Modding the JBL HT5 Surrounds for 3-way

JBL HT5 MODIFICATIONS

about the JBL HT5

The HT5 are the surround speakers in the JBL HT Series. As surrounds, they are perfectly fine. However, as HiFi main speakers, I find the clarity is somewhat lacking. Vocals are not well isolated from the mix. On top of that, there’s some boxiness in the male voices whereas female vocals sound slightly nasal. This modification will resolve all these issues.

JBL HT5 5.25″ midwoofer Thiele / Small

JBL HT5 WOOFER TSFig 1 – JBL HT5 midwoofer Thiele / Small Parameters

I was quite surprised with the 5.25″ midwoofer. The Fs is 166Hz. I believe JBL chose such a high Fs because they wanted an early roll-off. 

Remember, the HT5 are surround speakers. In Home Theater systems, the surrounds are normally rolled off at 80Hz (-3dB) because bass is not required.

JBL HT5 RAW Frequency Response

JBL HT5 WOOFER TWEETER FRFig 2 – JBL HT5 RAW Response of the Woofer and Tweeter. Measurements below 500Hz include room reflections.

The Black plot in Fig 2 is the Raw response of the midrange driver. See how early the bass rolls off. Because of this, there’s no necessity to use a large value capacitor to roll off the low frequencies.

Higher up the frequencies, there is a 5dB rise from 500Hz ~ 2.5kHz. That’s the effect of baffle step. At 5kHz, the driver cone starts to breakup.

The Red plot is the Raw response of the bi-radial horn tweeter. It is exceptionally smooth. No peaks and nulls anywhere. Moreover, the roll-off from 3kHz to 15kHz is constant and linear. This is a very well designed horn tweeter.

JBL HT5 Modified Crossover

JBL HT5 LP HPFig 3 – Modified Frequency Response of HT5 Midrange and Tweeter

Fig 3 shows the modified midwoofer response (Blue plot) and the horn tweeter (Red plot). Acoustically, the two drivers are crossing at about 2.5kHz.

Modified JBL HT5 Frequency Response

HT5_FR_JBL_MODFig 4 – Modded and Original HT5 Frequency Response

The Blue plot in Fig 4 is my modified response to enhance the midrange. It is similar to the original JBL HT5 response (Black plot) except for a slight increase in SPL from 400Hz ~ 3kHz.

Modified HT5 Cumulative Sprectral Decay (CSD)

MODDED HT5 CSDFig 5 – Modded HT5 CSD. Window = 1.3ms (769Hz), Time Range = 1.0ms, Rise Time = 0.1ms

Modded HT5 Toneburst Energy Storage
modded ht5 TES

Fig 6 – Modded HT5 TES. Impulse Window=5ms

Modded HT5 Spectrogram
JBL HT5 MOD SPECTROGRAM

Fig 7 – Modded HT5 Spectrogram. Impulse Window=5ms

Despite the midrange cone breakup, the Waterfall (Fig 5), Toneburst Energy Storage (Fig 6) and the Spectrogram (Fig 7) all indicate excellent damping in the crossover region.

Modded HT5 Harmonic Distortion
MOD JBL HT5 DISTORTION

Fig 8 – Modded HT5 harmonic Distortion

There is nothing unusual in the Modded HT5 Harmonic Distortion plot. The 2nd (Red) and 3rd (Violet) Harmonics are about -55dB below the fundamental. Measurements below 500Hz are inaccurate as they include room reflections.

HT5 MOD SYSTEMFig 9 – Modded JBL HT5 Bi-amp System

Fig 9 shows my modified JBL HT5 system. It is a purely passive bi-amp setup. There are no electronic crossovers.

DAYTON SD215A-88 BANDPASSFig 10 – Frequency Response of Dayton SD215A-88 Bandpass Sub with 3mH

This is possible because bandpass subs already have a low pass build-in. Nonetheless, I recommend installing a 3mH inductor at the bandpass input to roll-off the midrange before they enter the sub. This will reduce the midrange emitting from the bandpass even further. If you use active subwoofers, set the crossover in your sub at 125Hz.

the sound of the Modded JBL HT5

I am rather pleased with the way the mod turned out. From indigestible to actually enjoying my music. 

This is the way I like my audio to sound like. Good separation between the subwoofer bass and the midrange, a slightly forward midrange with no veil and no nasalness in female vocals. I can’t ask for more.

If you want to know what nasalness is, listen to the Girl in the Other Room (Diania Krall) with the JBL HT5. She sounds like her nose is blocked.  

Disclaimer

If you’re interested in this modification, kindly send me a mail for the crossover and the Dayton SD215A-88 Bandpass Sub dimensions. You agree to undertake this modification at your own risk. I am not responsible for any damage to your speakers.