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Multi-Way Conventional loudspeakers with crossovers

Geddes on Waveguides
Geddes on Waveguides
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Old 8th May 2011, 06:14 PM   #5281
_Wim_ is offline _Wim_  Belgium
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Quote:
Originally Posted by mabat View Post
Differences with/without foam for 0 - 90 deg. Sorry for missing labels (green is on-axis).
Very nice measurements! Apparently the foam has the most effect on axis, which seems also logical if you have an axi-symmetric waveguide. Which type of waveguide were you measuring? Did you use a 30 PPI foam plug?
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Old 8th May 2011, 07:00 PM   #5282
gedlee is offline gedlee  United States
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Quote:
Originally Posted by mabat View Post
Differences with/without foam for 0 - 90 deg. Sorry for missing labels (green is on-axis).
Could you post or E-mail me the Holm zip file with the complete measurement session? Then I can plot it using my techniques for a one to one comparison to mine.
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Old 8th May 2011, 07:34 PM   #5283
mabat is offline mabat  Czech Republic
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_Wim_

I used 12" WG - it's the one Autotech.pl is selling, only with somewhat refined throat by myself (). Actually these were the very first pieces that were made and which I've specified shape for. The foam is Bulpren S 28190 (see the link) that I cut with hot wire and scissors () - maybe it's a bit denser than the original. You can see some more photos on my web. It was a lot of work, but I would do it again anytime as the result is simply fabulous, whatever the foam does and despite I'm sure I've still made some errors. It was measured with the woofer in place, BTW.

gedlee

Sure, I'll send you an E-mail.

At this point I would like to thank Dr. Geddes for publicating all this work as it totally changed my view on loudspeakers and home reproduction once for all. Earl, thank you.
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Last edited by mabat; 8th May 2011 at 07:38 PM.
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Old 8th May 2011, 11:29 PM   #5284
PLB is offline PLB  United Kingdom
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Hi Elias,

In your post #5272, you said the following;

“It seems that the foam is making the waveguide impulse response worse !”

If you compare the frequency response of one loudspeaker with a similar loudspeaker that has a slightly different frequency response, there will be a corresponding slight difference in their time domain responses. By adding the foam, you are changing the frequency response and therefore its time domain response. To evaluate the effects of the foam by the method you are using, I think you need to equalize their frequency responses so they are the same.

Can you tell me what criteria you use to determine that the foam is making the waveguide worse ?

A question for you – I think it would be quite a simple task for me to extract the frequency response (magnitude v frequency) directly from your posted graphs by plotting the magnitude from the color changes along the t=0 line together with their corresponding frequencies. However, I don’t see how I could do the same thing for the impulse response (magnitude v. time). How are you able to determine the impulse response from your graphs ?

Regards

Peter
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Old 9th May 2011, 05:17 AM   #5285
mige0 is offline mige0  Austria
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Quote:
Originally Posted by PLB View Post
If you compare the frequency response of one loudspeaker with a similar loudspeaker that has a slightly different frequency response, there will be a corresponding slight difference in their time domain responses.
The main thing to distinguish between is that there are "simple" filter effects seen in any analysis and effects that stem from reflections.

What you have in mind is that wiggles in frequency response that stem from "simple" filter effects should be EQed in order to also optimize time domain behaviour - ig - decay.

What is perfectly valid for "simple" filter effects is totally different for reflections (and looped reflections).

To easily distinguish between the two you only have to know that a "simple" filter effect *always* has a monotony falling decay - meaning, you never see higher SPL in that frequency band popping up later on.

So, whenever/ wherever in a wavelet (or any other time frequency analysis) you see "ghost structures" along the time axis popping up, you can be sure that you are facing reflections/ echoes - and *not* a "simple" filter behaviour.

Those reflections are a totally different animal compared to "simple" filters and EQing isnt possible with a parametric or graphic equalizer.

The normalization of the wavelet plots aid in watching out for those reflections (CMP effects / ASAR patterns) and are by no means an "equalization".

If you have further interest in the differences between "simple" filters behaviour and "reflections" may I suggest you to go through this :

http://www.diyaudio.com/forums/every...ml#post2536088
http://www.diyaudio.com/forums/multi...ml#post2090939
http://www.diyaudio.com/forums/multi...ml#post2134729


Michael

Last edited by mige0; 9th May 2011 at 05:42 AM.
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Old 9th May 2011, 08:04 AM   #5286
gainphile is offline gainphile  Australia
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Quote:
Originally Posted by Elias View Post


It seems that the foam is making the waveguide impulse response worse !


Am I the only one to see this !?


- Elias
I did not like the foam-insert. Or to be specific "a love-hate situation."

I tried it using matched frequency response to be exactly the same. However with the foam the high frequency resolution is missing (music sounded muted?). Subjectively the "shimmer" and "airiness" of music is gone and it sounded "dead". Upper midrange was smoother though.

Click the image to open in full size.
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Old 9th May 2011, 08:43 AM   #5287
454Casull is offline 454Casull  Canada
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Quote:
Originally Posted by gainphile View Post
I did not like the foam-insert. Or to be specific "a love-hate situation."

I tried it using matched frequency response to be exactly the same. However with the foam the high frequency resolution is missing (music sounded muted?). Subjectively the "shimmer" and "airiness" of music is gone and it sounded "dead". Upper midrange was smoother though.

Click the image to open in full size.
The problem is that it can be difficult to separate audio and optical cues (no fault of your own). Best way to test, of course, would have been double-blind.
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Old 9th May 2011, 10:58 AM   #5288
Robh3606 is offline Robh3606  United States
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Quote:
Subjectively the "shimmer" and "airiness" of music is gone and it sounded "dead". Upper midrange was smoother though.
Did you change the CD compensation so you had the same frequency response with and without the foam??

Rob
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Old 9th May 2011, 12:21 PM   #5289
gedlee is offline gedlee  United States
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Quote:
Originally Posted by Robh3606 View Post
Did you change the CD compensation so you had the same frequency response with and without the foam??

Rob
He has answered that question and yes, he claims that he did. In any case, I think that Gainphile is in the extreme minority here since hundreds of other people who have been listening through foam have come to love its effect. It is different, thats almost immediately obvious, but if its not what you expected or want to hear then you might not like it. He says that " "shimmer" and "airiness" of music is gone and it sounded "dead"." Maybe this is his name for my "the harshness is gone" - who knows. And "dead" is a comment that I have heard before about my speakers at first hearing them. They "lack" for everything, i.e. they add nothing, I can understand how someone could call this "dead". They are completely passive, almost as if they weren't there - "dead"? I might say "ghost", but that implies "dead".

At any rate, make no mistake about it the foam does do something audible. That some will not like it is always going to be the case.
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Old 9th May 2011, 12:27 PM   #5290
peterbrorsson is offline peterbrorsson  Sweden
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Would it not be cheaper and easier to put the foam in the ears?
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