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[Tim Duffin]

So, you want to use them for outdoor shows.  I wouldn't  recommend that unless you somehow can have 4 on one side and 4 on the other--
The reason is because they do not behave like a front loaded 2x18 cabinet outside.  The bass seems to dissipate much faster in front of the horns as you walk away than with a stack of say--4JBL 4719x cabinets.  In fact, I had placed 4 servo's in a cluster outside and was not at all impressed with their performance far away.  

Conversely, I placed 2 4719x cabinets stacked on each side of the stage at the same venue and found that they were MUCH louder far away than the servos.  up close (5 feet) there is just nothing that can describe the feeling....hmm...well... imagine the ground being pushed down under your feet and causing your leg muscles to involuntarily force you to hop backwards slightly and add to that your eyeballs unable to focus on anything and the impending headache because its difficult to breathe.

It's easy to test out servo's before you buy them.  Plug them in, if any of them make a farting sound--dont buy them or open it up and look at the module.  Even if I didnt use them I would purchase them in a heartbeat just so you could say "I have the most powerful subwoofer ever created"  Which generally tends to sound impressive to customers even if they don't rent them.

Tim

[John Halliburton]

"The bass seems to dissipate much faster in front of the horns as you walk away than with a stack of say--4JBL 4719x cabinets. In fact, I had placed 4 servo's in a cluster outside and was not at all impressed with their performance far away."

I'd really suspect that they were not set up properly-that is not the norm.  As Tom Danley has pointed out before(and others), the radiating area of the mouth vs. cones causes the "less intense" feeling up close.  However, at distance I have heard it and measured the difference, the BT7, Labhorn, BeDeep(and other horn loaded subs) hold up much better, that is one reason Tom measures at 10 meters and calculates efficiency back to 1meter, to get a more meaningful figure.

"The BT7 are rated at 800Watts "Peak RMS" for 15 Seconds"

Antone, this is a pretty robust figure too.  However, as long as you're not clipping the amps that you have, you're good.  It is fairly common practice to use 2X the continuous power rating for the amp channel, so a Macrotech 2400 is a nice match, as one channel into a 4ohm load produces 750watts continuous(at 20-20khz, the more conservative spec).  Better to have the clean headroom.

Best regards,

John

[Adam Mottley]

Thanks for all of the informative replies. You guys are great.

After careful review, I have decided not to get the ServoDrives based on size and weight considerations. At 45"x45"x22.5", four BT-7's are just too much for my current truck pack.

If anyone wants to check out this deal, check here:

http://www.soundpro.com/SpecDetail.asp?ID=187

Priced @ $495, USD, this deal seems hard to beat if someone is in the market for four BT-7's.

Thanks again for all of the help.

Adam

[edit] removed image

[The Guy]

John Halliburton wrote on Sun, 09 October 2005 20:51

To JimB's comments about not having a lot of punch(kick drum in the 70hz region is how I interpret that), I've not had that problem-I think the fact they have a lower cutoff than many other subs causes the balance of the sub to sound "different", and the lower distortion output probably contributes as well.

John,

I agree with you totally.  I wasn't at all ragging on the subs.  As a labhorn user myself I understand that the lack of harmonic distortion can be interpreted as lacking 'punch.'  I was advising that (like a LAB) they should not be run up too high in the crossover point, as they tend to get that "not so good" sound going.  IMO, the BT7's really rock in the 30-60 range.  Additionally, when I've mixed on them (not my PA) time alignment may have been an issue.  But man, down low....damn!

-JB

[John Halliburton]

Jim,

No problem.  There are so many variables that it can be almost impossible to determine anything without actually being there and working through things.  You point out another very realistic possibility-the time alignment with the top boxes.

Take care,

John

[ThomasDameron]

JB and everybody else,

I haven't heard or mixed on bt7's but I understand what you're saying about keeping the x-over low.  How high do you think would be reasonable?  Do you think 110-120hz would be acceptable or does it really need to be 70-80hz?

thanks,
thomas d.

[Chris Davis]

ThomasDameron wrote on Mon, 10 October 2005 22:40

JB and everybody else, I haven't heard or mixed on bt7's but I understand what you're saying about keeping the x-over low.  How high do you think would be reasonable?  Do you think 110-120hz would be acceptable or does it really need to be 70-80hz? thanks, thomas d.

I think they could probably be run as high as 80 Hz, 100 if you are covering for some bass shy tops.  Overall the sound down from the very bottom up to 60-80 is very pure.  Moreso than with other types of horns.  At higher frequencies, not the servo transducers, but the horn itself starts to do strange things with reflections and in my opinion start to get muddy.  This seems to me to be a phenomenon exhibited with ANY bass horn (not just the BT7).  So if you do operate it up to 100 - 120 or so the upper bass will not sound the same as if you had boxes designed to play in that range.  It will at least still have power up to 100 Hz though.

I think they are doable up to 100 Hz but I also EQ them some and don't push them that hard either.  I have found that replacing the foam tape inside where the wooden servo module seals up against the mouth of the horn will greatly improve the upper bass response.  Easy enough to get in there and do it, and while you are at it you can inspect the module too.

I do agree with the blanket statement of keeping the crossover low when using horn loaded subs.  I would say you should at least start off with  80-90 Hz or so and see how good that sounds before you start tweaking.  You might actually be more satisfied with having a little bit of a frequency "hole" in the upper bass instead.

Chris

[Ivan Beaver]

ThomasDameron wrote on Mon, 10 October 2005 22:40

JB and everybody else, I haven't heard or mixed on bt7's but I understand what you're saying about keeping the x-over low.  How high do you think would be reasonable?  Do you think 110-120hz would be acceptable or does it really need to be 70-80hz? thanks, thomas d.

Many times people confuse electrical xover and acoustical.  The electrical is often lower than the acoustical (in the bass/sub region).  Since subs are typically run at a ligher level (to compensate for the Fletcher/Munson curves of our ears) the point at which they "cross over" to the upper cabinets is higher than the electrical crossover point.  I would suggest the highest slope low pass you have.

And these are SUB cabinets-not bass cabinets, so they are not intended to used that high.

[Chris Davis]

Ivan Beaver wrote on Tue, 11 October 2005 07:33

ThomasDameron wrote on Mon, 10 October 2005 22:40 JB and everybody else, I haven't heard or mixed on bt7's but I understand what you're saying about keeping the x-over low.  How high do you think would be reasonable?  Do you think 110-120hz would be acceptable or does it really need to be 70-80hz? thanks, thomas d. Many times people confuse electrical xover and acoustical.  The electrical is often lower than the acoustical (in the bass/sub region).  Since subs are typically run at a ligher level (to compensate for the Fletcher/Munson curves of our ears) the point at which they "cross over" to the upper cabinets is higher than the electrical crossover point.  I would suggest the highest slope low pass you have. And these are SUB cabinets-not bass cabinets, so they are not intended to used that high.

Hi Ivan, I was just curious, is there a horn-loaded "woofer" you or someone else  might have personal experience with and recommend to bridge the gap between a large-format horn-loaded sub (similar to LabSub or BT7) and oh...say 200-300 Hz?  This is for a club system where the tops (horn-loaded dedicated mid-high) are already purchased but just need to be filled out.  Size is not an issue.  I am not the one calling the final shots on this, but just looking for some feasible options to bring to the table.

Thanks
Chris

[E2]

Test tracks...

I use Al Dimeola's Scenario Album, track titled Cachaca... has short accents in the 35 - 40hz range. A real head turner.