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Discussion Starter #22
Yep, I get that it's on a horn, and that certainly is better than the version without. Not to keep beating this horse, but I'm a directivity freak and I think a lot of people downplay it's importance. The op did seem to be concerned with the match up. I've included an actual 0-20-40° measurement.....credit for the data goes to Brandon (augerpro).

I did a quick course sim of a 12" in driver on an infinite baffle as well. The measured result and the sim aren't quite as bad as I was envisioning. Looks like it's at 50-60° at 1.6-1.8khz. Again, I'm NOT saying that this won't sound good or that I'm trying to deter you from what you're doing and it will be cool to see how these turn out.
Hey so thanks very much for this info. I appreciate it.

So your data, that's from a TD12M measurement isnt it? I have seen that over at DIY Audio forum. Would that data vary at all for my speaker? I have the V2 version of the 12p80 also which does extend quite a bit higher than the previous revision and has a lot less distortion... Not sure if those numbers would change based on that.

And if I get this right, you are saying 1600hz crossover would be around 60 degrees, the AMT has an 80/40 horn on it, would I be right in assuming the beyma would be at 80 degrees at that point? Is that really so bad?

There is also this dispersion prediction (based on the TD12M though) at DIY Audio too:

http://www.diyaudio.com/forums/multi-way/269641-beyma-ultimate-hi-eff-speaker-project-3.html



Is that a bad prediction?

They other thing is, my room and these speakers are going to be toed in and facing the center of a couch with 3 seats, that will be the listening position. 3 seats wide. My setup is on the long walls of a rectangular room so on one side I have curtains and glass, the other side has 5m of air before it hits the next wall. The rear of my room is treated with about 8 acoustic panels and there is my bookshelf probably acting as a diffuser too.

I know I did say I wanted the Left and Right channels to be as best as they can be for stereo playback, but what are we actually talking about here? I'm just trying to get a grip on what this data means. You say they probably wont sound bad given these issues, but my question is, if I am sitting in the listening position hearing these speakers, and the towers are facing me and anyone who is enjoying the music or film with me is sitting right next to me and essentially by extension they would be on axis to the speaker, what detrimental effects will I experience? Are we talking purely off axis here? What is 60 degrees? Is that 30 degrees to either side of the speaker? If that's the case and the Beyma AMT is at 80 degrees (I have already listened to the AMT where they will live aimed at the listening position and have experienced its dispersion) is an extra 10 degrees side to side really a horrible thing? Or am I interpreting this data incorrectly?
 

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Yeah, 60deg is +-30deg. Like I said the pattern doesn't narrow as much on the TD12 as I was thinking it would, and with the right xo the blend off axis could be fairly smooth I think. I'm a stickler for a smooth off-axis transition through the xo region, but in reality you're fairly close. The main thing is that there aren't any huge changes off axis, like you might see with an 8" midbass and a 1" dome tweeter. In that configuration the 8" would be pretty directive at the xo while the dome is omni or near omni.

You're right that quibbling over a 10deg mismatch in the xo isn't a huge deal. Speaker design is all about compromise and you've certainly got some nice parts to work with!

A smooth off-axis response for a loudspeaker is important for a couple reasons. One, if you have a wide seating area a smooth polar will ensure that all seats are getting a similar facsimile of the axial response for the main lp. It's also important for the reflected energy to not have excess at certain frequencies that a speaker with a highly irregular polar response would have. In a small room the reflected sound has an effect on imaging, spaciousness, and intelligibility afaik; a smooth polar will help keep the spectrum of the reflections similar to that of the axial response which will improve sq.

Don't mind me, carry on ;)
 

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Yeah, 60deg is +-30deg. Like I said the pattern doesn't narrow as much on the TD12 as I was thinking it would, and with the right xo the blend off axis could be fairly smooth I think. I'm a stickler for a smooth off-axis transition through the xo region, but in reality you're fairly close. The main thing is that there aren't any huge changes off axis, like you might see with an 8" midbass and a 1" dome tweeter. In that configuration the 8" would be pretty directive at the xo while the dome is omni or near omni.

You're right that quibbling over a 10deg mismatch in the xo isn't a huge deal. Speaker design is all about compromise and you've certainly got some nice parts to work with!

A smooth off-axis response for a loudspeaker is important for a couple reasons. One, if you have a wide seating area a smooth polar will ensure that all seats are getting a similar facsimile of the axial response for the main lp. It's also important for the reflected energy to not have excess at certain frequencies that a speaker with a highly irregular polar response would have. In a small room the reflected sound has an effect on imaging, spaciousness, and intelligibility afaik; a smooth polar will help keep the spectrum of the reflections similar to that of the axial response which will improve sq.

