Please comment on the following setup. I plan to redesign my TMW to a TMMW for higher sensitivity. The W is a Shiva which will be in a cabinet as part of the entire speaker, front-firing. The TMM will be in its own cabinet on top. The whole setup is 4-way active. The crossover frrequencies are at 2500 & 200.
The drivers are:
Tweeter : Vifa D27
Mid : Vifa P13
Woofer : Shiva
My doubts are:
1) Whether I can get away without padding the TMM since the sensitivity will be much higher than the Shiva's. Since some gain is expected, will room gain make up for the 88db sensitivity of the Shiva's ? The Shiva cabinet will have a Qtc around 0.6 for accurate bass ( primarily music ).
2) In a TMM is driver offset an issue ?
cheers,
sunil
The drivers are:
Tweeter : Vifa D27
Mid : Vifa P13
Woofer : Shiva
My doubts are:
1) Whether I can get away without padding the TMM since the sensitivity will be much higher than the Shiva's. Since some gain is expected, will room gain make up for the 88db sensitivity of the Shiva's ? The Shiva cabinet will have a Qtc around 0.6 for accurate bass ( primarily music ).
2) In a TMM is driver offset an issue ?
cheers,
sunil
Hi Pat ( hope that is is your real name ),
The x-over design is what is available from Rod Elliot / Dave Pomann. Nothing fancy. Although when the current 2-way materialises to the 4-way I will use the design as published by Luc Henderieckx's. The drivers are all from favours by friends.
In Bangalore the ONLY option I know for good drivers are from www.corrson.com. Nice people to deal with though. They have very good accessories including a "tar" based damping material.
Cheers,
sunil
The x-over design is what is available from Rod Elliot / Dave Pomann. Nothing fancy. Although when the current 2-way materialises to the 4-way I will use the design as published by Luc Henderieckx's. The drivers are all from favours by friends.
In Bangalore the ONLY option I know for good drivers are from www.corrson.com. Nice people to deal with though. They have very good accessories including a "tar" based damping material.
Cheers,
sunil
I'd go MTMW; you'll get much better horizontal dispersion and lessened early reflections. Driver offset isn't a particular problem, your time align differential is far too short to be audible. The differing sensitivity situation isn't a problem either; remember that the mids are rated at 88 dB in a standard baffle, but normally your're not going to get that in a narrow box due to the diffraction step, so the additional 6dB of voltage sensitivity merely balances out the baffle step anyway.
I'd also reconsider the 200 Hz crossover; your post isn't specific but if those mids are P13WH-00-08 midwoofers they should be used for the directional frequencies, right down to 100 Hz or so, for the best result.
I'd also reconsider the 200 Hz crossover; your post isn't specific but if those mids are P13WH-00-08 midwoofers they should be used for the directional frequencies, right down to 100 Hz or so, for the best result.
Bill,
Thanx for the reply. Before I go ahead I should mention I made a mistake with the original post. I had intended to write, the setup is a 3-way active, not 4-way. I don't understand something.
Is'nt the P13 weak at below 200hz ? Why not x/o at 200hz ? I'm going by the spec sheets as I have not measured the drivers. The Shiva's are to be on the same plane as the P13's & the D27's, so are the directional frequencies still going to be a problem ?
Thanx,
sunil
Thanx for the reply. Before I go ahead I should mention I made a mistake with the original post. I had intended to write, the setup is a 3-way active, not 4-way. I don't understand something.
Is'nt the P13 weak at below 200hz ? Why not x/o at 200hz ? I'm going by the spec sheets as I have not measured the drivers. The Shiva's are to be on the same plane as the P13's & the D27's, so are the directional frequencies still going to be a problem ?
Thanx,
sunil
many years ago I heard a pair of P13s and asked the owner/designer what was wrong. he said that the P13's are not dyunamic as they have a high damping surround. they are very flat in their freq. resp. though. then we heard a scanspeak that had a low damping surround and while the paper freq. resp specs were not as flat as the P13s the sound was closer to live music. given this experience i think that your orignal XO of 200Hz is not bad. Yes the P13 s can go quite low but when you ahve dedicated woofers for the bottom octave or 2 why not use it. I suggest email Lynn Olson. He has a lot of experience with the P13s.
As fasr as the midwoofs/tweeter are concerned they are the focus point of the system directionally speaking, and you don't want that focus disturbed by another source, which the woofer could be if crossed over that high. With a single P13 you would have some issues going down to 100 Hz, but with two it shouldn't be problematic. But it's a rather moot point if you're going active, since adjusting the crossover frequency will be a matter of turning a knob anyway, and you can alter it to whatever sounds best in room.
