Theoretical question concerning SPL /driver matching

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Hi,

Supposing that I have four (4) drivers (mid-woofers) of the same type whose SPL measures at 85 dB (1w), wired in series and parallel to maintain the same impedance (Z=8 Ohms, Re=6.5); also, the tweeter measures at 92 dB (1w) (Z=5 Ohms, Re=4.6).

How much attenuation should I use on the L-Pad for the tweeter?

I've run a few calculators, but am unsure what the SPL difference will be. At the moment, I'm willing to experiment to find what sounds best to my ears, but wouldn't mind a starting point based in theory.

Thanks in advance!
 
sreten said:
Hi,

The 4 drivers will be theorectically 91dB.

The answer to your question though depends on how good the design is.

:)/sreten.

It absolutely depends on the overall design, but I'm being told to pad the tweeter down by 8dB by someone who offers crossover design services (I wanted a sanity check on my design and this doesn't seem sane).

While I can admit to my amateur ideas that very well may flub the entire design, this confuses me as to why he would suggest it (and a second time after I expressed my concern that it seemed incorrect).
 
Cal Weldon said:
Doesn't sound correct to me either. If you like your top end, perhaps you don't need padding. If you wish to bring it in line with the woofer consider 2 dB as you never seem to get the theoretical 6 dB gain by grouping 4 drivers.

Noted, and thanks! I really just wanted a starting point so that I can tune to personal tastes with my own ears. In any event, I snagged a load of resistors of various values so I've got some flexibility.

I won't get into their total disregard about BSC or that they suggested 16 Ga. air-core inductors, which seems excessive (though I understand the DCR is lower) since I doubt they'll ever have more than 60-75 watts @ 8 Ohms applied.
 
Hi,

Well 4 drivers in series / parallel are never going to mate well with a tweeter.

In anything other than a box with a large and wide baffle you are
going to need baffle step compensation ~ 4dB to 6dB, this is also
assuming the drivers response is flat, usually its not and typically
there is rise in the midrange = more electrical EQ included in "BSC".

8dB of cut could be perfectly sensible, or not depending on circumstances.

:)/sreten.
 
sreten said:
Hi,

Well 4 drivers in series / parallel are never going to mate well with a tweeter.

In anything other than a box with a large and wide baffle you are
going to need baffle step compensation ~ 4dB to 6dB, this is also
assuming the drivers response is flat, usually its not and typically
there is rise in the midrange = more electrical EQ included in "BSC".

8dB of cut could be perfectly sensible, or not depending on circumstances.

The baffle is 5", and I'm about 99% sure it's going to need some kind of BSC. Still, their answer was that it is categorically unnecessary.
 
p0lar said:

The baffle is 5", and I'm about 99% sure it's going to need some kind
of BSC. Still, their answer was that it is categorically unnecessary.

Hi,

Who are they ? what are more exact details of the design ?
The drivers, box , c/o details etc.

A 5" wide baffle will have a very strong midrange lift.
Even more so if the 4 drivers start exhibiting line effects.

A single driver on a large baffle :
HIVI-B3S-FR.gif


The response in a 5" wide box :
audio-speaker18-channelmatching.gif


Ignoring below 200Hz, 200Hz to 2Khz is very different.

:)/sreten.
 
sreten said:
Who are they ? what are more exact details of the design ?
The drivers, box , c/o details etc.
I'm trying to be polite since it was a free service. I'll leave it at that since they were quite helpful otherwise. The drivers are HiVi B4N's, and I'll spare the details on how I acquired them or why I must use 4 on a 5" wide baffle (very long story), but let's just say I have very little to lose personally if it fails miserably! :) The enclosure is 22L, vented (tune at 50Hz), with 3/4" MDF.

At the original onset of design, and based on augerpro's farfield response plots of the B4N (which don't really agree with those of HiVi), I was planning to cross them at 3 KHz using a LR2 alignment to a HiVi K1. (my contribution at $12!)

I've got a LR2 on the tweeter, with a 1-2 dB L-Pad to start; plus a LR2 on the mid-woofers and a zobel. I was planning on adding BSC, but am unsure how much may be necessary. Is it possible to build BSC into the inductor on that circuit or am I looking at something far more problematic?

A 5" wide baffle will have a very strong midrange lift.
Even more so if the 4 drivers start exhibiting line effects.
Agreed!
 
Hi,

Well if you went MMMTM with 0.5 way on the bottom 2 MM's
you would need around 6dB attenuation on the tweeter.

due to line effects the above is your best option.

I cannot see your free advice making much sense,
BSC not needed but still 8dB ? assumes 4 drivers
are the same sensitivity as one ?

Note that 2nd order L/R should implemented acoustically.
You cannot use text book 8 ohm L/R filters. 3kHz is fine.

http://www.rjbaudio.com/Audiofiles/FRDtools.html
http://www.geocities.com/woove99/Spkrbldg/DesigningXO.htm

:)/sreten.
 
sreten said:
Well if you went MMMTM with 0.5 way on the bottom 2 MM's
you would need around 6dB attenuation on the tweeter.

due to line effects the above is your best option.
This option is most preferred from what I've gathered so far.


I cannot see your free advice making much sense,
BSC not needed but still 8dB ? assumes 4 drivers
are the same sensitivity as one ?
Yeah, I guess I get what I paid for -- except in the case of that HiVi K1 -- with a few trials, I was most impressed with what $12 could buy. I'm also interested in the new Vifa DQ25SC with the chance of crossing over a bit lower, but that's another story and I couldn't get one locally. Back on topic...

Note that 2nd order L/R should implemented acoustically.
You cannot use text book 8 ohm L/R filters. 3kHz is fine.
I was using some calculators based on the 5Ohm tweeter/8Ohm woofer impedance, but am unsure how to implement a LR2 acoustically vs electrically. I'll pore over those links and have made a note to get back to this. Everything I've done to date has been a simple MT based on others plans, with only minor electrical variations to BSC and/or L-Pads to suit personal taste or room variants. (aside from different enclosure experiments, heh, some of which have failed miserably)


Thanks for the info!!
 
Cal Weldon said:
Hmm... this is beginning to sound awfully familiar. :)

I was about to ask where you crossed them and with which alignment, but I think I found your post where you described using them in your HT setup ...


Originally posted by Cal Weldon on 09-08-2006 04:57 PM
I have the K1's in my HT system. I find them very good value for the money. To test them, I ran some Supertramp at about 100 watts. They are crossed over at 3K with a 12 dB. I don't think you have to worry about power handling. Heck of a tweeter for the money.

I don't think these will be driven anywhere near 100 watts, or not without the B4Ns becoming objectionable at the limits of their xmax, but it's good to know that's well within their range.
 
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