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jezzaboy

Passive speaker and class D amp

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All these topics about FRFR has got me thinking. On the rare occasions when I have to gig with my own back line one of these setups might be ideal. 

Has anyone tried a passive speaker with a small class d head? I ask this because I have a TC BQ 500 and am looking at the RCF Art 315 mk 3 at £214 on Thomman. It`s rated at 300 watts which would be ok with the TC or even the ABM I own. It would be used for the odd pub gig without pa support. Normally on a gig like this, I would use my Ashdown 2 x 10 cab with one of the heads.

I don`t really have the budget to get a decent powered speaker and was just having a think.

Any opinions?

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A few years back my speaker cab went on the fritz and to get me through a rehearsal I used a spare PA cab we had. Quite an oldish one but reasonable quality and i was absolutely knocked out by how it sounded.

Had it hooked up to a MarkBass LM3 and i spent the whole rehearsal thinking "should I use a PA cab instead of a bass cab?". It was smaller, lighter and I think it would be perfect for stage monitoring but not too sure how it would be as a back line solution.

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I'm confused (to be fair it doesn't take much) 

Isn't that what everyone who has an amp head and cab doing? Or am I misunderstand something here? 

Why would you need an active / powered speaker if you're using an amp? 

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I haven't used an RCF 315 so I'm unsure how loud that one in particular goes, and importantly what happens to the low end as the volume goes up.

In general though, if it's just for backline, it comes down to do you want a transparent cab, or one which changes the mids, rolls off a bit of top end, and perhaps the very low end?  Either could sound good - I think it comes down to personal preference, type of instrument/musical style. Are you unhappy with the Ashdown 2x10 in some way?

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2 hours ago, Newfoundfreedom said:

I'm confused (to be fair it doesn't take much) 

Isn't that what everyone who has an amp head and cab doing? Or am I misunderstand something here? 

Why would you need an active / powered speaker if you're using an amp? 

The RCF speaker I have mentioned is passive.

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1 hour ago, jrixn1 said:

I haven't used an RCF 315 so I'm unsure how loud that one in particular goes, and importantly what happens to the low end as the volume goes up.

In general though, if it's just for backline, it comes down to do you want a transparent cab, or one which changes the mids, rolls off a bit of top end, and perhaps the very low end?  Either could sound good - I think it comes down to personal preference, type of instrument/musical style. Are you unhappy with the Ashdown 2x10 in some way?

No the Ashdown is fine but I sometimes travel with the guitarist and any space that can be saved is a bonus. Also I just fancy trying out a pa cab to see if I prefer the sound. I may end up going with a powered cab but I`m just trying to weigh up different options.

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11 minutes ago, jezzaboy said:

The RCF speaker I have mentioned is passive.

Yes I know. You said in your initial post you don't have the budget for a powered cab. My point was you don't need a powered cab. Running from an amp head into a passive PA speaker is technically exactly the same as running into a cab, except the PA cab would be full range and voiced differently. However, it would work exactly the same way. 

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Posted (edited)

Spot on, the pa cab would be full range and voiced differently. 

When I think about it, there have been topics like this in the past, some of which I might have started or contributed to so off to use the search function I go!

 

 

Edited by jezzaboy

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4 hours ago, jezzaboy said:

Spot on, the pa cab would be full range and voiced differently. 

When I think about it, there have been topics like this in the past, some of which I might have started or contributed to so off to use the search function I go!

 

 

Would it be full range though? 

The ideal bass cab would go lower than a PA cab, designed to cross over into subs, would tend to be designed for. 

Whether any of the bass cabs most of us use are anywhere near “ideal” is a different question. 

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1 hour ago, LukeFRC said:

Would it be full range though?

It's listed as -10dB at 50Hz. That's not full range. It's what you'd expect from a main intended for pole mounting, with subs handling below 80Hz. The only advantage I see to it is that the 1.8kHz crossover from the woofer to HF horn makes far more sense than the usual 3.5kHz or higher crossover from woofer to tweeter in bass cabs. Not that a 3.5kHz or higher crossover from a woofer to tweeter makes any sense. It doesn't. 🙄

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I can't comment on the particular speaker you're taking about, but on smaller gigs I D.I from my amp head into the PA to save space and carting my cabs around and it sounds just fine. In fact I'd go as far as to say it sounds great, and we don't use any subs. Just standard 15" PA speakers. Granted this is slightly different to what you're talking about as it's the PA and not the amp head doing the legwork, but I can't see why it wouldn't work pretty much the same running the amp directly into a PA speaker. I just don't see what the benefits would be over using a dedicated cab. In a band situation if you are limited for space and the band already has a PA then it makes sense to utilise it. If you're taking about using a PA speaker just for the bass, then why not just use a small, lightweight cab, which you already own? 

 

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4 hours ago, LukeFRC said:

The ideal bass cab would go lower than a PA cab, designed to cross over into subs, would tend to be designed for.

Would it though? I use a PA speaker which claims it is "50 Hz - 20 kHz"; additionally I high-pass at 80Hz.
I think it sounds really good.

 

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6 hours ago, jrixn1 said:

Would it though? I use a PA speaker which claims it is "50 Hz - 20 kHz"; additionally I high-pass at 80Hz.
I think it sounds really good.

