Zilch's AK Design Collaborative - Econowave Speaker

[DigitalChris]

Thanks for looking that up for me

As far as testing the compression driver, when you say a protective cap, do you mean a capacitor that I put in line with the speaker wire? I'm a little unsure how to test the compression driver alone.

Also, am I testing the compression driver for that hump at 2khz, or am I testing the compression driver for the high-frequency roll off? All three of them seem to roll off at a fairly similar rate but with a difference in decibel level. What could be the reason for that?

 

[DigitalChris]

Chris, back up and get the driver in the waveguide measured with no crossover in a way that matches what's already posted here and elsewhere. You would probably be best off going straight to gated measurements in HolmImpulse, ARTA, or etc. Then, go to measurements of just the driver in the waveguide with the crossover (still gated), and see how that compares.

Sorry dumptruck, I didn't mean to skim over your post or not comment on it, but you went way over my head when you started talking about gated measurements in HolmImpulse, ARTA, etc. If you still feel this is something I should look into, would you mind explaining what these techniques are?

Another thing I meant to ask is about the high-frequency pot I have on the back of the cabinet. There was something in the plans saying that if I were to use drivers other than the ones listed, I would then adjust the pot to match the high frequencies to the mid and lower frequencies? The instructions said that turning the pot all the way up would be the same as jumping two points on the board and is fine to do when using the planned components.

 

[skywave-rider]

Thanks for looking that up for me

As far as testing the compression driver, when you say a protective cap, do you mean a capacitor that I put in line with the speaker wire? I'm a little unsure how to test the compression driver alone.

Also, am I testing the compression driver for that hump at 2khz, or am I testing the compression driver for the high-frequency roll off? All three of them seem to roll off at a fairly similar rate but with a difference in decibel level. What could be the reason for that?

The protection cap is merely a single pole filter which cuts lower frequencies. You put it in series with the compression driver. Either terminal, but the positive is standard. So direct out of the amp, but one side, the pos side, has the cap in series.

The value of the capacitor will determine where the rolloff of lows occurs. That will be gradual, since it is a first order filter. You ideally want to pick your frequency about an octave below your intended frq of use. This will protect the compression driver from being driven at too low a frequency, where it's not intended to go. Also, when you turn on or off the amp, you might get a big low frequency thump which will deliver a lot of low frequency energy and, unfiltered, that is a potential cause of driver failure.

4343 and I suggested some values in this post:
http://www.audiokarma.org/forums/showpost.php?p=5741090&postcount=14478

I think it would be cool if we could both run the tests and compare. I could cobble together some caps to equal about 30uF. I also just found some 33uF NPE (non polarized electrolytics) which are not good quality for speaker crossovers, especially HF, some say, but might be OK for a rough test of the compression driver. If you don't have decent crossover (film) caps totaling 33 or so uF, let me know. I can mail you a 33uF NPE. PM your address if you want me to send it.

 

[DigitalChris]

Can I use this and this in line with each other to protect the compression driver? I can also check in store to see what others they offer but worst case, maybe I can use these together.

 

[dumptruck]

it dipped quite a bit between 1khz-8khz.

Did you save that one? To make your nonpolar cap like you are asking about, you'll need much larger values than 10 and 22. That would only be ~7uf in series, which is a higher crossover point than you want.

...gated measurements in HolmImpulse, ARTA, etc. If you still feel this is something I should look into, would you mind explaining what these techniques are?

That's how you keep reflected sound from the room out of your measurements. It's more important for designing a speaker, but since the most of the ewave measurements were done this way, it would make sense to compare apples to apples. It's probably not essential for sorting out this treble roll-off problem.

Another thing I meant to ask is about the high-frequency pot I have on the back of the cabinet. There was something in the plans saying that if I were to use drivers other than the ones listed, I would then adjust the pot to match the high frequencies to the mid and lower frequencies? The instructions said that turning the pot all the way up would be the same as jumping two points on the board and is fine to do when using the planned components.

The L-pad should be adjusted until you get a response that looks close to this (red line):

Since you're getting abnormal high frequencies right now, that's hard to judge, but see the small peaks at 1k and 2k above? If you turn yours down, I think you might see the same thing.

 

[wiredbecker]

AK, I missed you earlier....

I did too! I was out on vacation for 2 weeks with my gal and when I got back the board was down. :tears:

Glad to be back online again. Very glad to see you and Dumptruck holding down the fort here in the Econowave thread!

I have some serious reading to do...

 

[DigitalChris]

Did you save that one? To make your nonpolar cap like you are asking about, you'll need much larger values than 10 and 22. That would only be ~7uf in series, which is a higher crossover point than you want.


That's how you keep reflected sound from the room out of your measurements. It's more important for designing a speaker, but since the most of the ewave measurements were done this way, it would make sense to compare apples to apples. It's probably not essential for sorting out this treble roll-off problem.


The L-pad should be adjusted until you get a response that looks close to this (red line):

Since you're getting abnormal high frequencies right now, that's hard to judge, but see the small peaks at 1k and 2k above? If you turn yours down, I think you might see the same thing.

Thanks for the reply, I understand about gated measurements now.

My L-Pad is adjusted full open right now, I can't turn it up any more. Are there a reason that you can gether from my graph that would point toward me turning it down?

