I'm an educated newbie (dangerous and annoying, I know), so thank you in advance for your patience.
I'm building a 3-way system. Using BassBox 6 Pro and X-over Pro, I designed the towers with a QTC of .707 based on the bass driver. If I just mount the mid on the same baffle as the bass driver, the mid driver has a very low QTC due to the volume of the bass section of the tower. Should I mount it in its own enclosure within the tower to get a QTC of .707?
In this situation, is the QTC of the mid driver important?
I am sure I am missing some theory here, so please speak up and give me the skinny! I'm a polite and fast learner!
I'm building a 3-way system. Using BassBox 6 Pro and X-over Pro, I designed the towers with a QTC of .707 based on the bass driver. If I just mount the mid on the same baffle as the bass driver, the mid driver has a very low QTC due to the volume of the bass section of the tower. Should I mount it in its own enclosure within the tower to get a QTC of .707?
In this situation, is the QTC of the mid driver important?
I am sure I am missing some theory here, so please speak up and give me the skinny! I'm a polite and fast learner!
You absolutely need to give the mid its own enclosure, simply so it won't be pushed around by the woofer.
As to what Q to give it, that is harder to say. In the end you will be adding crossover to it and shooting for some kind of acoustical rolloff that is the combination of the mids rolloff and the crossover highpass. No need to shoot for .707 and probably best to keep the resonance somewhat low to keep it away from the crossover point.
Regards,
David S.
As to what Q to give it, that is harder to say. In the end you will be adding crossover to it and shooting for some kind of acoustical rolloff that is the combination of the mids rolloff and the crossover highpass. No need to shoot for .707 and probably best to keep the resonance somewhat low to keep it away from the crossover point.
Regards,
David S.
I should have added that this has only become an issue during xover modeling. The mid enclosure is part of the xover calculations. The xover point on the low end of the mid is 300hz.
A .04 cu.ft. enclosure for the mid driver gives a QTS of .707. A .5 cu.ft. enclosure (much easier to build with my cabinet design) gives a QTS of approximately .45. Is this a meaningful figure in my situation? What issues might I run into?
Thanks again!
A .04 cu.ft. enclosure for the mid driver gives a QTS of .707. A .5 cu.ft. enclosure (much easier to build with my cabinet design) gives a QTS of approximately .45. Is this a meaningful figure in my situation? What issues might I run into?
Thanks again!
If your midrange driver isn't acting pistonically the size (volume) really isn't a problem.
Have you determined the resonant frequency in each sized enclosure? if you have and the resonance is more than to or three octaves above the drivers Fs then the size isn't that important.
300 Hz means that the mids Fs should be lower than 300/4 or 75Hz in the box
Have you determined the resonant frequency in each sized enclosure? if you have and the resonance is more than to or three octaves above the drivers Fs then the size isn't that important.
300 Hz means that the mids Fs should be lower than 300/4 or 75Hz in the box
Pistonically? Is that a real word? 
That's wonderific!!
Please define, thanks.
The mid driver is a 4" cone style. Its Fs is 68hz.
A .0468 cu. ft. enclosure gives a Q of .707, an Fb of 132.5hz, and an F3 of 130hz.
A .5 cu.ft. enclosure gives a QTC of .428, an Fb of 132.5hz and an F3 of 139hz.
When switching between these choices, the xover curve is effected between 100 and 200hz. Oddly, the .5 cu.ft enclosure gives a flatter response with my xover modeling, but my fear is I am missing some essential knowledge concerning this issue. I know that I'll inevitably have to tweak the xover once I get everything built, but rebuilding the cab is just not in the budget.
Should I be concerned about going with the .5 cu.ft. enclosure?
That's wonderific!! Please define, thanks.
The mid driver is a 4" cone style. Its Fs is 68hz.
A .0468 cu. ft. enclosure gives a Q of .707, an Fb of 132.5hz, and an F3 of 130hz.
A .5 cu.ft. enclosure gives a QTC of .428, an Fb of 132.5hz and an F3 of 139hz.
When switching between these choices, the xover curve is effected between 100 and 200hz. Oddly, the .5 cu.ft enclosure gives a flatter response with my xover modeling, but my fear is I am missing some essential knowledge concerning this issue. I know that I'll inevitably have to tweak the xover once I get everything built, but rebuilding the cab is just not in the budget.
Should I be concerned about going with the .5 cu.ft. enclosure?
Something's up here. Your larger enclosure should show a lower fb. The lower fb will be the good thing here.
