Ported Enclosures - Low Qes design

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Low Qes design

Printed From: Speakerplans.com
Category: Plans
Forum Name: Ported Enclosures
Forum Description: Post all your reflex and bandpass and 'other' boxes with holes in stuff here...
URL: https://forum.speakerplans.com/forum_posts.asp?TID=88629
Printed Date: 26 March 2026 at 4:28pm
Software Version: Web Wiz Forums 12.08 - https://www.webwizforums.com

Topic: Low Qes design

Posted By: Surfdude
Subject: Low Qes design
Date Posted: 12 September 2014 at 6:20pm

My current project is designing and building a vented subwoofer. I would like to base it on either the PRV 18W2200 8 Ohm or the 2+2 version of that one use at 4 Ohm. Preferably the last one as it is easier to drive it at high power levels and is currently locally available (I live on a small island where the choice is limited or have to order it from abroad).

http://prvaudio.com/18sw2200. - http://prvaudio.com/18sw2200.html

http://prvaudio.com/18sw2200-22. - http://prvaudio.com/18sw2200-22.html

Though I'm a bit stuck on the design of the vented box the 2+2. According to the software the box should only be about 57 liters for the maximally flat response. But that only gives an F3 of 78Hz, which is way to high of course.

I've read about extended bass shelf design, basically increasing the volume and adjust the port parameters. Did this in several tools, but they all give quite different results while for the 8 Ohm driver they all pretty much agree. I'm not sure what to believe now and how accurate the curves are that I'll get with increased volume, which do lower the F3 compromising a less flat response.

I would really appreciate your insights on this case. If you could include a compromise you could live with, that would be great. Please also include some of the reasoning behind it as I'm very willing to expand my knowledge about speaker design. I've also read that these kind of drivers work best with a horn loaded design, but that's not an option in this case. Though if that's the conclusion, then I'll have to with another driver.

Thanks in advance!

Replies:

Posted By: Elliot Thompson
Date Posted: 12 September 2014 at 7:12pm

You have already scaled the driver in a simulator in addition to understanding the driver you are considering is best suited for horn-loaded purposes. Stop looking the other way and face the harsh reality. The driver is not suited for your requirements and you must move to a different driver with the appropriate parameters in order to attain the desired frequency response you are aiming for.

Best Regards,

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Elliot Thompson

Posted By: Surfdude
Date Posted: 13 September 2014 at 4:07pm

Thanks Elliot, your message is clear ;)

As you probably understood, I'm not that experienced with speaker building. Only one out of X websites (that I read) mentioned the thing about the horn loaded sub. Others only state that for high EBP a vented or 6th order bandpass is more suitable (and also software like Winisd), so that's what a rookie like me takes as a first guidance...

Also I ran into this low profile sub:

http://www.grundaudio.com/index.php?type=SOUN&application=GTS&model=GT-LPB-36CX

I did a rough calculation on it and estimated it has about 80 liters per driver, so that must be a quite low Qes driver and some kind of EBS design. Although they don't even supply a technical datasheet or response curve, I believe Grund is a respected manufacturer that wouldn't offer a product like this if it wouldn't be worth it...

Maybe I could get some satisfactory results, but will probably need some experimenting. I'm tempted to try it as size is a factor for this design (though I could live with the 200 liters for the 8 Ohm design), but lack the time for experimenting... :)

Or maybe I should just go for a 15" driver... ;)

Thanks!

Posted By: Elliot Thompson
Date Posted: 14 September 2014 at 5:54pm

Many do not measure the driver’s full frequency response in free air (20 Hz – 20,000 kHz) to determine how efficient the driver is within the desired frequency they are looking to produce. It does not make sense having an EBP of 100 in which, all the efficiency lies from 200 Hz on up, while the efficiency declines rapidly under 100 Hz.

Fortunately, there are thousands of eighteens in addition to fifteen-inch drivers available around the globe so there is no need to settle for woofers that will not meet your requirements.

Just remember the most popular speakers many are gloating about are the worst choice for a reflex box. It would be wise to take heed to those claiming such and such speaker is great in a horn when, you are looking to design a reflex cabinet. True bass reflex subs and true bass horns will not have any similarities on the type of woofer needed (from a TS Parameters perspective) in order to achieve optimum results.

Best Regards,

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Elliot Thompson

Posted By: Meat
Date Posted: 14 September 2014 at 8:53pm

The 8ohm one looks alright based on the data sheet.

However, I'm suspicious about the parameters though. Sd looks way too big. 1200cm^2 is about normal for an 18. I've never seen one with it over 1400cm^2. BL seems very, very high too... ...33+...
...thats serious if true.

I don't have a garden but if I did you'd find me sat on the fence.

