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reflex design questions,,,, again

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PoteirosCorp View Drop Down
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    Posted: 27 January 2005 at 2:00am

hello

I'm playing with WinISD simulatin 2x15" boxes, and some questions came out to my mind 

Wich is the best way to choose the perfromance graphic (dont know if its properly said), i.e. using 2 beyma sm-115n   200liters box tuned at 40hz         &n bsp;         &n bsp;      0dB at 76hz   -3dB at 53hz and -10dB  36hz  

I know the response must be flatern as possible, but I try to know wich one is the minium aceptable  to have a decent bass (dont want this boxes to loud , just a nice extension, cause I be playing till 45hz)     

I bought some LX60 15",  but I had to sold them cause money issues      
now I have this sm115n on my hands

tahnks for your help  

cheers

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mobiele eenheid View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mobiele eenheid Quote  Post ReplyReply Direct Link To This Post Posted: 27 January 2005 at 5:26am

A 200 ltr box tuned @ 40 hz is pretty much safe design. You'll get a f6 of about 45Hz. And a very nice groupdelay.

Usually the sm-115 is used for PA in a slightly larger box with a little higher tuning, more like 240 ltr tuned @ 44 Hz (for a double). This won't change the f6 much, but the f3 will be reasonable lower. Since there is no free lunch, the groupdelay will become slightly more noticeable, tho that doesn't seem to bother most users.

Most professional designers will take only the f3 in account, since a 3 dB difference is just slightly hear-able. If manufacturers use the f10 point it's usually to impress the people that don't know what to look for. A 10 dB difference is a very big difference. If the usable frequency limits are given, without stated if it's f3 or f10 you can bet it's the f10 points given.

If you're using WinISD Pro 0.44 it might be a good idea to upgrade to WinISD Pro 0.50a6 or 0.50a7. a7 has some improvements over a6 but since it has a bug a6 is much nicer to work with. The Pro versions will leave 0.44 far behind, since they give much more essential information and are still freeware.

I've written a small guide that explains the important parts of the newer versions. It's in Dutch but I could translate it and put it on speakerplans as an topic if you'll like, or just e-mail it. Could be ready before the end of the week.

Cheers



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PoteirosCorp View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote PoteirosCorp Quote  Post ReplyReply Direct Link To This Post Posted: 28 January 2005 at 1:03am

thanks
I'm using pro 0.50a7 version  
sorry but I never think that when you say f3  f6  f 10  you're talking about the -3dB   -6dB  etc  point in frecuency,  right ??
 (hahaha   I figured out today while playing on simulations)

The dimensions are given to fit my Ford Van (subs and tops with a lot of drums)  so what should I do: higger tunning??  bigger box   ??
Thanks again

by the way  if you can send me the guide to paul_fernaNOSPAM@yahoo.com  

Cheers

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Post Options Post Options   Thanks (0) Thanks(0)   Quote mobiele eenheid Quote  Post ReplyReply Direct Link To This Post Posted: 28 January 2005 at 3:06am

Yes, f3 = the -3dB point, etc.

Hmm....Using a double 15" in a van (ehhrr... for inside?? or free party drive-in style; cops show up, close the doors and get the **** out of there )

The problem is that if you want a flat frequency response (performance graphic) you'll have to take the roomgain into account. You''ll have a lot of gain in a car for the lower frequencies. No idea how much exactly, depends on the dimensions of your van. So if you design it to have a straight frequency response (performance graphic) you'll end up with a huge bump in the low frequencies response.

In a "normal" volumed car the room gain starts beneath 60-80 Hz. So if the frequency response starts to roll off at that point it's pretty much ok. At 20 Hz it can be as much as 9 dB of gain.

But since I don't know enough about the room gain in a car I'm probably not the right person to talk to about the tuning (thought you were talking PA wise). My best bet would be to put it on a car audio forum.

Guide coming at ya this weekend.

Cheers

 



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Calitri View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Calitri Quote  Post ReplyReply Direct Link To This Post Posted: 28 January 2005 at 3:55am
You also have to think about the crossover. The flatness of the responce curve depends on at what frequency you cross it. Since you're using WinISD, it has the EQ/Filter settings tab so you can test what would be the best settings for your cabinet.

I would probably use about the same as you, because I like to have a bit extened responce too. And like mobiele eenheid said 200 litres @ 40 Hz is always a safe design. If you want extend it more and make it a flat responce do it the way Electrovoice used to do it. Put a high pass filter around 35 Hz and parametric EQ also @ 35 Hz about 3-6 dB of boost. That way you can get -3db to about 45-40 Hz and you have protection for your speakers as well and you can get it quite loud also if ever need that.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote PoteirosCorp Quote  Post ReplyReply Direct Link To This Post Posted: 28 January 2005 at 12:21pm

hahah   my english is not so good

I'm talking about PA    I said to fit my van cause with those dimentions I can put 4 boxes inside, my currently big tops (later I gonna shrink them) and all my drums     The Van is a Ford Econoline 86
I play recorded music with live drums         & nbsp;  I mostly  play in house partys or little venues; so,  no bigs amount of SPL is needed

Calitri, I take your advised and get a parametric EQ  

By the way, answering my first question...  wich f3 will be a nice one ??   I saw some manufacters singles 15" that have f3 50-55hz  f10 35hz  (the same as my simulation)
and those are about 150 liters   
 

Cheers  and thanks again

 

P.S.  Just have to say "mostly" ??
or the word "always" is needed??    you know what I try to mean 

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Post Options Post Options   Thanks (0) Thanks(0)   Quote mobiele eenheid Quote  Post ReplyReply Direct Link To This Post Posted: 30 January 2005 at 7:47pm

Quote The Van is a Ford Econoline 86

Don't know much about cars (or van's for that matter) can you give the dimensions of the space the cabs have to be fitted in?

Quote By the way, answering my first question...  which f3 will be a nice one ??

There isn't really a limit to what would be a nice f3. It's more about what is possible in this case. The speaker is the first limiting factor, the cabsize the second.

In an approximate cabsize of 240 ltr tuned to 45 Hz you will have a f3 of about 48,5 hz at full power. That's what can be done without sacrificing too much powerhandling and/or groupdelay. If the sizes allows that it would be my best bet.

Usually the calculated volume times 1,55 will be the total volume (cabmaterial, loudspeaker, loudspeaker safespace, speakerfoam and bracing). So about 380 ltr per cab and weighing about 60 kg (say 135 lbs) if made from Finnish ply.

Personally I would favor single driver cabs as they would be lighter, easier moved and perhaps would even fit nicer into your van. I would only think about doubles if I had a two man crew, don't know if you do?

I will post the first part of the guide (about the powerdip) in a new topic, in the hope someone could check it for proper English. By posting it down here it would probably only distort this topic. By sending it straight to you it could be too sloppy to read.

Cheers



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Post Options Post Options   Thanks (0) Thanks(0)   Quote PoteirosCorp Quote  Post ReplyReply Direct Link To This Post Posted: 31 January 2005 at 2:01am

45cmX90cmX55cm = 222 (minus speaker, ports and braces vllume) = 200

that way I can fit 4 (8 at full space with the new small 12" tops I want)    I guess my "desing" isn't that bulletproof (hahah just kiding)

I'll check if I can go up to 240ltrs          ;   and taking consideration of single 15"'s   120liters 45hz   give a f3 of  48.99 

So, thank you very much

 

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