Low Qes design

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   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!

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Surfdude Members Profile Send Private Message Find Members Posts Add to Buddy List New Member Joined: 12 September 2014 Location: Aruba Status: Offline Points: 5	Post Options Post Reply Quote Surfdude Report Post Thanks(0) Quote Reply Topic: Low Qes design 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!

Elliot Thompson Members Profile Send Private Message Find Members Posts Add to Buddy List Old Croc Joined: 02 April 2004 Location: United States Status: Offline Points: 5365	Post Options Post Reply Quote Elliot Thompson Report Post Thanks(0) Quote Reply 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,
	Elliot Thompson

Surfdude Members Profile Send Private Message Find Members Posts Add to Buddy List New Member Joined: 12 September 2014 Location: Aruba Status: Offline Points: 5	Post Options Post Reply Quote Surfdude Report Post Thanks(0) Quote Reply 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!

Elliot Thompson Members Profile Send Private Message Find Members Posts Add to Buddy List Old Croc Joined: 02 April 2004 Location: United States Status: Offline Points: 5365	Post Options Post Reply Quote Elliot Thompson Report Post Thanks(0) Quote Reply 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,
	Elliot Thompson

Meat Members Profile Send Private Message Find Members Posts Add to Buddy List Old Croc Joined: 05 June 2009 Location: Manc Status: Offline Points: 1513	Post Options Post Reply Quote Meat Report Post Thanks(0) Quote Reply 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.
	Don't test the champignon sound

Surfdude Members Profile Send Private Message Find Members Posts Add to Buddy List New Member Joined: 12 September 2014 Location: Aruba Status: Offline Points: 5	Post Options Post Reply Quote Surfdude Report Post Thanks(0) Quote Reply 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!

AndyWave Members Profile Send Private Message Find Members Posts Add to Buddy List Registered User Joined: 30 March 2008 Location: Finland Status: Offline Points: 381	Post Options Post Reply Quote AndyWave Report Post Thanks(0) Quote Reply 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....
	torturing electrons since ......

Meat Members Profile Send Private Message Find Members Posts Add to Buddy List Old Croc Joined: 05 June 2009 Location: Manc Status: Offline Points: 1513	Post Options Post Reply Quote Meat Report Post Thanks(0) Quote Reply 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.
	Don't test the champignon sound

AndyWave Members Profile Send Private Message Find Members Posts Add to Buddy List Registered User Joined: 30 March 2008 Location: Finland Status: Offline Points: 381	Post Options Post Reply Quote AndyWave Report Post Thanks(0) Quote Reply 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....
	torturing electrons since ......

Elliot Thompson Members Profile Send Private Message Find Members Posts Add to Buddy List Old Croc Joined: 02 April 2004 Location: United States Status: Offline Points: 5365	Post Options Post Reply Quote Elliot Thompson Report Post Thanks(0) Quote Reply 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, Edited by Elliot Thompson - 20 September 2014 at 2:34pm
	Elliot Thompson

MarjanM Members Profile Send Private Message Find Members Posts Add to Buddy List Old Croc Joined: 10 February 2005 Location: Macedonia Status: Offline Points: 7844	Post Options Post Reply Quote MarjanM Report Post Thanks(0) Quote Reply Posted: 20 September 2014 at 3:14pm
	Just forget the PRV.
	Marjan Milosevic MM-Acoustics www.mm-acoustics.com https://www.facebook.com/pages/MM-Acoustics/608901282527713

Keen Members Profile Send Private Message Find Members Posts Add to Buddy List Young Croc Joined: 30 May 2011 Location: Brisbane, Aus Status: Offline Points: 1271	Post Options Post Reply Quote Keen Report Post Thanks(0) Quote Reply Posted: 21 September 2014 at 12:43am
	lol