 

That’s why I added: “Whether any of the bass cabs most of us use are anywhere near “ideal” is a different question.“

I have no doubt that what you’re doing sounds good, and Myself have high-passed bass there or higher... but it doesn’t help anyone if we say “all PA speakers are full range” because it doesn’t help us understand the difference between them and a bass cab, or even between a passive PA speaker or an active one with the DSP helping.

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Posted (edited)

FRFR would require a cab which linearly covers the full range of audible frequencies, or at least the ones required for bass (which reading here it sounds like the RCF doesn't) and a linear pre and amplifier, which the TC or Ashdown won't be.

FRFR has a purpose, either that the bass is reproduced without any colouration of the original signal, such as into a console and PA speakers/studio monitors, or for modelling, so that the uncoloured system will let you use an emulation of an SVT one night, a Trace Elliot the next, and then a cranked Marshall Super Bass on Sunday afternoon.

You may love the sound of the TC/Ashdown into the RCF, and it may also suit you with the size and weight issues you mentioned, but don't kid yourself that you will be moving to a system with full range and flat response, because you won't. That is neither a good nor a bad thing, just a thing!

FRFR has become a bit of a buzzword around here, and there is some fervent evangelism going on in some quarters, such that you might be led to believe there is only one true way, and we're all doing it wrong until we have an active PA cab with DSP to flatten the response to miraculous smoothness. The fact is that there are many wonderful ways to skin the bass-cat, and loads of very portable options designed for bass, as well as ones designed for source reproduction. Don't get suckered into dogma or do something just because others are shouting louder than everyone else. It sounds to me that you may be shoehorning a concept in where it may not be necessary, and that there could be cheaper and easier solutions available to you (if I might be so bold!).

Edited by Jus Lukin
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"If it sounds good, it is good". Duke Ellington.

Even before the current FRFR craze there was the 'set it for flat response' craze, where players would automatically set all the tone controls at noon, resisting advice to do otherwise, because they wanted flat response. It was a silly notion, because nothing in the signal chain is flat, starting with the pickups, ending with the room. If they somehow had managed to get truly flat response it would have been as bland as flat beer.

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Posted (edited)

Very true, Bill.

We're heading off topic a little, but also worth noting that 'flat' is usually quoted within a tolerance, +/-3db being considered very flat response, but even that has swings of 6db between peaks and troughs, and frequency ranges are often quoted between -10db points, those points still considered 'usable'. All of that is within the system itself which will then be making noise in some physical space which will affect the sound- even outside there is at least one boundary to reflect and alter the response. Anechoic chambers aside, even the best treated mastering suite will have wide tolerances in it's room response, and a part of a good mastering tech's job is knowing the space well.

Point being, that ruler flat response in physical reality is practically impossible, 'flat' is ultimately nominal, and there is a big difference between 'clinically flat' and 'flat enough to do the job'.

Add in the fact that most FRFR bass rigs seem to be built around a preamp or emulator to add in the colour which is flattering to a bass guitar, and the whole operation starts to look more like an exercise in having the greatest flexibility from the least amount of gear than an ideal way forward for everybody. For anyone simply looking for one great bass sound there are simpler and cheaper ways to do just as good a job.

For context, and others would no doubt dissagree, I find my 12" Barefaced cabs and Markbass LMII or Crown power amp to be 'flat enough' to give 'straight into the desk'' response, or to use accurately with Sansamps and digital emulations.in real world contexts. I also have a 100watt valve amp and old style 4x12, because everything which is wrong with that setup is also bloody awesome!

Edited by Jus Lukin

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Spot on, Bill. Setting the eq at noon merely gives you the preamp designer's tonal preference. 

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Posted (edited)

If the EQ is flat at noon what it gives you is the same result as if they weren't there at all. They're not supposed to be merely for decoration. It's a far cry from the 60s, when we all played valve amps with mediocre speakers. The usual protocol then was to turn everything to '10', unless of course you had the option to go to '11'. 😎

Edited by Bill Fitzmaurice

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Bill is right that a passive cab wit that response is a PA top. The problem is when you put it on the floor, the low end becomes unpredictable (unless you designed it, then yopu could predict it.

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People are being far too pessimistic. The RCF is a good quality PA speaker designed to have as flat a response as they could get. It will use the same drivers as the powered version and peole have had good results with RCF speakers. The point about your bass amp not being flat is valid. Room problems apply the same to any speaker and by 'flat' we simply mean it tracks the output from the bass pickups, whatever that is.

you are talking about small gigs so output below 59Hz is usually little more than a nuisance to be filtered out. the only other issue is whether the speakers can handle bass without damage, that shouldn't be an issue with a 15" RCF driver, PA drivers are designed to have similar heat dispersion to bass speakers and the bass only driver is likely to have better excursion than a bass instrument speaker if there is indeed any difference. The advantage of an active speaker is that the matching of amp to speaker is done for you and it is easy to build in protection for the speaker.

There are plenty of old PA cabs around, borrow one and see if you like the sound. The RCF is probably going to be an upgrade on most PA speakers but just check you like the cleaned up sound before you spend any money. It won't be exactly like the RCF but it's better than just a leap into the dark.

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Phil my point was that it was designed for pole top mounting and would not perform as designed. It will have more bottom end and that may or may not be a good thing.

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