What will happen if I do this?

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chuck55

Member
Joined 2003
#1
What will happen if I use one of these Seas woofers:

Seas H1471 (CA22RNY) 8" Paper Cone

SEAS Prestige CA26RFX (H1305) 10" Coated Paper Cone Woofer


with one of these Seas tweeters that would best match the sound characteristics and blend well with the woofer ( I don't know much about selecting tweeters. That is why there are so many here):

SEAS Excel T29CF-002 (E0040) Crescendo Fabric Dome Tweeter

Seas Excel T35C-002 35mm Mid-Tweeter

SEAS Prestige 27TFFC (H0881) Textile Dome Tweeter

https://www.madisoundspeakerstore.c...s-prestige-27tdfc-h1189-textile-dome-tweeter/

https://www.madisoundspeakerstore.c...stige-27tffnc/g-h1396-1-textile-dome-tweeter/

https://www.madisoundspeakerstore.c...s-prestige-25tffc-h0519-textile-dome-tweeter/

https://www.madisoundspeakerstore.c...ters/seas-prestige-29tff/w-h1318-fabric-dome/


in a vented Parts Express cabinet:

https://www.parts-express.com/Dayton-Audio-MTMC-1.0BK-1.0-ft-MTM-Curved-Cabinet-Gloss-Bla-302-751

with no crossover?

I am trying to use 2 drivers for near full-range sound but without crossover.
 
#3
With no crossover? With more than a few watts, tweeter distortion will rocket through over excursion, and if there is a significant low frequency dynamic peak, you will probably blow it even at low average SPLs. You will also have severe phasing and combing issues due to the different acoustic centres and offsets (which somewhat pale into insignificance if you kill the tweeter, which you will, very quickly 😉 ). This is what crossovers are for: to protect drive units and ensure a quality response.

If you want to run a tweeter sans crossover, then you'll be better off with a small wideband / fullrange driver, which can at least handle some LF power without releasing the magic smoke. You'll still need an inductor (or shunt cap if series wiring) on the woofer though to help address some of the major response issues you will otherwise likely encounter, deal with the slightly rising inherent response of the woofers, and provide some compensation for step-loss.
 
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#5
Examples? Which crossovers, precisely, so some context can be assessed?

Call me a boring killjoy, but I very strongly advise you (the OP) not to do this without properly considering exactly what you doing. Certainly, do not just jump in because you're told 'try it, it'll be fine'. Unless of course you have money to burn: some of the drivers you list cost several hundred pounds apiece, and it's very easy for us faceless buggers on the forum to casually tell people to risk that (and sans any kind of context, it most certainly is a massive risk), since it's not our money that is likely to go up in smoke.

I make no apologies: without any kind of context, the laws of engineering and common sense are very clear on this point. Do not chuck a tweeter into a box, sans crossover, and expect it to survive long on normal music playback, even if it doesn't sound catastrophic before it croaks, which in many cases it will.
 
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#6
The only way I can see of doing a no-cap crossover would be to put an inductor across the tweeter, and stick a resistor in series with that. A chunky low-DCR inductor would be required.

Apart from that, I think adason is referring to piezo tweeters, which are innately capacitve. ie, not a normal tweeter.

I found out the interesting way that it's possible to run a compression driver full-range at moderately high levels. The sound of the diaphragm hitting the phase plug are what clued me into the crossover being set improperly. I don't know how long they would have lasted thermally.

Chris
 
#9
So what are you referring to? You can do a series filter with a shunt inductor (providing an electrical high pass) but that is a 1st order series (high pass) crossover. You can also do a 1st order parallel high pass crossover with a series resistor and shunt inductor (classical RL high pass), providing there is a large excess of sensitivity in the tweeter over the woofer, and you can cope with the resulting impedance drop. Neither of which are in any way, shape or form relevant to what the OP was referring to, since he said very clearly 'no crossover'. Which I interpret as meaning 'no crossover' not 'no series capacitor on the tweeter'. Perhaps he does mean the latter, but without clarification, I would take it as-written.
 
