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Mullard speaker box strange impedance resonances
Mullard speaker box strange impedance resonances
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Old 13th March 2019, 07:34 PM   #1
powerpz is offline powerpz  Bulgaria
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Default Mullard speaker box strange impedance resonances

I designed speaker box for two Philips 9710 fullrange speakers, following completely Mullard engineers specification from 1959
Result is fullrange massive speaker box, very nice and bright highs, middles are wide and realistic, bass.. also good level
First I heard some specific resonance, which I suppose comes, because enclosure is not right damped or tight enough. When I red specification as in the picture - there are 2 impedance tops - at 30Hz and 100Hz. First one is excellent and nice, but second.. 100Hz resonance sound like barrel or cartoon box. Why it is there and can it be removed

Other speaker box I tried to put bassreflex which is adjustable. In this case there is only one resonace about 81Hz and it is not moved even if I change bassreflex depth ?! These drivers have a good resonance about 45Hz and with 93 litter enclosure can I pull it down more or at least keep it, but please not more than 50Hz ?
Attached Images
File Type: png mull1.png (225.4 KB, 172 views)
File Type: png mull2.png (90.5 KB, 177 views)
File Type: jpg rsz_img_20190313_211620.jpg (26.6 KB, 168 views)
File Type: jpg rsz_img_20190313_211613.jpg (20.8 KB, 167 views)

Last edited by powerpz; 13th March 2019 at 07:57 PM.
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Old 13th March 2019, 08:55 PM   #2
powerpz is offline powerpz  Bulgaria
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Okay, I was pretty fast I think and went to a wrong direction. Box resonance is in a result of box impedance not equal:

http://images.audiojudgement.com/201...***-reflex.jpg

Depending on how the 2 peaks compare to each other, in terms of height, we can consider 3 particular cases :

The two peaks match in height. This means that the resonant frequency of the driver in free air (fs) matches the resonant frequency of the box (fb).
The first peak is higher than the second. This means that fb > fs.
The second peak is higher than the first peak. This means that fb < fs.

In my case fb < fs and according Mullard manual F = 35Hz. Why I hear higher resonace and how to measure and improve the boxes - damping ?
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Old 13th March 2019, 09:00 PM   #3
powerpz is offline powerpz  Bulgaria
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Okay,
I was pretty fast, box resonace is not equal to box impedance, but result of it as in the picture. According Mullard f = 35Hz, which is pretty low? Can I calulated it f1=30Hz and U=140mV, f2=98Hz and U=177mV
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File Type: jpg impedance-bass-reflex.jpg (43.7 KB, 162 views)
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Old 13th March 2019, 09:33 PM   #4
powerpz is offline powerpz  Bulgaria
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Bass is too louder in original vent and makes U-u-u-u time to time

In bassreflex bass is light "uuuu" situation is not observed but sounds like suppressed a bit. I removed there also all damping material (empty box)

Here is frequence response
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File Type: png mull3.png (104.5 KB, 41 views)

Last edited by powerpz; 13th March 2019 at 09:37 PM.
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Old 13th March 2019, 11:39 PM   #5
freddi is offline freddi  United States
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Mullard speaker box strange impedance resonances
did you try just the "hole" in the vent's cover by itself without a port tube?
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Old 14th March 2019, 12:39 AM   #6
Galu is offline Galu  Scotland
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There appears to be some confusion here.

The graph of impedance against frequency in post #1 does not indicate the frequency response of the speaker. If you are hearing resonances, they are not related to the humps in the impedance curve.

The frequency response graph in post #4 appears to be that of a pickup cartridge and not that of the loudspeaker.
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Old 14th March 2019, 12:43 AM   #7
turk 182 is online now turk 182  Canada
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well you don't have any actual measurement or do you?

old copied graphs that are for something else just doesn't seem right.

and there's a difference between what's seen in the impedance curve and actual sound output i.e.frequency response.
if the Mullard box was so good why didn't this guy use it Philips 9710/
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Old 14th March 2019, 09:18 AM   #8
powerpz is offline powerpz  Bulgaria
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Quote:
Originally Posted by freddi View Post
did you try just the "hole" in the vent's cover by itself without a port tube?
Freddy, you mean something interesting, but please let me know your thought!

Yes, it was interesting I continued with tries and found that as plastic vent goes shorter, the same sound goes better, which is in opposite of the bassreflex theory (long vent makes bass more low). Later on I left only round hole, removed plastic bassreflex

@Galu- thanks for clarifications, firstly I mess impedance with frequency resonances

@turk_182 - my enclosure has absolutely same resonances and responses like in the copied graphs. People use 9710 in different cases, but if you are putting it in crossover project, this driver is going to be useless. His advantage is fullrange projects
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Old 14th March 2019, 09:27 AM   #9
powerpz is offline powerpz  Bulgaria
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Finalizing my current experience:
1. Original box has too much bass, which is not only sub-basa, but also includes low mid frequences causes to "U-u-u-uh" sometimes. Can I remove "curtains" damping in original project and use appropriate damping? My expectation is to allow only low bass, but also dont want to lose perfect middle freqs on this driver

2. Second bassreflex plastic obviously didn't gave more good result - plastic tube sound very light in bass (but it is low) no matter of the vent length, even removing the tube and left a hole is better

I have to found decision somewhere in the middle ...
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Old 14th March 2019, 05:12 PM   #10
Galu is offline Galu  Scotland
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To help analyse your problem, could you explain what you mean by "U-u-u-uh"?

The curtains are intended to damp resonances in the mid to high frequency range, but do not effect the bass.

The quality of the bass depends only on the enclosure design.

If there is too much bass, try closing the reflex opening to see what the fullrangers sound like in a sealed box.
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