Midrange distortion on 15" PA driver

[mark100]

That would be better way, but I would first need amplifier capable of doing that and hope neighbors won't kill me.
Maybe, when they are finished.

I do alot of testing outdoors in suburbia, and have found neighbors don't really care.
I think because lawnmowers, weed whackers, leaf blowers, etc...make even more SPL...or at least more annoying SPL.


One thing I've found that does help keep down testing annoyance, is to limit the freq range of the sine sweeps to no higher than needed...

 

[scholl]

That's not bad. Maybe consider crossing at 700hz to use the crossover to level out the peak and better match horn dispersions. The Faital 1.4" drivers will work well with their tractrix or the Eighteen sound 1.4" horn to 700.

 

[LightBit]

I already have Beyma TPL-150H, which can't go lower.

 

[TMM]

It seems good, but I kinda expected it to be better, because all that surface area.

Unfortunately, increasing the size of the voicecoil (and therefore inductance), and lowering of cone breakup often negates the benefit of reduced excursion.

5-8" drivers are usually optimal from 200Hz-1kHz. Multiple drivers further lowers distortion and increases sensitivity at the expense of polar response.

 

[LightBit]

Now, I know. But bass should be much better than 8" driver with 2mm Xmax.

I can still add midrange driver. Tweeter will be in separate enclosure.

 

[LightBit]

I finally put them in box and measured outside. Now I'm even more confused.

Something really weird is happening from 100Hz to 300Hz. Distortion peak moves a bit when I reposition mic.
Anyone has any idea what this might be?

 

[phase_accurate]

Are they in a vented box ? If yes, does anything change if you stuff the port(s) ? What is the length of your port ?

Regards

Charles

 

[KaffiMann]

60 some db's is still a bit low IMO.
That squiggle centered ca 170hz seems to be a box resonance thing, and if it goes out the port, no wonder there's higher distortion.

That's my 2c or so.

 

[LightBit]

Yes it is vented. I did not try to stuff port.
Length is 30cm and diameter is 16cm.

Maybe port is not sturdy enough? It is PVC (sewage) pipe.
Maybe it was cable vibrating (I could hear it, if I did not hold it). Cable went through port. Maybe it was still vibrating inside?

Mic is not calibrated. It was definitely more than 60dB. Should have been more than 100dB. Box is 25mm birch plywood.

 

[KaffiMann]

When I'm saying "Box resonance" I do not think about materials or stiffness etc. But the distances between surfaces and driver, and how they relate to eachother.
It's actual resonances inside the box that escape through the port, not a bracing or stiffness related issue.

Do you have internal and external dimensions/measurements of the box?

Edit:
It could be a cable vibrating, but I somehow doubt it. The distortion seems to stem from the squiggles centered around 170hz to my eyes, and it may correlate well with certain box dimensions (IE tall-ish box for 15").

 

[LightBit]

It is a bit tallish. I didn't notice that dip, I thought it is reflection.
I think it is possible that it is second harmonic of box. When I simulated as MLTL it showed small dip at 210Hz.
Didn't know this also causes distortion.

Depth: 30cm (35cm external)
Width: 50cm (55cm external)
Height: 85cm (90cm external)

Driver is close to top (driver center is 60cm from bottom, I think). Port is 20cm from bottom on side.

Box is only lined with foam. I could stuff it.

 

[KaffiMann]

I had to guess at some dimensions, and simming the box like you said, I see the resonance centered around 213hz.
But if you just for fun add 20cm just to see what happens if you move port away from bottom, you get a resonance centered at 174hz (ignore everything else, it's just for looking at what can come out of the port after bouncing around a bit).

 

[KaffiMann]

So perhaps it would be interesting to see what happens if you put a bit more fill in the box, and plug the port.

 

[LightBit]

Yes, I will try that.

Thank you.

 

[Charles Darwin]

Personally I would go 3way.

Haven't used the TP150H myself as it is a wee bit beyond what I would pay for a tweeter but from everything many others posted who have used it it would seem that it clearly benefits from NOT being run to it's very limits.
With that in mind I would find me at a good 8 or 10 inch mid driver to go between TP and 15 and run it high enough to match dispersion which would be 1.6-2k at a quick guess. Beyma themselves make a rather good looking (on paper) 10" which matches the efficiency of the TP but it is certainly not cheap.

 

[KaffiMann]

run it high enough to match dispersion which would be 1.6-2k at a quick guess.

I've seen some in-depth recommendations taking into account some very relevant concerns that 1.8khz is a good spot for crossing over.

 

[LightBit]

Beyma AMT has resonance on ~1.6kHz (there is distortion spike). Not good below 1.8kHz. I probably would not buy it again. I usualy buy cheaper stuff.

Maybe woofer can be used up to 2kHz, but it seems like abuse. Dispersion won't match. What do you guys think?
I was looking Beyma 8MC300Nd for midrange. It might even have slightly lower distortion in midrange.
There is also Beyma 8MI100 which is cheaper, but I'm woried because it is MI (musical instruments).

 

[KaffiMann]

Hmmm...
If you're looking at Beyma and want an absolute perfect match for the TP150H then perhaps the new 6MCF200ND should be considered.
You'd be closing in on a fairly high performing 3-way pending on xo and amp choices.

Almost tempted to look at these things for myself, but I really don't need any more speakers...

Edit:
Or the 10MCF400ND

 

[LightBit]

6MCF200ND has too high Fs. I would use it from 300-400Hz to 2-3kHz.
10MCF400ND is quite expensive.

 

[phase_accurate]

I would consult the "monster midbass" thread where you can see heaps of 10" midwoofers measured by a forum member. Most of these cost much less than that closed-back Beyma.

Regards

Charles