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Don't test the champignon sound

Posted By: Surfdude
Date Posted: 17 September 2014 at 5:11pm

Thanks again Elliot, highly appreciated! New stock with various models should be available on the island soon. So I'll check it out and see what can work with for my project.

Thanks Andrew, the parameters seemed a bit extreme indeed so I wrote an email to PRV and guess what: One employee appeared to be remeasuring their speakers at the moment and he gave me the new values right away:

18SW2200 (EBP 97.9):

Vas: 265.70 liters

Fs: 32.30

Qms: 11.41

Qes: 0.33

Qts: 0.32

Sd: 1238 cm^2

Mms: 196.70

BL: 25.87 Tm

Re: 5.57 ohms

Lower BL and Sd indeed, but the EBP went up from 83 to 98! Curious what those numbers are gonna bring design wise...

18SW2200-2+2 (EBP 119.8)

Fs = 26.24 Hz

Qms = 10.89

Vas = 302.5 liters

Cms = 0.139 mm/N

Mms = 264.7 g

Rms = 4.007 kg/s

Xmax = 9 mm

Xmech = 18 mm

P-Dia = 397 mm

Sd = 1238 sq.cm

P-Vd = 1.114 liters

--Electrical Parameters--

Qes = 0.219

Re = 1.11 ohms

Z = 1.332 ohms

BL = 14.87 Tm

--Electromech. Parameters--

Qts = 0.215

no = 2.406 %

1-W SPL = 95.96 dB

2.83-V SPL = 105.8 dB

Lower Sd, Fs and Qes. Overall EBP came down a bit, doesn't really change the conclusion.

Cheers!

Posted By: AndyWave
Date Posted: 18 September 2014 at 9:14pm

8 ohm version seems most suitable with the Qts value near 0.312 for BR cabinet, tuned to Fs of the driver and cabinet volume of 1/2....1/1 of Vas (130-260L), watch out for the excursion peak above box tuning. But with the Xmax of "only" 9mm, no infrasonic wonder expected.

2+2 ohm version goes lower with more limited by Xmax and so maximum SPL is more limited, in similar sized cabinet with lower tuning.

This assuming both versions have similar Xmax values.

No computers were harmed during these assumptions in my head....

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torturing electrons since ......

Posted By: Meat
Date Posted: 19 September 2014 at 8:23am

If you're on a little island then what amps do you have available?

If you're struggling for big enough amps then take the 2+2 if it sims ok in a bandpass box.

If not or power isn't a problem and waiting for it to come from the mainland is ok then the 8ohm one looks like a pretty bread and butter good reflex driver.

If I was going to have either it'd be a pair of the 8ohm ones all day.

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Don't test the champignon sound

Posted By: AndyWave
Date Posted: 20 September 2014 at 10:18am

snip_
the parameters seemed a bit extreme indeed so I wrote an email to PRV and guess what: One employee appeared to be remeasuring their speakers at the moment and he gave me the new values right away:
snip_

I quickly looked the specs of PRV 18" drivers and I'd take those specs with pinch of salt...

At least for me they look all over the place on some models.

Indeed they should get their driver parameters measured by 3rd party.

If you can get 'em in good price, why not try to measure the parameters by yourself, added cone mass method is quite easy or measure in free air first and then in closed box of known volume....

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torturing electrons since ......

Posted By: Elliot Thompson
Date Posted: 20 September 2014 at 2:33pm

It appears PRV TS Parameters fluctuates severely. This is the third time I have heard them re-measuring their drivers to conclude the nominal TS Parameters. Their inconsistency of offering the proper TS Parameters reminds me of P Audio.

Best Regards,

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Elliot Thompson

Posted By: MarjanM
Date Posted: 20 September 2014 at 3:14pm

Just forget the PRV.

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Marjan Milosevic
MM-Acoustics
www.mm-acoustics.com
https://www.facebook.com/pages/MM-Acoustics/608901282527713

Posted By: Keen
Date Posted: 21 September 2014 at 12:43am

lol

Posted By: Surfdude
Date Posted: 22 September 2014 at 2:02am

I'll see what it will be. I can also bridge the amp to have enough voltage range and drive two 8 Ohms in parallel.

The 2+2 was measured at 1 Ohm, now only I wonder is if/in which way the Qes changes when using the two coils in series for the 4 Ohm...?

I've been googling and thinking, but ain't sure yet (R changes, but the amount of wire/windings doesn't...). Also because I've found 3 different kind of answers: stays equal, doubles and quadruples...

Any inputs?

Posted By: _djk_
Date Posted: 23 September 2014 at 1:21am

"I wonder is if/in which way the Qes changes when using the two http://www.shopping.com/coils/products?CLT=SCH&linkin_id=8058742&subTrackingID=%5bUSERID%5d" rel="nofollow - coils in series for the 4 Ohm...?"

It doesn't change.

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djk