# Desktop Open Baffles



## killa12222 (Jun 8, 2011)

Just thought I share my little project I made out of boredom with leftover MDF from my TH build. Nothing fancy but it does sound real nice on instrumental music. Function over form imo 

Will neaten it up and give it a coat of black paint sometime in the future, but I am pretty happy with it at the moment.

The drivers used had no labels whatsoever but it came off a china made "Coby" tower speaker. 

XO Setup: 
6 db/octave passive hi-pass @ 2500hz for the 1" tweeters
24db/octave active hi-pass @ 70hz for the 6.5" woofers
Smoothed out the overall response using the kX DSP parametric equaliser.











The video was recorded using my really old Sony digital camera but the audio was from a Behringer C1-U condenser mic.

Comments and improvement suggestions appreciated


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## Theresa (Aug 23, 2010)

You may have lots of distortion from that tweeter with just a 6db/octave crossover at that frequency.


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## killa12222 (Jun 8, 2011)

Sounds fine to me. I think the actual XO frequency might be higher. 2500hz was a rough estimate.


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## fusseli (May 1, 2007)

Theresa said:


> You may have lots of distortion from that tweeter with just a 6db/octave crossover at that frequency.


Might not be so bad, I bet those are rarely getting over 1W sitting right in front of his face like that!

Do you not have any LPF on the woofer to soften its breakup modes? With a woofer that cheap I doubt it's natural response is a nice smooth roll-off. Do you know when their response starts peeling off? Having those open ended up high is even a batter reason to put your tweeter HPF up a lot higher since it's role in such a setup is just top add some top end sparkle. I'd try a few kHz higher and see how it sounds.

Also, that's the most rediculous mousepad I've ever seen.


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## Theresa (Aug 23, 2010)

You might be right about being loud enough in the near field. The thing is that at 6db/octave, its only down 12db at 600 Hz. Then again the OP states the crossover might be higher than that.


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## killa12222 (Jun 8, 2011)

fusseli said:


> Might not be so bad, I bet those are rarely getting over 1W sitting right in front of his face like that!
> 
> Do you not have any LPF on the woofer to soften its breakup modes? With a woofer that cheap I doubt it's natural response is a nice smooth roll-off. Do you know when their response starts peeling off? Having those open ended up high is even a batter reason to put your tweeter HPF up a lot higher since it's role in such a setup is just top add some top end sparkle. I'd try a few kHz higher and see how it sounds.
> 
> Also, that's the most rediculous mousepad I've ever seen.


Nope, there is no LPF on the woofer because I have no idea how to wind inductors.. Pardon my newbiness but how does a breakup mode sound like? I'll do a couple of sweeps in REW in the morning (12.30am over here)

Yep, it is unnecessariy large but I got it real cheap and it works well .


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## fusseli (May 1, 2007)

It will likely sound harsh.

The breakup modes are where the upper response starts to diminish. Instead of a nice rolloff like bass frequencies do, the response often is full of sharp peaks and deep nulls as the big cone tries the highs. Here's an example http://www.parts-express.com/pdf/290-300.pdf Notice how big the mode at 4.5kHz is, and how rocky the response gets!


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## killa12222 (Jun 8, 2011)

Ah, I see! 

Here are the sweeps with 1/48 smoothing. The woofer was measured at 15cm with the tweet disconnected. The tweeter was measured with the existing XO in place and woofer disconnected. Mic used was the Behringer C1-U.



During the sweep, I heard the tweeter 'crackle' a little bit which I assumed was distorting. 

Thoughts?


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## Theresa (Aug 23, 2010)

somehow get an inductor that will work with the cap to make it a 12db/octave filter at maybe 3000 Hz or so. There are all sorts of free programs available that will help you find the correct value for crossover networks. Building speakers is usually far more complex than a newcomer expects.


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## fusseli (May 1, 2007)

Yikes. Ya, look at that huge resonance spike on the tweeter at 1.5k. That needs to be tamed! Crackling was probably the tweet trying to play down low since it looks like you gave it a full range sweep. You can see your woofer breakup, I'd say that for sure needs some kind of LPF. You could try a simple first order LPF, which is just a series inductor. Is the bottom (pink) graph both playing together?

Looks like you can also _see_ your baffle step at 500Hz and below. Take care of some BSC and that should liven up the midbass and bass considerably.


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## killa12222 (Jun 8, 2011)

Alright. So I will be crossing the woofer and tweets at 3000hz using a 12/db per octave XO. Now I just have to get me some nice polypropylene caps.

Yes, I had to bring the upper frequencies <300hz down by 6db. Sounds pretty good actually. Will post another sweep with all the EQ included.


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## Theresa (Aug 23, 2010)

Congratulations for all you've learned. Fun, isn't it?


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## killa12222 (Jun 8, 2011)

Wow, this looks erm rocky? Measured from listening position which is about 3ft away. Strangely, they still sound pretty good :blink:


Here is my EQ settings tuned based on REW sweeps and by ear. The EQ on the left just attenuates the treble. 


Crossover is set at 70hz @24db/octave.



Theresa said:


> Congratulations for all you've learned. Fun, isn't it?


It has been indeed


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## GranteedEV (Aug 8, 2010)

Open baffles are a bit problematic. Here is something you may as well read:

http://www.musicanddesign.com/A_B_C_Dipole.html

What kind of gating are you using to measure?