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#11
As noted, that is a 1st order RL electrical high pass. Otherwise known as 'a crossover'. The OP said 'no crossover', not 'some alternative type of crossover'. Also as noted, the RL high pass typically only becomes practical if you have a large effective excess of output in the tweeter (or relevant driver) over the target system sensitivity, since the resistor values need to be relatively high to prevent excess impedance drop.
 
#15
chuck55 said:
What will happen if I use one of these Seas woofers:

[..drivers..]

with one of these Seas tweeters that would best match the sound characteristics and blend well with the woofer ( I don't know much about selecting tweeters. That is why there are so many here):

[..tweeters..]


in a vented Parts Express cabinet:

[..enclosure..]

with no crossover?

I am trying to use 2 drivers for near full-range sound but without crossover.
Click to expand...

The tweeter will highly distort, starting at low volume already. Why? Because tweeters are practically all underhung, the VC always stays in the magnet gap. Underhung motor drivers got a very even magnet field, delivering the lowest distortion. The unfiltered low frequencies cause huge excursions (at least for a tweeter) and the VC leaves the homogenous magnet field which means the motor suddenly changes from the VC being completely in the gap to only partly being within the gap. That sudden change in motor propulsion causes high non-linear distortion, which is the worst to the ear.

A high amplitude in the bass can also damage the tweeter mechanically. I suggest you try it but use a very cheap tweeter which won't hurt if/when you 're killing it.
 
#16
Absolutely, running a tweeter without a high pass (passive or active) is an almost certain method for killing it. Good to know I'm not alone in thinking this, or pointing out possible safer means of experimenting... 😉

I've never heard of a resistor alone being considered a crossover before. That's certainly a new one on me, and I can't quite follow the reasoning behind it. Aside from a tiny amount of series inductance in primarily wire-wound types, a resistor has no electrical transfer function per se, it just attenuates and / or damps depending on use, so all you'd be doing with it on a tweeter is some extent of level matching or impedance flattening; the mechanical FR is otherwise unchanged. So while you would to some extent have a crossover in terms of the ultimate mechanical rolloffs, that isn't generally how the term 'crossover' is employed -a crossover is normally considered to be an electrical circuit that shapes the responses of one or more drive units beyond that of their natural curves & levels. Speaking of which, I realise I am now on our friend adason's ignore list for pointing out inconvenient fact, but as I recall, Sonus Faber have in the past used an RL high pass in some of their models, which may be what he remembered. Works if the drivers allow it to be implemented, but appears to be irrelevant for this thread, since the OP did not ask about 'high pass crossovers without a series capacitor', but simply 'no crossover' and 'without crossover'.
 
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#18
Thanks all. I was thinking about Epos M15. But you are right, that had a high pass capacitor? I could live with that.
A 4" driver can run FR nicely if volumes stay below 80dB. But it lacks bass energy and high end sparkle. I have yet to find an eq that will not do more harm than good.
 
#19
You could run the woofer full range and use a high pass filter for the tweeter, no crossover
Click to expand...

Depending on circumstance, that's still generally classed as a crossover, albeit a very simple one, since you have components with transfer functions that are shaping the response. The Dynaco A25 & its modern Seas equivalent are a good example of that. Granted, it's also something of a grey area, since many wideband driver enthusiasts talk of 'capping off' a supertweeter, and do not regard that as the same thing as a crossover -quite why is open to question, perhaps because they may not have a specific response target in mind.
 
#20
chuck55 said:
Thanks all. I was thinking about Epos M15. But you are right, that had a high pass capacitor? I could live with that.
A 4" driver can run FR nicely if volumes stay below 80dB. But it lacks bass energy and high end sparkle. I have yet to find an eq that will not do more harm than good.
Click to expand...

OK, now we're getting somewhere. Yes, the M15 had a high pass with a simple series cap on the tweeter (the warranty repairs would have been lethal otherwise, and it shaped the tweeter response 😉 ). Since you say you're happy with a simple high pass filter, I suggest you have a gander at the Seas A26 kit, which sounds more or less exactly what you are looking for: SEAS A26 Kit
 
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