Beyma 18P80Nd in sub horn: Am I missing something? - Page 5 - diyAudio
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Old 16th June 2013, 09:58 AM   #41
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Before I continue, let me explain something. I am planning on building matching tops (preferably synergy-like, suggestions welcome ) that fit in the drum riser/sub for transport. This means I have to account for their space and be careful not to put the mouth bracing in the way. So I haven't braced the last half of the horn yet. Also, I haven't attached the front panel. I'm hoping to find a way I can open and close the panel to put the tops in AND make it strong enough to withstand the sub-violence .

And another thing: the front panel isn't cut to size yet. As EPA said, it can be used to tune the box. In the sims above EPA suggested 72 cm's; the panel now is 84 cm's, so the box is tuned even a little lower at the cost of some SPL.

That being said, I was very eager to hear the results, so after the glue set I did some initial listenings. Man, this thing is efficient . And it plays really low for a single cab outside. There's a big difference when I leave the front panel off: it doesn't play as low compared to when the panel is on, but the kick is a couple of dB's louder, so even more efficiency . Sadly I don't have the space outside at home to really fire it up, but I have access to a suitable place where I will make some measurements. Then it was time for band practice...

Later on, when the band had left, I hauled the fridge (American style, not the small European fridges ) into my rehearsal room, which is about 4.5 by 5.5 meters and heavily soundproofed and turned it up a little. I just used a Powersoft D2002 (350W/8 Ohms, the Beyma 18P80Nd is 8 Ohms) that was set up for vocal amplification in the room and a DCX2496 for filtering (HP 35Hz, L-R48, LP 119 L-R48, no eq, the settings I use for my two BF Titan 48's). Then I played some different styles of music, ranging from metal to top40 to dubstep, watching the cone excursion carefully.
I ended up turning it up all the way (that is 'just' 350W) and enjoying even the lowest notes of Skrillex's Summit (Bangarang -2011) at full SPL . No signs of overexcursion whatsoever. 350W isn't going to be able to do that. I did notice that with the front panel off, excursion decreased immensely while playing those low dubstep bass lines, as did the efficiency, but the "smell of hot coil" started to come from the woofer, so I quickly decided this was not a good idea. (Too little travel and apparently too little cooling of the voice coil).
I do need to buy some broom sticks. The max span on the top and bottom panels is too big. The 16cm span with 12mm BB is excellent, very little flexing.
Talking about flexing... the large unbraced sides of the mouth flex like crazy . The front panel that fits in very tightly just pops out at higher SPL. Even two clamps and a strap have a really hard time keeping it from rattling. The mouth end of the panel flexes about 5mm to each side at the middle of the 50 cm span... definately needs bracing !

I had some songs with some low 30 Hz/upper 20 Hz notes and I figured I could lower the HP somewhat, since excursion stayed well within the limits of the woofer. It turned out this drastically expanded the range of the sub . There was a LOT more really low end this thing was able to produce!
But time was against me and at 10PM I decided to call it a night and keep the peace in the neighborhood . I had a dog to walk and a birthday party to visit...

I am now even more eager to see measurements of this Colossus.

EPA, I didn't discuss this with you, but as I was building, I remeasured the space I had available in my car and I added another 5 cm's to the width of the cab, so it's now 160(outside)x94(outside)x50(inside) cm's. I figured a longer path length (I extended the inner panel by 2.5 cm's) would not be very detrimental to the end result.
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Old 16th June 2013, 11:23 AM   #42
epa is offline epa  Netherlands
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nice to hear it works out.
5 cm extra gives you about 10cm extra path lengte.
to determen the correct hp filter you need a frequenty generator(maybe an app on your phone),then put a white dot on the cone of the driver,disable/bypass the hp filter.
put the generator signal on and find the freq where the excursion is minimum(somewher between 30 and 40 hz)
this is easy to see whit the white dot on the cone.
once this freq is known,whe go back to the sim in hr,and adjust the lenght according to real live condition.
then use the filter wizzard to determen the hp filter.

what are you thinking of for the tops?
something like 2 x10"+1"?
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Old 16th June 2013, 04:58 PM   #43
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Those are some clean instructions, Eric. Thanks.

Why exactly do I need to know at what frequency the displacement is minimal? Do I need this to adjust the data in HR to get the same minimum in the sims? (and then use the filter wizard)

BTW, I've never really paid any attention to the filter wizard, but I just had a look at it and damn, that's exactly what I was missing. With this tool it's really easy to determine your HP settings and protect your speakers !

For tops: something like what you mentioned seems ok. Or something like 4x8"+ 1.5". I need to be able to hit 130dB. I still need to figure out at what frequency I can cross over to the sub, but with the filter wizard that seems peanuts .
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Old 16th June 2013, 06:44 PM   #44
epa is offline epa  Netherlands
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correct
transfering "reality"back to the sim,and adjust the hpf accordingly.

normaly i would say ~100 hz is the max x-over point,you could go higher,but that depends on what you find acceptable soundwise.
the extension runs over 200 hz eq'ed but the phase go's haywire above 100 hz

for tops 130db seems an a lot to me ,
if you got 325 watts for the sub it puts out 127/128 db,so in that case i would say 127db max for 2 tops.
usualy tops wil needs less then that.
just my on that
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Old 16th June 2013, 07:36 PM   #45
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The sub can put out 130dB+ @ max power, according to HR (no power compression), so that's how I came up with that amount. I'm not sure how loud a real life snare drum is, but I think it's quite loud. I'd imagine 130dB isn't a bad idea. And otherwise, I have some headroom for dynamic playing .

I have more power available for the sub, that's not the problem. I just used that amp as it was in reach. I'll have a look at what HR has to say about the maximum power it can take once I get the "reality" data (the speaker is rated at 800W RMS, 1600W peak, so it depends on the excursion, I guess).

I'd like for the tops to be able to take over from 100Hz. That would mean they would be reproducing the snare sound without the help of the sub. And a good "twack" can be felt in the chest, that's another reason for my 130dB statement.

I feel almost guilty for leaving for a week of holidays starting Tuesday :s...
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Old 17th June 2013, 02:03 PM   #46
epa is offline epa  Netherlands
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at 750 watts excursion is 15 mm=x-max *2
any higher it wil sound bad ,but truh you over 130db by then.
best protection for the driver is the man behind the nobs.
so you need 130 db for the pair.


a frend of mine got a pair of beyma 650 ti drivers ,maybe your intrested.
200 euro for 2.
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Old 17th June 2013, 08:32 PM   #47
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As soon as I have matching tops built I'll set it all up and measure the whole system out in the open (true 2Pi measurement).
Yeah, I know HP and limiters are not optional. They're mandatory! Luckily HR seems to help out quite a lot (as do your suggestions and help with designing the sub, Eric. Very much appreciated!).

I think I need to decide on or design the tops first, before I start throwing money at drivers, but thanks for the tip anyway! Now I'm off for a nice trip to the south of Europe .

...without my laptop .

Cheers.
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Old 18th June 2013, 03:09 PM   #48
epa is offline epa  Netherlands
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happy holidays
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Old 27th October 2013, 07:50 AM   #49
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Matching tops build started .

Synergy with BMS 4550, Visaton M10 and ...
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