HornResp results: please advice

[morfeas]

Attached are the input parameters to hornresp and the result for a BLH using an Altec 604-8G.

The SPL responce is combined direct radiator + horn mouth. Does this look ok? Do I miss something?

Thanks,

 

[morfeas]

.

 

[GM]

Greets!

Not to me, but then it depends on what level of performance/SQ you want, room conditions, etc.. FWIW here's my calc'd compact BLH (big vent BR) with linear expansion:

Vb = 3.55621 ft^3 (100.7 L)
L = 43.46" (110.4 cm)
St = 91.45"^2 (590 cm^2)
Sm = 1016"^2 (6555 cm^2)

This assumes the cab will be at least 28" wide, not in a corner, the measured specs I used may be different, and of course if you use a high output impedance amp, it can change the Vb considerably, but at least it gives you a starting point for a relatively smooth response. At least it should sim good, I don't use Hornresp.

If you're wanting a high SQ (as BLH go) wide BW horn to better match to the HF horn's efficiency, it will need to be huge.

GM

 

[johninCR]

FWIW, that SPL graph is horn output only. I think the huge Vas on that driver may be what's killing you. Try doubling up on that CC size as GM suggested, which will increase the bottom end extension. I'd also go to a horn length around 2m and a upper horn cutoff in the 100hz range to get the phase relationship right where the horn output drops off and the front radiation takes over, but then you end up with a Jensen Imperial type design.

 

[AndrewT]

Hi Johncr,
how do you know that VAS is big, where does it tell you?

What is CC?

 

[johninCR]

Hi Johncr,
how do you know that VAS is big, where does it tell you?

What is CC?

I saw the high CMS number and thought maybe he input too high a Vas. So I looked the driver up here: http://www.thielesmall.com/database.asp
and Vas is 625L.

CC is "Compression Chamber". In the HornResp inputs, since this is a rear horn, it is VTC and which is in cc's, 50000 cc's is 50L.

 

[GM]

Greets!

Yeah, the Jensen Imperial is the 'one stop shop' BLH for any of the low Fs, Qts/high Vas drivers, and for semi-compact BLHs, I much prefer a Voigt concept tapered ML-TL over the popular big vent BRs:

L = 48.5"
eta = 0.5
SO = 4"^2 (effective for simming)
SL = 1016"^2

linear taper:

Lhorn = 0.75"
St = 128"^2
Sm = 128"^2

BTW, I just downloaded Hornresp 8.40 and according to the Help Menu it allegedly has a BLH Wizard that sums/plots the driver's and horn's response, though for whatever reason I couldn't get what I consider remotely accurate results.

GM

 

[morfeas]

Thanks for the replies.

I also think hornresp results in the back horn calculation seem not accurate.

The listening room is quiet small and one of the speakers can be placed in a corner.

Have tried also ML-Util calculations and the results are as the attached images

 

[morfeas]

.

 

[morfeas]

Input the ML-Util's output to hornresp... assuming a corner placement

 

[morfeas]

I get the following FR from the horn

 

[morfeas]

and the combined horn & direct radiator

 

[johninCR]

That big null is due to the phase problem at the acoustical XO of the horn and direct radiation. Make that horn length 207cm and watch what happens when you play around with the VTC. The null should go away and you should get a lot more down low. I'll have to warn you though that as a sub it will work, but Jensen found the best sound came for full range using a woofer with an Fs above the 40hz cutoff, so regardless of what HornResp says, it may not sound good with that driver since it has such a low Fs. How high did you plan to let the woofer run?

 

[morfeas]

How high did you plan to let the woofer run?

This a doublex loudspeaker with a HF driver mounted concentric. The original XO is >1KHz.

I have tried the 620 BR cabinet and the mid bass was not satisfactory at all.

This assumes the cab will be at least 28" wide, not in a corner, the measured specs I used may be different, and of course if you use a high output impedance amp, it can change the Vb considerably, but at least it gives you a starting point for a relatively smooth response.

Time to learn something... How the output impedance of the amp will effect the calculations of the horn?

 

[GM]

Greets!

Adding series resistance in any form, be it a tube amp's high output impedance (DF), a resistor or inductor in series raises the driver's effective Qes/Qts, ergo rolls off the driver's rising response and increases the cab Vb required for the desired alignment.

For instance, all the early Altec cab designs assumes the driver would be driven by an amp with variable DF (bass tone control) that could be as high as 20 ohms back in the day when drivers were a nominal 16 ohms. Since your drivers sound 'thin' in the 620, all you need do is add some series R until the tonal balance from Fb to the horn's XO sounds right to you. If you're using a SS amp, typically you will need between 1/2 - 1x the woofer's DCR to 'fill in' the big dip in the speaker's response between ~200 Hz and Fb and a bypass cap around the HF horn's attenuator will be required to 'lift up'
the highs to compensate for the horn's roll off combined with the attenuation required to flatten its in-room response.

Bottom line, unless you're using a flea power amp, there's no need for a BLH with this driver in a typical HIFI app, just some EQ, and even then some folks find they still don't need the extra efficiency.

GM

 

[morfeas]

Thanks!

Yes, I could use every bit of efficiency I could get, since my amps (future ones also) are/would be in the single digit wattage.

Have also experimenting with my gainclones adding series resistance (~1 Ohm) but not in the range you are proposing (~driver's Re).

Thanks again for the support.