# Crossover help



## jszmgpolk (Jun 17, 2009)

I am going to be building inwall surrounds for my theater setup. I will be using the following components in a 2-way design. I need help in designing a crossover and was wondering if someone could help. These will only be used for surround speakers only. Also I am open to different components and want to limit my budget to around $200-300.

Dayton Audio DC28F-8 1-1/8" Silk Dome Tweeter
Part # 275-070
Resonant Frequency (Fs)637.2 Hz
DC Resistance (Re)5.50 ohms
Voice Coil Inductance (Le)0.09 mH
Mechanical Q (Qms)0.82
Electromagnetic Q (Qes)0.90
Total Q (Qts)0.43




Dayton Audio ND140-4 5-1/4" Aluminum Cone Midbass Driver 4 Ohm
Part # 290-216
Resonant Frequency (Fs)54 Hz
DC Resistance (Re)3.7 ohms
Voice Coil Inductance (Le)0.72 mH
Mechanical Q (Qms)6.59
Electromagnetic Q (Qes)0.74
Total Q (Qts)0.66
Compliance Equivalent Volume (Vas)0.36 ft.³
Mechanical Compliance of Suspension (Cms)0.97 mm/N
BL Product (BL)3.9 Tm
Diaphragm Mass Inc. Airload (Mms)9g
Maximum Linear Excursion (Xmax)4 mm
Surface Area of Cone (Sd)86.6 cm²


----------



## ngjockey (Jul 29, 2013)

Essentially, infinite baffle. This means you can SPLTrace factory frequency response and impedance curves and get pretty close, without measuring tools. Dayton specs are fairly reliable and consistent. Import those traces into PCD7 (free) or WinPCD (if you don't have 32 bit Excel). You also have to input polars and z axis offsets. For a flat baffle, the z-axis of a 5-1/4 can be guesstimated as -21mm although these programs expect that in meters. From there, you get to play. You won't need BSC. With a flat baffle, expect to use assymetric slopes, ie: 1st/2nd electrical or 2nd/3rd. You should also know what a Zobel is and try simulating that, particularly on the low pass. There are a few ways to pad a tweeter, series before xover, lpad after xover and split. You'll see how in phase you're getting by checking the reverse null. That's also useful for determining the best crossover point. It'll tend to "lean" in the direction it wants to be.

For box/port sizing you can use WinISD or calculators or simply follow manufacturer/distributor recommendations. All this can get decent results in this IB context, but still less than the ideal of actual measurements. Still, a lot better than using off-the-shelf crossovers or just a calculator. An OmniMic (or equivalent) and DATS or WT3 are good investments because, once you start building speakers, ...


----------



## GranteedEV (Aug 8, 2010)

Although ngjockey is spot-on with his comments about simulating a design, I still recommend getting yourself some measurement gear. You will want at least a measurement mic/preamp and something to measure impedance with. 

One thing neglected in the above post is the effect of baffle diffraction / step losses.


----------