When you say the Shiva will be on the same plane as the other drivers I assume that you mean vertically speaking.
When you say the Shiva will be on the same plane as the other drivers I assume that you mean vertically speaking.
Hi Navin,
I remember you mentioned the same thing in some other thread. I decided on the dual P13's after reading about the success people have had with the Ariel's.
Bill,
Does that mean, with a dual setup I can push them to 100hz without any equalization of any sort ???? I checked it with "Unibox" & two P13's just about manage at 100hz. What do you think ? Is there something I'm missing here ?
If not 100hz, is 120 a more appropriate x/o frequency ?
Thanx,
sunil
I remember you mentioned the same thing in some other thread. I decided on the dual P13's after reading about the success people have had with the Ariel's.
Bill,
Does that mean, with a dual setup I can push them to 100hz without any equalization of any sort ???? I checked it with "Unibox" & two P13's just about manage at 100hz. What do you think ? Is there something I'm missing here ?
If not 100hz, is 120 a more appropriate x/o frequency ?
Thanx,
sunil
It depends on your alignment. 2 drivers maximally flat in a .2 cu ft sealed box gives an F3 at about 140 Hz; in a .4 cu ft VB the F3 comes in at 80 Hz. If it was me I'd be going the VB route, so that if you find in room that a 100 Hz crossover sounds better you can do so without stressing the drivers. For that matter you may even decide that 80 Hz is better still, but with the sealed box you'd never know since it wouldn't give you that option. I know that sealed is often preferred for midbasses, but the main reason for the bad rap that vented gets is insufficient damping of the box.
On the other hand if you really want a killer rig go TL instead, that way you could go to 80 Hz no problem at all and still have the sonic characteristics of a sealed box.
On the other hand if you really want a killer rig go TL instead, that way you could go to 80 Hz no problem at all and still have the sonic characteristics of a sealed box.
BillFitzmaurice said:
Oh well....TL for mids I thnk is fantastic. since the tuning is above 100hz one can have a reasonably short line if one goes for 1/4 wave TL. It absolves you of the sealed/VB issue and allows you to tune the bass by adding/removing stuffing. now I am getting jealous.
BTW do you have a design for the box?
Bill/Navin,
Thanx for the idea. A T/L is looking mighty complicated. If I t/l the midbass how do I cut get an x/o at 80. I'm going with a 2-box approach. That way I can change/switch later. I really like to go with a sealed box. Is expecting a smooth response at an x/o of 120 expecting too much ? If I go with a t/l what's the line length like ?
cheers,
sunil
Thanx for the idea. A T/L is looking mighty complicated. If I t/l the midbass how do I cut get an x/o at 80. I'm going with a 2-box approach. That way I can change/switch later. I really like to go with a sealed box. Is expecting a smooth response at an x/o of 120 expecting too much ? If I go with a t/l what's the line length like ?
cheers,
sunil
TLs are very simple actually, though also very misunderstood. Take look at the Thor TL at the Madisound site. That box is tuned at 44 Hz with an 81 inch line. An 80 Hz line would have to be about 42 inches long, and you could do that with a scaled down version of Thor if you wanted to keep the box short for stacking on top of the woofer boxes or keep it the same height and eliminate the fold for stand-alone. You'd also make the cabinet an inch or two narrower to compensate for the smaller diameter midwoofs. The only major alteration to the design necessary would be a sharper taper to the line to keep the taper ratio of 3:1.
If you decide to go for this idea I'll help you with the final dimensions.
You don't tune a TL with the stuffing; what the stuffing does is eliminate resonances in the line to ensure smooth response. Insufficient stuffing will leave response peaks and dips. The line frequency is determined primarily by its length, with driver T/S specs also involved of course. The P13 specs work just fine for an 80 Hz line.
The advantages to a TL is smooth resonance-free response above the Fo, with the bass lift of a VB at the Fo but with the 12dB rolloff below Fo of a sealed box. They haven't been popular because until quite recently there weren't sims available to predict their response and their design criteria weren't well understood.
If you decide to go for this idea I'll help you with the final dimensions.
You don't tune a TL with the stuffing; what the stuffing does is eliminate resonances in the line to ensure smooth response. Insufficient stuffing will leave response peaks and dips. The line frequency is determined primarily by its length, with driver T/S specs also involved of course. The P13 specs work just fine for an 80 Hz line.
The advantages to a TL is smooth resonance-free response above the Fo, with the bass lift of a VB at the Fo but with the 12dB rolloff below Fo of a sealed box. They haven't been popular because until quite recently there weren't sims available to predict their response and their design criteria weren't well understood.
