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Multi-Way Conventional loudspeakers with crossovers

First attempt at designing a speaker and crossover. I'm sure that I've done it wrong.
First attempt at designing a speaker and crossover. I'm sure that I've done it wrong.
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Old 12th May 2018, 10:34 PM   #1
JustinRT is offline JustinRT  United States
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Default First attempt at designing a speaker and crossover. I'm sure that I've done it wrong.

Hey all,

I am going to be putting up a front projector, and in order to have the screen as big as I'd like, I'm going to have to use an acoustically transparent screen and place the speakers behind it. Rather than using in-wall speakers, I'd like to try my hand at designing and building an L/C/R set that will fit behind the screen, get decently loud, and sound good.

I am very new to diy speaker building -- having only just started seriously researching the topic in the last couple days -- so I'm sure that I've made mistakes in my initial design. I'm totally open to any advice/critique you can offer -- up to and including scrapping my current design/driver choices and doing something completely different (although, size and cost are concerns).

My idea is to make three identical MTMs that will mostly fit in cavities that I will cut into the wall, which is framed with 2x4s (there is some wiggle room, as I can build the projector screen to sit some ways off the wall). The drivers that I've designed the enclosure and crossover around are the Dayton Audio DS135-8 5" woofer and the Tymphany XT25BG60-04 1" tweeter. Will 5" drivers work for my needs, or should I be looking 6" or even 7" drivers? (Maybe the 6 1/2" Dayton Audio DC160 or the 7" RS180 -- although, with a larger woofer, would the super shallow depth cause more problems?)


First, the enclosure:

Click the image to open in full size.

I got the dimensions from the product page for the woofer on Parts Express, which lists the golden ratio ported cabinet dimensions as: 10-3/4"H x 6-5/8"W x 4-1/8"D, with a 1" dia. x 4"L port. I'm using a ported design, as I plan to cross these speakers over with my subs at 80 - 85 Hz, and it is the only way to get the low-end extension that I need with these woofers.

So, I just took the dimensions from Parts Express and essentially designed separate enclosures for each woofer within the cabinet. Is there a downside to building the cabinet this way? Also, am I going to regret going with a ported design?


The crossover:

I am sure that I am completely out of my league in trying to design a crossover, but I gave it a shot anyway. I'm just going to post a bunch of graphs and hope that you guys can tell the ways that I screwed up (and hopefully how to fix it ).

Schematic:

Click the image to open in full size.

Frequency Response with Phase Curves:

Click the image to open in full size.
It drops down 2-3 dB at around 5 kHz. If I changed the resistors in the high-pass to two 2 ohm resistors in parallel, the line stays pretty flat at 90 dB; however, if I do that, I'm worried that I'll deliver too much power to the tweeter. Any suggestions?

Regarding phase: I left the phase source "as measured" (as opposed to "derived"), but I don't know which way it should be done. So, the phase may be inaccurate.

Impedance:

Click the image to open in full size.
Am I going to be in trouble because it dips slightly below 4 ohms at 200 Hz?

Transfer Function (I think):

Click the image to open in full size.
I have no idea what I'm looking at here, So I have no idea if this graph looks bad.

Component Power Dissipation (with 100 W fed through the crossover to the speakers):

Click the image to open in full size.
This shows that the resistors are getting 20 W, but the resistors that I was looking at buying are only rated at 10 W; is this going to be a problem? Do I need to run four 8 ohm resistors in parallel instead?

----

Sorry for such a long post; if you made it all the way through, thank you.

I've been having a lot of fun learning about speaker building, and this forum has been a huge part of that. Any and all advice you can give will be greatly appreciated. Assuming that I can come up with a design that will work, I'm really looking forward to building my first set of speakers.
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Old 12th May 2018, 10:39 PM   #2
eriksquires is offline eriksquires  United States
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The crossover and design looks good.... but!

You need to measure in cabinet. Since this is a two way, I recommend you stick to far-field, gated. Measure the drivers in place.

Make sure you re-measure the impedance of the woofer.

