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Multi-Way Conventional loudspeakers with crossovers

Seas 27TBFC/G vs 27TDFC/G
Seas 27TBFC/G vs 27TDFC/G
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Old 3rd February 2018, 09:39 AM   #1
Dave Bullet is offline Dave Bullet  New Zealand
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Default Seas 27TBFC/G harsh compared to 27TDFC/G

I'm building a 3-way and have a pair of Seas 27TDFC/G and 27TBFC/G to choose from.

I like to try each driver with its crossover alone, just to see if there is anything that sounds harsh or fatiguing.

The crossover hits a 4th order acoustic slope @ 2KHz. There's no impedance compensation and no other notch or other filters (2nd order plus conventional Lpad).

Knowing the 27TD and 27TB are very similar, I switched between them in the same cabinet.

The 27TDFC/G was pleasant to listen to.

The 27TBFC/G was not. I need to do some measurements to compare them but there was a harshness to the B tweeter. I couldn't listen to it for more than a couple of minutes.

Given the B is well regarded, arguably has lower odd order harmonic distortion, I was disappointed and surprised. Certain vocals or bright rock recordings were just far too in your face. Not so with the D tweeter.

I do know the breakup mode ~ 26Khz of the aluminimum diaphram is seen lower down, could this be the cause of the unpleasantness?

Last edited by Dave Bullet; 3rd February 2018 at 10:04 AM.
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Old 3rd February 2018, 10:31 AM   #2
TMM is offline TMM  Australia
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Quote:
Originally Posted by Dave Bullet View Post
I do know the breakup mode ~ 26Khz of the aluminimum diaphram is seen lower down, could this be the cause of the unpleasantness?
Even if a harmonic lands on the 26KHz breakup node, it's still inaudible (unless the listener is a dog ). The breakup of the TBFC should not contribute anything to the audible sound of the driver.

While both tweeters have respectably low distortion the TBFC has significantly higher non linear distortion below 2kHz and is still a little worse in the 3-5kHz region than the TDFC. If you are listening to the tweeter in isolation it is quite plausible that you could hear a difference from the content below the crossover point alone, even if it is playing greatly attenuated. This is because it is possible for our hearing to compensate for a non-flat frequency response over time. In the presence of a mid/woofer any low level distortion products (generated by the tweeter below the xo point) become inaudible because the mid/woofer is playing loudly and our hearing sensitivity goes back down in that region.

The TBFC is also some 1-2dB more sensitive than the TDFC, are you accounting for this? It's also worth investigating if the impedance of the drivers you have are the same. Even if they should be almost identical, it's not uncommon for resonant frequencies to vary with production batches, sometimes by 5% or more and that will change the transfer function of the crossover. Sensitivity also varies batch to batch.

Last edited by TMM; 3rd February 2018 at 10:40 AM.
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Old 3rd February 2018, 10:34 AM   #3
Zvu is offline Zvu  Serbia
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You really have to measure and then draw the conclusion. Given that it is 2KHz crossover, 0,5dB higher level in 27TB could give that impression, let alone 1 or 2 dB. It is only 0,5dB but from 2KHz-20KHz span and that is a lot. That's why i use 2dB and sometimes even 1dB grid when measuring gated. It gives me unique insight into deviations that looks small and irrelevant on 5dB or, god forbid, 10dB grid.
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Last edited by Zvu; 3rd February 2018 at 10:38 AM.
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Old 3rd February 2018, 02:52 PM   #4
Zuhl is offline Zuhl  England
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I have a pair of 27TBFC/Gs. While vocals were pretty good they had the most un-natural sounding cymbals I've heard on any tweeter.

So, nice response and low distortion - shame about the sound.
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Old 3rd February 2018, 06:35 PM   #5
Dave Bullet is offline Dave Bullet  New Zealand
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Thanks for your replies.I don't think the sensitivity difference matters. I adjusted volume levels on both and the B didn't get better. Whereas I could increase the D volume and it was fine. Sure, level matching is important in a finished system.

In terms of ears being more sensitive without a balanced spectrum being played, my concern is the forward vocals on the B:
a) drowned out the subtly of percussion and other high frequency content (I dont' think filling in lower frequency will offset this)
b) won't get any better when more energy is provided when other drivers are added... .unless they cancel out the "extra" the B is adding. but then that would introduce other issues.

Re distortion, I'll try and take my own measurements. I'm not sure I can trust them as my previous distortion measurements weren't that good, but my measurement setup is better now. I do notice looking at Zaph's measurements the B has higher 3rd order HD below 2KHz and maybe that's what I'm sensitive to?

Good to note Zuhl the B wasn't that good on cymbals. I personally think it will be great (even though it drops away +16Khz - I can't hear that high these days)... Reason being, my point a) above - I think the forwardness is masking the upper end brilliance.

Anyway - onto measurements today hopefully, then I'll post them up.

The reason I'm testing all this in isolation is before I stump up for my big crossover parts order. I'm recycling some parts which I can make the tweeter section, so thought I'd audition it first.
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Old 3rd February 2018, 06:37 PM   #6
mctavish is offline mctavish  Austria
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I had a pair of the alu domes... for years I tried to like them, but couldn't.

Maybe some of us are more sensitive to the ultrasonic ringing than others...
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Old 3rd February 2018, 07:19 PM   #7
TNT is offline TNT  Sweden
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Maybe the B is more revealing of what you put in and the D is more like a filter?

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Old 4th February 2018, 02:44 AM   #8
andy2 is offline andy2  United States
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"Sounding forward and in your face" is usually a matter of speaker voicing. I don't think it's distortion unless the distortion is really bad. I have not used this specific tweeter but I doubt Seas would put out a bad tweeter.
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Old 4th February 2018, 06:48 AM   #9
Dave Bullet is offline Dave Bullet  New Zealand
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Originally Posted by mctavish View Post
I had a pair of the alu domes... for years I tried to like them, but couldn't.

Maybe some of us are more sensitive to the ultrasonic ringing than others...
I'm not sure its the ultrasonic ringing. I don't think my upstream is capable of exciting the 26KHz breakup mode (therefore lower frequency even and odd order harmonics).

I bought them on the basis "they are great" but they are not good for the 70's and 80's music I like. I think a lot of recording engineers were taking advantage of new more "resolute" technologies and really jamming certain frequencies to the fore. This made for very in your face / bright recordings.

Sadly - I like this era of music and I don't think the 27tbfcg is suited to it. I didn't get time to measure today.... but I think a lot of speaker designers don't position a certain speaker as to the genre of music listened to. Maybe this is important. Measurement may... or may not tell (making it more so).
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Old 4th February 2018, 06:50 AM   #10
Dave Bullet is offline Dave Bullet  New Zealand
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Maybe the B is more revealing of what you put in and the D is more like a filter?

//
That could well be true and also reflect some of the overly forward / bright mixes of artists I like.

Take for example Huey Lewis and The News - greatest hits album. Most of this is ear shrilling on the 27tbfcg but the 27tddfc tames it just enough to be listenable. I like Huey and couldn't listen on the 27tbfcg. More accurate driver?.... yes. More suitable?.... no.
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