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High Quality 92 db 2-way Speakers Using JBL 127H-1 and Dayton RST 28 F-4

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High Sensitvity 92 db 2-way Speakers Using JBL 127H-1 and Dayton RST 28-4F

 

The modern high quality HT speakers tend to have typically 86db/2.83v sensitivity, limited primarily by the relatively smallish woofers used in them. The newly introduced Dayton RST-28F4 has a sensitivity of 93.5db even without a waveguide or horn. In addition, it can be crossed low(1400 hz). I jumped at the opportunity to use it in a pair experimental 2-way high quality DIY speakers with sensitivity around 92 db/2.83v.

 

For the woofer, I just happen to have a pair JBL 127H1 woofers available. JBL127H1 has advanced magnetic structure, 2-inch voice coil and was used in many commercial and professional speakers (4410A, XPL 160A, L80T and T3). The measured sensitivity was 92db with very low distortions (less than 0.5% even at 95db SPL for most frequencies), according to a review by High Fidelity magazine.

 

In a fully stuffed sealed cabinet of 0.7Ft3, I estimate the Q of the box will be around 1.1 and -3 db around 60 hz, plenty low for a HT speaker. One can choose other options if deeper bass is desired. TS parameters and suggested enclosure sizes are published here. http://ampslab.com/blog/2018/05/06/jbl-127h1/

 

The current crossover (GS-1) is voiced mostly by listening and probably can be simplified further.

 

My reference speakers are Infinity Reference 162 as reviewed here. https://www.soundandvision.com/content/infinity-reference-r162-speaker-system-test-bench.

 

My big surprise is the spectral balance of my JBL127H1 /RST28 F4 is very similar to Infinity R162 and certainly no lacking of details and spaciousness. I would rate the transient response of both speakers to be equally outstanding. I can listen to either speaker for a long time without listening fatigue.

 

In conclusion, you can build a higher sensitivity speaker by using a high  quality large diameter woofer without losing sound quality. IMG_5664.thumb.JPG.badcf6754acb1ac491d31cb2c8f7b118.JPGIMG_5665.thumb.JPG.957247262f51ed1bfa539b7253fbef47.JPGIMG_5666.thumb.JPG.30a1719fbf679200f2b1ce17c598a9a6.JPG

Edited by ligs
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13 minutes ago, ligs said:

For the woofer, I just happen to have a pair JBL 127H1 woofers available. JBL127H1 has advanced magnetic structure, 2-inch voice coil and was used in many commercial and professional speakers (4410A, XPL 160A, L80T and T3).

Is this the same woofer below?  This is an LSR 6332.

image.png.d7e63fde2d2d2e68e8b46a0d0e2801de.png

 

 

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LSR 6332 has a newer 12" woofer.

The picture of JBL127 H1 is here. It has a nice cast frame and a nice large magnet. 1175618182_JBL127H1picture.thumb.jpg.ce0cf6418e1e169cfd1bd3bd06aa83f9.jpg

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Just put the tweeter in a more permanent housing. There is a strip of felt between the bottom of the tweeter and the top of the woofer cabinet to reduce the diffraction effect.  Both male and female sound very natural. I did not expect the midrange could sound this good with a 10 inch woofer crossovered to a 1 1/8" tweeter. The same configuration works well with an 8" woofer(Dayton RS225-4) too.

 

IMG_5667.thumb.JPG.0b33e7a9e0d552899e5f0301580b6eaa.JPGn.

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The tweeter highpass crossover is very similar to that of 

http://techtalk.parts-express.com/forum/tech-talk-forum/42977-my-rs180-mtm-design

Therefore the crossover frequency  is estimated to be around 1500  hz similar to in the above design. 

The woofer crossover has gone through a few reiterations, starting with a simpler 2nd order but ending in 2 inductors ,2 capacitors and a resistor. For someone who can do sims the parts number probably can be reduced. 

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While I was listening to a solo guitar CD from  Journey to the New World by Sharon Isbin, I noticed it sounded somewhat flat not as vibrant as the real guitar would.  Recalling Stereophile review of JBL XPL 160(the same woofer was used),  the midrange and tweeter were stepped back from the woofer so the voice coils of all 3 drivers would be aligned in the same plane.  https://www.stereophile.com/content/jbl-xpl-160-loudspeaker.