Best,


E
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Old 12th May 2018, 10:54 PM   #3
Dave Bullet is offline Dave Bullet  New Zealand
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Quote:
Originally Posted by JustinRT View Post
Regarding phase: I left the phase source "as measured" (as opposed to "derived"), but I don't know which way it should be done. So, the phase may be inaccurate.
I'm assuming your FR curves are from someone elses design or manufacturers specifications?

The only valid scenario to use "as measured" is if you actually measured the drivers in cabinet and did not move the mic between measurements

Otherwise you should use dervived, where you extract minimum phase and include a Z plane offset (to account for voice coil recess of the woofers).

So not quite back to the drawing board, but you have to get your data right for simulation to be correct.
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Old 12th May 2018, 10:54 PM   #4
JustinRT is offline JustinRT  United States
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Quote:
Originally Posted by eriksquires View Post
The crossover and design looks good.... but!

You need to measure in cabinet. Since this is a two way, I recommend you stick to far-field, gated. Measure the drivers in place.

Make sure you re-measure the impedance of the woofer.

Best,


E
Thanks for the response. That seems like great advice. It will be awhile before I can take these measurements, as I'll have to wait until the room is built. I suspect that I should also have the screen in place in front of the speakers before I measure them.

Is using a multimeter to measure the impedance accurate enough?
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Old 12th May 2018, 10:58 PM   #5
kevinkr is offline kevinkr  United States
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First attempt at designing a speaker and crossover. I'm sure that I've done it wrong.
Other than the tweeter levels coming up a few dB it looks like a starting point. You could consider MiniDSP hardware and a couple of amps and go fully active which would allow you to easily tune the system response to the drivers, room and your preferences.

Subwoofer may be a worthwhile investment for FX. (Kits exist)
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Old 12th May 2018, 11:00 PM   #6
kevinkr is offline kevinkr  United States
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First attempt at designing a speaker and crossover. I'm sure that I've done it wrong.
Quote:
Originally Posted by JustinRT View Post
<snip>

Is using a multimeter to measure the impedance accurate enough?
You cannot measure driver impedance with a multimeter.

Something like this is required: Dayton Audio DATS V2 Computer Based Audio Component Test System
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Old 12th May 2018, 11:16 PM   #7
JustinRT is offline JustinRT  United States
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Quote:
Originally Posted by Dave Bullet View Post
I'm assuming your FR curves are from someone elses design or manufacturers specifications?

The only valid scenario to use "as measured" is if you actually measured the drivers in cabinet and did not move the mic between measurements

Otherwise you should use dervived, where you extract minimum phase and include a Z plane offset (to account for voice coil recess of the woofers).

So not quite back to the drawing board, but you have to get your data right for simulation to be correct.
I got the frd/zma files for the woofer from the product page on Parts Express. For the tweeter, I used a program called FPGraphTracer, and got them from the spec sheet on the product page.

I assumed that I would need to use derived, but I'm not sure what I should input for the tails and frequency slope settings. I'll have to try to find some documentation or something.

I just guessed at 1/3 inch z plane offset, but obviously I'm going to have to buy the drivers and measure them.
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Old 12th May 2018, 11:19 PM   #8
eriksquires is offline eriksquires  United States
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Quote:
Is using a multimeter to measure the impedance accurate enough?

No. The impedance is a curve, not a single point. I use an OmniMic/DATS package, but you can also use Room EQ Wizard with some hacks.

Impedance Measurement

I find the DATS package accurate and well worth it.


Best,

E
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Old 12th May 2018, 11:21 PM   #9
eriksquires is offline eriksquires  United States
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One other thing. The woofers and tweeter are far to wide apart. You do not need to build a separate enclosure for the tweeter.

The two woofers may share an acoustic space so long as the signal to them is identical.

Best,

E
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Old 12th May 2018, 11:22 PM   #10
JustinRT is offline JustinRT  United States
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Quote:
Originally Posted by kevinkr View Post
Other than the tweeter levels coming up a few dB it looks like a starting point. You could consider MiniDSP hardware and a couple of amps and go fully active which would allow you to easily tune the system response to the drivers, room and your preferences.

Subwoofer may be a worthwhile investment for FX. (Kits exist)
I'll definitely look into going with a minidsp. I planned to buy one to use as a peq for my subs.

Can a single minidsp be used for all three L/C/R speakers?
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