K 145

[Earl K]

Hi Roland

Hmmm, Perhaps I can "borrow" some test boxes to make the tests.

- I recommend that you "delay" constructing anything ( but test boxes ) until 2005 .

I don't have access to a work shop, so I'm forced to do almost everything in my kitchen.

- "That" will be a significant impediment to the ultimate success of this project .
- If you can only "muster" one buildup or "kick at the can", then its absolutely paramount that the front baffles of both the bottom & top boxes, be "removeable" for at least some form of "testing phase".

On the other hand, if it's a real possibility that the woofers need to be closer to each other, then maybe I should try to do that right from the beginning.

- That would be nice, but there are just too many variables, to get it right the first time out, on a "hybrid" project of this sort.
- If you want a bullet-proof project, then go "traditional". "Flip" the top box back to a normal orientation, with the 2123 over top of the 2215 and the horn over top of the 2123.

I think a few cm would be possible to take away, but then I won't be able to use the 2445J.

- Well, I thought you had some 2441s to use. They do have a smaller magnet which helps .

What would be the optimal distance from the Selenium, if there is such a thing, at, say, HP 700Hz/-48dB/oct Butterworth, or 750Hz/-24dB/oct Butterworth?

- The crossover slopes you keep mentioning, I feel , will be too steep for this sort of arrangement. If you are committed to these slopes - make a "tight-pack" of these components, arranged in a normal 43XX orientation .

- Again, ( for a hybrid MTM ) there is no optimal distance when one factors in the components you are committed to using. The spread distance to some degree will be dictated by the sonic "personality" that is created when the 2215 reaches up and shakes hands with the 2123 ( when operating in the MTM mode ). I anticipate the 300 hz to 600 hz area will be too pronounced. So, it's possible the woofer may need to physically "drop" down some - this is based on the fact that at it's present height ( which I don't remember ), "floor-bounce, ( from reflective floors" ) will cause about a 3 db deep / octave wide null "or dish-out" , centered at some frequency ( below 350 hz ). Because the 2123h is a "lightweight performer" below @ 300 hz, it just won't sufficiently fill in that null. A speaker with better "lowmid" performance would. Therefore something has to physically move, to pickup the slack and correct the situation. Finding the correct working "heights" and distances between the woofers is all about some sonic "deal-making" or compromising. Additionally, the "narrowness" of these boxes works against supporting bass and midbass frequencies. That also will work to enhance midrange. Putting a bigger spread between the woofers, will help break apart this midrange - but the spreading also starts to break apart any homogeneous blend. This is very much like "pushing" string on a table .

Conclusion:
- You either have to have test boxes to find out all this stuff or you need a system of "removeable baffles" to accomplish the same.

- I wish you hadn't deleted the other pictures because they had useful information in them.
- The remaining picture is now lacking all of the dimensioning lines, which I need for a reference .
Earl K ( over, out and gone for the holidays )

[pangea]

-Earl K!
Don't worry about the kitchen! I've got most of the tools needed to build almost what ever I fancy. It's only the nabors I worry about if I have to build a lot of test gear.

I haven’t figured out yet how to make the baffles removable tho, considering the chosen design (the sloping 45 degree corners).
But I'm confident I'll solve that and find a way. I'm usually quite creative.
I have a few boards I can use for test baffles, when I've figured out how to make the baffle removable.

You're right, I will use the 2441 drivers, I just thought that if for some reason I would want to test the 2445's, it just won’t be happening now, but that's OK.

Actually I prefer the 6 and 12 dB Bessel filter characteristic's, but it's just that with the Behringer UltraDrive it's been so much easier to use the steeper slopes, making it possible to set the x-over point lower for the Selenium horn.

Should the 300 to 600Hz area be to pronounced, it's no problem for the UltraDrive.
Also, the UltraCurve will detect any peaks and dips in the response, so I don't think that will pose any problems.

I've also put back the picture with the measurements.
If you would like any of the other pictures, I could easily mail them.



BTW, what's a "tight-pack"?

Take care.


BR
Roland

[paragon]

Is it possible to get this four foam rings at the outer side of the basket as a spare part ?

Eckhard

[pangea]

First of all I would like to wish everyone a HAPPY NEW YEAR, although the new year celebrations have been very somber here, since estimates say that more than 150 000 people have died in Asia, of which more than 3000 were Swedes.

None the less I have been occupied trying to learn some about my project.

I'm anxiously awaiting the return of Earl K and hoping the discussion will continue soon.

-Earl K
In case you're back already, there have emerged a few questions during the holidays, which I would be grateful if you would like to address first.

You wrote:

While Operating in 43XX mode :
- This concept of some form of overlap within the 4-way crossovers' slopes ( between bass and mids ) is something I believe you can do with your Behringer. This will help provide some sonic "glue" for the split between the 2215 and the 2123 . You'll need to experiment some to find the best combination .
For example ; the 2215h lowpass could be set for around 340 hz, while the 2123H hipass might be set around for 120hz ( you will need to port/tune) the 2123 to add a bit of midbass extension. I'd mix and match slopes , like 12db for the 2215 lowpass and 6db for the 2123 hipass .

