BASS EXPERIMENT WITH RTA12c's AND......

soundfreak1

Imagine this if you will; starting with the sys. listed in my sig. Adding a two way external crossover set to send 800hrz and above to my Krell powering the rta 12c's than adding a parasound HCA 2003 ( just out of shop after rebuild ) at 800hrz and below to a pair of vintage JBL bass drivers( L123a's I believe out of a pair of JBL L100's) temporarily mounted in some sda 2 cabs with the cut outs for the 6.5" holes stuffed with foam and the tweets hole open for a port.btw parasound benched at 220 a side.the results are as follows... WOW.OMG.SUNNY BEACHES. ECT. ECT. THE WOUNDERFULL SOUND of the polks ,(just moded 170 hours so far) plus a bass that reaches out and SLAMS you in the chest ( from the jbl 12" drivers) and yet is so musical and clean that it has left a smile on my face that death couldnt remove.im just awed by the resulting sound this combo has achived.

soundfreak1

Oh yea picts.

Faustin

Out of curiosity what are your thoughts of the 12c's bass without anything added? My 12c's have probably around 250 plus hours since the rebuild and they seem to be getting better and better. When I initially played them beside my rebuilt 10a's that have been burned in the bass of the 12's was very disappointing compared to the 10's.

TennMan

You need to throw in some electrostatics and a few horns.

soundfreak1

I have found the bass in the 10's boomier than the rta's but the bass in the rta have never "SLAMED" just not built for it. But they are so great in what they do as to become my favorite speakers but always laked the bass slam I wanted. This bi-amping with the crossover has brought the sound to another level. It gives me the warmth of the polks with the very musical bass slam I have been wanting without the typical results of using subs ie boomie sloppy bass. These jbl drivers are very fast, tight and deep but still accurate and musical.

soundfreak1

TennMan wrote: »

You need to throw in some electrostatics and a few horns.

Dont really care for stats and the 12c's do very nice in the mid bass and highs especially after the recap and tweet upgrade. My besr friend ( who provided tje xover and jbl drivers) has a tri- amp system with JBL C,50's ( from the 60's) and the hornes in open air and twin supper tweets powred by a couple of Mac amps and a pair od Dynoco mark lll's but that system leaves you with bruses after listening for a while. I love the warmth of the polks but just wanyed more bass slam.

soundfreak1

Faustin what caps did you use?

Faustin

Clarity esa on the high and dayton on the low. Acually westmassguy did the c/o's for me. Did the dynamat, hurricane nuts,etc. Have RDO-194's in them. Found a Peerless from Denmark while in LA last week to go with another good one I had but I put them in my 10a's I have had since 1979. The originals blew quite a few years ago. I am going to veneer the 12's this winter, as the vinyl veneer is a bit beat up - not horrible but I can picture them looking like a fine piece of furniture. Had to appease the wife and am in the process of refinishing an old kitchen table that belonged to her parents. 2 more coats of finish and it is done. Then on to the 12's. Just have to decide what kind of wood to use.

Nightfall

I've never been disappointed with the bass of my RTA's, for just two 6.5" woofers they dig impressively deep. Maybe the different models, with different midwoofers, produce different bass? Mine are 6600X's.

Faustin

I believe my 6.5's are 6501's.

Nightfall

If Geppy happens to find this thread he can comment on the differences in bass quality and quantity between the different models.

soundfreak1

Its less a dissapointment with the rta's as it is a want for a diff type of bass attack they just cant provide. I consider the rta's my favorite speaker ive have owned! But with the second amp and the crossover on the JBL drivers I was able to get the bass atack I wanted without altering the character of the polks. Best of two worlds! It is truly incredible how the jbl drivers seamlessly blend with the polks as if they were in one cab and gives me control of the bass that I can "dial" in as I wish. At the 800 hrz range (and below) the polks are not really missing anything they can deal with very well but at that range the JBL drivers just slam the bass so cleanly and accurately it gives me goose bumps when I listen to them! It has to be heard to be believed.

Mystery

Nightfall wrote: »

If Geppy happens to find this thread he can comment on the differences in bass quality and quantity between the different models.

Me no Geppy but having owned both plus many more JBL's I can chime in.

RTA-12C on themselves have great bass. In fact, they go deeper and lower than my L100T's.
So much bass that a small 8-10" subwoofer doesn't affect anything unless I really turn the sub up too high.
Polks that use flat PR like SDA-2B, CRS+, RTA-12C etc... all have great bass but the bass is soft, rumbles like a subwoofer and bass note hang on longer.
I really like that when watching movies.

However, JBL's have the kick, slam, pound, grunt etc... whatever you want to call it.
That may be due to different kind of bass or just because they are active woofers.
When I first watched a movie clip on L166's, I felt like I was in a theater. It had so much chest thumping kick and grunt.

L100T's bass is very wide, open and big.
Basically, there is no softness on JBL bass where as Polks have big bass but softer/calmer.
Yes you can crank Polks and shake everything in the house and bass will run you out of the house but it's on the polite side compared to JBL's.
For movies, I do like bass notes to hang on a while like in Polks so JBL's with a subwoofer with good excursion will be great combo.
Specially on explosions, the rumbling bass notes for a while sounds really good.
The JBL's I have (L20t, L26, L36, L100T, L80t3, L166) don't have that but they do kick ****.