As far as the cap goes, if I had to add multiple caps in series, what would I look for if I can't find one thats close to 32uf?

 

[DCinDC]

I understand about gated measurements now.

I don't. Can someone splain me?

 

[DigitalChris]

Also, as far as I have read before I built these baby's, these cabs have no problem being flush mounted into the wall like I have them? They stick out a good inch though and are not toed in at the moment, do you recommend I toe them in? I didn't read too much on whether or not this design requires toe in.

Also, when I treat the wall these are mounted on, is it ok for the fiberglass to protrude past the surface of the speaker baffles? I'm not sure if this will hurt it's response or not.

Thanks

 

[dumptruck]

My L-Pad is adjusted full open right now, I can't turn it up any more. Are there a reason that you can gether from my graph that would point toward me turning it down?

Two things:
1. Since there is something weird in the upper treble of your graph, I'm looking at 1-3kHz for where the L-pad should be. It looks about 4dB too hot there, so that's what points toward turning it down.
2. Seriously it's all the way up? Something is very wrong. Even after the CD compensation, the tweeter should be around 10dB louder than the woofer until turned down by the L-pad...

Also, the design is intended to be toed in very steeply to point at a little in front of the expected listening position. This is what gives them extra clear imaging and lets them keep an even stereo image as you move side-to-side. The latter will be lessened for sure if they are not toed in, the clarity in general will only be lessened to the extent that you have too much side wall reflections or not. Other than that issue, flush mounting should be fine, although response would be a little different (nothing like we're seeing your measurements). Can we see the measurement with the tweeter polarity switched?

 

[skywave-rider]

DigitalChris,
Let me know if you want the 33uF cap, I'll mail it.
I think we should compare HF. No crossover.

 

[skywave-rider]

I don't. Can someone splain me?

Basically, gating sets a time window. Your measurement data is then limited to that time constraint. The concept is to allow enough time for the direct sound from the speaker to arrive at the measurement position, but cut off the measurement before reflections arrive at the mic. The reflections take longer because the path is longer, not line of sight.

These kind of measurements are referred to as "semi anechoic."

The cutoff part of the gate, where the window closes, can be abrupt, or rectangular (squared off) or have a slope. Zilch often used a "half hanning" window which has it's characteristic shape. I can post some examples showing what the 2 look like.

The thing to remember is that the gate pretty much determines the frequency range where your readings are reliable.
For example:

A gate of 2.6 ms will give you a resolution down to about 380Hz.
A gate of 3.6 ms will give you a resolution down to about 277Hz.

You set the gate by closely looking at the impulse response graph for blips after the direct impulse. Those are reflections, echoes. And you want to exclude them when setting the window time. You can also do it with trig. It's pretty easy, though not the trig, for me.

Here are measurements from my current main speakers at home. (JBL 123A-1 woofers in sealed PE KDT with QSC 152i on top (DE250 driver and modified 4Pi crossover.) [Gate set to 2.61 ms/383.48 kHz.] The theory on the shape of the gating is that some contours transition better outside the gate time. I generally only use the data within the window, so I have not been concerned with the shape much.

Half Hanning:

Rectangular:

If you use the half hanning window as your standard, my speakers are within +- 1.5dB with a gentle downward slope toward the highs. That's what Zilch would call "done."
I hope this is helpful.

 

[DCinDC]

Ok, got that. Now what equipment has that feature?

 

[dumptruck]

It's a software, i.e. mathematical, process, not dependent on equipment.

 

[skywave-rider]

Yes, what dumptruck says.
He posted earlier some free software which have gating features.
As for my "system," I use Fuzzmeasure software, which is for MAC.
I also use a calibrated mic from Cross Spectrum Labs.
I usually use a Tascam US144 interface.
Fuzzmeasure allows the use of calibration files and has a loop-through feature which will correct for response variables within the interface.
So it's pretty damn amazing how accurate you can get with a low buck investment. It's more about the technique and interpretation after a certain point.

 

[Zonker92]

On another note, there is a pair of C60 Sovereign cabinets on eBay right now. Empty boxes in Southern California, for local pickup only. Talk about the ultimate eWave!

 

[DigitalChris]

First graph shows fully open pot (purple) vs 3/4 open pot (green)...

This graph shows polarity change. Normal polarity which by instructions is normally reversed anyway, so positive to negative (purple) and swapped polarity, positive to positive (green)...

 

[dumptruck]

Okay so in your reverse (or reverse-reverse, as it were) polarity that's a fairly clear notch at maximum driver overlap, so that's good. We should really be focusing on the HF, but just because it's bugging me, your L-pad should be set more like this (not the best mouse-drawn line, but you get the idea):

 

[aedaza]

Hi everyone,
Is there a project anywhere with these characteristics?
Econowave, DIY for the cab and woofer and budget conscious

I want to have a nice speaker that has the Econowave on it, but I dont have currently a set of good old speakers to match it, so I was wondering if DIY the whole speaker (Econowave+Woofer) is a good way to go, while being still budget minded as the Econowave is in spirit.

What do you guys think?

 

[dumptruck]

How budget conscious? The cheapest one is the "standard kit" that DigitalChris is working with above there, which I think comes to $300-400/pair.