what sounds best . . . Low Qts in small cab or higher Qts in bigger cab - Page 2 - diyAudio
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Old 5th July 2009, 01:45 PM   #11
mikelm is offline mikelm  England
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Quote:
Originally posted by AndrewT
both will need some form of equalisation to get bass from the installation.
I'm not sure that my neighbors will necessarily agree with you

Quote:
Originally posted by AndrewT
But that does not get close to answering the original question.
Does size affect the sound?
I suspect that in practice there is no simple answer to this question. If one could produce the perfect cabinet then I think big is better but in real life the bigger the cab, the more the panel resonance etc so as always it's question of balancing compromises ( and for me that includes the neighbors )

I think my 1st proposal will be quite sufficient for me

cheers

mike
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Old 5th July 2009, 01:52 PM   #12
mikelm is offline mikelm  England
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Default p.s.

.

I once heard a system that had been equalized flat down to about 10hz - it was not a happy experience.

Until you reproduce it you have no idea what recordings will sound like with that much bass.

What I heard was not conducive to the enjoyment of music and some recordings sounded like an underground train was just passing close underneath the house.

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Old 5th July 2009, 02:10 PM   #13
KSTR is offline KSTR  Germany
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Higher Qts-alignents are more prone to side-effects from dynamic parameter shifts, especially Fs-shift of the driver. Also, a lower Qts will give deeper bass below the -3dB freq (or whereever you choose to normalize it to) than a higher Qts with the same -3dB point because of the gentler roll-off into the final -12dB/oct roll-off. Another plus is the nicer group delay response. The best from this perspective are critical (Qts=0.50) or Bessel (Qts=0.58) alignments. Depending on room size, this also gives flattest bass reponse when the roll-of is (partly) compensated by the room gain effect of about +9dB/oct below the first mode.

Too small volumes tend to "compress the sound" and usually have higher distortion when compared to the same alignment with a bigger volume (and necessarily a different driver, unless you trick it with drive impedance and/or Linkwitz-Transform) but this depends, to a certain extend, very much on the driver's qualities. But even with a pefect driver there is distortion when the volume is "modulated" too much by the driver's excursion.

EDIT: Qts to be read as the in-situ Q (ts=total system), not the mere driver parameter.

- Klaus
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Old 5th July 2009, 05:39 PM   #14
MaVo is offline MaVo  Germany
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A small sealed box will need more amplifier power to get the same low frequency output as a bigger box. Box size vs amplifier size is the tradeoff you can do here. With a big amplifier and drivers that can take the heat, you can make a smaller box.

However, the maximum SPL is the same with all boxes, as the maximum excursion is the same - it only needs different amounts of power to be reached.

As to sound quality, i doubt there is much difference. I couldnt really spot a difference between a 300 liter tapped horn and a 30 liter closed box, once i equalized them to the same response, so you can guess that the difference between different sealed boxes is even smaller.

The room has much more influence. Shove the box a few meters around and it will sound completely different.
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Old 14th July 2009, 12:31 AM   #15
tinitus is offline tinitus  Europe
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Quote:
Originally posted by mikelm
thanks to all for your comments


2 x Dayton 15" IB385-8 on open baffles per channel.

cheers

mike

Might work in big closed box
Or maybe isobaric pushpull, if its worth the exstra cost?

But be warned that to achieve more lowend by using high Q design is potential risk of major problems
When going very low you want control

But for dipole bass, AE IB15 is cheaper and better looking

And AEs underhung Dipole10 and 12 looks really tempting, on top of my list as of now
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Old 14th July 2009, 04:20 PM   #16
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Wouldn't things like Vas come into play - a high Vas in a small box means frequency response isn't so good...
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Old 15th July 2009, 08:16 AM   #17
AndrewT is online now AndrewT  Scotland
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but when you apply the linkwitz transform the frequency response of any driver in any box can be made to match any desired rolloff frequency.
The problem is that the gain required at the low end must be subtracted from the effective sensitivity where the applied EQ is near zero and this results in a much lower maximum SPL from the small box than from the larger box.
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Old 15th July 2009, 09:38 AM   #18
MaVo is offline MaVo  Germany
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Quote:
Originally posted by AndrewT
The problem is that the gain required at the low end must be subtracted from the effective sensitivity where the applied EQ is near zero and this results in a much lower maximum SPL from the small box than from the larger box.
Thats wrong (and i repeat myself here). The reduced sensitivity of the small box goes hand in hand with a reduced excursion. Maximum output is the same (has to be the same, since the woofers mechanical excursion and by this the amount of air it can moove is the same), it just needs different amount of amplifier power to reach.
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Old 15th July 2009, 10:46 AM   #19
AndrewT is online now AndrewT  Scotland
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Quote:
Originally posted by MaVo
That's wrong (and i repeat myself here). The reduced sensitivity of the small box goes hand in hand with a reduced excursion. Maximum output is the same (has to be the same, since the woofers mechanical excursion and by this the amount of air it can move is the same), it just needs different amount of amplifier power to reach.
I don't think we are talking about the same thing.
You are referring to the maximum output of the driver at maximum excursion.

If one applies +20dB of LF gain at say 40Hz and zero gain at 100Hz, then the speaker is power limited by the LF gain.
The output at >=100Hz is controlled by the driver sensitivity and the 0dB gain.
It is effectively 20dB less sensitive at 100Hz and thus the speaker is SPL limited due to the +20dB of LF gain.
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