JBL 3-way Rebuild

[mkballer]

I have two 3-way JBL MRV 308s that I have decided to rebuild. I want to use the same enclosures, but swap out the speakers. They come with an 8" woofer, 6.5" mid, 1/2" tweeter from the factory, so I'd like to match the sizes with the new speakers I buy. I have taken out the crossover and all wiring, so it's just an empty box. I just purchased a 150 watt rms @ 8 ohms QSC amplifier, so I would like to make sure these speakers are in that range so I can use this amp to power them. Could someone please direct me to a kit or give me direction into what speakers and crossover i would need to purchase to get these up-and-running? any help is greatly appreciated! The manual with specs is here: nodevice.com/manual/newmans/jblharman/MRV308_tspdf/get47144.html

thanks!

 

[irishtom]

What do you hope to accomplish, what's the goal? In what ways do you hope to improve over the JBL? You have to have some notion. Otherwise you're unlikely to improve over the stock JBL.

Regards

 

[mkballer]

well, the reason i am replacing the old jbl speakers is because they were blown by playing too loud for too long. i want to use the new speakers mainly for music listening; and i prefer crisp, detailed, quality, full-ranged sound over loudness. and, again, i would like to be able to use my new amplifier to power them. the jbl's lacked in the low range, so bass is quite important to me, as well.

thanks again

 

[irishtom]

well, the reason i am replacing the old jbl speakers is because they were blown by playing too loud for too long. i want to use the new speakers mainly for music listening; and i prefer crisp, detailed, quality, full-ranged sound over loudness. and, again, i would like to be able to use my new amplifier to power them. the jbl's lacked in the low range, so bass is quite important to me, as well.

thanks again

I can't help you MK because my DIY speaker efforts have been with a totally different school of speakers. But now that your goals are stated it will be easier for others to help you.

I also suggest the forum at the Lansing Heritage site where lots of astute JBL guys hang around and the Parts Express "tech talk" forum where some really sharp DIY speaker guys can be found.

www.audioheritage.org

www.partsexpress.com

 

[highfigh]

I have two 3-way JBL MRV 308s that I have decided to rebuild. I want to use the same enclosures, but swap out the speakers. They come with an 8" woofer, 6.5" mid, 1/2" tweeter from the factory, so I'd like to match the sizes with the new speakers I buy. I have taken out the crossover and all wiring, so it's just an empty box. I just purchased a 150 watt rms @ 8 ohms QSC amplifier, so I would like to make sure these speakers are in that range so I can use this amp to power them. Could someone please direct me to a kit or give me direction into what speakers and crossover i would need to purchase to get these up-and-running? any help is greatly appreciated! The manual with specs is here: nodevice.com/manual/newmans/jblharman/MRV308_tspdf/get47144.html

thanks!

If the woofers blew, you can have them reconed. Tweeters and mids can be replaced.

FYI- the woofer's parameters determine the cabinet dimensions and along with the requirements of the speaker system, they determine the port's dimensions. Making the cabinet to fit the woofer is a lot easier than shooting an arrow in the air in an attempt to hit a target. Finding a suitable woofer can happen but it takes a lot of time.

 

[mkballer]

thank you for your comments! i will try the altec lansing forum.

 

[TLS Guy]

I have two 3-way JBL MRV 308s that I have decided to rebuild. I want to use the same enclosures, but swap out the speakers. They come with an 8" woofer, 6.5" mid, 1/2" tweeter from the factory, so I'd like to match the sizes with the new speakers I buy. I have taken out the crossover and all wiring, so it's just an empty box. I just purchased a 150 watt rms @ 8 ohms QSC amplifier, so I would like to make sure these speakers are in that range so I can use this amp to power them. Could someone please direct me to a kit or give me direction into what speakers and crossover i would need to purchase to get these up-and-running? any help is greatly appreciated! The manual with specs is here: nodevice.com/manual/newmans/jblharman/MRV308_tspdf/get47144.html

thanks!

I took a look at your link.

That speaker is a dreadful piece of rubbish and not worth any effort.

The bass and mid drivers are in the same space. Two drivers of different dimensions have to have different Thiel/Small parameters, so the box can never have been tuned properly. In any event the mid cone would have had to have basically looked like a huge tuning leak to the bass driver alignment.

The crossover is not even three way. The bass, low pass filter is second order, and the woofer and mid are fed the same signal! They relied on the acoustic and mid roll offs of the bass and mid range drivers for the lower end of the band pass crossover. The HF, high bass crossover is third order at 3.5KHz.

There is no HF cut off to the mid range driver. So there is no band pass electrical filter at all. That speaker is a total mess, and will be what ever you do to it.

A proper three way has the mid in its own enclosure. The woofer is fed via a low pass filter, the mid by a band pass filter, and the tweeter by a high pass filter. The slopes of the filters are customized to the response curves of the drivers selected.

If you want to build a speaker we will assist you starting from scratch. That will be a lot easier, and there is a much better chance of you having something to show for your efforts.

Sorry, but I doubt anyone on these forums wants to donate time and effort, and it takes a lot of both, into that project. I know I don't.

 

[irishtom]

Many excellent loudspeakers have used minimalist crossovers and allowed the driver's natural roll-off to act without additional filtering. Some would make the case that's it's a better way to make a system especially if you make your own drivers and can control the roll-off.

