Center Channel Design Questions

[weinstro]

Hi,

I've been noodling through a center channel design for my brother that has some tight constraints: Height = 4.5 in., Depth = 5.0 in. Width is relatively unrestricted but should be less than or equal to the width of the TV, say 48 in. If I assume 0.25" stock, and have allowances for ports, drivers, etc., I arrive at an internal volume of 11 L. I also need to be able to match ZA5.3 left/right mains.

Given the acoustic lobing issues associated with horizontal orientations, I'm leaning towards a WW(T/M)WW configuration. Rather than a T/M, I'm thinking of using a full range driver with a 2.5 way xover, so WW-FR-WW. Hypothetically, I should be able to cross low enough to avoid serious living issues. Sound good so far?

In terms of drivers, I noticed that Tang Band has an ample selection of 3-4 in drivers. Based on some limited modeling, I'm thinking of 4 W4-1320SJF and 1 W3-2141, crossed at 8-900 Hz.

I have zero information on dispersion or distortion data for the Tang Bands, other than claims on the spec sheet.

Are these good driver choices?
Would you propose any alternative drivers?
Am I whistling in the dark?

Thanks and regards,

Rob

[rpb]

Re: Center Channel Design Questions

Hi,

I've been noodling through a center channel design for my brother that has some tight constraints: Height = 4.5 in., Depth = 5.0 in. Width is relatively unrestricted but should be less than or equal to the width of the TV, say 48 in. If I assume 0.25" stock, and have allowances for ports, drivers, etc., I arrive at an internal volume of 11 L. I also need to be able to match ZA5.3 left/right mains.

Given the acoustic lobing issues associated with horizontal orientations, I'm leaning towards a WW(T/M)WW configuration. Rather than a T/M, I'm thinking of using a full range driver with a 2.5 way xover, so WW-FR-WW. Hypothetically, I should be able to cross low enough to avoid serious living issues. Sound good so far?

In terms of drivers, I noticed that Tang Band has an ample selection of 3-4 in drivers. Based on some limited modeling, I'm thinking of 4 W4-1320SJF and 1 W3-2141, crossed at 8-900 Hz.

I have zero information on dispersion or distortion data for the Tang Bands, other than claims on the spec sheet.

Are these good driver choices?
Would you propose any alternative drivers?
Am I whistling in the dark?

Thanks and regards,

Rob

Just thinking out loud, but the RS100P might work.

[jhollander]

Re: Center Channel Design Questions

I'm not sure the 2.5 would be a benefit as there would be little baffle step. I've not looked at the drivers but the 1 W3 is not likely to keep up with the 2 or 4 W4s.

If you have PCD, without loading anything but the driver piston diameters and spacing distances you can play around with different filters and horizontal listening angles.

[[email protected]]

Re: Center Channel Design Questions

I like the idea but a real tweeter could work just fine.

[weinstro]

Re: Center Channel Design Questions

Just thinking out loud, but the RS100P might work.

They are on my short list - along with 12 other drivers. Unibox predicts lowish Z of 3 ohms for the RS100P-4. Response in 11 L shows 4 dB droop from 120 Hz to 60 Hz, then drops to -24 dB/octave. Might be OK once baffle and boundaries are factored in.

Is there an advantage with RS100 vs Tang Band W4-xxxx?

I'm not sure the 2.5 would be a benefit as there would be little baffle step. I've not looked at the drivers but the 1 W3 is not likely to keep up with the 2 or 4 W4s.

If you have PCD, without loading anything but the driver piston diameters and spacing distances you can play around with different filters and horizontal listening angles.

Preliminary research, based on threads in this forum where others have tread before I, indicated that a horizontal WWTWW with a 2-way crossover exacerbated lobing issues.... Agreed I'll need to simulate this in PCD.

That's the concept! What crossover type and frequency was used?

Regards,

Rob

[[email protected]]

Re: Center Channel Design Questions

About 3500 parallel /series.

[rpb]

Re: Center Channel Design Questions

Maybe you could mount the tweeter from the back side of the baffle, and cut a simple wave guide. This would allow a mid that can be a little larger, and that can cross lower in frequency to the woofers. Peerless makes a 4" HDS driver. The frame is truncated which will give you some extra space on the baffle. If a smaller mid is needed, check out the Vifa TC9. A Morel mdt39 is a little pricy, but takes up very little room, and is an excellent tweeter for crossing above 2.5k or thereabouts.