I’ve been thinking, perhaps I should try to make the boxes sealed. I’ve read that sealed boxes have a much better transient response, so I was thinking of using a large (D, 30cm*L, 15cm) cardboard duct, for the 2123’s. For the bass-bin I was thinking of making it possible to go both sealed (80L) and vented (163L), by plugging the holes in the internal bracing.
Do you think a bit of shelving EQ, on both woofers would be able to extend the frequency range somewhat, as well as making it possible to lower the output, so that they won’t be as pronounced in the 300 - 600Hz region, like you said and at the same time keep the sonic “glue” intact?
Any comments on this?
I have also read somewhere that a first order x-over on the bass and mid-bass (giving a 90 degree phase shift), should be complemented by an equally first order x-over, or a third order (90 or 270 degree phase shift) x-over on the midrange, giving a total of 180 or 360 degree, or a full turn, phase alignment, which would give a perfect summation.
In my case, using the 2441, I think a third order x-over would be better/safer with a x-over at 1000Hz. Wouldn't you agree?
Then the task of time-aligning the drivers, would be much easier for the Behringer UltraDrive, at least I think.
While you were away for the holiday’s, I’ve also been busy trying to figure out the best/ideal x-over point between the 2441 and the 2123 and all things considered I think that 1000Hz/34cm distance between driver-center, seems best in my view.
I’ve also come across a program called XDir, which is supposed to calculate lobing-effects, though I’m not sure how it works, or how to find the best values. Perhaps you’re familiar with the program? http://www.tolvan.com/xdir/ .

BR
Roland

[lfh]

I’ve also come across a program called XDir, which is supposed to calculate lobing-effects, though I’m not sure how it works, or how to find the best values.

Hi Roland,

why don't you start a new thread about your speaker project (this subject interleaving gets confusing )?

As to the program in question, I haven't used it (and I won't since I'm too lazy to fire up the Windows emulator...), but I have written such stuff (and I know who the author of this one is - you can remove the "supposed" part ). Judging from the sparse documentation on the site, he uses the simplest possible transducer model - point sources (i.e. omnidirectional ones) - in a vertical line array and adds the contributions at positions along a half circle in the vertical plane. The program also takes source level and the relative phase difference into account, so effects of different crossovers could be studied (provided that you calculate filter attenuations and phase angles by other means). I think this little program should be useful to help gaining a basic understanding of how two or more sources combine when they are close compared to the wave-length respective far apart relative the wave-length, but it's not really a design tool. (I can imagine he wrote it when teaching electroacoustics at KTH.)

[pangea]

Hi Roland,

why don't you start a new thread about your speaker project (this subject interleaving gets confusing )?

As to the program in question, I haven't used it (and I won't since I'm too lazy to fire up the Windows emulator...), but I have written such stuff (and I know who the author of this one is - you can remove the "supposed" part ). Judging from the sparse documentation on the site, he uses the simplest possible transducer model - point sources (i.e. omnidirectional ones) - in a vertical line array and adds the contributions at positions along a half circle in the vertical plane. The program also takes source level and the relative phase difference into account, so effects of different crossovers could be studied (provided that you calculate filter attenuations and phase angles by other means). I think this little program should be useful to help gaining a basic understanding of how two or more sources combine when they are close compared to the wave-length respective far apart relative the wave-length, but it's not really a design tool. (I can imagine he wrote it when teaching electroacoustics at KTH.)

You are absolutely right! I almost did start a new thread for this reason, just before christmas, but wanted to keep the discussion going for as long as possible.

So from now on, I'll continue to write about this in a new thread.

About "Xdir", I'm sorry I used the word "supposed". It wasn't my intention to be critical or anything of the program, it only meant that I didn't know how to use it correctly.
So perhaps I should have said, "it is said to"..., instead.
I'm sure the program is very good.

BR
Roland

[lfh]

About "Xdir", I'm sorry I used the word "supposed". It wasn't my intention to be critical or anything of the program, it only meant that I didn't know how to use it correctly.
So perhaps I should have said, "it is said to"..., instead.
I'm sure the program is very good.

No worries, I just wanted to say that it most likely does what it's supposed to do (as opposed to some crappy freeware out there...). And yes, it should still be useful for your purposes. E.g. first look at the frequency range where the twin basses operate but the tweeter is silent (e.g. do one plot per octave) and then study what happens around the crossover frequency where all drivers contribute. Vary one parameter at a time (spacing/level diff/phase diff), and you'll get a good grasp of how the array works, and how the filter properties come into play. It should also be interesting to compare a conventional design and an MTM around the crossover frequeny.