Question for spkr cab experts

[Northern Pike]

For many years I’ve been using a bi-amped setup with a 15 TL and a 12TL, both loaded with JBL K series. The centre port is plugged on the 15, but not on the 12. I recently got a Genz Benz 3 for very small gigs and practice/rehearsal. Using it with a single 12 TL is good, but if I use 2 I’ll move more air and get max power out of the amp. For use with a single I’d like to block the centre port for more low end. I want to keep the other one unblocked for use with my bi-amped rig.
So the question is, if I use an unblocked one on top of a blocked one will there be any possible sonic conflict? Whaddaya think guys?
Thanks

[agedhorse]

Blocking a port does not necessicarily mean more low end and in fact if the cabinet is properly ported will result in less useful low end.

Now the K120 is not a very good performer on the low end by itself. In fact, it's pretty weak. I would suggest that you might get a much more pleasing sound with the 15 and the 12 together, no crossover at all. (I'm assuming when you use the term biamped, this means 2 power amp channels and an active crossover). You might also prefer just the 15 (in it's natural and normal ported condition), that's a bright 15 with so-so low end.

When you say your cabinets are TL's, are you refering to the EV TL series cabinets or do you mean TS ported boxes tuned with Theil-Small parameters?

[DukeLeJeune]

Vented boxes have fairly rapid rolloff and corresponding rapid phase shift. If one box is tuned significantly higher than the other, you could end up with partial cancellation in a region where you expected reinforcement, this due to their outputs not adding in-phase.

[Northern Pike]

Originally Posted by agedhorse

Blocking a port does not necessicarily mean more low end and in fact if the cabinet is properly ported will result in less useful low end.

When you say your cabinets are TL's, are you refering to the EV TL series cabinets or do you mean TS ported boxes tuned with Theil-Small parameters?

Yes, EV designed TL (606 I think). I built 2 15s and 2 12s way back in the 80s. I recall that the plans at that time stated blocking the centre port would lower the tuning. I was gigging every night in those (good old) days and experimented with the ports. My ears concluded that it sounded better blocked. I use the 12 for the highs so didn't block it. They have served me well. And yes, biamped w. stereo power amp and active crossover.

[Northern Pike]

Originally Posted by DukeLeJeune

Vented boxes have fairly rapid rolloff and corresponding rapid phase shift. If one box is tuned significantly higher than the other, you could end up with partial cancellation in a region where you expected reinforcement, this due to their outputs not adding in-phase.

That's exactly what I was wondering about/fearing. Would you think this difference would be "significant" enough to have that effect? I guess I should just make them both the same and be done with it.
Thanks for your input guys.

[Mr. Foxen]

Make two of the one you like the sound of and use that. If you are going to be trying to make something complicated, you need to roughly understand what is happening.

Basically, close but different is bad, totally different is OK if you are actually biamping (as in using a crossover, with one thing good at lows and one good at highs).

[agedhorse]

Originally Posted by Northern Pike

Yes, EV designed TL (606 I think). I built 2 15s and 2 12s way back in the 80s. I recall that the plans at that time stated blocking the centre port would lower the tuning. I was gigging every night in those (good old) days and experimented with the ports. My ears concluded that it sounded better blocked. I use the 12 for the highs so didn't block it. They have served me well. And yes, biamped w. stereo power amp and active crossover.

Ok, now did you calculate the porting of the TL style box (which is a TS box alignment) with your K-120's? If not, there's no way to predict the response of the speaker systems. The driver and the box/ports combine to create a SYSTEM where each component works together.

I suspect that this is a (or one) large part of the performance limitation you are experiencing. If the box was originally ported for the EVM-15B and you use the K130, the difference could be staggering.

[Northern Pike]

Originally Posted by agedhorse

I suspect that this is a (or one) large part of the performance limitation you are experiencing. If the box was originally ported for the EVM-15B and you use the K130, the difference could be staggering.

I didn't calculate anything. I simply tried with and without and preferred the sound of the K 140 with the blocked port. I originally used 2 K140s in separate cabs with an Acoustic 470. When I switched to stereo (Yamaha PB1 and Bryston 3B) I exchanged one for a 12" K120 to take the highs. I haven't experienced any performance limitations. I think it sounds great, which is why I've used it for so many years. Many musicians whom I respect have concurred over the years.
Maybe I got lucky, or I've got tin ears.

So, I've got a spare 15, and a spare 12.
My question is regarding using a single K120 in a ported cab with my new Shuttle 3.0, and then adding a second K120 in a similar cab, but with a 50% difference in port area.
Would I have an out of phase situation?
I appreciate your help.
And BTW, since I don't have a speaker cable with a Speakon, would there be any difference daisy chaining 2 cabs from the 1/4" out, versus using a separate out from the Shuttle for each of 2 cabs?
Thanks!

[Northern Pike]

Here's what I was referring to. 6th paragraph, P. 3

"For bass use..."

http://www.pa-anlagen.ch/Manuals/Ele...line%20EDS.pdf

[agedhorse]

Originally Posted by Northern Pike

My question is regarding using a single K120 in a ported cab with my new Shuttle 3.0, and then adding a second K120 in a similar cab, but with a 50% difference in port area.
Would I have an out of phase situation?
I appreciate your help.
And BTW, since I don't have a speaker cable with a Speakon, would there be any difference daisy chaining 2 cabs from the 1/4" out, versus using a separate out from the Shuttle for each of 2 cabs?
Thanks!

No way of knowing which cabinet would be better tuned, but I wouldn't recommend it because of the combined phase response in the low end.

I suggest that you take a look at some of the speaker design software and maximize what you have, the results and improvement may be more significant than you can imagine.