BillFitzmaurice said:
Thanks for this tip. I was using stuffing to increase/decrease the effective speed of sound in the TL. by doing that i figured one could affect F3. no wonder i was going nowhere and gave up.
i'd like to see a line with a 3:1 taper that you talk about. most lines i know start with an area that is 1.5*Sd and end with an area that is 0.75*Sd. with a 3:1 taper what would be the start and end areas (wrt Sd)?
Yes, that bit about using stuffing to change the speed of sound and thus allow a shorter line is pretty bogus; you don't have to be Einstein to realize that you're not going to alter the speed of sound by more than a few percentage points.
The idea of using Sd to compute the line array cross section is pretty much defunct. Current theory uses Vas instead, with the overall volume of the line calculated from the driver Vas. With Qts of .33 the Vp is equal to the Vas; at .41 Qts the Vp is equal to Vas x .9. Knowing the total volume of the line you then can figure the areas at either end for the 3:1 ratio, though 2:1 to 4:1 is usable without a lot of alteration to the result. I just built a pair of 100 Hz TLs with 2.5:1 ratio that work fine.
The idea of using Sd to compute the line array cross section is pretty much defunct. Current theory uses Vas instead, with the overall volume of the line calculated from the driver Vas. With Qts of .33 the Vp is equal to the Vas; at .41 Qts the Vp is equal to Vas x .9. Knowing the total volume of the line you then can figure the areas at either end for the 3:1 ratio, though 2:1 to 4:1 is usable without a lot of alteration to the result. I just built a pair of 100 Hz TLs with 2.5:1 ratio that work fine.
Bill,
If I go with a t/l to boost the P13's & get the response down to 80 won't there be phase problems. I mean, we have 2 P13's & their t/l port & the Shiva's. Is'nt there a phase mismatch at some point ?
If I x/o at 200hz, do you think the Shiva's can keep up with the rest of the system. It is an 4th order L/R. More importantly, are they designed to play from 200hz onwards.
Bill, I'm making a pair of t/l's for a friend using the P17's from Vifa. Can you help me design these ? The specs are:
fs : 37
Vas : 34.7
Qts : 0.35
Qtc : 0.60 ( If possible)
Thanx,
sunil
If I go with a t/l to boost the P13's & get the response down to 80 won't there be phase problems. I mean, we have 2 P13's & their t/l port & the Shiva's. Is'nt there a phase mismatch at some point ?
If I x/o at 200hz, do you think the Shiva's can keep up with the rest of the system. It is an 4th order L/R. More importantly, are they designed to play from 200hz onwards.
Bill, I'm making a pair of t/l's for a friend using the P17's from Vifa. Can you help me design these ? The specs are:
fs : 37
Vas : 34.7
Qts : 0.35
Qtc : 0.60 ( If possible)
Thanx,
sunil
Vp is the total line volume, so with Qts at .33 the line volume is equal to Vas, with it going smaller as Vas increases.
The only place that phase becomes problematic is below the Fb of the sub, where the phase shifts 180 degrees and output then drops by 24dB/octave, which is why you have Fb lower than your intended passband and use an infrasonic filter at approximately that frequency to prevent overexcursion. The TL does not shift phase below Fb, acting like a sealed box in that regard, one of the reasons TLs work so well. As for the crossover point I wouldn't worry about that until you play the system in room and then set it where it sounds the best; my experience is that you will prefer it around 80 Hz.
The P17s would work very well in a TL. They spec out very close to the Seas used in Thor and I'd use that design without alterations.
The only place that phase becomes problematic is below the Fb of the sub, where the phase shifts 180 degrees and output then drops by 24dB/octave, which is why you have Fb lower than your intended passband and use an infrasonic filter at approximately that frequency to prevent overexcursion. The TL does not shift phase below Fb, acting like a sealed box in that regard, one of the reasons TLs work so well. As for the crossover point I wouldn't worry about that until you play the system in room and then set it where it sounds the best; my experience is that you will prefer it around 80 Hz.
The P17s would work very well in a TL. They spec out very close to the Seas used in Thor and I'd use that design without alterations.
There are equations if you want bother with them, available from George Augsperger. To simplify the Vas to Vp ratio for Qts .33 is 1, Qts .35 is .9, Qts .41 is .6. Lower Qts than .3 is not recommended for a TL, and minimum Vas/Vp ratio for drivers of Qts .5 and higher is .5. Driver Qts higher than 1.0 also not recommended.
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