2-way: Waveguide + Cardioid-like

[gedlee]

Originally Posted by keyser

Doug20, I think you are being a bit unfair here. Geddes' speakers are expensive to buy, but that's probably in large extent because he simply doesn't produce very many of them. I'm sure if he did thousands a year, they would/could be a lot cheaper. I do think Earl cuts the things that don't matter and retains those aspects which in his opinion make a difference. So although performance is very important to him, he also keeps an eye on the costs.

I think that this is accurate. I am not going to respond to Doug20 because he has proven himself to be disrespectfull (as is obvious here) and yes he is usually unfair.

I think that poople would be shocked at what my speakers COULD be made for in terms of dollars. Does that mean that is what I should SELL them for? Its simple economics; First, each speaker is hand made by me (at the moment) - ridiculously inefficient and expensive. Then, I use premium Itallian made drivers (read very expensive) when I know for a fact that I could get just as good of a sound with custom Chinese made drivers at a fraction of the cost. These things make for a very expensive product because it is so inefficiently made.

Why not go high volume and drop the costs and (maybe) the prices? because I am not convinced that the volume is there. It's a business decision and its my money that is at risk, not some poster on DIY.

If you can find a better speaker at the price of mine then buy it. But since my speakers are far less cost than anything that I think is comparable I am not ashamed of my prices. In fact I think that they are still a good buy in comparison to the market.

I stopped selling stand alone waveguides because all people did was complain about them - they weren't fiunished enough, price was too high, whatever. It simply wasn't worth it. If some Polish company is willing to do the job then more power to them. But there is far more to my speakers than just a piece of fiberglass (which I don't use anymore because it is inferior.)

I am very close to stop selling kits altogether because to DIY nothing is ever good enough.

As to the subject of this thread, I didn't read it all so I don't know what it is about in detail. Cardiod loudspeaker by just cutting holes in the cabinet? I suppose this could work reasonably well in some situations, but I doubt that 1) the cardiod polar response would track in frequency very well and 2) I doubt that it is very predictable, meaning that it would take a lot of cut and try with no guarantee that any particular system would come out right.

Cardiod is certainly feasible with a second driver and this works over a fairly large bandwidth. I will try this at some point as I bring my DSP capabilities up to speed. Right now I am implimenting a DSP based active crossover and a multiple sub processor. A cardiod speaker with thuis same technology would be pretty easy.

[keyser]

Originally Posted by gedlee

I am very close to stop selling kits altogether because to DIY nothing is ever good enough.

Maybe this is worth a topic of its own. You are probably right. I Guess I wouldn't have targeted the DIY crowd in the first place.

Originally Posted by gedlee

As to the subject of this thread, I didn't read it all so I don't know what it is about in detail. Cardiod loudspeaker by just cutting holes in the cabinet? I suppose this could work reasonably well in some situations, but I doubt that 1) the cardiod polar response would track in frequency very well and 2) I doubt that it is very predictable, meaning that it would take a lot of cut and try with no guarantee that any particular system would come out right.

Cardiod is certainly feasible with a second driver and this works over a fairly large bandwidth. I will try this at some point as I bring my DSP capabilities up to speed. Right now I am implimenting a DSP based active crossover and a multiple sub processor. A cardiod speaker with thuis same technology would be pretty easy.

1 - The data is all there!

All measured outside:

1/6 oct. smoothing, ungated with reflections after a little over 10 ms).



1/24 oct. smoothing, gated.



Same data as above, 1/2 oct. smoothing, ungated.



1/24 oct. smoothing, gated, unweighted average of the rear response from 180 deg. to 90 deg. in 15 deg. increments.


2- Probably true. I didn't really expect my first try to be as successful as it turned out to be. But then again, I'm sure your waveguides required some tinkering with as well!

[doug20]

I would post a very accurate POV on Geddes and his speakers (lack of sales and why) but I enjoy this build and this thread.

I will just post that the subjective post about "disrepect" has nothing to do with the topic or defining the value of his speakers. This is one of those Geddes bad habits that does not help his professional status at all online. Its easier to attack/discredit a poster isn't it Discredit me all you want, it will not increase your sales it only has the possibility of doing the opposite

DIYers are not the reason you can not sell speakers

[gedlee]

Keyser

Could I get your data in raw form so that I can look at it and post it? I'd prefer 7.5 degree increments as 15 degrees is pretty coarse. Actually after a lot of trials I have found that 5 dgerees from 0 to 20, 10 degress from 20 to 60, 20 degrees from 60 to 120 and then 30 degrees to 180 (i.e. 0,5,10,15,20,30,40,50,60,80,100,120,150,180) to be ideal. From the theory the smaller angles can and will have the most rate of change with angle so they need the highest resolution. Very little happens from 90 -180.

To make any sense of any set of data one needs to be looking at the data in comparison with other designs and using a common format. I am trying to do this on my website.

("lack of sales" - that's hillarious.)

[keyser]

Originally Posted by gedlee

To make any sense of any set of data one needs to be looking at the data in comparison with other designs and using a common format.

Very true.

You've got mail!

