Passive Radiator system to Acoustic Suspension/Sealed

ARGuy

ARGuy

Audiophyte
Hey Guys,

Not sure I'm in the right forum or even the right website for this sort of question.

I'm picking up a set of old JVC SP-87BK speakers for nothing. I want them primarily for the decent quality cabinetry. Their initial design is a 3-way bass reflex (12" woofer) with a 12" passive radiator in 8 ohm resistance.

Now, I already own another brand of speaker with two 12" woofers per speaker in the bedroom (almost identical dimensions) and I really like the setup. For me, it works better than tower speakers that have smaller drivers with powered external subs chiefly because I'm in a condo and I can't have a whole lot of thumping. From experience, I know that two 12" woofers per speaker give me plenty of bass without being thunderous and will still maintain the peace I have with my neighbors.

I was thinking if gutting these JVC speakers and replacing the crossovers and all the drivers but migrating from a bass reflex/radiator system, to either sealed or acoustic suspension by discarding the passive rad and replacing it with a 12" woofer - so two 4 ohm woofers to maintain an 8 ohm resitance. I don't think I've seen this sort of question posed anywhere, or maybe I missed it someplace.

Still haven't done all the math, but is it doable? There aren't any ports on the speakers as the passive radiator is acting as the port. But once I seal that passive rad with another 12" woofer, I suppose I can go either sealed or acoustic suspension.

Appreciate any input or direction you can graciously supply.

39" tall x 15" wide x 12" deep
 
WaynePflughaupt

WaynePflughaupt

Audioholic Samurai

Wow, don’t think I’ve ever seen a speaker with no tweeter...

“Sealed” and “acoustic suspension” is the same thing.
https://en.wikipedia.org/wiki/Acoustic_suspension

Since they’re sharing the same acoustic space, you’ll have to get 12-inchers spec’d for half the internal volume of the cabinet.

That’s about all I can tell you about such things. I’m not a speaker builder, I just play one on TV.

Regards,
Wayne A. Pflughaupt
 
ARGuy

ARGuy

Audiophyte
Thanks, Wayne. Any bit helps and that does.

Yeah, I've brought them home and the highs are, well, unsophisticated would probably be a good description. Will replace the tweeters soon enough.

Mids were muddy and unclear, undefined and shallow. I've already replaced them and tonality has opened up a lot more - crisp vocals, more refined and detailed snares/synths/guitars and peaks are smoothed out.

Bass is very good - deep, smooth and resonant with a smooth roll-off which is what I'm looking for without that punchy bass reflex feel. I'm trying to avoid excessive dynamic bass since that's what gets complaints. I may even scrap my plans to add another 12" woofer; they sound similar to my ARs except those JVC highs are limping right now. These passive radiator systems are underrated IMO, glad I got them.
 
TLS Guy

TLS Guy

Seriously, I have no life.
Wow, don’t think I’ve ever seen a speaker with no tweeter...

“Sealed” and “acoustic suspension” is the same thing.
https://en.wikipedia.org/wiki/Acoustic_suspension

Since they’re sharing the same acoustic space, you’ll have to get 12-inchers spec’d for half the internal volume of the cabinet.

That’s about all I can tell you about such things. I’m not a speaker builder, I just play one on TV.

Regards,
Wayne A. Pflughaupt
Wikipedia is wrong. Sealed and acoustic suspension speakers are sealed, but a sealed speaker is not necessarily an acoustic suspension speaker and most are not. This is a common misconception.
An acoustic suspension speaker has a high Qts driver with a very free suspension so that almost all of the restoring force comes from the air compression.

This form of loading has rightly fallen out of favor.
 
B

Beave

Audioholic Chief
Another way of saying it: All acoustic suspension speakers are sealed, but not all sealed speakers are acoustic suspension.

And yet another way: All acoustic suspension speakers are sealed, but most sealed speakers are not acoustic suspension.
 
B

Beave

Audioholic Chief
My brothers and I each owned some Boston Acoustics bookshelf speakers from the 1980s that were true acoustic suspension designs (I think). The woofer surround was foamed rubber. Advent had designs like that around that time too, with foamed rubber woofer surrounds. The foamed rubber surrounds allowed for the very free suspension, as TLS Guy mentioned. The foamed rubber also dry-rotted and fell apart at about 15 years of life for all of us.