Think about being with a gentle lady vs a wild freaky one.

BTW, soundfreak, how about putting that JBL woofer in the same RTA-12C cabinet?
RTA is not using that cab volume for bass anyways since you are only sending 800hz and above.
That way, you can have one speaker to give Polk mids/highs and JBL lows as long as RTA cab has enough volume for the JBL woofer. :idea:

westmassguy

Mystery wrote: »

BTW, soundfreak, how about putting that JBL woofer in the same RTA-12C cabinet?
RTA is not using that cab volume for bass anyways since you are only sending 800hz and above.
That way, you can have one speaker to give Polk mids/highs and JBL lows as long as RTA cab has enough volume for the JBL woofer. :idea:

Mystery, that would be a disaster unless you put a separation between the upper and lower sections to isolate the Polk drivers from the JBLs. The JBLs would blow the cones right out of the Polk woofers.

Mystery

westmassguy wrote: »

Mystery, that would be a disaster unless you put a separation between the upper and lower sections to isolate the Polk drivers from the JBLs. The JBLs would blow the cones right out of the Polk woofers.

Yes, the lower chamber needs to be separated only for the JBL woofer.
And that's what I meant when I mentioned if the cab has enough volume otherwise the woofer won't have enough room for bass.
Or the mids can be mounted on their own pocket like Infinity mids (if that works with Polk) and use the whole cab.

soundfreak1

I wont mess with the polks by basterizing them, I will be getting sepporate enclousers for the JBL's and I can play with placement (thou I thing location wont mater much) but it is an amazing combo. The detail on bass drums and bass guitars is truly worth hearing! My wife thpught I was up to no good due to the stupified look on my face.everything we all love about the polks plus some **** kicking slam you upside the head bass.this is a good thing!

drumminman

Why don't you run the RTA 12's full range, and use a separate Xover to send the lows to the JBL's? Should be much more seamless and musical that way.

My modded RTA 12C's have plenty of accurate bass. JBL's are known for the west coast sound, i.e. artificially boosted bass and highs.

Faustin

Have to tell you, I am sitting here listening to some music with a friend that has not been over in a few weeks and the first thing he said about the 12's was "what did you do"? Reason being that the past couple of weeks the bass has become alive. Still not over thumpy but very noticeably deeper and better.

drumminman

How many hours do you have on your Xover rebuild? Typically it takes around 200 hours for the caps to fully burn in and the sound to settle.

soundfreak1

Im up to about 175 hours on the recap so far and I by no means lnock tje polk bass but wanted a faster and puncher bass than they could supply but also refused to give up the sweetness of the mid bass and high they produce.adding the jbl drivers gave me both without withstraining either.

Faustin

I have not kept track of the hours on my rebuild but I figure it is between 250 and 300 hours. I would leave a radio station play on a low volume sometimes for 24 hours at a time to speed things up.

soundfreak1

Question: what size (qubic ft wise) enclosure is best for the jbl (l123a) drivers in this configureation? Want to buy or build enclosures for them. Assistance would be greatly appreciated.

MAD

Soundfreak1,

I have a set of JBL 150A and I agree that the bass slam is quite exceptional. They are the model with a passive radiator. Although, I can't handle that metal dome tweeter, it's very harsh.

You are making me want to get out my crossover, run a separate amp and start experimenting.

soundfreak1

MAD wrote: »

Soundfreak1,

I have a set of JBL 150A and I agree that the bass slam is quite exceptional. They are the model with a passive radiator. Although, I can't handle that metal dome tweeter, it's very harsh.

You are making me want to get out my crossover, run a separate amp and start experimenting.

Try it bypass yhe mids and tweets in the jbl's use just the active base driver and at least with the L123a's drivets it is quite stunning.

soundfreak1

UPDATE! 8 months later.

A few tweeks have been made;
Exterrior xover now set to 1 k
Parasound amp replaced with a mcintosh MC2120
( Much tighter, more musical bass, a lot more punch)
Polks are fully broken in ( new caps)
There are just no words to describe the sound I've ended up with, everything I wanted! Absolutly amazing!

Next step is to work on my phono source. Cartridge too start with. Considering a denon 110 MC cartridge, open to suggustions on this though.

MarkCianciolo

I would like to hear this, but I know a thing or two about both of those speakers. Those 123a's were designed to be a ported rolled off driver, If I were you I would be looking for a pair of JBL L 88's They have the correct cab displacement, port size and location, plus you could either just unplug the lone tweeter and leave it in the box, or remove and plug just that one hole. Check it out.

soundfreak1

MarkCianciolo wrote: »

I would like to hear this, but I know a thing or two about both of those speakers. Those 123a's were designed to be a ported rolled off driver, If I were you I would be looking for a pair of JBL L 88's They have the correct cab displacement, port size and location, plus you could either just unplug the lone tweeter and leave it in the box, or remove and plug just that one hole. Check it out.

Right now I have them housed in some old cabs ported . Will have cabs built when I can for looks and proper size, I believe they need about 3/4 L of volume. Still have do more research on this. But for now they sound fantastic where they are driven by the mc2120 @ 1k and below. They were original in the l100 JBL'S and rolled off at about 1500 hrz.