Don't mind me, carry on ;)
This is still great information! Thanks for the discussion.
 

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Discussion Starter #25 (Edited)
Don't mind me, carry on ;)

Again thanks so much for chiming in, I think I have a much better understanding of what you are saying now. I will do some measurements and see if I can get away with 1500/1600hz for those reasons.

I definitely understand where you are coming from here!

Wow so an 8 inch and dome tweeter have even larger problems?? Didn't know that. Sounds like Im in for a good sounding speaker if I can get the crossover nice and smooth.

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Glad to help. I DON'T want to sound like a know it all (because I don't!) but I try to relate my experience to the theory and research that I've found. And when I'm wrong, I'm wrong :rolleyes:. If you find the psychoacoustic stuff interesting I'd suggest skipping the middle man and checking out "Sound Reproduction" by Floyd Toole.
 

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Discussion Starter #27
Thanks Nate.

For those interested, I just watched a 1 hour keynote from Mr Floyd Toole summarizing his book. VERY interesting. Enlightening.


Looks like I will be OK if I can get the directivity as close as possible at the crossover without it being a huge change... So sounds like I will be playing around with a 1400-1600hz crossover on the AMT. I don't think I will ever run these speakers too much over 100db anyway unless I am keen on damaging my ears so hopefully the AMT wont fare too bad at 1400hz if that's what turns out to be the best match.
 

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So sounds like I will be playing around with a 1400-1600hz crossover on the AMT. I don't think I will ever run these speakers too much over 100db anyway unless I am keen on damaging my ears so hopefully the AMT wont fare too bad at 1400hz if that's what turns out to be the best match.
I liked them crossed closer to 2K. Although measurements were fine at lower frequencies, subjectively I preferred a higher crossover point.
 

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Discussion Starter #29
I liked them crossed closer to 2K. Although measurements were fine at lower frequencies, subjectively I preferred a higher crossover point.
Yeah 1800hz would be the max I am willing to do given the size of the mid I am using (Beaming - above discussion) and also going by what many arrived at being the best for the mid/AMT combo I have.

Do you have the same mid as me? The 12p80 is supposed to have utterly amazing transients. Thats where the 1800hz number came from. That combo. The TD12M is supposedly pretty close too.

I will go lower if beaming seems to have a major detrimental effect at 1800hz. One person has measured and said no major issues with 40degree of axis measurements at 1800hz with that combo but will have to see.

OmniMic kit just arrived. Just need to get these boxes built now and its game on with in box measurements, and we will really see what is what.

Will definitely be posting a bunch of graphs here once I get the hang of using it and have built my boxes. Will definitely get feedback from everyone before deciding on a final number.
 

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Discussion Starter #30
I liked them crossed closer to 2K. Although measurements were fine at lower frequencies, subjectively I preferred a higher crossover point.
Hang on you built Mikes baffle wall crossover right? He ended up at 1800hz yes? Did you see any beaming issues with his setup?

He has the TD12M yes?
 

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Discussion Starter #33
Javs, did you make anymore headway?
Yep indeed.

Final tech drawings are done. Should be getting CNC cut this week and I can build the boxes...

Ill post the drawings up later. Going to be a good build!
 

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Discussion Starter #35
Here are the drawings which have been handed over to the CNC guys... I have left out some of the more boring pages but you get the idea.

Should have the cuts done in the next few days then I can begin gluing!

Towers are M/T/W/W



 

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Discussion Starter #37
Ok, So I got the CNC cuts done today!

Baffles fit the drivers pretty good! Just one oddity of about 0.5mm on the Beyma Mid section on my Centre channel, but I can sand that and it will fit fine...

Oh and the port hole is missing from the L&R baffles :eek:

Not to worry, taking the baffles back tomorrow to get sorted. Lucky the CNC shop is close by.

Here is a really quick test fit of the drivers... Cant wait now!





Going to be a slow gluing process though. I am going to completely Glue, sand, veneer the enclosures before I get to the measuring and crossover build. Somewhere in there I need to go on holiday for 2 weeks. So I am thinking these will be finished by early December.

I have a glue question for you guys...

I got some great PVA Wood working glue. For enclosures this big and heavy (25mm MDF) are there any tricks you guys swear by? You think the glue will be strong enough to hold the box together when its cured, I am led to believe so. Or, should I be hammering pins in there too when I glue them?

Planning to use ratchet straps and a few quick grip clamps while gluing. Will let the glue dry for 24 hours before moving on.
 

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Looks good, you'll probably be fine with just glue but I'd have more peace of mind myself if at least the front baffle used PL.
 

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Discussion Starter #39
Looks good, you'll probably be fine with just glue but I'd have more peace of mind myself if at least the front baffle used PL.

What is PL?


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