[chrisn]

Re: Center Channel Design Questions

A 3 way with a vertical TM or a coaxial driver would be ideal. Here are some mid and tweeter suggestions:

https://www.parts-express.com/dayton...frame--295-336
https://www.parts-express.com/dayton...-ohms--285-143
https://www.parts-express.com/dayton...4-ohm--290-204
https://www.parts-express.com/morel-...range--287-020
https://www.parts-express.com/dayton...eeter--275-025
https://www.parts-express.com/tympha...eter--264-1002

[Chris Roemer]

Re: Center Channel Design Questions

I think you NEED a tweeter (for dispersion - if your theater will only have one seat and dispersion's not an issue, then neither will be off-axis lobing). If your height is severely limited (but you still need bass), then your small drivers will need lots of Xmax (like ND105-4s, ND90-8s/AURA NS3-8s, or possibly ND91s).

[kevin007]

Re: Center Channel Design Questions

You could build a OS Center channel...



Kevin

[andy19191]

Re: Center Channel Design Questions

Given the acoustic lobing issues associated with horizontal orientations, I'm leaning towards a WW(T/M)WW configuration. Rather than a T/M, I'm thinking of using a full range driver with a 2.5 way xover, so WW-FR-WW. Hypothetically, I should be able to cross low enough to avoid serious living issues. Sound good so far?

A full range driver will have a bad high frequency directivity for those sitting off-axis. A better option might be something like this or equivalent. Not only would the high frequency directivity be substantially better it will also work comfortably down to 400Hz or lower enabling the handover to 2 or 4 purpose designed small woofer/subwoofers.

[rpb]

Re: Center Channel Design Questions

Here's a tiny tweeter that might work for you.

http://www.parts-express.com/tang-ba...-pair--264-841

[weinstro]

Re: Center Channel Design Questions

Lots of great suggestions to ponder!!

A 3 way with a vertical TM or a coaxial driver would be ideal. Here are some mid and tweeter suggestions:

https://www.parts-express.com/dayton...frame--295-336
https://www.parts-express.com/dayton...-ohms--285-143
https://www.parts-express.com/dayton...4-ohm--290-204
https://www.parts-express.com/morel-...range--287-020
https://www.parts-express.com/dayton...eeter--275-025
https://www.parts-express.com/tympha...eter--264-1002

I don't think I have enough baffle height (only 4.5") to pull off a vertical T/M, although I may have to give that MDM-55 and the two tweeters a closer assessment.

Maybe my thinking for the driver matching is flawed-
LR channels will be Zaph ZA5.3 MTM's. These max out at about 103 dB. So I was aiming to get the 4 "woofers" output up to this level or greater. For most 4" drivers, this isn't much of a challenge, but the real challenge comes with the full range driver.

I really wanted to like the TC9FD18-08, but the sensitivity is way below a quad of small woofers. The TB W4-1320SJF is a lot better, but it has high frequency dispersion issues. This leaves the TB W4-1805S which on paper and in simple modeling looks good, but will be more of a challenge to filter out cone breakup modes.

My two favorites for the woofers are the RS100-4 and the 830855. The other RS100's and the Peerless 830870 are contenders as well.

I looked at the OS center channel early on. I think the sensitivity of the B3N's are too low. But this is one of several designs where the woofers are crossed directly to a tweeter, w/o a dedicated midrange driver. Perhaps I should be thinking about doing that as well.....

Thanks,

Rob

[weinstro]

Re: Center Channel Design Questions

I have some Response Modeler questions:

1. I have boundary and baffle diffraction FRD's for each driver position. However, my combined box volume for 4 woofers in series-parallel is 13L. In Response Modeler, series-parallel isn't an option, so how do I handle this scenario? Can I model two woofers in parallel with half the box volume? Would I need to adjust the port size for modeling purposes? Are there other options?

2. I'm confused about measured vs. modeled impedance. The documentation indicates that the purpose of the impedance modeling is to match the inductance curve of the driver. In the case of the RS100-4, I can use the provided ZMA files (which presumably originate from a measurement), trace a graph, or measure one myself. All approaches will result in a free-air impedance curve that includes the driver's inductive impedance rise at higher frequencies. So, what does the modeling fulfill? I can understand if we're trying to make sure that the inductive rise is still there after the box impedance is added, but isn't this a low frequency effect? I have a very curious mind - I would appreciate it greatly if someone could please explain what problem is being addressed here.

Thanks and regards,

Rob

[jhollander]

Re: Center Channel Design Questions

You can model each driver individually in 3.25 liters with the same box tuning (FB). In PCD you would combine the woofers in series parallel. Having individual driver files will work the best when looking at off axis summations.

For the impedance files use the modeled with the TS parameters and the 3.25 liters box and same box tuning.

The modeled simulation shows the box effect on the driver’s impedance.