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Old 7th October 2008, 05:20 PM   #1
p0lar is offline p0lar  Canada
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Default Theoretical question concerning SPL /driver matching

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!
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Old 7th October 2008, 05:37 PM   #2
sreten is offline sreten  United Kingdom
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Hi,

The 4 drivers will be theorectically 91dB.

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

/sreten.
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Old 7th October 2008, 07:21 PM   #3
p0lar is offline p0lar  Canada
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Quote:
Originally posted by sreten
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).
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Old 7th October 2008, 07:28 PM   #4
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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.
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Old 7th October 2008, 08:06 PM   #5
p0lar is offline p0lar  Canada
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Quote:
Originally posted by Cal Weldon
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.
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Old 8th October 2008, 12:10 PM   #6
sreten is offline sreten  United Kingdom
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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.
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Old 8th October 2008, 03:44 PM   #7
p0lar is offline p0lar  Canada
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Quote:
Originally posted by sreten
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.
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Old 8th October 2008, 04:14 PM   #8
sreten is offline sreten  United Kingdom
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Quote:
Originally posted by p0lar

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 :
Click the image to open in full size.

The response in a 5" wide box :
Click the image to open in full size.

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

/sreten.
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Old 8th October 2008, 05:13 PM   #9
p0lar is offline p0lar  Canada
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Quote:
Originally posted by sreten
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?

Quote:
A 5" wide baffle will have a very strong midrange lift.
Even more so if the 4 drivers start exhibiting line effects.
Agreed!
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Old 8th October 2008, 06:10 PM   #10
sreten is offline sreten  United Kingdom
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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/Spk...esigningXO.htm

/sreten.
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