a nice compromise without the need for a boost filter?

Oh, you are not using the Seas woofer units, could that make a diffference in the low freq performance of your Pluto?

Thanks!

 

[gainphile]

Perhaps. Look at the curve of transfer function of PMT1 xo:

400Hz is just about the right peak for phoenix and orion as well.


On the pluto, SL specifies 103dB reproduction level, which I and my neighbors dont really need . So I can even extend the frequency down to -3db at 20Hz (original pluto is 40Hz). Yeah it's scary (fun?) seeing them working hard but definitely not at very high level. Good for night listening and to impress friends

The only shortcoming is the expected boomy bass from sealed woofers/monopole. I'm still waiting for someone to sell those cheap woofers in ebay and then try the "multiple sub" method.

 

[CFT]

Thanks gainphile!

I don't have my Pluto and OB speakers side by side, and so can't say how boomy the Pluto sounds, but I like it so far.

BTW - the Peerless driver that was chosen for Pluto 1 is now on sale at Madisound. You may want to take a look.

And I would really love to know how my vintage fieldcoils on OB with my Virtue amp fare with the contempary system : )

Anyway, will try it out!