NHT has made many sealed bookshelf speaker models in the last 10-20 years that are not acoustic suspension.
 
ARGuy

ARGuy

Audiophyte
So I've done a bit of work on these speakers. First off, I've put back the original mid-range driver. The reason it sounded muddy & unclear is because it was fading out intermittently. The Italian made Faital Pro replacement mid-range was too efficient (97db @ 1 meter) for the other drivers and it was over-powering on certain music genres, so I had a look at the original mid-range and repaired the short. Sounds fine now. It is a bright & crisp mid and is now properly balanced with regards to the other drivers.

I managed to get my hands on another woofer produced by JVC, it was actually in a Pioneer speaker. Got these all Japanese made woofers for nothing. So I pulled the JVC passive radiator and mounted the second 12" woofer in parallel. Overall speaker impedance dropped from 8 ohms to between 4 & 6 ohms, still fine for my amp. I also replaced the tweeter a few times with a Jensen, JBL, an old Tannoy and an AR tweeter - all were very good but their volume was too low on account of their low efficiency rating. So I chose this 105db @ 1 meter Piezo tweeter. My top-end hearing isn't what it used to be, so this one worked out much better. I field tested them with jazz, some classical, hip-hop, house, Paul Oakenfold techno and some 80s rock. They handled them all no probs.

These Franken-speakers are now the perfect speakers for my den. Mid-range is smooth and not peaky, mid definition is good too - but not as good as the Faital Pro mid. May hunt for another mid going forward. Highs are dynamic & crisp without being harsh. Harsh is always something I'm trying to avoid. The previous JVC tweeters sounded boxy and closed, these new tweeters are open and much less directional - speakers sound similar when I walk around the room.

Not sure what I've made these into, whether they are still semi-passive rad or are now semi-sealed is tough to say - there is no port and certainly no lack of bass. The math says there is enough volume in the cabinet to support a sealed or semi-sealed design, but my ears were the final verdict. I'm glad I ignored the math and just used my ears. The whole idea of this was to get that bass I was after, modern designs w/ 6/5" woofers just don't do it for me unless there's a sub attached and I didn't want that in this application. They now have excellent bass, much smoother and more well rounded on the bottom end, nothing quite like dual 12" woofers. I feel the extra sound dispersion is from just having 2 extra drivers to produce more sound projection, so more bass, more perceived volume.

Just in case I was polishing a turd, I invited a couple of audio snobs over and after a good laugh at my creation, they enjoyed the sound and especially the deep bass. They liked the Faital Pro mids better though, I'll work on that.
 

Attachments

theJman

theJman

Audioholic Chief
Glad it worked out so well for you. It certainly is an interesting solution, but there's always something cool about building it yourself.
 
ARGuy

ARGuy

Audiophyte
Thanks Jman. Yeah, it is fun 'building' your own set for sure. Though it's more like swapping/assembling than building. Not many appreciate the satisfaction of such great sound with just a few mods, this is an excellent solution for someone wanting high end audio on the cheap. I grew up w/ big sound, AR9s and the like - so today's speakers just don't do it for me. This assembled setup sounds very clean w/ smooth punchy bass and at a resonant point perfect for a condo.

When I was recording and producing music in the studio, we dragged in bass cabinets with four 18" and 21" woofers and guitar setups with 4 sets of stacks each containing eight 12" speakers. I find it difficult to produce that sound & feel w/ today's solution of a few 6" woofers and a sub or two. IMO, dual 12" woofers are a good start for home audio.

Guess I was forced into assembling my own systems because it's difficult finding such setups unless one is willing to pay upwards of $4k. Large woofers in modern systems are very rare - these new manufacturers in the mid price range all seem to be on the cheap and it shows with their weak bottom end. So for me, it's best to get the old enclosures w/ the larger baffle holes and gut them to install new modern components. I don't have provisions of a workshop so I use existing enclosures, which works out well because the math has already been done by someone else - I'm just swapping out components w/ similar specs.

