Vifa P17 TMM questions

weddie

Member
2004-08-01 8:50 am
MN
Hello all,

Ok here's me situation. I own 4 Vifa P17, which are 8 ohm, and the Vifa D27TG35, and my plan is to put them in a TMM config. in a 1 cubic foot box, about 30 liters, sealed. I'm sealing the box because I'm planing to roll off the Vifa's into a 10" Peerless at 300hz. But lets assume I don't have the Peeless yet. Also, I going to use a 3000hz x-over for the D27.

Here are my questions: 1: The specs for the P17's suggest a 30 liter vented box for one driver, what happens if I place two drivers within the same box, do I double the volume or will they behave as if they are the only driver in the box. I like tight bass and clear mids, should I vent or seal the box, based on the previous statement.

2: Will the P17's be 8 ohm or 4 ohm when connected to the crossover. Example: http://www.speakerbuilder.net/web_files/Projects/Eros Project/ersoxo1.gif
Are the P17's in parallel or series in this x-over and how do I plan my crossover for this? Do i assume 4 or 8 ohm.

Thanks for all your suggestions in advance.

Weddie
 
Q1:
Depending on the driver params, you will get a peak in some bass freq by halving the volume and rapid roll off thereof. It might sound boomy if used for bass. If used for midbass (with peerless) you are better off sealed because of better transient response.

Again unless you have the T/S for it, we cannot say exactly at which freqs will the peaks occur and roll-off thereof.

Q2: It will be 4 ohm.

K-

PS: I am on the rd and cannot do this calcs for you this week. ;-)
 

weddie

Member
2004-08-01 8:50 am
MN
Specs of P17

Here are the T/S of the P17

Specifications:* Power handling: 70 watts RMS/100 watts max * Voice coil diameter: 1-1/4" * Voice coil inductance: .55 mH * Nominal impedance: 8 ohms * DC resistance: 5.8 ohms * Frequency response: 37-5,000 Hz * Fs: 37 Hz * SPL: 88 dB 1W/1m * Vas: 1.23 cu. ft. * Qms: 1.55 * Qes: .45 * Qts: .35 * Xmax: 4.0mm *

And my plan is to find the perfect sealed box so that the mid-range is solid. I really just need the TMM to goto 300hz clean with no peaks. A zobel network might be used also, but for now I guess I would just like some suggestions on what size box to go with.

Thanks,

Weddie
 
Are these complete T/S or cut and paste from PE's description? I suspect the latter, regardless, I am on the road and do not have access to my own PC hence cannot make calculations for you.

If you can send a reminder on saturday by bumping the post (if someone has not helped already) it would be nice,

Thanks!

K-
 

weddie

Member
2004-08-01 8:50 am
MN
Thoughts

OK here is what I'm planing so far.

I will have a TMM config. in a 23L sealed box. The drivers should roll off at 75hz. I will no be using a zobel network since the imdence is just perfect when the P17's operate over 100hz. I guess I would like some help with a x-over then. The P17's will be in parallel so they will be 4 ohms and the Vifa D27TG35-06 is 6 ohms at 91 DB. There are so many different types of x-overs out there so if anyone has any good examples that would be great. I do plan on x-over at around 3000hz for the tweeter. This brings up two questions. Should I cross the P17's and the tweeter at the same frequency or should I put a gap in there. Also, if you put two woofers in the same box, does their sensitivy go up by 3db or 6db? If it goes up by 6 how do I messure the DC resitance of the speaker, there are in parallel, so does the resitance also drop? Thanks for your help

Weddie
 
Re: Thoughts

Originally posted by weddie
will have a TMM config. in a 23L sealed box. The drivers should roll off at 75hz.


That jives with what my modeler spits out....

XOs... can't help much there -- i avoid them. If i have to use one, i prefer either very simple or active.

dave
 

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Re: Thoughts

weddie said:
This brings up two questions. Should I cross the P17's and the tweeter at the same frequency or should I put a gap in there. Also, if you put two woofers in the same box, does their sensitivy go up by 3db or 6db? If it goes up by 6 how do I messure the DC resitance of the speaker, there are in parallel, so does the resitance also drop? Thanks for your help

Weddie

Good questions that I'd like answer too as well, Dave? :)
 
weddie said:
This brings up two questions. Should I cross the P17's and the tweeter at the same frequency or should I put a gap in there. Also, if you put two woofers in the same box, does their sensitivy go up by 3db or 6db? If it goes up by 6 how do I messure the DC resitance of the speaker, there are in parallel, so does the resitance also drop? Thanks for your help


Good questions that I'd like answer too as well, Dave? :)

Well if you are asking me, then the answer is... put the second one on the back of the cabinet, load it push-push and roll it off at(or just above) the baffle step (or let it run FR)

dave
 
K-amps said:
Looks like a 200Hz XO would be in order for a relatively high SPL system.

If you are going to XO that high the P13MH might be a better choice... active XO at 200 Hz and let it run all the way up, bringing a T in at 4-5 k

PS: I read the spl of the P13Wh as 88db, and you have it at 86... does it matter? [/B]

Just the numbers that were in my database... doesn't affect the curve. The MH is also a bit more sensitive.

dave
 
Ofcourse, I will triamp... I got two PPI Pro 12 pairs for the bass , each Pro 12 pair will handle 30Hz to 200Hz or so.

Basically:

Two Pro 12 = 30Hz to 200Hz
Two P13WH = 200Hz to 2500Hz (MTM)
One XT25 = 2500Hz to 40kHz.

Using a Behringer CX-3400 crossover.

I am leaning towards a Orion/ Bob 5 design.