# Adivice for Passive Radiator Design Requested



## pietschu (Jan 18, 2010)

Hi All,

I'm new here and since it seems that a number of members here have used passive readiators in their subs, I thought I would ask a few questions.

I am using Unibox to come up with an enclosure volume for a pair of SDX15s with a pair of AE PR18-2500s. To keep things small as the placement and size is limited by the SAF, my first thought was a 110 liter box using the drivers in an isobric configuration. This results in a nice flat curve to about 20 Hz with a 24 dB per octve rolloff below 20 Hz (at least in theory) and F3 is 17.7 Hz. I can get to 106.5 dB (my design goal) with about 165 Watts which works with the single channel 200 watt Outlaw amp I am planning to get.

I was pretty happy with that, small box, response pretty much identical to a ported system.

I do however like "tight" bass and if I had to pick sound quality over bass extension I'd go with sound quality.

I also started to think about room response which I have not measured but since the room in the basement has an opening at one end that leads to the stairs to the main floor, I'm guessing that room gain won't be all that significant.

From my reading stuff here and there, the "tightest" bass is achieved using a sealed box. That would be nice but then F3 moves up to 39.5 Hz. Hmmm - tradeoffs.

I then noticed that if I were to only use 1 PR18-2500 in the box described above or put a single SDX15 in a 220 liter enclosure with 2 PR18-2500s, the resulting theoretcial response curve is about half way between the flat curve and the sealed box curve with a F3 of 27.3 Hz. Is this a reasonable approach? Are there any issues with going with this in between design sonically?


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## Veltinorian (Dec 28, 2009)

The lower you tune the box the preciser it will get at the chest basses you like, i.e. the transients or the delays will be significally reduced, but the roll-off at higher basses comes quicker its the trade off here again.


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## Mike P. (Apr 6, 2007)

> ......with a pair of AE PR18-2500s.


Do you mean the PR18-2100?

http://aespeakers.com/shop/catalog/product_info.php?cPath=24&products_id=39

Wiring the subs together for a single channel amp means either a 2 ohm or a 8 ohm load. Is the Outlaw amp 2 ohm stable?


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## pietschu (Jan 18, 2010)

:doh:


Veltinorian said:


> The lower you tune the box the preciser it will get at the chest basses you like, i.e. the transients or the delays will be significally reduced, but the roll-off at higher basses comes quicker its the trade off here again.


Thanks for the response. I just refreshed my memory on the ported enclosure alignments. Always the trade-offs.


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## pietschu (Jan 18, 2010)

Mike P. said:


> Do you mean the PR18-2100?
> 
> Wiring the subs together for a single channel amp means either a 2 ohm or a 8 ohm load. Is the Outlaw amp 2 ohm stable?


No, definitely meant PR18-2500. I first saw one on Bob's CSS site. It is not listed on the AE site but I emailed them and they will make them. I think they just add mass to the PR18-2100.

I will wire the SDX15s in series for the nominal 8 ohms. I don't think the Outlaw amp is rated for driving 2 ohms.


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## Mike P. (Apr 6, 2007)

That would be the PR18-2100 with another 400 grams of mass added, Fs 3.3 hz and a Qms of 74. With both subs wired for 8 ohms for a single channel amp the Re changes to 7.2, 165 watts will produce 100 db at 20 hz as shown by the yellow line. To get 106 db and have a bit of headroom you would need 1000 watts as shown by the green line. 

The subs could easily handle 2000 watts in this setup and cone excursion is a non issue, there would be no need for a Hi-Pass filter. Give it a try with the Outlaw amp, you can upgrade the amp later if you find you'd like more output.


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## pietschu (Jan 18, 2010)

Mike P. said:


> With both subs wired for 8 ohms for a single channel amp the Re changes to 7.2, 165 watts will produce 100 db at 20 hz as shown by the yellow line. To get 106 db and have a bit of headroom you would need 1000 watts as shown by the green line.


Thanks for the info.

I must be doing soemthing wrong with unibox as it shows 106.5 dB at 168 Watts. Any ideas?


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## Mike P. (Apr 6, 2007)

Did you change the Re?


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## pietschu (Jan 18, 2010)

Mike P. said:


> Did you change the Re?


I did not change any of the driver parameters in Unibox. Maybe I am using it incorrectly. I assumed that changing the "Drive Unit Configuration" values would take care of the parameters. I've attached 4 screen grabs below moving from single driver to 2 drivers in series, 2 driver in parallel, and finally 2 driver in series and compound (isobaric). Do the resulting values seem correct?


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## pietschu (Jan 18, 2010)

*Re: Simplified SPL Calculation*

I just wanted to check to make sure my basic understanding is correct.

The SDX15 is rated at 87.3 dB at 1 m and 1 Watt. As far as I understand thing, you have to double the power for every 3 dB increase in SPL. That gets us :

SPL Watts
87.3 1
90.3 2
93.3 4
96.3 8
99.3 16
102.3 32
105.3 64
108.3 128

Is this simplification basically correct?


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## Mike P. (Apr 6, 2007)

In theory , yes. The final output levels will include the effect of power compression, room gain, room interaction issues, etc. And also if you sit more them one meter away from the sub.


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