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## killa12222 (Jun 8, 2011)

Cool program. But I do not have any t/s specs for these drivers. I will definitely be using this program in my next build 

What's gating?


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## Theresa (Aug 23, 2010)

Actually that doesn't look too bad. I would probably crossover somewhere above 70 Hz. Inexpensive 6" don't do well in the bass. You have learned so much.


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## killa12222 (Jun 8, 2011)

Yep, they are crossed at 80hz @24db/octave to my midbass transmission line which is then crossed at 55hz @24db/octave to my tapped horn. 

Definitely! I have always been a bass-head but realised that good sounding highs do make all the difference


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## fusseli (May 1, 2007)

>


That lobing effect (comb filter looking) across your FR could be due to your mic placement and/or a phase issue between either of the two speakers? Or maybe a room effect if you're really measuring at ~95dB.

The sag in the 2-3khz range looks crossover related, especially since it looks like you have it EQ'd and it still sags that much. Try reversing polarity on your tweeters and re-measuring.


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## GranteedEV (Aug 8, 2010)

killa12222 said:


> What's gating?


REW takes a frequency response measurement and somewhat averages it out over a period of time. In order to simulate an anechoic (room-free) measurement, you need to place the speaker somewhere with no nearby boundaries within 1m, place the microphone 1m away, and then in REW --> Tools --> IR Window set the left window as 1 and the right window as 5. This should give you a 6ms gated measurement which means reflections are not part of the response graph. For example, here is a measurement which is gated, and then the exact same measurement ungated. No smoothing is applied to either measurement. As you can see, one shows you too much room and not enough speaker, and while you can smooth it to make it look better, it's not AS indicative of the speaker as an unsmoothed, gated measurement.

By designing like this, you can take other factors such as the room out of the equation and focus on the speaker first.


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## killa12222 (Jun 8, 2011)

GranteedEV said:


> By designing like this, you can take other factors such as the room out of the equation and focus on the speaker first.


Now that is cool! Here are some new measurements using your gating settings. Doesn't look as bad as i thought. I added an 6db/octave lowpass inductor (wound it myself!) to the woofer that should be crossing at ~1000hz.

Here is a sweep with the previous eq settings :coocoo:


Measurements were done @ 1 meter with the mic positioned in between both speakers.


With the new settings, music sounds less muffled and clearer sounding (insert audiophile term here :whistling


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## killa12222 (Jun 8, 2011)

fusseli said:


> That lobing effect (comb filter looking) across your FR could be due to your mic placement and/or a phase issue between either of the two speakers? Or maybe a room effect if you're really measuring at ~95dB.
> 
> The sag in the 2-3khz range looks crossover related, especially since it looks like you have it EQ'd and it still sags that much. Try reversing polarity on your tweeters and re-measuring.


Ignore the SPL figures. I didn't actually have a proper spl meter to refer to :rofl:
Yes I did that on my right speaker and it flattened out! Sweeps are above ^^


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## fusseli (May 1, 2007)

To be honest, if it were me I wouldn't waste the time getting a flat "true to speaker" response. I get the impression these speakers aren't going anywhere! You might as well go straight to flattening your total in-room response, speakers + sub(s).

What are you taking your measurements with?? What mic?


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## killa12222 (Jun 8, 2011)

Was just aiming for a relatively flat response with no massive dips and such. The bass department is all good, except a ~45hz flat spot in my room. Doesn't really bother me though. More sweeps in the morning!

Measurements are done using my Behringer C1-U microphone. May not be the best choice but its the best mic i've got


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## GranteedEV (Aug 8, 2010)

fusseli said:


> To be honest, if it were me I wouldn't waste the time getting a flat "true to speaker" response. I get the impression these speakers aren't going anywhere! You might as well go straight to flattening your total in-room response, speakers + sub(s).
> 
> What are you taking your measurements with?? What mic?


Bear in mind this is an open baffle speaker by a person with limited crossover design experience.

I was hoping first he could focus on getting the crossover correct with proper acoustic summing of the drivers in the forward plane. In the room, the back wave of the open baffle speaker is surely contributing to the tonality and adding its own response issues, so i was hoping to isolate that away from the core crossover and let that be a secondary equalization. There's no point equalizing a speaker if it's got serious phase cancelations or diffraction issues that can be dealt with in other ways (edge roundovers, tweeter offsets, baffle width, tweeter polarity). I was under the impression we didn't know if the "basics" were out of the way. Once the basics look a lot flatter, we can perhaps try to do dipole peak notch filter equalization. 

On that note, to the OP, i recommend doing MONO sweeps of just one speaker, rather than letting both speakers sweep at the same time and cause measurement artifacts.

Now one thing that you'll notice is the gated measurement only goes down to 167hz. That is because it is a 6ms (1m) gate that avoids 1m worth of reflections. However bass below 167hz will not have had time to acoustically "form" to be a sufficient measurement. If you play around with the gating time and mic distance as well as distance to nearby reflection objects IE tables etc, you'll notice the response shape change but also the bass start to add or remove itself from the measurement.


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## killa12222 (Jun 8, 2011)

I don't really want to spend too much money on these speakers because they aren't actually good speakers to begin with! However, they do sound good to my ears, especially after I flipped the tweeters polarity. 

My next build would be using some better drivers however that is will not be anytime soon.


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## Zeitgeist (Apr 4, 2009)

Interesting. I must have missed this thread before.

I've never seen open-baffle desktop speakers..

Looks like a fun project (and learning experience).


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