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Discussion Starter #1
I'm designing a 3 way speaker where the mid drivers (2 of them) will be too loud for the bass section. I will have to use resistors to reduce the mid section. My question(s) are these.

does the use of resistance in the xo degrade the sound quality. and how much resistance is too much to acheive a flat response?
there could be a descrepency of 6-8 DB between bass and mid before padding down is applied. I would like to use two mid drivers for head room and a cleaner sound at higher DB.
 

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I'm designing a 3 way speaker where the mid drivers (2 of them) will be too loud for the bass section. I will have to use resistors to reduce the mid section. My question(s) are these.

does the use of resistance in the xo degrade the sound quality. and how much resistance is too much to acheive a flat response?
there could be a descrepency of 6-8 DB between bass and mid before padding down is applied. I would like to use two mid drivers for head room and a cleaner sound at higher DB.
I think these are the answers you're looking for:
  1. I'd argue that everything that is put between the amp and the speaker will degrade the sound quality to some extent. Obviously that doesn't mean I think there should be "nothing" there, just that I have a prejudice for a less is more belief system.
  2. What I think you're trying to do is create an lpad. There are several online calculators. I found this one after a quick search. As with most calculations of this type, I look at the "answer" as a good starting point. Surpriisingly (at least to me) they're usually pretty spot on, but occasionally, some experimentation and measurements is in order.
 

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I could be misunderstanding the post, but it seems to me rather pointless to use two mid drivers when the sensitivity of a single one exceeds your requirements. Is there an issue with power handling and/or distortions that require doubling of the drivers?
 

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An MTM configuration is more than just getting the db boost from multiple mid drivers. Done properly, off axis response is improved and you are presented with a single source of sound -- the mid point between the drivers is the "center" which also happens to be where your tweeter is.

Usually, you need to pad the tweeter down, even with a MTM arrangement. Those must me some pretty efficient mids or one fairly inefficient tweet.
 

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Discussion Starter #5
JCD, 1/ The mid to tweeter sensitivity difference isn't too high. 2x mid drivers will give approx 94 db this is accounting for the 4ohm load when wired in parrallel, instead of 8 ohms. the tweeter will be 91-92 db. so some Lpadding will be needed for mids. YES I am looking to make a MTM D'Appolito config. but there is a woofer to be operating below the mids. crossed over at 300 HZ. the woofers I am deciding between are an 88 DB kevlar unit and 91.5 DB paper cone. I'm favouring the kevlar for its more rigid cone and higher x-max but it is too low in sensitivity + i don't want to use two of them because of size and expensehence the question of L-pads

Mario. Yes I am worried about distortion from the 4" paper TB mids and their power handling. but otherwise they sound great. plus the MTM appeals to me.
 

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Hi

Theoretically it should be ok to add some resistors. It seems you'll only have to lower the sensitivity by a few dbs to match the tweeter. I favour the MOX resistors, I can't say that they degrade the sound.

Could you give some more details on the drivers? The kevlar one seems to have a quite heavy cone, which would account for the rather low sensitivity. This probably is a knock out criteria in this case. The paper one sounds to me to be the better choice.

BTW: With the crossover in place you will again lose some sensitivity due to the coils resistance added in the signal path. Did you already account for that? The sensitivity of the bass will most probably suffer even more... Is there a possibility to use a larger bass driver?
 
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