As another example, I assembled this set for my sister's bedroom. I was given this old Technics 3 way set by a mover who couldn't sell it. I've always found Technics tower speakers a bit muddy & somewhat boomy - but their build quality is very good if you overlook the faky wood veneer - there's lots of cabinet bracing and insulation as well as thick enclosure walls for minimal vibration. I swapped out the crossover and all of the drivers using Italian made Faital-Pro 10" woofers and 5 inch mid-range drivers. Not only is it highly efficient in the 95db territory as well as smooth sounding, but now it can take over 300 watts of clean power (they're much nicer to look at too). It sure is great sitting back and listening to your results in such a short time, I hated giving them up to my sister...
 

Attachments

Irvrobinson

Irvrobinson

Audioholic Spartan
Wikipedia is wrong. Sealed and acoustic suspension speakers are sealed, but a sealed speaker is not necessarily an acoustic suspension speaker and most are not. This is a common misconception.
An acoustic suspension speaker has a high Qts driver with a very free suspension so that almost all of the restoring force comes from the air compression.

This form of loading has rightly fallen out of favor.
True. The only new acoustic suspension speaker I've seen recent years is the Benchmark Media thing, and even they discontinued it:

https://benchmarkmedia.com/products/benchmark-sms1-loudspeaker
 
D

Dennis Murphy

Audioholic General
The new KLH speakers look to be using true acoustic suspension, not all that surprising since Henry Kloss was the brainchild of that original design.
Has someone done a review with woofer parameters? I'm not sure how we could determine the woofer compliance without data on Qts and Vas.
 
ARGuy

ARGuy

Audiophyte
Just a quick update:

I swapped out the tweeter again (I think it's my 5th one). I was playng around with the midrange speaker but strangely enough, whatever I put in made little difference to me. It appears it was the mid highs to upper highs that were not quite there; I thought it was the midrange speaker all along. I'm finally happy with this JBL Selenium tweeter. It grabs those really fine spatial highs (echos & such) that can be elusive for some tweeters and also handles the mid highs in a smoother fashion than the other 4 I've thrown in there.

As for the switch to acoustic suspension/sealed or whatever it is I've created, it seems to be going along very well without issue. I managed to blast it for the first time this morning w/ the new JBL tweeter; the volume on each component was consistent with each other - no surprises. Bass held out great too with no boominess now that there's an extra 12" woofer in each enclosure rather than the passive rad. I was concerned about amp overload but no clipping on the amp either, so it looks as if the impedance worked out too. I find now I need to concentrate less on the mids as this tweeter has cleaned up that part of the sound image that was lacking.

I've been using a standard reference set of 28 songs encompassing 5 or 6 genres (rock/electronica/house/classical/soundtrack/jazz) to tune these speakers. It's been a bit of a journey with multiple driver swaps, but it's all been worth it. They seem to have achieved the sound that I won't tire of.
JBL2.jpg


I'll bring back those audio snobs for another review in the coming weeks, but I don't need them to know that this is working out.
 
TLS Guy

TLS Guy

Seriously, I have no life.
Just a quick update:

I swapped out the tweeter again (I think it's my 5th one). I was playng around with the midrange speaker but strangely enough, whatever I put in made little difference to me. It appears it was the mid highs to upper highs that were not quite there; I thought it was the midrange speaker all along. I'm finally happy with this JBL Selenium tweeter. It grabs those really fine spatial highs (echos & such) that can be elusive for some tweeters and also handles the mid highs in a smoother fashion than the other 4 I've thrown in there.

As for the switch to acoustic suspension/sealed or whatever it is I've created, it seems to be going along very well without issue. I managed to blast it for the first time this morning w/ the new JBL tweeter; the volume on each component was consistent with each other - no surprises. Bass held out great too with no boominess now that there's an extra 12" woofer in each enclosure rather than the passive rad. I was concerned about amp overload but no clipping on the amp either, so it looks as if the impedance worked out too. I find now I need to concentrate less on the mids as this tweeter has cleaned up that part of the sound image that was lacking.

I've been using a standard reference set of 28 songs encompassing 5 or 6 genres (rock/electronica/house/classical/soundtrack/jazz) to tune these speakers. It's been a bit of a journey with multiple driver swaps, but it's all been worth it. They seem to have achieved the sound that I won't tire of.View attachment 25165

I'll bring back those audio snobs for another review in the coming weeks, but I don't need them to know that this is working out.
I hope you realize that when you added that second woofer you lowered the crossover point of the woofers by a factor of 2, leaving a gap between the woofers and mid.
 

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