Design help

[sunil]

Gurus,

I want to build a speaker with the foll units.
I'm very particular that it should be a "closed box"
& should have only 61/2" drivers for a narrow front profile.

Not very particular about bass extension below 50hz.
I plan to use a 4th order on the T/Mid & an active on the Mid/W

Tweeter: D2905-9300 (SS)
Mid : P17WJ-00-08 (Vifa)
Woofer : 18W8545 (SS)

I'm worried about the disparity in power between the
Scanspeaks & the Vifa which is rated at 40W. Now going by actual power ratings hitting 40w@88db/1W should give an SPL of about 116db@32W. Is this for real. Will it match the Scanspeaks.

Any thoughts & ideas on this is welcome.

Thanx,
sunil

 

[kelticwizard]

Sunil:

I have not used Vifa drivers. However, I do know that they are used in systems costing $2000 or more.

I do not believe that they have the reputation they do by only being able to handle 40 watts.

For some reason, Vifa lists the short term max power as 350W, the long term max power as 150W, and the "nominal power"(?) as only 40W. What this means, I do not know. I would guess that the first number means part of a second, the second a few seconds, and the third number a constant drive.

Considering Vifa's reputation, I would think you could use a 100W amp with them without worrying. If anyone has used Vifa midbasses, please jump in.

Normally I would not answer this question since I have not used Vifa, but nobody else answered it either. So that is my best guess-hook them up to a 100W amp and you should not have to worry.

How big an amp were you planning on using?

PS: The voice coil diameter is 1.25", (32mm). The general rule of thumb is that a 1", (25mm), voice coil is good for at least 100 Watts. So you should have some headroom over 100 Watts, even.

 

[sunil]

I'll be using an Audiolab 8000 c/p for the T/M & a cambridge p100 for the bass. Both are capable of 175@4, but with the design being "closed box" I'm sceptical it will hit peak xmax's when I turn up the volume.

Do you think getting 100db out of this design is unrealistic ?

 

[kelticwizard]

A) Where do you plan to cross over the woofer to the mid? 150 Hz?

B) How big a Closed Box for the Scan Speak woofer?

C) How big a Closed Box for the Vifa midbass?

I could work the sizes out for you if you don't have a specific answer for those box sizes.

 

[pinkmouse]

I'm worried about the disparity in power between the
Scanspeaks & the Vifa which is rated at 40W. Now going by actual power ratings hitting 40w@88db/1W should give an SPL of about 116db@32W. Is this for real. Will it match the Scanspeaks.

You should be fine using the 100w amp into the Vifa, I suspect the power rating is for continual RMS power, like a sine wave, and that quickly kills voice coils, due to heating. You will have an intermitent signal, and this will put far less strain on the driver.

It is also good practice to use a bigger amp than speakers anyway, it prevents distortion from amp clipping destroying your drivers, and provides headroom for transients.

Have you thought of using an active crossover, or even bi-amping the mids and tweets, this would then make balancing your differing sensitivities easier?

 

[cm961]

IMHO, Vifa makes excellent drivers for a decent price, and I wouldn't worry about blowing them. Bi-amping is also a good idea if you have the amps to power them. I bi-amped a set of 50W RMS 4-1/2" OEM drivers ($7.50 USD each) to a set of vifa tweeters ($17 USD each) and they sound incredible. I mean incredible. The OEM drivers put out too much distortion at low frequencies (they go down to about 30Hz or 35Hz I suspect).

So in response to your original question. You've probably selected great drivers, and you should consider bi-amping.

Pete

 

[Nappylady]

I think that the high long-term power rating means that the voice coils will sustain 350W instantaneous without blowing up, and 150W RMS for a while without blowing up, but only 40W before their THD gets past a certain point. I could, however, be completely wrong.

If the speaker is 88 dB efficient at 1 watt, and you can put only 40 watts through it before it distorts unacceptably, you're only going to get 10log(40) + 88 = ~104 dB out of it maximum. Don't know where you're getting 116 dB. Check your math again.

 

[sunil]

Nappylady, Youre' right it is 104db.

I'm going with a QTts of .85 so it'll be whatever the calculators work out to.

cm961 & pinkmouse,

I will be bi-amping the system. I'm thinking of crossing the t/mid at 2500 & the m/woof at 150.

Right now I'm thinking again of cost so may decide on something else. The Vifa M18WO-09-08 has an f3 of 66.

What is in-room response ?

Will the location of the driver on the panel (closer/further from the floor) affect the response ? Will the apparent bass be more ?

If it does what is a good way to go about calculating the expected response ?

Now comes the big one. I have small room & am not worried too much about d-e-e-e-p bass. Right now I have the 731 pros from MISSION. Not too much bass, if I remember right they start rolling off pretty steep at around 80. So compared to this what can I expect with the sub ? It'll be a closed box tuned to a Qts of 8.5 (hopefully the stuffing will lower it further).

 

[JOE DIRT®]

Re: Re: Design help

You should be fine using the 100w amp into the Vifa, I suspect the power rating is for continual RMS power, like a sine wave, and that quickly kills voice coils, due to heating. You will have an intermitent signal, and this will put far less strain on the driver.

It is also good practice to use a bigger amp than speakers anyway, it prevents distortion from amp clipping destroying your drivers, and provides headroom for transients.

Have you thought of using an active crossover, or even bi-amping the mids and tweets, this would then make balancing your differing sensitivities easier?

you hit that right on the nail Pink....most people dont realise that


and 150HZ is great for Mid bass as long the the crossover is not to steep.....my preference is 12db/octave in that region...........I find some good action going at 250 HZ....but heck what do I know..LOL

 

[taufern]

sunil...by going to a closed box you are actually increasing the effective power handling of the driver...its a common trick most car audio manufacturers use...advertising a 10" woofer capable of 500 watts...you will be fine with 100 watts...you could essentially run the speakers with 200 watts of power depending on your crossover but you