Myself I tend to listen to a speaker before dismissing it as dreadful rubbish, even if it doesn't meet my notions of what good should be, ya never know.

 

[TLS Guy]

Many excellent loudspeakers have used minimalist crossovers and allowed the driver's natural roll-off to act without additional filtering. Some would make the case that's it's a better way to make a system especially if you make your own drivers and can control the roll-off.

Myself I tend to listen to a speaker before dismissing it as dreadful rubbish, even if it doesn't meet my notions of what good should be, ya never know.

That speaker has to be rubbish. Even if you overlook the crossover, you have two different drivers in the same tuned space. It then has to defy the laws of physics for the speaker to be any good. The OP stated that the speaker lacked bass. If you look at the design it had to. It will still lack bass whatever drivers you put in it.

The speaker is not a three way how ever you look at it. It is a poorly executed bizarre two way.

That speaker was slapped together to make the unwary think they were buying a three way speaker, which it isn't.

Another example of deplorable corporate ethics, that is all a part of the pickle we find ourselves in. There is just no way of looking at a product like that any other way.

The label might say JBL, but it might just as well be "white van."

 

[irishtom]

That speaker has to be rubbish. Even if you overlook the crossover, you have two different drivers in the same tuned space. It then has to defy the laws of physics for the speaker to be any good. The OP stated that the speaker lacked bass. If you look at the design it had to. It will still lack bass whatever drivers you put in it.

You sure are cocksure of yourself, you can judge a speaker's quality having never heard it. Without a trace of doubt.

No doubt it's compromised but all speakers are. Without hearing it you've no idea if the engineer chose his compromises wisely. Maybe he was more clever than you are and you don't understand his thinking. If the woofer and midrange drivers are covering the same range and the woofer's top rolloff and the mid's bottom rolloff are well controlled then the engineer is getting a wide range response for his money without the monetary and sonic expense of passive components. Yeah, just might be very clever engineering at the price point.

And yeah, the speaker could've had bass, it could as likely have an excess of bass as lack. Could be it lacks bass because for the box size the engineer chose sensitivity over bass depth. Might be the midrange cone and woofer relationship would lead to greater bass at resonance rather than less, a clever engineer could work that out easily enough. And there's also empirical design; just because you don't think it could work doesn't mean they don't know how to make it work.

And maybe it's junk. But I'm open to possiblities you're not open too. And I haven't heard it.

 

[TLS Guy]

You sure are cocksure of yourself, you can judge a speaker's quality having never heard it. Without a trace of doubt.

No doubt it's compromised but all speakers are. Without hearing it you've no idea if the engineer chose his compromises wisely. Maybe he was more clever than you are and you don't understand his thinking. If the woofer and midrange drivers are covering the same range and the woofer's top rolloff and the mid's bottom rolloff are well controlled then the engineer is getting a wide range response for his money without the monetary and sonic expense of passive components. Yeah, just might be very clever engineering at the price point.

And yeah, the speaker could've had bass, it could as likely have an excess of bass as lack. Could be it lacks bass because for the box size the engineer chose sensitivity over bass depth. Might be the midrange cone and woofer relationship would lead to greater bass at resonance rather than less, a clever engineer could work that out easily enough. And there's also empirical design; just because you don't think it could work doesn't mean they don't know how to make it work.

And maybe it's junk. But I'm open to possiblities you're not open too. And I haven't heard it.

Sometimes you can indeed look at a design and say with certainty that the speaker is so flawed that it will be very poor. This is one of those occasions.

You just can't put two different drivers in a ported box. If you had worked with speakers as closely as I have for over fifty years, those sort of issues become instantly intuitive.

 

[Shock]

Sounds like you two need a beer.

 

[irishtom]

Sometimes you can indeed look at a design and say with certainty that the speaker is so flawed that it will be very poor. This is one of those occasions.

You just can't put two different drivers in a ported box. If you had worked with speakers as closely as I have for over fifty years, those sort of issues become instantly intuitive.

How can you judge when you don't know the characteristics of the drivers?

What you're doing is arguing that a notion that runs counter to yours MUST be fatally flawed. Note that almost every school of speaker design out there has detractors who think it fatally flawed AND people who think it's the only proper way to make a speaker. In an endeavor in which designers can't even decide on what a perfect speaker should actually do subjective values then become very important but are in the end subjective after all. Especially given the compromises made in all speakers. It's unreasonable to think that when a designer chooses different compromises than you the result must be a poor speaker.

Had you cast your views as speculative opinion rather than objective fact, not as ex cathedra dogma, you'd be a great deal more reasonable.

I did my first DIY speaker about 40 years ago and I know a little bit myself. And I've learned that all kinds of things can sound good, whether I approve on a theoretical basis or not. One would think that with all the experience you claim you'd have learned the same.

 

[R-Carpenter]

While “Rubbish” statement may be a bit rough and straightforward, it is essentially true for this design.
It's a budget minded high Q speaker designed to rock the house at the expense of a quite a few shortcuts. The woofer will create strong sonic drift of the midrange and to think that the designer planned for it to happen is strange. Speakers like this are designed by marketing department and actual speaker designers have little to do with it.
Sometimes if it looks like a duck, walks like a duck it's very unlikely that it's a 1943 T34 tank.

Going back to the initial question, it is possible but would it make sense? It's an old speaker and not a very good one by any standard.