[daniel]

Originally Posted by keyser

The concept is a 2-way speaker with a 12” woofer and a 1" compression driver with a 12” waveguide, crossed passively at 1 khz...

.....
Initially I intended to put the drivers in a closed box, but in order to get the smoothest possible powerresponse through the crossover-region a simple box seemed not to be the best solution. Although others have already shown that the closed box format is very workable if you cross at the frequency where the directivity of the woofer and waveguide match, below the crossover frequency directivity usually decreases quite fast. Therefore I decided to experiment with an open box – a box with holes in it. The box is stuffed to the brim with rockwool (I intended to use glasswool, my favorite, but I didn’t have it at the time) and I use carpet without backing to finish the sides....

Excellent speaker you have there! Couple questions:
using 12" driver you have still greater directivity from 200-1000Hz than a regular 6,5" 'Hi-fi' speaker. While in the ILD dominated hearing region high directivity is beneficial, hearing works differently below ~800Hz. Is going cardioid worth the extra (system)complexity? You listened non-cardioid variant also? Interested in your side-by-side impressions.

See, I would really like to scale down the approach to a 6" or 8"+waveguide. In itself this combo only has the designed directivity from 2kHz up, but if going cardioid can extend this an octave lower, I wouldn't need to haul a 12"-15" monster in a living room. It's not tragic if this speaker wouldn't go below 200Hz either, different solutions are needed below Schroeder frequency anyway.

[gedlee]

Originally Posted by daniel

While in the ILD dominated hearing region high directivity is beneficial, hearing works differently below ~800Hz. Is going cardioid worth the extra (system)complexity?

This is precisely my concern as well! Quite perceptive. Answer this question and even I'll do this.

See, I would really like to scale down the approach to a 6" or 8"+waveguide. In itself this combo only has the designed directivity from 2kHz up, but if going cardioid can extend this an octave lower, I wouldn't need to haul a 12"-15" monster in a living room. It's not tragic if this speaker wouldn't go below 200Hz either, different solutions are needed below Schroeder frequency anyway.

Are you suggesting "going cardiod" on the HF? Otherwise a smaller waveguide moves the directivity control higher in frequency making the problem worse. This technique is never going to make a small speaker have a narrow directivity above the frequency where the rear radiation to the front is insignificant. IOW, above some frequency the directivity is that of the piston regardless of what you do on the back. I'm afrraid that you are stuck with big waveguides and drivers above a few hundered Hz, and, as you say, its not clear that this approach will have any significant audible effect at the frequencies where it might work.

[gedlee]

Some more thoughts on "cardiod".

To be a cardiod there must be a mixture of a monopole and a dipole. Since the dipole efficiency is far lower than the monopole, there is always going to be an efficiency loss whenever one creates a cardiod passively. If, like me, one uses a passive crossover, then you are stuck because you can't get a flat response (without serious degradation of the entire systems efficiency). This is a very high price to pay to for a questionable benefit.

Actively you can get exactly what is desired, especially if you use a second driver on the back - remember that this driver need not be of a very high quality since it only affects the directivity and hardly radiates any signal into the direct field. Hence a smaller lower cost driver on the back driven with DSP on both the front and rear drivers and one can achieve a very precise cardiod with both a flat axial response and a flat power response.

If I do go cardiod, thats basically the way that I would do it.

(This entire concept is actually discussed in my transducer book.)

[CLS]

Another view of efficiency:

From a sealed box mono pole to a partially open back passive cardioid, the efficiency indeed drops.

OTOH, from an OB dipole to a U frame with stuffing type of cardioid, the efficiency is going up No?

[daniel]

Originally Posted by gedlee

......Are you suggesting "going cardiod" on the HF? Otherwise a smaller waveguide moves the directivity control higher in frequency making the problem worse.

No, not on the HF, but where an 8" starts to get omni, from 800-2000Hz. My reasoning was that using cardioid up to 2000Hz on the 8" I could get a little higher directivity index than without. From about 2000Hz waveguide would have DI above 10 already.

Originally Posted by gedlee

This technique is never going to make a small speaker have a narrow directivity above the frequency where the rear radiation to the front is insignificant. IOW, above some frequency the directivity is that of the piston regardless of what you do on the back. I'm afrraid that you are stuck with big waveguides and drivers above a few hundered Hz, and, as you say, its not clear that this approach will have any significant audible effect at the frequencies where it might work.

So if the wavelenght is too small compared to source size, cardioid pattern doesn't 'develop' - it would have greater directivity from 200-800Hz, but not where it's needed the most: 1k-2kHz? Instead the pattern would look like a twisted bipole, front lobe size dictated by piston diameter. Damn physics!

Originally Posted by gedlee

If, like me, one uses a passive crossover, then you are stuck because you can't get a flat response (without serious degradation of the entire systems efficiency). This is a very high price to pay to for a questionable benefit..

There is also possible to use a 'hybrid' approach - passive XO between drivers, active shelving to get the low end response up. HT receivers should have the necessary EQ functionality built-in.

Anyone up for a 'quick' study how directivity from 200-1000Hz affects perception? Keyser?