Simply, if you can get your box resonance out of the way, the crossover will remove it from play and become the new rolloff controlling the response, the excursion, etc. so your larger box may be OK. If it is too large the response may droop before you cross it, as the modelling should show.
Last edited:
Qtc of 1 would work even given those figures but a cup of around 5 litres seems to be standard among speaker suppliers.
Fs is low enough and I did mean Fb ( in the box )
Midrange Enclosure 3 Litre'
Midrange Enclosure 0.8 litre
I have used empty friction top tin cans and cardboard tubes to do the same job and you can do a transmission line going from front to back and open at the rear.
you could even make the mids Di-pole using 2 mids in each box one front firing and the other rear firing and wired in parallel but that is starting to get into non-beginner territory
Fs is low enough and I did mean Fb ( in the box )
Midrange Enclosure 3 Litre'
Midrange Enclosure 0.8 litre
I have used empty friction top tin cans and cardboard tubes to do the same job and you can do a transmission line going from front to back and open at the rear.
you could even make the mids Di-pole using 2 mids in each box one front firing and the other rear firing and wired in parallel but that is starting to get into non-beginner territory
Very interesting.
Arlen (Speaker Building 201) used a similar idea with is "Bones" system, PVC tubes with aperiodic vents in the rear.
And those cups are it!! Quickly solves the construction issue, doesn't it?
In the end, what would be a reasonable and safe middle ground in this case? (That is, considering the info I have listed.)
Arlen (Speaker Building 201) used a similar idea with is "Bones" system, PVC tubes with aperiodic vents in the rear.
And those cups are it!! Quickly solves the construction issue, doesn't it?
In the end, what would be a reasonable and safe middle ground in this case? (That is, considering the info I have listed.)
With a passive crossover, or simple opamp active crossover, I try to tune for Qtc=0.7 sealed box because it easily combines with electric Butterworth slopes. I find it very important to absorb the midrange rear wave to avoid reflected energy hitting the back of the cone. I use an odd shaped box that is wide at the front and narrowing toward to rear plus odd shaped bracing all to help to reduce resonances. I use a lot of stuffing at the rear of the box, but I have found that putting stuffing up front right next to the speaker muffles some detail.
B&W uses a sphere with a rear tapered tube. Several quality speakers use a plastic elliptical cone in back of the midrange to create a volume. Several DIY experts use complicated internal volume shapes to break up rear reflected energy.
B&W uses a sphere with a rear tapered tube. Several quality speakers use a plastic elliptical cone in back of the midrange to create a volume. Several DIY experts use complicated internal volume shapes to break up rear reflected energy.
The mid driver we are talking about is the Morel EM-428.
AllenB, it is odd that it has a lower F3 in a .0468 cu.ft. enclosure than a .5 when calculated using BassBox Pro.
But it is the only speaker of about 15 in my db that does that. Very odd.
I am sure some engineer has the answer.
Linesource, the bass section is .7, you bet. Getting mixed response about the Qtc of the mid though. Minimizing the reflected energy sounds reasonable. And I'll heed your warning about stuffing.
The mid is a 2nd order Butterworth with a zobel. X-over Pro models that flatter with a Qtc of .47 than .7. Not sure how to analyze that.....
AllenB, it is odd that it has a lower F3 in a .0468 cu.ft. enclosure than a .5 when calculated using BassBox Pro.
But it is the only speaker of about 15 in my db that does that. Very odd.
I am sure some engineer has the answer.
Linesource, the bass section is .7, you bet. Getting mixed response about the Qtc of the mid though. Minimizing the reflected energy sounds reasonable. And I'll heed your warning about stuffing.
The mid is a 2nd order Butterworth with a zobel. X-over Pro models that flatter with a Qtc of .47 than .7. Not sure how to analyze that.....
Attachments
I believe the Fs is 68hz, not 320. But I have seen that spec listed elsewhere, just not at the Morel site. I have yet to actually test the drivers; I've been using the data sheets. So I'm not even sure myself.
http://www.morelhifi.com/products/pdf/Midrange/EM/Specs sheet EM 428.pdf
And thanks much for the lesson! But I still am about my original question.
Will a low Qtc (.468) cause issues in the mid-driver section of the tower? The bass section is at .707.
http://www.morelhifi.com/products/pdf/Midrange/EM/Specs sheet EM 428.pdf
And thanks much for the lesson! But I still am about my original question.
Will a low Qtc (.468) cause issues in the mid-driver section of the tower? The bass section is at .707.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.