[Northern Pike]

Yes, I think what you say makes perfect sense. I suspected there might be a conflict which is why I asked, but it helps to get an expert opinion to confirm my suspicion. Thanks.
I suppose there's always room for improvement on anything. I'm not aware of the software you mentioned but could probably search some out. As you can tell, I've got 4 of these cabs which have served me well for decades. I want to continue using them if I can. I've been playing professionally for over 30 years but haven't been much of a gearhead. I have other interests and hobbies for which I *am* a gearhead, and most of my web involvement has been with them. Music has been more of a job than anything else. Maybe this site will set me off on another expensive tangent.
I guess a single 15 would work with my Shuttle as a small setup, but I was thinking small-est. There isn't much I can do to alter a 12 TL, other than mess around with the porting. Presumably, the port blocking would have same lowering effect on the 12 as the 15, just working at different frequencies.
Cheers!

[billfitzmaurice]

You don't say where you're crossing over, but if it's 200Hz or higher the K120 will have the same response in a sealed cab as it will vented, and it only needs a 1/2 cubic foot net box to do it.

[agedhorse]

Originally Posted by Northern Pike

Presumably, the port blocking would have same lowering effect on the 12 as the 15, just working at different frequencies.
Cheers!

Maybe, maybe the opposite. There's no way to guess accurately.

[Nightbass]

Originally Posted by Northern Pike

Yes, EV designed TL (606 I think). I built 2 15s and 2 12s way back in the 80s. I recall that the plans at that time stated blocking the centre port would lower the tuning. I was gigging every night in those (good old) days and experimented with the ports. My ears concluded that it sounded better blocked. I use the 12 for the highs so didn't block it. They have served me well. And yes, biamped w. stereo power amp and active crossover.

The E-V TL Series builder's plans also say that if you block the middle port ("step down tuning") that you need to apply EQ to boost the bass in order to restore the relative flatness and tone of the cab. Everyone forgets about that part.

For the 1x15, blocking the middle port reduces the box tuning from 55 to 40 Hz. Then you're supposed to give it a 6 dB boost at 45 Hz (using a second-order, underdamped highpass filter, Q=2).

For the 1x12, blocking the port reduces the tuning from 62 to 52 Hz, and the corresponding filter is to have a peak at 60 Hz.

Since your goal is to use one 1x12 with your biamp rig and two 1x12s with your Shuttle, my suggestion would be to configure both 12s the same, with the middle port blocked (and some gentle EQing as above). The sound of the biamped rig won't be affected, and the Shuttle rig will sound as good as it can, given the limitations of the K-120 and TL-806 box design.

[agedhorse]

Originally Posted by Nightbass

The E-V TL Series builder's plans also say that if you block the middle port ("step down tuning") that you need to apply EQ to boost the bass in order to restore the relative flatness and tone of the cab. Everyone forgets about that part.

For the 1x15, blocking the middle port reduces the box tuning from 55 to 40 Hz. Then you're supposed to give it a 6 dB boost at 45 Hz (using a second-order, underdamped highpass filter, Q=2).

For the 1x12, blocking the port reduces the tuning from 62 to 52 Hz, and the corresponding filter is to have a peak at 60 Hz.

Certainly EV's information only applies to EV's driver parameters (SRO-12L or EVM-12L) and not to JBL's K-120 which is totally different. Without calculating the system response for the specific conditions, there is no way to generalize what the response might be. The box is only one part of the equation that is closely coupled to the driver's properties.

[billfitzmaurice]

The box frequency is derived purely from the box and port dimensions, and is independent of the driver. As far as the K120 is concerned it will work best in a 30 liter (net) box tuned to 70 Hz, which gives an EBS alignment with a 70Hz F3. Anything larger or tuned lower won't give an appreciably better result.
While they have very different specs oddly enough the SRO-12 and EVM 12L give a very similar result.

[agedhorse]

For clarity, I was referring specifically to the system response and not the "box" exclusive of the driver. Nobody listens to the box by itself or the driver by itself. The only response that matters is the response due to the combination of a specific driver with a specific enclosure.

[Northern Pike]

Man, this is a busy forum! Took a couple days off for Christmas and we're already back 9 pages. Anyway, here's a couple of pics to illustrate what I've been talking about. I guess that's the end of this one. I'm going to make a couple of covers for the ports on my 12s and take it from there. This has been very helpful.
I'm digging this forum. I'm gonna trust my ears though, lest I get caught up in the hype and start buying a new rig every couple of weeks, like a guitar player.
Thanks!

[fingerbun]

Originally Posted by DukeLeJeune

Vented boxes have fairly rapid rolloff and corresponding rapid phase shift. If one box is tuned significantly higher than the other, you could end up with partial cancellation in a region where you expected reinforcement, this due to their outputs not adding in-phase.

Hi, hoping I can revive this old thread to ask about this post.

Can someone please explain this relationship between rolloff and phase shift? I tried googling it and I just don't understand what is being said.

For example right now I pair a Hartke 2x10 which is non-vented with an old EV TL606. The Hartke goes down to 50Hz. The TL goes down to either 63 Hz (3db down point) or 45 Hz ("Usable" frequency). Does this mean I am getting phase cancelations between 63 and 50 or 45 and 50? Given the Hartke box is non-vented, does this change things?

I assume the bottom A on a 4 string bass is 55Hz, is that right? What frequency is the bottom E? I thought from when I bought the TL (MANY years ago) that the bottom frequency was 41.3 Hz, and that didn't quite get to the fundamental of bottm E on a four string bass. I am assuming the 45 I quoted above (from documentation on the box) is the 41.3 I remember.

[Mokebass]

I wouldn't block any of the ports unless you want to blow the speaker.

All good cabinets should be properly tuned out of the box. Front ported is my preference but really i wouldn't try to block them without professional electronic advice.