The illusion of space thus the imaging of these speakers did improve considerably by moving each  tweeter backward for about 3.5 inches from the edge of the woofer cabinet. With this tweaking, the solo instruments like guitar and violin now sounded better than before.  I continue to marvel that our hearing is a lot more sensitive and complex than perhaps the microphones are capable of detecting. 

 

 

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Dayton audio recently introduced 2 new reference series 28 mm dome tweeters(RST 28F-4 and RST 28A-4) replacing the highly praised RS 28F-4 and RS 28A-4. The F version is soft fabric dome and A version is hard anodized aluminum dome. The RST 28F-4 and RST 28A-4) now have 92.5 db and 93.5 db sensitivity, some 3db more sensitivity than their predecessors. The combination of high sensitivity and the ability to cross low as 1400-1500 hz make them extremely attractive for DIY projects.

 

 

Carspeak even recommended RS 28F-4 as a replacement tweeter for Advent NAL with highs extended flat to beyond 20k hz.

 

I have been playing several reiterations of JBL 127 H-1/Dayton RST 28 F-4 for months. The latest crossover (GSL-A) represents the most balanced sound so far. The same crossover works also with RST 28 A-4. Both F and A versions are highly listenable.IMG_5772.thumb.JPG.beeecb924c7c1da6efea9e30b2623df1.JPG

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Maybe I am missing the point here and a bit naive but couldn't you use a DSP amp to power and crossover these speakers and dispense with the the hand-made crossover.  There may be disadvantages I don't see but one advantage would be you could set the hi/lo pass frequency by pushing a button. 

Adams

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Good question. I would probably  try that some day. Interestingly,   many expensive speakers such as  Wilson and Revel still use passive crossovers while in theory they could use DSP and be done with it. I don't know if it has to do digital(DSP) vs analog(passive). What do you think? 

 

George

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6 hours ago, ligs said:

What do you think? 

I do not have the knowledge to create a handmade custom crossover.  The only way I would know how to do it is with a DSP.  A stereo power amp with an integrated DSP would be most convenient but you would need an amp for each pass band.  For a 3way speaker you would need 3 amps.   The only ones I know about are the Crowns which are programmed to use Linkwitz Reilly 24db octave. 

I haven't seen any outboard DSPs that are not made for powered speakers and even then more for surround sound use.   

I notice MiniDSP has a 2x8 outboard processor specifically for stereo inputs but still need a power amp for each pass band.  3 way six channels 4 way 8 channels.  

Adams

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I searched the literature for comparing speakers using passive vs digital crossovers(processors). 

The first one is not an apple to apple comparison between Revel 106M vs NHT Xd Active DSP System.

https://hometheaterhifi.com/reviews/speaker/bookshelf/revel-performa3-m106-2-way-bookshelf-monitor-loudspeaker-review-part-three/

The second one is a comparison between passive KEF LS 50 vs KEF LS 50 wireless(active DSP).

https://forum.audiogon.com/discussions/kef-ls50-wireless-vs-passive

I admit I am an old fashioned hobbyist who enjoys playing with surplus electronics parts. The speakers with passive crossovers allow me more opportunities to keep busy:)

 

George

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On 10/9/2018 at 7:13 AM, ligs said:

I searched the literature for comparing speakers using passive vs digital crossovers(processors). 

I read the articles about the speakers with on board DSPs.  IMO it doesn't make sense from a hobbyists standpoint because the DSP can't be reprogrammed but it is an advantage for the consumer because the DSP is customized to operate with a single amp per stereo side. 

DSPs outboard with respect to the speaker, would be perfect for a hobbyist wanting to select and test a variety of drivers in combination.    Passive speakers in combo with outboard DSPs is a more flexible arrangement but requires an amp per pass band on each channel.  I think the line array systems setup on big music venue sound stages are done this way.

At home it would not be any different than bi-amping, tri-amping or even quad- amping a stereo pair of speakers but the crossover would be entirely outboard and programmable.  Speaker system manufacturers could bypass or eliminate passive crossovers and specify the recommended crossover settings to be set in an outboard DSP crossover. 

Edit: Just found a nerd thread from 2017 about this very topic. https://audiosciencereview.com/forum/index.php?threads/crossover-less-passive-speakers.1951/

 

Adams

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